draft-ietf-httpbis-semantics-08.txt   draft-ietf-httpbis-semantics-09.txt 
HTTP Working Group R. Fielding, Ed. HTTP Working Group R. Fielding, Ed.
Internet-Draft Adobe Internet-Draft Adobe
Obsoletes: 2818,7230,7231,7232,7233,7235 M. Nottingham, Ed. Obsoletes: 2818,7230,7231,7232,7233,7235 M. Nottingham, Ed.
,7538,7615,7694 (if approved) Fastly ,7538,7615,7694 (if approved) Fastly
Intended status: Standards Track J. Reschke, Ed. Intended status: Standards Track J. Reschke, Ed.
Expires: November 27, 2020 greenbytes Expires: January 12, 2021 greenbytes
May 26, 2020 July 11, 2020
HTTP Semantics HTTP Semantics
draft-ietf-httpbis-semantics-08 draft-ietf-httpbis-semantics-09
Abstract Abstract
The Hypertext Transfer Protocol (HTTP) is a stateless application- The Hypertext Transfer Protocol (HTTP) is a stateless application-
level protocol for distributed, collaborative, hypertext information level protocol for distributed, collaborative, hypertext information
systems. This document defines the semantics of HTTP: its systems. This document defines the semantics of HTTP: its
architecture, terminology, the "http" and "https" Uniform Resource architecture, terminology, the "http" and "https" Uniform Resource
Identifier (URI) schemes, core request methods, request header Identifier (URI) schemes, core request methods, request header
fields, response status codes, response header fields, and content fields, response status codes, response header fields, and content
negotiation. negotiation.
skipping to change at page 1, line 39 skipping to change at page 1, line 39
This note is to be removed before publishing as an RFC. This note is to be removed before publishing as an RFC.
Discussion of this draft takes place on the HTTP working group Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at
<https://lists.w3.org/Archives/Public/ietf-http-wg/>. <https://lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information can be found at <https://httpwg.org/>; Working Group information can be found at <https://httpwg.org/>;
source code and issues list for this draft can be found at source code and issues list for this draft can be found at
<https://github.com/httpwg/http-core>. <https://github.com/httpwg/http-core>.
The changes in this draft are summarized in Appendix D.9. The changes in this draft are summarized in Appendix D.10.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 27, 2020. This Internet-Draft will expire on January 12, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 3, line 12 skipping to change at page 3, line 12
2.5.1. http URI Scheme . . . . . . . . . . . . . . . . . . . 18 2.5.1. http URI Scheme . . . . . . . . . . . . . . . . . . . 18
2.5.2. https URI Scheme . . . . . . . . . . . . . . . . . . 18 2.5.2. https URI Scheme . . . . . . . . . . . . . . . . . . 18
2.5.3. http and https URI Normalization and Comparison . . . 19 2.5.3. http and https URI Normalization and Comparison . . . 19
2.5.4. Deprecated userinfo . . . . . . . . . . . . . . . . . 20 2.5.4. Deprecated userinfo . . . . . . . . . . . . . . . . . 20
2.5.5. Fragment Identifiers on http(s) URI References . . . 20 2.5.5. Fragment Identifiers on http(s) URI References . . . 20
3. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 21 3. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1. Implementation Diversity . . . . . . . . . . . . . . . . 21 3.1. Implementation Diversity . . . . . . . . . . . . . . . . 21
3.2. Role-based Requirements . . . . . . . . . . . . . . . . . 21 3.2. Role-based Requirements . . . . . . . . . . . . . . . . . 21
3.3. Parsing Elements . . . . . . . . . . . . . . . . . . . . 22 3.3. Parsing Elements . . . . . . . . . . . . . . . . . . . . 22
3.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 23 3.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 23
3.5. Protocol Versioning . . . . . . . . . . . . . . . . . . . 23 4. Extending and Versioning HTTP . . . . . . . . . . . . . . . . 23
4. Header and Trailer Fields . . . . . . . . . . . . . . . . . . 24 4.1. Extending HTTP . . . . . . . . . . . . . . . . . . . . . 23
4.1. Field Ordering and Combination . . . . . . . . . . . . . 25 4.2. Protocol Versioning . . . . . . . . . . . . . . . . . . . 24
4.2. Field Limits . . . . . . . . . . . . . . . . . . . . . . 26 5. Header and Trailer Fields . . . . . . . . . . . . . . . . . . 25
4.3. Field Names . . . . . . . . . . . . . . . . . . . . . . . 27 5.1. Field Ordering and Combination . . . . . . . . . . . . . 26
4.3.1. Field Extensibility . . . . . . . . . . . . . . . . . 27 5.2. Field Limits . . . . . . . . . . . . . . . . . . . . . . 27
4.3.2. Field Name Registry . . . . . . . . . . . . . . . . . 28 5.3. Field Names . . . . . . . . . . . . . . . . . . . . . . . 28
4.4. Field Values . . . . . . . . . . . . . . . . . . . . . . 29 5.3.1. Field Extensibility . . . . . . . . . . . . . . . . . 28
4.4.1. Common Field Value Components . . . . . . . . . . . . 30 5.3.2. Field Name Registry . . . . . . . . . . . . . . . . . 29
4.5. ABNF List Extension: #rule . . . . . . . . . . . . . . . 32 5.4. Field Values . . . . . . . . . . . . . . . . . . . . . . 30
4.5.1. Sender Requirements . . . . . . . . . . . . . . . . . 32 5.4.1. Common Field Value Components . . . . . . . . . . . . 31
4.5.2. Recipient Requirements . . . . . . . . . . . . . . . 32 5.5. ABNF List Extension: #rule . . . . . . . . . . . . . . . 35
4.6. Trailer Fields . . . . . . . . . . . . . . . . . . . . . 33 5.5.1. Sender Requirements . . . . . . . . . . . . . . . . . 35
4.6.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 33 5.5.2. Recipient Requirements . . . . . . . . . . . . . . . 36
4.6.2. Limitations . . . . . . . . . . . . . . . . . . . . . 34 5.6. Trailer Fields . . . . . . . . . . . . . . . . . . . . . 36
4.6.3. Trailer . . . . . . . . . . . . . . . . . . . . . . . 34 5.6.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 36
4.7. Considerations for New HTTP Fields . . . . . . . . . . . 35 5.6.2. Limitations . . . . . . . . . . . . . . . . . . . . . 37
4.8. Fields Defined In This Document . . . . . . . . . . . . . 36 5.6.3. Trailer . . . . . . . . . . . . . . . . . . . . . . . 37
5. Message Routing . . . . . . . . . . . . . . . . . . . . . . . 38 5.7. Considerations for New HTTP Fields . . . . . . . . . . . 38
5.1. Identifying a Target Resource . . . . . . . . . . . . . . 38 5.8. Fields Defined In This Document . . . . . . . . . . . . . 39
5.2. Determining Origin . . . . . . . . . . . . . . . . . . . 38 6. Message Routing . . . . . . . . . . . . . . . . . . . . . . . 41
5.3. Routing Inbound . . . . . . . . . . . . . . . . . . . . . 39 6.1. Identifying a Target Resource . . . . . . . . . . . . . . 41
5.4. Direct Authoritative Access . . . . . . . . . . . . . . . 40 6.2. Determining Origin . . . . . . . . . . . . . . . . . . . 42
5.4.1. http origins . . . . . . . . . . . . . . . . . . . . 40 6.3. Routing Inbound . . . . . . . . . . . . . . . . . . . . . 42
5.4.2. https origins . . . . . . . . . . . . . . . . . . . . 41 6.4. Direct Authoritative Access . . . . . . . . . . . . . . . 43
5.4.3. Initiating HTTP Over TLS . . . . . . . . . . . . . . 42 6.4.1. http origins . . . . . . . . . . . . . . . . . . . . 43
5.5. Reconstructing the Target URI . . . . . . . . . . . . . . 44 6.4.2. https origins . . . . . . . . . . . . . . . . . . . . 44
5.6. Host . . . . . . . . . . . . . . . . . . . . . . . . . . 44 6.4.3. Initiating HTTP Over TLS . . . . . . . . . . . . . . 45
5.7. Message Forwarding . . . . . . . . . . . . . . . . . . . 45 6.5. Reconstructing the Target URI . . . . . . . . . . . . . . 47
5.7.1. Via . . . . . . . . . . . . . . . . . . . . . . . . . 46 6.6. Host . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.7.2. Transformations . . . . . . . . . . . . . . . . . . . 47 6.7. Message Forwarding . . . . . . . . . . . . . . . . . . . 48
6. Representations . . . . . . . . . . . . . . . . . . . . . . . 49 6.7.1. Via . . . . . . . . . . . . . . . . . . . . . . . . . 49
6.1. Representation Data . . . . . . . . . . . . . . . . . . . 49 6.7.2. Transformations . . . . . . . . . . . . . . . . . . . 51
6.1.1. Media Type . . . . . . . . . . . . . . . . . . . . . 49 7. Representations . . . . . . . . . . . . . . . . . . . . . . . 52
6.1.2. Content Codings . . . . . . . . . . . . . . . . . . . 52 7.1. Representation Data . . . . . . . . . . . . . . . . . . . 52
6.1.3. Language Tags . . . . . . . . . . . . . . . . . . . . 53 7.1.1. Media Type . . . . . . . . . . . . . . . . . . . . . 53
6.1.4. Range Units . . . . . . . . . . . . . . . . . . . . . 54 7.1.2. Content Codings . . . . . . . . . . . . . . . . . . . 55
6.2. Representation Metadata . . . . . . . . . . . . . . . . . 58 7.1.3. Language Tags . . . . . . . . . . . . . . . . . . . . 57
6.2.1. Content-Type . . . . . . . . . . . . . . . . . . . . 59 7.1.4. Range Units . . . . . . . . . . . . . . . . . . . . . 57
6.2.2. Content-Encoding . . . . . . . . . . . . . . . . . . 60 7.2. Representation Metadata . . . . . . . . . . . . . . . . . 61
6.2.3. Content-Language . . . . . . . . . . . . . . . . . . 61 7.2.1. Content-Type . . . . . . . . . . . . . . . . . . . . 62
6.2.4. Content-Length . . . . . . . . . . . . . . . . . . . 61 7.2.2. Content-Encoding . . . . . . . . . . . . . . . . . . 63
6.2.5. Content-Location . . . . . . . . . . . . . . . . . . 63 7.2.3. Content-Language . . . . . . . . . . . . . . . . . . 64
6.3. Payload . . . . . . . . . . . . . . . . . . . . . . . . . 64 7.2.4. Content-Length . . . . . . . . . . . . . . . . . . . 64
6.3.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 65 7.2.5. Content-Location . . . . . . . . . . . . . . . . . . 66
6.3.2. Identification . . . . . . . . . . . . . . . . . . . 65 7.3. Payload . . . . . . . . . . . . . . . . . . . . . . . . . 68
6.3.3. Payload Body . . . . . . . . . . . . . . . . . . . . 66 7.3.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 68
6.3.4. Content-Range . . . . . . . . . . . . . . . . . . . . 67 7.3.2. Identification . . . . . . . . . . . . . . . . . . . 68
6.3.5. Media Type multipart/byteranges . . . . . . . . . . . 69 7.3.3. Payload Body . . . . . . . . . . . . . . . . . . . . 69
6.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 71 7.3.4. Content-Range . . . . . . . . . . . . . . . . . . . . 70
6.4.1. Proactive Negotiation . . . . . . . . . . . . . . . . 72 7.3.5. Media Type multipart/byteranges . . . . . . . . . . . 72
6.4.2. Reactive Negotiation . . . . . . . . . . . . . . . . 73 7.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 74
6.4.3. Request Payload Negotiation . . . . . . . . . . . . . 74 7.4.1. Proactive Negotiation . . . . . . . . . . . . . . . . 75
6.4.4. Quality Values . . . . . . . . . . . . . . . . . . . 74 7.4.2. Reactive Negotiation . . . . . . . . . . . . . . . . 76
7. Request Methods . . . . . . . . . . . . . . . . . . . . . . . 74 7.4.3. Request Payload Negotiation . . . . . . . . . . . . . 77
7.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 74 7.4.4. Quality Values . . . . . . . . . . . . . . . . . . . 77
7.2. Common Method Properties . . . . . . . . . . . . . . . . 76 8. Request Methods . . . . . . . . . . . . . . . . . . . . . . . 77
7.2.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 77 8.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 77
7.2.2. Idempotent Methods . . . . . . . . . . . . . . . . . 78 8.2. Common Method Properties . . . . . . . . . . . . . . . . 79
7.2.3. Methods and Caching . . . . . . . . . . . . . . . . . 79 8.2.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 80
7.3. Method Definitions . . . . . . . . . . . . . . . . . . . 79 8.2.2. Idempotent Methods . . . . . . . . . . . . . . . . . 81
7.3.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 79 8.2.3. Methods and Caching . . . . . . . . . . . . . . . . . 82
7.3.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 80 8.3. Method Definitions . . . . . . . . . . . . . . . . . . . 82
7.3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . 81 8.3.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 82
7.3.4. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 82 8.3.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 83
7.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . 84 8.3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . 84
7.3.6. CONNECT . . . . . . . . . . . . . . . . . . . . . . . 85 8.3.4. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 85
7.3.7. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . 87 8.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . 87
7.3.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . 88 8.3.6. CONNECT . . . . . . . . . . . . . . . . . . . . . . . 88
7.4. Method Extensibility . . . . . . . . . . . . . . . . . . 88 8.3.7. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . 90
7.4.1. Method Registry . . . . . . . . . . . . . . . . . . . 88 8.3.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . 91
7.4.2. Considerations for New Methods . . . . . . . . . . . 89 8.4. Method Extensibility . . . . . . . . . . . . . . . . . . 91
8. Request Header Fields . . . . . . . . . . . . . . . . . . . . 89 8.4.1. Method Registry . . . . . . . . . . . . . . . . . . . 92
8.1. Controls . . . . . . . . . . . . . . . . . . . . . . . . 90 8.4.2. Considerations for New Methods . . . . . . . . . . . 92
8.1.1. Expect . . . . . . . . . . . . . . . . . . . . . . . 90 9. Request Header Fields . . . . . . . . . . . . . . . . . . . . 93
8.1.2. Max-Forwards . . . . . . . . . . . . . . . . . . . . 92 9.1. Controls . . . . . . . . . . . . . . . . . . . . . . . . 93
8.2. Preconditions . . . . . . . . . . . . . . . . . . . . . . 93 9.1.1. Expect . . . . . . . . . . . . . . . . . . . . . . . 93
8.2.1. Evaluation . . . . . . . . . . . . . . . . . . . . . 94 9.1.2. Max-Forwards . . . . . . . . . . . . . . . . . . . . 96
8.2.2. Precedence . . . . . . . . . . . . . . . . . . . . . 95 9.2. Preconditions . . . . . . . . . . . . . . . . . . . . . . 96
8.2.3. If-Match . . . . . . . . . . . . . . . . . . . . . . 97 9.2.1. Evaluation . . . . . . . . . . . . . . . . . . . . . 97
8.2.4. If-None-Match . . . . . . . . . . . . . . . . . . . . 98 9.2.2. Precedence . . . . . . . . . . . . . . . . . . . . . 98
8.2.5. If-Modified-Since . . . . . . . . . . . . . . . . . . 99 9.2.3. If-Match . . . . . . . . . . . . . . . . . . . . . . 100
8.2.6. If-Unmodified-Since . . . . . . . . . . . . . . . . . 101 9.2.4. If-None-Match . . . . . . . . . . . . . . . . . . . . 101
8.2.7. If-Range . . . . . . . . . . . . . . . . . . . . . . 102 9.2.5. If-Modified-Since . . . . . . . . . . . . . . . . . . 103
8.3. Range . . . . . . . . . . . . . . . . . . . . . . . . . . 103 9.2.6. If-Unmodified-Since . . . . . . . . . . . . . . . . . 104
8.4. Negotiation . . . . . . . . . . . . . . . . . . . . . . . 105 9.2.7. If-Range . . . . . . . . . . . . . . . . . . . . . . 105
8.4.1. Accept . . . . . . . . . . . . . . . . . . . . . . . 106 9.3. Range . . . . . . . . . . . . . . . . . . . . . . . . . . 106
8.4.2. Accept-Charset . . . . . . . . . . . . . . . . . . . 108 9.4. Negotiation . . . . . . . . . . . . . . . . . . . . . . . 108
8.4.3. Accept-Encoding . . . . . . . . . . . . . . . . . . . 108 9.4.1. Accept . . . . . . . . . . . . . . . . . . . . . . . 109
8.4.4. Accept-Language . . . . . . . . . . . . . . . . . . . 110 9.4.2. Accept-Charset . . . . . . . . . . . . . . . . . . . 111
8.5. Authentication Credentials . . . . . . . . . . . . . . . 111 9.4.3. Accept-Encoding . . . . . . . . . . . . . . . . . . . 112
8.5.1. Challenge and Response . . . . . . . . . . . . . . . 112 9.4.4. Accept-Language . . . . . . . . . . . . . . . . . . . 114
8.5.2. Protection Space (Realm) . . . . . . . . . . . . . . 113 9.5. Authentication Credentials . . . . . . . . . . . . . . . 115
8.5.3. Authorization . . . . . . . . . . . . . . . . . . . . 114 9.5.1. Challenge and Response . . . . . . . . . . . . . . . 115
8.5.4. Proxy-Authorization . . . . . . . . . . . . . . . . . 115 9.5.2. Protection Space (Realm) . . . . . . . . . . . . . . 117
8.5.5. Authentication Scheme Extensibility . . . . . . . . . 115 9.5.3. Authorization . . . . . . . . . . . . . . . . . . . . 118
8.6. Request Context . . . . . . . . . . . . . . . . . . . . . 117 9.5.4. Proxy-Authorization . . . . . . . . . . . . . . . . . 118
8.6.1. From . . . . . . . . . . . . . . . . . . . . . . . . 118 9.5.5. Authentication Scheme Extensibility . . . . . . . . . 118
8.6.2. Referer . . . . . . . . . . . . . . . . . . . . . . . 118 9.6. Request Context . . . . . . . . . . . . . . . . . . . . . 121
8.6.3. User-Agent . . . . . . . . . . . . . . . . . . . . . 119 9.6.1. From . . . . . . . . . . . . . . . . . . . . . . . . 121
9. Response Status Codes . . . . . . . . . . . . . . . . . . . . 120 9.6.2. Referer . . . . . . . . . . . . . . . . . . . . . . . 122
9.1. Overview of Status Codes . . . . . . . . . . . . . . . . 121 9.6.3. User-Agent . . . . . . . . . . . . . . . . . . . . . 123
9.2. Informational 1xx . . . . . . . . . . . . . . . . . . . . 123 10. Response Status Codes . . . . . . . . . . . . . . . . . . . . 124
9.2.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 123 10.1. Overview of Status Codes . . . . . . . . . . . . . . . . 125
9.2.2. 101 Switching Protocols . . . . . . . . . . . . . . . 123 10.2. Informational 1xx . . . . . . . . . . . . . . . . . . . 126
9.3. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 124 10.2.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 127
9.3.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 124 10.2.2. 101 Switching Protocols . . . . . . . . . . . . . . 127
9.3.2. 201 Created . . . . . . . . . . . . . . . . . . . . . 124 10.3. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 127
9.3.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 125 10.3.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 127
9.3.4. 203 Non-Authoritative Information . . . . . . . . . . 125 10.3.2. 201 Created . . . . . . . . . . . . . . . . . . . . 128
9.3.5. 204 No Content . . . . . . . . . . . . . . . . . . . 125 10.3.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 128
9.3.6. 205 Reset Content . . . . . . . . . . . . . . . . . . 126 10.3.4. 203 Non-Authoritative Information . . . . . . . . . 129
9.3.7. 206 Partial Content . . . . . . . . . . . . . . . . . 127 10.3.5. 204 No Content . . . . . . . . . . . . . . . . . . . 129
9.4. Redirection 3xx . . . . . . . . . . . . . . . . . . . . . 130 10.3.6. 205 Reset Content . . . . . . . . . . . . . . . . . 130
9.4.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 131 10.3.7. 206 Partial Content . . . . . . . . . . . . . . . . 130
9.4.2. 301 Moved Permanently . . . . . . . . . . . . . . . . 132 10.4. Redirection 3xx . . . . . . . . . . . . . . . . . . . . 133
9.4.3. 302 Found . . . . . . . . . . . . . . . . . . . . . . 132 10.4.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 135
9.4.4. 303 See Other . . . . . . . . . . . . . . . . . . . . 133 10.4.2. 301 Moved Permanently . . . . . . . . . . . . . . . 136
9.4.5. 304 Not Modified . . . . . . . . . . . . . . . . . . 133 10.4.3. 302 Found . . . . . . . . . . . . . . . . . . . . . 136
9.4.6. 305 Use Proxy . . . . . . . . . . . . . . . . . . . . 134 10.4.4. 303 See Other . . . . . . . . . . . . . . . . . . . 137
9.4.7. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 134 10.4.5. 304 Not Modified . . . . . . . . . . . . . . . . . . 137
9.4.8. 307 Temporary Redirect . . . . . . . . . . . . . . . 134 10.4.6. 305 Use Proxy . . . . . . . . . . . . . . . . . . . 138
9.4.9. 308 Permanent Redirect . . . . . . . . . . . . . . . 135 10.4.7. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 138
9.5. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 135 10.4.8. 307 Temporary Redirect . . . . . . . . . . . . . . . 138
9.5.1. 400 Bad Request . . . . . . . . . . . . . . . . . . . 135 10.4.9. 308 Permanent Redirect . . . . . . . . . . . . . . . 139
9.5.2. 401 Unauthorized . . . . . . . . . . . . . . . . . . 135 10.5. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 139
9.5.3. 402 Payment Required . . . . . . . . . . . . . . . . 136 10.5.1. 400 Bad Request . . . . . . . . . . . . . . . . . . 139
9.5.4. 403 Forbidden . . . . . . . . . . . . . . . . . . . . 136 10.5.2. 401 Unauthorized . . . . . . . . . . . . . . . . . . 139
9.5.5. 404 Not Found . . . . . . . . . . . . . . . . . . . . 136 10.5.3. 402 Payment Required . . . . . . . . . . . . . . . . 140
9.5.6. 405 Method Not Allowed . . . . . . . . . . . . . . . 137 10.5.4. 403 Forbidden . . . . . . . . . . . . . . . . . . . 140
9.5.7. 406 Not Acceptable . . . . . . . . . . . . . . . . . 137 10.5.5. 404 Not Found . . . . . . . . . . . . . . . . . . . 140
9.5.8. 407 Proxy Authentication Required . . . . . . . . . . 137 10.5.6. 405 Method Not Allowed . . . . . . . . . . . . . . . 141
9.5.9. 408 Request Timeout . . . . . . . . . . . . . . . . . 137 10.5.7. 406 Not Acceptable . . . . . . . . . . . . . . . . . 141
9.5.10. 409 Conflict . . . . . . . . . . . . . . . . . . . . 138 10.5.8. 407 Proxy Authentication Required . . . . . . . . . 141
9.5.11. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 138 10.5.9. 408 Request Timeout . . . . . . . . . . . . . . . . 141
9.5.12. 411 Length Required . . . . . . . . . . . . . . . . . 138 10.5.10. 409 Conflict . . . . . . . . . . . . . . . . . . . . 142
9.5.13. 412 Precondition Failed . . . . . . . . . . . . . . . 139 10.5.11. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 142
9.5.14. 413 Payload Too Large . . . . . . . . . . . . . . . . 139 10.5.12. 411 Length Required . . . . . . . . . . . . . . . . 142
9.5.15. 414 URI Too Long . . . . . . . . . . . . . . . . . . 139 10.5.13. 412 Precondition Failed . . . . . . . . . . . . . . 143
9.5.16. 415 Unsupported Media Type . . . . . . . . . . . . . 139 10.5.14. 413 Payload Too Large . . . . . . . . . . . . . . . 143
9.5.17. 416 Range Not Satisfiable . . . . . . . . . . . . . . 140 10.5.15. 414 URI Too Long . . . . . . . . . . . . . . . . . . 143
9.5.18. 417 Expectation Failed . . . . . . . . . . . . . . . 140 10.5.16. 415 Unsupported Media Type . . . . . . . . . . . . . 143
9.5.19. 418 (Unused) . . . . . . . . . . . . . . . . . . . . 140 10.5.17. 416 Range Not Satisfiable . . . . . . . . . . . . . 144
9.5.20. 422 Unprocessable Payload . . . . . . . . . . . . . . 141 10.5.18. 417 Expectation Failed . . . . . . . . . . . . . . . 144
9.5.21. 426 Upgrade Required . . . . . . . . . . . . . . . . 141 10.5.19. 418 (Unused) . . . . . . . . . . . . . . . . . . . . 145
9.6. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 141 10.5.20. 422 Unprocessable Payload . . . . . . . . . . . . . 145
9.6.1. 500 Internal Server Error . . . . . . . . . . . . . . 142 10.5.21. 426 Upgrade Required . . . . . . . . . . . . . . . . 145
9.6.2. 501 Not Implemented . . . . . . . . . . . . . . . . . 142 10.6. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 145
9.6.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . . 142 10.6.1. 500 Internal Server Error . . . . . . . . . . . . . 146
9.6.4. 503 Service Unavailable . . . . . . . . . . . . . . . 142 10.6.2. 501 Not Implemented . . . . . . . . . . . . . . . . 146
9.6.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . . 142 10.6.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . 146
9.6.6. 505 HTTP Version Not Supported . . . . . . . . . . . 142 10.6.4. 503 Service Unavailable . . . . . . . . . . . . . . 146
9.7. Status Code Extensibility . . . . . . . . . . . . . . . . 143 10.6.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . 146
9.7.1. Status Code Registry . . . . . . . . . . . . . . . . 143 10.6.6. 505 HTTP Version Not Supported . . . . . . . . . . . 147
9.7.2. Considerations for New Status Codes . . . . . . . . . 143 10.7. Status Code Extensibility . . . . . . . . . . . . . . . 147
10. Response Header Fields . . . . . . . . . . . . . . . . . . . 144 10.7.1. Status Code Registry . . . . . . . . . . . . . . . . 147
10.1. Control Data . . . . . . . . . . . . . . . . . . . . . . 144 10.7.2. Considerations for New Status Codes . . . . . . . . 147
10.1.1. Origination Date . . . . . . . . . . . . . . . . . . 145 11. Response Header Fields . . . . . . . . . . . . . . . . . . . 148
10.1.2. Location . . . . . . . . . . . . . . . . . . . . . . 148 11.1. Control Data . . . . . . . . . . . . . . . . . . . . . . 149
10.1.3. Retry-After . . . . . . . . . . . . . . . . . . . . 149 11.1.1. Date . . . . . . . . . . . . . . . . . . . . . . . . 149
10.1.4. Vary . . . . . . . . . . . . . . . . . . . . . . . . 149 11.1.2. Location . . . . . . . . . . . . . . . . . . . . . . 150
10.2. Validators . . . . . . . . . . . . . . . . . . . . . . . 151 11.1.3. Retry-After . . . . . . . . . . . . . . . . . . . . 151
10.2.1. Weak versus Strong . . . . . . . . . . . . . . . . . 152 11.1.4. Vary . . . . . . . . . . . . . . . . . . . . . . . . 152
10.2.2. Last-Modified . . . . . . . . . . . . . . . . . . . 153 11.2. Validators . . . . . . . . . . . . . . . . . . . . . . . 153
10.2.3. ETag . . . . . . . . . . . . . . . . . . . . . . . . 155 11.2.1. Weak versus Strong . . . . . . . . . . . . . . . . . 154
10.2.4. When to Use Entity-Tags and Last-Modified Dates . . 159 11.2.2. Last-Modified . . . . . . . . . . . . . . . . . . . 155
10.3. Authentication Challenges . . . . . . . . . . . . . . . 159 11.2.3. ETag . . . . . . . . . . . . . . . . . . . . . . . . 157
10.3.1. WWW-Authenticate . . . . . . . . . . . . . . . . . . 160 11.2.4. When to Use Entity-Tags and Last-Modified Dates . . 161
10.3.2. Proxy-Authenticate . . . . . . . . . . . . . . . . . 161 11.3. Authentication Challenges . . . . . . . . . . . . . . . 161
10.3.3. Authentication-Info . . . . . . . . . . . . . . . . 161 11.3.1. WWW-Authenticate . . . . . . . . . . . . . . . . . . 162
10.3.4. Proxy-Authentication-Info . . . . . . . . . . . . . 162 11.3.2. Proxy-Authenticate . . . . . . . . . . . . . . . . . 163
10.4. Response Context . . . . . . . . . . . . . . . . . . . . 163 11.3.3. Authentication-Info . . . . . . . . . . . . . . . . 163
10.4.1. Accept-Ranges . . . . . . . . . . . . . . . . . . . 163 11.3.4. Proxy-Authentication-Info . . . . . . . . . . . . . 164
10.4.2. Allow . . . . . . . . . . . . . . . . . . . . . . . 163 11.4. Response Context . . . . . . . . . . . . . . . . . . . . 165
10.4.3. Server . . . . . . . . . . . . . . . . . . . . . . . 164 11.4.1. Accept-Ranges . . . . . . . . . . . . . . . . . . . 165
11. Security Considerations . . . . . . . . . . . . . . . . . . . 165 11.4.2. Allow . . . . . . . . . . . . . . . . . . . . . . . 165
11.1. Establishing Authority . . . . . . . . . . . . . . . . . 165 11.4.3. Server . . . . . . . . . . . . . . . . . . . . . . . 166
11.2. Risks of Intermediaries . . . . . . . . . . . . . . . . 166 12. Security Considerations . . . . . . . . . . . . . . . . . . . 167
11.3. Attacks Based on File and Path Names . . . . . . . . . . 167 12.1. Establishing Authority . . . . . . . . . . . . . . . . . 167
11.4. Attacks Based on Command, Code, or Query Injection . . . 167 12.2. Risks of Intermediaries . . . . . . . . . . . . . . . . 168
11.5. Attacks via Protocol Element Length . . . . . . . . . . 168 12.3. Attacks Based on File and Path Names . . . . . . . . . . 169
11.6. Disclosure of Personal Information . . . . . . . . . . . 168 12.4. Attacks Based on Command, Code, or Query Injection . . . 169
11.7. Privacy of Server Log Information . . . . . . . . . . . 168 12.5. Attacks via Protocol Element Length . . . . . . . . . . 170
11.8. Disclosure of Sensitive Information in URIs . . . . . . 169 12.6. Disclosure of Personal Information . . . . . . . . . . . 170
11.9. Disclosure of Fragment after Redirects . . . . . . . . . 169 12.7. Privacy of Server Log Information . . . . . . . . . . . 170
11.10. Disclosure of Product Information . . . . . . . . . . . 170 12.8. Disclosure of Sensitive Information in URIs . . . . . . 171
11.11. Browser Fingerprinting . . . . . . . . . . . . . . . . . 170 12.9. Disclosure of Fragment after Redirects . . . . . . . . . 171
11.12. Validator Retention . . . . . . . . . . . . . . . . . . 171 12.10. Disclosure of Product Information . . . . . . . . . . . 172
11.13. Denial-of-Service Attacks Using Range . . . . . . . . . 172 12.11. Browser Fingerprinting . . . . . . . . . . . . . . . . . 172
11.14. Authentication Considerations . . . . . . . . . . . . . 172 12.12. Validator Retention . . . . . . . . . . . . . . . . . . 173
11.14.1. Confidentiality of Credentials . . . . . . . . . . 172 12.13. Denial-of-Service Attacks Using Range . . . . . . . . . 174
11.14.2. Credentials and Idle Clients . . . . . . . . . . . 173 12.14. Authentication Considerations . . . . . . . . . . . . . 174
11.14.3. Protection Spaces . . . . . . . . . . . . . . . . . 173 12.14.1. Confidentiality of Credentials . . . . . . . . . . 174
11.14.4. Additional Response Fields . . . . . . . . . . . . 174 12.14.2. Credentials and Idle Clients . . . . . . . . . . . 175
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 174 12.14.3. Protection Spaces . . . . . . . . . . . . . . . . . 175
12.1. URI Scheme Registration . . . . . . . . . . . . . . . . 174 12.14.4. Additional Response Fields . . . . . . . . . . . . 176
12.2. Method Registration . . . . . . . . . . . . . . . . . . 174 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 176
12.3. Status Code Registration . . . . . . . . . . . . . . . . 174 13.1. URI Scheme Registration . . . . . . . . . . . . . . . . 176
12.4. HTTP Field Name Registration . . . . . . . . . . . . . . 175 13.2. Method Registration . . . . . . . . . . . . . . . . . . 176
12.5. Authentication Scheme Registration . . . . . . . . . . . 175 13.3. Status Code Registration . . . . . . . . . . . . . . . . 176
12.6. Content Coding Registration . . . . . . . . . . . . . . 175 13.4. HTTP Field Name Registration . . . . . . . . . . . . . . 177
12.7. Range Unit Registration . . . . . . . . . . . . . . . . 176 13.5. Authentication Scheme Registration . . . . . . . . . . . 177
12.8. Media Type Registration . . . . . . . . . . . . . . . . 176 13.6. Content Coding Registration . . . . . . . . . . . . . . 178
12.9. Port Registration . . . . . . . . . . . . . . . . . . . 176 13.7. Range Unit Registration . . . . . . . . . . . . . . . . 178
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 176 13.8. Media Type Registration . . . . . . . . . . . . . . . . 178
13.1. Normative References . . . . . . . . . . . . . . . . . . 176 13.9. Port Registration . . . . . . . . . . . . . . . . . . . 178
13.2. Informative References . . . . . . . . . . . . . . . . . 178 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 178
Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 184 14.1. Normative References . . . . . . . . . . . . . . . . . . 178
Appendix B. Changes from previous RFCs . . . . . . . . . . . . . 188 14.2. Informative References . . . . . . . . . . . . . . . . . 180
B.1. Changes from RFC 2818 . . . . . . . . . . . . . . . . . . 188 Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 187
B.2. Changes from RFC 7230 . . . . . . . . . . . . . . . . . . 188 Appendix B. Changes from previous RFCs . . . . . . . . . . . . . 191
B.3. Changes from RFC 7231 . . . . . . . . . . . . . . . . . . 189 B.1. Changes from RFC 2818 . . . . . . . . . . . . . . . . . . 191
B.4. Changes from RFC 7232 . . . . . . . . . . . . . . . . . . 190 B.2. Changes from RFC 7230 . . . . . . . . . . . . . . . . . . 191
B.5. Changes from RFC 7233 . . . . . . . . . . . . . . . . . . 190 B.3. Changes from RFC 7231 . . . . . . . . . . . . . . . . . . 192
B.6. Changes from RFC 7235 . . . . . . . . . . . . . . . . . . 190 B.4. Changes from RFC 7232 . . . . . . . . . . . . . . . . . . 193
B.7. Changes from RFC 7538 . . . . . . . . . . . . . . . . . . 190 B.5. Changes from RFC 7233 . . . . . . . . . . . . . . . . . . 193
B.8. Changes from RFC 7615 . . . . . . . . . . . . . . . . . . 190 B.6. Changes from RFC 7235 . . . . . . . . . . . . . . . . . . 193
Appendix C. Changes from RFC 7694 . . . . . . . . . . . . . . . 190 B.7. Changes from RFC 7538 . . . . . . . . . . . . . . . . . . 193
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 191 B.8. Changes from RFC 7615 . . . . . . . . . . . . . . . . . . 193
D.1. Between RFC723x and draft 00 . . . . . . . . . . . . . . 191 Appendix C. Changes from RFC 7694 . . . . . . . . . . . . . . . 193
D.2. Since draft-ietf-httpbis-semantics-00 . . . . . . . . . . 191 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 193
D.3. Since draft-ietf-httpbis-semantics-01 . . . . . . . . . . 192 D.1. Between RFC723x and draft 00 . . . . . . . . . . . . . . 194
D.4. Since draft-ietf-httpbis-semantics-02 . . . . . . . . . . 193 D.2. Since draft-ietf-httpbis-semantics-00 . . . . . . . . . . 194
D.5. Since draft-ietf-httpbis-semantics-03 . . . . . . . . . . 194 D.3. Since draft-ietf-httpbis-semantics-01 . . . . . . . . . . 195
D.6. Since draft-ietf-httpbis-semantics-04 . . . . . . . . . . 195 D.4. Since draft-ietf-httpbis-semantics-02 . . . . . . . . . . 196
D.7. Since draft-ietf-httpbis-semantics-05 . . . . . . . . . . 195 D.5. Since draft-ietf-httpbis-semantics-03 . . . . . . . . . . 197
D.8. Since draft-ietf-httpbis-semantics-06 . . . . . . . . . . 196 D.6. Since draft-ietf-httpbis-semantics-04 . . . . . . . . . . 198
D.9. Since draft-ietf-httpbis-semantics-07 . . . . . . . . . . 198 D.7. Since draft-ietf-httpbis-semantics-05 . . . . . . . . . . 198
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199 D.8. Since draft-ietf-httpbis-semantics-06 . . . . . . . . . . 199
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 209 D.9. Since draft-ietf-httpbis-semantics-07 . . . . . . . . . . 201
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 210 D.10. Since draft-ietf-httpbis-semantics-08 . . . . . . . . . . 202
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 213
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 214
1. Introduction 1. Introduction
The Hypertext Transfer Protocol (HTTP) is a stateless application- The Hypertext Transfer Protocol (HTTP) is a stateless application-
level request/response protocol that uses extensible semantics and level request/response protocol that uses extensible semantics and
self-descriptive messages for flexible interaction with network-based self-descriptive messages for flexible interaction with network-based
hypertext information systems. HTTP is defined by a series of hypertext information systems. HTTP is defined by a series of
documents that collectively form the HTTP/1.1 specification: documents that collectively form the HTTP/1.1 specification:
o "HTTP Semantics" (this document) o "HTTP Semantics" (this document)
skipping to change at page 9, line 9 skipping to change at page 9, line 11
listens on a connection for a request, parses each message received, listens on a connection for a request, parses each message received,
interprets the message semantics in relation to the identified target interprets the message semantics in relation to the identified target
resource, and responds to that request with one or more response resource, and responds to that request with one or more response
messages. A client constructs request messages to communicate messages. A client constructs request messages to communicate
specific intentions, examines received responses to see if the specific intentions, examines received responses to see if the
intentions were carried out, and determines how to interpret the intentions were carried out, and determines how to interpret the
results. results.
HTTP provides a uniform interface for interacting with a resource HTTP provides a uniform interface for interacting with a resource
(Section 2.5), regardless of its type, nature, or implementation, via (Section 2.5), regardless of its type, nature, or implementation, via
the manipulation and transfer of representations (Section 6). the manipulation and transfer of representations (Section 7).
This document defines semantics that are common to all versions of This document defines semantics that are common to all versions of
HTTP. HTTP semantics include the intentions defined by each request HTTP. HTTP semantics include the intentions defined by each request
method (Section 7), extensions to those semantics that might be method (Section 8), extensions to those semantics that might be
described in request header fields (Section 8), the meaning of status described in request header fields (Section 9), the meaning of status
codes to indicate a machine-readable response (Section 9), and the codes to indicate a machine-readable response (Section 10), and the
meaning of other control data and resource metadata that might be meaning of other control data and resource metadata that might be
given in response header fields (Section 10). given in response header fields (Section 11).
This document also defines representation metadata that describe how This document also defines representation metadata that describe how
a payload is intended to be interpreted by a recipient, the request a payload is intended to be interpreted by a recipient, the request
header fields that might influence content selection, and the various header fields that might influence content selection, and the various
selection algorithms that are collectively referred to as "content selection algorithms that are collectively referred to as "content
negotiation" (Section 6.4). negotiation" (Section 7.4).
This document defines HTTP range requests, partial responses, and the This document defines HTTP range requests, partial responses, and the
multipart/byteranges media type. multipart/byteranges media type.
This document obsoletes the portions of RFC 7230 that are independent This document obsoletes the portions of RFC 7230 that are independent
of the HTTP/1.1 messaging syntax and connection management, with the of the HTTP/1.1 messaging syntax and connection management, with the
changes being summarized in Appendix B.2. The other parts of RFC changes being summarized in Appendix B.2. The other parts of RFC
7230 are obsoleted by "HTTP/1.1 Messaging" [Messaging]. This 7230 are obsoleted by "HTTP/1.1 Messaging" [Messaging]. This
document also obsoletes RFC 2818 (see Appendix B.1), RFC 7231 (see document also obsoletes RFC 2818 (see Appendix B.1), RFC 7231 (see
Appendix B.3), RFC 7232 (see Appendix B.4), RFC 7233 (see Appendix B.3), RFC 7232 (see Appendix B.4), RFC 7233 (see
skipping to change at page 10, line 11 skipping to change at page 10, line 11
Conformance criteria and considerations regarding error handling are Conformance criteria and considerations regarding error handling are
defined in Section 3. defined in Section 3.
1.2. Syntax Notation 1.2. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF) This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234], extended with the notation for case- notation of [RFC5234], extended with the notation for case-
sensitivity in strings defined in [RFC7405]. sensitivity in strings defined in [RFC7405].
It also uses a list extension, defined in Section 4.5, that allows It also uses a list extension, defined in Section 5.5, that allows
for compact definition of comma-separated lists using a '#' operator for compact definition of comma-separated lists using a '#' operator
(similar to how the '*' operator indicates repetition). Appendix A (similar to how the '*' operator indicates repetition). Appendix A
shows the collected grammar with all list operators expanded to shows the collected grammar with all list operators expanded to
standard ABNF notation. standard ABNF notation.
As a convention, ABNF rule names prefixed with "obs-" denote As a convention, ABNF rule names prefixed with "obs-" denote
"obsolete" grammar rules that appear for historical reasons. "obsolete" grammar rules that appear for historical reasons.
The following core rules are included by reference, as defined in The following core rules are included by reference, as defined in
Appendix B.1 of [RFC5234]: ALPHA (letters), CR (carriage return), Appendix B.1 of [RFC5234]: ALPHA (letters), CR (carriage return),
CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double
quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF
(line feed), OCTET (any 8-bit sequence of data), SP (space), and (line feed), OCTET (any 8-bit sequence of data), SP (space), and
VCHAR (any visible US-ASCII character). VCHAR (any visible US-ASCII character).
Section 4.4.1 defines some generic syntactic components for field Section 5.4.1 defines some generic syntactic components for field
values. values.
The rules below are defined in [Messaging]: The rules below are defined in [Messaging]:
protocol-name = <protocol-name, see [Messaging], Section 9.9> protocol-name = <protocol-name, see [Messaging], Section 9.9>
protocol-version = <protocol-version, see [Messaging], Section 9.9> protocol-version = <protocol-version, see [Messaging], Section 9.9>
This specification uses the terms "character", "character encoding This specification uses the terms "character", "character encoding
scheme", "charset", and "protocol element" as they are defined in scheme", "charset", and "protocol element" as they are defined in
[RFC6365]. [RFC6365].
skipping to change at page 12, line 8 skipping to change at page 12, line 8
act as a client on some connections and a server on others. The term act as a client on some connections and a server on others. The term
"user agent" refers to any of the various client programs that "user agent" refers to any of the various client programs that
initiate a request, including (but not limited to) browsers, spiders initiate a request, including (but not limited to) browsers, spiders
(web-based robots), command-line tools, custom applications, and (web-based robots), command-line tools, custom applications, and
mobile apps. The term "origin server" refers to the program that can mobile apps. The term "origin server" refers to the program that can
originate authoritative responses for a given target resource. The originate authoritative responses for a given target resource. The
terms "sender" and "recipient" refer to any implementation that sends terms "sender" and "recipient" refer to any implementation that sends
or receives a given message, respectively. or receives a given message, respectively.
HTTP relies upon the Uniform Resource Identifier (URI) standard HTTP relies upon the Uniform Resource Identifier (URI) standard
[RFC3986] to indicate the target resource (Section 5.1) and [RFC3986] to indicate the target resource (Section 6.1) and
relationships between resources. relationships between resources.
Most HTTP communication consists of a retrieval request (GET) for a Most HTTP communication consists of a retrieval request (GET) for a
representation of some resource identified by a URI. In the simplest representation of some resource identified by a URI. In the simplest
case, this might be accomplished via a single bidirectional case, this might be accomplished via a single bidirectional
connection (===) between the user agent (UA) and the origin server connection (===) between the user agent (UA) and the origin server
(O). (O).
request > request >
UA ======================================= O UA ======================================= O
< response < response
Each major version of HTTP defines its own syntax for the inclusion Each major version of HTTP defines its own syntax for the inclusion
of information in messages. Nevertheless, a common abstraction is of information in messages. Nevertheless, a common abstraction is
that a message includes some form of envelope/framing, a potential that a message includes some form of envelope/framing, a potential
set of named fields up front (a header section), a potential body, set of named fields up front (a header section), a potential body,
and a potential following set of named fields (a trailer section). and a potential following set of named fields (a trailer section).
A client sends an HTTP request to a server in the form of a request A client sends an HTTP request to a server in the form of a request
message, beginning with a method (Section 7) and request target, message with a method (Section 8) and request target. The request
followed by header fields containing request modifiers, client might also contain header fields for request modifiers, client
information, and representation metadata (Section 4), and finally a information, and representation metadata (Section 5), a payload body
payload body (if any, Section 6.3.3). (Section 7.3.3) to be processed in accordance with the method, and
trailer fields for metadata collected while sending the payload.
A server responds to a client's request by sending one or more HTTP A server responds to a client's request by sending one or more HTTP
response messages, each beginning with a success or error code response messages, each including a success or error code
(Section 9), possibly followed by header fields containing server (Section 10). The response might also contain header fields for
information, resource metadata, and representation metadata server information, resource metadata, and representation metadata
(Section 4), and finally a payload body (if any, Section 6.3.3). (Section 5), a payload body (Section 7.3.3) to be interpreted in
accordance with the status code, and trailer fields for metadata
collected while sending the payload.
One of the functions of the message framing mechanism is to assure One of the functions of the message framing mechanism is to assure
that messages are complete. A message is considered complete when that messages are complete. A message is considered complete when
all of the octets indicated by its framing are available. Note that, all of the octets indicated by its framing are available. Note that,
when no explicit framing is used, a response message that is ended by when no explicit framing is used, a response message that is ended by
the transport connection's close is considered complete even though the transport connection's close is considered complete even though
it might be indistinguishable from an incomplete response, unless a it might be indistinguishable from an incomplete response, unless a
transport-level error indicates that it is not complete. transport-level error indicates that it is not complete.
A connection might be used for multiple request/response exchanges. A connection might be used for multiple request/response exchanges.
The mechanism used to correlate between request and response messages The mechanism used to correlate between request and response messages
is version dependent; some versions of HTTP use implicit ordering of is version dependent; some versions of HTTP use implicit ordering of
messages, while others use an explicit identifier. messages, while others use an explicit identifier.
Responses (both final and interim) can be sent at any time after a Responses (both final and interim) can be sent at any time after a
request is received, even if it is not yet complete. However, request is received, even if it is not yet complete. However,
clients (including intermediaries) might abandon a request if the clients (including intermediaries) might abandon a request if the
response is not forthcoming within a reasonable period of time. response is not forthcoming within a reasonable period of time.
The following example illustrates a typical message exchange for a The following example illustrates a typical message exchange for a
GET request (Section 7.3.1) on the URI "http://www.example.com/ GET request (Section 8.3.1) on the URI "http://www.example.com/
hello.txt": hello.txt":
Client request: Client request:
GET /hello.txt HTTP/1.1 GET /hello.txt HTTP/1.1
User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3 User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com Host: www.example.com
Accept-Language: en, mi Accept-Language: en, mi
Server response: Server response:
skipping to change at page 14, line 31 skipping to change at page 14, line 34
client, usually via local configuration rules, to receive requests client, usually via local configuration rules, to receive requests
for some type(s) of absolute URI and attempt to satisfy those for some type(s) of absolute URI and attempt to satisfy those
requests via translation through the HTTP interface. Some requests via translation through the HTTP interface. Some
translations are minimal, such as for proxy requests for "http" URIs, translations are minimal, such as for proxy requests for "http" URIs,
whereas other requests might require translation to and from entirely whereas other requests might require translation to and from entirely
different application-level protocols. Proxies are often used to different application-level protocols. Proxies are often used to
group an organization's HTTP requests through a common intermediary group an organization's HTTP requests through a common intermediary
for the sake of security, annotation services, or shared caching. for the sake of security, annotation services, or shared caching.
Some proxies are designed to apply transformations to selected Some proxies are designed to apply transformations to selected
messages or payloads while they are being forwarded, as described in messages or payloads while they are being forwarded, as described in
Section 5.7.2. Section 6.7.2.
A "gateway" (a.k.a. "reverse proxy") is an intermediary that acts as A "gateway" (a.k.a. "reverse proxy") is an intermediary that acts as
an origin server for the outbound connection but translates received an origin server for the outbound connection but translates received
requests and forwards them inbound to another server or servers. requests and forwards them inbound to another server or servers.
Gateways are often used to encapsulate legacy or untrusted Gateways are often used to encapsulate legacy or untrusted
information services, to improve server performance through information services, to improve server performance through
"accelerator" caching, and to enable partitioning or load balancing "accelerator" caching, and to enable partitioning or load balancing
of HTTP services across multiple machines. of HTTP services across multiple machines.
All HTTP requirements applicable to an origin server also apply to All HTTP requirements applicable to an origin server also apply to
skipping to change at page 17, line 23 skipping to change at page 17, line 23
query = <query, see [RFC3986], Section 3.4> query = <query, see [RFC3986], Section 3.4>
absolute-path = 1*( "/" segment ) absolute-path = 1*( "/" segment )
partial-URI = relative-part [ "?" query ] partial-URI = relative-part [ "?" query ]
Each protocol element in HTTP that allows a URI reference will Each protocol element in HTTP that allows a URI reference will
indicate in its ABNF production whether the element allows any form indicate in its ABNF production whether the element allows any form
of reference (URI-reference), only a URI in absolute form (absolute- of reference (URI-reference), only a URI in absolute form (absolute-
URI), only the path and optional query components, or some URI), only the path and optional query components, or some
combination of the above. Unless otherwise indicated, URI references combination of the above. Unless otherwise indicated, URI references
are parsed relative to the target URI (Section 5.1). are parsed relative to the target URI (Section 6.1).
It is RECOMMENDED that all senders and recipients support, at a It is RECOMMENDED that all senders and recipients support, at a
minimum, URIs with lengths of 8000 octets in protocol elements. Note minimum, URIs with lengths of 8000 octets in protocol elements. Note
that this implies some structures and on-wire representations (for that this implies some structures and on-wire representations (for
example, the request line in HTTP/1.1) will necessarily be larger in example, the request line in HTTP/1.1) will necessarily be larger in
some cases. some cases.
2.5. Resources 2.5. Resources
The target of an HTTP request is called a "resource". HTTP does not The target of an HTTP request is called a "resource". HTTP does not
limit the nature of a resource; it merely defines an interface that limit the nature of a resource; it merely defines an interface that
might be used to interact with resources. Most resources are might be used to interact with resources. Most resources are
identified by a Uniform Resource Identifier (URI), as described in identified by a Uniform Resource Identifier (URI), as described in
Section 2.4. Section 2.4.
One design goal of HTTP is to separate resource identification from One design goal of HTTP is to separate resource identification from
request semantics, which is made possible by vesting the request request semantics, which is made possible by vesting the request
semantics in the request method (Section 7) and a few request- semantics in the request method (Section 8) and a few request-
modifying header fields (Section 8). If there is a conflict between modifying header fields (Section 9). If there is a conflict between
the method semantics and any semantic implied by the URI itself, as the method semantics and any semantic implied by the URI itself, as
described in Section 7.2.1, the method semantics take precedence. described in Section 8.2.1, the method semantics take precedence.
IANA maintains the registry of URI Schemes [BCP35] at IANA maintains the registry of URI Schemes [BCP35] at
<https://www.iana.org/assignments/uri-schemes/>. Although requests <https://www.iana.org/assignments/uri-schemes/>. Although requests
might target any URI scheme, the following schemes are inherent to might target any URI scheme, the following schemes are inherent to
HTTP servers: HTTP servers:
+------------+------------------------------------+---------------+ +------------+------------------------------------+---------------+
| URI Scheme | Description | Reference | | URI Scheme | Description | Reference |
+------------+------------------------------------+---------------+ +------------+------------------------------------+---------------+
| http | Hypertext Transfer Protocol | Section 2.5.1 | | http | Hypertext Transfer Protocol | Section 2.5.1 |
skipping to change at page 18, line 34 skipping to change at page 18, line 34
server listening for TCP ([RFC0793]) connections on a given port. server listening for TCP ([RFC0793]) connections on a given port.
http-URI = "http" "://" authority path-abempty [ "?" query ] http-URI = "http" "://" authority path-abempty [ "?" query ]
The origin server for an "http" URI is identified by the authority The origin server for an "http" URI is identified by the authority
component, which includes a host identifier and optional port number component, which includes a host identifier and optional port number
([RFC3986], Section 3.2.2). If the port subcomponent is empty or not ([RFC3986], Section 3.2.2). If the port subcomponent is empty or not
given, TCP port 80 (the reserved port for WWW services) is the given, TCP port 80 (the reserved port for WWW services) is the
default. The origin determines who has the right to respond default. The origin determines who has the right to respond
authoritatively to requests that target the identified resource, as authoritatively to requests that target the identified resource, as
defined in Section 5.4.1. defined in Section 6.4.1.
A sender MUST NOT generate an "http" URI with an empty host A sender MUST NOT generate an "http" URI with an empty host
identifier. A recipient that processes such a URI reference MUST identifier. A recipient that processes such a URI reference MUST
reject it as invalid. reject it as invalid.
The hierarchical path component and optional query component identify The hierarchical path component and optional query component identify
the target resource within that origin server's name space. the target resource within that origin server's name space.
2.5.2. https URI Scheme 2.5.2. https URI Scheme
skipping to change at page 19, line 15 skipping to change at page 19, line 15
strong encryption. strong encryption.
https-URI = "https" "://" authority path-abempty [ "?" query ] https-URI = "https" "://" authority path-abempty [ "?" query ]
The origin server for an "https" URI is identified by the authority The origin server for an "https" URI is identified by the authority
component, which includes a host identifier and optional port number component, which includes a host identifier and optional port number
([RFC3986], Section 3.2.2). If the port subcomponent is empty or not ([RFC3986], Section 3.2.2). If the port subcomponent is empty or not
given, TCP port 443 (the reserved port for HTTP over TLS) is the given, TCP port 443 (the reserved port for HTTP over TLS) is the
default. The origin determines who has the right to respond default. The origin determines who has the right to respond
authoritatively to requests that target the identified resource, as authoritatively to requests that target the identified resource, as
defined in Section 5.4.2. defined in Section 6.4.2.
A sender MUST NOT generate an "https" URI with an empty host A sender MUST NOT generate an "https" URI with an empty host
identifier. A recipient that processes such a URI reference MUST identifier. A recipient that processes such a URI reference MUST
reject it as invalid. reject it as invalid.
The hierarchical path component and optional query component identify The hierarchical path component and optional query component identify
the target resource within that origin server's name space. the target resource within that origin server's name space.
A client MUST ensure that its HTTP requests for an "https" resource A client MUST ensure that its HTTP requests for an "https" resource
are secured, prior to being communicated, and that it only accepts are secured, prior to being communicated, and that it only accepts
skipping to change at page 20, line 42 skipping to change at page 20, line 42
authority for the sake of phishing attacks. authority for the sake of phishing attacks.
2.5.5. Fragment Identifiers on http(s) URI References 2.5.5. Fragment Identifiers on http(s) URI References
Fragment identifiers allow for indirect identification of a secondary Fragment identifiers allow for indirect identification of a secondary
resource, independent of the URI scheme, as defined in Section 3.5 of resource, independent of the URI scheme, as defined in Section 3.5 of
[RFC3986]. Some protocol elements that refer to a URI allow [RFC3986]. Some protocol elements that refer to a URI allow
inclusion of a fragment, while others do not. They are distinguished inclusion of a fragment, while others do not. They are distinguished
by use of the ABNF rule for elements where fragment is allowed; by use of the ABNF rule for elements where fragment is allowed;
otherwise, a specific rule that excludes fragments is used (see otherwise, a specific rule that excludes fragments is used (see
Section 5.1). Section 6.1).
Note: the fragment identifier component is not part of the actual Note: the fragment identifier component is not part of the actual
scheme definition for a URI scheme (see Section 4.3 of [RFC3986]), scheme definition for a URI scheme (see Section 4.3 of [RFC3986]),
thus does not appear in the ABNF definitions for the "http" and thus does not appear in the ABNF definitions for the "http" and
"https" URI schemes above. "https" URI schemes above.
3. Conformance 3. Conformance
3.1. Implementation Diversity 3.1. Implementation Diversity
skipping to change at page 23, line 28 skipping to change at page 23, line 28
protocol element from an invalid construct. HTTP does not define protocol element from an invalid construct. HTTP does not define
specific error handling mechanisms except when they have a direct specific error handling mechanisms except when they have a direct
impact on security, since different applications of the protocol impact on security, since different applications of the protocol
require different error handling strategies. For example, a Web require different error handling strategies. For example, a Web
browser might wish to transparently recover from a response where the browser might wish to transparently recover from a response where the
Location header field doesn't parse according to the ABNF, whereas a Location header field doesn't parse according to the ABNF, whereas a
systems control client might consider any form of error recovery to systems control client might consider any form of error recovery to
be dangerous. be dangerous.
Some requests can be automatically retried by a client in the event Some requests can be automatically retried by a client in the event
of an underlying connection failure, as described in Section 7.2.2. of an underlying connection failure, as described in Section 8.2.2.
3.5. Protocol Versioning 4. Extending and Versioning HTTP
While HTTP's core semantics don't change between protocol versions,
the expression of them "on the wire" can change, and so the HTTP
version number changes when incompatible changes are made to the wire
format. Additionally, HTTP allows incremental, backwards-compatible
changes to be made to the protocol without changing its version
through the use of defined extension points.
4.1. Extending HTTP
HTTP defines a number of generic extension points that can be used to
introduce capabilities to the protocol without introducing a new
version, including methods (Section 8.4), status codes
(Section 10.7), header and trailer fields (Section 5.7), and further
extensibility points within defined fields (such as Cache-Control in
Section 5.2.3 of [Caching]). Because the semantics of HTTP are not
versioned, these extension points are persistent; the version of the
protocol in use does not affect their semantics.
Version-independent extensions are discouraged from depending on or
interacting with the specific version of the protocol in use. When
this is unavoidable, careful consideration needs to be given to how
the extension can interoperate across versions.
Additionally, specific versions of HTTP might have their own
extensibility points, such as transfer-codings in HTTP/1.1
(Section 6.1 of [Messaging]) and HTTP/2 ([RFC7540]) SETTINGS or frame
types. These extension points are specific to the version of the
protocol they occur within.
Version-specific extensions cannot override or modify the semantics
of a version-independent mechanism or extension point (like a method
or header field) without explicitly being allowed by that protocol
element. For example, the CONNECT method (Section 8.3.6) allows
this.
These guidelines assure that the protocol operates correctly and
predictably, even when parts of the path implement different versions
of HTTP.
4.2. Protocol Versioning
The HTTP version number consists of two decimal digits separated by a The HTTP version number consists of two decimal digits separated by a
"." (period or decimal point). The first digit ("major version") "." (period or decimal point). The first digit ("major version")
indicates the HTTP messaging syntax, whereas the second digit ("minor indicates the HTTP messaging syntax, whereas the second digit ("minor
version") indicates the highest minor version within that major version") indicates the highest minor version within that major
version to which the sender is conformant and able to understand for version to which the sender is conformant and able to understand for
future communication. future communication.
The protocol version as a whole indicates the sender's conformance The protocol version as a whole indicates the sender's conformance
with the set of requirements laid out in that version's corresponding with the set of requirements laid out in that version's corresponding
skipping to change at page 24, line 41 skipping to change at page 25, line 35
message with a higher minor version, when sent to a recipient that message with a higher minor version, when sent to a recipient that
has not yet indicated support for that higher version, is has not yet indicated support for that higher version, is
sufficiently backwards-compatible to be safely processed by any sufficiently backwards-compatible to be safely processed by any
implementation of the same major version. implementation of the same major version.
When a major version of HTTP does not define any minor versions, the When a major version of HTTP does not define any minor versions, the
minor version "0" is implied and is used when referring to that minor version "0" is implied and is used when referring to that
protocol within a protocol element that requires sending a minor protocol within a protocol element that requires sending a minor
version. version.
4. Header and Trailer Fields 5. Header and Trailer Fields
HTTP messages use key/value pairs to convey data about the message, HTTP messages use key/value pairs to convey data about the message,
its payload, the target resource, or the connection (i.e., control its payload, the target resource, or the connection (i.e., control
data). They are called "HTTP fields" or just "fields". data). They are called "HTTP fields" or just "fields".
Every message can have two separate areas that such fields can occur Every message can have two separate areas that such fields can occur
within; the "header field section" (or just "header section") within; the "header field section" (or just "header section")
preceding the message body and containing "header fields" (or just preceding the message body and containing "header fields" (or just
"headers", colloquially) and the "trailer field section" (or just "headers", colloquially) and the "trailer field section" (or just
"trailer section") after the message body containing "trailer fields" "trailer section") after the message body containing "trailer fields"
(or just "trailers" colloquially). Header fields are more common; (or just "trailers" colloquially). Header fields are more common;
see Section 4.6 for discussion of the applicability and limitations see Section 5.6 for discussion of the applicability and limitations
of trailer fields. of trailer fields.
Both sections are composed of any number of "field lines", each with Both sections are composed of any number of "field lines", each with
a "field name" (see Section 4.3) identifying the field, and a "field a "field name" (see Section 5.3) identifying the field, and a "field
line value" that conveys data for the field. line value" that conveys data for the field.
Each field name present in a section has a corresponding "field Each field name present in a section has a corresponding "field
value" for that section, composed from all field line values with value" for that section, composed from all field line values with
that given field name in that section, concatenated together and that given field name in that section, concatenated together and
separated with commas. See Section 4.1 for further discussion of the separated with commas. See Section 5.1 for further discussion of the
semantics of field ordering and combination in messages, and semantics of field ordering and combination in messages, and
Section 4.4 for more discussion of field values. Section 5.4 for more discussion of field values.
For example, this section: For example, this section:
Example-Field: Foo, Bar Example-Field: Foo, Bar
Example-Field: Baz Example-Field: Baz
contains two field lines, both with the field name "Example-Field". contains two field lines, both with the field name "Example-Field".
The first field line has a field line value of "Foo, Bar", while the The first field line has a field line value of "Foo, Bar", while the
second field line value is "Baz". The field value for "Example- second field line value is "Baz". The field value for "Example-
Field" is a list with three members: "Foo", "Bar", and "Baz". Field" is a list with three members: "Foo", "Bar", and "Baz".
skipping to change at page 25, line 39 skipping to change at page 26, line 36
The interpretation of a field does not change between minor versions The interpretation of a field does not change between minor versions
of the same major HTTP version, though the default behavior of a of the same major HTTP version, though the default behavior of a
recipient in the absence of such a field can change. Unless recipient in the absence of such a field can change. Unless
specified otherwise, fields are defined for all versions of HTTP. In specified otherwise, fields are defined for all versions of HTTP. In
particular, the Host and Connection fields ought to be implemented by particular, the Host and Connection fields ought to be implemented by
all HTTP/1.x implementations whether or not they advertise all HTTP/1.x implementations whether or not they advertise
conformance with HTTP/1.1. conformance with HTTP/1.1.
New fields can be introduced without changing the protocol version if New fields can be introduced without changing the protocol version if
their defined semantics allow them to be safely ignored by recipients their defined semantics allow them to be safely ignored by recipients
that do not recognize them; see Section 4.3.1. that do not recognize them; see Section 5.3.1.
4.1. Field Ordering and Combination 5.1. Field Ordering and Combination
The order in which field lines with differing names are received in a The order in which field lines with differing names are received in a
message is not significant. However, it is good practice to send message is not significant. However, it is good practice to send
header fields that contain control data first, such as Host on header fields that contain control data first, such as Host on
requests and Date on responses, so that implementations can decide requests and Date on responses, so that implementations can decide
when not to handle a message as early as possible. A server MUST NOT when not to handle a message as early as possible. A server MUST NOT
apply a request to the target resource until the entire request apply a request to the target resource until the entire request
header section is received, since later header field lines might header section is received, since later header field lines might
include conditionals, authentication credentials, or deliberately include conditionals, authentication credentials, or deliberately
misleading duplicate header fields that would impact request misleading duplicate header fields that would impact request
skipping to change at page 26, line 25 skipping to change at page 27, line 20
proxy MUST NOT change the order of these field line values when proxy MUST NOT change the order of these field line values when
forwarding a message. forwarding a message.
This means that, aside from the well-known exception noted below, a This means that, aside from the well-known exception noted below, a
sender MUST NOT generate multiple field lines with the same name in a sender MUST NOT generate multiple field lines with the same name in a
message (whether in the headers or trailers), or append a field line message (whether in the headers or trailers), or append a field line
when a field line of the same name already exists in the message, when a field line of the same name already exists in the message,
unless that field's definition allows multiple field line values to unless that field's definition allows multiple field line values to
be recombined as a comma-separated list [i.e., at least one be recombined as a comma-separated list [i.e., at least one
alternative of the field's definition allows a comma-separated list, alternative of the field's definition allows a comma-separated list,
such as an ABNF rule of #(values) defined in Section 4.5]. such as an ABNF rule of #(values) defined in Section 5.5].
Note: In practice, the "Set-Cookie" header field ([RFC6265]) often Note: In practice, the "Set-Cookie" header field ([RFC6265]) often
appears in a response message across multiple field lines and does appears in a response message across multiple field lines and does
not use the list syntax, violating the above requirements on not use the list syntax, violating the above requirements on
multiple field lines with the same field name. Since it cannot be multiple field lines with the same field name. Since it cannot be
combined into a single field value, recipients ought to handle combined into a single field value, recipients ought to handle
"Set-Cookie" as a special case while processing fields. (See "Set-Cookie" as a special case while processing fields. (See
Appendix A.2.3 of [Kri2001] for details.) Appendix A.2.3 of [Kri2001] for details.)
4.2. Field Limits 5.2. Field Limits
HTTP does not place a predefined limit on the length of each field HTTP does not place a predefined limit on the length of each field
line, field value, or on the length of the header or trailer section line, field value, or on the length of the header or trailer section
as a whole, as described in Section 3. Various ad hoc limitations on as a whole, as described in Section 3. Various ad hoc limitations on
individual lengths are found in practice, often depending on the individual lengths are found in practice, often depending on the
specific field's semantics. specific field's semantics.
A server that receives a request header field line, field value, or A server that receives a request header field line, field value, or
set of fields larger than it wishes to process MUST respond with an set of fields larger than it wishes to process MUST respond with an
appropriate 4xx (Client Error) status code. Ignoring such header appropriate 4xx (Client Error) status code. Ignoring such header
fields would increase the server's vulnerability to request smuggling fields would increase the server's vulnerability to request smuggling
attacks (Section 11.2 of [Messaging]). attacks (Section 11.2 of [Messaging]).
A client MAY discard or truncate received field lines that are larger A client MAY discard or truncate received field lines that are larger
than the client wishes to process if the field semantics are such than the client wishes to process if the field semantics are such
that the dropped value(s) can be safely ignored without changing the that the dropped value(s) can be safely ignored without changing the
message framing or response semantics. message framing or response semantics.
4.3. Field Names 5.3. Field Names
The field-name token labels the corresponding field value as having The field-name token labels the corresponding field value as having
the semantics defined by that field. For example, the Date header the semantics defined by that field. For example, the Date header
field is defined in Section 10.1.1.2 as containing the origination field is defined in Section 11.1.1 as containing the origination
timestamp for the message in which it appears. timestamp for the message in which it appears.
field-name = token field-name = token
Field names are case-insensitive and ought to be registered within Field names are case-insensitive and ought to be registered within
the "Hypertext Transfer Protocol (HTTP) Field Name Registry"; see the "Hypertext Transfer Protocol (HTTP) Field Name Registry"; see
Section 4.3.2. Section 5.3.2.
Authors of specifications defining new fields are advised to choose a Authors of specifications defining new fields are advised to choose a
short but descriptive field name. Short names avoid needless data short but descriptive field name. Short names avoid needless data
transmission; descriptive names avoid confusion and "squatting" on transmission; descriptive names avoid confusion and "squatting" on
names that might have broader uses. names that might have broader uses.
To that end, limited-use fields (such as a header confined to a To that end, limited-use fields (such as a header confined to a
single application or use case) are encouraged to use a name that single application or use case) are encouraged to use a name that
includes its name (or an abbreviation) as a prefix; for example, if includes its name (or an abbreviation) as a prefix; for example, if
the Foo Application needs a Description field, it might use "Foo- the Foo Application needs a Description field, it might use "Foo-
skipping to change at page 27, line 46 skipping to change at page 28, line 44
SHOULD begin with an alphanumeric character. SHOULD begin with an alphanumeric character.
Field names ought not be prefixed with "X-"; see [BCP178] for further Field names ought not be prefixed with "X-"; see [BCP178] for further
information. information.
Other prefixes are sometimes used in HTTP field names; for example, Other prefixes are sometimes used in HTTP field names; for example,
"Accept-" is used in many content negotiation headers. These "Accept-" is used in many content negotiation headers. These
prefixes are only an aid to recognizing the purpose of a field, and prefixes are only an aid to recognizing the purpose of a field, and
do not trigger automatic processing. do not trigger automatic processing.
4.3.1. Field Extensibility 5.3.1. Field Extensibility
There is no limit on the introduction of new field names, each There is no limit on the introduction of new field names, each
presumably defining new semantics. presumably defining new semantics.
New fields can be defined such that, when they are understood by a New fields can be defined such that, when they are understood by a
recipient, they might override or enhance the interpretation of recipient, they might override or enhance the interpretation of
previously defined fields, define preconditions on request previously defined fields, define preconditions on request
evaluation, or refine the meaning of responses. evaluation, or refine the meaning of responses.
A proxy MUST forward unrecognized header fields unless the field name A proxy MUST forward unrecognized header fields unless the field name
is listed in the Connection header field (Section 9.1 of [Messaging]) is listed in the Connection header field (Section 9.1 of [Messaging])
or the proxy is specifically configured to block, or otherwise or the proxy is specifically configured to block, or otherwise
transform, such fields. Other recipients SHOULD ignore unrecognized transform, such fields. Other recipients SHOULD ignore unrecognized
header and trailer fields. These requirements allow HTTP's header and trailer fields. These requirements allow HTTP's
functionality to be enhanced without requiring prior update of functionality to be enhanced without requiring prior update of
deployed intermediaries. deployed intermediaries.
4.3.2. Field Name Registry 5.3.2. Field Name Registry
The "Hypertext Transfer Protocol (HTTP) Field Name Registry" defines The "Hypertext Transfer Protocol (HTTP) Field Name Registry" defines
the namespace for HTTP field names. the namespace for HTTP field names.
Any party can request registration of a HTTP field. See Section 4.7 Any party can request registration of a HTTP field. See Section 5.7
for considerations to take into account when creating a new HTTP for considerations to take into account when creating a new HTTP
field. field.
The "Hypertext Transfer Protocol (HTTP) Field Name Registry" is The "Hypertext Transfer Protocol (HTTP) Field Name Registry" is
located at "https://www.iana.org/assignments/http-fields/". located at <https://www.iana.org/assignments/http-fields/>.
Registration requests can be made by following the instructions Registration requests can be made by following the instructions
located there or by sending an email to the "ietf-http-wg@ietf.org" located there or by sending an email to the "ietf-http-wg@ietf.org"
mailing list. mailing list.
Field names are registered on the advice of a Designated Expert Field names are registered on the advice of a Designated Expert
(appointed by the IESG or their delegate). Fields with the status (appointed by the IESG or their delegate). Fields with the status
'permanent' are Specification Required (using terminology from 'permanent' are Specification Required ([RFC8126], Section 4.6).
[RFC8126]).
Registration requests consist of at least the following information: Registration requests consist of at least the following information:
o Field name: The requested field name. It MUST conform to the Field name:
field-name syntax defined in Section 4.3, and SHOULD be restricted The requested field name. It MUST conform to the field-name
to just letters, digits, hyphen ('-') and underscore ('_') syntax defined in Section 5.3, and SHOULD be restricted to just
characters, with the first character being a letter. letters, digits, hyphen ('-') and underscore ('_') characters,
with the first character being a letter.
o Status: "permanent" or "provisional" Status:
"permanent" or "provisional".
o Specification document(s): Reference to the document that Specification document(s):
specifies the field, preferably including a URI that can be used Reference to the document that specifies the field, preferably
to retrieve a copy of the document. An indication of the relevant including a URI that can be used to retrieve a copy of the
section(s) can also be included, but is not required. document. An indication of the relevant section(s) can also be
included, but is not required.
And, optionally:
Comments: Additional information, such as about reserved entries.
The Expert(s) can define additional fields to be collected in the The Expert(s) can define additional fields to be collected in the
registry, in consultation with the community. registry, in consultation with the community.
Standards-defined names have a status of "permanent". Other names Standards-defined names have a status of "permanent". Other names
can also be registered as permanent, if the Expert(s) find that they can also be registered as permanent, if the Expert(s) find that they
are in use, in consultation with the community. Other names should are in use, in consultation with the community. Other names should
be registered as "provisional". be registered as "provisional".
Provisional entries can be removed by the Expert(s) if -- in Provisional entries can be removed by the Expert(s) if -- in
consultation with the community -- the Expert(s) find that they are consultation with the community -- the Expert(s) find that they are
not in use. The Experts can change a provisional entry's status to not in use. The Experts can change a provisional entry's status to
permanent at any time. permanent at any time.
Note that names can be registered by third parties (including the Note that names can be registered by third parties (including the
Expert(s)), if the Expert(s) determines that an unregistered name is Expert(s)), if the Expert(s) determines that an unregistered name is
widely deployed and not likely to be registered in a timely manner widely deployed and not likely to be registered in a timely manner
otherwise. otherwise.
4.4. Field Values 5.4. Field Values
HTTP field values typically have their syntax defined using ABNF HTTP field values typically have their syntax defined using ABNF
([RFC5234]), using the extension defined in Section 4.5 as necessary, ([RFC5234]), using the extension defined in Section 5.5 as necessary,
and are usually constrained to the range of US-ASCII characters. and are usually constrained to the range of US-ASCII characters.
Fields needing a greater range of characters can use an encoding such Fields needing a greater range of characters can use an encoding such
as the one defined in [RFC8187]. as the one defined in [RFC8187].
field-value = *field-content field-value = *field-content
field-content = field-vchar field-content = field-vchar
[ 1*( SP / HTAB / field-vchar ) field-vchar ] [ 1*( SP / HTAB / field-vchar ) field-vchar ]
field-vchar = VCHAR / obs-text field-vchar = VCHAR / obs-text
Historically, HTTP allowed field content with text in the ISO-8859-1 Historically, HTTP allowed field content with text in the ISO-8859-1
charset [ISO-8859-1], supporting other charsets only through use of charset [ISO-8859-1], supporting other charsets only through use of
[RFC2047] encoding. In practice, most HTTP field values use only a [RFC2047] encoding. In practice, most HTTP field values use only a
subset of the US-ASCII charset [USASCII]. Newly defined fields subset of the US-ASCII charset [USASCII]. Newly defined fields
SHOULD limit their values to US-ASCII octets. A recipient SHOULD SHOULD limit their values to US-ASCII octets. A recipient SHOULD
treat other octets in field content (obs-text) as opaque data. treat other octets in field content (obs-text) as opaque data.
Field values containing control (CTL) characters such as CR or LF are
invalid; recipients MUST either reject a field value containing
control characters, or convert them to SP before processing or
forwarding the message.
Leading and trailing whitespace in raw field values is removed upon Leading and trailing whitespace in raw field values is removed upon
field parsing (Section 5.1 of [Messaging]). Field definitions where field parsing (Section 5.1 of [Messaging]). Field definitions where
leading or trailing whitespace in values is significant will have to leading or trailing whitespace in values is significant will have to
use a container syntax such as quoted-string (Section 4.4.1.2). use a container syntax such as quoted-string (Section 5.4.1.2).
Because commas (",") are used as a generic delimiter between members Because commas (",") are used as a generic delimiter between members
of a list-based field value, they need to be treated with care if of a list-based field value, they need to be treated with care if
they are allowed as data within those members. Typically, list they are allowed as data within those members. Typically, list
members that might contain a comma are enclosed in a quoted-string. members that might contain a comma are enclosed in a quoted-string.
For example, a textual date and a URI (either of which might contain For example, a textual date and a URI (either of which might contain
a comma) could be safely carried in list-based field values like a comma) could be safely carried in list-based field values like
these: these:
Example-URI-Field: "http://example.com/a.html,foo", Example-URI-Field: "http://example.com/a.html,foo",
"http://without-a-comma.example.com/" "http://without-a-comma.example.com/"
Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005" Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
Note that double-quote delimiters almost always are used with the Note that double-quote delimiters almost always are used with the
quoted-string production; using a different syntax inside double- quoted-string production; using a different syntax inside double-
quotes will likely cause unnecessary confusion. quotes will likely cause unnecessary confusion.
Many fields (such as Content-Type, defined in Section 6.2.1) use a Many fields (such as Content-Type, defined in Section 7.2.1) use a
common syntax for parameters that allows both unquoted (token) and common syntax for parameters that allows both unquoted (token) and
quoted (quoted-string) syntax for a parameter value quoted (quoted-string) syntax for a parameter value
(Section 4.4.1.4). Use of common syntax allows recipients to reuse (Section 5.4.1.4). Use of common syntax allows recipients to reuse
existing parser components. When allowing both forms, the meaning of existing parser components. When allowing both forms, the meaning of
a parameter value ought to be the same whether it was received as a a parameter value ought to be the same whether it was received as a
token or a quoted string. token or a quoted string.
Historically, HTTP field values could be extended over multiple lines Historically, HTTP field values could be extended over multiple lines
by preceding each extra line with at least one space or horizontal by preceding each extra line with at least one space or horizontal
tab (obs-fold). This document assumes that any such obsolete line tab (obs-fold). This document assumes that any such obsolete line
folding has been replaced with one or more SP octets prior to folding has been replaced with one or more SP octets prior to
interpreting the field value, as described in Section 5.2 of interpreting the field value, as described in Section 5.2 of
[Messaging]. [Messaging].
This specification does not use ABNF rules to define each "Field Note: This specification does not use ABNF rules to define each
Name: Field Value" pair, as was done in earlier editions. "Field Name: Field Value" pair, as was done in earlier editions
Instead, this specification uses ABNF rules that are named (published before [RFC7230]). Instead, ABNF rules are named
according to each registered field name, wherein the rule defines according to each registered field name, wherein the rule defines
the valid grammar for that field's corresponding field values the valid grammar for that field's corresponding field values
(i.e., after the field value has been extracted by a generic field (i.e., after the field value has been extracted by a generic field
parser). parser).
4.4.1. Common Field Value Components 5.4.1. Common Field Value Components
Many HTTP field values are defined using common syntax components, Many HTTP field values are defined using common syntax components,
separated by whitespace or specific delimiting characters. separated by whitespace or specific delimiting characters.
Delimiters are chosen from the set of US-ASCII visual characters not Delimiters are chosen from the set of US-ASCII visual characters not
allowed in a token (DQUOTE and "(),/:;<=>?@[\]{}"). allowed in a token (DQUOTE and "(),/:;<=>?@[\]{}").
4.4.1.1. Tokens 5.4.1.1. Tokens
Tokens are short textual identifiers that do not include whitespace Tokens are short textual identifiers that do not include whitespace
or delimiters. or delimiters.
token = 1*tchar token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*"
/ "+" / "-" / "." / "^" / "_" / "`" / "|" / "~" / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
/ DIGIT / ALPHA / DIGIT / ALPHA
; any VCHAR, except delimiters ; any VCHAR, except delimiters
4.4.1.2. Quoted Strings 5.4.1.2. Quoted Strings
A string of text is parsed as a single value if it is quoted using A string of text is parsed as a single value if it is quoted using
double-quote marks. double-quote marks.
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qdtext = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text qdtext = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text
obs-text = %x80-FF obs-text = %x80-FF
The backslash octet ("\") can be used as a single-octet quoting The backslash octet ("\") can be used as a single-octet quoting
mechanism within quoted-string and comment constructs. Recipients mechanism within quoted-string and comment constructs. Recipients
skipping to change at page 31, line 34 skipping to change at page 32, line 39
as if it were replaced by the octet following the backslash. as if it were replaced by the octet following the backslash.
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text ) quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
A sender SHOULD NOT generate a quoted-pair in a quoted-string except A sender SHOULD NOT generate a quoted-pair in a quoted-string except
where necessary to quote DQUOTE and backslash octets occurring within where necessary to quote DQUOTE and backslash octets occurring within
that string. A sender SHOULD NOT generate a quoted-pair in a comment that string. A sender SHOULD NOT generate a quoted-pair in a comment
except where necessary to quote parentheses ["(" and ")"] and except where necessary to quote parentheses ["(" and ")"] and
backslash octets occurring within that comment. backslash octets occurring within that comment.
4.4.1.3. Comments 5.4.1.3. Comments
Comments can be included in some HTTP fields by surrounding the Comments can be included in some HTTP fields by surrounding the
comment text with parentheses. Comments are only allowed in fields comment text with parentheses. Comments are only allowed in fields
containing "comment" as part of their field value definition. containing "comment" as part of their field value definition.
comment = "(" *( ctext / quoted-pair / comment ) ")" comment = "(" *( ctext / quoted-pair / comment ) ")"
ctext = HTAB / SP / %x21-27 / %x2A-5B / %x5D-7E / obs-text ctext = HTAB / SP / %x21-27 / %x2A-5B / %x5D-7E / obs-text
4.4.1.4. Parameters 5.4.1.4. Parameters
A parameter is a name=value pair that is often defined within field A parameter is a name=value pair that is often defined within field
values as a common syntax for appending auxiliary information to an values as a common syntax for appending auxiliary information to an
item. Each parameter is usually delimited by an immediately item. Each parameter is usually delimited by an immediately
preceding semicolon. preceding semicolon.
parameter = parameter-name "=" parameter-value parameter = parameter-name "=" parameter-value
parameter-name = token parameter-name = token
parameter-value = ( token / quoted-string ) parameter-value = ( token / quoted-string )
Parameter names are case-insensitive. Parameter values might or Parameter names are case-insensitive. Parameter values might or
might not be case-sensitive, depending on the semantics of the might not be case-sensitive, depending on the semantics of the
parameter name. Examples of parameters and some equivalent forms can parameter name. Examples of parameters and some equivalent forms can
be seen in media types (Section 6.1.1) and the Accept header field be seen in media types (Section 7.1.1) and the Accept header field
(Section 8.4.1). (Section 9.4.1).
A parameter value that matches the token production can be A parameter value that matches the token production can be
transmitted either as a token or within a quoted-string. The quoted transmitted either as a token or within a quoted-string. The quoted
and unquoted values are equivalent. and unquoted values are equivalent.
Note: Parameters do not allow whitespace (not even "bad" Note: Parameters do not allow whitespace (not even "bad"
whitespace) around the "=" character. whitespace) around the "=" character.
4.5. ABNF List Extension: #rule 5.4.1.5. Date/Time Formats
Prior to 1995, there were three different formats commonly used by
servers to communicate timestamps. For compatibility with old
implementations, all three are defined here. The preferred format is
a fixed-length and single-zone subset of the date and time
specification used by the Internet Message Format [RFC5322].
HTTP-date = IMF-fixdate / obs-date
An example of the preferred format is
Sun, 06 Nov 1994 08:49:37 GMT ; IMF-fixdate
Examples of the two obsolete formats are
Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
A recipient that parses a timestamp value in an HTTP field MUST
accept all three HTTP-date formats. When a sender generates a field
that contains one or more timestamps defined as HTTP-date, the sender
MUST generate those timestamps in the IMF-fixdate format.
An HTTP-date value represents time as an instance of Coordinated
Universal Time (UTC). The first two formats indicate UTC by the
three-letter abbreviation for Greenwich Mean Time, "GMT", a
predecessor of the UTC name; values in the asctime format are assumed
to be in UTC. A sender that generates HTTP-date values from a local
clock ought to use NTP ([RFC5905]) or some similar protocol to
synchronize its clock to UTC.
Preferred format:
IMF-fixdate = day-name "," SP date1 SP time-of-day SP GMT
; fixed length/zone/capitalization subset of the format
; see Section 3.3 of [RFC5322]
day-name = %s"Mon" / %s"Tue" / %s"Wed"
/ %s"Thu" / %s"Fri" / %s"Sat" / %s"Sun"
date1 = day SP month SP year
; e.g., 02 Jun 1982
day = 2DIGIT
month = %s"Jan" / %s"Feb" / %s"Mar" / %s"Apr"
/ %s"May" / %s"Jun" / %s"Jul" / %s"Aug"
/ %s"Sep" / %s"Oct" / %s"Nov" / %s"Dec"
year = 4DIGIT
GMT = %s"GMT"
time-of-day = hour ":" minute ":" second
; 00:00:00 - 23:59:60 (leap second)
hour = 2DIGIT
minute = 2DIGIT
second = 2DIGIT
Obsolete formats:
obs-date = rfc850-date / asctime-date
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
date2 = day "-" month "-" 2DIGIT
; e.g., 02-Jun-82
day-name-l = %s"Monday" / %s"Tuesday" / %s"Wednesday"
/ %s"Thursday" / %s"Friday" / %s"Saturday" / %s"Sunday"
asctime-date = day-name SP date3 SP time-of-day SP year
date3 = month SP ( 2DIGIT / ( SP 1DIGIT ))
; e.g., Jun 2
HTTP-date is case sensitive. A sender MUST NOT generate additional
whitespace in an HTTP-date beyond that specifically included as SP in
the grammar. The semantics of day-name, day, month, year, and time-
of-day are the same as those defined for the Internet Message Format
constructs with the corresponding name ([RFC5322], Section 3.3).
Recipients of a timestamp value in rfc850-date format, which uses a
two-digit year, MUST interpret a timestamp that appears to be more
than 50 years in the future as representing the most recent year in
the past that had the same last two digits.
Recipients of timestamp values are encouraged to be robust in parsing
timestamps unless otherwise restricted by the field definition. For
example, messages are occasionally forwarded over HTTP from a non-
HTTP source that might generate any of the date and time
specifications defined by the Internet Message Format.
Note: HTTP requirements for the date/time stamp format apply only
to their usage within the protocol stream. Implementations are
not required to use these formats for user presentation, request
logging, etc.
5.5. ABNF List Extension: #rule
A #rule extension to the ABNF rules of [RFC5234] is used to improve A #rule extension to the ABNF rules of [RFC5234] is used to improve
readability in the definitions of some list-based field values. readability in the definitions of some list-based field values.
A construct "#" is defined, similar to "*", for defining comma- A construct "#" is defined, similar to "*", for defining comma-
delimited lists of elements. The full form is "<n>#<m>element" delimited lists of elements. The full form is "<n>#<m>element"
indicating at least <n> and at most <m> elements, each separated by a indicating at least <n> and at most <m> elements, each separated by a
single comma (",") and optional whitespace (OWS). single comma (",") and optional whitespace (OWS).
4.5.1. Sender Requirements 5.5.1. Sender Requirements
In any production that uses the list construct, a sender MUST NOT In any production that uses the list construct, a sender MUST NOT
generate empty list elements. In other words, a sender MUST generate generate empty list elements. In other words, a sender MUST generate
lists that satisfy the following syntax: lists that satisfy the following syntax:
1#element => element *( OWS "," OWS element ) 1#element => element *( OWS "," OWS element )
and: and:
#element => [ 1#element ] #element => [ 1#element ]
and for n >= 1 and m > 1: and for n >= 1 and m > 1:
<n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element ) <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
4.5.2. Recipient Requirements Appendix A shows the collected ABNF for senders after the list
constructs have been expanded.
5.5.2. Recipient Requirements
Empty elements do not contribute to the count of elements present. A Empty elements do not contribute to the count of elements present. A
recipient MUST parse and ignore a reasonable number of empty list recipient MUST parse and ignore a reasonable number of empty list
elements: enough to handle common mistakes by senders that merge elements: enough to handle common mistakes by senders that merge
values, but not so much that they could be used as a denial-of- values, but not so much that they could be used as a denial-of-
service mechanism. In other words, a recipient MUST accept lists service mechanism. In other words, a recipient MUST accept lists
that satisfy the following syntax: that satisfy the following syntax:
#element => [ element ] *( OWS "," OWS [ element ] ) #element => [ element ] *( OWS "," OWS [ element ] )
Note that because of the potential presence of empty list elements, Note that because of the potential presence of empty list elements,
the RFC 5234 ABNF cannot enforce the cardinality of list elements, the RFC 5234 ABNF cannot enforce the cardinality of list elements,
and consequently all cases are mapped is if there was no cardinality and consequently all cases are mapped is if there was no cardinality
specified. specified.
For example, given these ABNF productions: For example, given these ABNF productions:
example-list = 1#example-list-elmt example-list = 1#example-list-elmt
example-list-elmt = token ; see Section 4.4.1.1 example-list-elmt = token ; see Section 5.4.1.1
Then the following are valid values for example-list (not including Then the following are valid values for example-list (not including
the double quotes, which are present for delimitation only): the double quotes, which are present for delimitation only):
"foo,bar" "foo,bar"
"foo ,bar," "foo ,bar,"
"foo , ,bar,charlie" "foo , ,bar,charlie"
In contrast, the following values would be invalid, since at least In contrast, the following values would be invalid, since at least
one non-empty element is required by the example-list production: one non-empty element is required by the example-list production:
"" ""
"," ","
", ," ", ,"
Appendix A shows the collected ABNF for recipients after the list 5.6. Trailer Fields
constructs have been expanded.
4.6. Trailer Fields
4.6.1. Purpose 5.6.1. Purpose
In some HTTP versions, additional metadata can be sent after the In some HTTP versions, additional metadata can be sent after the
initial header section has been completed (during or after initial header section has been completed (during or after
transmission of the payload body), such as a message integrity check, transmission of the payload body), such as a message integrity check,
digital signature, or post-processing status. For example, the digital signature, or post-processing status. For example, the
chunked coding in HTTP/1.1 allows a trailer section after the payload chunked coding in HTTP/1.1 allows a trailer section after the payload
body (Section 7.1.2 of [Messaging]) which can contain trailer fields: body (Section 7.1.2 of [Messaging]) which can contain trailer fields:
field names and values that share the same syntax and namespace as field names and values that share the same syntax and namespace as
header fields but that are received after the header section. header fields but that are received after the header section.
Trailer fields ought to be processed and stored separately from the Trailer fields ought to be processed and stored separately from the
fields in the header section to avoid contradicting message semantics fields in the header section to avoid contradicting message semantics
known at the time the header section was complete. The presence or known at the time the header section was complete. The presence or
absence of certain header fields might impact choices made for the absence of certain header fields might impact choices made for the
routing or processing of the message as a whole before the trailers routing or processing of the message as a whole before the trailers
are received; those choices cannot be unmade by the later discovery are received; those choices cannot be unmade by the later discovery
of trailer fields. of trailer fields.
4.6.2. Limitations 5.6.2. Limitations
Many fields cannot be processed outside the header section because Many fields cannot be processed outside the header section because
their evaluation is necessary prior to receiving the message body, their evaluation is necessary prior to receiving the message body,
such as those that describe message framing, routing, authentication, such as those that describe message framing, routing, authentication,
request modifiers, response controls, or payload format. A sender request modifiers, response controls, or payload format. A sender
MUST NOT generate a trailer field unless the sender knows the MUST NOT generate a trailer field unless the sender knows the
corresponding header field name's definition permits the field to be corresponding header field name's definition permits the field to be
sent in trailers. sent in trailers.
Trailer fields can be difficult to process by intermediaries that Trailer fields can be difficult to process by intermediaries that
skipping to change at page 34, line 41 skipping to change at page 37, line 47
downstream clients are willing to accept trailer fields in the downstream clients are willing to accept trailer fields in the
forwarded response. Note that the presence of "trailers" does not forwarded response. Note that the presence of "trailers" does not
mean that the client(s) will process any particular trailer field in mean that the client(s) will process any particular trailer field in
the response; only that the trailer section as a whole will not be the response; only that the trailer section as a whole will not be
dropped by any of the clients. dropped by any of the clients.
Because of the potential for trailer fields to be discarded in Because of the potential for trailer fields to be discarded in
transit, a server SHOULD NOT generate trailer fields that it believes transit, a server SHOULD NOT generate trailer fields that it believes
are necessary for the user agent to receive. are necessary for the user agent to receive.
4.6.3. Trailer 5.6.3. Trailer
The "Trailer" header field provides a list of field names that the The "Trailer" header field provides a list of field names that the
sender anticipates sending as trailer fields within that message. sender anticipates sending as trailer fields within that message.
This allows a recipient to prepare for receipt of the indicated This allows a recipient to prepare for receipt of the indicated
metadata before it starts processing the body. metadata before it starts processing the body.
Trailer = 1#field-name Trailer = 1#field-name
For example, a sender might indicate that a message integrity check For example, a sender might indicate that a message integrity check
will be computed as the payload is being streamed and provide the will be computed as the payload is being streamed and provide the
final signature as a trailer field. This allows a recipient to final signature as a trailer field. This allows a recipient to
perform the same check on the fly as the payload data is received. perform the same check on the fly as the payload data is received.
A sender that intends to generate one or more trailer fields in a A sender that intends to generate one or more trailer fields in a
message SHOULD generate a Trailer header field in the header section message SHOULD generate a Trailer header field in the header section
of that message to indicate which fields might be present in the of that message to indicate which fields might be present in the
trailers. trailers.
4.7. Considerations for New HTTP Fields 5.7. Considerations for New HTTP Fields
See Section 4.3 for a general requirements for field names, and See Section 5.3 for a general requirements for field names, and
Section 4.4 for a discussion of field values. Section 5.4 for a discussion of field values.
Authors of specifications defining new fields are advised to consider Authors of specifications defining new fields are advised to consider
documenting: documenting:
o Whether the field is a single value or whether it can be a list o Whether the field is a single value or whether it can be a list
(delimited by commas; see Section 4.4). (delimited by commas; see Section 5.4).
If it is not a list, document how to treat messages where the If it is not a list, document how to treat messages where the
field occurs multiple times (a sensible default would be to ignore field occurs multiple times (a sensible default would be to ignore
the field, but this might not always be the right choice). the field, but this might not always be the right choice).
Note that intermediaries and software libraries might combine Note that intermediaries and software libraries might combine
multiple field instances into a single one, despite the field's multiple field instances into a single one, despite the field's
definition not allowing the list syntax. A robust format enables definition not allowing the list syntax. A robust format enables
recipients to discover these situations (good example: "Content- recipients to discover these situations (good example: "Content-
Type", as the comma can only appear inside quoted strings; bad Type", as the comma can only appear inside quoted strings; bad
skipping to change at page 36, line 18 skipping to change at page 39, line 21
o Whether it is appropriate to list the field name in the Connection o Whether it is appropriate to list the field name in the Connection
header field (i.e., if the field is to be hop-by-hop; see header field (i.e., if the field is to be hop-by-hop; see
Section 9.1 of [Messaging]). Section 9.1 of [Messaging]).
o Under what conditions intermediaries are allowed to insert, o Under what conditions intermediaries are allowed to insert,
delete, or modify the field's value. delete, or modify the field's value.
o Whether it is appropriate to list the field name in a Vary o Whether it is appropriate to list the field name in a Vary
response header field (e.g., when the request header field is used response header field (e.g., when the request header field is used
by an origin server's content selection algorithm; see by an origin server's content selection algorithm; see
Section 10.1.4). Section 11.1.4).
o Whether the field is allowable in trailers (see Section 4.6). o Whether the field is allowable in trailers (see Section 5.6).
o Whether the field ought to be preserved across redirects. o Whether the field ought to be preserved across redirects.
o Whether it introduces any additional security considerations, such o Whether it introduces any additional security considerations, such
as disclosure of privacy-related data. as disclosure of privacy-related data.
4.8. Fields Defined In This Document 5.8. Fields Defined In This Document
The following fields are defined by this document: The following fields are defined by this document:
+---------------------------+------------+-------------------+ +---------------------------+------------+-----------------+
| Field Name | Status | Reference | | Field Name | Status | Reference |
+---------------------------+------------+-------------------+ +---------------------------+------------+-----------------+
| Accept | standard | Section 8.4.1 | | Accept | standard | Section 9.4.1 |
| Accept-Charset | deprecated | Section 8.4.2 | | Accept-Charset | deprecated | Section 9.4.2 |
| Accept-Encoding | standard | Section 8.4.3 | | Accept-Encoding | standard | Section 9.4.3 |
| Accept-Language | standard | Section 8.4.4 | | Accept-Language | standard | Section 9.4.4 |
| Accept-Ranges | standard | Section 10.4.1 | | Accept-Ranges | standard | Section 11.4.1 |
| Allow | standard | Section 10.4.2 | | Allow | standard | Section 11.4.2 |
| Authentication-Info | standard | Section 10.3.3 | | Authentication-Info | standard | Section 11.3.3 |
| Authorization | standard | Section 8.5.3 | | Authorization | standard | Section 9.5.3 |
| Content-Encoding | standard | Section 6.2.2 | | Content-Encoding | standard | Section 7.2.2 |
| Content-Language | standard | Section 6.2.3 | | Content-Language | standard | Section 7.2.3 |
| Content-Length | standard | Section 6.2.4 | | Content-Length | standard | Section 7.2.4 |
| Content-Location | standard | Section 6.2.5 | | Content-Location | standard | Section 7.2.5 |
| Content-Range | standard | Section 6.3.4 | | Content-Range | standard | Section 7.3.4 |
| Content-Type | standard | Section 6.2.1 | | Content-Type | standard | Section 7.2.1 |
| Date | standard | Section 10.1.1.2 | | Date | standard | Section 11.1.1 |
| ETag | standard | Section 10.2.3 | | ETag | standard | Section 11.2.3 |
| Expect | standard | Section 8.1.1 | | Expect | standard | Section 9.1.1 |
| From | standard | Section 8.6.1 | | From | standard | Section 9.6.1 |
| Host | standard | Section 5.6 | | Host | standard | Section 6.6 |
| If-Match | standard | Section 8.2.3 | | If-Match | standard | Section 9.2.3 |
| If-Modified-Since | standard | Section 8.2.5 | | If-Modified-Since | standard | Section 9.2.5 |
| If-None-Match | standard | Section 8.2.4 | | If-None-Match | standard | Section 9.2.4 |
| If-Range | standard | Section 8.2.7 | | If-Range | standard | Section 9.2.7 |
| If-Unmodified-Since | standard | Section 8.2.6 | | If-Unmodified-Since | standard | Section 9.2.6 |
| Last-Modified | standard | Section 10.2.2 | | Last-Modified | standard | Section 11.2.2 |
| Location | standard | Section 10.1.2 | | Location | standard | Section 11.1.2 |
| Max-Forwards | standard | Section 8.1.2 | | Max-Forwards | standard | Section 9.1.2 |
| Proxy-Authenticate | standard | Section 10.3.2 | | Proxy-Authenticate | standard | Section 11.3.2 |
| Proxy-Authentication-Info | standard | Section 10.3.4 | | Proxy-Authentication-Info | standard | Section 11.3.4 |
| Proxy-Authorization | standard | Section 8.5.4 | | Proxy-Authorization | standard | Section 9.5.4 |
| Range | standard | Section 8.3 | | Range | standard | Section 9.3 |
| Referer | standard | Section 8.6.2 | | Referer | standard | Section 9.6.2 |
| Retry-After | standard | Section 10.1.3 | | Retry-After | standard | Section 11.1.3 |
| Server | standard | Section 10.4.3 | | Server | standard | Section 11.4.3 |
| Trailer | standard | Section 4.6.3 | | Trailer | standard | Section 5.6.3 |
| User-Agent | standard | Section 8.6.3 | | User-Agent | standard | Section 9.6.3 |
| Vary | standard | Section 10.1.4 | | Vary | standard | Section 11.1.4 |
| Via | standard | Section 5.7.1 | | Via | standard | Section 6.7.1 |
| WWW-Authenticate | standard | Section 10.3.1 | | WWW-Authenticate | standard | Section 11.3.1 |
+---------------------------+------------+-------------------+ +---------------------------+------------+-----------------+
Table 1 Table 1
5. Message Routing Furthermore, the field name "*" is reserved, since using that name as
an HTTP header field might conflict with its special semantics in the
Vary header field (Section 11.1.4).
+------------+----------+--------------+-------------+
| Field Name | Status | Reference | Comments |
+------------+----------+--------------+-------------+
| * | standard | Section 5.8 | (reserved) |
+------------+----------+--------------+-------------+
6. Message Routing
HTTP request message routing is determined by each client based on HTTP request message routing is determined by each client based on
the target resource, the client's proxy configuration, and the target resource, the client's proxy configuration, and
establishment or reuse of an inbound connection. The corresponding establishment or reuse of an inbound connection. The corresponding
response routing follows the same connection chain back to the response routing follows the same connection chain back to the
client. client.
5.1. Identifying a Target Resource 6.1. Identifying a Target Resource
HTTP is used in a wide variety of applications, ranging from general- HTTP is used in a wide variety of applications, ranging from general-
purpose computers to home appliances. In some cases, communication purpose computers to home appliances. In some cases, communication
options are hard-coded in a client's configuration. However, most options are hard-coded in a client's configuration. However, most
HTTP clients rely on the same resource identification mechanism and HTTP clients rely on the same resource identification mechanism and
configuration techniques as general-purpose Web browsers. configuration techniques as general-purpose Web browsers.
HTTP communication is initiated by a user agent for some purpose. HTTP communication is initiated by a user agent for some purpose.
The purpose is a combination of request semantics and a target The purpose is a combination of request semantics and a target
resource upon which to apply those semantics. The "request target" resource upon which to apply those semantics. The "request target"
skipping to change at page 38, line 35 skipping to change at page 41, line 45
Typically, the request target is a URI reference (Section 2.4) which Typically, the request target is a URI reference (Section 2.4) which
a user agent would resolve to its absolute form in order to obtain a user agent would resolve to its absolute form in order to obtain
the "target URI". The target URI excludes the reference's fragment the "target URI". The target URI excludes the reference's fragment
component, if any, since fragment identifiers are reserved for component, if any, since fragment identifiers are reserved for
client-side processing ([RFC3986], Section 3.5). client-side processing ([RFC3986], Section 3.5).
However, there are two special, method-specific forms allowed for the However, there are two special, method-specific forms allowed for the
request target in specific circumstances: request target in specific circumstances:
o For CONNECT (Section 7.3.6), the request target is the host name o For CONNECT (Section 8.3.6), the request target is the host name
and port number of the tunnel destination, separated by a colon. and port number of the tunnel destination, separated by a colon.
o For OPTIONS (Section 7.3.7), the request target can be a single o For OPTIONS (Section 8.3.7), the request target can be a single
asterisk ("*"). asterisk ("*").
See the respective method definitions for details. These forms MUST See the respective method definitions for details. These forms MUST
NOT be used with other methods. NOT be used with other methods.
5.2. Determining Origin 6.2. Determining Origin
The "origin" for a given URI is the triple of scheme, host, and port The "origin" for a given URI is the triple of scheme, host, and port
after normalizing the scheme and host to lowercase and normalizing after normalizing the scheme and host to lowercase and normalizing
the port to remove any leading zeros. If port is elided from the the port to remove any leading zeros. If port is elided from the
URI, the default port for that scheme is used. For example, the URI URI, the default port for that scheme is used. For example, the URI
https://Example.Com/happy.js https://Example.Com/happy.js
would have the origin would have the origin
skipping to change at page 39, line 30 skipping to change at page 42, line 39
future. future.
Two origins are distinct if they differ in scheme, host, or port. Two origins are distinct if they differ in scheme, host, or port.
Even when it can be verified that the same entity controls two Even when it can be verified that the same entity controls two
distinct origins, the two namespaces under those origins are distinct distinct origins, the two namespaces under those origins are distinct
unless explicitly aliased by a server authoritative for that origin. unless explicitly aliased by a server authoritative for that origin.
Origin is also used within HTML and related Web protocols, beyond the Origin is also used within HTML and related Web protocols, beyond the
scope of this document, as described in [RFC6454]. scope of this document, as described in [RFC6454].
5.3. Routing Inbound 6.3. Routing Inbound
Once the target URI and its origin are determined, a client decides Once the target URI and its origin are determined, a client decides
whether a network request is necessary to accomplish the desired whether a network request is necessary to accomplish the desired
semantics and, if so, where that request is to be directed. semantics and, if so, where that request is to be directed.
If the client has a cache [Caching] and the request can be satisfied If the client has a cache [Caching] and the request can be satisfied
by it, then the request is usually directed there first. by it, then the request is usually directed there first.
If the request is not satisfied by a cache, then a typical client If the request is not satisfied by a cache, then a typical client
will check its configuration to determine whether a proxy is to be will check its configuration to determine whether a proxy is to be
skipping to change at page 40, line 7 skipping to change at page 43, line 16
to that proxy. to that proxy.
If no proxy is applicable, a typical client will invoke a handler If no proxy is applicable, a typical client will invoke a handler
routine, usually specific to the target URI's scheme, to connect routine, usually specific to the target URI's scheme, to connect
directly to an origin for the target resource. How that is directly to an origin for the target resource. How that is
accomplished is dependent on the target URI scheme and defined by its accomplished is dependent on the target URI scheme and defined by its
associated specification, similar to how this specification defines associated specification, similar to how this specification defines
origin server access for resolution of the "http" (Section 2.5.1) and origin server access for resolution of the "http" (Section 2.5.1) and
"https" (Section 2.5.2) schemes. "https" (Section 2.5.2) schemes.
5.4. Direct Authoritative Access 6.4. Direct Authoritative Access
5.4.1. http origins 6.4.1. http origins
Although HTTP is independent of the transport protocol, the "http" Although HTTP is independent of the transport protocol, the "http"
scheme is specific to associating authority with whomever controls scheme is specific to associating authority with whomever controls
the origin server listening for TCP connections on the indicated port the origin server listening for TCP connections on the indicated port
of whatever host is identified within the authority component. This of whatever host is identified within the authority component. This
is a very weak sense of authority because it depends on both client- is a very weak sense of authority because it depends on both client-
specific name resolution mechanisms and communication that might not specific name resolution mechanisms and communication that might not
be secured from man-in-the-middle attacks. Nevertheless, it is a be secured from man-in-the-middle attacks. Nevertheless, it is a
sufficient minimum for binding "http" identifiers to an origin server sufficient minimum for binding "http" identifiers to an origin server
for consistent resolution within a trusted environment. for consistent resolution within a trusted environment.
skipping to change at page 40, line 35 skipping to change at page 43, line 44
DNS, to find an address for an appropriate origin server. DNS, to find an address for an appropriate origin server.
When an "http" URI is used within a context that calls for access to When an "http" URI is used within a context that calls for access to
the indicated resource, a client MAY attempt access by resolving the the indicated resource, a client MAY attempt access by resolving the
host identifier to an IP address, establishing a TCP connection to host identifier to an IP address, establishing a TCP connection to
that address on the indicated port, and sending an HTTP request that address on the indicated port, and sending an HTTP request
message to the server containing the URI's identifying data message to the server containing the URI's identifying data
(Section 2 of [Messaging]). (Section 2 of [Messaging]).
If the server responds to such a request with a non-interim HTTP If the server responds to such a request with a non-interim HTTP
response message, as described in Section 9, then that response is response message, as described in Section 10, then that response is
considered an authoritative answer to the client's request. considered an authoritative answer to the client's request.
Note, however, that the above is not the only means for obtaining an Note, however, that the above is not the only means for obtaining an
authoritative response, nor does it imply that an authoritative authoritative response, nor does it imply that an authoritative
response is always necessary (see [Caching]). For example, the Alt- response is always necessary (see [Caching]). For example, the Alt-
Svc header field [RFC7838] allows an origin server to identify other Svc header field [RFC7838] allows an origin server to identify other
services that are also authoritative for that origin. Access to services that are also authoritative for that origin. Access to
"http" identified resources might also be provided by protocols "http" identified resources might also be provided by protocols
outside the scope of this document. outside the scope of this document.
See Section 11.1 for security considerations related to establishing See Section 12.1 for security considerations related to establishing
authority. authority.
5.4.2. https origins 6.4.2. https origins
The "https" scheme associates authority based on the ability of a The "https" scheme associates authority based on the ability of a
server to use a private key associated with a certificate that the server to use a private key associated with a certificate that the
client considers to be trustworthy for the identified host. If a client considers to be trustworthy for the identified host. If a
server presents a certificate that verifiably applies to the host, server presents a certificate that verifiably applies to the host,
along with proof that it controls the corresponding private key, then along with proof that it controls the corresponding private key, then
a client will accept a secured connection to that server as being a client will accept a secured connection to that server as being
authoritative for all origins with the same scheme and host. authoritative for all origins with the same scheme and host.
A client is therefore relying upon a chain of trust, conveyed from A client is therefore relying upon a chain of trust, conveyed from
some trust anchor (which is usually prearranged or configured), some trust anchor (which is usually prearranged or configured),
through a chain of certificates (e.g., [RFC5280]) to a final through a chain of certificates (e.g., [RFC5280]) to a final
certificate that binds a private key to the host name of the origin. certificate that binds a private key to the host name of the origin.
The handshake and certificate validation in Section 5.4.3 describe The handshake and certificate validation in Section 6.4.3 describe
how that final certificate can be used to initiate a secured how that final certificate can be used to initiate a secured
connection. connection.
Note that the "https" scheme does not rely on TCP and the connected Note that the "https" scheme does not rely on TCP and the connected
port number for associating authority, since both are outside the port number for associating authority, since both are outside the
secured communication and thus cannot be trusted as definitive. secured communication and thus cannot be trusted as definitive.
Hence, the HTTP communication might take place over any channel that Hence, the HTTP communication might take place over any channel that
has been secured, as defined in Section 2.5.2, including protocols has been secured, as defined in Section 2.5.2, including protocols
that don't use TCP. It is the origin's responsibility to ensure that that don't use TCP. It is the origin's responsibility to ensure that
any services provided with control over its certificate's private key any services provided with control over its certificate's private key
skipping to change at page 42, line 27 skipping to change at page 45, line 34
When an "https" URI is used within a context that calls for access to When an "https" URI is used within a context that calls for access to
the indicated resource, a client MAY attempt access by resolving the the indicated resource, a client MAY attempt access by resolving the
host identifier to an IP address, establishing a TCP connection to host identifier to an IP address, establishing a TCP connection to
that address on the indicated port, securing the connection end-to- that address on the indicated port, securing the connection end-to-
end by successfully initiating TLS over TCP with confidentiality and end by successfully initiating TLS over TCP with confidentiality and
integrity protection, and sending an HTTP request message to the integrity protection, and sending an HTTP request message to the
server over that secured connection containing the URI's identifying server over that secured connection containing the URI's identifying
data (Section 2 of [Messaging]). data (Section 2 of [Messaging]).
If the server responds to such a request with a non-interim HTTP If the server responds to such a request with a non-interim HTTP
response message, as described in Section 9, then that response is response message, as described in Section 10, then that response is
considered an authoritative answer to the client's request. considered an authoritative answer to the client's request.
Note, however, that the above is not the only means for obtaining an Note, however, that the above is not the only means for obtaining an
authoritative response, nor does it imply that an authoritative authoritative response, nor does it imply that an authoritative
response is always necessary (see [Caching]). response is always necessary (see [Caching]).
5.4.3. Initiating HTTP Over TLS 6.4.3. Initiating HTTP Over TLS
Conceptually, HTTP/TLS is very simple. Simply use HTTP over TLS Conceptually, HTTP/TLS is very simple. Simply use HTTP over TLS
precisely as you would use HTTP over TCP. precisely as you would use HTTP over TCP.
The agent acting as the HTTP client should also act as the TLS The agent acting as the HTTP client should also act as the TLS
client. It should initiate a connection to the server on the client. It should initiate a connection to the server on the
appropriate port and then send the TLS ClientHello to begin the TLS appropriate port and then send the TLS ClientHello to begin the TLS
handshake. When the TLS handshake has finished. The client may then handshake. When the TLS handshake has finished. The client may then
initiate the first HTTP request. All HTTP data MUST be sent as TLS initiate the first HTTP request. All HTTP data MUST be sent as TLS
"application data". Normal HTTP behavior, including retained "application data". Normal HTTP behavior, including retained
connections should be followed. connections should be followed.
5.4.3.1. Identifying HTTPS Servers 6.4.3.1. Identifying HTTPS Servers
In general, HTTP/TLS requests are generated by dereferencing a URI. In general, HTTP/TLS requests are generated by dereferencing a URI.
As a consequence, the hostname for the server is known to the client. As a consequence, the hostname for the server is known to the client.
If the hostname is available, the client MUST check it against the If the hostname is available, the client MUST check it against the
server's identity as presented in the server's Certificate message, server's identity as presented in the server's Certificate message,
in order to prevent man-in-the-middle attacks. in order to prevent man-in-the-middle attacks.
If the client has external information as to the expected identity of If the client has external information as to the expected identity of
the server, the hostname check MAY be omitted. (For instance, a the server, the hostname check MAY be omitted. (For instance, a
client may be connecting to a machine whose address and hostname are client may be connecting to a machine whose address and hostname are
skipping to change at page 44, line 5 skipping to change at page 47, line 14
Note that in many cases the URI itself comes from an untrusted Note that in many cases the URI itself comes from an untrusted
source. The above-described check provides no protection against source. The above-described check provides no protection against
attacks where this source is compromised. For example, if the URI attacks where this source is compromised. For example, if the URI
was obtained by clicking on an HTML page which was itself obtained was obtained by clicking on an HTML page which was itself obtained
without using HTTP/TLS, a man in the middle could have replaced the without using HTTP/TLS, a man in the middle could have replaced the
URI. In order to prevent this form of attack, users should carefully URI. In order to prevent this form of attack, users should carefully
examine the certificate presented by the server to determine if it examine the certificate presented by the server to determine if it
meets their expectations. meets their expectations.
5.4.3.2. Identifying HTTPS Clients 6.4.3.2. Identifying HTTPS Clients
Typically, the server has no external knowledge of what the client's Typically, the server has no external knowledge of what the client's
identity ought to be and so checks (other than that the client has a identity ought to be and so checks (other than that the client has a
certificate chain rooted in an appropriate CA) are not possible. If certificate chain rooted in an appropriate CA) are not possible. If
a server has such knowledge (typically from some source external to a server has such knowledge (typically from some source external to
HTTP or TLS) it SHOULD check the identity as described above. HTTP or TLS) it SHOULD check the identity as described above.
5.5. Reconstructing the Target URI 6.5. Reconstructing the Target URI
Once an inbound connection is obtained, the client sends an HTTP Once an inbound connection is obtained, the client sends an HTTP
request message (Section 2 of [Messaging]). request message (Section 2 of [Messaging]).
Depending on the nature of the request, the client's target URI might Depending on the nature of the request, the client's target URI might
be split into components and transmitted (or implied) within various be split into components and transmitted (or implied) within various
parts of a request message. These parts are recombined by each parts of a request message. These parts are recombined by each
recipient, in accordance with their local configuration and incoming recipient, in accordance with their local configuration and incoming
connection context, to determine the target URI. Appendix of connection context, to determine the target URI. Appendix of
[Messaging] defines how a server determines the target URI for an [Messaging] defines how a server determines the target URI for an
skipping to change at page 44, line 35 skipping to change at page 47, line 44
Once the target URI has been reconstructed, an origin server needs to Once the target URI has been reconstructed, an origin server needs to
decide whether or not to provide service for that URI via the decide whether or not to provide service for that URI via the
connection in which the request was received. For example, the connection in which the request was received. For example, the
request might have been misdirected, deliberately or accidentally, request might have been misdirected, deliberately or accidentally,
such that the information within a received Host header field differs such that the information within a received Host header field differs
from the host or port upon which the connection has been made. If from the host or port upon which the connection has been made. If
the connection is from a trusted gateway, that inconsistency might be the connection is from a trusted gateway, that inconsistency might be
expected; otherwise, it might indicate an attempt to bypass security expected; otherwise, it might indicate an attempt to bypass security
filters, trick the server into delivering non-public content, or filters, trick the server into delivering non-public content, or
poison a cache. See Section 11 for security considerations regarding poison a cache. See Section 12 for security considerations regarding
message routing. message routing.
Note: previous specifications defined the recomposed target URI as Note: previous specifications defined the recomposed target URI as
a distinct concept, the effective request URI. a distinct concept, the effective request URI.
5.6. Host 6.6. Host
The "Host" header field in a request provides the host and port The "Host" header field in a request provides the host and port
information from the target URI, enabling the origin server to information from the target URI, enabling the origin server to
distinguish among resources while servicing requests for multiple distinguish among resources while servicing requests for multiple
host names on a single IP address. host names on a single IP address.
Host = uri-host [ ":" port ] ; Section 2.4 Host = uri-host [ ":" port ] ; Section 2.4
A client MUST send a Host header field in all HTTP/1.1 request A client MUST send a Host header field in all HTTP/1.1 request
messages. If the target URI includes an authority component, then a messages. If the target URI includes an authority component, then a
skipping to change at page 45, line 33 skipping to change at page 48, line 46
Host field value for redirecting requests to internal servers, or for Host field value for redirecting requests to internal servers, or for
use as a cache key in a shared cache, without first verifying that use as a cache key in a shared cache, without first verifying that
the intercepted connection is targeting a valid IP address for that the intercepted connection is targeting a valid IP address for that
host. host.
A server MUST respond with a 400 (Bad Request) status code to any A server MUST respond with a 400 (Bad Request) status code to any
HTTP/1.1 request message that lacks a Host header field and to any HTTP/1.1 request message that lacks a Host header field and to any
request message that contains more than one Host header field or a request message that contains more than one Host header field or a
Host header field with an invalid field value. Host header field with an invalid field value.
5.7. Message Forwarding 6.7. Message Forwarding
As described in Section 2.2, intermediaries can serve a variety of As described in Section 2.2, intermediaries can serve a variety of
roles in the processing of HTTP requests and responses. Some roles in the processing of HTTP requests and responses. Some
intermediaries are used to improve performance or availability. intermediaries are used to improve performance or availability.
Others are used for access control or to filter content. Since an Others are used for access control or to filter content. Since an
HTTP stream has characteristics similar to a pipe-and-filter HTTP stream has characteristics similar to a pipe-and-filter
architecture, there are no inherent limits to the extent an architecture, there are no inherent limits to the extent an
intermediary can enhance (or interfere) with either direction of the intermediary can enhance (or interfere) with either direction of the
stream. stream.
skipping to change at page 46, line 13 skipping to change at page 49, line 25
ought to recognize its own server names, including any aliases, local ought to recognize its own server names, including any aliases, local
variations, or literal IP addresses, and respond to such requests variations, or literal IP addresses, and respond to such requests
directly. directly.
An HTTP message can be parsed as a stream for incremental processing An HTTP message can be parsed as a stream for incremental processing
or forwarding downstream. However, recipients cannot rely on or forwarding downstream. However, recipients cannot rely on
incremental delivery of partial messages, since some implementations incremental delivery of partial messages, since some implementations
will buffer or delay message forwarding for the sake of network will buffer or delay message forwarding for the sake of network
efficiency, security checks, or payload transformations. efficiency, security checks, or payload transformations.
5.7.1. Via 6.7.1. Via
The "Via" header field indicates the presence of intermediate The "Via" header field indicates the presence of intermediate
protocols and recipients between the user agent and the server (on protocols and recipients between the user agent and the server (on
requests) or between the origin server and the client (on responses), requests) or between the origin server and the client (on responses),
similar to the "Received" header field in email (Section 3.6.7 of similar to the "Received" header field in email (Section 3.6.7 of
[RFC5322]). Via can be used for tracking message forwards, avoiding [RFC5322]). Via can be used for tracking message forwards, avoiding
request loops, and identifying the protocol capabilities of senders request loops, and identifying the protocol capabilities of senders
along the request/response chain. along the request/response chain.
Via = 1#( received-protocol RWS received-by [ RWS comment ] ) Via = 1#( received-protocol RWS received-by [ RWS comment ] )
skipping to change at page 46, line 47 skipping to change at page 50, line 11
MUST send an appropriate Via header field in each inbound request MUST send an appropriate Via header field in each inbound request
message and MAY send a Via header field in forwarded response message and MAY send a Via header field in forwarded response
messages. messages.
For each intermediary, the received-protocol indicates the protocol For each intermediary, the received-protocol indicates the protocol
and protocol version used by the upstream sender of the message. and protocol version used by the upstream sender of the message.
Hence, the Via field value records the advertised protocol Hence, the Via field value records the advertised protocol
capabilities of the request/response chain such that they remain capabilities of the request/response chain such that they remain
visible to downstream recipients; this can be useful for determining visible to downstream recipients; this can be useful for determining
what backwards-incompatible features might be safe to use in what backwards-incompatible features might be safe to use in
response, or within a later request, as described in Section 3.5. response, or within a later request, as described in Section 4.2.
For brevity, the protocol-name is omitted when the received protocol For brevity, the protocol-name is omitted when the received protocol
is HTTP. is HTTP.
The received-by portion is normally the host and optional port number The received-by portion is normally the host and optional port number
of a recipient server or client that subsequently forwarded the of a recipient server or client that subsequently forwarded the
message. However, if the real host is considered to be sensitive message. However, if the real host is considered to be sensitive
information, a sender MAY replace it with a pseudonym. If a port is information, a sender MAY replace it with a pseudonym. If a port is
not provided, a recipient MAY interpret that as meaning it was not provided, a recipient MAY interpret that as meaning it was
received on the default TCP port, if any, for the received-protocol. received on the default TCP port, if any, for the received-protocol.
skipping to change at page 47, line 47 skipping to change at page 51, line 10
could be collapsed to could be collapsed to
Via: 1.0 ricky, 1.1 mertz, 1.0 lucy Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
A sender SHOULD NOT combine multiple list members unless they are all A sender SHOULD NOT combine multiple list members unless they are all
under the same organizational control and the hosts have already been under the same organizational control and the hosts have already been
replaced by pseudonyms. A sender MUST NOT combine members that have replaced by pseudonyms. A sender MUST NOT combine members that have
different received-protocol values. different received-protocol values.
5.7.2. Transformations 6.7.2. Transformations
Some intermediaries include features for transforming messages and Some intermediaries include features for transforming messages and
their payloads. A proxy might, for example, convert between image their payloads. A proxy might, for example, convert between image
formats in order to save cache space or to reduce the amount of formats in order to save cache space or to reduce the amount of
traffic on a slow link. However, operational problems might occur traffic on a slow link. However, operational problems might occur
when these transformations are applied to payloads intended for when these transformations are applied to payloads intended for
critical applications, such as medical imaging or scientific data critical applications, such as medical imaging or scientific data
analysis, particularly when integrity checks or digital signatures analysis, particularly when integrity checks or digital signatures
are used to ensure that the payload received is identical to the are used to ensure that the payload received is identical to the
original. original.
skipping to change at page 48, line 34 skipping to change at page 51, line 46
received when forwarding the request. A proxy MUST NOT change the received when forwarding the request. A proxy MUST NOT change the
host name if the target URI contains a fully qualified domain name. host name if the target URI contains a fully qualified domain name.
A proxy MUST NOT modify the "absolute-path" and "query" parts of the A proxy MUST NOT modify the "absolute-path" and "query" parts of the
received target URI when forwarding it to the next inbound server, received target URI when forwarding it to the next inbound server,
except as noted above to replace an empty path with "/" or "*". except as noted above to replace an empty path with "/" or "*".
A proxy MAY modify the message body through application or removal of A proxy MAY modify the message body through application or removal of
a transfer coding (Section 7 of [Messaging]). a transfer coding (Section 7 of [Messaging]).
A proxy MUST NOT transform the payload (Section 6.3) of a message A proxy MUST NOT transform the payload (Section 7.3) of a message
that contains a no-transform cache-control response directive that contains a no-transform cache-control response directive
(Section 5.2 of [Caching]). (Section 5.2 of [Caching]).
A proxy MAY transform the payload of a message that does not contain A proxy MAY transform the payload of a message that does not contain
a no-transform cache-control directive. A proxy that transforms the a no-transform cache-control directive. A proxy that transforms the
payload of a 200 (OK) response can inform downstream recipients that payload of a 200 (OK) response can inform downstream recipients that
a transformation has been applied by changing the response status a transformation has been applied by changing the response status
code to 203 (Non-Authoritative Information) (Section 9.3.4). code to 203 (Non-Authoritative Information) (Section 10.3.4).
A proxy SHOULD NOT modify header fields that provide information A proxy SHOULD NOT modify header fields that provide information
about the endpoints of the communication chain, the resource state, about the endpoints of the communication chain, the resource state,
or the selected representation (other than the payload) unless the or the selected representation (other than the payload) unless the
field's definition specifically allows such modification or the field's definition specifically allows such modification or the
modification is deemed necessary for privacy or security. modification is deemed necessary for privacy or security.
6. Representations 7. Representations
Considering that a resource could be anything, and that the uniform Considering that a resource could be anything, and that the uniform
interface provided by HTTP is similar to a window through which one interface provided by HTTP is similar to a window through which one
can observe and act upon such a thing only through the communication can observe and act upon such a thing only through the communication
of messages to some independent actor on the other side, an of messages to some independent actor on the other side, an
abstraction is needed to represent ("take the place of") the current abstraction is needed to represent ("take the place of") the current
or desired state of that thing in our communications. That or desired state of that thing in our communications. That
abstraction is called a representation [REST]. abstraction is called a representation [REST].
For the purposes of HTTP, a "representation" is information that is For the purposes of HTTP, a "representation" is information that is
skipping to change at page 49, line 27 skipping to change at page 52, line 35
resource, in a format that can be readily communicated via the resource, in a format that can be readily communicated via the
protocol, and that consists of a set of representation metadata and a protocol, and that consists of a set of representation metadata and a
potentially unbounded stream of representation data. potentially unbounded stream of representation data.
An origin server might be provided with, or be capable of generating, An origin server might be provided with, or be capable of generating,
multiple representations that are each intended to reflect the multiple representations that are each intended to reflect the
current state of a target resource. In such cases, some algorithm is current state of a target resource. In such cases, some algorithm is
used by the origin server to select one of those representations as used by the origin server to select one of those representations as
most applicable to a given request, usually based on content most applicable to a given request, usually based on content
negotiation. This "selected representation" is used to provide the negotiation. This "selected representation" is used to provide the
data and metadata for evaluating conditional requests (Section 8.2) data and metadata for evaluating conditional requests (Section 9.2)
and constructing the payload for 200 (OK), 206 (Partial Content), and and constructing the payload for 200 (OK), 206 (Partial Content), and
304 (Not Modified) responses to GET (Section 7.3.1). 304 (Not Modified) responses to GET (Section 8.3.1).
6.1. Representation Data 7.1. Representation Data
The representation data associated with an HTTP message is either The representation data associated with an HTTP message is either
provided as the payload body of the message or referred to by the provided as the payload body of the message or referred to by the
message semantics and the target URI. The representation data is in message semantics and the target URI. The representation data is in
a format and encoding defined by the representation metadata header a format and encoding defined by the representation metadata header
fields. fields.
The data type of the representation data is determined via the header The data type of the representation data is determined via the header
fields Content-Type and Content-Encoding. These define a two-layer, fields Content-Type and Content-Encoding. These define a two-layer,
ordered encoding model: ordered encoding model:
representation-data := Content-Encoding( Content-Type( bits ) ) representation-data := Content-Encoding( Content-Type( bits ) )
6.1.1. Media Type 7.1.1. Media Type
HTTP uses media types [RFC2046] in the Content-Type (Section 6.2.1) HTTP uses media types [RFC2046] in the Content-Type (Section 7.2.1)
and Accept (Section 8.4.1) header fields in order to provide open and and Accept (Section 9.4.1) header fields in order to provide open and
extensible data typing and type negotiation. Media types define both extensible data typing and type negotiation. Media types define both
a data format and various processing models: how to process that data a data format and various processing models: how to process that data
in accordance with each context in which it is received. in accordance with each context in which it is received.
media-type = type "/" subtype *( OWS ";" OWS parameter ) media-type = type "/" subtype *( OWS ";" OWS parameter )
type = token type = token
subtype = token subtype = token
The type and subtype tokens are case-insensitive. The type and subtype tokens are case-insensitive.
The type/subtype MAY be followed by semicolon-delimited parameters The type/subtype MAY be followed by semicolon-delimited parameters
(Section 4.4.1.4) in the form of name=value pairs. The presence or (Section 5.4.1.4) in the form of name=value pairs. The presence or
absence of a parameter might be significant to the processing of a absence of a parameter might be significant to the processing of a
media type, depending on its definition within the media type media type, depending on its definition within the media type
registry. Parameter values might or might not be case-sensitive, registry. Parameter values might or might not be case-sensitive,
depending on the semantics of the parameter name. depending on the semantics of the parameter name.
For example, the following media types are equivalent in describing For example, the following media types are equivalent in describing
HTML text data encoded in the UTF-8 character encoding scheme, but HTML text data encoded in the UTF-8 character encoding scheme, but
the first is preferred for consistency (the "charset" parameter value the first is preferred for consistency (the "charset" parameter value
is defined as being case-insensitive in [RFC2046], Section 4.1.2): is defined as being case-insensitive in [RFC2046], Section 4.1.2):
text/html;charset=utf-8 text/html;charset=utf-8
Text/HTML;Charset="utf-8" Text/HTML;Charset="utf-8"
text/html; charset="utf-8" text/html; charset="utf-8"
text/html;charset=UTF-8 text/html;charset=UTF-8
Media types ought to be registered with IANA according to the Media types ought to be registered with IANA according to the
procedures defined in [BCP13]. procedures defined in [BCP13].
6.1.1.1. Charset 7.1.1.1. Charset
HTTP uses charset names to indicate or negotiate the character HTTP uses charset names to indicate or negotiate the character
encoding scheme of a textual representation [RFC6365]. A charset is encoding scheme of a textual representation [RFC6365]. A charset is
identified by a case-insensitive token. identified by a case-insensitive token.
charset = token charset = token
Charset names ought to be registered in the IANA "Character Sets" Charset names ought to be registered in the IANA "Character Sets"
registry (<https://www.iana.org/assignments/character-sets>) registry (<https://www.iana.org/assignments/character-sets>)
according to the procedures defined in Section 2 of [RFC2978]. according to the procedures defined in Section 2 of [RFC2978].
skipping to change at page 50, line 45 skipping to change at page 54, line 4
identified by a case-insensitive token. identified by a case-insensitive token.
charset = token charset = token
Charset names ought to be registered in the IANA "Character Sets" Charset names ought to be registered in the IANA "Character Sets"
registry (<https://www.iana.org/assignments/character-sets>) registry (<https://www.iana.org/assignments/character-sets>)
according to the procedures defined in Section 2 of [RFC2978]. according to the procedures defined in Section 2 of [RFC2978].
Note: In theory, charset names are defined by the "mime-charset" Note: In theory, charset names are defined by the "mime-charset"
ABNF rule defined in Section 2.3 of [RFC2978] (as corrected in ABNF rule defined in Section 2.3 of [RFC2978] (as corrected in
[Err1912]). That rule allows two characters that are not included [Err1912]). That rule allows two characters that are not included
in "token" ("{" and "}"), but no charset name registered at the in "token" ("{" and "}"), but no charset name registered at the
time of this writing includes braces (see [Err5433]). time of this writing includes braces (see [Err5433]).
6.1.1.2. Canonicalization and Text Defaults 7.1.1.2. Canonicalization and Text Defaults
Media types are registered with a canonical form in order to be Media types are registered with a canonical form in order to be
interoperable among systems with varying native encoding formats. interoperable among systems with varying native encoding formats.
Representations selected or transferred via HTTP ought to be in Representations selected or transferred via HTTP ought to be in
canonical form, for many of the same reasons described by the canonical form, for many of the same reasons described by the
Multipurpose Internet Mail Extensions (MIME) [RFC2045]. However, the Multipurpose Internet Mail Extensions (MIME) [RFC2045]. However, the
performance characteristics of email deployments (i.e., store and performance characteristics of email deployments (i.e., store and
forward messages to peers) are significantly different from those forward messages to peers) are significantly different from those
common to HTTP and the Web (server-based information services). common to HTTP and the Web (server-based information services).
Furthermore, MIME's constraints for the sake of compatibility with Furthermore, MIME's constraints for the sake of compatibility with
skipping to change at page 51, line 35 skipping to change at page 54, line 39
addition, text media in HTTP is not limited to charsets that use addition, text media in HTTP is not limited to charsets that use
octets 13 and 10 for CR and LF, respectively. This flexibility octets 13 and 10 for CR and LF, respectively. This flexibility
regarding line breaks applies only to text within a representation regarding line breaks applies only to text within a representation
that has been assigned a "text" media type; it does not apply to that has been assigned a "text" media type; it does not apply to
"multipart" types or HTTP elements outside the payload body (e.g., "multipart" types or HTTP elements outside the payload body (e.g.,
header fields). header fields).
If a representation is encoded with a content-coding, the underlying If a representation is encoded with a content-coding, the underlying
data ought to be in a form defined above prior to being encoded. data ought to be in a form defined above prior to being encoded.
6.1.1.3. Multipart Types 7.1.1.3. Multipart Types
MIME provides for a number of "multipart" types -- encapsulations of MIME provides for a number of "multipart" types -- encapsulations of
one or more representations within a single message body. All one or more representations within a single message body. All
multipart types share a common syntax, as defined in Section 5.1.1 of multipart types share a common syntax, as defined in Section 5.1.1 of
[RFC2046], and include a boundary parameter as part of the media type [RFC2046], and include a boundary parameter as part of the media type
value. The message body is itself a protocol element; a sender MUST value. The message body is itself a protocol element; a sender MUST
generate only CRLF to represent line breaks between body parts. generate only CRLF to represent line breaks between body parts.
HTTP message framing does not use the multipart boundary as an HTTP message framing does not use the multipart boundary as an
indicator of message body length, though it might be used by indicator of message body length, though it might be used by
implementations that generate or process the payload. For example, implementations that generate or process the payload. For example,
the "multipart/form-data" type is often used for carrying form data the "multipart/form-data" type is often used for carrying form data
in a request, as described in [RFC7578], and the "multipart/ in a request, as described in [RFC7578], and the "multipart/
byteranges" type is defined by this specification for use in some 206 byteranges" type is defined by this specification for use in some 206
(Partial Content) responses (see Section 9.3.7). (Partial Content) responses (see Section 10.3.7).
6.1.2. Content Codings 7.1.2. Content Codings
Content coding values indicate an encoding transformation that has Content coding values indicate an encoding transformation that has
been or can be applied to a representation. Content codings are been or can be applied to a representation. Content codings are
primarily used to allow a representation to be compressed or primarily used to allow a representation to be compressed or
otherwise usefully transformed without losing the identity of its otherwise usefully transformed without losing the identity of its
underlying media type and without loss of information. Frequently, underlying media type and without loss of information. Frequently,
the representation is stored in coded form, transmitted directly, and the representation is stored in coded form, transmitted directly, and
only decoded by the final recipient. only decoded by the final recipient.
content-coding = token content-coding = token
All content codings are case-insensitive and ought to be registered All content codings are case-insensitive and ought to be registered
within the "HTTP Content Coding Registry", as defined in within the "HTTP Content Coding Registry", as defined in
Section 6.1.2.4 Section 7.1.2.4
Content-coding values are used in the Accept-Encoding (Section 8.4.3) Content-coding values are used in the Accept-Encoding (Section 9.4.3)
and Content-Encoding (Section 6.2.2) header fields. and Content-Encoding (Section 7.2.2) header fields.
The following content-coding values are defined by this The following content-coding values are defined by this
specification: specification:
+------------+------------------------------------------+-----------+ +------------+------------------------------------------+-----------+
| Name | Description | Reference | | Name | Description | Reference |
+------------+------------------------------------------+-----------+ +------------+------------------------------------------+-----------+
| compress | UNIX "compress" data format [Welch] | Section 6 | | compress | UNIX "compress" data format [Welch] | Section 7 |
| | | .1.2.1 | | | | .1.2.1 |
| deflate | "deflate" compressed data ([RFC1951]) | Section 6 | | deflate | "deflate" compressed data ([RFC1951]) | Section 7 |
| | inside the "zlib" data format | .1.2.2 | | | inside the "zlib" data format | .1.2.2 |
| | ([RFC1950]) | | | | ([RFC1950]) | |
| gzip | GZIP file format [RFC1952] | Section 6 | | gzip | GZIP file format [RFC1952] | Section 7 |
| | | .1.2.3 | | | | .1.2.3 |
| identity | Reserved (synonym for "no encoding" in | Section 8 | | identity | Reserved | Section 9 |
| | Accept-Encoding) | .4.3 | | | | .4.3 |
| x-compress | Deprecated (alias for compress) | Section 6 | | x-compress | Deprecated (alias for compress) | Section 7 |
| | | .1.2.1 | | | | .1.2.1 |
| x-gzip | Deprecated (alias for gzip) | Section 6 | | x-gzip | Deprecated (alias for gzip) | Section 7 |
| | | .1.2.3 | | | | .1.2.3 |
+------------+------------------------------------------+-----------+ +------------+------------------------------------------+-----------+
Table 2 Table 2
6.1.2.1. Compress Coding 7.1.2.1. Compress Coding
The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding
[Welch] that is commonly produced by the UNIX file compression [Welch] that is commonly produced by the UNIX file compression
program "compress". A recipient SHOULD consider "x-compress" to be program "compress". A recipient SHOULD consider "x-compress" to be
equivalent to "compress". equivalent to "compress".
6.1.2.2. Deflate Coding 7.1.2.2. Deflate Coding
The "deflate" coding is a "zlib" data format [RFC1950] containing a The "deflate" coding is a "zlib" data format [RFC1950] containing a
"deflate" compressed data stream [RFC1951] that uses a combination of "deflate" compressed data stream [RFC1951] that uses a combination of
the Lempel-Ziv (LZ77) compression algorithm and Huffman coding. the Lempel-Ziv (LZ77) compression algorithm and Huffman coding.
Note: Some non-conformant implementations send the "deflate" Note: Some non-conformant implementations send the "deflate"
compressed data without the zlib wrapper. compressed data without the zlib wrapper.
6.1.2.3. Gzip Coding 7.1.2.3. Gzip Coding
The "gzip" coding is an LZ77 coding with a 32-bit Cyclic Redundancy The "gzip" coding is an LZ77 coding with a 32-bit Cyclic Redundancy
Check (CRC) that is commonly produced by the gzip file compression Check (CRC) that is commonly produced by the gzip file compression
program [RFC1952]. A recipient SHOULD consider "x-gzip" to be program [RFC1952]. A recipient SHOULD consider "x-gzip" to be
equivalent to "gzip". equivalent to "gzip".
6.1.2.4. Content Coding Registry 7.1.2.4. Content Coding Registry
The "HTTP Content Coding Registry", maintained by IANA at The "HTTP Content Coding Registry", maintained by IANA at
<https://www.iana.org/assignments/http-parameters/>, registers <https://www.iana.org/assignments/http-parameters/>, registers
content-coding names. content-coding names.
Content coding registrations MUST include the following fields: Content coding registrations MUST include the following fields:
o Name o Name
o Description o Description
o Pointer to specification text o Pointer to specification text
Names of content codings MUST NOT overlap with names of transfer Names of content codings MUST NOT overlap with names of transfer
codings (Section 7 of [Messaging]), unless the encoding codings (Section 7 of [Messaging]), unless the encoding
transformation is identical (as is the case for the compression transformation is identical (as is the case for the compression
codings defined in Section 6.1.2). codings defined in Section 7.1.2).
Values to be added to this namespace require IETF Review (see Values to be added to this namespace require IETF Review (see
Section 4.8 of [RFC8126]) and MUST conform to the purpose of content Section 4.8 of [RFC8126]) and MUST conform to the purpose of content
coding defined in Section 6.1.2. coding defined in Section 7.1.2.
6.1.3. Language Tags 7.1.3. Language Tags
A language tag, as defined in [RFC5646], identifies a natural A language tag, as defined in [RFC5646], identifies a natural
language spoken, written, or otherwise conveyed by human beings for language spoken, written, or otherwise conveyed by human beings for
communication of information to other human beings. Computer communication of information to other human beings. Computer
languages are explicitly excluded. languages are explicitly excluded.
HTTP uses language tags within the Accept-Language and Content- HTTP uses language tags within the Accept-Language and Content-
Language header fields. Accept-Language uses the broader language- Language header fields. Accept-Language uses the broader language-
range production defined in Section 8.4.4, whereas Content-Language range production defined in Section 9.4.4, whereas Content-Language
uses the language-tag production defined below. uses the language-tag production defined below.
language-tag = <Language-Tag, see [RFC5646], Section 2.1> language-tag = <Language-Tag, see [RFC5646], Section 2.1>
A language tag is a sequence of one or more case-insensitive subtags, A language tag is a sequence of one or more case-insensitive subtags,
each separated by a hyphen character ("-", %x2D). In most cases, a each separated by a hyphen character ("-", %x2D). In most cases, a
language tag consists of a primary language subtag that identifies a language tag consists of a primary language subtag that identifies a
broad family of related languages (e.g., "en" = English), which is broad family of related languages (e.g., "en" = English), which is
optionally followed by a series of subtags that refine or narrow that optionally followed by a series of subtags that refine or narrow that
language's range (e.g., "en-CA" = the variety of English as language's range (e.g., "en-CA" = the variety of English as
communicated in Canada). Whitespace is not allowed within a language communicated in Canada). Whitespace is not allowed within a language
tag. Example tags include: tag. Example tags include:
fr, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN fr, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
See [RFC5646] for further information. See [RFC5646] for further information.
6.1.4. Range Units 7.1.4. Range Units
Representation data can be partitioned into subranges when there are Representation data can be partitioned into subranges when there are
addressable structural units inherent to that data's content coding addressable structural units inherent to that data's content coding
or media type. For example, octet (a.k.a., byte) boundaries are a or media type. For example, octet (a.k.a., byte) boundaries are a
structural unit common to all representation data, allowing structural unit common to all representation data, allowing
partitions of the data to be identified as a range of bytes at some partitions of the data to be identified as a range of bytes at some
offset from the start or end of that data. offset from the start or end of that data.
This general notion of a "range unit" is used in the Accept-Ranges This general notion of a "range unit" is used in the Accept-Ranges
(Section 10.4.1) response header field to advertise support for range (Section 11.4.1) response header field to advertise support for range
requests, the Range (Section 8.3) request header field to delineate requests, the Range (Section 9.3) request header field to delineate
the parts of a representation that are requested, and the Content- the parts of a representation that are requested, and the Content-
Range (Section 6.3.4) payload header field to describe which part of Range (Section 7.3.4) payload header field to describe which part of
a representation is being transferred. a representation is being transferred.
range-unit = token range-unit = token
All range unit names are case-insensitive and ought to be registered All range unit names are case-insensitive and ought to be registered
within the "HTTP Range Unit Registry", as defined in Section 6.1.4.4 within the "HTTP Range Unit Registry", as defined in Section 7.1.4.4
The following range unit names are defined by this document: The following range unit names are defined by this document:
+------------+-----------------------------------------+------------+ +------------+-----------------------------------------+------------+
| Range Unit | Description | Reference | | Range Unit | Description | Reference |
| Name | | | | Name | | |
+------------+-----------------------------------------+------------+ +------------+-----------------------------------------+------------+
| bytes | a range of octets | Section 6. | | bytes | a range of octets | Section 7. |
| | | 1.4.2 | | | | 1.4.2 |
| none | reserved as keyword to indicate range | Section 10 | | none | reserved as keyword to indicate range | Section 11 |
| | requests are not supported | .4.1 | | | requests are not supported | .4.1 |
+------------+-----------------------------------------+------------+ +------------+-----------------------------------------+------------+
Table 3 Table 3
6.1.4.1. Range Specifiers 7.1.4.1. Range Specifiers
Ranges are expressed in terms of a range unit paired with a set of Ranges are expressed in terms of a range unit paired with a set of
range specifiers. The range unit name determines what kinds of range specifiers. The range unit name determines what kinds of
range-spec are applicable to its own specifiers. Hence, the range-spec are applicable to its own specifiers. Hence, the
following gramar is generic: each range unit is expected to specify following gramar is generic: each range unit is expected to specify
requirements on when int-range, suffix-range, and other-range are requirements on when int-range, suffix-range, and other-range are
allowed. allowed.
A range request can specify a single range or a set of ranges within A range request can specify a single range or a set of ranges within
a single representation. a single representation.
skipping to change at page 56, line 15 skipping to change at page 59, line 15
suffix-range = "-" suffix-length suffix-range = "-" suffix-length
suffix-length = 1*DIGIT suffix-length = 1*DIGIT
To provide for extensibility, the other-range rule is a mostly To provide for extensibility, the other-range rule is a mostly
unconstrained grammar that allows application-specific or future unconstrained grammar that allows application-specific or future
range units to define additional range specifiers. range units to define additional range specifiers.
other-range = 1*( %x21-2B / %x2D-7E ) other-range = 1*( %x21-2B / %x2D-7E )
; 1*(VCHAR excluding comma) ; 1*(VCHAR excluding comma)
6.1.4.2. Byte Ranges 7.1.4.2. Byte Ranges
The "bytes" range unit is used to express subranges of a The "bytes" range unit is used to express subranges of a
representation data's octet sequence. Each byte range is expressed representation data's octet sequence. Each byte range is expressed
as an integer range at some offset, relative to either the beginning as an integer range at some offset, relative to either the beginning
(int-range) or end (suffix-range) of the representation data. Byte (int-range) or end (suffix-range) of the representation data. Byte
ranges do not use the other-range specifier. ranges do not use the other-range specifier.
The first-pos value in a bytes int-range gives the offset of the The first-pos value in a bytes int-range gives the offset of the
first byte in a range. The last-pos value gives the offset of the first byte in a range. The last-pos value gives the offset of the
last byte in the range; that is, the byte positions specified are last byte in the range; that is, the byte positions specified are
skipping to change at page 57, line 7 skipping to change at page 60, line 7
bytes=500-999 bytes=500-999
A client can limit the number of bytes requested without knowing the A client can limit the number of bytes requested without knowing the
size of the selected representation. If the last-pos value is size of the selected representation. If the last-pos value is
absent, or if the value is greater than or equal to the current absent, or if the value is greater than or equal to the current
length of the representation data, the byte range is interpreted as length of the representation data, the byte range is interpreted as
the remainder of the representation (i.e., the server replaces the the remainder of the representation (i.e., the server replaces the
value of last-pos with a value that is one less than the current value of last-pos with a value that is one less than the current
length of the selected representation). length of the selected representation).
A client can request the last N bytes of the selected representation A client can request the last N bytes (N > 0) of the selected
using a suffix-range. If the selected representation is shorter than representation using a suffix-range. If the selected representation
the specified suffix-length, the entire representation is used. is shorter than the specified suffix-length, the entire
representation is used.
Additional examples, assuming a representation of length 10000: Additional examples, assuming a representation of length 10000:
o The final 500 bytes (byte offsets 9500-9999, inclusive): o The final 500 bytes (byte offsets 9500-9999, inclusive):
bytes=-500 bytes=-500
Or: Or:
bytes=9500- bytes=9500-
skipping to change at page 58, line 5 skipping to change at page 61, line 5
bytes=500-600,601-999 bytes=500-600,601-999
bytes=500-700,601-999 bytes=500-700,601-999
If a valid bytes range-set includes at least one range-spec with a If a valid bytes range-set includes at least one range-spec with a
first-pos that is less than the current length of the representation, first-pos that is less than the current length of the representation,
or at least one suffix-range with a non-zero suffix-length, then the or at least one suffix-range with a non-zero suffix-length, then the
bytes range-set is satisfiable. Otherwise, the bytes range-set is bytes range-set is satisfiable. Otherwise, the bytes range-set is
unsatisfiable. unsatisfiable.
If the selected representation has zero length, the only satisfiable
form of range-spec is a suffix-range with a non-zero suffix-length.
In the byte-range syntax, first-pos, last-pos, and suffix-length are In the byte-range syntax, first-pos, last-pos, and suffix-length are
expressed as decimal number of octets. Since there is no predefined expressed as decimal number of octets. Since there is no predefined
limit to the length of a payload, recipients MUST anticipate limit to the length of a payload, recipients MUST anticipate
potentially large decimal numerals and prevent parsing errors due to potentially large decimal numerals and prevent parsing errors due to
integer conversion overflows. integer conversion overflows.
6.1.4.3. Other Range Units 7.1.4.3. Other Range Units
Other range units, such as format-specific boundaries like pages, Other range units, such as format-specific boundaries like pages,
sections, records, rows, or time, are potentially usable in HTTP for sections, records, rows, or time, are potentially usable in HTTP for
application-specific purposes, but are not commonly used in practice. application-specific purposes, but are not commonly used in practice.
Implementors of alternative range units ought to consider how they Implementors of alternative range units ought to consider how they
would work with content codings and general-purpose intermediaries. would work with content codings and general-purpose intermediaries.
Range units are intended to be extensible. New range units ought to Range units are intended to be extensible. New range units ought to
be registered with IANA, as defined in Section 6.1.4.4. be registered with IANA, as defined in Section 7.1.4.4.
6.1.4.4. Range Unit Registry 7.1.4.4. Range Unit Registry
The "HTTP Range Unit Registry" defines the namespace for the range The "HTTP Range Unit Registry" defines the namespace for the range
unit names and refers to their corresponding specifications. It is unit names and refers to their corresponding specifications. It is
maintained at <https://www.iana.org/assignments/http-parameters>. maintained at <https://www.iana.org/assignments/http-parameters>.
Registration of an HTTP Range Unit MUST include the following fields: Registration of an HTTP Range Unit MUST include the following fields:
o Name o Name
o Description o Description
o Pointer to specification text o Pointer to specification text
Values to be added to this namespace require IETF Review (see Values to be added to this namespace require IETF Review (see
[RFC8126], Section 4.8). [RFC8126], Section 4.8).
6.2. Representation Metadata 7.2. Representation Metadata
Representation header fields provide metadata about the Representation header fields provide metadata about the
representation. When a message includes a payload body, the representation. When a message includes a payload body, the
representation header fields describe how to interpret the representation header fields describe how to interpret the
representation data enclosed in the payload body. In a response to a representation data enclosed in the payload body. In a response to a
HEAD request, the representation header fields describe the HEAD request, the representation header fields describe the
representation data that would have been enclosed in the payload body representation data that would have been enclosed in the payload body
if the same request had been a GET. if the same request had been a GET.
The following header fields convey representation metadata: The following header fields convey representation metadata:
+------------------+---------------+ +------------------+---------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+------------------+---------------+ +------------------+---------------+
| Content-Type | Section 6.2.1 | | Content-Type | Section 7.2.1 |
| Content-Encoding | Section 6.2.2 | | Content-Encoding | Section 7.2.2 |
| Content-Language | Section 6.2.3 | | Content-Language | Section 7.2.3 |
| Content-Length | Section 6.2.4 | | Content-Length | Section 7.2.4 |
| Content-Location | Section 6.2.5 | | Content-Location | Section 7.2.5 |
+------------------+---------------+ +------------------+---------------+
6.2.1. Content-Type 7.2.1. Content-Type
The "Content-Type" header field indicates the media type of the The "Content-Type" header field indicates the media type of the
associated representation: either the representation enclosed in the associated representation: either the representation enclosed in the
message payload or the selected representation, as determined by the message payload or the selected representation, as determined by the
message semantics. The indicated media type defines both the data message semantics. The indicated media type defines both the data
format and how that data is intended to be processed by a recipient, format and how that data is intended to be processed by a recipient,
within the scope of the received message semantics, after any content within the scope of the received message semantics, after any content
codings indicated by Content-Encoding are decoded. codings indicated by Content-Encoding are decoded.
Content-Type = media-type Content-Type = media-type
Media types are defined in Section 6.1.1. An example of the field is Media types are defined in Section 7.1.1. An example of the field is
Content-Type: text/html; charset=ISO-8859-4 Content-Type: text/html; charset=ISO-8859-4
A sender that generates a message containing a payload body SHOULD A sender that generates a message containing a payload body SHOULD
generate a Content-Type header field in that message unless the generate a Content-Type header field in that message unless the
intended media type of the enclosed representation is unknown to the intended media type of the enclosed representation is unknown to the
sender. If a Content-Type header field is not present, the recipient sender. If a Content-Type header field is not present, the recipient
MAY either assume a media type of "application/octet-stream" MAY either assume a media type of "application/octet-stream"
([RFC2046], Section 4.5.1) or examine the data to determine its type. ([RFC2046], Section 4.5.1) or examine the data to determine its type.
skipping to change at page 60, line 5 skipping to change at page 63, line 5
representation. Some user agents examine a payload's content and, in representation. Some user agents examine a payload's content and, in
certain cases, override the received type (for example, see certain cases, override the received type (for example, see
[Sniffing]). This "MIME sniffing" risks drawing incorrect [Sniffing]). This "MIME sniffing" risks drawing incorrect
conclusions about the data, which might expose the user to additional conclusions about the data, which might expose the user to additional
security risks (e.g., "privilege escalation"). Furthermore, it is security risks (e.g., "privilege escalation"). Furthermore, it is
impossible to determine the sender's intended processing model by impossible to determine the sender's intended processing model by
examining the data format: many data formats match multiple media examining the data format: many data formats match multiple media
types that differ only in processing semantics. Implementers are types that differ only in processing semantics. Implementers are
encouraged to provide a means to disable such sniffing. encouraged to provide a means to disable such sniffing.
6.2.2. Content-Encoding 7.2.2. Content-Encoding
The "Content-Encoding" header field indicates what content codings The "Content-Encoding" header field indicates what content codings
have been applied to the representation, beyond those inherent in the have been applied to the representation, beyond those inherent in the
media type, and thus what decoding mechanisms have to be applied in media type, and thus what decoding mechanisms have to be applied in
order to obtain data in the media type referenced by the Content-Type order to obtain data in the media type referenced by the Content-Type
header field. Content-Encoding is primarily used to allow a header field. Content-Encoding is primarily used to allow a
representation's data to be compressed without losing the identity of representation's data to be compressed without losing the identity of
its underlying media type. its underlying media type.
Content-Encoding = 1#content-coding Content-Encoding = 1#content-coding
An example of its use is An example of its use is
Content-Encoding: gzip Content-Encoding: gzip
If one or more encodings have been applied to a representation, the If one or more encodings have been applied to a representation, the
sender that applied the encodings MUST generate a Content-Encoding sender that applied the encodings MUST generate a Content-Encoding
header field that lists the content codings in the order in which header field that lists the content codings in the order in which
they were applied. Additional information about the encoding they were applied. Note that the coding named "identity" is reserved
parameters can be provided by other header fields not defined by this for its special role in Accept-Encoding, and thus SHOULD NOT be
specification. included.
Additional information about the encoding parameters can be provided
by other header fields not defined by this specification.
Unlike Transfer-Encoding (Section 6.1 of [Messaging]), the codings Unlike Transfer-Encoding (Section 6.1 of [Messaging]), the codings
listed in Content-Encoding are a characteristic of the listed in Content-Encoding are a characteristic of the
representation; the representation is defined in terms of the coded representation; the representation is defined in terms of the coded
form, and all other metadata about the representation is about the form, and all other metadata about the representation is about the
coded form unless otherwise noted in the metadata definition. coded form unless otherwise noted in the metadata definition.
Typically, the representation is only decoded just prior to rendering Typically, the representation is only decoded just prior to rendering
or analogous usage. or analogous usage.
If the media type includes an inherent encoding, such as a data If the media type includes an inherent encoding, such as a data
skipping to change at page 61, line 5 skipping to change at page 64, line 9
choose to publish the same data as multiple representations that choose to publish the same data as multiple representations that
differ only in whether the coding is defined as part of Content-Type differ only in whether the coding is defined as part of Content-Type
or Content-Encoding, since some user agents will behave differently or Content-Encoding, since some user agents will behave differently
in their handling of each response (e.g., open a "Save as ..." dialog in their handling of each response (e.g., open a "Save as ..." dialog
instead of automatic decompression and rendering of content). instead of automatic decompression and rendering of content).
An origin server MAY respond with a status code of 415 (Unsupported An origin server MAY respond with a status code of 415 (Unsupported
Media Type) if a representation in the request message has a content Media Type) if a representation in the request message has a content
coding that is not acceptable. coding that is not acceptable.
6.2.3. Content-Language 7.2.3. Content-Language
The "Content-Language" header field describes the natural language(s) The "Content-Language" header field describes the natural language(s)
of the intended audience for the representation. Note that this of the intended audience for the representation. Note that this
might not be equivalent to all the languages used within the might not be equivalent to all the languages used within the
representation. representation.
Content-Language = 1#language-tag Content-Language = 1#language-tag
Language tags are defined in Section 6.1.3. The primary purpose of Language tags are defined in Section 7.1.3. The primary purpose of
Content-Language is to allow a user to identify and differentiate Content-Language is to allow a user to identify and differentiate
representations according to the users' own preferred language. representations according to the users' own preferred language.
Thus, if the content is intended only for a Danish-literate audience, Thus, if the content is intended only for a Danish-literate audience,
the appropriate field is the appropriate field is
Content-Language: da Content-Language: da
If no Content-Language is specified, the default is that the content If no Content-Language is specified, the default is that the content
is intended for all language audiences. This might mean that the is intended for all language audiences. This might mean that the
sender does not consider it to be specific to any natural language, sender does not consider it to be specific to any natural language,
skipping to change at page 61, line 44 skipping to change at page 64, line 48
However, just because multiple languages are present within a However, just because multiple languages are present within a
representation does not mean that it is intended for multiple representation does not mean that it is intended for multiple
linguistic audiences. An example would be a beginner's language linguistic audiences. An example would be a beginner's language
primer, such as "A First Lesson in Latin", which is clearly intended primer, such as "A First Lesson in Latin", which is clearly intended
to be used by an English-literate audience. In this case, the to be used by an English-literate audience. In this case, the
Content-Language would properly only include "en". Content-Language would properly only include "en".
Content-Language MAY be applied to any media type -- it is not Content-Language MAY be applied to any media type -- it is not
limited to textual documents. limited to textual documents.
6.2.4. Content-Length 7.2.4. Content-Length
[[CREF1: The "Content-Length" header field indicates the number of [[CREF1: The "Content-Length" header field indicates the number of
data octets (body length) for the representation. In some cases, data octets (body length) for the representation. In some cases,
Content-Length is used to define or estimate message framing. ]] Content-Length is used to define or estimate message framing. ]]
Content-Length = 1*DIGIT Content-Length = 1*DIGIT
An example is An example is
Content-Length: 3495 Content-Length: 3495
A sender MUST NOT send a Content-Length header field in any message A sender MUST NOT send a Content-Length header field in any message
that contains a Transfer-Encoding header field. that contains a Transfer-Encoding header field.
A user agent SHOULD send a Content-Length in a request message when A user agent SHOULD send a Content-Length in a request message when
no Transfer-Encoding is sent and the request method defines a meaning no Transfer-Encoding is sent and the request method defines a meaning
for an enclosed payload body. For example, a Content-Length header for an enclosed payload body. For example, a Content-Length header
field is normally sent in a POST request even when the value is 0 field is normally sent in a POST request even when the value is 0
(indicating an empty payload body). A user agent SHOULD NOT send a (indicating an empty payload body). A user agent SHOULD NOT send a
Content-Length header field when the request message does not contain Content-Length header field when the request message does not contain
a payload body and the method semantics do not anticipate such a a payload body and the method semantics do not anticipate such a
body. body.
A server MAY send a Content-Length header field in a response to a A server MAY send a Content-Length header field in a response to a
HEAD request (Section 7.3.2); a server MUST NOT send Content-Length HEAD request (Section 8.3.2); a server MUST NOT send Content-Length
in such a response unless its field value equals the decimal number in such a response unless its field value equals the decimal number
of octets that would have been sent in the payload body of a response of octets that would have been sent in the payload body of a response
if the same request had used the GET method. if the same request had used the GET method.
A server MAY send a Content-Length header field in a 304 (Not A server MAY send a Content-Length header field in a 304 (Not
Modified) response to a conditional GET request (Section 9.4.5); a Modified) response to a conditional GET request (Section 10.4.5); a
server MUST NOT send Content-Length in such a response unless its server MUST NOT send Content-Length in such a response unless its
field value equals the decimal number of octets that would have been field value equals the decimal number of octets that would have been
sent in the payload body of a 200 (OK) response to the same request. sent in the payload body of a 200 (OK) response to the same request.
A server MUST NOT send a Content-Length header field in any response A server MUST NOT send a Content-Length header field in any response
with a status code of 1xx (Informational) or 204 (No Content). A with a status code of 1xx (Informational) or 204 (No Content). A
server MUST NOT send a Content-Length header field in any 2xx server MUST NOT send a Content-Length header field in any 2xx
(Successful) response to a CONNECT request (Section 7.3.6). (Successful) response to a CONNECT request (Section 8.3.6).
Aside from the cases defined above, in the absence of Transfer- Aside from the cases defined above, in the absence of Transfer-
Encoding, an origin server SHOULD send a Content-Length header field Encoding, an origin server SHOULD send a Content-Length header field
when the payload body size is known prior to sending the complete when the payload body size is known prior to sending the complete
header section. This will allow downstream recipients to measure header section. This will allow downstream recipients to measure
transfer progress, know when a received message is complete, and transfer progress, know when a received message is complete, and
potentially reuse the connection for additional requests. potentially reuse the connection for additional requests.
Any Content-Length field value greater than or equal to zero is Any Content-Length field value greater than or equal to zero is
valid. Since there is no predefined limit to the length of a valid. Since there is no predefined limit to the length of a
payload, a recipient MUST anticipate potentially large decimal payload, a recipient MUST anticipate potentially large decimal
numerals and prevent parsing errors due to integer conversion numerals and prevent parsing errors due to integer conversion
overflows (Section 11.5). overflows (Section 12.5).
If a message is received that has a Content-Length header field value If a message is received that has a Content-Length header field value
consisting of the same decimal value as a comma-separated list consisting of the same decimal value as a comma-separated list
(Section 4.5) -- for example, "Content-Length: 42, 42" -- indicating (Section 5.5) -- for example, "Content-Length: 42, 42" -- indicating
that duplicate Content-Length header fields have been generated or that duplicate Content-Length header fields have been generated or
combined by an upstream message processor, then the recipient MUST combined by an upstream message processor, then the recipient MUST
either reject the message as invalid or replace the duplicated field either reject the message as invalid or replace the duplicated field
values with a single valid Content-Length field containing that values with a single valid Content-Length field containing that
decimal value prior to determining the message body length or decimal value prior to determining the message body length or
forwarding the message. forwarding the message.
6.2.5. Content-Location 7.2.5. Content-Location
The "Content-Location" header field references a URI that can be used The "Content-Location" header field references a URI that can be used
as an identifier for a specific resource corresponding to the as an identifier for a specific resource corresponding to the
representation in this message's payload. In other words, if one representation in this message's payload. In other words, if one
were to perform a GET request on this URI at the time of this were to perform a GET request on this URI at the time of this
message's generation, then a 200 (OK) response would contain the same message's generation, then a 200 (OK) response would contain the same
representation that is enclosed as payload in this message. representation that is enclosed as payload in this message.
Content-Location = absolute-URI / partial-URI Content-Location = absolute-URI / partial-URI
The field value is either an absolute-URI or a partial-URI. In the The field value is either an absolute-URI or a partial-URI. In the
latter case (Section 2.4), the referenced URI is relative to the latter case (Section 2.4), the referenced URI is relative to the
target URI ([RFC3986], Section 5). target URI ([RFC3986], Section 5).
The Content-Location value is not a replacement for the target URI The Content-Location value is not a replacement for the target URI
(Section 5.1). It is representation metadata. It has the same (Section 6.1). It is representation metadata. It has the same
syntax and semantics as the header field of the same name defined for syntax and semantics as the header field of the same name defined for
MIME body parts in Section 4 of [RFC2557]. However, its appearance MIME body parts in Section 4 of [RFC2557]. However, its appearance
in an HTTP message has some special implications for HTTP recipients. in an HTTP message has some special implications for HTTP recipients.
If Content-Location is included in a 2xx (Successful) response If Content-Location is included in a 2xx (Successful) response
message and its value refers (after conversion to absolute form) to a message and its value refers (after conversion to absolute form) to a
URI that is the same as the target URI, then the recipient MAY URI that is the same as the target URI, then the recipient MAY
consider the payload to be a current representation of that resource consider the payload to be a current representation of that resource
at the time indicated by the message origination date. For a GET at the time indicated by the message origination date. For a GET
(Section 7.3.1) or HEAD (Section 7.3.2) request, this is the same as (Section 8.3.1) or HEAD (Section 8.3.2) request, this is the same as
the default semantics when no Content-Location is provided by the the default semantics when no Content-Location is provided by the
server. For a state-changing request like PUT (Section 7.3.4) or server. For a state-changing request like PUT (Section 8.3.4) or
POST (Section 7.3.3), it implies that the server's response contains POST (Section 8.3.3), it implies that the server's response contains
the new representation of that resource, thereby distinguishing it the new representation of that resource, thereby distinguishing it
from representations that might only report about the action (e.g., from representations that might only report about the action (e.g.,
"It worked!"). This allows authoring applications to update their "It worked!"). This allows authoring applications to update their
local copies without the need for a subsequent GET request. local copies without the need for a subsequent GET request.
If Content-Location is included in a 2xx (Successful) response If Content-Location is included in a 2xx (Successful) response
message and its field value refers to a URI that differs from the message and its field value refers to a URI that differs from the
target URI, then the origin server claims that the URI is an target URI, then the origin server claims that the URI is an
identifier for a different resource corresponding to the enclosed identifier for a different resource corresponding to the enclosed
representation. Such a claim can only be trusted if both identifiers representation. Such a claim can only be trusted if both identifiers
skipping to change at page 64, line 48 skipping to change at page 68, line 5
For example, if a client makes a PUT request on a negotiated resource For example, if a client makes a PUT request on a negotiated resource
and the origin server accepts that PUT (without redirection), then and the origin server accepts that PUT (without redirection), then
the new state of that resource is expected to be consistent with the the new state of that resource is expected to be consistent with the
one representation supplied in that PUT; the Content-Location cannot one representation supplied in that PUT; the Content-Location cannot
be used as a form of reverse content selection identifier to update be used as a form of reverse content selection identifier to update
only one of the negotiated representations. If the user agent had only one of the negotiated representations. If the user agent had
wanted the latter semantics, it would have applied the PUT directly wanted the latter semantics, it would have applied the PUT directly
to the Content-Location URI. to the Content-Location URI.
6.3. Payload 7.3. Payload
Some HTTP messages transfer a complete or partial representation as Some HTTP messages transfer a complete or partial representation as
the message "payload". In some cases, a payload might contain only the message "payload". In some cases, a payload might contain only
the associated representation's header fields (e.g., responses to the associated representation's header fields (e.g., responses to
HEAD) or only some part(s) of the representation data (e.g., the 206 HEAD) or only some part(s) of the representation data (e.g., the 206
(Partial Content) status code). (Partial Content) status code).
Header fields that specifically describe the payload, rather than the Header fields that specifically describe the payload, rather than the
associated representation, are referred to as "payload header associated representation, are referred to as "payload header
fields". Payload header fields are defined in other parts of this fields". Payload header fields are defined in other parts of this
specification, due to their impact on message parsing. specification, due to their impact on message parsing.
+-------------------+----------------------------+ +-------------------+----------------------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+-------------------+----------------------------+ +-------------------+----------------------------+
| Content-Range | Section 6.3.4 | | Content-Range | Section 7.3.4 |
| Trailer | Section 4.6.3 | | Trailer | Section 5.6.3 |
| Transfer-Encoding | Section 6.1 of [Messaging] | | Transfer-Encoding | Section 6.1 of [Messaging] |
+-------------------+----------------------------+ +-------------------+----------------------------+
6.3.1. Purpose 7.3.1. Purpose
The purpose of a payload in a request is defined by the method The purpose of a payload in a request is defined by the method
semantics. For example, a representation in the payload of a PUT semantics. For example, a representation in the payload of a PUT
request (Section 7.3.4) represents the desired state of the target request (Section 8.3.4) represents the desired state of the target
resource if the request is successfully applied, whereas a resource if the request is successfully applied, whereas a
representation in the payload of a POST request (Section 7.3.3) representation in the payload of a POST request (Section 8.3.3)
represents information to be processed by the target resource. represents information to be processed by the target resource.
In a response, the payload's purpose is defined by both the request In a response, the payload's purpose is defined by both the request
method and the response status code. For example, the payload of a method and the response status code. For example, the payload of a
200 (OK) response to GET (Section 7.3.1) represents the current state 200 (OK) response to GET (Section 8.3.1) represents the current state
of the target resource, as observed at the time of the message of the target resource, as observed at the time of the message
origination date (Section 10.1.1.2), whereas the payload of the same origination date (Section 11.1.1), whereas the payload of the same
status code in a response to POST might represent either the status code in a response to POST might represent either the
processing result or the new state of the target resource after processing result or the new state of the target resource after
applying the processing. Response messages with an error status code applying the processing. Response messages with an error status code
usually contain a payload that represents the error condition, such usually contain a payload that represents the error condition, such
that it describes the error state and what next steps are suggested that it describes the error state and what next steps are suggested
for resolving it. for resolving it.
6.3.2. Identification 7.3.2. Identification
When a complete or partial representation is transferred in a message When a complete or partial representation is transferred in a message
payload, it is often desirable for the sender to supply, or the payload, it is often desirable for the sender to supply, or the
recipient to determine, an identifier for a resource corresponding to recipient to determine, an identifier for a resource corresponding to
that representation. that representation.
For a request message: For a request message:
o If the request has a Content-Location header field, then the o If the request has a Content-Location header field, then the
sender asserts that the payload is a representation of the sender asserts that the payload is a representation of the
skipping to change at page 66, line 17 skipping to change at page 69, line 22
might still be useful for revision history links. might still be useful for revision history links.
o Otherwise, the payload is unidentified. o Otherwise, the payload is unidentified.
For a response message, the following rules are applied in order For a response message, the following rules are applied in order
until a match is found: until a match is found:
1. If the request method is GET or HEAD and the response status code 1. If the request method is GET or HEAD and the response status code
is 200 (OK), 204 (No Content), 206 (Partial Content), or 304 (Not is 200 (OK), 204 (No Content), 206 (Partial Content), or 304 (Not
Modified), the payload is a representation of the resource Modified), the payload is a representation of the resource
identified by the target URI (Section 5.1). identified by the target URI (Section 6.1).
2. If the request method is GET or HEAD and the response status code 2. If the request method is GET or HEAD and the response status code
is 203 (Non-Authoritative Information), the payload is a is 203 (Non-Authoritative Information), the payload is a
potentially modified or enhanced representation of the target potentially modified or enhanced representation of the target
resource as provided by an intermediary. resource as provided by an intermediary.
3. If the response has a Content-Location header field and its field 3. If the response has a Content-Location header field and its field
value is a reference to the same URI as the target URI, the value is a reference to the same URI as the target URI, the
payload is a representation of the target resource. payload is a representation of the target resource.
4. If the response has a Content-Location header field and its field 4. If the response has a Content-Location header field and its field
value is a reference to a URI different from the target URI, then value is a reference to a URI different from the target URI, then
the sender asserts that the payload is a representation of the the sender asserts that the payload is a representation of the
resource identified by the Content-Location field value. resource identified by the Content-Location field value.
However, such an assertion cannot be trusted unless it can be However, such an assertion cannot be trusted unless it can be
verified by other means (not defined by this specification). verified by other means (not defined by this specification).
5. Otherwise, the payload is unidentified. 5. Otherwise, the payload is unidentified.
6.3.3. Payload Body 7.3.3. Payload Body
The payload body contains the data of a request or response. This is The payload body contains the data of a request or response. This is
distinct from the message body (e.g., Section 6 of [Messaging]), distinct from the message body (e.g., Section 6 of [Messaging]),
which is how the payload body is transferred "on the wire", and might which is how the payload body is transferred "on the wire", and might
be encoded, depending on the HTTP version in use. be encoded, depending on the HTTP version in use.
It is also distinct from a request or response's representation data It is also distinct from a request or response's representation data
(Section 6.1), which can be inferred from protocol operation, rather (Section 7.1), which can be inferred from protocol operation, rather
than necessarily appearing "on the wire." than necessarily appearing "on the wire."
The presence of a payload body in a request depends on whether the The presence of a payload body in a request depends on whether the
request method used defines semantics for it. request method used defines semantics for it.
The presence of a payload body in a response depends on both the The presence of a payload body in a response depends on both the
request method to which it is responding and the response status code request method to which it is responding and the response status code
(Section 9). (Section 10).
Responses to the HEAD request method (Section 7.3.2) never include a Responses to the HEAD request method (Section 8.3.2) never include a
payload body because the associated response header fields indicate payload body because the associated response header fields indicate
only what their values would have been if the request method had been only what their values would have been if the request method had been
GET (Section 7.3.1). GET (Section 8.3.1).
2xx (Successful) responses to a CONNECT request method 2xx (Successful) responses to a CONNECT request method
(Section 7.3.6) switch the connection to tunnel mode instead of (Section 8.3.6) switch the connection to tunnel mode instead of
having a payload body. having a payload body.
All 1xx (Informational), 204 (No Content), and 304 (Not Modified) All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
responses do not include a payload body. responses do not include a payload body.
All other responses do include a payload body, although that body All other responses do include a payload body, although that body
might be of zero length. might be of zero length.
6.3.4. Content-Range 7.3.4. Content-Range
The "Content-Range" header field is sent in a single part 206 The "Content-Range" header field is sent in a single part 206
(Partial Content) response to indicate the partial range of the (Partial Content) response to indicate the partial range of the
selected representation enclosed as the message payload, sent in each selected representation enclosed as the message payload, sent in each
part of a multipart 206 response to indicate the range enclosed part of a multipart 206 response to indicate the range enclosed
within each body part, and sent in 416 (Range Not Satisfiable) within each body part, and sent in 416 (Range Not Satisfiable)
responses to provide information about the selected representation. responses to provide information about the selected representation.
Content-Range = range-unit SP Content-Range = range-unit SP
( range-resp / unsatisfied-range ) ( range-resp / unsatisfied-range )
range-resp = incl-range "/" ( complete-length / "*" ) range-resp = incl-range "/" ( complete-length / "*" )
incl-range = first-pos "-" last-pos incl-range = first-pos "-" last-pos
unsatisfied-range = "*/" complete-length unsatisfied-range = "*/" complete-length
complete-length = 1*DIGIT complete-length = 1*DIGIT
If a 206 (Partial Content) response contains a Content-Range header If a 206 (Partial Content) response contains a Content-Range header
field with a range unit (Section 6.1.4) that the recipient does not field with a range unit (Section 7.1.4) that the recipient does not
understand, the recipient MUST NOT attempt to recombine it with a understand, the recipient MUST NOT attempt to recombine it with a
stored representation. A proxy that receives such a message SHOULD stored representation. A proxy that receives such a message SHOULD
forward it downstream. forward it downstream.
For byte ranges, a sender SHOULD indicate the complete length of the For byte ranges, a sender SHOULD indicate the complete length of the
representation from which the range has been extracted, unless the representation from which the range has been extracted, unless the
complete length is unknown or difficult to determine. An asterisk complete length is unknown or difficult to determine. An asterisk
character ("*") in place of the complete-length indicates that the character ("*") in place of the complete-length indicates that the
representation length was unknown when the header field was representation length was unknown when the header field was
generated. generated.
skipping to change at page 69, line 13 skipping to change at page 72, line 15
Content-Range: bytes 500-999/1234 Content-Range: bytes 500-999/1234
o All except for the first 500 bytes: o All except for the first 500 bytes:
Content-Range: bytes 500-1233/1234 Content-Range: bytes 500-1233/1234
o The last 500 bytes: o The last 500 bytes:
Content-Range: bytes 734-1233/1234 Content-Range: bytes 734-1233/1234
6.3.5. Media Type multipart/byteranges 7.3.5. Media Type multipart/byteranges
When a 206 (Partial Content) response message includes the content of When a 206 (Partial Content) response message includes the content of
multiple ranges, they are transmitted as body parts in a multipart multiple ranges, they are transmitted as body parts in a multipart
message body ([RFC2046], Section 5.1) with the media type of message body ([RFC2046], Section 5.1) with the media type of
"multipart/byteranges". "multipart/byteranges".
The multipart/byteranges media type includes one or more body parts, The multipart/byteranges media type includes one or more body parts,
each with its own Content-Type and Content-Range fields. The each with its own Content-Type and Content-Range fields. The
required boundary parameter specifies the boundary string used to required boundary parameter specifies the boundary string used to
separate each body part. separate each body part.
skipping to change at page 70, line 37 skipping to change at page 73, line 37
Subtype name: byteranges Subtype name: byteranges
Required parameters: boundary Required parameters: boundary
Optional parameters: N/A Optional parameters: N/A
Encoding considerations: only "7bit", "8bit", or "binary" are Encoding considerations: only "7bit", "8bit", or "binary" are
permitted permitted
Security considerations: see Section 11 Security considerations: see Section 12
Interoperability considerations: N/A Interoperability considerations: N/A
Published specification: This specification (see Section 6.3.5). Published specification: This specification (see Section 7.3.5).
Applications that use this media type: HTTP components supporting Applications that use this media type: HTTP components supporting
multiple ranges in a single request. multiple ranges in a single request.
Fragment identifier considerations: N/A Fragment identifier considerations: N/A
Additional information: Additional information:
Deprecated alias names for this type: N/A Deprecated alias names for this type: N/A
skipping to change at page 71, line 19 skipping to change at page 74, line 19
hors' Addresses section. hors' Addresses section.
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: N/A Restrictions on usage: N/A
Author: See Authors' Addresses section. Author: See Authors' Addresses section.
Change controller: IESG Change controller: IESG
6.4. Content Negotiation 7.4. Content Negotiation
When responses convey payload information, whether indicating a When responses convey payload information, whether indicating a
success or an error, the origin server often has different ways of success or an error, the origin server often has different ways of
representing that information; for example, in different formats, representing that information; for example, in different formats,
languages, or encodings. Likewise, different users or user agents languages, or encodings. Likewise, different users or user agents
might have differing capabilities, characteristics, or preferences might have differing capabilities, characteristics, or preferences
that could influence which representation, among those available, that could influence which representation, among those available,
would be best to deliver. For this reason, HTTP provides mechanisms would be best to deliver. For this reason, HTTP provides mechanisms
for content negotiation. for content negotiation.
skipping to change at page 72, line 7 skipping to change at page 75, line 7
These patterns are not mutually exclusive, and each has trade-offs in These patterns are not mutually exclusive, and each has trade-offs in
applicability and practicality. applicability and practicality.
Note that, in all cases, HTTP is not aware of the resource semantics. Note that, in all cases, HTTP is not aware of the resource semantics.
The consistency with which an origin server responds to requests, The consistency with which an origin server responds to requests,
over time and over the varying dimensions of content negotiation, and over time and over the varying dimensions of content negotiation, and
thus the "sameness" of a resource's observed representations over thus the "sameness" of a resource's observed representations over
time, is determined entirely by whatever entity or algorithm selects time, is determined entirely by whatever entity or algorithm selects
or generates those responses. or generates those responses.
6.4.1. Proactive Negotiation 7.4.1. Proactive Negotiation
When content negotiation preferences are sent by the user agent in a When content negotiation preferences are sent by the user agent in a
request to encourage an algorithm located at the server to select the request to encourage an algorithm located at the server to select the
preferred representation, it is called proactive negotiation (a.k.a., preferred representation, it is called proactive negotiation (a.k.a.,
server-driven negotiation). Selection is based on the available server-driven negotiation). Selection is based on the available
representations for a response (the dimensions over which it might representations for a response (the dimensions over which it might
vary, such as language, content-coding, etc.) compared to various vary, such as language, content-coding, etc.) compared to various
information supplied in the request, including both the explicit information supplied in the request, including both the explicit
negotiation fields of Section 8.4 and implicit characteristics, such negotiation fields of Section 9.4 and implicit characteristics, such
as the client's network address or parts of the User-Agent field. as the client's network address or parts of the User-Agent field.
Proactive negotiation is advantageous when the algorithm for Proactive negotiation is advantageous when the algorithm for
selecting from among the available representations is difficult to selecting from among the available representations is difficult to
describe to a user agent, or when the server desires to send its describe to a user agent, or when the server desires to send its
"best guess" to the user agent along with the first response (hoping "best guess" to the user agent along with the first response (hoping
to avoid the round trip delay of a subsequent request if the "best to avoid the round trip delay of a subsequent request if the "best
guess" is good enough for the user). In order to improve the guess" is good enough for the user). In order to improve the
server's guess, a user agent MAY send request header fields that server's guess, a user agent MAY send request header fields that
describe its preferences. describe its preferences.
skipping to change at page 73, line 5 skipping to change at page 76, line 5
algorithms for generating responses to a request; and, algorithms for generating responses to a request; and,
o It limits the reusability of responses for shared caching. o It limits the reusability of responses for shared caching.
A user agent cannot rely on proactive negotiation preferences being A user agent cannot rely on proactive negotiation preferences being
consistently honored, since the origin server might not implement consistently honored, since the origin server might not implement
proactive negotiation for the requested resource or might decide that proactive negotiation for the requested resource or might decide that
sending a response that doesn't conform to the user agent's sending a response that doesn't conform to the user agent's
preferences is better than sending a 406 (Not Acceptable) response. preferences is better than sending a 406 (Not Acceptable) response.
A Vary header field (Section 10.1.4) is often sent in a response A Vary header field (Section 11.1.4) is often sent in a response
subject to proactive negotiation to indicate what parts of the subject to proactive negotiation to indicate what parts of the
request information were used in the selection algorithm. request information were used in the selection algorithm.
6.4.2. Reactive Negotiation 7.4.2. Reactive Negotiation
With reactive negotiation (a.k.a., agent-driven negotiation), With reactive negotiation (a.k.a., agent-driven negotiation),
selection of the best response representation (regardless of the selection of the best response representation (regardless of the
status code) is performed by the user agent after receiving an status code) is performed by the user agent after receiving an
initial response from the origin server that contains a list of initial response from the origin server that contains a list of
resources for alternative representations. If the user agent is not resources for alternative representations. If the user agent is not
satisfied by the initial response representation, it can perform a satisfied by the initial response representation, it can perform a
GET request on one or more of the alternative resources, selected GET request on one or more of the alternative resources, selected
based on metadata included in the list, to obtain a different form of based on metadata included in the list, to obtain a different form of
representation for that response. Selection of alternatives might be representation for that response. Selection of alternatives might be
skipping to change at page 74, line 5 skipping to change at page 77, line 5
caches are used to distribute server load and reduce network usage. caches are used to distribute server load and reduce network usage.
Reactive negotiation suffers from the disadvantages of transmitting a Reactive negotiation suffers from the disadvantages of transmitting a
list of alternatives to the user agent, which degrades user-perceived list of alternatives to the user agent, which degrades user-perceived
latency if transmitted in the header section, and needing a second latency if transmitted in the header section, and needing a second
request to obtain an alternate representation. Furthermore, this request to obtain an alternate representation. Furthermore, this
specification does not define a mechanism for supporting automatic specification does not define a mechanism for supporting automatic
selection, though it does not prevent such a mechanism from being selection, though it does not prevent such a mechanism from being
developed as an extension. developed as an extension.
6.4.3. Request Payload Negotiation 7.4.3. Request Payload Negotiation
When content negotiation preferences are sent in a server's response, When content negotiation preferences are sent in a server's response,
the listed preferences are called request payload negotiation because the listed preferences are called request payload negotiation because
they intend to influence selection of an appropriate payload for they intend to influence selection of an appropriate payload for
subsequent requests to that resource. For example, the Accept- subsequent requests to that resource. For example, the Accept-
Encoding field (Section 8.4.3) can be sent in a response to indicate Encoding field (Section 9.4.3) can be sent in a response to indicate
preferred content codings for subsequent requests to that resource preferred content codings for subsequent requests to that resource
[RFC7694]. [RFC7694].
Similarly, Section 3.1 of [RFC5789] defines the "Accept-Patch" Similarly, Section 3.1 of [RFC5789] defines the "Accept-Patch"
response header field which allows discovery of which content response header field which allows discovery of which content
types are accepted in PATCH requests. types are accepted in PATCH requests.
6.4.4. Quality Values 7.4.4. Quality Values
The content negotiation fields defined by this specification use a The content negotiation fields defined by this specification use a
common parameter, named "q" (case-insensitive), to assign a relative common parameter, named "q" (case-insensitive), to assign a relative
"weight" to the preference for that associated kind of content. This "weight" to the preference for that associated kind of content. This
weight is referred to as a "quality value" (or "qvalue") because the weight is referred to as a "quality value" (or "qvalue") because the
same parameter name is often used within server configurations to same parameter name is often used within server configurations to
assign a weight to the relative quality of the various assign a weight to the relative quality of the various
representations that can be selected for a resource. representations that can be selected for a resource.
The weight is normalized to a real number in the range 0 through 1, The weight is normalized to a real number in the range 0 through 1,
skipping to change at page 74, line 42 skipping to change at page 77, line 42
the default weight is 1. the default weight is 1.
weight = OWS ";" OWS "q=" qvalue weight = OWS ";" OWS "q=" qvalue
qvalue = ( "0" [ "." 0*3DIGIT ] ) qvalue = ( "0" [ "." 0*3DIGIT ] )
/ ( "1" [ "." 0*3("0") ] ) / ( "1" [ "." 0*3("0") ] )
A sender of qvalue MUST NOT generate more than three digits after the A sender of qvalue MUST NOT generate more than three digits after the
decimal point. User configuration of these values ought to be decimal point. User configuration of these values ought to be
limited in the same fashion. limited in the same fashion.
7. Request Methods 8. Request Methods
7.1. Overview 8.1. Overview
The request method token is the primary source of request semantics; The request method token is the primary source of request semantics;
it indicates the purpose for which the client has made this request it indicates the purpose for which the client has made this request
and what is expected by the client as a successful result. and what is expected by the client as a successful result.
The request method's semantics might be further specialized by the The request method's semantics might be further specialized by the
semantics of some header fields when present in a request (Section 8) semantics of some header fields when present in a request (Section 9)
if those additional semantics do not conflict with the method. For if those additional semantics do not conflict with the method. For
example, a client can send conditional request header fields example, a client can send conditional request header fields
(Section 8.2) to make the requested action conditional on the current (Section 9.2) to make the requested action conditional on the current
state of the target resource. state of the target resource.
method = token method = token
HTTP was originally designed to be usable as an interface to HTTP was originally designed to be usable as an interface to
distributed object systems. The request method was envisioned as distributed object systems. The request method was envisioned as
applying semantics to a target resource in much the same way as applying semantics to a target resource in much the same way as
invoking a defined method on an identified object would apply invoking a defined method on an identified object would apply
semantics. semantics.
skipping to change at page 76, line 8 skipping to change at page 79, line 8
defined, a standardized method ought to have the same semantics when defined, a standardized method ought to have the same semantics when
applied to any resource, though each resource determines for itself applied to any resource, though each resource determines for itself
whether those semantics are implemented or allowed. whether those semantics are implemented or allowed.
This specification defines a number of standardized methods that are This specification defines a number of standardized methods that are
commonly used in HTTP, as outlined by the following table. commonly used in HTTP, as outlined by the following table.
+---------+-------------------------------------------------+-------+ +---------+-------------------------------------------------+-------+
| Method | Description | Sec. | | Method | Description | Sec. |
+---------+-------------------------------------------------+-------+ +---------+-------------------------------------------------+-------+
| GET | Transfer a current representation of the target | 7.3.1 | | GET | Transfer a current representation of the target | 8.3.1 |
| | resource. | | | | resource. | |
| HEAD | Same as GET, but do not transfer the response | 7.3.2 | | HEAD | Same as GET, but do not transfer the response | 8.3.2 |
| | body. | | | | body. | |
| POST | Perform resource-specific processing on the | 7.3.3 | | POST | Perform resource-specific processing on the | 8.3.3 |
| | request payload. | | | | request payload. | |
| PUT | Replace all current representations of the | 7.3.4 | | PUT | Replace all current representations of the | 8.3.4 |
| | target resource with the request payload. | | | | target resource with the request payload. | |
| DELETE | Remove all current representations of the | 7.3.5 | | DELETE | Remove all current representations of the | 8.3.5 |
| | target resource. | | | | target resource. | |
| CONNECT | Establish a tunnel to the server identified by | 7.3.6 | | CONNECT | Establish a tunnel to the server identified by | 8.3.6 |
| | the target resource. | | | | the target resource. | |
| OPTIONS | Describe the communication options for the | 7.3.7 | | OPTIONS | Describe the communication options for the | 8.3.7 |
| | target resource. | | | | target resource. | |
| TRACE | Perform a message loop-back test along the path | 7.3.8 | | TRACE | Perform a message loop-back test along the path | 8.3.8 |
| | to the target resource. | | | | to the target resource. | |
+---------+-------------------------------------------------+-------+ +---------+-------------------------------------------------+-------+
Table 4 Table 4
All general-purpose servers MUST support the methods GET and HEAD. All general-purpose servers MUST support the methods GET and HEAD.
All other methods are OPTIONAL. All other methods are OPTIONAL.
The set of methods allowed by a target resource can be listed in an The set of methods allowed by a target resource can be listed in an
Allow header field (Section 10.4.2). However, the set of allowed Allow header field (Section 11.4.2). However, the set of allowed
methods can change dynamically. When a request method is received methods can change dynamically. When a request method is received
that is unrecognized or not implemented by an origin server, the that is unrecognized or not implemented by an origin server, the
origin server SHOULD respond with the 501 (Not Implemented) status origin server SHOULD respond with the 501 (Not Implemented) status
code. When a request method is received that is known by an origin code. When a request method is received that is known by an origin
server but not allowed for the target resource, the origin server server but not allowed for the target resource, the origin server
SHOULD respond with the 405 (Method Not Allowed) status code. SHOULD respond with the 405 (Method Not Allowed) status code.
7.2. Common Method Properties 8.2. Common Method Properties
+---------+------+------------+----------------+ +---------+------+------------+----------------+
| Method | Safe | Idempotent | Reference | | Method | Safe | Idempotent | Reference |
+---------+------+------------+----------------+ +---------+------+------------+----------------+
| CONNECT | no | no | Section 7.3.6 | | CONNECT | no | no | Section 8.3.6 |
| DELETE | no | yes | Section 7.3.5 | | DELETE | no | yes | Section 8.3.5 |
| GET | yes | yes | Section 7.3.1 | | GET | yes | yes | Section 8.3.1 |
| HEAD | yes | yes | Section 7.3.2 | | HEAD | yes | yes | Section 8.3.2 |
| OPTIONS | yes | yes | Section 7.3.7 | | OPTIONS | yes | yes | Section 8.3.7 |
| POST | no | no | Section 7.3.3 | | POST | no | no | Section 8.3.3 |
| PUT | no | yes | Section 7.3.4 | | PUT | no | yes | Section 8.3.4 |
| TRACE | yes | yes | Section 7.3.8 | | TRACE | yes | yes | Section 8.3.8 |
+---------+------+------------+----------------+ +---------+------+------------+----------------+
Table 5 Table 5
7.2.1. Safe Methods 8.2.1. Safe Methods
Request methods are considered "safe" if their defined semantics are Request methods are considered "safe" if their defined semantics are
essentially read-only; i.e., the client does not request, and does essentially read-only; i.e., the client does not request, and does
not expect, any state change on the origin server as a result of not expect, any state change on the origin server as a result of
applying a safe method to a target resource. Likewise, reasonable applying a safe method to a target resource. Likewise, reasonable
use of a safe method is not expected to cause any harm, loss of use of a safe method is not expected to cause any harm, loss of
property, or unusual burden on the origin server. property, or unusual burden on the origin server.
This definition of safe methods does not prevent an implementation This definition of safe methods does not prevent an implementation
from including behavior that is potentially harmful, that is not from including behavior that is potentially harmful, that is not
skipping to change at page 78, line 22 skipping to change at page 81, line 22
the request method semantics. For example, it is common for Web- the request method semantics. For example, it is common for Web-
based content editing software to use actions within query based content editing software to use actions within query
parameters, such as "page?do=delete". If the purpose of such a parameters, such as "page?do=delete". If the purpose of such a
resource is to perform an unsafe action, then the resource owner MUST resource is to perform an unsafe action, then the resource owner MUST
disable or disallow that action when it is accessed using a safe disable or disallow that action when it is accessed using a safe
request method. Failure to do so will result in unfortunate side request method. Failure to do so will result in unfortunate side
effects when automated processes perform a GET on every URI reference effects when automated processes perform a GET on every URI reference
for the sake of link maintenance, pre-fetching, building a search for the sake of link maintenance, pre-fetching, building a search
index, etc. index, etc.
7.2.2. Idempotent Methods 8.2.2. Idempotent Methods
A request method is considered "idempotent" if the intended effect on A request method is considered "idempotent" if the intended effect on
the server of multiple identical requests with that method is the the server of multiple identical requests with that method is the
same as the effect for a single such request. Of the request methods same as the effect for a single such request. Of the request methods
defined by this specification, PUT, DELETE, and safe request methods defined by this specification, PUT, DELETE, and safe request methods
are idempotent. are idempotent.
Like the definition of safe, the idempotent property only applies to Like the definition of safe, the idempotent property only applies to
what has been requested by the user; a server is free to log each what has been requested by the user; a server is free to log each
request separately, retain a revision control history, or implement request separately, retain a revision control history, or implement
skipping to change at page 79, line 17 skipping to change at page 82, line 17
retrying the requests that failed. retrying the requests that failed.
Some clients use weaker signals to initiate automatic retries. For Some clients use weaker signals to initiate automatic retries. For
example, when a POST request is sent, but the underlying transport example, when a POST request is sent, but the underlying transport
connection is closed before any part of the response is received. connection is closed before any part of the response is received.
Although this is commonly implemented, it is not recommended. Although this is commonly implemented, it is not recommended.
A proxy MUST NOT automatically retry non-idempotent requests. A A proxy MUST NOT automatically retry non-idempotent requests. A
client SHOULD NOT automatically retry a failed automatic retry. client SHOULD NOT automatically retry a failed automatic retry.
7.2.3. Methods and Caching 8.2.3. Methods and Caching
For a cache to store and use a response, the associated method needs For a cache to store and use a response, the associated method needs
to explicitly allow caching, and detail under what conditions a to explicitly allow caching, and detail under what conditions a
response can be used to satisfy subsequent requests; a method response can be used to satisfy subsequent requests; a method
definition which does not do so cannot be cached. For additional definition which does not do so cannot be cached. For additional
requirements see [Caching]. requirements see [Caching].
This specification defines caching semantics for GET, HEAD, and POST, This specification defines caching semantics for GET, HEAD, and POST,
although the overwhelming majority of cache implementations only although the overwhelming majority of cache implementations only
support GET and HEAD. support GET and HEAD.
7.3. Method Definitions 8.3. Method Definitions
7.3.1. GET 8.3.1. GET
The GET method requests transfer of a current selected representation The GET method requests transfer of a current selected representation
for the target resource. GET is the primary mechanism of information for the target resource. GET is the primary mechanism of information
retrieval and the focus of almost all performance optimizations. retrieval and the focus of almost all performance optimizations.
Hence, when people speak of retrieving some identifiable information Hence, when people speak of retrieving some identifiable information
via HTTP, they are generally referring to making a GET request. via HTTP, they are generally referring to making a GET request.
The GET method is specifically intended to reflect the quality of The GET method is specifically intended to reflect the quality of
"sameness" identified by the request URI as if it were referenced as "sameness" identified by the request URI as if it were referenced as
an ordinary hypertext link. an ordinary hypertext link.
It is tempting to think of resource identifiers as remote file system It is tempting to think of resource identifiers as remote file system
pathnames and of representations as being a copy of the contents of pathnames and of representations as being a copy of the contents of
such files. In fact, that is how many resources are implemented (see such files. In fact, that is how many resources are implemented (see
Section 11.3 for related security considerations). However, there Section 12.3 for related security considerations). However, there
are no such limitations in practice. The HTTP interface for a are no such limitations in practice. The HTTP interface for a
resource is just as likely to be implemented as a tree of content resource is just as likely to be implemented as a tree of content
objects, a programmatic view on various database records, or a objects, a programmatic view on various database records, or a
gateway to other information systems. Even when the URI mapping gateway to other information systems. Even when the URI mapping
mechanism is tied to a file system, an origin server might be mechanism is tied to a file system, an origin server might be
configured to execute the files with the request as input and send configured to execute the files with the request as input and send
the output as the representation rather than transfer the files the output as the representation rather than transfer the files
directly. Regardless, only the origin server needs to know how each directly. Regardless, only the origin server needs to know how each
of its resource identifiers corresponds to an implementation and how of its resource identifiers corresponds to an implementation and how
each implementation manages to select and send a current each implementation manages to select and send a current
representation of the target resource in a response to GET. representation of the target resource in a response to GET.
A client can alter the semantics of GET to be a "range request", A client can alter the semantics of GET to be a "range request",
requesting transfer of only some part(s) of the selected requesting transfer of only some part(s) of the selected
representation, by sending a Range header field in the request representation, by sending a Range header field in the request
(Section 8.3). (Section 9.3).
A client SHOULD NOT generate a body in a GET request. A payload A client SHOULD NOT generate a body in a GET request. A payload
received in a GET request has no defined semantics, cannot alter the received in a GET request has no defined semantics, cannot alter the
meaning or target of the request, and might lead some implementations meaning or target of the request, and might lead some implementations
to reject the request and close the connection because of its to reject the request and close the connection because of its
potential as a request smuggling attack (Section 11.2 of potential as a request smuggling attack (Section 11.2 of
[Messaging]). [Messaging]).
The response to a GET request is cacheable; a cache MAY use it to The response to a GET request is cacheable; a cache MAY use it to
satisfy subsequent GET and HEAD requests unless otherwise indicated satisfy subsequent GET and HEAD requests unless otherwise indicated
by the Cache-Control header field (Section 5.2 of [Caching]). A by the Cache-Control header field (Section 5.2 of [Caching]). A
cache that receives a payload in a GET request is likely to ignore cache that receives a payload in a GET request is likely to ignore
that payload and cache regardless of the payload contents. that payload and cache regardless of the payload contents.
7.3.2. HEAD 8.3.2. HEAD
The HEAD method is identical to GET except that the server MUST NOT The HEAD method is identical to GET except that the server MUST NOT
send a message body in the response (i.e., the response terminates at send a message body in the response (i.e., the response terminates at
the end of the header section). The server SHOULD send the same the end of the header section). The server SHOULD send the same
header fields in response to a HEAD request as it would have sent if header fields in response to a HEAD request as it would have sent if
the request had been a GET, except that the payload header fields the request had been a GET, except that the payload header fields
(Section 6.3) MAY be omitted. This method can be used for obtaining (Section 7.3) MAY be omitted. This method can be used for obtaining
metadata about the selected representation without transferring the metadata about the selected representation without transferring the
representation data and is often used for testing hypertext links for representation data and is often used for testing hypertext links for
validity, accessibility, and recent modification. validity, accessibility, and recent modification.
A payload within a HEAD request message has no defined semantics; A payload within a HEAD request message has no defined semantics;
sending a payload body on a HEAD request might cause some existing sending a payload body on a HEAD request might cause some existing
implementations to reject the request. implementations to reject the request.
The response to a HEAD request is cacheable; a cache MAY use it to The response to a HEAD request is cacheable; a cache MAY use it to
satisfy subsequent HEAD requests unless otherwise indicated by the satisfy subsequent HEAD requests unless otherwise indicated by the
Cache-Control header field (Section 5.2 of [Caching]). A HEAD Cache-Control header field (Section 5.2 of [Caching]). A HEAD
response might also have an effect on previously cached responses to response might also have an effect on previously cached responses to
GET; see Section 4.3.5 of [Caching]. GET; see Section 4.3.5 of [Caching].
7.3.3. POST 8.3.3. POST
The POST method requests that the target resource process the The POST method requests that the target resource process the
representation enclosed in the request according to the resource's representation enclosed in the request according to the resource's
own specific semantics. For example, POST is used for the following own specific semantics. For example, POST is used for the following
functions (among others): functions (among others):
o Providing a block of data, such as the fields entered into an HTML o Providing a block of data, such as the fields entered into an HTML
form, to a data-handling process; form, to a data-handling process;
o Posting a message to a bulletin board, newsgroup, mailing list, o Posting a message to a bulletin board, newsgroup, mailing list,
skipping to change at page 81, line 34 skipping to change at page 84, line 34
appropriate status code depending on the result of processing the appropriate status code depending on the result of processing the
POST request; almost all of the status codes defined by this POST request; almost all of the status codes defined by this
specification might be received in a response to POST (the exceptions specification might be received in a response to POST (the exceptions
being 206 (Partial Content), 304 (Not Modified), and 416 (Range Not being 206 (Partial Content), 304 (Not Modified), and 416 (Range Not
Satisfiable)). Satisfiable)).
If one or more resources has been created on the origin server as a If one or more resources has been created on the origin server as a
result of successfully processing a POST request, the origin server result of successfully processing a POST request, the origin server
SHOULD send a 201 (Created) response containing a Location header SHOULD send a 201 (Created) response containing a Location header
field that provides an identifier for the primary resource created field that provides an identifier for the primary resource created
(Section 10.1.2) and a representation that describes the status of (Section 11.1.2) and a representation that describes the status of
the request while referring to the new resource(s). the request while referring to the new resource(s).
Responses to POST requests are only cacheable when they include Responses to POST requests are only cacheable when they include
explicit freshness information (see Section 4.2.1 of [Caching]) and a explicit freshness information (see Section 4.2.1 of [Caching]) and a
Content-Location header field that has the same value as the POST's Content-Location header field that has the same value as the POST's
target URI (Section 6.2.5). A cached POST response can be reused to target URI (Section 7.2.5). A cached POST response can be reused to
satisfy a later GET or HEAD request, but not a POST request, since satisfy a later GET or HEAD request, but not a POST request, since
POST is required to be written through to the origin server, because POST is required to be written through to the origin server, because
it is unsafe; see Section 4 of [Caching]. it is unsafe; see Section 4 of [Caching].
If the result of processing a POST would be equivalent to a If the result of processing a POST would be equivalent to a
representation of an existing resource, an origin server MAY redirect representation of an existing resource, an origin server MAY redirect
the user agent to that resource by sending a 303 (See Other) response the user agent to that resource by sending a 303 (See Other) response
with the existing resource's identifier in the Location field. This with the existing resource's identifier in the Location field. This
has the benefits of providing the user agent a resource identifier has the benefits of providing the user agent a resource identifier
and transferring the representation via a method more amenable to and transferring the representation via a method more amenable to
shared caching, though at the cost of an extra request if the user shared caching, though at the cost of an extra request if the user
agent does not already have the representation cached. agent does not already have the representation cached.
7.3.4. PUT 8.3.4. PUT
The PUT method requests that the state of the target resource be The PUT method requests that the state of the target resource be
created or replaced with the state defined by the representation created or replaced with the state defined by the representation
enclosed in the request message payload. A successful PUT of a given enclosed in the request message payload. A successful PUT of a given
representation would suggest that a subsequent GET on that same representation would suggest that a subsequent GET on that same
target resource will result in an equivalent representation being target resource will result in an equivalent representation being
sent in a 200 (OK) response. However, there is no guarantee that sent in a 200 (OK) response. However, there is no guarantee that
such a state change will be observable, since the target resource such a state change will be observable, since the target resource
might be acted upon by other user agents in parallel, or might be might be acted upon by other user agents in parallel, or might be
subject to dynamic processing by the origin server, before any subject to dynamic processing by the origin server, before any
skipping to change at page 83, line 24 skipping to change at page 86, line 24
agent request and the semantics of the origin server response. It agent request and the semantics of the origin server response. It
does not define what a resource might be, in any sense of that word, does not define what a resource might be, in any sense of that word,
beyond the interface provided via HTTP. It does not define how beyond the interface provided via HTTP. It does not define how
resource state is "stored", nor how such storage might change as a resource state is "stored", nor how such storage might change as a
result of a change in resource state, nor how the origin server result of a change in resource state, nor how the origin server
translates resource state into representations. Generally speaking, translates resource state into representations. Generally speaking,
all implementation details behind the resource interface are all implementation details behind the resource interface are
intentionally hidden by the server. intentionally hidden by the server.
An origin server MUST NOT send a validator header field An origin server MUST NOT send a validator header field
(Section 10.2), such as an ETag or Last-Modified field, in a (Section 11.2), such as an ETag or Last-Modified field, in a
successful response to PUT unless the request's representation data successful response to PUT unless the request's representation data
was saved without any transformation applied to the body (i.e., the was saved without any transformation applied to the body (i.e., the
resource's new representation data is identical to the representation resource's new representation data is identical to the representation
data received in the PUT request) and the validator field value data received in the PUT request) and the validator field value
reflects the new representation. This requirement allows a user reflects the new representation. This requirement allows a user
agent to know when the representation body it has in memory remains agent to know when the representation body it has in memory remains
current as a result of the PUT, thus not in need of being retrieved current as a result of the PUT, thus not in need of being retrieved
again from the origin server, and that the new validator(s) received again from the origin server, and that the new validator(s) received
in the response can be used for future conditional requests in order in the response can be used for future conditional requests in order
to prevent accidental overwrites (Section 8.2). to prevent accidental overwrites (Section 9.2).
The fundamental difference between the POST and PUT methods is The fundamental difference between the POST and PUT methods is
highlighted by the different intent for the enclosed representation. highlighted by the different intent for the enclosed representation.
The target resource in a POST request is intended to handle the The target resource in a POST request is intended to handle the
enclosed representation according to the resource's own semantics, enclosed representation according to the resource's own semantics,
whereas the enclosed representation in a PUT request is defined as whereas the enclosed representation in a PUT request is defined as
replacing the state of the target resource. Hence, the intent of PUT replacing the state of the target resource. Hence, the intent of PUT
is idempotent and visible to intermediaries, even though the exact is idempotent and visible to intermediaries, even though the exact
effect is only known by the origin server. effect is only known by the origin server.
skipping to change at page 84, line 20 skipping to change at page 87, line 20
identifying "the current version" (a resource) that is separate from identifying "the current version" (a resource) that is separate from
the URIs identifying each particular version (different resources the URIs identifying each particular version (different resources
that at one point shared the same state as the current version that at one point shared the same state as the current version
resource). A successful PUT request on "the current version" URI resource). A successful PUT request on "the current version" URI
might therefore create a new version resource in addition to changing might therefore create a new version resource in addition to changing
the state of the target resource, and might also cause links to be the state of the target resource, and might also cause links to be
added between the related resources. added between the related resources.
An origin server that allows PUT on a given target resource MUST send An origin server that allows PUT on a given target resource MUST send
a 400 (Bad Request) response to a PUT request that contains a a 400 (Bad Request) response to a PUT request that contains a
Content-Range header field (Section 6.3.4), since the payload is Content-Range header field (Section 7.3.4), since the payload is
likely to be partial content that has been mistakenly PUT as a full likely to be partial content that has been mistakenly PUT as a full
representation. Partial content updates are possible by targeting a representation. Partial content updates are possible by targeting a
separately identified resource with state that overlaps a portion of separately identified resource with state that overlaps a portion of
the larger resource, or by using a different method that has been the larger resource, or by using a different method that has been
specifically defined for partial updates (for example, the PATCH specifically defined for partial updates (for example, the PATCH
method defined in [RFC5789]). method defined in [RFC5789]).
Responses to the PUT method are not cacheable. If a successful PUT Responses to the PUT method are not cacheable. If a successful PUT
request passes through a cache that has one or more stored responses request passes through a cache that has one or more stored responses
for the target URI, those stored responses will be invalidated (see for the target URI, those stored responses will be invalidated (see
Section 4.4 of [Caching]). Section 4.4 of [Caching]).
7.3.5. DELETE 8.3.5. DELETE
The DELETE method requests that the origin server remove the The DELETE method requests that the origin server remove the
association between the target resource and its current association between the target resource and its current
functionality. In effect, this method is similar to the rm command functionality. In effect, this method is similar to the rm command
in UNIX: it expresses a deletion operation on the URI mapping of the in UNIX: it expresses a deletion operation on the URI mapping of the
origin server rather than an expectation that the previously origin server rather than an expectation that the previously
associated information be deleted. associated information be deleted.
If the target resource has one or more current representations, they If the target resource has one or more current representations, they
might or might not be destroyed by the origin server, and the might or might not be destroyed by the origin server, and the
skipping to change at page 85, line 39 skipping to change at page 88, line 39
A client SHOULD NOT generate a body in a DELETE request. A payload A client SHOULD NOT generate a body in a DELETE request. A payload
received in a DELETE request has no defined semantics, cannot alter received in a DELETE request has no defined semantics, cannot alter
the meaning or target of the request, and might lead some the meaning or target of the request, and might lead some
implementations to reject the request. implementations to reject the request.
Responses to the DELETE method are not cacheable. If a successful Responses to the DELETE method are not cacheable. If a successful
DELETE request passes through a cache that has one or more stored DELETE request passes through a cache that has one or more stored
responses for the target URI, those stored responses will be responses for the target URI, those stored responses will be
invalidated (see Section 4.4 of [Caching]). invalidated (see Section 4.4 of [Caching]).
7.3.6. CONNECT 8.3.6. CONNECT
The CONNECT method requests that the recipient establish a tunnel to The CONNECT method requests that the recipient establish a tunnel to
the destination origin server identified by the request target and, the destination origin server identified by the request target and,
if successful, thereafter restrict its behavior to blind forwarding if successful, thereafter restrict its behavior to blind forwarding
of data, in both directions, until the tunnel is closed. Tunnels are of data, in both directions, until the tunnel is closed. Tunnels are
commonly used to create an end-to-end virtual connection, through one commonly used to create an end-to-end virtual connection, through one
or more proxies, which can then be secured using TLS (Transport Layer or more proxies, which can then be secured using TLS (Transport Layer
Security, [RFC8446]). Security, [RFC8446]).
Because CONNECT changes the request/response nature of an HTTP
connection, specific HTTP versions might have different ways of
mapping its semantics into the protocol's wire format.
CONNECT is intended only for use in requests to a proxy. An origin CONNECT is intended only for use in requests to a proxy. An origin
server that receives a CONNECT request for itself MAY respond with a server that receives a CONNECT request for itself MAY respond with a
2xx (Successful) status code to indicate that a connection is 2xx (Successful) status code to indicate that a connection is
established. However, most origin servers do not implement CONNECT. established. However, most origin servers do not implement CONNECT.
A client sending a CONNECT request MUST send the authority component A client sending a CONNECT request MUST send the authority component
(described in Section 3.2 of [RFC3986]) as the request target; i.e., (described in Section 3.2 of [RFC3986]) as the request target; i.e.,
the request target consists of only the host name and port number of the request target consists of only the host name and port number of
the tunnel destination, separated by a colon. For example, the tunnel destination, separated by a colon. For example,
skipping to change at page 87, line 11 skipping to change at page 90, line 16
fields in a 2xx (Successful) response to CONNECT. A client MUST fields in a 2xx (Successful) response to CONNECT. A client MUST
ignore any Content-Length or Transfer-Encoding header fields received ignore any Content-Length or Transfer-Encoding header fields received
in a successful response to CONNECT. in a successful response to CONNECT.
A payload within a CONNECT request message has no defined semantics; A payload within a CONNECT request message has no defined semantics;
sending a payload body on a CONNECT request might cause some existing sending a payload body on a CONNECT request might cause some existing
implementations to reject the request. implementations to reject the request.
Responses to the CONNECT method are not cacheable. Responses to the CONNECT method are not cacheable.
7.3.7. OPTIONS 8.3.7. OPTIONS
The OPTIONS method requests information about the communication The OPTIONS method requests information about the communication
options available for the target resource, at either the origin options available for the target resource, at either the origin
server or an intervening intermediary. This method allows a client server or an intervening intermediary. This method allows a client
to determine the options and/or requirements associated with a to determine the options and/or requirements associated with a
resource, or the capabilities of a server, without implying a resource, or the capabilities of a server, without implying a
resource action. resource action.
An OPTIONS request with an asterisk ("*") as the request target An OPTIONS request with an asterisk ("*") as the request target
(Section 5.1) applies to the server in general rather than to a (Section 6.1) applies to the server in general rather than to a
specific resource. Since a server's communication options typically specific resource. Since a server's communication options typically
depend on the resource, the "*" request is only useful as a "ping" or depend on the resource, the "*" request is only useful as a "ping" or
"no-op" type of method; it does nothing beyond allowing the client to "no-op" type of method; it does nothing beyond allowing the client to
test the capabilities of the server. For example, this can be used test the capabilities of the server. For example, this can be used
to test a proxy for HTTP/1.1 conformance (or lack thereof). to test a proxy for HTTP/1.1 conformance (or lack thereof).
If the request target is not an asterisk, the OPTIONS request applies If the request target is not an asterisk, the OPTIONS request applies
to the options that are available when communicating with the target to the options that are available when communicating with the target
resource. resource.
skipping to change at page 87, line 43 skipping to change at page 90, line 48
header that might indicate optional features implemented by the header that might indicate optional features implemented by the
server and applicable to the target resource (e.g., Allow), including server and applicable to the target resource (e.g., Allow), including
potential extensions not defined by this specification. The response potential extensions not defined by this specification. The response
payload, if any, might also describe the communication options in a payload, if any, might also describe the communication options in a
machine or human-readable representation. A standard format for such machine or human-readable representation. A standard format for such
a representation is not defined by this specification, but might be a representation is not defined by this specification, but might be
defined by future extensions to HTTP. defined by future extensions to HTTP.
A client MAY send a Max-Forwards header field in an OPTIONS request A client MAY send a Max-Forwards header field in an OPTIONS request
to target a specific recipient in the request chain (see to target a specific recipient in the request chain (see
Section 8.1.2). A proxy MUST NOT generate a Max-Forwards header Section 9.1.2). A proxy MUST NOT generate a Max-Forwards header
field while forwarding a request unless that request was received field while forwarding a request unless that request was received
with a Max-Forwards field. with a Max-Forwards field.
A client that generates an OPTIONS request containing a payload body A client that generates an OPTIONS request containing a payload body
MUST send a valid Content-Type header field describing the MUST send a valid Content-Type header field describing the
representation media type. Note that this specification does not representation media type. Note that this specification does not
define any use for such a payload. define any use for such a payload.
Responses to the OPTIONS method are not cacheable. Responses to the OPTIONS method are not cacheable.
7.3.8. TRACE 8.3.8. TRACE
The TRACE method requests a remote, application-level loop-back of The TRACE method requests a remote, application-level loop-back of
the request message. The final recipient of the request SHOULD the request message. The final recipient of the request SHOULD
reflect the message received, excluding some fields described below, reflect the message received, excluding some fields described below,
back to the client as the message body of a 200 (OK) response with a back to the client as the message body of a 200 (OK) response with a
Content-Type of "message/http" (Section 10.1 of [Messaging]). The Content-Type of "message/http" (Section 10.1 of [Messaging]). The
final recipient is either the origin server or the first server to final recipient is either the origin server or the first server to
receive a Max-Forwards value of zero (0) in the request receive a Max-Forwards value of zero (0) in the request
(Section 8.1.2). (Section 9.1.2).
A client MUST NOT generate fields in a TRACE request containing A client MUST NOT generate fields in a TRACE request containing
sensitive data that might be disclosed by the response. For example, sensitive data that might be disclosed by the response. For example,
it would be foolish for a user agent to send stored user credentials it would be foolish for a user agent to send stored user credentials
Section 8.5 or cookies [RFC6265] in a TRACE request. The final Section 9.5 or cookies [RFC6265] in a TRACE request. The final
recipient of the request SHOULD exclude any request fields that are recipient of the request SHOULD exclude any request fields that are
likely to contain sensitive data when that recipient generates the likely to contain sensitive data when that recipient generates the
response body. response body.
TRACE allows the client to see what is being received at the other TRACE allows the client to see what is being received at the other
end of the request chain and use that data for testing or diagnostic end of the request chain and use that data for testing or diagnostic
information. The value of the Via header field (Section 5.7.1) is of information. The value of the Via header field (Section 6.7.1) is of
particular interest, since it acts as a trace of the request chain. particular interest, since it acts as a trace of the request chain.
Use of the Max-Forwards header field allows the client to limit the Use of the Max-Forwards header field allows the client to limit the
length of the request chain, which is useful for testing a chain of length of the request chain, which is useful for testing a chain of
proxies forwarding messages in an infinite loop. proxies forwarding messages in an infinite loop.
A client MUST NOT send a message body in a TRACE request. A client MUST NOT send a message body in a TRACE request.
Responses to the TRACE method are not cacheable. Responses to the TRACE method are not cacheable.
7.4. Method Extensibility 8.4. Method Extensibility
Additional methods, outside the scope of this specification, have Additional methods, outside the scope of this specification, have
been specified for use in HTTP. All such methods ought to be been specified for use in HTTP. All such methods ought to be
registered within the "Hypertext Transfer Protocol (HTTP) Method registered within the "Hypertext Transfer Protocol (HTTP) Method
Registry". Registry".
7.4.1. Method Registry 8.4.1. Method Registry
The "Hypertext Transfer Protocol (HTTP) Method Registry", maintained The "Hypertext Transfer Protocol (HTTP) Method Registry", maintained
by IANA at <https://www.iana.org/assignments/http-methods>, registers by IANA at <https://www.iana.org/assignments/http-methods>, registers
method names. method names.
HTTP method registrations MUST include the following fields: HTTP method registrations MUST include the following fields:
o Method Name (see Section 7) o Method Name (see Section 8)
o Safe ("yes" or "no", see Section 7.2.1)
o Idempotent ("yes" or "no", see Section 7.2.2) o Safe ("yes" or "no", see Section 8.2.1)
o Idempotent ("yes" or "no", see Section 8.2.2)
o Pointer to specification text o Pointer to specification text
Values to be added to this namespace require IETF Review (see Values to be added to this namespace require IETF Review (see
[RFC8126], Section 4.8). [RFC8126], Section 4.8).
7.4.2. Considerations for New Methods 8.4.2. Considerations for New Methods
Standardized methods are generic; that is, they are potentially Standardized methods are generic; that is, they are potentially
applicable to any resource, not just one particular media type, kind applicable to any resource, not just one particular media type, kind
of resource, or application. As such, it is preferred that new of resource, or application. As such, it is preferred that new
methods be registered in a document that isn't specific to a single methods be registered in a document that isn't specific to a single
application or data format, since orthogonal technologies deserve application or data format, since orthogonal technologies deserve
orthogonal specification. orthogonal specification.
Since message parsing (Section 6 of [Messaging]) needs to be Since message parsing (Section 6 of [Messaging]) needs to be
independent of method semantics (aside from responses to HEAD), independent of method semantics (aside from responses to HEAD),
definitions of new methods cannot change the parsing algorithm or definitions of new methods cannot change the parsing algorithm or
prohibit the presence of a message body on either the request or the prohibit the presence of a message body on either the request or the
response message. Definitions of new methods can specify that only a response message. Definitions of new methods can specify that only a
zero-length message body is allowed by requiring a Content-Length zero-length message body is allowed by requiring a Content-Length
header field with a value of "0". header field with a value of "0".
A new method definition needs to indicate whether it is safe A new method definition needs to indicate whether it is safe
(Section 7.2.1), idempotent (Section 7.2.2), cacheable (Section 8.2.1), idempotent (Section 8.2.2), cacheable
(Section 7.2.3), what semantics are to be associated with the payload (Section 8.2.3), what semantics are to be associated with the payload
body if any is present in the request and what refinements the method body if any is present in the request and what refinements the method
makes to header field or status code semantics. If the new method is makes to header field or status code semantics. If the new method is
cacheable, its definition ought to describe how, and under what cacheable, its definition ought to describe how, and under what
conditions, a cache can store a response and use it to satisfy a conditions, a cache can store a response and use it to satisfy a
subsequent request. The new method ought to describe whether it can subsequent request. The new method ought to describe whether it can
be made conditional (Section 8.2) and, if so, how a server responds be made conditional (Section 9.2) and, if so, how a server responds
when the condition is false. Likewise, if the new method might have when the condition is false. Likewise, if the new method might have
some use for partial response semantics (Section 8.3), it ought to some use for partial response semantics (Section 9.3), it ought to
document this, too. document this, too.
Note: Avoid defining a method name that starts with "M-", since Note: Avoid defining a method name that starts with "M-", since
that prefix might be misinterpreted as having the semantics that prefix might be misinterpreted as having the semantics
assigned to it by [RFC2774]. assigned to it by [RFC2774].
8. Request Header Fields 9. Request Header Fields
A client sends request header fields to provide more information A client sends request header fields to provide more information
about the request context, make the request conditional based on the about the request context, make the request conditional based on the
target resource state, suggest preferred formats for the response, target resource state, suggest preferred formats for the response,
supply authentication credentials, or modify the expected request supply authentication credentials, or modify the expected request
processing. These fields act as request modifiers, similar to the processing. These fields act as request modifiers, similar to the
parameters on a programming language method invocation. parameters on a programming language method invocation.
8.1. Controls 9.1. Controls
Controls are request header fields that direct specific handling of Controls are request header fields that direct specific handling of
the request. the request.
+---------------+----------------------------+ +---------------+----------------------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+---------------+----------------------------+ +---------------+----------------------------+
| Cache-Control | Section 5.2 of [Caching] | | Cache-Control | Section 5.2 of [Caching] |
| Expect | Section 8.1.1 | | Expect | Section 9.1.1 |
| Host | Section 5.6 | | Host | Section 6.6 |
| Max-Forwards | Section 8.1.2 | | Max-Forwards | Section 9.1.2 |
| Pragma | Section 5.4 of [Caching] | | Pragma | Section 5.4 of [Caching] |
| TE | Section 7.4 of [Messaging] | | TE | Section 7.4 of [Messaging] |
+---------------+----------------------------+ +---------------+----------------------------+
8.1.1. Expect 9.1.1. Expect
The "Expect" header field in a request indicates a certain set of The "Expect" header field in a request indicates a certain set of
behaviors (expectations) that need to be supported by the server in behaviors (expectations) that need to be supported by the server in
order to properly handle this request. The only such expectation order to properly handle this request. The only such expectation
defined by this specification is 100-continue. defined by this specification is 100-continue.
Expect = "100-continue" Expect = "100-continue"
The Expect field value is case-insensitive. The Expect field value is case-insensitive.
skipping to change at page 92, line 42 skipping to change at page 96, line 5
Note: The Expect header field was added after the original Note: The Expect header field was added after the original
publication of HTTP/1.1 [RFC2068] as both the means to request an publication of HTTP/1.1 [RFC2068] as both the means to request an
interim 100 (Continue) response and the general mechanism for interim 100 (Continue) response and the general mechanism for
indicating must-understand extensions. However, the extension indicating must-understand extensions. However, the extension
mechanism has not been used by clients and the must-understand mechanism has not been used by clients and the must-understand
requirements have not been implemented by many servers, rendering requirements have not been implemented by many servers, rendering
the extension mechanism useless. This specification has removed the extension mechanism useless. This specification has removed
the extension mechanism in order to simplify the definition and the extension mechanism in order to simplify the definition and
processing of 100-continue. processing of 100-continue.
8.1.2. Max-Forwards 9.1.2. Max-Forwards
The "Max-Forwards" header field provides a mechanism with the TRACE The "Max-Forwards" header field provides a mechanism with the TRACE
(Section 7.3.8) and OPTIONS (Section 7.3.7) request methods to limit (Section 8.3.8) and OPTIONS (Section 8.3.7) request methods to limit
the number of times that the request is forwarded by proxies. This the number of times that the request is forwarded by proxies. This
can be useful when the client is attempting to trace a request that can be useful when the client is attempting to trace a request that
appears to be failing or looping mid-chain. appears to be failing or looping mid-chain.
Max-Forwards = 1*DIGIT Max-Forwards = 1*DIGIT
The Max-Forwards value is a decimal integer indicating the remaining The Max-Forwards value is a decimal integer indicating the remaining
number of times this request message can be forwarded. number of times this request message can be forwarded.
Each intermediary that receives a TRACE or OPTIONS request containing Each intermediary that receives a TRACE or OPTIONS request containing
skipping to change at page 93, line 21 skipping to change at page 96, line 31
intermediary MUST NOT forward the request; instead, the intermediary intermediary MUST NOT forward the request; instead, the intermediary
MUST respond as the final recipient. If the received Max-Forwards MUST respond as the final recipient. If the received Max-Forwards
value is greater than zero, the intermediary MUST generate an updated value is greater than zero, the intermediary MUST generate an updated
Max-Forwards field in the forwarded message with a field value that Max-Forwards field in the forwarded message with a field value that
is the lesser of a) the received value decremented by one (1) or b) is the lesser of a) the received value decremented by one (1) or b)
the recipient's maximum supported value for Max-Forwards. the recipient's maximum supported value for Max-Forwards.
A recipient MAY ignore a Max-Forwards header field received with any A recipient MAY ignore a Max-Forwards header field received with any
other request methods. other request methods.
8.2. Preconditions 9.2. Preconditions
A conditional request is an HTTP request with one or more request A conditional request is an HTTP request with one or more request
header fields that indicate a precondition to be tested before header fields that indicate a precondition to be tested before
applying the request method to the target resource. Section 8.2.1 applying the request method to the target resource. Section 9.2.1
defines when preconditions are applied. Section 8.2.2 defines the defines when preconditions are applied. Section 9.2.2 defines the
order of evaluation when more than one precondition is present. order of evaluation when more than one precondition is present.
Conditional GET requests are the most efficient mechanism for HTTP Conditional GET requests are the most efficient mechanism for HTTP
cache updates [Caching]. Conditionals can also be applied to state- cache updates [Caching]. Conditionals can also be applied to state-
changing methods, such as PUT and DELETE, to prevent the "lost changing methods, such as PUT and DELETE, to prevent the "lost
update" problem: one client accidentally overwriting the work of update" problem: one client accidentally overwriting the work of
another client that has been acting in parallel. another client that has been acting in parallel.
Conditional request preconditions are based on the state of the Conditional request preconditions are based on the state of the
target resource as a whole (its current value set) or the state as target resource as a whole (its current value set) or the state as
observed in a previously obtained representation (one value in that observed in a previously obtained representation (one value in that
set). A resource might have multiple current representations, each set). A resource might have multiple current representations, each
with its own observable state. The conditional request mechanisms with its own observable state. The conditional request mechanisms
assume that the mapping of requests to a selected representation assume that the mapping of requests to a selected representation
(Section 6) will be consistent over time if the server intends to (Section 7) will be consistent over time if the server intends to
take advantage of conditionals. Regardless, if the mapping is take advantage of conditionals. Regardless, if the mapping is
inconsistent and the server is unable to select the appropriate inconsistent and the server is unable to select the appropriate
representation, then no harm will result when the precondition representation, then no harm will result when the precondition
evaluates to false. evaluates to false.
The following request header fields allow a client to place a The following request header fields allow a client to place a
precondition on the state of the target resource, so that the action precondition on the state of the target resource, so that the action
corresponding to the method semantics will not be applied if the corresponding to the method semantics will not be applied if the
precondition evaluates to false. Each precondition defined by this precondition evaluates to false. Each precondition defined by this
specification consists of a comparison between a set of validators specification consists of a comparison between a set of validators
obtained from prior representations of the target resource to the obtained from prior representations of the target resource to the
current state of validators for the selected representation current state of validators for the selected representation
(Section 10.2). Hence, these preconditions evaluate whether the (Section 11.2). Hence, these preconditions evaluate whether the
state of the target resource has changed since a given state known by state of the target resource has changed since a given state known by
the client. The effect of such an evaluation depends on the method the client. The effect of such an evaluation depends on the method
semantics and choice of conditional, as defined in Section 8.2.1. semantics and choice of conditional, as defined in Section 9.2.1.
+---------------------+---------------+ +---------------------+---------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+---------------------+---------------+ +---------------------+---------------+
| If-Match | Section 8.2.3 | | If-Match | Section 9.2.3 |
| If-None-Match | Section 8.2.4 | | If-None-Match | Section 9.2.4 |
| If-Modified-Since | Section 8.2.5 | | If-Modified-Since | Section 9.2.5 |
| If-Unmodified-Since | Section 8.2.6 | | If-Unmodified-Since | Section 9.2.6 |
| If-Range | Section 8.2.7 | | If-Range | Section 9.2.7 |
+---------------------+---------------+ +---------------------+---------------+
8.2.1. Evaluation 9.2.1. Evaluation
Except when excluded below, a recipient cache or origin server MUST Except when excluded below, a recipient cache or origin server MUST
evaluate received request preconditions after it has successfully evaluate received request preconditions after it has successfully
performed its normal request checks and just before it would perform performed its normal request checks and just before it would perform
the action associated with the request method. A server MUST ignore the action associated with the request method. A server MUST ignore
all received preconditions if its response to the same request all received preconditions if its response to the same request
without those conditions would have been a status code other than a without those conditions would have been a status code other than a
2xx (Successful) or 412 (Precondition Failed). In other words, 2xx (Successful) or 412 (Precondition Failed). In other words,
redirects and failures take precedence over the evaluation of redirects and failures take precedence over the evaluation of
preconditions in conditional requests. preconditions in conditional requests.
skipping to change at page 95, line 15 skipping to change at page 98, line 25
if the recipient understands and implements that field ([RFC4918], if the recipient understands and implements that field ([RFC4918],
Section 10.4). Section 10.4).
Although conditional request header fields are defined as being Although conditional request header fields are defined as being
usable with the HEAD method (to keep HEAD's semantics consistent with usable with the HEAD method (to keep HEAD's semantics consistent with
those of GET), there is no point in sending a conditional HEAD those of GET), there is no point in sending a conditional HEAD
because a successful response is around the same size as a 304 (Not because a successful response is around the same size as a 304 (Not
Modified) response and more useful than a 412 (Precondition Failed) Modified) response and more useful than a 412 (Precondition Failed)
response. response.
8.2.2. Precedence 9.2.2. Precedence
When more than one conditional request header field is present in a When more than one conditional request header field is present in a
request, the order in which the fields are evaluated becomes request, the order in which the fields are evaluated becomes
important. In practice, the fields defined in this document are important. In practice, the fields defined in this document are
consistently implemented in a single, logical order, since "lost consistently implemented in a single, logical order, since "lost
update" preconditions have more strict requirements than cache update" preconditions have more strict requirements than cache
validation, a validated cache is more efficient than a partial validation, a validated cache is more efficient than a partial
response, and entity tags are presumed to be more accurate than date response, and entity tags are presumed to be more accurate than date
validators. validators.
A recipient cache or origin server MUST evaluate the request A recipient cache or origin server MUST evaluate the request
preconditions defined by this specification in the following order: preconditions defined by this specification in the following order:
1. When recipient is the origin server and If-Match is present, 1. When recipient is the origin server and If-Match is present,
evaluate the If-Match precondition: evaluate the If-Match precondition:
* if true, continue to step 3 * if true, continue to step 3
* if false, respond 412 (Precondition Failed) unless it can be * if false, respond 412 (Precondition Failed) unless it can be
determined that the state-changing request has already determined that the state-changing request has already
succeeded (see Section 8.2.3) succeeded (see Section 9.2.3)
2. When recipient is the origin server, If-Match is not present, and 2. When recipient is the origin server, If-Match is not present, and
If-Unmodified-Since is present, evaluate the If-Unmodified-Since If-Unmodified-Since is present, evaluate the If-Unmodified-Since
precondition: precondition:
* if true, continue to step 3 * if true, continue to step 3
* if false, respond 412 (Precondition Failed) unless it can be * if false, respond 412 (Precondition Failed) unless it can be
determined that the state-changing request has already determined that the state-changing request has already
succeeded (see Section 8.2.6) succeeded (see Section 9.2.6)
3. When If-None-Match is present, evaluate the If-None-Match 3. When If-None-Match is present, evaluate the If-None-Match
precondition: precondition:
* if true, continue to step 5 * if true, continue to step 5
* if false for GET/HEAD, respond 304 (Not Modified) * if false for GET/HEAD, respond 304 (Not Modified)
* if false for other methods, respond 412 (Precondition Failed) * if false for other methods, respond 412 (Precondition Failed)
skipping to change at page 97, line 10 skipping to change at page 100, line 15
6. Otherwise, 6. Otherwise,
* all conditions are met, so perform the requested action and * all conditions are met, so perform the requested action and
respond according to its success or failure. respond according to its success or failure.
Any extension to HTTP that defines additional conditional request Any extension to HTTP that defines additional conditional request
header fields ought to define its own expectations regarding the header fields ought to define its own expectations regarding the
order for evaluating such fields in relation to those defined in this order for evaluating such fields in relation to those defined in this
document and other conditionals that might be found in practice. document and other conditionals that might be found in practice.
8.2.3. If-Match 9.2.3. If-Match
The "If-Match" header field makes the request method conditional on The "If-Match" header field makes the request method conditional on
the recipient origin server either having at least one current the recipient origin server either having at least one current
representation of the target resource, when the field value is "*", representation of the target resource, when the field value is "*",
or having a current representation of the target resource that has an or having a current representation of the target resource that has an
entity-tag matching a member of the list of entity-tags provided in entity-tag matching a member of the list of entity-tags provided in
the field value. the field value.
An origin server MUST use the strong comparison function when An origin server MUST use the strong comparison function when
comparing entity-tags for If-Match (Section 10.2.3.2), since the comparing entity-tags for If-Match (Section 11.2.3.2), since the
client intends this precondition to prevent the method from being client intends this precondition to prevent the method from being
applied if there have been any changes to the representation data. applied if there have been any changes to the representation data.
If-Match = "*" / 1#entity-tag If-Match = "*" / 1#entity-tag
Examples: Examples:
If-Match: "xyzzy" If-Match: "xyzzy"
If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
If-Match: * If-Match: *
If-Match is most often used with state-changing methods (e.g., POST, If-Match is most often used with state-changing methods (e.g., POST,
PUT, DELETE) to prevent accidental overwrites when multiple user PUT, DELETE) to prevent accidental overwrites when multiple user
agents might be acting in parallel on the same resource (i.e., to agents might be acting in parallel on the same resource (i.e., to
prevent the "lost update" problem). It can also be used with safe prevent the "lost update" problem). It can also be used with safe
methods to abort a request if the selected representation does not methods to abort a request if the selected representation does not
match one already stored (or partially stored) from a prior request. match one already stored (or partially stored) from a prior request.
An origin server that receives an If-Match header field MUST evaluate An origin server that receives an If-Match header field MUST evaluate
the condition prior to performing the method (Section 8.2.1). the condition as per Section 9.2.1 prior to performing the method.
To evaluate a received If-Match header field: To evaluate a received If-Match header field:
1. If the field value is "*", the condition is true if the origin 1. If the field value is "*", the condition is true if the origin
server has a current representation for the target resource. server has a current representation for the target resource.
2. If the field value is a list of entity-tags, the condition is 2. If the field value is a list of entity-tags, the condition is
true if any of the listed tags match the entity-tag of the true if any of the listed tags match the entity-tag of the
selected representation. selected representation.
skipping to change at page 98, line 22 skipping to change at page 101, line 31
succeeded, but the user agent might not be aware of it, perhaps succeeded, but the user agent might not be aware of it, perhaps
because the prior response was lost or a compatible change was made because the prior response was lost or a compatible change was made
by some other user agent). In the latter case, the origin server by some other user agent). In the latter case, the origin server
MUST NOT send a validator header field in the response unless it can MUST NOT send a validator header field in the response unless it can
verify that the request is a duplicate of an immediately prior change verify that the request is a duplicate of an immediately prior change
made by the same user agent. made by the same user agent.
The If-Match header field can be ignored by caches and intermediaries The If-Match header field can be ignored by caches and intermediaries
because it is not applicable to a stored response. because it is not applicable to a stored response.
8.2.4. If-None-Match Note that an If-Match header field with a list value containing "*"
and other values (including other instances of "*") is unlikely to be
interoperable.
9.2.4. If-None-Match
The "If-None-Match" header field makes the request method conditional The "If-None-Match" header field makes the request method conditional
on a recipient cache or origin server either not having any current on a recipient cache or origin server either not having any current
representation of the target resource, when the field value is "*", representation of the target resource, when the field value is "*",
or having a selected representation with an entity-tag that does not or having a selected representation with an entity-tag that does not
match any of those listed in the field value. match any of those listed in the field value.
A recipient MUST use the weak comparison function when comparing A recipient MUST use the weak comparison function when comparing
entity-tags for If-None-Match (Section 10.2.3.2), since weak entity- entity-tags for If-None-Match (Section 11.2.3.2), since weak entity-
tags can be used for cache validation even if there have been changes tags can be used for cache validation even if there have been changes
to the representation data. to the representation data.
If-None-Match = "*" / 1#entity-tag If-None-Match = "*" / 1#entity-tag
Examples: Examples:
If-None-Match: "xyzzy" If-None-Match: "xyzzy"
If-None-Match: W/"xyzzy" If-None-Match: W/"xyzzy"
If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
skipping to change at page 99, line 9 skipping to change at page 102, line 24
stored responses that have entity-tags, the client SHOULD generate an stored responses that have entity-tags, the client SHOULD generate an
If-None-Match header field containing a list of those entity-tags If-None-Match header field containing a list of those entity-tags
when making a GET request; this allows recipient servers to send a when making a GET request; this allows recipient servers to send a
304 (Not Modified) response to indicate when one of those stored 304 (Not Modified) response to indicate when one of those stored
responses matches the selected representation. responses matches the selected representation.
If-None-Match can also be used with a value of "*" to prevent an If-None-Match can also be used with a value of "*" to prevent an
unsafe request method (e.g., PUT) from inadvertently modifying an unsafe request method (e.g., PUT) from inadvertently modifying an
existing representation of the target resource when the client existing representation of the target resource when the client
believes that the resource does not have a current representation believes that the resource does not have a current representation
(Section 7.2.1). This is a variation on the "lost update" problem (Section 8.2.1). This is a variation on the "lost update" problem
that might arise if more than one client attempts to create an that might arise if more than one client attempts to create an
initial representation for the target resource. initial representation for the target resource.
An origin server that receives an If-None-Match header field MUST An origin server that receives an If-None-Match header field MUST
evaluate the condition prior to performing the method evaluate the condition as per Section 9.2.1 prior to performing the
(Section 8.2.1). method.
To evaluate a received If-None-Match header field: To evaluate a received If-None-Match header field:
1. If the field value is "*", the condition is false if the origin 1. If the field value is "*", the condition is false if the origin
server has a current representation for the target resource. server has a current representation for the target resource.
2. If the field value is a list of entity-tags, the condition is 2. If the field value is a list of entity-tags, the condition is
false if one of the listed tags matches the entity-tag of the false if one of the listed tags matches the entity-tag of the
selected representation. selected representation.
skipping to change at page 99, line 37 skipping to change at page 103, line 5
An origin server MUST NOT perform the requested method if the An origin server MUST NOT perform the requested method if the
condition evaluates to false; instead, the origin server MUST respond condition evaluates to false; instead, the origin server MUST respond
with either a) the 304 (Not Modified) status code if the request with either a) the 304 (Not Modified) status code if the request
method is GET or HEAD or b) the 412 (Precondition Failed) status code method is GET or HEAD or b) the 412 (Precondition Failed) status code
for all other request methods. for all other request methods.
Requirements on cache handling of a received If-None-Match header Requirements on cache handling of a received If-None-Match header
field are defined in Section 4.3.2 of [Caching]. field are defined in Section 4.3.2 of [Caching].
8.2.5. If-Modified-Since Note that an If-None-Match header field with a list value containing
"*" and other values (including other instances of "*") is unlikely
to be interoperable.
9.2.5. If-Modified-Since
The "If-Modified-Since" header field makes a GET or HEAD request The "If-Modified-Since" header field makes a GET or HEAD request
method conditional on the selected representation's modification date method conditional on the selected representation's modification date
being more recent than the date provided in the field value. being more recent than the date provided in the field value.
Transfer of the selected representation's data is avoided if that Transfer of the selected representation's data is avoided if that
data has not changed. data has not changed.
If-Modified-Since = HTTP-date If-Modified-Since = HTTP-date
An example of the field is: An example of the field is:
skipping to change at page 100, line 43 skipping to change at page 104, line 16
When used for limiting the scope of retrieval to a recent time When used for limiting the scope of retrieval to a recent time
window, a user agent will generate an If-Modified-Since field value window, a user agent will generate an If-Modified-Since field value
based on either its own local clock or a Date header field received based on either its own local clock or a Date header field received
from the server in a prior response. Origin servers that choose an from the server in a prior response. Origin servers that choose an
exact timestamp match based on the selected representation's Last- exact timestamp match based on the selected representation's Last-
Modified field will not be able to help the user agent limit its data Modified field will not be able to help the user agent limit its data
transfers to only those changed during the specified window. transfers to only those changed during the specified window.
An origin server that receives an If-Modified-Since header field An origin server that receives an If-Modified-Since header field
SHOULD evaluate the condition prior to performing the method SHOULD evaluate the condition as per Section 9.2.1 prior to
(Section 8.2.1). The origin server SHOULD NOT perform the requested performing the method. The origin server SHOULD NOT perform the
method if the selected representation's last modification date is requested method if the selected representation's last modification
earlier than or equal to the date provided in the field value; date is earlier than or equal to the date provided in the field
instead, the origin server SHOULD generate a 304 (Not Modified) value; instead, the origin server SHOULD generate a 304 (Not
response, including only those metadata that are useful for Modified) response, including only those metadata that are useful for
identifying or updating a previously cached response. identifying or updating a previously cached response.
Requirements on cache handling of a received If-Modified-Since header Requirements on cache handling of a received If-Modified-Since header
field are defined in Section 4.3.2 of [Caching]. field are defined in Section 4.3.2 of [Caching].
8.2.6. If-Unmodified-Since 9.2.6. If-Unmodified-Since
The "If-Unmodified-Since" header field makes the request method The "If-Unmodified-Since" header field makes the request method
conditional on the selected representation's last modification date conditional on the selected representation's last modification date
being earlier than or equal to the date provided in the field value. being earlier than or equal to the date provided in the field value.
This field accomplishes the same purpose as If-Match for cases where This field accomplishes the same purpose as If-Match for cases where
the user agent does not have an entity-tag for the representation. the user agent does not have an entity-tag for the representation.
If-Unmodified-Since = HTTP-date If-Unmodified-Since = HTTP-date
An example of the field is: An example of the field is:
skipping to change at page 101, line 43 skipping to change at page 105, line 14
If-Unmodified-Since is most often used with state-changing methods If-Unmodified-Since is most often used with state-changing methods
(e.g., POST, PUT, DELETE) to prevent accidental overwrites when (e.g., POST, PUT, DELETE) to prevent accidental overwrites when
multiple user agents might be acting in parallel on a resource that multiple user agents might be acting in parallel on a resource that
does not supply entity-tags with its representations (i.e., to does not supply entity-tags with its representations (i.e., to
prevent the "lost update" problem). It can also be used with safe prevent the "lost update" problem). It can also be used with safe
methods to abort a request if the selected representation does not methods to abort a request if the selected representation does not
match one already stored (or partially stored) from a prior request. match one already stored (or partially stored) from a prior request.
An origin server that receives an If-Unmodified-Since header field An origin server that receives an If-Unmodified-Since header field
MUST evaluate the condition (Section 8.2.1) prior to performing the MUST evaluate the condition as per Section 9.2.1 prior to performing
method. the method.
If the selected representation has a last modification date, the If the selected representation has a last modification date, the
origin server MUST NOT perform the requested method if that date is origin server MUST NOT perform the requested method if that date is
more recent than the date provided in the field value. Instead, the more recent than the date provided in the field value. Instead, the
origin server MUST respond with either a) the 412 (Precondition origin server MUST respond with either a) the 412 (Precondition
Failed) status code or b) one of the 2xx (Successful) status codes if Failed) status code or b) one of the 2xx (Successful) status codes if
the origin server has verified that a state change is being requested the origin server has verified that a state change is being requested
and the final state is already reflected in the current state of the and the final state is already reflected in the current state of the
target resource (i.e., the change requested by the user agent has target resource (i.e., the change requested by the user agent has
already succeeded, but the user agent might not be aware of that already succeeded, but the user agent might not be aware of that
because the prior response message was lost or a compatible change because the prior response message was lost or a compatible change
was made by some other user agent). In the latter case, the origin was made by some other user agent). In the latter case, the origin
server MUST NOT send a validator header field in the response unless server MUST NOT send a validator header field in the response unless
it can verify that the request is a duplicate of an immediately prior it can verify that the request is a duplicate of an immediately prior
change made by the same user agent. change made by the same user agent.
The If-Unmodified-Since header field can be ignored by caches and The If-Unmodified-Since header field can be ignored by caches and
intermediaries because it is not applicable to a stored response. intermediaries because it is not applicable to a stored response.
8.2.7. If-Range 9.2.7. If-Range
The "If-Range" header field provides a special conditional request The "If-Range" header field provides a special conditional request
mechanism that is similar to the If-Match and If-Unmodified-Since mechanism that is similar to the If-Match and If-Unmodified-Since
header fields but that instructs the recipient to ignore the Range header fields but that instructs the recipient to ignore the Range
header field if the validator doesn't match, resulting in transfer of header field if the validator doesn't match, resulting in transfer of
the new selected representation instead of a 412 (Precondition the new selected representation instead of a 412 (Precondition
Failed) response. Failed) response.
If a client has a partial copy of a representation and wishes to have If a client has a partial copy of a representation and wishes to have
an up-to-date copy of the entire representation, it could use the an up-to-date copy of the entire representation, it could use the
skipping to change at page 102, line 50 skipping to change at page 106, line 23
does not contain a Range header field. A server MUST ignore an If- does not contain a Range header field. A server MUST ignore an If-
Range header field received in a request that does not contain a Range header field received in a request that does not contain a
Range header field. An origin server MUST ignore an If-Range header Range header field. An origin server MUST ignore an If-Range header
field received in a request for a target resource that does not field received in a request for a target resource that does not
support Range requests. support Range requests.
A client MUST NOT generate an If-Range header field containing an A client MUST NOT generate an If-Range header field containing an
entity-tag that is marked as weak. A client MUST NOT generate an If- entity-tag that is marked as weak. A client MUST NOT generate an If-
Range header field containing an HTTP-date unless the client has no Range header field containing an HTTP-date unless the client has no
entity-tag for the corresponding representation and the date is a entity-tag for the corresponding representation and the date is a
strong validator in the sense defined by Section 10.2.2.2. strong validator in the sense defined by Section 11.2.2.2.
A server that evaluates an If-Range precondition MUST use the strong A server that evaluates an If-Range precondition MUST use the strong
comparison function when comparing entity-tags (Section 10.2.3.2) and comparison function when comparing entity-tags (Section 11.2.3.2) and
MUST evaluate the condition as false if an HTTP-date validator is MUST evaluate the condition as false if an HTTP-date validator is
provided that is not a strong validator in the sense defined by provided that is not a strong validator in the sense defined by
Section 10.2.2.2. A valid entity-tag can be distinguished from a Section 11.2.2.2. A valid entity-tag can be distinguished from a
valid HTTP-date by examining the first two characters for a DQUOTE. valid HTTP-date by examining the first two characters for a DQUOTE.
If the validator given in the If-Range header field matches the If the validator given in the If-Range header field matches the
current validator for the selected representation of the target current validator for the selected representation of the target
resource, then the server SHOULD process the Range header field as resource, then the server SHOULD process the Range header field as
requested. If the validator does not match, the server MUST ignore requested. If the validator does not match, the server MUST ignore
the Range header field. Note that this comparison by exact match, the Range header field. Note that this comparison by exact match,
including when the validator is an HTTP-date, differs from the including when the validator is an HTTP-date, differs from the
"earlier than or equal to" comparison used when evaluating an If- "earlier than or equal to" comparison used when evaluating an If-
Unmodified-Since conditional. Unmodified-Since conditional.
8.3. Range 9.3. Range
The "Range" header field on a GET request modifies the method The "Range" header field on a GET request modifies the method
semantics to request transfer of only one or more subranges of the semantics to request transfer of only one or more subranges of the
selected representation data (Section 6.1), rather than the entire selected representation data (Section 7.1), rather than the entire
selected representation. selected representation.
Range = ranges-specifier Range = ranges-specifier
Clients often encounter interrupted data transfers as a result of Clients often encounter interrupted data transfers as a result of
canceled requests or dropped connections. When a client has stored a canceled requests or dropped connections. When a client has stored a
partial representation, it is desirable to request the remainder of partial representation, it is desirable to request the remainder of
that representation in a subsequent request rather than transfer the that representation in a subsequent request rather than transfer the
entire representation. Likewise, devices with limited local storage entire representation. Likewise, devices with limited local storage
might benefit from being able to request only a subset of a larger might benefit from being able to request only a subset of a larger
skipping to change at page 104, line 17 skipping to change at page 107, line 35
byte ranges. byte ranges.
An origin server MUST ignore a Range header field that contains a An origin server MUST ignore a Range header field that contains a
range unit it does not understand. A proxy MAY discard a Range range unit it does not understand. A proxy MAY discard a Range
header field that contains a range unit it does not understand. header field that contains a range unit it does not understand.
A server that supports range requests MAY ignore or reject a Range A server that supports range requests MAY ignore or reject a Range
header field that consists of more than two overlapping ranges, or a header field that consists of more than two overlapping ranges, or a
set of many small ranges that are not listed in ascending order, set of many small ranges that are not listed in ascending order,
since both are indications of either a broken client or a deliberate since both are indications of either a broken client or a deliberate
denial-of-service attack (Section 11.13). A client SHOULD NOT denial-of-service attack (Section 12.13). A client SHOULD NOT
request multiple ranges that are inherently less efficient to process request multiple ranges that are inherently less efficient to process
and transfer than a single range that encompasses the same data. and transfer than a single range that encompasses the same data.
A server that supports range requests MAY ignore a Range header field
when the selected representation has no body (i.e., the selected
representation data is of zero length).
A client that is requesting multiple ranges SHOULD list those ranges A client that is requesting multiple ranges SHOULD list those ranges
in ascending order (the order in which they would typically be in ascending order (the order in which they would typically be
received in a complete representation) unless there is a specific received in a complete representation) unless there is a specific
need to request a later part earlier. For example, a user agent need to request a later part earlier. For example, a user agent
processing a large representation with an internal catalog of parts processing a large representation with an internal catalog of parts
might need to request later parts first, particularly if the might need to request later parts first, particularly if the
representation consists of pages stored in reverse order and the user representation consists of pages stored in reverse order and the user
agent wishes to transfer one page at a time. agent wishes to transfer one page at a time.
The Range header field is evaluated after evaluating the precondition The Range header field is evaluated after evaluating the precondition
header fields defined in Section 8.2, and only if the result in header fields defined in Section 9.2, and only if the result in
absence of the Range header field would be a 200 (OK) response. In absence of the Range header field would be a 200 (OK) response. In
other words, Range is ignored when a conditional GET would result in other words, Range is ignored when a conditional GET would result in
a 304 (Not Modified) response. a 304 (Not Modified) response.
The If-Range header field (Section 8.2.7) can be used as a The If-Range header field (Section 9.2.7) can be used as a
precondition to applying the Range header field. precondition to applying the Range header field.
If all of the preconditions are true, the server supports the Range If all of the preconditions are true, the server supports the Range
header field for the target resource, and the specified range(s) are header field for the target resource, and the specified range(s) are
valid and satisfiable (as defined in Section 6.1.4.2), the server valid and satisfiable (as defined in Section 7.1.4.2), the server
SHOULD send a 206 (Partial Content) response with a payload SHOULD send a 206 (Partial Content) response with a payload
containing one or more partial representations that correspond to the containing one or more partial representations that correspond to the
satisfiable ranges requested. satisfiable ranges requested.
If all of the preconditions are true, the server supports the Range If all of the preconditions are true, the server supports the Range
header field for the target resource, and the specified range(s) are header field for the target resource, and the specified range(s) are
invalid or unsatisfiable, the server SHOULD send a 416 (Range Not invalid or unsatisfiable, the server SHOULD send a 416 (Range Not
Satisfiable) response. Satisfiable) response.
8.4. Negotiation 9.4. Negotiation
The following request header fields can be sent by a user agent to The following request header fields can be sent by a user agent to
engage in proactive negotiation of the response content, as defined engage in proactive negotiation of the response content, as defined
in Section 6.4.1. The preferences sent in these fields apply to any in Section 7.4.1. The preferences sent in these fields apply to any
content in the response, including representations of the target content in the response, including representations of the target
resource, representations of error or processing status, and resource, representations of error or processing status, and
potentially even the miscellaneous text strings that might appear potentially even the miscellaneous text strings that might appear
within the protocol. within the protocol.
+-----------------+---------------+ +-----------------+---------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+-----------------+---------------+ +-----------------+---------------+
| Accept | Section 8.4.1 | | Accept | Section 9.4.1 |
| Accept-Charset | Section 8.4.2 | | Accept-Charset | Section 9.4.2 |
| Accept-Encoding | Section 8.4.3 | | Accept-Encoding | Section 9.4.3 |
| Accept-Language | Section 8.4.4 | | Accept-Language | Section 9.4.4 |
+-----------------+---------------+ +-----------------+---------------+
For each of these header fields, a request that does not contain it For each of these header fields, a request that does not contain it
implies that the user agent has no preference on that axis of implies that the user agent has no preference on that axis of
negotiation. If the header field is present in a request and none of negotiation. If the header field is present in a request and none of
the available representations for the response can be considered the available representations for the response can be considered
acceptable according to it, the origin server can either honor the acceptable according to it, the origin server can either honor the
header field by sending a 406 (Not Acceptable) response or disregard header field by sending a 406 (Not Acceptable) response or disregard
the header field by treating the response as if it is not subject to the header field by treating the response as if it is not subject to
content negotiation for that request header field. This does not content negotiation for that request header field. This does not
imply, however, that the client will be able to use the imply, however, that the client will be able to use the
representation. representation.
Note: Sending these header fields makes it easier for a server to Note: Sending these header fields makes it easier for a server to
identify an individual by virtue of the user agent's request identify an individual by virtue of the user agent's request
characteristics (Section 11.11). characteristics (Section 12.11).
Each of these header fields defines a wildcard value (often, "*") to Each of these header fields defines a wildcard value (often, "*") to
select unspecified values. If no wildcard is present, all values not select unspecified values. If no wildcard is present, all values not
explicitly mentioned in the field are considered "not acceptable" to explicitly mentioned in the field are considered "not acceptable" to
the client. the client.
Note: In practice, using wildcards in content negotiation has limited Note: In practice, using wildcards in content negotiation has limited
practical value, because it is seldom useful to say, for example, "I practical value, because it is seldom useful to say, for example, "I
prefer image/* more or less than (some other specific value)". prefer image/* more or less than (some other specific value)".
Clients can explicitly request a 406 (Not Acceptable) response if a Clients can explicitly request a 406 (Not Acceptable) response if a
more preferred format is not available by sending Accept: */*;q=0, more preferred format is not available by sending Accept: */*;q=0,
but they still need to be able to handle a different response, since but they still need to be able to handle a different response, since
the server is allowed to ignore their preference. the server is allowed to ignore their preference.
8.4.1. Accept 9.4.1. Accept
The "Accept" header field can be used by user agents to specify their The "Accept" header field can be used by user agents to specify their
preferences regarding response media types. For example, Accept preferences regarding response media types. For example, Accept
header fields can be used to indicate that the request is header fields can be used to indicate that the request is
specifically limited to a small set of desired types, as in the case specifically limited to a small set of desired types, as in the case
of a request for an in-line image. of a request for an in-line image.
When sent by a server in a response, Accept provides information
about what content types are preferred in the payload of a subsequent
request to the same resource.
Accept = #( media-range [ accept-params ] ) Accept = #( media-range [ accept-params ] )
media-range = ( "*/*" media-range = ( "*/*"
/ ( type "/" "*" ) / ( type "/" "*" )
/ ( type "/" subtype ) / ( type "/" subtype )
) *( OWS ";" OWS parameter ) ) *( OWS ";" OWS parameter )
accept-params = weight *( accept-ext ) accept-params = weight *( accept-ext )
accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ] accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
The asterisk "*" character is used to group media types into ranges, The asterisk "*" character is used to group media types into ranges,
with "*/*" indicating all media types and "type/*" indicating all with "*/*" indicating all media types and "type/*" indicating all
subtypes of that type. The media-range can include media type subtypes of that type. The media-range can include media type
parameters that are applicable to that range. parameters that are applicable to that range.
Each media-range might be followed by zero or more applicable media Each media-range might be followed by zero or more applicable media
type parameters (e.g., charset), an optional "q" parameter for type parameters (e.g., charset), an optional "q" parameter for
indicating a relative weight (Section 6.4.4), and then zero or more indicating a relative weight (Section 7.4.4), and then zero or more
extension parameters. The "q" parameter is necessary if any extension parameters. The "q" parameter is necessary if any
extensions (accept-ext) are present, since it acts as a separator extensions (accept-ext) are present, since it acts as a separator
between the two parameter sets. between the two parameter sets.
Note: Use of the "q" parameter name to separate media type Note: Use of the "q" parameter name to separate media type
parameters from Accept extension parameters is due to historical parameters from Accept extension parameters is due to historical
practice. Although this prevents any media type parameter named practice. Although this prevents any media type parameter named
"q" from being used with a media range, such an event is believed "q" from being used with a media range, such an event is believed
to be unlikely given the lack of any "q" parameters in the IANA to be unlikely given the lack of any "q" parameters in the IANA
media type registry and the rare usage of any media type media type registry and the rare usage of any media type
skipping to change at page 107, line 27 skipping to change at page 111, line 4
have the following precedence: have the following precedence:
1. text/plain;format=flowed 1. text/plain;format=flowed
2. text/plain 2. text/plain
3. text/* 3. text/*
4. */* 4. */*
The media type quality factor associated with a given type is The media type quality factor associated with a given type is
determined by finding the media range with the highest precedence determined by finding the media range with the highest precedence
that matches the type. For example, that matches the type. For example,
Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1, Accept: text/*;q=0.3, text/plain;q=0.7, text/plain;format=flowed,
text/html;level=2;q=0.4, */*;q=0.5 text/plain;format=fixed;q=0.4, */*;q=0.5
would cause the following values to be associated: would cause the following values to be associated:
+-------------------+---------------+ +--------------------------+---------------+
| Media Type | Quality Value | | Media Type | Quality Value |
+-------------------+---------------+ +--------------------------+---------------+
| text/html;level=1 | 1 | | text/plain;format=flowed | 1 |
| text/html | 0.7 | | text/plain | 0.7 |
| text/plain | 0.3 | | text/html | 0.3 |
| image/jpeg | 0.5 | | image/jpeg | 0.5 |
| text/html;level=2 | 0.4 | | text/plain;format=fixed | 0.4 |
| text/html;level=3 | 0.7 | | text/html;level=3 | 0.7 |
+-------------------+---------------+ +--------------------------+---------------+
Note: A user agent might be provided with a default set of quality Note: A user agent might be provided with a default set of quality
values for certain media ranges. However, unless the user agent is a values for certain media ranges. However, unless the user agent is a
closed system that cannot interact with other rendering agents, this closed system that cannot interact with other rendering agents, this
default set ought to be configurable by the user. default set ought to be configurable by the user.
8.4.2. Accept-Charset 9.4.2. Accept-Charset
The "Accept-Charset" header field can be sent by a user agent to The "Accept-Charset" header field can be sent by a user agent to
indicate its preferences for charsets in textual response content. indicate its preferences for charsets in textual response content.
For example, this field allows user agents capable of understanding For example, this field allows user agents capable of understanding
more comprehensive or special-purpose charsets to signal that more comprehensive or special-purpose charsets to signal that
capability to an origin server that is capable of representing capability to an origin server that is capable of representing
information in those charsets. information in those charsets.
Accept-Charset = 1#( ( charset / "*" ) [ weight ] ) Accept-Charset = 1#( ( charset / "*" ) [ weight ] )
Charset names are defined in Section 6.1.1.1. A user agent MAY Charset names are defined in Section 7.1.1.1. A user agent MAY
associate a quality value with each charset to indicate the user's associate a quality value with each charset to indicate the user's
relative preference for that charset, as defined in Section 6.4.4. relative preference for that charset, as defined in Section 7.4.4.
An example is An example is
Accept-Charset: iso-8859-5, unicode-1-1;q=0.8 Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
The special value "*", if present in the Accept-Charset field, The special value "*", if present in the Accept-Charset field,
matches every charset that is not mentioned elsewhere in the Accept- matches every charset that is not mentioned elsewhere in the Accept-
Charset field. Charset field.
Note: Accept-Charset is deprecated because UTF-8 has become nearly Note: Accept-Charset is deprecated because UTF-8 has become nearly
ubiquitous and sending a detailed list of user-preferred charsets ubiquitous and sending a detailed list of user-preferred charsets
wastes bandwidth, increases latency, and makes passive fingerprinting wastes bandwidth, increases latency, and makes passive fingerprinting
far too easy (Section 11.11). Most general-purpose user agents do far too easy (Section 12.11). Most general-purpose user agents do
not send Accept-Charset, unless specifically configured to do so. not send Accept-Charset, unless specifically configured to do so.
8.4.3. Accept-Encoding 9.4.3. Accept-Encoding
The "Accept-Encoding" header field can be used to indicate The "Accept-Encoding" header field can be used to indicate
preferences regarding the use of content codings (Section 6.1.2). preferences regarding the use of content codings (Section 7.1.2).
When sent by a user agent in a request, Accept-Encoding indicates the When sent by a user agent in a request, Accept-Encoding indicates the
content codings acceptable in a response. content codings acceptable in a response.
When sent by a server in a response, Accept-Encoding provides When sent by a server in a response, Accept-Encoding provides
information about what content codings are preferred in the payload information about what content codings are preferred in the payload
of a subsequent request to the same resource. of a subsequent request to the same resource.
An "identity" token is used as a synonym for "no encoding" in order An "identity" token is used as a synonym for "no encoding" in order
to communicate when no encoding is preferred. to communicate when no encoding is preferred.
Accept-Encoding = #( codings [ weight ] ) Accept-Encoding = #( codings [ weight ] )
codings = content-coding / "identity" / "*" codings = content-coding / "identity" / "*"
Each codings value MAY be given an associated quality value Each codings value MAY be given an associated quality value
representing the preference for that encoding, as defined in representing the preference for that encoding, as defined in
Section 6.4.4. The asterisk "*" symbol in an Accept-Encoding field Section 7.4.4. The asterisk "*" symbol in an Accept-Encoding field
matches any available content-coding not explicitly listed in the matches any available content-coding not explicitly listed in the
header field. header field.
For example, For example,
Accept-Encoding: compress, gzip Accept-Encoding: compress, gzip
Accept-Encoding: Accept-Encoding:
Accept-Encoding: * Accept-Encoding: *
Accept-Encoding: compress;q=0.5, gzip;q=1.0 Accept-Encoding: compress;q=0.5, gzip;q=1.0
Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0 Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
skipping to change at page 109, line 30 skipping to change at page 113, line 8
is considered acceptable by the user agent. is considered acceptable by the user agent.
2. If the representation has no content-coding, then it is 2. If the representation has no content-coding, then it is
acceptable by default unless specifically excluded by the Accept- acceptable by default unless specifically excluded by the Accept-
Encoding field stating either "identity;q=0" or "*;q=0" without a Encoding field stating either "identity;q=0" or "*;q=0" without a
more specific entry for "identity". more specific entry for "identity".
3. If the representation's content-coding is one of the content- 3. If the representation's content-coding is one of the content-
codings listed in the Accept-Encoding field value, then it is codings listed in the Accept-Encoding field value, then it is
acceptable unless it is accompanied by a qvalue of 0. (As acceptable unless it is accompanied by a qvalue of 0. (As
defined in Section 6.4.4, a qvalue of 0 means "not acceptable".) defined in Section 7.4.4, a qvalue of 0 means "not acceptable".)
4. If multiple content-codings are acceptable, then the acceptable 4. If multiple content-codings are acceptable, then the acceptable
content-coding with the highest non-zero qvalue is preferred. content-coding with the highest non-zero qvalue is preferred.
An Accept-Encoding header field with a field value that is empty An Accept-Encoding header field with a field value that is empty
implies that the user agent does not want any content-coding in implies that the user agent does not want any content-coding in
response. If an Accept-Encoding header field is present in a request response. If an Accept-Encoding header field is present in a request
and none of the available representations for the response have a and none of the available representations for the response have a
content-coding that is listed as acceptable, the origin server SHOULD content-coding that is listed as acceptable, the origin server SHOULD
send a response without any content-coding. send a response without any content-coding.
skipping to change at page 110, line 27 skipping to change at page 114, line 5
be used to indicate to clients that content codings are supported, to be used to indicate to clients that content codings are supported, to
optimize future interactions. For example, a resource might include optimize future interactions. For example, a resource might include
it in a 2xx (Successful) response when the request payload was big it in a 2xx (Successful) response when the request payload was big
enough to justify use of a compression coding but the client failed enough to justify use of a compression coding but the client failed
do so. do so.
Note: Most HTTP/1.0 applications do not recognize or obey qvalues Note: Most HTTP/1.0 applications do not recognize or obey qvalues
associated with content-codings. This means that qvalues might associated with content-codings. This means that qvalues might
not work and are not permitted with x-gzip or x-compress. not work and are not permitted with x-gzip or x-compress.
8.4.4. Accept-Language 9.4.4. Accept-Language
The "Accept-Language" header field can be used by user agents to The "Accept-Language" header field can be used by user agents to
indicate the set of natural languages that are preferred in the indicate the set of natural languages that are preferred in the
response. Language tags are defined in Section 6.1.3. response. Language tags are defined in Section 7.1.3.
Accept-Language = 1#( language-range [ weight ] ) Accept-Language = 1#( language-range [ weight ] )
language-range = language-range =
<language-range, see [RFC4647], Section 2.1> <language-range, see [RFC4647], Section 2.1>
Each language-range can be given an associated quality value Each language-range can be given an associated quality value
representing an estimate of the user's preference for the languages representing an estimate of the user's preference for the languages
specified by that range, as defined in Section 6.4.4. For example, specified by that range, as defined in Section 7.4.4. For example,
Accept-Language: da, en-gb;q=0.8, en;q=0.7 Accept-Language: da, en-gb;q=0.8, en;q=0.7
would mean: "I prefer Danish, but will accept British English and would mean: "I prefer Danish, but will accept British English and
other types of English". other types of English".
Note that some recipients treat the order in which language tags are Note that some recipients treat the order in which language tags are
listed as an indication of descending priority, particularly for tags listed as an indication of descending priority, particularly for tags
that are assigned equal quality values (no value is the same as q=1). that are assigned equal quality values (no value is the same as q=1).
However, this behavior cannot be relied upon. For consistency and to However, this behavior cannot be relied upon. For consistency and to
skipping to change at page 111, line 15 skipping to change at page 114, line 41
found in Section 2.3 of [RFC4647]. found in Section 2.3 of [RFC4647].
For matching, Section 3 of [RFC4647] defines several matching For matching, Section 3 of [RFC4647] defines several matching
schemes. Implementations can offer the most appropriate matching schemes. Implementations can offer the most appropriate matching
scheme for their requirements. The "Basic Filtering" scheme scheme for their requirements. The "Basic Filtering" scheme
([RFC4647], Section 3.3.1) is identical to the matching scheme that ([RFC4647], Section 3.3.1) is identical to the matching scheme that
was previously defined for HTTP in Section 14.4 of [RFC2616]. was previously defined for HTTP in Section 14.4 of [RFC2616].
It might be contrary to the privacy expectations of the user to send It might be contrary to the privacy expectations of the user to send
an Accept-Language header field with the complete linguistic an Accept-Language header field with the complete linguistic
preferences of the user in every request (Section 11.11). preferences of the user in every request (Section 12.11).
Since intelligibility is highly dependent on the individual user, Since intelligibility is highly dependent on the individual user,
user agents need to allow user control over the linguistic preference user agents need to allow user control over the linguistic preference
(either through configuration of the user agent itself or by (either through configuration of the user agent itself or by
defaulting to a user controllable system setting). A user agent that defaulting to a user controllable system setting). A user agent that
does not provide such control to the user MUST NOT send an Accept- does not provide such control to the user MUST NOT send an Accept-
Language header field. Language header field.
Note: User agents ought to provide guidance to users when setting Note: User agents ought to provide guidance to users when setting
a preference, since users are rarely familiar with the details of a preference, since users are rarely familiar with the details of
language matching as described above. For example, users might language matching as described above. For example, users might
assume that on selecting "en-gb", they will be served any kind of assume that on selecting "en-gb", they will be served any kind of
English document if British English is not available. A user English document if British English is not available. A user
agent might suggest, in such a case, to add "en" to the list for agent might suggest, in such a case, to add "en" to the list for
better matching behavior. better matching behavior.
8.5. Authentication Credentials 9.5. Authentication Credentials
HTTP provides a general framework for access control and HTTP provides a general framework for access control and
authentication, via an extensible set of challenge-response authentication, via an extensible set of challenge-response
authentication schemes, which can be used by a server to challenge a authentication schemes, which can be used by a server to challenge a
client request and by a client to provide authentication information. client request and by a client to provide authentication information.
Two header fields are used for carrying authentication credentials. Two header fields are used for carrying authentication credentials.
Note that various custom mechanisms for user authentication use the Note that various custom mechanisms for user authentication use the
Cookie header field for this purpose, as defined in [RFC6265]. Cookie header field for this purpose, as defined in [RFC6265].
+---------------------+---------------+ +---------------------+---------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+---------------------+---------------+ +---------------------+---------------+
| Authorization | Section 8.5.3 | | Authorization | Section 9.5.3 |
| Proxy-Authorization | Section 8.5.4 | | Proxy-Authorization | Section 9.5.4 |
+---------------------+---------------+ +---------------------+---------------+
8.5.1. Challenge and Response 9.5.1. Challenge and Response
HTTP provides a simple challenge-response authentication framework HTTP provides a simple challenge-response authentication framework
that can be used by a server to challenge a client request and by a that can be used by a server to challenge a client request and by a
client to provide authentication information. It uses a case- client to provide authentication information. It uses a case-
insensitive token as a means to identify the authentication scheme, insensitive token as a means to identify the authentication scheme,
followed by additional information necessary for achieving followed by additional information necessary for achieving
authentication via that scheme. The latter can be either a comma- authentication via that scheme. The latter can be either a comma-
separated list of parameters or a single sequence of characters separated list of parameters or a single sequence of characters
capable of holding base64-encoded information. capable of holding base64-encoded information.
skipping to change at page 113, line 19 skipping to change at page 116, line 42
Both the Authorization field value and the Proxy-Authorization field Both the Authorization field value and the Proxy-Authorization field
value contain the client's credentials for the realm of the resource value contain the client's credentials for the realm of the resource
being requested, based upon a challenge received in a response being requested, based upon a challenge received in a response
(possibly at some point in the past). When creating their values, (possibly at some point in the past). When creating their values,
the user agent ought to do so by selecting the challenge with what it the user agent ought to do so by selecting the challenge with what it
considers to be the most secure auth-scheme that it understands, considers to be the most secure auth-scheme that it understands,
obtaining credentials from the user as appropriate. Transmission of obtaining credentials from the user as appropriate. Transmission of
credentials within header field values implies significant security credentials within header field values implies significant security
considerations regarding the confidentiality of the underlying considerations regarding the confidentiality of the underlying
connection, as described in Section 11.14.1. connection, as described in Section 12.14.1.
credentials = auth-scheme [ 1*SP ( token68 / #auth-param ) ] credentials = auth-scheme [ 1*SP ( token68 / #auth-param ) ]
Upon receipt of a request for a protected resource that omits Upon receipt of a request for a protected resource that omits
credentials, contains invalid credentials (e.g., a bad password) or credentials, contains invalid credentials (e.g., a bad password) or
partial credentials (e.g., when the authentication scheme requires partial credentials (e.g., when the authentication scheme requires
more than one round trip), an origin server SHOULD send a 401 more than one round trip), an origin server SHOULD send a 401
(Unauthorized) response that contains a WWW-Authenticate header field (Unauthorized) response that contains a WWW-Authenticate header field
with at least one (possibly new) challenge applicable to the with at least one (possibly new) challenge applicable to the
requested resource. requested resource.
Likewise, upon receipt of a request that omits proxy credentials or Likewise, upon receipt of a request that omits proxy credentials or
contains invalid or partial proxy credentials, a proxy that requires contains invalid or partial proxy credentials, a proxy that requires
authentication SHOULD generate a 407 (Proxy Authentication Required) authentication SHOULD generate a 407 (Proxy Authentication Required)
response that contains a Proxy-Authenticate header field with at response that contains a Proxy-Authenticate header field with at
least one (possibly new) challenge applicable to the proxy. least one (possibly new) challenge applicable to the proxy.
A server that receives valid credentials that are not adequate to A server that receives valid credentials that are not adequate to
gain access ought to respond with the 403 (Forbidden) status code gain access ought to respond with the 403 (Forbidden) status code
(Section 9.5.4). (Section 10.5.4).
HTTP does not restrict applications to this simple challenge-response HTTP does not restrict applications to this simple challenge-response
framework for access authentication. Additional mechanisms can be framework for access authentication. Additional mechanisms can be
used, such as authentication at the transport level or via message used, such as authentication at the transport level or via message
encapsulation, and with additional header fields specifying encapsulation, and with additional header fields specifying
authentication information. However, such additional mechanisms are authentication information. However, such additional mechanisms are
not defined by this specification. not defined by this specification.
8.5.2. Protection Space (Realm) 9.5.2. Protection Space (Realm)
The "realm" authentication parameter is reserved for use by The "realm" authentication parameter is reserved for use by
authentication schemes that wish to indicate a scope of protection. authentication schemes that wish to indicate a scope of protection.
A protection space is defined by the canonical root URI (the scheme A protection space is defined by the canonical root URI (the scheme
and authority components of the target URI; see Section 5.1) of the and authority components of the target URI; see Section 6.1) of the
server being accessed, in combination with the realm value if server being accessed, in combination with the realm value if
present. These realms allow the protected resources on a server to present. These realms allow the protected resources on a server to
be partitioned into a set of protection spaces, each with its own be partitioned into a set of protection spaces, each with its own
authentication scheme and/or authorization database. The realm value authentication scheme and/or authorization database. The realm value
is a string, generally assigned by the origin server, that can have is a string, generally assigned by the origin server, that can have
additional semantics specific to the authentication scheme. Note additional semantics specific to the authentication scheme. Note
that a response can have multiple challenges with the same auth- that a response can have multiple challenges with the same auth-
scheme but with different realms. scheme but with different realms.
The protection space determines the domain over which credentials can The protection space determines the domain over which credentials can
skipping to change at page 114, line 30 skipping to change at page 118, line 7
authentication scheme, parameters, and/or user preferences (such as a authentication scheme, parameters, and/or user preferences (such as a
configurable inactivity timeout). Unless specifically allowed by the configurable inactivity timeout). Unless specifically allowed by the
authentication scheme, a single protection space cannot extend authentication scheme, a single protection space cannot extend
outside the scope of its server. outside the scope of its server.
For historical reasons, a sender MUST only generate the quoted-string For historical reasons, a sender MUST only generate the quoted-string
syntax. Recipients might have to support both token and quoted- syntax. Recipients might have to support both token and quoted-
string syntax for maximum interoperability with existing clients that string syntax for maximum interoperability with existing clients that
have been accepting both notations for a long time. have been accepting both notations for a long time.
8.5.3. Authorization 9.5.3. Authorization
The "Authorization" header field allows a user agent to authenticate The "Authorization" header field allows a user agent to authenticate
itself with an origin server -- usually, but not necessarily, after itself with an origin server -- usually, but not necessarily, after
receiving a 401 (Unauthorized) response. Its value consists of receiving a 401 (Unauthorized) response. Its value consists of
credentials containing the authentication information of the user credentials containing the authentication information of the user
agent for the realm of the resource being requested. agent for the realm of the resource being requested.
Authorization = credentials Authorization = credentials
If a request is authenticated and a realm specified, the same If a request is authenticated and a realm specified, the same
credentials are presumed to be valid for all other requests within credentials are presumed to be valid for all other requests within
this realm (assuming that the authentication scheme itself does not this realm (assuming that the authentication scheme itself does not
require otherwise, such as credentials that vary according to a require otherwise, such as credentials that vary according to a
challenge value or using synchronized clocks). challenge value or using synchronized clocks).
A proxy forwarding a request MUST NOT modify any Authorization fields A proxy forwarding a request MUST NOT modify any Authorization fields
in that request. See Section 3.3 of [Caching] for details of and in that request. See Section 3.3 of [Caching] for details of and
requirements pertaining to handling of the Authorization field by requirements pertaining to handling of the Authorization field by
HTTP caches. HTTP caches.
8.5.4. Proxy-Authorization 9.5.4. Proxy-Authorization
The "Proxy-Authorization" header field allows the client to identify The "Proxy-Authorization" header field allows the client to identify
itself (or its user) to a proxy that requires authentication. Its itself (or its user) to a proxy that requires authentication. Its
value consists of credentials containing the authentication value consists of credentials containing the authentication
information of the client for the proxy and/or realm of the resource information of the client for the proxy and/or realm of the resource
being requested. being requested.
Proxy-Authorization = credentials Proxy-Authorization = credentials
Unlike Authorization, the Proxy-Authorization header field applies Unlike Authorization, the Proxy-Authorization header field applies
only to the next inbound proxy that demanded authentication using the only to the next inbound proxy that demanded authentication using the
Proxy-Authenticate field. When multiple proxies are used in a chain, Proxy-Authenticate field. When multiple proxies are used in a chain,
the Proxy-Authorization header field is consumed by the first inbound the Proxy-Authorization header field is consumed by the first inbound
proxy that was expecting to receive credentials. A proxy MAY relay proxy that was expecting to receive credentials. A proxy MAY relay
the credentials from the client request to the next proxy if that is the credentials from the client request to the next proxy if that is
the mechanism by which the proxies cooperatively authenticate a given the mechanism by which the proxies cooperatively authenticate a given
request. request.
8.5.5. Authentication Scheme Extensibility 9.5.5. Authentication Scheme Extensibility
Aside from the general framework, this document does not specify any Aside from the general framework, this document does not specify any
authentication schemes. New and existing authentication schemes are authentication schemes. New and existing authentication schemes are
specified independently and ought to be registered within the specified independently and ought to be registered within the
"Hypertext Transfer Protocol (HTTP) Authentication Scheme Registry". "Hypertext Transfer Protocol (HTTP) Authentication Scheme Registry".
For example, the "basic" and "digest" authentication schemes are For example, the "basic" and "digest" authentication schemes are
defined by RFC 7617 and RFC 7616, respectively. defined by RFC 7617 and RFC 7616, respectively.
8.5.5.1. Authentication Scheme Registry 9.5.5.1. Authentication Scheme Registry
The "Hypertext Transfer Protocol (HTTP) Authentication Scheme The "Hypertext Transfer Protocol (HTTP) Authentication Scheme
Registry" defines the namespace for the authentication schemes in Registry" defines the namespace for the authentication schemes in
challenges and credentials. It is maintained at challenges and credentials. It is maintained at
<https://www.iana.org/assignments/http-authschemes>. <https://www.iana.org/assignments/http-authschemes>.
Registrations MUST include the following fields: Registrations MUST include the following fields:
o Authentication Scheme Name o Authentication Scheme Name
o Pointer to specification text o Pointer to specification text
o Notes (optional) o Notes (optional)
Values to be added to this namespace require IETF Review (see Values to be added to this namespace require IETF Review (see
[RFC8126], Section 4.8). [RFC8126], Section 4.8).
8.5.5.2. Considerations for New Authentication Schemes 9.5.5.2. Considerations for New Authentication Schemes
There are certain aspects of the HTTP Authentication framework that There are certain aspects of the HTTP Authentication framework that
put constraints on how new authentication schemes can work: put constraints on how new authentication schemes can work:
o HTTP authentication is presumed to be stateless: all of the o HTTP authentication is presumed to be stateless: all of the
information necessary to authenticate a request MUST be provided information necessary to authenticate a request MUST be provided
in the request, rather than be dependent on the server remembering in the request, rather than be dependent on the server remembering
prior requests. Authentication based on, or bound to, the prior requests. Authentication based on, or bound to, the
underlying connection is outside the scope of this specification underlying connection is outside the scope of this specification
and inherently flawed unless steps are taken to ensure that the and inherently flawed unless steps are taken to ensure that the
connection cannot be used by any party other than the connection cannot be used by any party other than the
authenticated user (see Section 2.2). authenticated user (see Section 2.2).
o The authentication parameter "realm" is reserved for defining o The authentication parameter "realm" is reserved for defining
protection spaces as described in Section 8.5.2. New schemes MUST protection spaces as described in Section 9.5.2. New schemes MUST
NOT use it in a way incompatible with that definition. NOT use it in a way incompatible with that definition.
o The "token68" notation was introduced for compatibility with o The "token68" notation was introduced for compatibility with
existing authentication schemes and can only be used once per existing authentication schemes and can only be used once per
challenge or credential. Thus, new schemes ought to use the auth- challenge or credential. Thus, new schemes ought to use the auth-
param syntax instead, because otherwise future extensions will be param syntax instead, because otherwise future extensions will be
impossible. impossible.
o The parsing of challenges and credentials is defined by this o The parsing of challenges and credentials is defined by this
specification and cannot be modified by new authentication specification and cannot be modified by new authentication
skipping to change at page 117, line 28 skipping to change at page 121, line 8
Therefore, new authentication schemes that choose not to carry Therefore, new authentication schemes that choose not to carry
credentials in the Authorization header field (e.g., using a newly credentials in the Authorization header field (e.g., using a newly
defined header field) will need to explicitly disallow caching, by defined header field) will need to explicitly disallow caching, by
mandating the use of Cache-Control response directives (e.g., mandating the use of Cache-Control response directives (e.g.,
"private"). "private").
o Schemes using Authentication-Info, Proxy-Authentication-Info, or o Schemes using Authentication-Info, Proxy-Authentication-Info, or
any other authentication related response header field need to any other authentication related response header field need to
consider and document the related security considerations (see consider and document the related security considerations (see
Section 11.14.4). Section 12.14.4).
8.6. Request Context 9.6. Request Context
The following request header fields provide additional information The following request header fields provide additional information
about the request context, including information about the user, user about the request context, including information about the user, user
agent, and resource behind the request. agent, and resource behind the request.
+------------+---------------+ +------------+---------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+------------+---------------+ +------------+---------------+
| From | Section 8.6.1 | | From | Section 9.6.1 |
| Referer | Section 8.6.2 | | Referer | Section 9.6.2 |
| User-Agent | Section 8.6.3 | | User-Agent | Section 9.6.3 |
+------------+---------------+ +------------+---------------+
8.6.1. From 9.6.1. From
The "From" header field contains an Internet email address for a The "From" header field contains an Internet email address for a
human user who controls the requesting user agent. The address ought human user who controls the requesting user agent. The address ought
to be machine-usable, as defined by "mailbox" in Section 3.4 of to be machine-usable, as defined by "mailbox" in Section 3.4 of
[RFC5322]: [RFC5322]:
From = mailbox From = mailbox
mailbox = <mailbox, see [RFC5322], Section 3.4> mailbox = <mailbox, see [RFC5322], Section 3.4>
skipping to change at page 118, line 34 skipping to change at page 122, line 9
A robotic user agent SHOULD send a valid From header field so that A robotic user agent SHOULD send a valid From header field so that
the person responsible for running the robot can be contacted if the person responsible for running the robot can be contacted if
problems occur on servers, such as if the robot is sending excessive, problems occur on servers, such as if the robot is sending excessive,
unwanted, or invalid requests. unwanted, or invalid requests.
A server SHOULD NOT use the From header field for access control or A server SHOULD NOT use the From header field for access control or
authentication, since most recipients will assume that the field authentication, since most recipients will assume that the field
value is public information. value is public information.
8.6.2. Referer 9.6.2. Referer
The "Referer" [sic] header field allows the user agent to specify a The "Referer" [sic] header field allows the user agent to specify a
URI reference for the resource from which the target URI was obtained URI reference for the resource from which the target URI was obtained
(i.e., the "referrer", though the field name is misspelled). A user (i.e., the "referrer", though the field name is misspelled). A user
agent MUST NOT include the fragment and userinfo components of the agent MUST NOT include the fragment and userinfo components of the
URI reference [RFC3986], if any, when generating the Referer field URI reference [RFC3986], if any, when generating the Referer field
value. value.
Referer = absolute-URI / partial-URI Referer = absolute-URI / partial-URI
skipping to change at page 119, line 26 skipping to change at page 122, line 50
The Referer field has the potential to reveal information about the The Referer field has the potential to reveal information about the
request context or browsing history of the user, which is a privacy request context or browsing history of the user, which is a privacy
concern if the referring resource's identifier reveals personal concern if the referring resource's identifier reveals personal
information (such as an account name) or a resource that is supposed information (such as an account name) or a resource that is supposed
to be confidential (such as behind a firewall or internal to a to be confidential (such as behind a firewall or internal to a
secured service). Most general-purpose user agents do not send the secured service). Most general-purpose user agents do not send the
Referer header field when the referring resource is a local "file" or Referer header field when the referring resource is a local "file" or
"data" URI. A user agent MUST NOT send a Referer header field in an "data" URI. A user agent MUST NOT send a Referer header field in an
unsecured HTTP request if the referring page was received with a unsecured HTTP request if the referring page was received with a
secure protocol. See Section 11.8 for additional security secure protocol. See Section 12.8 for additional security
considerations. considerations.
Some intermediaries have been known to indiscriminately remove Some intermediaries have been known to indiscriminately remove
Referer header fields from outgoing requests. This has the Referer header fields from outgoing requests. This has the
unfortunate side effect of interfering with protection against CSRF unfortunate side effect of interfering with protection against CSRF
attacks, which can be far more harmful to their users. attacks, which can be far more harmful to their users.
Intermediaries and user agent extensions that wish to limit Intermediaries and user agent extensions that wish to limit
information disclosure in Referer ought to restrict their changes to information disclosure in Referer ought to restrict their changes to
specific edits, such as replacing internal domain names with specific edits, such as replacing internal domain names with
pseudonyms or truncating the query and/or path components. An pseudonyms or truncating the query and/or path components. An
intermediary SHOULD NOT modify or delete the Referer header field intermediary SHOULD NOT modify or delete the Referer header field
when the field value shares the same scheme and host as the target when the field value shares the same scheme and host as the target
URI. URI.
8.6.3. User-Agent 9.6.3. User-Agent
The "User-Agent" header field contains information about the user The "User-Agent" header field contains information about the user
agent originating the request, which is often used by servers to help agent originating the request, which is often used by servers to help
identify the scope of reported interoperability problems, to work identify the scope of reported interoperability problems, to work
around or tailor responses to avoid particular user agent around or tailor responses to avoid particular user agent
limitations, and for analytics regarding browser or operating system limitations, and for analytics regarding browser or operating system
use. A user agent SHOULD send a User-Agent field in each request use. A user agent SHOULD send a User-Agent field in each request
unless specifically configured not to do so. unless specifically configured not to do so.
User-Agent = product *( RWS ( product / comment ) ) User-Agent = product *( RWS ( product / comment ) )
The User-Agent field value consists of one or more product The User-Agent field value consists of one or more product
identifiers, each followed by zero or more comments identifiers, each followed by zero or more comments
(Section 4.4.1.3), which together identify the user agent software (Section 5.4.1.3), which together identify the user agent software
and its significant subproducts. By convention, the product and its significant subproducts. By convention, the product
identifiers are listed in decreasing order of their significance for identifiers are listed in decreasing order of their significance for
identifying the user agent software. Each product identifier identifying the user agent software. Each product identifier
consists of a name and optional version. consists of a name and optional version.
product = token ["/" product-version] product = token ["/" product-version]
product-version = token product-version = token
A sender SHOULD limit generated product identifiers to what is A sender SHOULD limit generated product identifiers to what is
necessary to identify the product; a sender MUST NOT generate necessary to identify the product; a sender MUST NOT generate
skipping to change at page 120, line 42 skipping to change at page 124, line 19
identified against their wishes ("fingerprinting"). identified against their wishes ("fingerprinting").
Likewise, implementations are encouraged not to use the product Likewise, implementations are encouraged not to use the product
tokens of other implementations in order to declare compatibility tokens of other implementations in order to declare compatibility
with them, as this circumvents the purpose of the field. If a user with them, as this circumvents the purpose of the field. If a user
agent masquerades as a different user agent, recipients can assume agent masquerades as a different user agent, recipients can assume
that the user intentionally desires to see responses tailored for that the user intentionally desires to see responses tailored for
that identified user agent, even if they might not work as well for that identified user agent, even if they might not work as well for
the actual user agent being used. the actual user agent being used.
9. Response Status Codes 10. Response Status Codes
The (response) status code is a three-digit integer code giving the The (response) status code is a three-digit integer code giving the
result of the attempt to understand and satisfy the request. result of the attempt to understand and satisfy the request.
HTTP status codes are extensible. HTTP clients are not required to HTTP status codes are extensible. HTTP clients are not required to
understand the meaning of all registered status codes, though such understand the meaning of all registered status codes, though such
understanding is obviously desirable. However, a client MUST understanding is obviously desirable. However, a client MUST
understand the class of any status code, as indicated by the first understand the class of any status code, as indicated by the first
digit, and treat an unrecognized status code as being equivalent to digit, and treat an unrecognized status code as being equivalent to
the x00 status code of that class. the x00 status code of that class.
skipping to change at page 121, line 34 skipping to change at page 125, line 13
fulfilled fulfilled
o 5xx (Server Error): The server failed to fulfill an apparently o 5xx (Server Error): The server failed to fulfill an apparently
valid request valid request
A single request can have multiple associated responses: zero or more A single request can have multiple associated responses: zero or more
interim (non-final) responses with status codes in the interim (non-final) responses with status codes in the
"informational" (1xx) range, followed by exactly one final response "informational" (1xx) range, followed by exactly one final response
with a status code in one of the other ranges. with a status code in one of the other ranges.
9.1. Overview of Status Codes 10.1. Overview of Status Codes
The status codes listed below are defined in this specification. The The status codes listed below are defined in this specification. The
reason phrases listed here are only recommendations -- they can be reason phrases listed here are only recommendations -- they can be
replaced by local equivalents without affecting the protocol. replaced by local equivalents without affecting the protocol.
Responses with status codes that are defined as heuristically Responses with status codes that are defined as heuristically
cacheable (e.g., 200, 203, 204, 206, 300, 301, 404, 405, 410, 414, cacheable (e.g., 200, 203, 204, 206, 300, 301, 308, 404, 405, 410,
and 501 in this specification) can be reused by a cache with 414, and 501 in this specification) can be reused by a cache with
heuristic expiration unless otherwise indicated by the method heuristic expiration unless otherwise indicated by the method
definition or explicit cache controls [Caching]; all other status definition or explicit cache controls [Caching]; all other status
codes are not heuristically cacheable. codes are not heuristically cacheable.
+-------+-------------------------------+-----------------+ +-------+-------------------------------+------------------+
| Value | Description | Reference | | Value | Description | Reference |
+-------+-------------------------------+-----------------+ +-------+-------------------------------+------------------+
| 100 | Continue | Section 9.2.1 | | 100 | Continue | Section 10.2.1 |
| 101 | Switching Protocols | Section 9.2.2 | | 101 | Switching Protocols | Section 10.2.2 |
| 200 | OK | Section 9.3.1 | | 200 | OK | Section 10.3.1 |
| 201 | Created | Section 9.3.2 | | 201 | Created | Section 10.3.2 |
| 202 | Accepted | Section 9.3.3 | | 202 | Accepted | Section 10.3.3 |
| 203 | Non-Authoritative Information | Section 9.3.4 | | 203 | Non-Authoritative Information | Section 10.3.4 |
| 204 | No Content | Section 9.3.5 | | 204 | No Content | Section 10.3.5 |
| 205 | Reset Content | Section 9.3.6 | | 205 | Reset Content | Section 10.3.6 |
| 206 | Partial Content | Section 9.3.7 | | 206 | Partial Content | Section 10.3.7 |
| 300 | Multiple Choices | Section 9.4.1 | | 300 | Multiple Choices | Section 10.4.1 |
| 301 | Moved Permanently | Section 9.4.2 | | 301 | Moved Permanently | Section 10.4.2 |
| 302 | Found | Section 9.4.3 | | 302 | Found | Section 10.4.3 |
| 303 | See Other | Section 9.4.4 | | 303 | See Other | Section 10.4.4 |
| 304 | Not Modified | Section 9.4.5 | | 304 | Not Modified | Section 10.4.5 |
| 305 | Use Proxy | Section 9.4.6 | | 305 | Use Proxy | Section 10.4.6 |
| 306 | (Unused) | Section 9.4.7 | | 306 | (Unused) | Section 10.4.7 |
| 307 | Temporary Redirect | Section 9.4.8 | | 307 | Temporary Redirect | Section 10.4.8 |
| 308 | Permanent Redirect | Section 9.4.9 | | 308 | Permanent Redirect | Section 10.4.9 |
| 400 | Bad Request | Section 9.5.1 | | 400 | Bad Request | Section 10.5.1 |
| 401 | Unauthorized | Section 9.5.2 | | 401 | Unauthorized | Section 10.5.2 |
| 402 | Payment Required | Section 9.5.3 | | 402 | Payment Required | Section 10.5.3 |
| 403 | Forbidden | Section 9.5.4 | | 403 | Forbidden | Section 10.5.4 |
| 404 | Not Found | Section 9.5.5 | | 404 | Not Found | Section 10.5.5 |
| 405 | Method Not Allowed | Section 9.5.6 | | 405 | Method Not Allowed | Section 10.5.6 |
| 406 | Not Acceptable | Section 9.5.7 | | 406 | Not Acceptable | Section 10.5.7 |
| 407 | Proxy Authentication Required | Section 9.5.8 | | 407 | Proxy Authentication Required | Section 10.5.8 |
| 408 | Request Timeout | Section 9.5.9 | | 408 | Request Timeout | Section 10.5.9 |
| 409 | Conflict | Section 9.5.10 | | 409 | Conflict | Section 10.5.10 |
| 410 | Gone | Section 9.5.11 | | 410 | Gone | Section 10.5.11 |
| 411 | Length Required | Section 9.5.12 | | 411 | Length Required | Section 10.5.12 |
| 412 | Precondition Failed | Section 9.5.13 | | 412 | Precondition Failed | Section 10.5.13 |
| 413 | Payload Too Large | Section 9.5.14 | | 413 | Payload Too Large | Section 10.5.14 |
| 414 | URI Too Long | Section 9.5.15 | | 414 | URI Too Long | Section 10.5.15 |
| 415 | Unsupported Media Type | Section 9.5.16 | | 415 | Unsupported Media Type | Section 10.5.16 |
| 416 | Range Not Satisfiable | Section 9.5.17 | | 416 | Range Not Satisfiable | Section 10.5.17 |
| 417 | Expectation Failed | Section 9.5.18 | | 417 | Expectation Failed | Section 10.5.18 |
| 418 | (Unused) | Section 9.5.19 | | 418 | (Unused) | Section 10.5.19 |
| 422 | Unprocessable Payload | Section 9.5.20 | | 422 | Unprocessable Payload | Section 10.5.20 |
| 426 | Upgrade Required | Section 9.5.21 | | 426 | Upgrade Required | Section 10.5.21 |
| 500 | Internal Server Error | Section 9.6.1 | | 500 | Internal Server Error | Section 10.6.1 |
| 501 | Not Implemented | Section 9.6.2 | | 501 | Not Implemented | Section 10.6.2 |
| 502 | Bad Gateway | Section 9.6.3 | | 502 | Bad Gateway | Section 10.6.3 |
| 503 | Service Unavailable | Section 9.6.4 | | 503 | Service Unavailable | Section 10.6.4 |
| 504 | Gateway Timeout | Section 9.6.5 | | 504 | Gateway Timeout | Section 10.6.5 |
| 505 | HTTP Version Not Supported | Section 9.6.6 | | 505 | HTTP Version Not Supported | Section 10.6.6 |
+-------+-------------------------------+-----------------+ +-------+-------------------------------+------------------+
Table 6 Table 6
Note that this list is not exhaustive -- it does not include Note that this list is not exhaustive -- it does not include
extension status codes defined in other specifications (Section 9.7). extension status codes defined in other specifications
(Section 10.7).
9.2. Informational 1xx 10.2. Informational 1xx
The 1xx (Informational) class of status code indicates an interim The 1xx (Informational) class of status code indicates an interim
response for communicating connection status or request progress response for communicating connection status or request progress
prior to completing the requested action and sending a final prior to completing the requested action and sending a final
response. 1xx responses are terminated by the end of the header response. 1xx responses are terminated by the end of the header
section. Since HTTP/1.0 did not define any 1xx status codes, a section. Since HTTP/1.0 did not define any 1xx status codes, a
server MUST NOT send a 1xx response to an HTTP/1.0 client. server MUST NOT send a 1xx response to an HTTP/1.0 client.
A client MUST be able to parse one or more 1xx responses received A client MUST be able to parse one or more 1xx responses received
prior to a final response, even if the client does not expect one. A prior to a final response, even if the client does not expect one. A
user agent MAY ignore unexpected 1xx responses. user agent MAY ignore unexpected 1xx responses.
A proxy MUST forward 1xx responses unless the proxy itself requested A proxy MUST forward 1xx responses unless the proxy itself requested
the generation of the 1xx response. For example, if a proxy adds an the generation of the 1xx response. For example, if a proxy adds an
"Expect: 100-continue" field when it forwards a request, then it need "Expect: 100-continue" field when it forwards a request, then it need
not forward the corresponding 100 (Continue) response(s). not forward the corresponding 100 (Continue) response(s).
9.2.1. 100 Continue 10.2.1. 100 Continue
The 100 (Continue) status code indicates that the initial part of a The 100 (Continue) status code indicates that the initial part of a
request has been received and has not yet been rejected by the request has been received and has not yet been rejected by the
server. The server intends to send a final response after the server. The server intends to send a final response after the
request has been fully received and acted upon. request has been fully received and acted upon.
When the request contains an Expect header field that includes a When the request contains an Expect header field that includes a
100-continue expectation, the 100 response indicates that the server 100-continue expectation, the 100 response indicates that the server
wishes to receive the request payload body, as described in wishes to receive the request payload body, as described in
Section 8.1.1. The client ought to continue sending the request and Section 9.1.1. The client ought to continue sending the request and
discard the 100 response. discard the 100 response.
If the request did not contain an Expect header field containing the If the request did not contain an Expect header field containing the
100-continue expectation, the client can simply discard this interim 100-continue expectation, the client can simply discard this interim
response. response.
9.2.2. 101 Switching Protocols 10.2.2. 101 Switching Protocols
The 101 (Switching Protocols) status code indicates that the server The 101 (Switching Protocols) status code indicates that the server
understands and is willing to comply with the client's request, via understands and is willing to comply with the client's request, via
the Upgrade header field (Section 9.9 of [Messaging]), for a change the Upgrade header field (Section 9.9 of [Messaging]), for a change
in the application protocol being used on this connection. The in the application protocol being used on this connection. The
server MUST generate an Upgrade header field in the response that server MUST generate an Upgrade header field in the response that
indicates which protocol(s) will be switched to immediately after the indicates which protocol(s) will be switched to immediately after the
empty line that terminates the 101 response. empty line that terminates the 101 response.
It is assumed that the server will only agree to switch protocols It is assumed that the server will only agree to switch protocols
when it is advantageous to do so. For example, switching to a newer when it is advantageous to do so. For example, switching to a newer
version of HTTP might be advantageous over older versions, and version of HTTP might be advantageous over older versions, and
switching to a real-time, synchronous protocol might be advantageous switching to a real-time, synchronous protocol might be advantageous
when delivering resources that use such features. when delivering resources that use such features.
9.3. Successful 2xx 10.3. Successful 2xx
The 2xx (Successful) class of status code indicates that the client's The 2xx (Successful) class of status code indicates that the client's
request was successfully received, understood, and accepted. request was successfully received, understood, and accepted.
9.3.1. 200 OK 10.3.1. 200 OK
The 200 (OK) status code indicates that the request has succeeded. The 200 (OK) status code indicates that the request has succeeded.
The payload sent in a 200 response depends on the request method. The payload sent in a 200 response depends on the request method.
For the methods defined by this specification, the intended meaning For the methods defined by this specification, the intended meaning
of the payload can be summarized as: of the payload can be summarized as:
GET a representation of the target resource; GET a representation of the target resource;
HEAD the same representation as GET, but without the representation HEAD the same representation as GET, but without the representation
data; data;
POST a representation of the status of, or results obtained from, POST a representation of the status of, or results obtained from,
the action; the action;
PUT, DELETE a representation of the status of the action; PUT, DELETE a representation of the status of the action;
OPTIONS a representation of the communications options; OPTIONS a representation of the communications options;
skipping to change at page 124, line 45 skipping to change at page 128, line 28
though an origin server MAY generate a payload body of zero length. though an origin server MAY generate a payload body of zero length.
If no payload is desired, an origin server ought to send 204 (No If no payload is desired, an origin server ought to send 204 (No
Content) instead. For CONNECT, no payload is allowed because the Content) instead. For CONNECT, no payload is allowed because the
successful result is a tunnel, which begins immediately after the 200 successful result is a tunnel, which begins immediately after the 200
response header section. response header section.
A 200 response is heuristically cacheable; i.e., unless otherwise A 200 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [Caching]). Section 4.2.2 of [Caching]).
9.3.2. 201 Created 10.3.2. 201 Created
The 201 (Created) status code indicates that the request has been The 201 (Created) status code indicates that the request has been
fulfilled and has resulted in one or more new resources being fulfilled and has resulted in one or more new resources being
created. The primary resource created by the request is identified created. The primary resource created by the request is identified
by either a Location header field in the response or, if no Location by either a Location header field in the response or, if no Location
field is received, by the target URI. field is received, by the target URI.
The 201 response payload typically describes and links to the The 201 response payload typically describes and links to the
resource(s) created. See Section 10.2 for a discussion of the resource(s) created. See Section 11.2 for a discussion of the
meaning and purpose of validator header fields, such as ETag and meaning and purpose of validator header fields, such as ETag and
Last-Modified, in a 201 response. Last-Modified, in a 201 response.
9.3.3. 202 Accepted 10.3.3. 202 Accepted
The 202 (Accepted) status code indicates that the request has been The 202 (Accepted) status code indicates that the request has been
accepted for processing, but the processing has not been completed. accepted for processing, but the processing has not been completed.
The request might or might not eventually be acted upon, as it might The request might or might not eventually be acted upon, as it might
be disallowed when processing actually takes place. There is no be disallowed when processing actually takes place. There is no
facility in HTTP for re-sending a status code from an asynchronous facility in HTTP for re-sending a status code from an asynchronous
operation. operation.
The 202 response is intentionally noncommittal. Its purpose is to The 202 response is intentionally noncommittal. Its purpose is to
allow a server to accept a request for some other process (perhaps a allow a server to accept a request for some other process (perhaps a
batch-oriented process that is only run once per day) without batch-oriented process that is only run once per day) without
requiring that the user agent's connection to the server persist requiring that the user agent's connection to the server persist
until the process is completed. The representation sent with this until the process is completed. The representation sent with this
response ought to describe the request's current status and point to response ought to describe the request's current status and point to
(or embed) a status monitor that can provide the user with an (or embed) a status monitor that can provide the user with an
estimate of when the request will be fulfilled. estimate of when the request will be fulfilled.
9.3.4. 203 Non-Authoritative Information 10.3.4. 203 Non-Authoritative Information
The 203 (Non-Authoritative Information) status code indicates that The 203 (Non-Authoritative Information) status code indicates that
the request was successful but the enclosed payload has been modified the request was successful but the enclosed payload has been modified
from that of the origin server's 200 (OK) response by a transforming from that of the origin server's 200 (OK) response by a transforming
proxy (Section 5.7.2). This status code allows the proxy to notify proxy (Section 6.7.2). This status code allows the proxy to notify
recipients when a transformation has been applied, since that recipients when a transformation has been applied, since that
knowledge might impact later decisions regarding the content. For knowledge might impact later decisions regarding the content. For
example, future cache validation requests for the content might only example, future cache validation requests for the content might only
be applicable along the same request path (through the same proxies). be applicable along the same request path (through the same proxies).
The 203 response is similar to the Warning code of 214 Transformation The 203 response is similar to the Warning code of 214 Transformation
Applied (Section 5.5 of [Caching]), which has the advantage of being Applied (Section 5.5 of [Caching]), which has the advantage of being
applicable to responses with any status code. applicable to responses with any status code.
A 203 response is heuristically cacheable; i.e., unless otherwise A 203 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [Caching]). Section 4.2.2 of [Caching]).
9.3.5. 204 No Content 10.3.5. 204 No Content
The 204 (No Content) status code indicates that the server has The 204 (No Content) status code indicates that the server has
successfully fulfilled the request and that there is no additional successfully fulfilled the request and that there is no additional
content to send in the response payload body. Metadata in the content to send in the response payload body. Metadata in the
response header fields refer to the target resource and its selected response header fields refer to the target resource and its selected
representation after the requested action was applied. representation after the requested action was applied.
For example, if a 204 status code is received in response to a PUT For example, if a 204 status code is received in response to a PUT
request and the response contains an ETag field, then the PUT was request and the response contains an ETag field, then the PUT was
successful and the ETag field value contains the entity-tag for the successful and the ETag field value contains the entity-tag for the
skipping to change at page 126, line 33 skipping to change at page 130, line 18
frequently used with interfaces that expect automated data transfers frequently used with interfaces that expect automated data transfers
to be prevalent, such as within distributed version control systems. to be prevalent, such as within distributed version control systems.
A 204 response is terminated by the first empty line after the header A 204 response is terminated by the first empty line after the header
fields because it cannot contain a message body. fields because it cannot contain a message body.
A 204 response is heuristically cacheable; i.e., unless otherwise A 204 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [Caching]). Section 4.2.2 of [Caching]).
9.3.6. 205 Reset Content 10.3.6. 205 Reset Content
The 205 (Reset Content) status code indicates that the server has The 205 (Reset Content) status code indicates that the server has
fulfilled the request and desires that the user agent reset the fulfilled the request and desires that the user agent reset the
"document view", which caused the request to be sent, to its original "document view", which caused the request to be sent, to its original
state as received from the origin server. state as received from the origin server.
This response is intended to support a common data entry use case This response is intended to support a common data entry use case
where the user receives content that supports data entry (a form, where the user receives content that supports data entry (a form,
notepad, canvas, etc.), enters or manipulates data in that space, notepad, canvas, etc.), enters or manipulates data in that space,
causes the entered data to be submitted in a request, and then the causes the entered data to be submitted in a request, and then the
data entry mechanism is reset for the next entry so that the user can data entry mechanism is reset for the next entry so that the user can
easily initiate another input action. easily initiate another input action.
Since the 205 status code implies that no additional content will be Since the 205 status code implies that no additional content will be
provided, a server MUST NOT generate a payload in a 205 response. provided, a server MUST NOT generate a payload in a 205 response.
9.3.7. 206 Partial Content 10.3.7. 206 Partial Content
The 206 (Partial Content) status code indicates that the server is The 206 (Partial Content) status code indicates that the server is
successfully fulfilling a range request for the target resource by successfully fulfilling a range request for the target resource by
transferring one or more parts of the selected representation. transferring one or more parts of the selected representation.
When a 206 response is generated, the server MUST generate the When a 206 response is generated, the server MUST generate the
following header fields, in addition to those required in the following header fields, in addition to those required in the
subsections below, if the field would have been sent in a 200 (OK) subsections below, if the field would have been sent in a 200 (OK)
response to the same request: Date, Cache-Control, ETag, Expires, response to the same request: Date, Cache-Control, ETag, Expires,
Content-Location, and Vary. Content-Location, and Vary.
skipping to change at page 127, line 29 skipping to change at page 131, line 11
header fields beyond those required, because the client is understood header fields beyond those required, because the client is understood
to already have a prior response containing those header fields. to already have a prior response containing those header fields.
Otherwise, the sender MUST generate all of the representation header Otherwise, the sender MUST generate all of the representation header
fields that would have been sent in a 200 (OK) response to the same fields that would have been sent in a 200 (OK) response to the same
request. request.
A 206 response is heuristically cacheable; i.e., unless otherwise A 206 response is heuristically cacheable; i.e., unless otherwise
indicated by explicit cache controls (see Section 4.2.2 of indicated by explicit cache controls (see Section 4.2.2 of
[Caching]). [Caching]).
9.3.7.1. Single Part 10.3.7.1. Single Part
If a single part is being transferred, the server generating the 206 If a single part is being transferred, the server generating the 206
response MUST generate a Content-Range header field, describing what response MUST generate a Content-Range header field, describing what
range of the selected representation is enclosed, and a payload range of the selected representation is enclosed, and a payload
consisting of the range. For example: consisting of the range. For example:
HTTP/1.1 206 Partial Content HTTP/1.1 206 Partial Content
Date: Wed, 15 Nov 1995 06:25:24 GMT Date: Wed, 15 Nov 1995 06:25:24 GMT
Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
Content-Range: bytes 21010-47021/47022 Content-Range: bytes 21010-47021/47022
Content-Length: 26012 Content-Length: 26012
Content-Type: image/gif Content-Type: image/gif
... 26012 bytes of partial image data ... ... 26012 bytes of partial image data ...
9.3.7.2. Multiple Parts 10.3.7.2. Multiple Parts
If multiple parts are being transferred, the server generating the If multiple parts are being transferred, the server generating the
206 response MUST generate a "multipart/byteranges" payload, as 206 response MUST generate a "multipart/byteranges" payload, as
defined in Section 6.3.5, and a Content-Type header field containing defined in Section 7.3.5, and a Content-Type header field containing
the multipart/byteranges media type and its required boundary the multipart/byteranges media type and its required boundary
parameter. To avoid confusion with single-part responses, a server parameter. To avoid confusion with single-part responses, a server
MUST NOT generate a Content-Range header field in the HTTP header MUST NOT generate a Content-Range header field in the HTTP header
section of a multiple part response (this field will be sent in each section of a multiple part response (this field will be sent in each
part instead). part instead).
Within the header area of each body part in the multipart payload, Within the header area of each body part in the multipart payload,
the server MUST generate a Content-Range header field corresponding the server MUST generate a Content-Range header field corresponding
to the range being enclosed in that body part. If the selected to the range being enclosed in that body part. If the selected
representation would have had a Content-Type header field in a 200 representation would have had a Content-Type header field in a 200
skipping to change at page 129, line 15 skipping to change at page 133, line 5
When a multipart response payload is generated, the server SHOULD When a multipart response payload is generated, the server SHOULD
send the parts in the same order that the corresponding range-spec send the parts in the same order that the corresponding range-spec
appeared in the received Range header field, excluding those ranges appeared in the received Range header field, excluding those ranges
that were deemed unsatisfiable or that were coalesced into other that were deemed unsatisfiable or that were coalesced into other
ranges. A client that receives a multipart response MUST inspect the ranges. A client that receives a multipart response MUST inspect the
Content-Range header field present in each body part in order to Content-Range header field present in each body part in order to
determine which range is contained in that body part; a client cannot determine which range is contained in that body part; a client cannot
rely on receiving the same ranges that it requested, nor the same rely on receiving the same ranges that it requested, nor the same
order that it requested. order that it requested.
9.3.7.3. Combining Parts 10.3.7.3. Combining Parts
A response might transfer only a subrange of a representation if the A response might transfer only a subrange of a representation if the
connection closed prematurely or if the request used one or more connection closed prematurely or if the request used one or more
Range specifications. After several such transfers, a client might Range specifications. After several such transfers, a client might
have received several ranges of the same representation. These have received several ranges of the same representation. These
ranges can only be safely combined if they all have in common the ranges can only be safely combined if they all have in common the
same strong validator (Section 10.2.1). same strong validator (Section 11.2.1).
A client that has received multiple partial responses to GET requests A client that has received multiple partial responses to GET requests
on a target resource MAY combine those responses into a larger on a target resource MAY combine those responses into a larger
continuous range if they share the same strong validator. continuous range if they share the same strong validator.
If the most recent response is an incomplete 200 (OK) response, then If the most recent response is an incomplete 200 (OK) response, then
the header fields of that response are used for any combined response the header fields of that response are used for any combined response
and replace those of the matching stored responses. and replace those of the matching stored responses.
If the most recent response is a 206 (Partial Content) response and If the most recent response is a 206 (Partial Content) response and
skipping to change at page 130, line 7 skipping to change at page 133, line 46
representation, then the client MUST process the combined response as representation, then the client MUST process the combined response as
if it were a complete 200 (OK) response, including a Content-Length if it were a complete 200 (OK) response, including a Content-Length
header field that reflects the complete length. Otherwise, the header field that reflects the complete length. Otherwise, the
client MUST process the set of continuous ranges as one of the client MUST process the set of continuous ranges as one of the
following: an incomplete 200 (OK) response if the combined response following: an incomplete 200 (OK) response if the combined response
is a prefix of the representation, a single 206 (Partial Content) is a prefix of the representation, a single 206 (Partial Content)
response containing a multipart/byteranges body, or multiple 206 response containing a multipart/byteranges body, or multiple 206
(Partial Content) responses, each with one continuous range that is (Partial Content) responses, each with one continuous range that is
indicated by a Content-Range header field. indicated by a Content-Range header field.
9.4. Redirection 3xx 10.4. Redirection 3xx
The 3xx (Redirection) class of status code indicates that further The 3xx (Redirection) class of status code indicates that further
action needs to be taken by the user agent in order to fulfill the action needs to be taken by the user agent in order to fulfill the
request. If a Location header field (Section 10.1.2) is provided, request. If a Location header field (Section 11.1.2) is provided,
the user agent MAY automatically redirect its request to the URI the user agent MAY automatically redirect its request to the URI
referenced by the Location field value, even if the specific status referenced by the Location field value, even if the specific status
code is not understood. Automatic redirection needs to be done with code is not understood. Automatic redirection needs to be done with
care for methods not known to be safe, as defined in Section 7.2.1, care for methods not known to be safe, as defined in Section 8.2.1,
since the user might not wish to redirect an unsafe request. since the user might not wish to redirect an unsafe request.
There are several types of redirects: There are several types of redirects:
1. Redirects that indicate the resource might be available at a 1. Redirects that indicate the resource might be available at a
different URI, as provided by the Location field, as in the different URI, as provided by the Location field, as in the
status codes 301 (Moved Permanently), 302 (Found), 307 (Temporary status codes 301 (Moved Permanently), 302 (Found), 307 (Temporary
Redirect), and 308 (Permanent Redirect). Redirect), and 308 (Permanent Redirect).
2. Redirection that offers a choice of matching resources, each 2. Redirection that offers a choice of matching resources, each
skipping to change at page 131, line 21 skipping to change at page 135, line 13
original request is POST. original request is POST.
A client SHOULD detect and intervene in cyclical redirections (i.e., A client SHOULD detect and intervene in cyclical redirections (i.e.,
"infinite" redirection loops). "infinite" redirection loops).
Note: An earlier version of this specification recommended a Note: An earlier version of this specification recommended a
maximum of five redirections ([RFC2068], Section 10.3). Content maximum of five redirections ([RFC2068], Section 10.3). Content
developers need to be aware that some clients might implement such developers need to be aware that some clients might implement such
a fixed limitation. a fixed limitation.
9.4.1. 300 Multiple Choices 10.4.1. 300 Multiple Choices
The 300 (Multiple Choices) status code indicates that the target The 300 (Multiple Choices) status code indicates that the target
resource has more than one representation, each with its own more resource has more than one representation, each with its own more
specific identifier, and information about the alternatives is being specific identifier, and information about the alternatives is being
provided so that the user (or user agent) can select a preferred provided so that the user (or user agent) can select a preferred
representation by redirecting its request to one or more of those representation by redirecting its request to one or more of those
identifiers. In other words, the server desires that the user agent identifiers. In other words, the server desires that the user agent
engage in reactive negotiation to select the most appropriate engage in reactive negotiation to select the most appropriate
representation(s) for its needs (Section 6.4). representation(s) for its needs (Section 7.4).
If the server has a preferred choice, the server SHOULD generate a If the server has a preferred choice, the server SHOULD generate a
Location header field containing a preferred choice's URI reference. Location header field containing a preferred choice's URI reference.
The user agent MAY use the Location field value for automatic The user agent MAY use the Location field value for automatic
redirection. redirection.
For request methods other than HEAD, the server SHOULD generate a For request methods other than HEAD, the server SHOULD generate a
payload in the 300 response containing a list of representation payload in the 300 response containing a list of representation
metadata and URI reference(s) from which the user or user agent can metadata and URI reference(s) from which the user or user agent can
choose the one most preferred. The user agent MAY make a selection choose the one most preferred. The user agent MAY make a selection
skipping to change at page 132, line 16 skipping to change at page 136, line 7
URI header field as providing a list of alternative URI header field as providing a list of alternative
representations, such that it would be usable for 200, 300, and representations, such that it would be usable for 200, 300, and
406 responses and be transferred in responses to the HEAD method. 406 responses and be transferred in responses to the HEAD method.
However, lack of deployment and disagreement over syntax led to However, lack of deployment and disagreement over syntax led to
both URI and Alternates (a subsequent proposal) being dropped from both URI and Alternates (a subsequent proposal) being dropped from
this specification. It is possible to communicate the list as a this specification. It is possible to communicate the list as a
Link header field value [RFC8288] whose members have a Link header field value [RFC8288] whose members have a
relationship of "alternate", though deployment is a chicken-and- relationship of "alternate", though deployment is a chicken-and-
egg problem. egg problem.
9.4.2. 301 Moved Permanently 10.4.2. 301 Moved Permanently
The 301 (Moved Permanently) status code indicates that the target The 301 (Moved Permanently) status code indicates that the target
resource has been assigned a new permanent URI and any future resource has been assigned a new permanent URI and any future
references to this resource ought to use one of the enclosed URIs. references to this resource ought to use one of the enclosed URIs.
Clients with link-editing capabilities ought to automatically re-link Clients with link-editing capabilities ought to automatically re-link
references to the target URI to one or more of the new references references to the target URI to one or more of the new references
sent by the server, where possible. sent by the server, where possible.
The server SHOULD generate a Location header field in the response The server SHOULD generate a Location header field in the response
containing a preferred URI reference for the new permanent URI. The containing a preferred URI reference for the new permanent URI. The
skipping to change at page 132, line 40 skipping to change at page 136, line 31
Note: For historical reasons, a user agent MAY change the request Note: For historical reasons, a user agent MAY change the request
method from POST to GET for the subsequent request. If this method from POST to GET for the subsequent request. If this
behavior is undesired, the 308 (Permanent Redirect) status code behavior is undesired, the 308 (Permanent Redirect) status code
can be used instead. can be used instead.
A 301 response is heuristically cacheable; i.e., unless otherwise A 301 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [Caching]). Section 4.2.2 of [Caching]).
9.4.3. 302 Found 10.4.3. 302 Found
The 302 (Found) status code indicates that the target resource The 302 (Found) status code indicates that the target resource
resides temporarily under a different URI. Since the redirection resides temporarily under a different URI. Since the redirection
might be altered on occasion, the client ought to continue to use the might be altered on occasion, the client ought to continue to use the
target URI for future requests. target URI for future requests.
The server SHOULD generate a Location header field in the response The server SHOULD generate a Location header field in the response
containing a URI reference for the different URI. The user agent MAY containing a URI reference for the different URI. The user agent MAY
use the Location field value for automatic redirection. The server's use the Location field value for automatic redirection. The server's
response payload usually contains a short hypertext note with a response payload usually contains a short hypertext note with a
hyperlink to the different URI(s). hyperlink to the different URI(s).
Note: For historical reasons, a user agent MAY change the request Note: For historical reasons, a user agent MAY change the request
method from POST to GET for the subsequent request. If this method from POST to GET for the subsequent request. If this
behavior is undesired, the 307 (Temporary Redirect) status code behavior is undesired, the 307 (Temporary Redirect) status code
can be used instead. can be used instead.
9.4.4. 303 See Other 10.4.4. 303 See Other
The 303 (See Other) status code indicates that the server is The 303 (See Other) status code indicates that the server is
redirecting the user agent to a different resource, as indicated by a redirecting the user agent to a different resource, as indicated by a
URI in the Location header field, which is intended to provide an URI in the Location header field, which is intended to provide an
indirect response to the original request. A user agent can perform indirect response to the original request. A user agent can perform
a retrieval request targeting that URI (a GET or HEAD request if a retrieval request targeting that URI (a GET or HEAD request if
using HTTP), which might also be redirected, and present the eventual using HTTP), which might also be redirected, and present the eventual
result as an answer to the original request. Note that the new URI result as an answer to the original request. Note that the new URI
in the Location header field is not considered equivalent to the in the Location header field is not considered equivalent to the
target URI. target URI.
skipping to change at page 133, line 44 skipping to change at page 137, line 39
might result in a representation that is useful to recipients without might result in a representation that is useful to recipients without
implying that it represents the original target resource. Note that implying that it represents the original target resource. Note that
answers to the questions of what can be represented, what answers to the questions of what can be represented, what
representations are adequate, and what might be a useful description representations are adequate, and what might be a useful description
are outside the scope of HTTP. are outside the scope of HTTP.
Except for responses to a HEAD request, the representation of a 303 Except for responses to a HEAD request, the representation of a 303
response ought to contain a short hypertext note with a hyperlink to response ought to contain a short hypertext note with a hyperlink to
the same URI reference provided in the Location header field. the same URI reference provided in the Location header field.
9.4.5. 304 Not Modified 10.4.5. 304 Not Modified
The 304 (Not Modified) status code indicates that a conditional GET The 304 (Not Modified) status code indicates that a conditional GET
or HEAD request has been received and would have resulted in a 200 or HEAD request has been received and would have resulted in a 200
(OK) response if it were not for the fact that the condition (OK) response if it were not for the fact that the condition
evaluated to false. In other words, there is no need for the server evaluated to false. In other words, there is no need for the server
to transfer a representation of the target resource because the to transfer a representation of the target resource because the
request indicates that the client, which made the request request indicates that the client, which made the request
conditional, already has a valid representation; the server is conditional, already has a valid representation; the server is
therefore redirecting the client to make use of that stored therefore redirecting the client to make use of that stored
representation as if it were the payload of a 200 (OK) response. representation as if it were the payload of a 200 (OK) response.
skipping to change at page 134, line 28 skipping to change at page 138, line 23
Requirements on a cache that receives a 304 response are defined in Requirements on a cache that receives a 304 response are defined in
Section 4.3.4 of [Caching]. If the conditional request originated Section 4.3.4 of [Caching]. If the conditional request originated
with an outbound client, such as a user agent with its own cache with an outbound client, such as a user agent with its own cache
sending a conditional GET to a shared proxy, then the proxy SHOULD sending a conditional GET to a shared proxy, then the proxy SHOULD
forward the 304 response to that client. forward the 304 response to that client.
A 304 response cannot contain a message-body; it is always terminated A 304 response cannot contain a message-body; it is always terminated
by the first empty line after the header fields. by the first empty line after the header fields.
9.4.6. 305 Use Proxy 10.4.6. 305 Use Proxy
The 305 (Use Proxy) status code was defined in a previous version of The 305 (Use Proxy) status code was defined in a previous version of
this specification and is now deprecated (Appendix B of [RFC7231]). this specification and is now deprecated (Appendix B of [RFC7231]).
9.4.7. 306 (Unused) 10.4.7. 306 (Unused)
The 306 status code was defined in a previous version of this The 306 status code was defined in a previous version of this
specification, is no longer used, and the code is reserved. specification, is no longer used, and the code is reserved.
9.4.8. 307 Temporary Redirect 10.4.8. 307 Temporary Redirect
The 307 (Temporary Redirect) status code indicates that the target The 307 (Temporary Redirect) status code indicates that the target
resource resides temporarily under a different URI and the user agent resource resides temporarily under a different URI and the user agent
MUST NOT change the request method if it performs an automatic MUST NOT change the request method if it performs an automatic
redirection to that URI. Since the redirection can change over time, redirection to that URI. Since the redirection can change over time,
the client ought to continue using the original target URI for future the client ought to continue using the original target URI for future
requests. requests.
The server SHOULD generate a Location header field in the response The server SHOULD generate a Location header field in the response
containing a URI reference for the different URI. The user agent MAY containing a URI reference for the different URI. The user agent MAY
use the Location field value for automatic redirection. The server's use the Location field value for automatic redirection. The server's
response payload usually contains a short hypertext note with a response payload usually contains a short hypertext note with a
hyperlink to the different URI(s). hyperlink to the different URI(s).
9.4.9. 308 Permanent Redirect 10.4.9. 308 Permanent Redirect
The 308 (Permanent Redirect) status code indicates that the target The 308 (Permanent Redirect) status code indicates that the target
resource has been assigned a new permanent URI and any future resource has been assigned a new permanent URI and any future
references to this resource ought to use one of the enclosed URIs. references to this resource ought to use one of the enclosed URIs.
Clients with link editing capabilities ought to automatically re-link Clients with link editing capabilities ought to automatically re-link
references to the target URI to one or more of the new references references to the target URI to one or more of the new references
sent by the server, where possible. sent by the server, where possible.
The server SHOULD generate a Location header field in the response The server SHOULD generate a Location header field in the response
containing a preferred URI reference for the new permanent URI. The containing a preferred URI reference for the new permanent URI. The
skipping to change at page 135, line 28 skipping to change at page 139, line 28
hypertext note with a hyperlink to the new URI(s). hypertext note with a hyperlink to the new URI(s).
A 308 response is heuristically cacheable; i.e., unless otherwise A 308 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [Caching]). Section 4.2.2 of [Caching]).
Note: This status code is much younger (June 2014) than its Note: This status code is much younger (June 2014) than its
sibling codes, and thus might not be recognized everywhere. See sibling codes, and thus might not be recognized everywhere. See
Section 4 of [RFC7538] for deployment considerations. Section 4 of [RFC7538] for deployment considerations.
9.5. Client Error 4xx 10.5. Client Error 4xx
The 4xx (Client Error) class of status code indicates that the client The 4xx (Client Error) class of status code indicates that the client
seems to have erred. Except when responding to a HEAD request, the seems to have erred. Except when responding to a HEAD request, the
server SHOULD send a representation containing an explanation of the server SHOULD send a representation containing an explanation of the
error situation, and whether it is a temporary or permanent error situation, and whether it is a temporary or permanent
condition. These status codes are applicable to any request method. condition. These status codes are applicable to any request method.
User agents SHOULD display any included representation to the user. User agents SHOULD display any included representation to the user.
9.5.1. 400 Bad Request 10.5.1. 400 Bad Request
The 400 (Bad Request) status code indicates that the server cannot or The 400 (Bad Request) status code indicates that the server cannot or
will not process the request due to something that is perceived to be will not process the request due to something that is perceived to be
a client error (e.g., malformed request syntax, invalid request a client error (e.g., malformed request syntax, invalid request
message framing, or deceptive request routing). message framing, or deceptive request routing).
9.5.2. 401 Unauthorized 10.5.2. 401 Unauthorized
The 401 (Unauthorized) status code indicates that the request has not The 401 (Unauthorized) status code indicates that the request has not
been applied because it lacks valid authentication credentials for been applied because it lacks valid authentication credentials for
the target resource. The server generating a 401 response MUST send the target resource. The server generating a 401 response MUST send
a WWW-Authenticate header field (Section 10.3.1) containing at least a WWW-Authenticate header field (Section 11.3.1) containing at least
one challenge applicable to the target resource. one challenge applicable to the target resource.
If the request included authentication credentials, then the 401 If the request included authentication credentials, then the 401
response indicates that authorization has been refused for those response indicates that authorization has been refused for those
credentials. The user agent MAY repeat the request with a new or credentials. The user agent MAY repeat the request with a new or
replaced Authorization header field (Section 8.5.3). If the 401 replaced Authorization header field (Section 9.5.3). If the 401
response contains the same challenge as the prior response, and the response contains the same challenge as the prior response, and the
user agent has already attempted authentication at least once, then user agent has already attempted authentication at least once, then
the user agent SHOULD present the enclosed representation to the the user agent SHOULD present the enclosed representation to the
user, since it usually contains relevant diagnostic information. user, since it usually contains relevant diagnostic information.
9.5.3. 402 Payment Required 10.5.3. 402 Payment Required
The 402 (Payment Required) status code is reserved for future use. The 402 (Payment Required) status code is reserved for future use.
9.5.4. 403 Forbidden 10.5.4. 403 Forbidden
The 403 (Forbidden) status code indicates that the server understood The 403 (Forbidden) status code indicates that the server understood
the request but refuses to fulfill it. A server that wishes to make the request but refuses to fulfill it. A server that wishes to make
public why the request has been forbidden can describe that reason in public why the request has been forbidden can describe that reason in
the response payload (if any). the response payload (if any).
If authentication credentials were provided in the request, the If authentication credentials were provided in the request, the
server considers them insufficient to grant access. The client server considers them insufficient to grant access. The client
SHOULD NOT automatically repeat the request with the same SHOULD NOT automatically repeat the request with the same
credentials. The client MAY repeat the request with new or different credentials. The client MAY repeat the request with new or different
credentials. However, a request might be forbidden for reasons credentials. However, a request might be forbidden for reasons
unrelated to the credentials. unrelated to the credentials.
An origin server that wishes to "hide" the current existence of a An origin server that wishes to "hide" the current existence of a
forbidden target resource MAY instead respond with a status code of forbidden target resource MAY instead respond with a status code of
404 (Not Found). 404 (Not Found).
9.5.5. 404 Not Found 10.5.5. 404 Not Found
The 404 (Not Found) status code indicates that the origin server did The 404 (Not Found) status code indicates that the origin server did
not find a current representation for the target resource or is not not find a current representation for the target resource or is not
willing to disclose that one exists. A 404 status code does not willing to disclose that one exists. A 404 status code does not
indicate whether this lack of representation is temporary or indicate whether this lack of representation is temporary or
permanent; the 410 (Gone) status code is preferred over 404 if the permanent; the 410 (Gone) status code is preferred over 404 if the
origin server knows, presumably through some configurable means, that origin server knows, presumably through some configurable means, that
the condition is likely to be permanent. the condition is likely to be permanent.
A 404 response is heuristically cacheable; i.e., unless otherwise A 404 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [Caching]). Section 4.2.2 of [Caching]).
9.5.6. 405 Method Not Allowed 10.5.6. 405 Method Not Allowed
The 405 (Method Not Allowed) status code indicates that the method The 405 (Method Not Allowed) status code indicates that the method
received in the request-line is known by the origin server but not received in the request-line is known by the origin server but not
supported by the target resource. The origin server MUST generate an supported by the target resource. The origin server MUST generate an
Allow header field in a 405 response containing a list of the target Allow header field in a 405 response containing a list of the target
resource's currently supported methods. resource's currently supported methods.
A 405 response is heuristically cacheable; i.e., unless otherwise A 405 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [Caching]). Section 4.2.2 of [Caching]).
9.5.7. 406 Not Acceptable 10.5.7. 406 Not Acceptable
The 406 (Not Acceptable) status code indicates that the target The 406 (Not Acceptable) status code indicates that the target
resource does not have a current representation that would be resource does not have a current representation that would be
acceptable to the user agent, according to the proactive negotiation acceptable to the user agent, according to the proactive negotiation
header fields received in the request (Section 8.4), and the server header fields received in the request (Section 9.4), and the server
is unwilling to supply a default representation. is unwilling to supply a default representation.
The server SHOULD generate a payload containing a list of available The server SHOULD generate a payload containing a list of available
representation characteristics and corresponding resource identifiers representation characteristics and corresponding resource identifiers
from which the user or user agent can choose the one most from which the user or user agent can choose the one most
appropriate. A user agent MAY automatically select the most appropriate. A user agent MAY automatically select the most
appropriate choice from that list. However, this specification does appropriate choice from that list. However, this specification does
not define any standard for such automatic selection, as described in not define any standard for such automatic selection, as described in
Section 9.4.1. Section 10.4.1.
9.5.8. 407 Proxy Authentication Required 10.5.8. 407 Proxy Authentication Required
The 407 (Proxy Authentication Required) status code is similar to 401 The 407 (Proxy Authentication Required) status code is similar to 401
(Unauthorized), but it indicates that the client needs to (Unauthorized), but it indicates that the client needs to
authenticate itself in order to use a proxy for this request. The authenticate itself in order to use a proxy for this request. The
proxy MUST send a Proxy-Authenticate header field (Section 10.3.2) proxy MUST send a Proxy-Authenticate header field (Section 11.3.2)
containing a challenge applicable to that proxy for the request. The containing a challenge applicable to that proxy for the request. The
client MAY repeat the request with a new or replaced Proxy- client MAY repeat the request with a new or replaced Proxy-
Authorization header field (Section 8.5.4). Authorization header field (Section 9.5.4).
9.5.9. 408 Request Timeout 10.5.9. 408 Request Timeout
The 408 (Request Timeout) status code indicates that the server did The 408 (Request Timeout) status code indicates that the server did
not receive a complete request message within the time that it was not receive a complete request message within the time that it was
prepared to wait. If the client has an outstanding request in prepared to wait. If the client has an outstanding request in
transit, the client MAY repeat that request on a new connection. transit, the client MAY repeat that request on a new connection.
9.5.10. 409 Conflict 10.5.10. 409 Conflict
The 409 (Conflict) status code indicates that the request could not The 409 (Conflict) status code indicates that the request could not
be completed due to a conflict with the current state of the target be completed due to a conflict with the current state of the target
resource. This code is used in situations where the user might be resource. This code is used in situations where the user might be
able to resolve the conflict and resubmit the request. The server able to resolve the conflict and resubmit the request. The server
SHOULD generate a payload that includes enough information for a user SHOULD generate a payload that includes enough information for a user
to recognize the source of the conflict. to recognize the source of the conflict.
Conflicts are most likely to occur in response to a PUT request. For Conflicts are most likely to occur in response to a PUT request. For
example, if versioning were being used and the representation being example, if versioning were being used and the representation being
PUT included changes to a resource that conflict with those made by PUT included changes to a resource that conflict with those made by
an earlier (third-party) request, the origin server might use a 409 an earlier (third-party) request, the origin server might use a 409
response to indicate that it can't complete the request. In this response to indicate that it can't complete the request. In this
case, the response representation would likely contain information case, the response representation would likely contain information
useful for merging the differences based on the revision history. useful for merging the differences based on the revision history.
9.5.11. 410 Gone 10.5.11. 410 Gone
The 410 (Gone) status code indicates that access to the target The 410 (Gone) status code indicates that access to the target
resource is no longer available at the origin server and that this resource is no longer available at the origin server and that this
condition is likely to be permanent. If the origin server does not condition is likely to be permanent. If the origin server does not
know, or has no facility to determine, whether or not the condition know, or has no facility to determine, whether or not the condition
is permanent, the status code 404 (Not Found) ought to be used is permanent, the status code 404 (Not Found) ought to be used
instead. instead.
The 410 response is primarily intended to assist the task of web The 410 response is primarily intended to assist the task of web
maintenance by notifying the recipient that the resource is maintenance by notifying the recipient that the resource is
skipping to change at page 138, line 45 skipping to change at page 142, line 45
for limited-time, promotional services and for resources belonging to for limited-time, promotional services and for resources belonging to
individuals no longer associated with the origin server's site. It individuals no longer associated with the origin server's site. It
is not necessary to mark all permanently unavailable resources as is not necessary to mark all permanently unavailable resources as
"gone" or to keep the mark for any length of time -- that is left to "gone" or to keep the mark for any length of time -- that is left to
the discretion of the server owner. the discretion of the server owner.
A 410 response is heuristically cacheable; i.e., unless otherwise A 410 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [Caching]). Section 4.2.2 of [Caching]).
9.5.12. 411 Length Required 10.5.12. 411 Length Required
The 411 (Length Required) status code indicates that the server The 411 (Length Required) status code indicates that the server
refuses to accept the request without a defined Content-Length refuses to accept the request without a defined Content-Length
(Section 6.2.4). The client MAY repeat the request if it adds a (Section 7.2.4). The client MAY repeat the request if it adds a
valid Content-Length header field containing the length of the valid Content-Length header field containing the length of the
message body in the request message. message body in the request message.
9.5.13. 412 Precondition Failed 10.5.13. 412 Precondition Failed
The 412 (Precondition Failed) status code indicates that one or more The 412 (Precondition Failed) status code indicates that one or more
conditions given in the request header fields evaluated to false when conditions given in the request header fields evaluated to false when
tested on the server. This response status code allows the client to tested on the server. This response status code allows the client to
place preconditions on the current resource state (its current place preconditions on the current resource state (its current
representations and metadata) and, thus, prevent the request method representations and metadata) and, thus, prevent the request method
from being applied if the target resource is in an unexpected state. from being applied if the target resource is in an unexpected state.
9.5.14. 413 Payload Too Large 10.5.14. 413 Payload Too Large
The 413 (Payload Too Large) status code indicates that the server is The 413 (Payload Too Large) status code indicates that the server is
refusing to process a request because the request payload is larger refusing to process a request because the request payload is larger
than the server is willing or able to process. The server MAY than the server is willing or able to process. The server MAY
terminate the request, if the protocol version in use allows it; terminate the request, if the protocol version in use allows it;
otherwise, the server MAY close the connection. otherwise, the server MAY close the connection.
If the condition is temporary, the server SHOULD generate a Retry- If the condition is temporary, the server SHOULD generate a Retry-
After header field to indicate that it is temporary and after what After header field to indicate that it is temporary and after what
time the client MAY try again. time the client MAY try again.
9.5.15. 414 URI Too Long 10.5.15. 414 URI Too Long
The 414 (URI Too Long) status code indicates that the server is The 414 (URI Too Long) status code indicates that the server is
refusing to service the request because the target URI is longer than refusing to service the request because the target URI is longer than
the server is willing to interpret. This rare condition is only the server is willing to interpret. This rare condition is only
likely to occur when a client has improperly converted a POST request likely to occur when a client has improperly converted a POST request
to a GET request with long query information, when the client has to a GET request with long query information, when the client has
descended into a "black hole" of redirection (e.g., a redirected URI descended into a "black hole" of redirection (e.g., a redirected URI
prefix that points to a suffix of itself) or when the server is under prefix that points to a suffix of itself) or when the server is under
attack by a client attempting to exploit potential security holes. attack by a client attempting to exploit potential security holes.
A 414 response is heuristically cacheable; i.e., unless otherwise A 414 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [Caching]). Section 4.2.2 of [Caching]).
9.5.16. 415 Unsupported Media Type 10.5.16. 415 Unsupported Media Type
The 415 (Unsupported Media Type) status code indicates that the The 415 (Unsupported Media Type) status code indicates that the
origin server is refusing to service the request because the payload origin server is refusing to service the request because the payload
is in a format not supported by this method on the target resource. is in a format not supported by this method on the target resource.
The format problem might be due to the request's indicated Content- The format problem might be due to the request's indicated Content-
Type or Content-Encoding, or as a result of inspecting the data Type or Content-Encoding, or as a result of inspecting the data
directly. If the problem was caused by an unsupported content directly.
coding, the Accept-Encoding response header field (Section 8.4.3)
ought to be used to indicate what (if any) content codings would have
been accepted in the request.
9.5.17. 416 Range Not Satisfiable If the problem was caused by an unsupported content coding, the
Accept-Encoding response header field (Section 9.4.3) ought to be
used to indicate what (if any) content codings would have been
accepted in the request.
The 416 (Range Not Satisfiable) status code indicates that none of On the other hand, if the cause was an unsupported media type, the
the ranges in the request's Range header field (Section 8.3) overlap Accept response header field (Section 9.4.1) can be used to indicate
the current extent of the selected representation or that the set of what media types would have been accepted in the request.
ranges requested has been rejected due to invalid ranges or an
excessive request of small or overlapping ranges.
For byte ranges, failing to overlap the current extent means that the 10.5.17. 416 Range Not Satisfiable
first-pos of all of the range-spec values were greater than or equal
to the current length of the selected representation. When this The 416 (Range Not Satisfiable) status code indicates that the set of
status code is generated in response to a byte-range request, the ranges in the request's Range header field (Section 9.3) has been
sender SHOULD generate a Content-Range header field specifying the rejected either because none of the requested ranges are satisfiable
current length of the selected representation (Section 6.3.4). or because the client has requested an excessive number of small or
overlapping ranges (a potential denial of service attack).
Each range unit defines what is required for its own range sets to be
satisfiable. For example, Section 7.1.4.2 defines what makes a bytes
range set satisfiable.
When this status code is generated in response to a byte-range
request, the sender SHOULD generate a Content-Range header field
specifying the current length of the selected representation
(Section 7.3.4).
For example: For example:
HTTP/1.1 416 Range Not Satisfiable HTTP/1.1 416 Range Not Satisfiable
Date: Fri, 20 Jan 2012 15:41:54 GMT Date: Fri, 20 Jan 2012 15:41:54 GMT
Content-Range: bytes */47022 Content-Range: bytes */47022
Note: Because servers are free to ignore Range, many Note: Because servers are free to ignore Range, many
implementations will simply respond with the entire selected implementations will respond with the entire selected
representation in a 200 (OK) response. That is partly because representation in a 200 (OK) response. That is partly because
most clients are prepared to receive a 200 (OK) to complete the most clients are prepared to receive a 200 (OK) to complete the
task (albeit less efficiently) and partly because clients might task (albeit less efficiently) and partly because clients might
not stop making an invalid partial request until they have not stop making an invalid partial request until they have
received a complete representation. Thus, clients cannot depend received a complete representation. Thus, clients cannot depend
on receiving a 416 (Range Not Satisfiable) response even when it on receiving a 416 (Range Not Satisfiable) response even when it
is most appropriate. is most appropriate.
9.5.18. 417 Expectation Failed 10.5.18. 417 Expectation Failed
The 417 (Expectation Failed) status code indicates that the The 417 (Expectation Failed) status code indicates that the
expectation given in the request's Expect header field expectation given in the request's Expect header field
(Section 8.1.1) could not be met by at least one of the inbound (Section 9.1.1) could not be met by at least one of the inbound
servers. servers.
9.5.19. 418 (Unused) 10.5.19. 418 (Unused)
[RFC2324] was an April 1 RFC that lampooned the various ways HTTP was [RFC2324] was an April 1 RFC that lampooned the various ways HTTP was
abused; one such abuse was the definition of an application-specific abused; one such abuse was the definition of an application-specific
418 status code. In the intervening years, this status code has been 418 status code. In the intervening years, this status code has been
widely implemented as an "Easter Egg", and therefore is effectively widely implemented as an "Easter Egg", and therefore is effectively
consumed by this use. consumed by this use.
Therefore, the 418 status code is reserved in the IANA HTTP Status Therefore, the 418 status code is reserved in the IANA HTTP Status
Code Registry. This indicates that the status code cannot be Code Registry. This indicates that the status code cannot be
assigned to other applications currently. If future circumstances assigned to other applications currently. If future circumstances
require its use (e.g., exhaustion of 4NN status codes), it can be re- require its use (e.g., exhaustion of 4NN status codes), it can be re-
assigned to another use. assigned to another use.
9.5.20. 422 Unprocessable Payload 10.5.20. 422 Unprocessable Payload
The 422 (Unprocessable Payload) status code indicates that the server The 422 (Unprocessable Payload) status code indicates that the server
understands the content type of the request payload (hence a 415 understands the content type of the request payload (hence a 415
(Unsupported Media Type) status code is inappropriate), and the (Unsupported Media Type) status code is inappropriate), and the
syntax of the request payload is correct, but was unable to process syntax of the request payload is correct, but was unable to process
the contained instructions. For example, this status code can be the contained instructions. For example, this status code can be
sent if an XML request payload contains well-formed (i.e., sent if an XML request payload contains well-formed (i.e.,
syntactically correct), but semantically erroneous XML instructions. syntactically correct), but semantically erroneous XML instructions.
9.5.21. 426 Upgrade Required 10.5.21. 426 Upgrade Required
The 426 (Upgrade Required) status code indicates that the server The 426 (Upgrade Required) status code indicates that the server
refuses to perform the request using the current protocol but might refuses to perform the request using the current protocol but might
be willing to do so after the client upgrades to a different be willing to do so after the client upgrades to a different
protocol. The server MUST send an Upgrade header field in a 426 protocol. The server MUST send an Upgrade header field in a 426
response to indicate the required protocol(s) (Section 9.9 of response to indicate the required protocol(s) (Section 9.9 of
[Messaging]). [Messaging]).
Example: Example:
HTTP/1.1 426 Upgrade Required HTTP/1.1 426 Upgrade Required
Upgrade: HTTP/3.0 Upgrade: HTTP/3.0
Connection: Upgrade Connection: Upgrade
Content-Length: 53 Content-Length: 53
Content-Type: text/plain Content-Type: text/plain
This service requires use of the HTTP/3.0 protocol. This service requires use of the HTTP/3.0 protocol.
9.6. Server Error 5xx 10.6. Server Error 5xx
The 5xx (Server Error) class of status code indicates that the server The 5xx (Server Error) class of status code indicates that the server
is aware that it has erred or is incapable of performing the is aware that it has erred or is incapable of performing the
requested method. Except when responding to a HEAD request, the requested method. Except when responding to a HEAD request, the
server SHOULD send a representation containing an explanation of the server SHOULD send a representation containing an explanation of the
error situation, and whether it is a temporary or permanent error situation, and whether it is a temporary or permanent
condition. A user agent SHOULD display any included representation condition. A user agent SHOULD display any included representation
to the user. These response codes are applicable to any request to the user. These response codes are applicable to any request
method. method.
9.6.1. 500 Internal Server Error 10.6.1. 500 Internal Server Error
The 500 (Internal Server Error) status code indicates that the server The 500 (Internal Server Error) status code indicates that the server
encountered an unexpected condition that prevented it from fulfilling encountered an unexpected condition that prevented it from fulfilling
the request. the request.
9.6.2. 501 Not Implemented 10.6.2. 501 Not Implemented
The 501 (Not Implemented) status code indicates that the server does The 501 (Not Implemented) status code indicates that the server does
not support the functionality required to fulfill the request. This not support the functionality required to fulfill the request. This
is the appropriate response when the server does not recognize the is the appropriate response when the server does not recognize the
request method and is not capable of supporting it for any resource. request method and is not capable of supporting it for any resource.
A 501 response is heuristically cacheable; i.e., unless otherwise A 501 response is heuristically cacheable; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [Caching]). Section 4.2.2 of [Caching]).
9.6.3. 502 Bad Gateway 10.6.3. 502 Bad Gateway
The 502 (Bad Gateway) status code indicates that the server, while The 502 (Bad Gateway) status code indicates that the server, while
acting as a gateway or proxy, received an invalid response from an acting as a gateway or proxy, received an invalid response from an
inbound server it accessed while attempting to fulfill the request. inbound server it accessed while attempting to fulfill the request.
9.6.4. 503 Service Unavailable 10.6.4. 503 Service Unavailable
The 503 (Service Unavailable) status code indicates that the server The 503 (Service Unavailable) status code indicates that the server
is currently unable to handle the request due to a temporary overload is currently unable to handle the request due to a temporary overload
or scheduled maintenance, which will likely be alleviated after some or scheduled maintenance, which will likely be alleviated after some
delay. The server MAY send a Retry-After header field delay. The server MAY send a Retry-After header field
(Section 10.1.3) to suggest an appropriate amount of time for the (Section 11.1.3) to suggest an appropriate amount of time for the
client to wait before retrying the request. client to wait before retrying the request.
Note: The existence of the 503 status code does not imply that a Note: The existence of the 503 status code does not imply that a
server has to use it when becoming overloaded. Some servers might server has to use it when becoming overloaded. Some servers might
simply refuse the connection. simply refuse the connection.
9.6.5. 504 Gateway Timeout 10.6.5. 504 Gateway Timeout
The 504 (Gateway Timeout) status code indicates that the server, The 504 (Gateway Timeout) status code indicates that the server,
while acting as a gateway or proxy, did not receive a timely response while acting as a gateway or proxy, did not receive a timely response
from an upstream server it needed to access in order to complete the from an upstream server it needed to access in order to complete the
request. request.
9.6.6. 505 HTTP Version Not Supported 10.6.6. 505 HTTP Version Not Supported
The 505 (HTTP Version Not Supported) status code indicates that the The 505 (HTTP Version Not Supported) status code indicates that the
server does not support, or refuses to support, the major version of server does not support, or refuses to support, the major version of
HTTP that was used in the request message. The server is indicating HTTP that was used in the request message. The server is indicating
that it is unable or unwilling to complete the request using the same that it is unable or unwilling to complete the request using the same
major version as the client, as described in Section 3.5, other than major version as the client, as described in Section 4.2, other than
with this error message. The server SHOULD generate a representation with this error message. The server SHOULD generate a representation
for the 505 response that describes why that version is not supported for the 505 response that describes why that version is not supported
and what other protocols are supported by that server. and what other protocols are supported by that server.
9.7. Status Code Extensibility 10.7. Status Code Extensibility
Additional status codes, outside the scope of this specification, Additional status codes, outside the scope of this specification,
have been specified for use in HTTP. All such status codes ought to have been specified for use in HTTP. All such status codes ought to
be registered within the "Hypertext Transfer Protocol (HTTP) Status be registered within the "Hypertext Transfer Protocol (HTTP) Status
Code Registry". Code Registry".
9.7.1. Status Code Registry 10.7.1. Status Code Registry
The "Hypertext Transfer Protocol (HTTP) Status Code Registry", The "Hypertext Transfer Protocol (HTTP) Status Code Registry",
maintained by IANA at <https://www.iana.org/assignments/http-status- maintained by IANA at <https://www.iana.org/assignments/http-status-
codes>, registers status code numbers. codes>, registers status code numbers.
A registration MUST include the following fields: A registration MUST include the following fields:
o Status Code (3 digits) o Status Code (3 digits)
o Short Description o Short Description
o Pointer to specification text o Pointer to specification text
Values to be added to the HTTP status code namespace require IETF Values to be added to the HTTP status code namespace require IETF
Review (see [RFC8126], Section 4.8). Review (see [RFC8126], Section 4.8).
9.7.2. Considerations for New Status Codes 10.7.2. Considerations for New Status Codes
When it is necessary to express semantics for a response that are not When it is necessary to express semantics for a response that are not
defined by current status codes, a new status code can be registered. defined by current status codes, a new status code can be registered.
Status codes are generic; they are potentially applicable to any Status codes are generic; they are potentially applicable to any
resource, not just one particular media type, kind of resource, or resource, not just one particular media type, kind of resource, or
application of HTTP. As such, it is preferred that new status codes application of HTTP. As such, it is preferred that new status codes
be registered in a document that isn't specific to a single be registered in a document that isn't specific to a single
application. application.
New status codes are required to fall under one of the categories New status codes are required to fall under one of the categories
defined in Section 9. To allow existing parsers to process the defined in Section 10. To allow existing parsers to process the
response message, new status codes cannot disallow a payload, response message, new status codes cannot disallow a payload,
although they can mandate a zero-length payload body. although they can mandate a zero-length payload body.
Proposals for new status codes that are not yet widely deployed ought Proposals for new status codes that are not yet widely deployed ought
to avoid allocating a specific number for the code until there is to avoid allocating a specific number for the code until there is
clear consensus that it will be registered; instead, early drafts can clear consensus that it will be registered; instead, early drafts can
use a notation such as "4NN", or "3N0" .. "3N9", to indicate the use a notation such as "4NN", or "3N0" .. "3N9", to indicate the
class of the proposed status code(s) without consuming a number class of the proposed status code(s) without consuming a number
prematurely. prematurely.
skipping to change at page 144, line 33 skipping to change at page 148, line 39
The definition of a new status code ought to specify whether or not The definition of a new status code ought to specify whether or not
it is cacheable. Note that all status codes can be cached if the it is cacheable. Note that all status codes can be cached if the
response they occur in has explicit freshness information; however, response they occur in has explicit freshness information; however,
status codes that are defined as being cacheable are allowed to be status codes that are defined as being cacheable are allowed to be
cached without explicit freshness information. Likewise, the cached without explicit freshness information. Likewise, the
definition of a status code can place constraints upon cache definition of a status code can place constraints upon cache
behavior. See [Caching] for more information. behavior. See [Caching] for more information.
Finally, the definition of a new status code ought to indicate Finally, the definition of a new status code ought to indicate
whether the payload has any implied association with an identified whether the payload has any implied association with an identified
resource (Section 6.3.2). resource (Section 7.3.2).
10. Response Header Fields 11. Response Header Fields
The response header fields allow the server to pass additional The response header fields allow the server to pass additional
information about the response beyond the status code. These header information about the response beyond the status code. These header
fields give information about the server, about further access to the fields give information about the server, about further access to the
target resource, or about related resources. target resource, or about related resources.
Although each response header field has a defined meaning, in Although each response header field has a defined meaning, in
general, the precise semantics might be further refined by the general, the precise semantics might be further refined by the
semantics of the request method and/or response status code. semantics of the request method and/or response status code.
10.1. Control Data 11.1. Control Data
Response header fields can supply control data that supplements the Response header fields can supply control data that supplements the
status code, directs caching, or instructs the client where to go status code, directs caching, or instructs the client where to go
next. next.
+---------------+--------------------------+ +---------------+--------------------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+---------------+--------------------------+ +---------------+--------------------------+
| Age | Section 5.1 of [Caching] | | Age | Section 5.1 of [Caching] |
| Cache-Control | Section 5.2 of [Caching] | | Cache-Control | Section 5.2 of [Caching] |
| Expires | Section 5.3 of [Caching] | | Expires | Section 5.3 of [Caching] |
| Date | Section 10.1.1.2 | | Date | Section 11.1.1 |
| Location | Section 10.1.2 | | Location | Section 11.1.2 |
| Retry-After | Section 10.1.3 | | Retry-After | Section 11.1.3 |
| Vary | Section 10.1.4 | | Vary | Section 11.1.4 |
| Warning | Section 5.5 of [Caching] | | Warning | Section 5.5 of [Caching] |
+---------------+--------------------------+ +---------------+--------------------------+
10.1.1. Origination Date 11.1.1. Date
10.1.1.1. Date/Time Formats
Prior to 1995, there were three different formats commonly used by
servers to communicate timestamps. For compatibility with old
implementations, all three are defined here. The preferred format is
a fixed-length and single-zone subset of the date and time
specification used by the Internet Message Format [RFC5322].
HTTP-date = IMF-fixdate / obs-date
An example of the preferred format is
Sun, 06 Nov 1994 08:49:37 GMT ; IMF-fixdate
Examples of the two obsolete formats are
Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
A recipient that parses a timestamp value in an HTTP field MUST
accept all three HTTP-date formats. When a sender generates a field
that contains one or more timestamps defined as HTTP-date, the sender
MUST generate those timestamps in the IMF-fixdate format.
An HTTP-date value represents time as an instance of Coordinated
Universal Time (UTC). The first two formats indicate UTC by the
three-letter abbreviation for Greenwich Mean Time, "GMT", a
predecessor of the UTC name; values in the asctime format are assumed
to be in UTC. A sender that generates HTTP-date values from a local
clock ought to use NTP ([RFC5905]) or some similar protocol to
synchronize its clock to UTC.
Preferred format:
IMF-fixdate = day-name "," SP date1 SP time-of-day SP GMT
; fixed length/zone/capitalization subset of the format
; see Section 3.3 of [RFC5322]
day-name = %s"Mon" / %s"Tue" / %s"Wed"
/ %s"Thu" / %s"Fri" / %s"Sat" / %s"Sun"
date1 = day SP month SP year
; e.g., 02 Jun 1982
day = 2DIGIT
month = %s"Jan" / %s"Feb" / %s"Mar" / %s"Apr"
/ %s"May" / %s"Jun" / %s"Jul" / %s"Aug"
/ %s"Sep" / %s"Oct" / %s"Nov" / %s"Dec"
year = 4DIGIT
GMT = %s"GMT"
time-of-day = hour ":" minute ":" second
; 00:00:00 - 23:59:60 (leap second)
hour = 2DIGIT
minute = 2DIGIT
second = 2DIGIT
Obsolete formats:
obs-date = rfc850-date / asctime-date
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
date2 = day "-" month "-" 2DIGIT
; e.g., 02-Jun-82
day-name-l = %s"Monday" / %s"Tuesday" / %s"Wednesday"
/ %s"Thursday" / %s"Friday" / %s"Saturday" / %s"Sunday"
asctime-date = day-name SP date3 SP time-of-day SP year
date3 = month SP ( 2DIGIT / ( SP 1DIGIT ))
; e.g., Jun 2
HTTP-date is case sensitive. A sender MUST NOT generate additional
whitespace in an HTTP-date beyond that specifically included as SP in
the grammar. The semantics of day-name, day, month, year, and time-
of-day are the same as those defined for the Internet Message Format
constructs with the corresponding name ([RFC5322], Section 3.3).
Recipients of a timestamp value in rfc850-date format, which uses a
two-digit year, MUST interpret a timestamp that appears to be more
than 50 years in the future as representing the most recent year in
the past that had the same last two digits.
Recipients of timestamp values are encouraged to be robust in parsing
timestamps unless otherwise restricted by the field definition. For
example, messages are occasionally forwarded over HTTP from a non-
HTTP source that might generate any of the date and time
specifications defined by the Internet Message Format.
Note: HTTP requirements for the date/time stamp format apply only
to their usage within the protocol stream. Implementations are
not required to use these formats for user presentation, request
logging, etc.
10.1.1.2. Date
The "Date" header field represents the date and time at which the The "Date" header field represents the date and time at which the
message was originated, having the same semantics as the Origination message was originated, having the same semantics as the Origination
Date Field (orig-date) defined in Section 3.6.1 of [RFC5322]. The Date Field (orig-date) defined in Section 3.6.1 of [RFC5322]. The
field value is an HTTP-date, as defined in Section 10.1.1.1. field value is an HTTP-date, as defined in Section 5.4.1.5.
Date = HTTP-date Date = HTTP-date
An example is An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT Date: Tue, 15 Nov 1994 08:12:31 GMT
When a Date header field is generated, the sender SHOULD generate its When a Date header field is generated, the sender SHOULD generate its
field value as the best available approximation of the date and time field value as the best available approximation of the date and time
of message generation. In theory, the date ought to represent the of message generation. In theory, the date ought to represent the
skipping to change at page 148, line 8 skipping to change at page 150, line 14
corresponding Date header field to the message's header section if it corresponding Date header field to the message's header section if it
is cached or forwarded downstream. is cached or forwarded downstream.
A user agent MAY send a Date header field in a request, though A user agent MAY send a Date header field in a request, though
generally will not do so unless it is believed to convey useful generally will not do so unless it is believed to convey useful
information to the server. For example, custom applications of HTTP information to the server. For example, custom applications of HTTP
might convey a Date if the server is expected to adjust its might convey a Date if the server is expected to adjust its
interpretation of the user's request based on differences between the interpretation of the user's request based on differences between the
user agent and server clocks. user agent and server clocks.
10.1.2. Location 11.1.2. Location
The "Location" header field is used in some responses to refer to a The "Location" header field is used in some responses to refer to a
specific resource in relation to the response. The type of specific resource in relation to the response. The type of
relationship is defined by the combination of request method and relationship is defined by the combination of request method and
status code semantics. status code semantics.
Location = URI-reference Location = URI-reference
The field value consists of a single URI-reference. When it has the The field value consists of a single URI-reference. When it has the
form of a relative reference ([RFC3986], Section 4.2), the final form of a relative reference ([RFC3986], Section 4.2), the final
skipping to change at page 149, line 15 skipping to change at page 151, line 21
There are circumstances in which a fragment identifier in a Location There are circumstances in which a fragment identifier in a Location
value would not be appropriate. For example, the Location header value would not be appropriate. For example, the Location header
field in a 201 (Created) response is supposed to provide a URI that field in a 201 (Created) response is supposed to provide a URI that
is specific to the created resource. is specific to the created resource.
Note: Some recipients attempt to recover from Location fields that Note: Some recipients attempt to recover from Location fields that
are not valid URI references. This specification does not mandate are not valid URI references. This specification does not mandate
or define such processing, but does allow it for the sake of or define such processing, but does allow it for the sake of
robustness. robustness.
Note: The Content-Location header field (Section 6.2.5) differs Note: The Content-Location header field (Section 7.2.5) differs
from Location in that the Content-Location refers to the most from Location in that the Content-Location refers to the most
specific resource corresponding to the enclosed representation. specific resource corresponding to the enclosed representation.
It is therefore possible for a response to contain both the It is therefore possible for a response to contain both the
Location and Content-Location header fields. Location and Content-Location header fields.
10.1.3. Retry-After 11.1.3. Retry-After
Servers send the "Retry-After" header field to indicate how long the Servers send the "Retry-After" header field to indicate how long the
user agent ought to wait before making a follow-up request. When user agent ought to wait before making a follow-up request. When
sent with a 503 (Service Unavailable) response, Retry-After indicates sent with a 503 (Service Unavailable) response, Retry-After indicates
how long the service is expected to be unavailable to the client. how long the service is expected to be unavailable to the client.
When sent with any 3xx (Redirection) response, Retry-After indicates When sent with any 3xx (Redirection) response, Retry-After indicates
the minimum time that the user agent is asked to wait before issuing the minimum time that the user agent is asked to wait before issuing
the redirected request. the redirected request.
The value of this field can be either an HTTP-date or a number of The value of this field can be either an HTTP-date or a number of
skipping to change at page 149, line 48 skipping to change at page 152, line 5
delay-seconds = 1*DIGIT delay-seconds = 1*DIGIT
Two examples of its use are Two examples of its use are
Retry-After: Fri, 31 Dec 1999 23:59:59 GMT Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
Retry-After: 120 Retry-After: 120
In the latter example, the delay is 2 minutes. In the latter example, the delay is 2 minutes.
10.1.4. Vary 11.1.4. Vary
The "Vary" header field in a response describes what parts of a The "Vary" header field in a response describes what parts of a
request message, aside from the method, Host header field, and target request message, aside from the method, Host header field, and target
URI, might influence the origin server's process for selecting and URI, might influence the origin server's process for selecting and
representing this response. The value consists of either a single representing this response.
asterisk ("*") or a list of header field names (case-insensitive).
Vary = "*" / 1#field-name Vary = 1#( "*" / field-name )
A Vary field value of "*" signals that anything about the request A Vary field value is a list of request field names, known as the
might play a role in selecting the response representation, possibly selecting header fields, that might have a role in selecting the
including elements outside the message syntax (e.g., the client's representation for this response. Potential selecting header fields
network address). A recipient will not be able to determine whether are not limited to those defined by this specification.
this response is appropriate for a later request without forwarding
the request to the origin server. A proxy MUST NOT generate a Vary
field with a "*" value.
A Vary field value consisting of a list of field names indicates that If the list contains "*", it signals that other aspects of the
the named request header fields, known as the selecting header request might play a role in selecting the response representation,
fields, might have a role in selecting the representation. The possibly including elements outside the message syntax (e.g., the
potential selecting header fields are not limited to those defined by client's network address). A recipient will not be able to determine
this specification. whether this response is appropriate for a later request without
forwarding the request to the origin server. A proxy MUST NOT
generate "*" in a Vary field value.
For example, a response that contains For example, a response that contains
Vary: accept-encoding, accept-language Vary: accept-encoding, accept-language
indicates that the origin server might have used the request's indicates that the origin server might have used the request's
Accept-Encoding and Accept-Language fields (or lack thereof) as Accept-Encoding and Accept-Language fields (or lack thereof) as
determining factors while choosing the content for this response. determining factors while choosing the content for this response.
An origin server might send Vary with a list of fields for two An origin server might send Vary with a list of fields for two
purposes: purposes:
1. To inform cache recipients that they MUST NOT use this response 1. To inform cache recipients that they MUST NOT use this response
to satisfy a later request unless the later request has the same to satisfy a later request unless the later request has the same
values for the listed fields as the original request (Section 4.1 values for the listed fields as the original request (Section 4.1
of [Caching]). In other words, Vary expands the cache key of [Caching]). In other words, Vary expands the cache key
required to match a new request to the stored cache entry. required to match a new request to the stored cache entry.
2. To inform user agent recipients that this response is subject to 2. To inform user agent recipients that this response is subject to
content negotiation (Section 8.4) and that a different content negotiation (Section 9.4) and that a different
representation might be sent in a subsequent request if representation might be sent in a subsequent request if
additional parameters are provided in the listed header fields additional parameters are provided in the listed header fields
(proactive negotiation). (proactive negotiation).
An origin server SHOULD send a Vary header field when its algorithm An origin server SHOULD send a Vary header field when its algorithm
for selecting a representation varies based on aspects of the request for selecting a representation varies based on aspects of the request
message other than the method and target URI, unless the variance message other than the method and target URI, unless the variance
cannot be crossed or the origin server has been deliberately cannot be crossed or the origin server has been deliberately
configured to prevent cache transparency. For example, there is no configured to prevent cache transparency. For example, there is no
need to send the Authorization field name in Vary because reuse need to send the Authorization field name in Vary because reuse
across users is constrained by the field definition (Section 8.5.3). across users is constrained by the field definition (Section 9.5.3).
Likewise, an origin server might use Cache-Control response Likewise, an origin server might use Cache-Control response
directives (Section 5.2 of [Caching]) to supplant Vary if it directives (Section 5.2 of [Caching]) to supplant Vary if it
considers the variance less significant than the performance cost of considers the variance less significant than the performance cost of
Vary's impact on caching. Vary's impact on caching.
10.2. Validators 11.2. Validators
Validator header fields convey metadata about the selected Validator header fields convey metadata about the selected
representation (Section 6). In responses to safe requests, validator representation (Section 7). In responses to safe requests, validator
fields describe the selected representation chosen by the origin fields describe the selected representation chosen by the origin
server while handling the response. Note that, depending on the server while handling the response. Note that, depending on the
status code semantics, the selected representation for a given status code semantics, the selected representation for a given
response is not necessarily the same as the representation enclosed response is not necessarily the same as the representation enclosed
as response payload. as response payload.
In a successful response to a state-changing request, validator In a successful response to a state-changing request, validator
fields describe the new representation that has replaced the prior fields describe the new representation that has replaced the prior
selected representation as a result of processing the request. selected representation as a result of processing the request.
For example, an ETag field in a 201 (Created) response communicates For example, an ETag field in a 201 (Created) response communicates
the entity-tag of the newly created resource's representation, so the entity-tag of the newly created resource's representation, so
that it can be used in later conditional requests to prevent the that it can be used in later conditional requests to prevent the
"lost update" problem Section 8.2. "lost update" problem Section 9.2.
+---------------+----------------+ +---------------+----------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+---------------+----------------+ +---------------+----------------+
| ETag | Section 10.2.3 | | ETag | Section 11.2.3 |
| Last-Modified | Section 10.2.2 | | Last-Modified | Section 11.2.2 |
+---------------+----------------+ +---------------+----------------+
This specification defines two forms of metadata that are commonly This specification defines two forms of metadata that are commonly
used to observe resource state and test for preconditions: used to observe resource state and test for preconditions:
modification dates (Section 10.2.2) and opaque entity tags modification dates (Section 11.2.2) and opaque entity tags
(Section 10.2.3). Additional metadata that reflects resource state (Section 11.2.3). Additional metadata that reflects resource state
has been defined by various extensions of HTTP, such as Web has been defined by various extensions of HTTP, such as Web
Distributed Authoring and Versioning (WebDAV, [RFC4918]), that are Distributed Authoring and Versioning (WebDAV, [RFC4918]), that are
beyond the scope of this specification. A resource metadata value is beyond the scope of this specification. A resource metadata value is
referred to as a "validator" when it is used within a precondition. referred to as a "validator" when it is used within a precondition.
10.2.1. Weak versus Strong 11.2.1. Weak versus Strong
Validators come in two flavors: strong or weak. Weak validators are Validators come in two flavors: strong or weak. Weak validators are
easy to generate but are far less useful for comparisons. Strong easy to generate but are far less useful for comparisons. Strong
validators are ideal for comparisons but can be very difficult (and validators are ideal for comparisons but can be very difficult (and
occasionally impossible) to generate efficiently. Rather than impose occasionally impossible) to generate efficiently. Rather than impose
that all forms of resource adhere to the same strength of validator, that all forms of resource adhere to the same strength of validator,
HTTP exposes the type of validator in use and imposes restrictions on HTTP exposes the type of validator in use and imposes restrictions on
when weak validators can be used as preconditions. when weak validators can be used as preconditions.
A "strong validator" is representation metadata that changes value A "strong validator" is representation metadata that changes value
skipping to change at page 153, line 41 skipping to change at page 155, line 41
they differ only in the representation metadata, such as when two they differ only in the representation metadata, such as when two
different media types are available for the same representation data. different media types are available for the same representation data.
Strong validators are usable for all conditional requests, including Strong validators are usable for all conditional requests, including
cache validation, partial content ranges, and "lost update" cache validation, partial content ranges, and "lost update"
avoidance. Weak validators are only usable when the client does not avoidance. Weak validators are only usable when the client does not
require exact equality with previously obtained representation data, require exact equality with previously obtained representation data,
such as when validating a cache entry or limiting a web traversal to such as when validating a cache entry or limiting a web traversal to
recent changes. recent changes.
10.2.2. Last-Modified 11.2.2. Last-Modified
The "Last-Modified" header field in a response provides a timestamp The "Last-Modified" header field in a response provides a timestamp
indicating the date and time at which the origin server believes the indicating the date and time at which the origin server believes the
selected representation was last modified, as determined at the selected representation was last modified, as determined at the
conclusion of handling the request. conclusion of handling the request.
Last-Modified = HTTP-date Last-Modified = HTTP-date
An example of its use is An example of its use is
Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
10.2.2.1. Generation 11.2.2.1. Generation
An origin server SHOULD send Last-Modified for any selected An origin server SHOULD send Last-Modified for any selected
representation for which a last modification date can be reasonably representation for which a last modification date can be reasonably
and consistently determined, since its use in conditional requests and consistently determined, since its use in conditional requests
and evaluating cache freshness ([Caching]) results in a substantial and evaluating cache freshness ([Caching]) results in a substantial
reduction of HTTP traffic on the Internet and can be a significant reduction of HTTP traffic on the Internet and can be a significant
factor in improving service scalability and reliability. factor in improving service scalability and reliability.
A representation is typically the sum of many parts behind the A representation is typically the sum of many parts behind the
resource interface. The last-modified time would usually be the most resource interface. The last-modified time would usually be the most
skipping to change at page 154, line 43 skipping to change at page 156, line 43
the last modification time is derived from implementation-specific the last modification time is derived from implementation-specific
metadata that evaluates to some time in the future, according to the metadata that evaluates to some time in the future, according to the
origin server's clock, then the origin server MUST replace that value origin server's clock, then the origin server MUST replace that value
with the message origination date. This prevents a future with the message origination date. This prevents a future
modification date from having an adverse impact on cache validation. modification date from having an adverse impact on cache validation.
An origin server without a clock MUST NOT assign Last-Modified values An origin server without a clock MUST NOT assign Last-Modified values
to a response unless these values were associated with the resource to a response unless these values were associated with the resource
by some other system or user with a reliable clock. by some other system or user with a reliable clock.
10.2.2.2. Comparison 11.2.2.2. Comparison
A Last-Modified time, when used as a validator in a request, is A Last-Modified time, when used as a validator in a request, is
implicitly weak unless it is possible to deduce that it is strong, implicitly weak unless it is possible to deduce that it is strong,
using the following rules: using the following rules:
o The validator is being compared by an origin server to the actual o The validator is being compared by an origin server to the actual
current validator for the representation and, current validator for the representation and,
o That origin server reliably knows that the associated o That origin server reliably knows that the associated
representation did not change twice during the second covered by representation did not change twice during the second covered by
skipping to change at page 155, line 42 skipping to change at page 157, line 42
This method relies on the fact that if two different responses were This method relies on the fact that if two different responses were
sent by the origin server during the same second, but both had the sent by the origin server during the same second, but both had the
same Last-Modified time, then at least one of those responses would same Last-Modified time, then at least one of those responses would
have a Date value equal to its Last-Modified time. The arbitrary have a Date value equal to its Last-Modified time. The arbitrary
60-second limit guards against the possibility that the Date and 60-second limit guards against the possibility that the Date and
Last-Modified values are generated from different clocks or at Last-Modified values are generated from different clocks or at
somewhat different times during the preparation of the response. An somewhat different times during the preparation of the response. An
implementation MAY use a value larger than 60 seconds, if it is implementation MAY use a value larger than 60 seconds, if it is
believed that 60 seconds is too short. believed that 60 seconds is too short.
10.2.3. ETag 11.2.3. ETag
The "ETag" field in a response provides the current entity-tag for The "ETag" field in a response provides the current entity-tag for
the selected representation, as determined at the conclusion of the selected representation, as determined at the conclusion of
handling the request. An entity-tag is an opaque validator for handling the request. An entity-tag is an opaque validator for
differentiating between multiple representations of the same differentiating between multiple representations of the same
resource, regardless of whether those multiple representations are resource, regardless of whether those multiple representations are
due to resource state changes over time, content negotiation due to resource state changes over time, content negotiation
resulting in multiple representations being valid at the same time, resulting in multiple representations being valid at the same time,
or both. An entity-tag consists of an opaque quoted string, possibly or both. An entity-tag consists of an opaque quoted string, possibly
prefixed by a weakness indicator. prefixed by a weakness indicator.
skipping to change at page 156, line 33 skipping to change at page 158, line 33
Examples: Examples:
ETag: "xyzzy" ETag: "xyzzy"
ETag: W/"xyzzy" ETag: W/"xyzzy"
ETag: "" ETag: ""
An entity-tag can be either a weak or strong validator, with strong An entity-tag can be either a weak or strong validator, with strong
being the default. If an origin server provides an entity-tag for a being the default. If an origin server provides an entity-tag for a
representation and the generation of that entity-tag does not satisfy representation and the generation of that entity-tag does not satisfy
all of the characteristics of a strong validator (Section 10.2.1), all of the characteristics of a strong validator (Section 11.2.1),
then the origin server MUST mark the entity-tag as weak by prefixing then the origin server MUST mark the entity-tag as weak by prefixing
its opaque value with "W/" (case-sensitive). its opaque value with "W/" (case-sensitive).
A sender MAY send the Etag field in a trailer section (see A sender MAY send the Etag field in a trailer section (see
Section 4.6). However, since trailers are often ignored, it is Section 5.6). However, since trailers are often ignored, it is
preferable to send Etag as a header field unless the entity-tag is preferable to send Etag as a header field unless the entity-tag is
generated while sending the message body. generated while sending the message body.
10.2.3.1. Generation 11.2.3.1. Generation
The principle behind entity-tags is that only the service author The principle behind entity-tags is that only the service author
knows the implementation of a resource well enough to select the most knows the implementation of a resource well enough to select the most
accurate and efficient validation mechanism for that resource, and accurate and efficient validation mechanism for that resource, and
that any such mechanism can be mapped to a simple sequence of octets that any such mechanism can be mapped to a simple sequence of octets
for easy comparison. Since the value is opaque, there is no need for for easy comparison. Since the value is opaque, there is no need for
the client to be aware of how each entity-tag is constructed. the client to be aware of how each entity-tag is constructed.
For example, a resource that has implementation-specific versioning For example, a resource that has implementation-specific versioning
applied to all changes might use an internal revision number, perhaps applied to all changes might use an internal revision number, perhaps
skipping to change at page 157, line 17 skipping to change at page 159, line 17
representation content, a combination of various file attributes, or representation content, a combination of various file attributes, or
a modification timestamp that has sub-second resolution. a modification timestamp that has sub-second resolution.
An origin server SHOULD send an ETag for any selected representation An origin server SHOULD send an ETag for any selected representation
for which detection of changes can be reasonably and consistently for which detection of changes can be reasonably and consistently
determined, since the entity-tag's use in conditional requests and determined, since the entity-tag's use in conditional requests and
evaluating cache freshness ([Caching]) can result in a substantial evaluating cache freshness ([Caching]) can result in a substantial
reduction of HTTP network traffic and can be a significant factor in reduction of HTTP network traffic and can be a significant factor in
improving service scalability and reliability. improving service scalability and reliability.
10.2.3.2. Comparison 11.2.3.2. Comparison
There are two entity-tag comparison functions, depending on whether There are two entity-tag comparison functions, depending on whether
or not the comparison context allows the use of weak validators: or not the comparison context allows the use of weak validators:
o Strong comparison: two entity-tags are equivalent if both are not o Strong comparison: two entity-tags are equivalent if both are not
weak and their opaque-tags match character-by-character. weak and their opaque-tags match character-by-character.
o Weak comparison: two entity-tags are equivalent if their opaque- o Weak comparison: two entity-tags are equivalent if their opaque-
tags match character-by-character, regardless of either or both tags match character-by-character, regardless of either or both
being tagged as "weak". being tagged as "weak".
skipping to change at page 157, line 41 skipping to change at page 159, line 41
+--------+--------+-------------------+-----------------+ +--------+--------+-------------------+-----------------+
| ETag 1 | ETag 2 | Strong Comparison | Weak Comparison | | ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |
+--------+--------+-------------------+-----------------+ +--------+--------+-------------------+-----------------+
| W/"1" | W/"1" | no match | match | | W/"1" | W/"1" | no match | match |
| W/"1" | W/"2" | no match | no match | | W/"1" | W/"2" | no match | no match |
| W/"1" | "1" | no match | match | | W/"1" | "1" | no match | match |
| "1" | "1" | match | match | | "1" | "1" | match | match |
+--------+--------+-------------------+-----------------+ +--------+--------+-------------------+-----------------+
10.2.3.3. Example: Entity-Tags Varying on Content-Negotiated Resources 11.2.3.3. Example: Entity-Tags Varying on Content-Negotiated Resources
Consider a resource that is subject to content negotiation Consider a resource that is subject to content negotiation
(Section 6.4), and where the representations sent in response to a (Section 7.4), and where the representations sent in response to a
GET request vary based on the Accept-Encoding request header field GET request vary based on the Accept-Encoding request header field
(Section 8.4.3): (Section 9.4.3):
>> Request: >> Request:
GET /index HTTP/1.1 GET /index HTTP/1.1
Host: www.example.com Host: www.example.com
Accept-Encoding: gzip Accept-Encoding: gzip
In this case, the response might or might not use the gzip content In this case, the response might or might not use the gzip content
coding. If it does not, the response might look like: coding. If it does not, the response might look like:
skipping to change at page 159, line 5 skipping to change at page 161, line 5
...binary data... ...binary data...
Note: Content codings are a property of the representation data, Note: Content codings are a property of the representation data,
so a strong entity-tag for a content-encoded representation has to so a strong entity-tag for a content-encoded representation has to
be distinct from the entity tag of an unencoded representation to be distinct from the entity tag of an unencoded representation to
prevent potential conflicts during cache updates and range prevent potential conflicts during cache updates and range
requests. In contrast, transfer codings (Section 7 of requests. In contrast, transfer codings (Section 7 of
[Messaging]) apply only during message transfer and do not result [Messaging]) apply only during message transfer and do not result
in distinct entity-tags. in distinct entity-tags.
10.2.4. When to Use Entity-Tags and Last-Modified Dates 11.2.4. When to Use Entity-Tags and Last-Modified Dates
In 200 (OK) responses to GET or HEAD, an origin server: In 200 (OK) responses to GET or HEAD, an origin server:
o SHOULD send an entity-tag validator unless it is not feasible to o SHOULD send an entity-tag validator unless it is not feasible to
generate one. generate one.
o MAY send a weak entity-tag instead of a strong entity-tag, if o MAY send a weak entity-tag instead of a strong entity-tag, if
performance considerations support the use of weak entity-tags, or performance considerations support the use of weak entity-tags, or
if it is unfeasible to send a strong entity-tag. if it is unfeasible to send a strong entity-tag.
skipping to change at page 159, line 42 skipping to change at page 161, line 42
o MAY send the Last-Modified value in subrange cache validation o MAY send the Last-Modified value in subrange cache validation
requests (using If-Unmodified-Since) if only a Last-Modified value requests (using If-Unmodified-Since) if only a Last-Modified value
has been provided by an HTTP/1.0 origin server. The user agent has been provided by an HTTP/1.0 origin server. The user agent
SHOULD provide a way to disable this, in case of difficulty. SHOULD provide a way to disable this, in case of difficulty.
o SHOULD send both validators in cache validation requests if both o SHOULD send both validators in cache validation requests if both
an entity-tag and a Last-Modified value have been provided by the an entity-tag and a Last-Modified value have been provided by the
origin server. This allows both HTTP/1.0 and HTTP/1.1 caches to origin server. This allows both HTTP/1.0 and HTTP/1.1 caches to
respond appropriately. respond appropriately.
10.3. Authentication Challenges 11.3. Authentication Challenges
Authentication challenges indicate what mechanisms are available for Authentication challenges indicate what mechanisms are available for
the client to provide authentication credentials in future requests. the client to provide authentication credentials in future requests.
+--------------------+----------------+ +--------------------+----------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+--------------------+----------------+ +--------------------+----------------+
| WWW-Authenticate | Section 10.3.1 | | WWW-Authenticate | Section 11.3.1 |
| Proxy-Authenticate | Section 10.3.2 | | Proxy-Authenticate | Section 11.3.2 |
+--------------------+----------------+ +--------------------+----------------+
Furthermore, the "Authentication-Info" and "Proxy-Authentication- Furthermore, the "Authentication-Info" and "Proxy-Authentication-
Info" response header fields are defined for use in authentication Info" response header fields are defined for use in authentication
schemes that need to return information once the client's schemes that need to return information once the client's
authentication credentials have been accepted. authentication credentials have been accepted.
+---------------------------+----------------+ +---------------------------+----------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+---------------------------+----------------+ +---------------------------+----------------+
| Authentication-Info | Section 10.3.3 | | Authentication-Info | Section 11.3.3 |
| Proxy-Authentication-Info | Section 10.3.4 | | Proxy-Authentication-Info | Section 11.3.4 |
+---------------------------+----------------+ +---------------------------+----------------+
10.3.1. WWW-Authenticate 11.3.1. WWW-Authenticate
The "WWW-Authenticate" header field indicates the authentication The "WWW-Authenticate" header field indicates the authentication
scheme(s) and parameters applicable to the target resource. scheme(s) and parameters applicable to the target resource.
WWW-Authenticate = 1#challenge WWW-Authenticate = 1#challenge
A server generating a 401 (Unauthorized) response MUST send a WWW- A server generating a 401 (Unauthorized) response MUST send a WWW-
Authenticate header field containing at least one challenge. A Authenticate header field containing at least one challenge. A
server MAY generate a WWW-Authenticate header field in other response server MAY generate a WWW-Authenticate header field in other response
messages to indicate that supplying credentials (or different messages to indicate that supplying credentials (or different
skipping to change at page 161, line 7 skipping to change at page 163, line 7
"type" and "title", and another one for the "Basic" scheme with a "type" and "title", and another one for the "Basic" scheme with a
realm value of "simple". realm value of "simple".
Note: The challenge grammar production uses the list syntax as Note: The challenge grammar production uses the list syntax as
well. Therefore, a sequence of comma, whitespace, and comma can well. Therefore, a sequence of comma, whitespace, and comma can
be considered either as applying to the preceding challenge, or to be considered either as applying to the preceding challenge, or to
be an empty entry in the list of challenges. In practice, this be an empty entry in the list of challenges. In practice, this
ambiguity does not affect the semantics of the header field value ambiguity does not affect the semantics of the header field value
and thus is harmless. and thus is harmless.
10.3.2. Proxy-Authenticate 11.3.2. Proxy-Authenticate
The "Proxy-Authenticate" header field consists of at least one The "Proxy-Authenticate" header field consists of at least one
challenge that indicates the authentication scheme(s) and parameters challenge that indicates the authentication scheme(s) and parameters
applicable to the proxy for this request. A proxy MUST send at least applicable to the proxy for this request. A proxy MUST send at least
one Proxy-Authenticate header field in each 407 (Proxy Authentication one Proxy-Authenticate header field in each 407 (Proxy Authentication
Required) response that it generates. Required) response that it generates.
Proxy-Authenticate = 1#challenge Proxy-Authenticate = 1#challenge
Unlike WWW-Authenticate, the Proxy-Authenticate header field applies Unlike WWW-Authenticate, the Proxy-Authenticate header field applies
skipping to change at page 161, line 29 skipping to change at page 163, line 29
because only the client that chose a given proxy is likely to have because only the client that chose a given proxy is likely to have
the credentials necessary for authentication. However, when multiple the credentials necessary for authentication. However, when multiple
proxies are used within the same administrative domain, such as proxies are used within the same administrative domain, such as
office and regional caching proxies within a large corporate network, office and regional caching proxies within a large corporate network,
it is common for credentials to be generated by the user agent and it is common for credentials to be generated by the user agent and
passed through the hierarchy until consumed. Hence, in such a passed through the hierarchy until consumed. Hence, in such a
configuration, it will appear as if Proxy-Authenticate is being configuration, it will appear as if Proxy-Authenticate is being
forwarded because each proxy will send the same challenge set. forwarded because each proxy will send the same challenge set.
Note that the parsing considerations for WWW-Authenticate apply to Note that the parsing considerations for WWW-Authenticate apply to
this header field as well; see Section 10.3.1 for details. this header field as well; see Section 11.3.1 for details.
10.3.3. Authentication-Info 11.3.3. Authentication-Info
HTTP authentication schemes can use the Authentication-Info response HTTP authentication schemes can use the Authentication-Info response
header field to communicate information after the client's header field to communicate information after the client's
authentication credentials have been accepted. This information can authentication credentials have been accepted. This information can
include a finalization message from the server (e.g., it can contain include a finalization message from the server (e.g., it can contain
the server authentication). the server authentication).
The field value is a list of parameters (name/value pairs), using the The field value is a list of parameters (name/value pairs), using the
"auth-param" syntax defined in Section 8.5.1. This specification "auth-param" syntax defined in Section 9.5.1. This specification
only describes the generic format; authentication schemes using only describes the generic format; authentication schemes using
Authentication-Info will define the individual parameters. The Authentication-Info will define the individual parameters. The
"Digest" Authentication Scheme, for instance, defines multiple "Digest" Authentication Scheme, for instance, defines multiple
parameters in Section 3.5 of [RFC7616]. parameters in Section 3.5 of [RFC7616].
Authentication-Info = #auth-param Authentication-Info = #auth-param
The Authentication-Info header field can be used in any HTTP The Authentication-Info header field can be used in any HTTP
response, independently of request method and status code. Its response, independently of request method and status code. Its
semantics are defined by the authentication scheme indicated by the semantics are defined by the authentication scheme indicated by the
Authorization header field (Section 8.5.3) of the corresponding Authorization header field (Section 9.5.3) of the corresponding
request. request.
A proxy forwarding a response is not allowed to modify the field A proxy forwarding a response is not allowed to modify the field
value in any way. value in any way.
Authentication-Info can be used inside trailers (Section 4.6) when Authentication-Info can be used inside trailers (Section 5.6) when
the authentication scheme explicitly allows this. the authentication scheme explicitly allows this.
10.3.3.1. Parameter Value Format 11.3.3.1. Parameter Value Format
Parameter values can be expressed either as "token" or as "quoted- Parameter values can be expressed either as "token" or as "quoted-
string" (Section 4.4.1). string" (Section 5.4.1).
Authentication scheme definitions need to allow both notations, both Authentication scheme definitions need to allow both notations, both
for senders and recipients. This allows recipients to use generic for senders and recipients. This allows recipients to use generic
parsing components, independent of the authentication scheme in use. parsing components, independent of the authentication scheme in use.
For backwards compatibility, authentication scheme definitions can For backwards compatibility, authentication scheme definitions can
restrict the format for senders to one of the two variants. This can restrict the format for senders to one of the two variants. This can
be important when it is known that deployed implementations will fail be important when it is known that deployed implementations will fail
when encountering one of the two formats. when encountering one of the two formats.
10.3.4. Proxy-Authentication-Info 11.3.4. Proxy-Authentication-Info
The Proxy-Authentication-Info response header field is equivalent to The Proxy-Authentication-Info response header field is equivalent to
Authentication-Info, except that it applies to proxy authentication Authentication-Info, except that it applies to proxy authentication
(Section 8.5.1) and its semantics are defined by the authentication (Section 9.5.1) and its semantics are defined by the authentication
scheme indicated by the Proxy-Authorization header field scheme indicated by the Proxy-Authorization header field
(Section 8.5.4) of the corresponding request: (Section 9.5.4) of the corresponding request:
Proxy-Authentication-Info = #auth-param Proxy-Authentication-Info = #auth-param
However, unlike Authentication-Info, the Proxy-Authentication-Info However, unlike Authentication-Info, the Proxy-Authentication-Info
header field applies only to the next outbound client on the response header field applies only to the next outbound client on the response
chain. This is because only the client that chose a given proxy is chain. This is because only the client that chose a given proxy is
likely to have the credentials necessary for authentication. likely to have the credentials necessary for authentication.
However, when multiple proxies are used within the same However, when multiple proxies are used within the same
administrative domain, such as office and regional caching proxies administrative domain, such as office and regional caching proxies
within a large corporate network, it is common for credentials to be within a large corporate network, it is common for credentials to be
generated by the user agent and passed through the hierarchy until generated by the user agent and passed through the hierarchy until
consumed. Hence, in such a configuration, it will appear as if consumed. Hence, in such a configuration, it will appear as if
Proxy-Authentication-Info is being forwarded because each proxy will Proxy-Authentication-Info is being forwarded because each proxy will
send the same field value. send the same field value.
10.4. Response Context 11.4. Response Context
The remaining response header fields provide more information about The remaining response header fields provide more information about
the target resource for potential use in later requests. the target resource for potential use in later requests.
+---------------+----------------+ +---------------+----------------+
| Field Name | Defined in... | | Field Name | Defined in... |
+---------------+----------------+ +---------------+----------------+
| Accept-Ranges | Section 10.4.1 | | Accept-Ranges | Section 11.4.1 |
| Allow | Section 10.4.2 | | Allow | Section 11.4.2 |
| Server | Section 10.4.3 | | Server | Section 11.4.3 |
+---------------+----------------+ +---------------+----------------+
10.4.1. Accept-Ranges 11.4.1. Accept-Ranges
The "Accept-Ranges" header field allows a server to indicate that it The "Accept-Ranges" header field allows a server to indicate that it
supports range requests for the target resource. supports range requests for the target resource.
Accept-Ranges = acceptable-ranges Accept-Ranges = acceptable-ranges
acceptable-ranges = 1#range-unit / "none" acceptable-ranges = 1#range-unit / "none"
An origin server that supports byte-range requests for a given target An origin server that supports byte-range requests for a given target
resource MAY send resource MAY send
Accept-Ranges: bytes Accept-Ranges: bytes
to indicate what range units are supported. A client MAY generate to indicate what range units are supported. A client MAY generate
range requests without having received this header field for the range requests without having received this header field for the
resource involved. Range units are defined in Section 6.1.4. resource involved. Range units are defined in Section 7.1.4.
A server that does not support any kind of range request for the A server that does not support any kind of range request for the
target resource MAY send target resource MAY send
Accept-Ranges: none Accept-Ranges: none
to advise the client not to attempt a range request. to advise the client not to attempt a range request.
10.4.2. Allow 11.4.2. Allow
The "Allow" header field lists the set of methods advertised as The "Allow" header field lists the set of methods advertised as
supported by the target resource. The purpose of this field is supported by the target resource. The purpose of this field is
strictly to inform the recipient of valid request methods associated strictly to inform the recipient of valid request methods associated
with the resource. with the resource.
Allow = #method Allow = #method
Example of use: Example of use:
skipping to change at page 164, line 18 skipping to change at page 166, line 18
the time of each request. An origin server MUST generate an Allow the time of each request. An origin server MUST generate an Allow
field in a 405 (Method Not Allowed) response and MAY do so in any field in a 405 (Method Not Allowed) response and MAY do so in any
other response. An empty Allow field value indicates that the other response. An empty Allow field value indicates that the
resource allows no methods, which might occur in a 405 response if resource allows no methods, which might occur in a 405 response if
the resource has been temporarily disabled by configuration. the resource has been temporarily disabled by configuration.
A proxy MUST NOT modify the Allow header field -- it does not need to A proxy MUST NOT modify the Allow header field -- it does not need to
understand all of the indicated methods in order to handle them understand all of the indicated methods in order to handle them
according to the generic message handling rules. according to the generic message handling rules.
10.4.3. Server 11.4.3. Server
The "Server" header field contains information about the software The "Server" header field contains information about the software
used by the origin server to handle the request, which is often used used by the origin server to handle the request, which is often used
by clients to help identify the scope of reported interoperability by clients to help identify the scope of reported interoperability
problems, to work around or tailor requests to avoid particular problems, to work around or tailor requests to avoid particular
server limitations, and for analytics regarding server or operating server limitations, and for analytics regarding server or operating
system use. An origin server MAY generate a Server field in its system use. An origin server MAY generate a Server field in its
responses. responses.
Server = product *( RWS ( product / comment ) ) Server = product *( RWS ( product / comment ) )
The Server field value consists of one or more product identifiers, The Server field value consists of one or more product identifiers,
each followed by zero or more comments (Section 4.4.1.3), which each followed by zero or more comments (Section 5.4.1.3), which
together identify the origin server software and its significant together identify the origin server software and its significant
subproducts. By convention, the product identifiers are listed in subproducts. By convention, the product identifiers are listed in
decreasing order of their significance for identifying the origin decreasing order of their significance for identifying the origin
server software. Each product identifier consists of a name and server software. Each product identifier consists of a name and
optional version, as defined in Section 8.6.3. optional version, as defined in Section 9.6.3.
Example: Example:
Server: CERN/3.0 libwww/2.17 Server: CERN/3.0 libwww/2.17
An origin server SHOULD NOT generate a Server field containing An origin server SHOULD NOT generate a Server field containing
needlessly fine-grained detail and SHOULD limit the addition of needlessly fine-grained detail and SHOULD limit the addition of
subproducts by third parties. Overly long and detailed Server field subproducts by third parties. Overly long and detailed Server field
values increase response latency and potentially reveal internal values increase response latency and potentially reveal internal
implementation details that might make it (slightly) easier for implementation details that might make it (slightly) easier for
attackers to find and exploit known security holes. attackers to find and exploit known security holes.
11. Security Considerations 12. Security Considerations
This section is meant to inform developers, information providers, This section is meant to inform developers, information providers,
and users of known security concerns relevant to HTTP semantics and and users of known security concerns relevant to HTTP semantics and
its use for transferring information over the Internet. its use for transferring information over the Internet.
Considerations related to message syntax, parsing, and routing are Considerations related to message syntax, parsing, and routing are
discussed in Section 11 of [Messaging]. discussed in Section 11 of [Messaging].
The list of considerations below is not exhaustive. Most security The list of considerations below is not exhaustive. Most security
concerns related to HTTP semantics are about securing server-side concerns related to HTTP semantics are about securing server-side
applications (code behind the HTTP interface), securing user agent applications (code behind the HTTP interface), securing user agent
processing of payloads received via HTTP, or secure use of the processing of payloads received via HTTP, or secure use of the
Internet in general, rather than security of the protocol. Various Internet in general, rather than security of the protocol. Various
organizations maintain topical information and links to current organizations maintain topical information and links to current
research on Web application security (e.g., [OWASP]). research on Web application security (e.g., [OWASP]).
11.1. Establishing Authority 12.1. Establishing Authority
HTTP relies on the notion of an authoritative response: a response HTTP relies on the notion of an authoritative response: a response
that has been determined by (or at the direction of) the origin that has been determined by (or at the direction of) the origin
server identified within the target URI to be the most appropriate server identified within the target URI to be the most appropriate
response for that request given the state of the target resource at response for that request given the state of the target resource at
the time of response message origination. the time of response message origination.
When a registered name is used in the authority component, the "http" When a registered name is used in the authority component, the "http"
URI scheme (Section 2.5.1) relies on the user's local name resolution URI scheme (Section 2.5.1) relies on the user's local name resolution
service to determine where it can find authoritative responses. This service to determine where it can find authoritative responses. This
skipping to change at page 165, line 48 skipping to change at page 167, line 48
[RFC4033]) are one way to improve authenticity. [RFC4033]) are one way to improve authenticity.
Furthermore, after an IP address is obtained, establishing authority Furthermore, after an IP address is obtained, establishing authority
for an "http" URI is vulnerable to attacks on Internet Protocol for an "http" URI is vulnerable to attacks on Internet Protocol
routing. routing.
The "https" scheme (Section 2.5.2) is intended to prevent (or at The "https" scheme (Section 2.5.2) is intended to prevent (or at
least reveal) many of these potential attacks on establishing least reveal) many of these potential attacks on establishing
authority, provided that the negotiated TLS connection is secured and authority, provided that the negotiated TLS connection is secured and
the client properly verifies that the communicating server's identity the client properly verifies that the communicating server's identity
matches the target URI's authority component (Section 5.4.3.1). matches the target URI's authority component (Section 6.4.3.1).
Correctly implementing such verification can be difficult (see Correctly implementing such verification can be difficult (see
[Georgiev]). [Georgiev]).
Authority for a given origin server can be delegated through protocol Authority for a given origin server can be delegated through protocol
extensions; for example, [RFC7838]. Likewise, the set of servers extensions; for example, [RFC7838]. Likewise, the set of servers
that a connection is considered authoritative for can be changed with that a connection is considered authoritative for can be changed with
a protocol extension like [RFC8336]. a protocol extension like [RFC8336].
Providing a response from a non-authoritative source, such as a Providing a response from a non-authoritative source, such as a
shared proxy cache, is often useful to improve performance and shared proxy cache, is often useful to improve performance and
skipping to change at page 166, line 26 skipping to change at page 168, line 26
For example, phishing is an attack on the user's perception of For example, phishing is an attack on the user's perception of
authority, where that perception can be misled by presenting similar authority, where that perception can be misled by presenting similar
branding in hypertext, possibly aided by userinfo obfuscating the branding in hypertext, possibly aided by userinfo obfuscating the
authority component (see Section 2.5.1). User agents can reduce the authority component (see Section 2.5.1). User agents can reduce the
impact of phishing attacks by enabling users to easily inspect a impact of phishing attacks by enabling users to easily inspect a
target URI prior to making an action, by prominently distinguishing target URI prior to making an action, by prominently distinguishing
(or rejecting) userinfo when present, and by not sending stored (or rejecting) userinfo when present, and by not sending stored
credentials and cookies when the referring document is from an credentials and cookies when the referring document is from an
unknown or untrusted source. unknown or untrusted source.
11.2. Risks of Intermediaries 12.2. Risks of Intermediaries
By their very nature, HTTP intermediaries are men-in-the-middle and, By their very nature, HTTP intermediaries are men-in-the-middle and,
thus, represent an opportunity for man-in-the-middle attacks. thus, represent an opportunity for man-in-the-middle attacks.
Compromise of the systems on which the intermediaries run can result Compromise of the systems on which the intermediaries run can result
in serious security and privacy problems. Intermediaries might have in serious security and privacy problems. Intermediaries might have
access to security-related information, personal information about access to security-related information, personal information about
individual users and organizations, and proprietary information individual users and organizations, and proprietary information
belonging to users and content providers. A compromised belonging to users and content providers. A compromised
intermediary, or an intermediary implemented or configured without intermediary, or an intermediary implemented or configured without
regard to security and privacy considerations, might be used in the regard to security and privacy considerations, might be used in the
skipping to change at page 167, line 5 skipping to change at page 169, line 5
to cache poisoning attacks, as described in Section 7 of [Caching]. to cache poisoning attacks, as described in Section 7 of [Caching].
Implementers need to consider the privacy and security implications Implementers need to consider the privacy and security implications
of their design and coding decisions, and of the configuration of their design and coding decisions, and of the configuration
options they provide to operators (especially the default options they provide to operators (especially the default
configuration). configuration).
Users need to be aware that intermediaries are no more trustworthy Users need to be aware that intermediaries are no more trustworthy
than the people who run them; HTTP itself cannot solve this problem. than the people who run them; HTTP itself cannot solve this problem.
11.3. Attacks Based on File and Path Names 12.3. Attacks Based on File and Path Names
Origin servers frequently make use of their local file system to Origin servers frequently make use of their local file system to
manage the mapping from target URI to resource representations. Most manage the mapping from target URI to resource representations. Most
file systems are not designed to protect against malicious file or file systems are not designed to protect against malicious file or
path names. Therefore, an origin server needs to avoid accessing path names. Therefore, an origin server needs to avoid accessing
names that have a special significance to the system when mapping the names that have a special significance to the system when mapping the
target resource to files, folders, or directories. target resource to files, folders, or directories.
For example, UNIX, Microsoft Windows, and other operating systems use For example, UNIX, Microsoft Windows, and other operating systems use
".." as a path component to indicate a directory level above the ".." as a path component to indicate a directory level above the
skipping to change at page 167, line 29 skipping to change at page 169, line 29
systems have an annoying tendency to prefer user-friendliness over systems have an annoying tendency to prefer user-friendliness over
security when handling invalid or unexpected characters, security when handling invalid or unexpected characters,
recomposition of decomposed characters, and case-normalization of recomposition of decomposed characters, and case-normalization of
case-insensitive names. case-insensitive names.
Attacks based on such special names tend to focus on either denial- Attacks based on such special names tend to focus on either denial-
of-service (e.g., telling the server to read from a COM port) or of-service (e.g., telling the server to read from a COM port) or
disclosure of configuration and source files that are not meant to be disclosure of configuration and source files that are not meant to be
served. served.
11.4. Attacks Based on Command, Code, or Query Injection 12.4. Attacks Based on Command, Code, or Query Injection
Origin servers often use parameters within the URI as a means of Origin servers often use parameters within the URI as a means of
identifying system services, selecting database entries, or choosing identifying system services, selecting database entries, or choosing
a data source. However, data received in a request cannot be a data source. However, data received in a request cannot be
trusted. An attacker could construct any of the request data trusted. An attacker could construct any of the request data
elements (method, target URI, header fields, or body) to contain data elements (method, target URI, header fields, or body) to contain data
that might be misinterpreted as a command, code, or query when passed that might be misinterpreted as a command, code, or query when passed
through a command invocation, language interpreter, or database through a command invocation, language interpreter, or database
interface. interface.
skipping to change at page 168, line 11 skipping to change at page 170, line 11
Parameters ought to be compared to fixed strings and acted upon as a Parameters ought to be compared to fixed strings and acted upon as a
result of that comparison, rather than passed through an interface result of that comparison, rather than passed through an interface
that is not prepared for untrusted data. Received data that isn't that is not prepared for untrusted data. Received data that isn't
based on fixed parameters ought to be carefully filtered or encoded based on fixed parameters ought to be carefully filtered or encoded
to avoid being misinterpreted. to avoid being misinterpreted.
Similar considerations apply to request data when it is stored and Similar considerations apply to request data when it is stored and
later processed, such as within log files, monitoring tools, or when later processed, such as within log files, monitoring tools, or when
included within a data format that allows embedded scripts. included within a data format that allows embedded scripts.
11.5. Attacks via Protocol Element Length 12.5. Attacks via Protocol Element Length
Because HTTP uses mostly textual, character-delimited fields, parsers Because HTTP uses mostly textual, character-delimited fields, parsers
are often vulnerable to attacks based on sending very long (or very are often vulnerable to attacks based on sending very long (or very
slow) streams of data, particularly where an implementation is slow) streams of data, particularly where an implementation is
expecting a protocol element with no predefined length (Section 3.3). expecting a protocol element with no predefined length (Section 3.3).
To promote interoperability, specific recommendations are made for To promote interoperability, specific recommendations are made for
minimum size limits on request-line (Section 3 of [Messaging]) and minimum size limits on request-line (Section 3 of [Messaging]) and
fields (Section 4). These are minimum recommendations, chosen to be fields (Section 5). These are minimum recommendations, chosen to be
supportable even by implementations with limited resources; it is supportable even by implementations with limited resources; it is
expected that most implementations will choose substantially higher expected that most implementations will choose substantially higher
limits. limits.
A server can reject a message that has a target URI that is too long A server can reject a message that has a target URI that is too long
(Section 9.5.15) or a request payload that is too large (Section 10.5.15) or a request payload that is too large
(Section 9.5.14). Additional status codes related to capacity limits (Section 10.5.14). Additional status codes related to capacity
have been defined by extensions to HTTP [RFC6585]. limits have been defined by extensions to HTTP [RFC6585].
Recipients ought to carefully limit the extent to which they process Recipients ought to carefully limit the extent to which they process
other protocol elements, including (but not limited to) request other protocol elements, including (but not limited to) request
methods, response status phrases, field names, numeric values, and methods, response status phrases, field names, numeric values, and
body chunks. Failure to limit such processing can result in buffer body chunks. Failure to limit such processing can result in buffer
overflows, arithmetic overflows, or increased vulnerability to overflows, arithmetic overflows, or increased vulnerability to
denial-of-service attacks. denial-of-service attacks.
11.6. Disclosure of Personal Information 12.6. Disclosure of Personal Information
Clients are often privy to large amounts of personal information, Clients are often privy to large amounts of personal information,
including both information provided by the user to interact with including both information provided by the user to interact with
resources (e.g., the user's name, location, mail address, passwords, resources (e.g., the user's name, location, mail address, passwords,
encryption keys, etc.) and information about the user's browsing encryption keys, etc.) and information about the user's browsing
activity over time (e.g., history, bookmarks, etc.). Implementations activity over time (e.g., history, bookmarks, etc.). Implementations
need to prevent unintentional disclosure of personal information. need to prevent unintentional disclosure of personal information.
11.7. Privacy of Server Log Information 12.7. Privacy of Server Log Information
A server is in the position to save personal data about a user's A server is in the position to save personal data about a user's
requests over time, which might identify their reading patterns or requests over time, which might identify their reading patterns or
subjects of interest. In particular, log information gathered at an subjects of interest. In particular, log information gathered at an
intermediary often contains a history of user agent interaction, intermediary often contains a history of user agent interaction,
across a multitude of sites, that can be traced to individual users. across a multitude of sites, that can be traced to individual users.
HTTP log information is confidential in nature; its handling is often HTTP log information is confidential in nature; its handling is often
constrained by laws and regulations. Log information needs to be constrained by laws and regulations. Log information needs to be
securely stored and appropriate guidelines followed for its analysis. securely stored and appropriate guidelines followed for its analysis.
skipping to change at page 169, line 23 skipping to change at page 171, line 23
characteristics. As such, access traces that are keyed to a specific characteristics. As such, access traces that are keyed to a specific
client are unsafe to publish even if the key is pseudonymous. client are unsafe to publish even if the key is pseudonymous.
To minimize the risk of theft or accidental publication, log To minimize the risk of theft or accidental publication, log
information ought to be purged of personally identifiable information ought to be purged of personally identifiable
information, including user identifiers, IP addresses, and user- information, including user identifiers, IP addresses, and user-
provided query parameters, as soon as that information is no longer provided query parameters, as soon as that information is no longer
necessary to support operational needs for security, auditing, or necessary to support operational needs for security, auditing, or
fraud control. fraud control.
11.8. Disclosure of Sensitive Information in URIs 12.8. Disclosure of Sensitive Information in URIs
URIs are intended to be shared, not secured, even when they identify URIs are intended to be shared, not secured, even when they identify
secure resources. URIs are often shown on displays, added to secure resources. URIs are often shown on displays, added to
templates when a page is printed, and stored in a variety of templates when a page is printed, and stored in a variety of
unprotected bookmark lists. It is therefore unwise to include unprotected bookmark lists. It is therefore unwise to include
information within a URI that is sensitive, personally identifiable, information within a URI that is sensitive, personally identifiable,
or a risk to disclose. or a risk to disclose.
Authors of services ought to avoid GET-based forms for the submission Authors of services ought to avoid GET-based forms for the submission
of sensitive data because that data will be placed in the target URI. of sensitive data because that data will be placed in the target URI.
Many existing servers, proxies, and user agents log or display the Many existing servers, proxies, and user agents log or display the
target URI in places where it might be visible to third parties. target URI in places where it might be visible to third parties.
Such services ought to use POST-based form submission instead. Such services ought to use POST-based form submission instead.
Since the Referer header field tells a target site about the context Since the Referer header field tells a target site about the context
that resulted in a request, it has the potential to reveal that resulted in a request, it has the potential to reveal
information about the user's immediate browsing history and any information about the user's immediate browsing history and any
personal information that might be found in the referring resource's personal information that might be found in the referring resource's
URI. Limitations on the Referer header field are described in URI. Limitations on the Referer header field are described in
Section 8.6.2 to address some of its security considerations. Section 9.6.2 to address some of its security considerations.
11.9. Disclosure of Fragment after Redirects 12.9. Disclosure of Fragment after Redirects
Although fragment identifiers used within URI references are not sent Although fragment identifiers used within URI references are not sent
in requests, implementers ought to be aware that they will be visible in requests, implementers ought to be aware that they will be visible
to the user agent and any extensions or scripts running as a result to the user agent and any extensions or scripts running as a result
of the response. In particular, when a redirect occurs and the of the response. In particular, when a redirect occurs and the
original request's fragment identifier is inherited by the new original request's fragment identifier is inherited by the new
reference in Location (Section 10.1.2), this might have the effect of reference in Location (Section 11.1.2), this might have the effect of
disclosing one site's fragment to another site. If the first site disclosing one site's fragment to another site. If the first site
uses personal information in fragments, it ought to ensure that uses personal information in fragments, it ought to ensure that
redirects to other sites include a (possibly empty) fragment redirects to other sites include a (possibly empty) fragment
component in order to block that inheritance. component in order to block that inheritance.
11.10. Disclosure of Product Information 12.10. Disclosure of Product Information
The User-Agent (Section 8.6.3), Via (Section 5.7.1), and Server The User-Agent (Section 9.6.3), Via (Section 6.7.1), and Server
(Section 10.4.3) header fields often reveal information about the (Section 11.4.3) header fields often reveal information about the
respective sender's software systems. In theory, this can make it respective sender's software systems. In theory, this can make it
easier for an attacker to exploit known security holes; in practice, easier for an attacker to exploit known security holes; in practice,
attackers tend to try all potential holes regardless of the apparent attackers tend to try all potential holes regardless of the apparent
software versions being used. software versions being used.
Proxies that serve as a portal through a network firewall ought to Proxies that serve as a portal through a network firewall ought to
take special precautions regarding the transfer of header information take special precautions regarding the transfer of header information
that might identify hosts behind the firewall. The Via header field that might identify hosts behind the firewall. The Via header field
allows intermediaries to replace sensitive machine names with allows intermediaries to replace sensitive machine names with
pseudonyms. pseudonyms.
11.11. Browser Fingerprinting 12.11. Browser Fingerprinting
Browser fingerprinting is a set of techniques for identifying a Browser fingerprinting is a set of techniques for identifying a
specific user agent over time through its unique set of specific user agent over time through its unique set of
characteristics. These characteristics might include information characteristics. These characteristics might include information
related to its TCP behavior, feature capabilities, and scripting related to its TCP behavior, feature capabilities, and scripting
environment, though of particular interest here is the set of unique environment, though of particular interest here is the set of unique
characteristics that might be communicated via HTTP. Fingerprinting characteristics that might be communicated via HTTP. Fingerprinting
is considered a privacy concern because it enables tracking of a user is considered a privacy concern because it enables tracking of a user
agent's behavior over time ([Bujlow]) without the corresponding agent's behavior over time ([Bujlow]) without the corresponding
controls that the user might have over other forms of data collection controls that the user might have over other forms of data collection
skipping to change at page 171, line 5 skipping to change at page 173, line 5
desired by the user. Likewise, Cookie header fields are deliberately desired by the user. Likewise, Cookie header fields are deliberately
designed to enable re-identification, so fingerprinting concerns only designed to enable re-identification, so fingerprinting concerns only
apply to situations where cookies are disabled or restricted by the apply to situations where cookies are disabled or restricted by the
user agent's configuration. user agent's configuration.
The User-Agent header field might contain enough information to The User-Agent header field might contain enough information to
uniquely identify a specific device, usually when combined with other uniquely identify a specific device, usually when combined with other
characteristics, particularly if the user agent sends excessive characteristics, particularly if the user agent sends excessive
details about the user's system or extensions. However, the source details about the user's system or extensions. However, the source
of unique information that is least expected by users is proactive of unique information that is least expected by users is proactive
negotiation (Section 8.4), including the Accept, Accept-Charset, negotiation (Section 9.4), including the Accept, Accept-Charset,
Accept-Encoding, and Accept-Language header fields. Accept-Encoding, and Accept-Language header fields.
In addition to the fingerprinting concern, detailed use of the In addition to the fingerprinting concern, detailed use of the
Accept-Language header field can reveal information the user might Accept-Language header field can reveal information the user might
consider to be of a private nature. For example, understanding a consider to be of a private nature. For example, understanding a
given language set might be strongly correlated to membership in a given language set might be strongly correlated to membership in a
particular ethnic group. An approach that limits such loss of particular ethnic group. An approach that limits such loss of
privacy would be for a user agent to omit the sending of Accept- privacy would be for a user agent to omit the sending of Accept-
Language except for sites that have been whitelisted, perhaps via Language except for sites that have been whitelisted, perhaps via
interaction after detecting a Vary header field that indicates interaction after detecting a Vary header field that indicates
language negotiation might be useful. language negotiation might be useful.
In environments where proxies are used to enhance privacy, user In environments where proxies are used to enhance privacy, user
agents ought to be conservative in sending proactive negotiation agents ought to be conservative in sending proactive negotiation
header fields. General-purpose user agents that provide a high header fields. General-purpose user agents that provide a high
degree of header field configurability ought to inform users about degree of header field configurability ought to inform users about
the loss of privacy that might result if too much detail is provided. the loss of privacy that might result if too much detail is provided.
As an extreme privacy measure, proxies could filter the proactive As an extreme privacy measure, proxies could filter the proactive
negotiation header fields in relayed requests. negotiation header fields in relayed requests.
11.12. Validator Retention 12.12. Validator Retention
The validators defined by this specification are not intended to The validators defined by this specification are not intended to
ensure the validity of a representation, guard against malicious ensure the validity of a representation, guard against malicious
changes, or detect man-in-the-middle attacks. At best, they enable changes, or detect man-in-the-middle attacks. At best, they enable
more efficient cache updates and optimistic concurrent writes when more efficient cache updates and optimistic concurrent writes when
all participants are behaving nicely. At worst, the conditions will all participants are behaving nicely. At worst, the conditions will
fail and the client will receive a response that is no more harmful fail and the client will receive a response that is no more harmful
than an HTTP exchange without conditional requests. than an HTTP exchange without conditional requests.
An entity-tag can be abused in ways that create privacy risks. For An entity-tag can be abused in ways that create privacy risks. For
skipping to change at page 172, line 5 skipping to change at page 174, line 5
entity-tag that is unique to the user or user agent, send it in a entity-tag that is unique to the user or user agent, send it in a
cacheable response with a long freshness time, and then read that cacheable response with a long freshness time, and then read that
entity-tag in later conditional requests as a means of re-identifying entity-tag in later conditional requests as a means of re-identifying
that user or user agent. Such an identifying tag would become a that user or user agent. Such an identifying tag would become a
persistent identifier for as long as the user agent retained the persistent identifier for as long as the user agent retained the
original cache entry. User agents that cache representations ought original cache entry. User agents that cache representations ought
to ensure that the cache is cleared or replaced whenever the user to ensure that the cache is cleared or replaced whenever the user
performs privacy-maintaining actions, such as clearing stored cookies performs privacy-maintaining actions, such as clearing stored cookies
or changing to a private browsing mode. or changing to a private browsing mode.
11.13. Denial-of-Service Attacks Using Range 12.13. Denial-of-Service Attacks Using Range
Unconstrained multiple range requests are susceptible to denial-of- Unconstrained multiple range requests are susceptible to denial-of-
service attacks because the effort required to request many service attacks because the effort required to request many
overlapping ranges of the same data is tiny compared to the time, overlapping ranges of the same data is tiny compared to the time,
memory, and bandwidth consumed by attempting to serve the requested memory, and bandwidth consumed by attempting to serve the requested
data in many parts. Servers ought to ignore, coalesce, or reject data in many parts. Servers ought to ignore, coalesce, or reject
egregious range requests, such as requests for more than two egregious range requests, such as requests for more than two
overlapping ranges or for many small ranges in a single set, overlapping ranges or for many small ranges in a single set,
particularly when the ranges are requested out of order for no particularly when the ranges are requested out of order for no
apparent reason. Multipart range requests are not designed to apparent reason. Multipart range requests are not designed to
support random access. support random access.
11.14. Authentication Considerations 12.14. Authentication Considerations
Everything about the topic of HTTP authentication is a security Everything about the topic of HTTP authentication is a security
consideration, so the list of considerations below is not exhaustive. consideration, so the list of considerations below is not exhaustive.
Furthermore, it is limited to security considerations regarding the Furthermore, it is limited to security considerations regarding the
authentication framework, in general, rather than discussing all of authentication framework, in general, rather than discussing all of
the potential considerations for specific authentication schemes the potential considerations for specific authentication schemes
(which ought to be documented in the specifications that define those (which ought to be documented in the specifications that define those
schemes). Various organizations maintain topical information and schemes). Various organizations maintain topical information and
links to current research on Web application security (e.g., links to current research on Web application security (e.g.,
[OWASP]), including common pitfalls for implementing and using the [OWASP]), including common pitfalls for implementing and using the
authentication schemes found in practice. authentication schemes found in practice.
11.14.1. Confidentiality of Credentials 12.14.1. Confidentiality of Credentials
The HTTP authentication framework does not define a single mechanism The HTTP authentication framework does not define a single mechanism
for maintaining the confidentiality of credentials; instead, each for maintaining the confidentiality of credentials; instead, each
authentication scheme defines how the credentials are encoded prior authentication scheme defines how the credentials are encoded prior
to transmission. While this provides flexibility for the development to transmission. While this provides flexibility for the development
of future authentication schemes, it is inadequate for the protection of future authentication schemes, it is inadequate for the protection
of existing schemes that provide no confidentiality on their own, or of existing schemes that provide no confidentiality on their own, or
that do not sufficiently protect against replay attacks. that do not sufficiently protect against replay attacks.
Furthermore, if the server expects credentials that are specific to Furthermore, if the server expects credentials that are specific to
each individual user, the exchange of those credentials will have the each individual user, the exchange of those credentials will have the
skipping to change at page 173, line 7 skipping to change at page 175, line 7
HTTP depends on the security properties of the underlying transport- HTTP depends on the security properties of the underlying transport-
or session-level connection to provide confidential transmission of or session-level connection to provide confidential transmission of
fields. In other words, if a server limits access to authenticated fields. In other words, if a server limits access to authenticated
users using this framework, the server needs to ensure that the users using this framework, the server needs to ensure that the
connection is properly secured in accordance with the nature of the connection is properly secured in accordance with the nature of the
authentication scheme used. For example, services that depend on authentication scheme used. For example, services that depend on
individual user authentication often require a connection to be individual user authentication often require a connection to be
secured with TLS ("Transport Layer Security", [RFC8446]) prior to secured with TLS ("Transport Layer Security", [RFC8446]) prior to
exchanging any credentials. exchanging any credentials.
11.14.2. Credentials and Idle Clients 12.14.2. Credentials and Idle Clients
Existing HTTP clients and user agents typically retain authentication Existing HTTP clients and user agents typically retain authentication
information indefinitely. HTTP does not provide a mechanism for the information indefinitely. HTTP does not provide a mechanism for the
origin server to direct clients to discard these cached credentials, origin server to direct clients to discard these cached credentials,
since the protocol has no awareness of how credentials are obtained since the protocol has no awareness of how credentials are obtained
or managed by the user agent. The mechanisms for expiring or or managed by the user agent. The mechanisms for expiring or
revoking credentials can be specified as part of an authentication revoking credentials can be specified as part of an authentication
scheme definition. scheme definition.
Circumstances under which credential caching can interfere with the Circumstances under which credential caching can interfere with the
skipping to change at page 173, line 33 skipping to change at page 175, line 33
o Applications that include a session termination indication (such o Applications that include a session termination indication (such
as a "logout" or "commit" button on a page) after which the server as a "logout" or "commit" button on a page) after which the server
side of the application "knows" that there is no further reason side of the application "knows" that there is no further reason
for the client to retain the credentials. for the client to retain the credentials.
User agents that cache credentials are encouraged to provide a User agents that cache credentials are encouraged to provide a
readily accessible mechanism for discarding cached credentials under readily accessible mechanism for discarding cached credentials under
user control. user control.
11.14.3. Protection Spaces 12.14.3. Protection Spaces
Authentication schemes that solely rely on the "realm" mechanism for Authentication schemes that solely rely on the "realm" mechanism for
establishing a protection space will expose credentials to all establishing a protection space will expose credentials to all
resources on an origin server. Clients that have successfully made resources on an origin server. Clients that have successfully made
authenticated requests with a resource can use the same authenticated requests with a resource can use the same
authentication credentials for other resources on the same origin authentication credentials for other resources on the same origin
server. This makes it possible for a different resource to harvest server. This makes it possible for a different resource to harvest
authentication credentials for other resources. authentication credentials for other resources.
This is of particular concern when an origin server hosts resources This is of particular concern when an origin server hosts resources
for multiple parties under the same canonical root URI for multiple parties under the same canonical root URI
(Section 8.5.2). Possible mitigation strategies include restricting (Section 9.5.2). Possible mitigation strategies include restricting
direct access to authentication credentials (i.e., not making the direct access to authentication credentials (i.e., not making the
content of the Authorization request header field available), and content of the Authorization request header field available), and
separating protection spaces by using a different host name (or port separating protection spaces by using a different host name (or port
number) for each party. number) for each party.
11.14.4. Additional Response Fields 12.14.4. Additional Response Fields
Adding information to responses that are sent over an unencrypted Adding information to responses that are sent over an unencrypted
channel can affect security and privacy. The presence of the channel can affect security and privacy. The presence of the
Authentication-Info and Proxy-Authentication-Info header fields alone Authentication-Info and Proxy-Authentication-Info header fields alone
indicates that HTTP authentication is in use. Additional information indicates that HTTP authentication is in use. Additional information
could be exposed by the contents of the authentication-scheme could be exposed by the contents of the authentication-scheme
specific parameters; this will have to be considered in the specific parameters; this will have to be considered in the
definitions of these schemes. definitions of these schemes.
12. IANA Considerations 13. IANA Considerations
The change controller for the following registrations is: "IETF The change controller for the following registrations is: "IETF
(iesg@ietf.org) - Internet Engineering Task Force". (iesg@ietf.org) - Internet Engineering Task Force".
12.1. URI Scheme Registration 13.1. URI Scheme Registration
Please update the registry of URI Schemes [BCP35] at Please update the registry of URI Schemes [BCP35] at
<https://www.iana.org/assignments/uri-schemes/> with the permanent <https://www.iana.org/assignments/uri-schemes/> with the permanent
schemes listed in the first table of Section 2.5. schemes listed in the first table of Section 2.5.
12.2. Method Registration 13.2. Method Registration
Please update the "Hypertext Transfer Protocol (HTTP) Method Please update the "Hypertext Transfer Protocol (HTTP) Method
Registry" at <https://www.iana.org/assignments/http-methods> with the Registry" at <https://www.iana.org/assignments/http-methods> with the
registration procedure of Section 7.4.1 and the method names registration procedure of Section 8.4.1 and the method names
summarized in the table of Section 7.2. summarized in the table of Section 8.2.
12.3. Status Code Registration Furthermore, the method name "*" is reserved, since using that name
as HTTP method name might conflict with special semantics in fields
such as "Access-Control-Request-Method". Thus, please add the entry
below to the registry:
Method Name: *
Safe: no
Idempotent: no
Reference: Section 13.2
13.3. Status Code Registration
Please update the "Hypertext Transfer Protocol (HTTP) Status Code Please update the "Hypertext Transfer Protocol (HTTP) Status Code
Registry" at <https://www.iana.org/assignments/http-status-codes> Registry" at <https://www.iana.org/assignments/http-status-codes>
with the registration procedure of Section 9.7.1 and the status code with the registration procedure of Section 10.7.1 and the status code
values summarized in the table of Section 9.1. values summarized in the table of Section 10.1.
Additionally, please update the following entry in the Hypertext Additionally, please update the following entry in the Hypertext
Transfer Protocol (HTTP) Status Code Registry: Transfer Protocol (HTTP) Status Code Registry:
Value: 418 Value: 418
Description: (Unused) Description: (Unused)
Reference Section 9.5.19 Reference Section 10.5.19
12.4. HTTP Field Name Registration 13.4. HTTP Field Name Registration
Please create a new registry as outlined in Section 4.3.2. Please create a new registry as outlined in Section 5.3.2.
After creating the registry, all entries in the Permanent and After creating the registry, all entries in the Permanent and
Provisional Message Header Registries with the protocol 'http' are to Provisional Message Header Registries with the protocol 'http' are to
be moved to it, with the following changes applied: be moved to it, with the following changes applied:
1. The 'Applicable Protocol' field is to be omitted. 1. The 'Applicable Protocol' field is to be omitted.
2. Entries with a status of 'standard', 'experimental', 'reserved', 2. Entries with a status of 'standard', 'experimental', 'reserved',
or 'informational' are to have a status of 'permanent'. or 'informational' are to have a status of 'permanent'.
skipping to change at page 175, line 31 skipping to change at page 177, line 40
4. Permanent entries without a status (after confirmation that the 4. Permanent entries without a status (after confirmation that the
registration document did not define one) will have a status of registration document did not define one) will have a status of
'provisional'. The Expert(s) can choose to update their status 'provisional'. The Expert(s) can choose to update their status
if there is evidence that another is more appropriate. if there is evidence that another is more appropriate.
Please annotate the Permanent and Provisional Message Header Please annotate the Permanent and Provisional Message Header
registries to indicate that HTTP field name registrations have moved, registries to indicate that HTTP field name registrations have moved,
with an appropriate link. with an appropriate link.
After that is complete, please update the new registry with the field After that is complete, please update the new registry with the field
names listed in the table of Section 4.8. names listed in the table of Section 5.8.
Finally, please update the "Content-MD5" entry in the new registry to Finally, please update the "Content-MD5" entry in the new registry to
have a status of 'obsoleted' with references to Section 14.15 of have a status of 'obsoleted' with references to Section 14.15 of
[RFC2616] (for the definition of the header field) and Appendix B of [RFC2616] (for the definition of the header field) and Appendix B of
[RFC7231] (which removed the field definition from the updated [RFC7231] (which removed the field definition from the updated
specification). specification).
12.5. Authentication Scheme Registration 13.5. Authentication Scheme Registration
Please update the "Hypertext Transfer Protocol (HTTP) Authentication Please update the "Hypertext Transfer Protocol (HTTP) Authentication
Scheme Registry" at <https://www.iana.org/assignments/http- Scheme Registry" at <https://www.iana.org/assignments/http-
authschemes> with the registration procedure of Section 8.5.5.1. No authschemes> with the registration procedure of Section 9.5.5.1. No
authentication schemes are defined in this document. authentication schemes are defined in this document.
12.6. Content Coding Registration 13.6. Content Coding Registration
Please update the "HTTP Content Coding Registry" at Please update the "HTTP Content Coding Registry" at
<https://www.iana.org/assignments/http-parameters/> with the <https://www.iana.org/assignments/http-parameters/> with the
registration procedure of Section 6.1.2.4 and the content coding registration procedure of Section 7.1.2.4 and the content coding
names summarized in the table of Section 6.1.2. names summarized in the table of Section 7.1.2.
12.7. Range Unit Registration 13.7. Range Unit Registration
Please update the "HTTP Range Unit Registry" at Please update the "HTTP Range Unit Registry" at
<https://www.iana.org/assignments/http-parameters/> with the <https://www.iana.org/assignments/http-parameters/> with the
registration procedure of Section 6.1.4.4 and the range unit names registration procedure of Section 7.1.4.4 and the range unit names
summarized in the table of Section 6.1.4. summarized in the table of Section 7.1.4.
12.8. Media Type Registration 13.8. Media Type Registration
Please update the "Media Types" registry at Please update the "Media Types" registry at
<https://www.iana.org/assignments/media-types> with the registration <https://www.iana.org/assignments/media-types> with the registration
information in Section 6.3.5 for the media type "multipart/ information in Section 7.3.5 for the media type "multipart/
byteranges". byteranges".
12.9. Port Registration 13.9. Port Registration
Please update the "Service Name and Transport Protocol Port Number" Please update the "Service Name and Transport Protocol Port Number"
registry at <https://www.iana.org/assignments/service-names-port- registry at <https://www.iana.org/assignments/service-names-port-
numbers/> for the services on ports 80 and 443 that use UDP or TCP numbers/> for the services on ports 80 and 443 that use UDP or TCP
to: to:
1. use this document as "Reference", and 1. use this document as "Reference", and
2. when currently unspecified, set "Assignee" to "IESG" and 2. when currently unspecified, set "Assignee" to "IESG" and
"Contact" to "IETF_Chair". "Contact" to "IETF_Chair".
13. References 14. References
13.1. Normative References 14.1. Normative References
[Caching] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [Caching] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Caching", draft-ietf-httpbis-cache-08 (work in Ed., "HTTP Caching", draft-ietf-httpbis-cache-09 (work in
progress), May 2020. progress), July 2020.
[Messaging] [Messaging]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP/1.1 Messaging", draft-ietf-httpbis-messaging-08 Ed., "HTTP/1.1 Messaging", draft-ietf-httpbis-messaging-09
(work in progress), May 2020. (work in progress), July 2020.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981, RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>. <https://www.rfc-editor.org/info/rfc793>.
[RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data Format [RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data Format
Specification version 3.3", RFC 1950, Specification version 3.3", RFC 1950,
DOI 10.17487/RFC1950, May 1996, DOI 10.17487/RFC1950, May 1996,
<https://www.rfc-editor.org/info/rfc1950>. <https://www.rfc-editor.org/info/rfc1950>.
skipping to change at page 178, line 31 skipping to change at page 180, line 42
[USASCII] American National Standards Institute, "Coded Character [USASCII] American National Standards Institute, "Coded Character
Set -- 7-bit American Standard Code for Information Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986. Interchange", ANSI X3.4, 1986.
[Welch] Welch, T., "A Technique for High-Performance Data [Welch] Welch, T., "A Technique for High-Performance Data
Compression", IEEE Computer 17(6), Compression", IEEE Computer 17(6),
DOI 10.1109/MC.1984.1659158, June 1984, DOI 10.1109/MC.1984.1659158, June 1984,
<https://ieeexplore.ieee.org/document/1659158/>. <https://ieeexplore.ieee.org/document/1659158/>.
13.2. Informative References 14.2. Informative References
[BCP13] Freed, N., Klensin, J., and T. Hansen, "Media Type [BCP13] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, Specifications and Registration Procedures", BCP 13,
RFC 6838, January 2013, RFC 6838, January 2013,
<https://www.rfc-editor.org/info/bcp13>. <https://www.rfc-editor.org/info/bcp13>.
[BCP178] Saint-Andre, P., Crocker, D., and M. Nottingham, [BCP178] Saint-Andre, P., Crocker, D., and M. Nottingham,
"Deprecating the "X-" Prefix and Similar Constructs in "Deprecating the "X-" Prefix and Similar Constructs in
Application Protocols", BCP 178, RFC 6648, June 2012, Application Protocols", BCP 178, RFC 6648, June 2012,
<https://www.rfc-editor.org/info/bcp178>. <https://www.rfc-editor.org/info/bcp178>.
skipping to change at page 182, line 38 skipping to change at page 185, line 5
[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Authentication", RFC 7235, Protocol (HTTP/1.1): Authentication", RFC 7235,
DOI 10.17487/RFC7235, June 2014, DOI 10.17487/RFC7235, June 2014,
<https://www.rfc-editor.org/info/rfc7235>. <https://www.rfc-editor.org/info/rfc7235>.
[RFC7538] Reschke, J., "The Hypertext Transfer Protocol Status Code [RFC7538] Reschke, J., "The Hypertext Transfer Protocol Status Code
308 (Permanent Redirect)", RFC 7538, DOI 10.17487/RFC7538, 308 (Permanent Redirect)", RFC 7538, DOI 10.17487/RFC7538,
April 2015, <https://www.rfc-editor.org/info/rfc7538>. April 2015, <https://www.rfc-editor.org/info/rfc7538>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC7578] Masinter, L., "Returning Values from Forms: multipart/ [RFC7578] Masinter, L., "Returning Values from Forms: multipart/
form-data", RFC 7578, DOI 10.17487/RFC7578, July 2015, form-data", RFC 7578, DOI 10.17487/RFC7578, July 2015,
<https://www.rfc-editor.org/info/rfc7578>. <https://www.rfc-editor.org/info/rfc7578>.
[RFC7615] Reschke, J., "HTTP Authentication-Info and Proxy- [RFC7615] Reschke, J., "HTTP Authentication-Info and Proxy-
Authentication-Info Response Header Fields", RFC 7615, Authentication-Info Response Header Fields", RFC 7615,
DOI 10.17487/RFC7615, September 2015, DOI 10.17487/RFC7615, September 2015,
<https://www.rfc-editor.org/info/rfc7615>. <https://www.rfc-editor.org/info/rfc7615>.
[RFC7616] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP [RFC7616] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP
skipping to change at page 184, line 8 skipping to change at page 187, line 8
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[Sniffing] [Sniffing]
WHATWG, "MIME Sniffing", WHATWG, "MIME Sniffing",
<https://mimesniff.spec.whatwg.org>. <https://mimesniff.spec.whatwg.org>.
Appendix A. Collected ABNF Appendix A. Collected ABNF
In the collected ABNF below, list rules are expanded as per In the collected ABNF below, list rules are expanded as per
Section 4.5. Section 5.5.1.
Accept = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [ Accept = [ ( media-range [ accept-params ] ) *( OWS "," OWS (
OWS ( media-range [ accept-params ] ) ] ) ] media-range [ accept-params ] ) ) ]
Accept-Charset = *( "," OWS ) ( ( charset / "*" ) [ weight ] ) *( OWS Accept-Charset = ( ( charset / "*" ) [ weight ] ) *( OWS "," OWS ( (
"," [ OWS ( ( charset / "*" ) [ weight ] ) ] ) charset / "*" ) [ weight ] ) )
Accept-Encoding = [ ( "," / ( codings [ weight ] ) ) *( OWS "," [ OWS Accept-Encoding = [ ( codings [ weight ] ) *( OWS "," OWS ( codings [
( codings [ weight ] ) ] ) ] weight ] ) ) ]
Accept-Language = *( "," OWS ) ( language-range [ weight ] ) *( OWS Accept-Language = ( language-range [ weight ] ) *( OWS "," OWS (
"," [ OWS ( language-range [ weight ] ) ] ) language-range [ weight ] ) )
Accept-Ranges = acceptable-ranges Accept-Ranges = acceptable-ranges
Allow = [ method ] *( OWS "," OWS [ method ] ) Allow = [ method *( OWS "," OWS method ) ]
Authentication-Info = [ auth-param ] *( OWS "," OWS [ auth-param ] ) Authentication-Info = [ auth-param *( OWS "," OWS auth-param ) ]
Authorization = credentials Authorization = credentials
BWS = OWS BWS = OWS
Content-Encoding = [ content-coding ] *( OWS "," OWS [ content-coding Content-Encoding = content-coding *( OWS "," OWS content-coding )
] ) Content-Language = language-tag *( OWS "," OWS language-tag )
Content-Language = [ language-tag ] *( OWS "," OWS [ language-tag ]
)
Content-Length = 1*DIGIT Content-Length = 1*DIGIT
Content-Location = absolute-URI / partial-URI Content-Location = absolute-URI / partial-URI
Content-Range = range-unit SP ( range-resp / unsatisfied-range ) Content-Range = range-unit SP ( range-resp / unsatisfied-range )
Content-Type = media-type Content-Type = media-type
Date = HTTP-date Date = HTTP-date
ETag = entity-tag ETag = entity-tag
Expect = "100-continue" Expect = "100-continue"
From = mailbox From = mailbox
GMT = %x47.4D.54 ; GMT GMT = %x47.4D.54 ; GMT
HTTP-date = IMF-fixdate / obs-date HTTP-date = IMF-fixdate / obs-date
Host = uri-host [ ":" port ] Host = uri-host [ ":" port ]
IMF-fixdate = day-name "," SP date1 SP time-of-day SP GMT IMF-fixdate = day-name "," SP date1 SP time-of-day SP GMT
If-Match = "*" / ( [ entity-tag ] *( OWS "," OWS [ entity-tag ] ) ) If-Match = "*" / ( entity-tag *( OWS "," OWS entity-tag ) )
If-Modified-Since = HTTP-date If-Modified-Since = HTTP-date
If-None-Match = "*" / ( [ entity-tag ] *( OWS "," OWS [ entity-tag ] If-None-Match = "*" / ( entity-tag *( OWS "," OWS entity-tag ) )
) )
If-Range = entity-tag / HTTP-date If-Range = entity-tag / HTTP-date
If-Unmodified-Since = HTTP-date If-Unmodified-Since = HTTP-date
Last-Modified = HTTP-date Last-Modified = HTTP-date
Location = URI-reference Location = URI-reference
Max-Forwards = 1*DIGIT Max-Forwards = 1*DIGIT
OWS = *( SP / HTAB ) OWS = *( SP / HTAB )
Proxy-Authenticate = [ challenge ] *( OWS "," OWS [ challenge ] ) Proxy-Authenticate = challenge *( OWS "," OWS challenge )
Proxy-Authentication-Info = [ auth-param ] *( OWS "," OWS [ Proxy-Authentication-Info = [ auth-param *( OWS "," OWS auth-param )
auth-param ] ) ]
Proxy-Authorization = credentials Proxy-Authorization = credentials
RWS = 1*( SP / HTAB ) RWS = 1*( SP / HTAB )
Range = ranges-specifier Range = ranges-specifier
Referer = absolute-URI / partial-URI Referer = absolute-URI / partial-URI
Retry-After = HTTP-date / delay-seconds Retry-After = HTTP-date / delay-seconds
Server = product *( RWS ( product / comment ) ) Server = product *( RWS ( product / comment ) )
Trailer = [ field-name ] *( OWS "," OWS [ field-name ] ) Trailer = field-name *( OWS "," OWS field-name )
URI-reference = <URI-reference, see [RFC3986], Section 4.1> URI-reference = <URI-reference, see [RFC3986], Section 4.1>
User-Agent = product *( RWS ( product / comment ) ) User-Agent = product *( RWS ( product / comment ) )
Vary = "*" / ( [ field-name ] *( OWS "," OWS [ field-name ] ) ) Vary = ( "*" / field-name ) *( OWS "," OWS ( "*" / field-name ) )
Via = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment Via = ( received-protocol RWS received-by [ RWS comment ] ) *( OWS
] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS "," OWS ( received-protocol RWS received-by [ RWS comment ] ) )
comment ] ) ] )
WWW-Authenticate = [ challenge ] *( OWS "," OWS [ challenge ] ) WWW-Authenticate = challenge *( OWS "," OWS challenge )
absolute-URI = <absolute-URI, see [RFC3986], Section 4.3> absolute-URI = <absolute-URI, see [RFC3986], Section 4.3>
absolute-path = 1*( "/" segment ) absolute-path = 1*( "/" segment )
accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ] accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
accept-params = weight *accept-ext accept-params = weight *accept-ext
acceptable-ranges = ( [ range-unit ] *( OWS "," OWS [ range-unit ] ) acceptable-ranges = ( range-unit *( OWS "," OWS range-unit ) ) /
) / "none" "none"
asctime-date = day-name SP date3 SP time-of-day SP year asctime-date = day-name SP date3 SP time-of-day SP year
auth-param = token BWS "=" BWS ( token / quoted-string ) auth-param = token BWS "=" BWS ( token / quoted-string )
auth-scheme = token auth-scheme = token
authority = <authority, see [RFC3986], Section 3.2> authority = <authority, see [RFC3986], Section 3.2>
challenge = auth-scheme [ 1*SP ( token68 / ( [ auth-param ] *( OWS challenge = auth-scheme [ 1*SP ( token68 / [ auth-param *( OWS ","
"," OWS [ auth-param ] ) ) ) ] OWS auth-param ) ] ) ]
charset = token charset = token
codings = content-coding / "identity" / "*" codings = content-coding / "identity" / "*"
comment = "(" *( ctext / quoted-pair / comment ) ")" comment = "(" *( ctext / quoted-pair / comment ) ")"
complete-length = 1*DIGIT complete-length = 1*DIGIT
content-coding = token content-coding = token
credentials = auth-scheme [ 1*SP ( token68 / ( [ auth-param ] *( OWS credentials = auth-scheme [ 1*SP ( token68 / [ auth-param *( OWS ","
"," OWS [ auth-param ] ) ) ) ] OWS auth-param ) ] ) ]
ctext = HTAB / SP / %x21-27 ; '!'-''' ctext = HTAB / SP / %x21-27 ; '!'-'''
/ %x2A-5B ; '*'-'[' / %x2A-5B ; '*'-'['
/ %x5D-7E ; ']'-'~' / %x5D-7E ; ']'-'~'
/ obs-text / obs-text
date1 = day SP month SP year date1 = day SP month SP year
date2 = day "-" month "-" 2DIGIT date2 = day "-" month "-" 2DIGIT
date3 = month SP ( 2DIGIT / ( SP DIGIT ) ) date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
day = 2DIGIT day = 2DIGIT
day-name = %x4D.6F.6E ; Mon day-name = %x4D.6F.6E ; Mon
skipping to change at page 188, line 4 skipping to change at page 190, line 47
protocol-version = <protocol-version, see [Messaging], Section 9.9> protocol-version = <protocol-version, see [Messaging], Section 9.9>
pseudonym = token pseudonym = token
qdtext = HTAB / SP / "!" / %x23-5B ; '#'-'[' qdtext = HTAB / SP / "!" / %x23-5B ; '#'-'['
/ %x5D-7E ; ']'-'~' / %x5D-7E ; ']'-'~'
/ obs-text / obs-text
query = <query, see [RFC3986], Section 3.4> query = <query, see [RFC3986], Section 3.4>
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text ) quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] ) qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
range-resp = incl-range "/" ( complete-length / "*" ) range-resp = incl-range "/" ( complete-length / "*" )
range-set = [ range-spec ] *( OWS "," OWS [ range-spec ] ) range-set = range-spec *( OWS "," OWS range-spec )
range-spec = int-range / suffix-range / other-range range-spec = int-range / suffix-range / other-range
range-unit = token range-unit = token
ranges-specifier = range-unit "=" range-set ranges-specifier = range-unit "=" range-set
received-by = pseudonym [ ":" port ] received-by = pseudonym [ ":" port ]
received-protocol = [ protocol-name "/" ] protocol-version received-protocol = [ protocol-name "/" ] protocol-version
relative-part = <relative-part, see [RFC3986], Section 4.2> relative-part = <relative-part, see [RFC3986], Section 4.2>
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
second = 2DIGIT second = 2DIGIT
segment = <segment, see [RFC3986], Section 3.3> segment = <segment, see [RFC3986], Section 3.3>
skipping to change at page 188, line 50 skipping to change at page 191, line 46
None yet. None yet.
B.2. Changes from RFC 7230 B.2. Changes from RFC 7230
The sections introducing HTTP's design goals, history, architecture, The sections introducing HTTP's design goals, history, architecture,
conformance criteria, protocol versioning, URIs, message routing, and conformance criteria, protocol versioning, URIs, message routing, and
header fields have been moved here (without substantive change). header fields have been moved here (without substantive change).
"Field value" now refers to the value after multiple instances are "Field value" now refers to the value after multiple instances are
combined with commas -- by far the most common use. To refer to a combined with commas -- by far the most common use. To refer to a
single header line's value, use "field line value". (Section 4) single header line's value, use "field line value". (Section 5)
Trailer field semantics now transcend the specifics of chunked Trailer field semantics now transcend the specifics of chunked
encoding. Use of trailer fields has been further limited to only encoding. Use of trailer fields has been further limited to only
allow generation as a trailer field when the sender knows the field allow generation as a trailer field when the sender knows the field
defines that usage and to only allow merging into the header section defines that usage and to only allow merging into the header section
if the recipient knows the corresponding field definition permits and if the recipient knows the corresponding field definition permits and
defines how to merge. In all other cases, implementations are defines how to merge. In all other cases, implementations are
encouraged to either store the trailer fields separately or discard encouraged to either store the trailer fields separately or discard
them instead of merging. (Section 4.6.2) them instead of merging. (Section 5.6.2)
Made the priority of the absolute form of the request URI over the Made the priority of the absolute form of the request URI over the
Host header by origin servers explicit, to align with proxy handling. Host header by origin servers explicit, to align with proxy handling.
(Section 5.6) (Section 6.6)
The grammar definition for the Via field's "received-by" was expanded The grammar definition for the Via field's "received-by" was expanded
in 7230 due to changes in the URI grammar for host [RFC3986] that are in 7230 due to changes in the URI grammar for host [RFC3986] that are
not desirable for Via. For simplicity, we have removed uri-host from not desirable for Via. For simplicity, we have removed uri-host from
the received-by production because it can be encompassed by the the received-by production because it can be encompassed by the
existing grammar for pseudonym. In particular, this change removed existing grammar for pseudonym. In particular, this change removed
comma from the allowed set of charaters for a host name in received- comma from the allowed set of charaters for a host name in received-
by. (Section 5.7.1) by. (Section 6.7.1)
Added status code 308 (previously defined in [RFC7538]) so that it's Added status code 308 (previously defined in [RFC7538]) so that it's
defined closer to status codes 301, 302, and 307. (Section 9.4.9) defined closer to status codes 301, 302, and 307. (Section 10.4.9)
Added status code 422 (previously defined in Section 11.2 of Added status code 422 (previously defined in Section 11.2 of
[RFC4918]) because of its general applicability. (Section 9.5.20) [RFC4918]) because of its general applicability. (Section 10.5.20)
The description of an origin and authoritative access to origin The description of an origin and authoritative access to origin
servers has been extended for both "http" and "https" URIs to account servers has been extended for both "http" and "https" URIs to account
for alternative services and secured connections that are not for alternative services and secured connections that are not
necessarily based on TCP. (Section 2.5.1, Section 2.5.2, necessarily based on TCP. (Section 2.5.1, Section 2.5.2,
Section 5.2, Section 5.4) Section 6.2, Section 6.4)
B.3. Changes from RFC 7231 B.3. Changes from RFC 7231
Minimum URI lengths to be supported by implementations are now Minimum URI lengths to be supported by implementations are now
recommended. (Section 2.5) recommended. (Section 2.5)
Clarify that control characters in field values are to be rejected or
mapped to SP. (Section 5.4)
The term "effective request URI" has been replaced with "target URI". The term "effective request URI" has been replaced with "target URI".
(Section 5.1) (Section 6.1)
Range units are compared in a case insensitive fashion. Range units are compared in a case insensitive fashion.
(Section 6.1.4) (Section 7.1.4)
Restrictions on client retries have been loosened, to reflect Restrictions on client retries have been loosened, to reflect
implementation behavior. (Section 7.2.2) implementation behavior. (Section 8.2.2)
Clarified that request bodies on GET and DELETE are not
interoperable. (Section 7.3.1, Section 7.3.5)
Clarified that request bodies on GET and DELETE are not
interoperable. (Section 8.3.1, Section 8.3.5)
Removed a superfluous requirement about setting Content-Length from Removed a superfluous requirement about setting Content-Length from
the description of the OPTIONS method. (Section 7.3.7) the description of the OPTIONS method. (Section 8.3.7)
Allow Accept-Encoding in response messages, as introduced by Allow Accept and Accept-Encoding in response messages; the latter was
[RFC7694]. (Section 8.4) introduced by [RFC7694]. (Section 9.4)
B.4. Changes from RFC 7232 B.4. Changes from RFC 7232
Clarify that If-Unmodified-Since doesn't apply to a resource without Clarify that If-Unmodified-Since doesn't apply to a resource without
a concept of modification time. (Section 8.2.6) a concept of modification time. (Section 9.2.6)
B.5. Changes from RFC 7233 B.5. Changes from RFC 7233
Refactored the range-unit and ranges-specifier grammars to simplify Refactored the range-unit and ranges-specifier grammars to simplify
and reduce artificial distinctions between bytes and other and reduce artificial distinctions between bytes and other
(extension) range units, removing the overlapping grammar of other- (extension) range units, removing the overlapping grammar of other-
range-unit by defining range units generically as a token and placing range-unit by defining range units generically as a token and placing
extensions within the scope of a range-spec (other-range). This extensions within the scope of a range-spec (other-range). This
disambiguates the role of list syntax (commas) in all range sets, disambiguates the role of list syntax (commas) in all range sets,
including extension range units, for indicating a range-set of more including extension range units, for indicating a range-set of more
skipping to change at page 192, line 48 skipping to change at page 195, line 46
<https://www.rfc-editor.org/errata/eid4664>) <https://www.rfc-editor.org/errata/eid4664>)
o Resolved erratum 4072, no change needed here o Resolved erratum 4072, no change needed here
(<https://github.com/httpwg/http-core/issues/84>, (<https://github.com/httpwg/http-core/issues/84>,
<https://www.rfc-editor.org/errata/eid4072>) <https://www.rfc-editor.org/errata/eid4072>)
o Clarify DELETE status code suggestions o Clarify DELETE status code suggestions
(<https://github.com/httpwg/http-core/issues/85>, (<https://github.com/httpwg/http-core/issues/85>,
<https://www.rfc-editor.org/errata/eid4436>) <https://www.rfc-editor.org/errata/eid4436>)
o In Section 6.3.4, fix ABNF for "other-range-resp" to use VCHAR o In Section 7.3.4, fix ABNF for "other-range-resp" to use VCHAR
instead of CHAR (<https://github.com/httpwg/http-core/issues/86>, instead of CHAR (<https://github.com/httpwg/http-core/issues/86>,
<https://www.rfc-editor.org/errata/eid4707>) <https://www.rfc-editor.org/errata/eid4707>)
o Resolved erratum 5162, no change needed here o Resolved erratum 5162, no change needed here
(<https://github.com/httpwg/http-core/issues/89>, (<https://github.com/httpwg/http-core/issues/89>,
<https://www.rfc-editor.org/errata/eid5162>) <https://www.rfc-editor.org/errata/eid5162>)
o Replace "response code" with "response status code" and "status- o Replace "response code" with "response status code" and "status-
code" (the ABNF production name from the HTTP/1.1 message format) code" (the ABNF production name from the HTTP/1.1 message format)
by "status code" (<https://github.com/httpwg/http-core/issues/94>, by "status code" (<https://github.com/httpwg/http-core/issues/94>,
<https://www.rfc-editor.org/errata/eid4050>) <https://www.rfc-editor.org/errata/eid4050>)
o Added a missing word in Section 9.4 (<https://github.com/httpwg/ o Added a missing word in Section 10.4 (<https://github.com/httpwg/
http-core/issues/98>, <https://www.rfc-editor.org/errata/eid4452>) http-core/issues/98>, <https://www.rfc-editor.org/errata/eid4452>)
o In Section 4.5, fixed an example that had trailing whitespace o In Section 5.5, fixed an example that had trailing whitespace
where it shouldn't (<https://github.com/httpwg/http-core/ where it shouldn't (<https://github.com/httpwg/http-core/
issues/104>, <https://www.rfc-editor.org/errata/eid4169>) issues/104>, <https://www.rfc-editor.org/errata/eid4169>)
o In Section 9.3.7, remove words that were potentially misleading o In Section 10.3.7, remove words that were potentially misleading
with respect to the relation to the requested ranges with respect to the relation to the requested ranges
(<https://github.com/httpwg/http-core/issues/102>, (<https://github.com/httpwg/http-core/issues/102>,
<https://www.rfc-editor.org/errata/eid4358>) <https://www.rfc-editor.org/errata/eid4358>)
D.4. Since draft-ietf-httpbis-semantics-02 D.4. Since draft-ietf-httpbis-semantics-02
o Included (Proxy-)Auth-Info header field definition from RFC 7615 o Included (Proxy-)Auth-Info header field definition from RFC 7615
(<https://github.com/httpwg/http-core/issues/9>) (<https://github.com/httpwg/http-core/issues/9>)
o In Section 7.3.3, clarify POST caching o In Section 8.3.3, clarify POST caching
(<https://github.com/httpwg/http-core/issues/17>) (<https://github.com/httpwg/http-core/issues/17>)
o Add Section 9.5.19 to reserve the 418 status code o Add Section 10.5.19 to reserve the 418 status code
(<https://github.com/httpwg/http-core/issues/43>) (<https://github.com/httpwg/http-core/issues/43>)
o In Section 2.1 and Section 8.1.1, clarified when a response can be o In Section 2.1 and Section 9.1.1, clarified when a response can be
sent (<https://github.com/httpwg/http-core/issues/82>) sent (<https://github.com/httpwg/http-core/issues/82>)
o In Section 6.1.1.1, explain the difference between the "token" o In Section 7.1.1.1, explain the difference between the "token"
production, the RFC 2978 ABNF for charset names, and the actual production, the RFC 2978 ABNF for charset names, and the actual
registration practice (<https://github.com/httpwg/http-core/ registration practice (<https://github.com/httpwg/http-core/
issues/100>, <https://www.rfc-editor.org/errata/eid4689>) issues/100>, <https://www.rfc-editor.org/errata/eid4689>)
o In Section 2.5, removed the fragment component in the URI scheme o In Section 2.5, removed the fragment component in the URI scheme
definitions as per Section 4.3 of [RFC3986], furthermore moved definitions as per Section 4.3 of [RFC3986], furthermore moved
fragment discussion into a separate section fragment discussion into a separate section
(<https://github.com/httpwg/http-core/issues/103>, (<https://github.com/httpwg/http-core/issues/103>,
<https://www.rfc-editor.org/errata/eid4251>, <https://www.rfc- <https://www.rfc-editor.org/errata/eid4251>, <https://www.rfc-
editor.org/errata/eid4252>) editor.org/errata/eid4252>)
o In Section 3.5, add language about minor HTTP version number o In Section 4.2, add language about minor HTTP version number
defaulting (<https://github.com/httpwg/http-core/issues/115>) defaulting (<https://github.com/httpwg/http-core/issues/115>)
o Added Section 9.5.20 for status code 422, previously defined in o Added Section 10.5.20 for status code 422, previously defined in
Section 11.2 of [RFC4918] (<https://github.com/httpwg/http-core/ Section 11.2 of [RFC4918] (<https://github.com/httpwg/http-core/
issues/123>) issues/123>)
o In Section 9.5.17, fixed prose about byte range comparison o In Section 10.5.17, fixed prose about byte range comparison
(<https://github.com/httpwg/http-core/issues/135>, (<https://github.com/httpwg/http-core/issues/135>,
<https://www.rfc-editor.org/errata/eid5474>) <https://www.rfc-editor.org/errata/eid5474>)
o In Section 2.1, explain that request/response correlation is o In Section 2.1, explain that request/response correlation is
version specific (<https://github.com/httpwg/http-core/ version specific (<https://github.com/httpwg/http-core/
issues/145>) issues/145>)
D.5. Since draft-ietf-httpbis-semantics-03 D.5. Since draft-ietf-httpbis-semantics-03
o In Section 9.4.9, include status code 308 from RFC 7538 o In Section 10.4.9, include status code 308 from RFC 7538
(<https://github.com/httpwg/http-core/issues/3>) (<https://github.com/httpwg/http-core/issues/3>)
o In Section 6.1.1, clarify that the charset parameter value is o In Section 7.1.1, clarify that the charset parameter value is
case-insensitive due to the definition in RFC 2046 case-insensitive due to the definition in RFC 2046
(<https://github.com/httpwg/http-core/issues/13>) (<https://github.com/httpwg/http-core/issues/13>)
o Define a separate registry for HTTP header field names o Define a separate registry for HTTP header field names
(<https://github.com/httpwg/http-core/issues/42>) (<https://github.com/httpwg/http-core/issues/42>)
o In Section 8.4, refactor and clarify description of wildcard ("*") o In Section 9.4, refactor and clarify description of wildcard ("*")
handling (<https://github.com/httpwg/http-core/issues/46>) handling (<https://github.com/httpwg/http-core/issues/46>)
o Deprecate Accept-Charset (<https://github.com/httpwg/http-core/ o Deprecate Accept-Charset (<https://github.com/httpwg/http-core/
issues/61>) issues/61>)
o In Section 8.2.1, mention Cache-Control: immutable o In Section 9.2.1, mention Cache-Control: immutable
(<https://github.com/httpwg/http-core/issues/69>) (<https://github.com/httpwg/http-core/issues/69>)
o In Section 4.1, clarify when header field combination is allowed o In Section 5.1, clarify when header field combination is allowed
(<https://github.com/httpwg/http-core/issues/74>) (<https://github.com/httpwg/http-core/issues/74>)
o In Section 12.4, instruct IANA to mark Content-MD5 as obsolete o In Section 13.4, instruct IANA to mark Content-MD5 as obsolete
(<https://github.com/httpwg/http-core/issues/93>) (<https://github.com/httpwg/http-core/issues/93>)
o Use RFC 7405 ABNF notation for case-sensitive string constants o Use RFC 7405 ABNF notation for case-sensitive string constants
(<https://github.com/httpwg/http-core/issues/133>) (<https://github.com/httpwg/http-core/issues/133>)
o Rework Section 2.1 to be more version-independent o Rework Section 2.1 to be more version-independent
(<https://github.com/httpwg/http-core/issues/142>) (<https://github.com/httpwg/http-core/issues/142>)
o In Section 7.3.5, clarify that DELETE needs to be successful to o In Section 8.3.5, clarify that DELETE needs to be successful to
invalidate cache (<https://github.com/httpwg/http-core/ invalidate cache (<https://github.com/httpwg/http-core/
issues/167>, <https://www.rfc-editor.org/errata/eid5541>) issues/167>, <https://www.rfc-editor.org/errata/eid5541>)
D.6. Since draft-ietf-httpbis-semantics-04 D.6. Since draft-ietf-httpbis-semantics-04
o In Section 4.4, fix field-content ABNF o In Section 5.4, fix field-content ABNF
(<https://github.com/httpwg/http-core/issues/19>, (<https://github.com/httpwg/http-core/issues/19>,
<https://www.rfc-editor.org/errata/eid4189>) <https://www.rfc-editor.org/errata/eid4189>)
o Move Section 4.4.1.4 into its own section o Move Section 5.4.1.4 into its own section
(<https://github.com/httpwg/http-core/issues/45>) (<https://github.com/httpwg/http-core/issues/45>)
o In Section 6.2.1, reference MIME Sniffing o In Section 7.2.1, reference MIME Sniffing
(<https://github.com/httpwg/http-core/issues/51>) (<https://github.com/httpwg/http-core/issues/51>)
o In Section 4.5, simplify the #rule mapping for recipients o In Section 5.5, simplify the #rule mapping for recipients
(<https://github.com/httpwg/http-core/issues/164>, (<https://github.com/httpwg/http-core/issues/164>,
<https://www.rfc-editor.org/errata/eid5257>) <https://www.rfc-editor.org/errata/eid5257>)
o In Section 7.3.7, remove misleading text about "extension" of HTTP o In Section 8.3.7, remove misleading text about "extension" of HTTP
is needed to define method payloads (<https://github.com/httpwg/ is needed to define method payloads (<https://github.com/httpwg/
http-core/issues/204>) http-core/issues/204>)
o Fix editorial issue in Section 6 (<https://github.com/httpwg/http- o Fix editorial issue in Section 7 (<https://github.com/httpwg/http-
core/issues/223>) core/issues/223>)
o In Section 9.5.20, rephrase language not to use "entity" anymore, o In Section 10.5.20, rephrase language not to use "entity" anymore,
and also avoid lowercase "may" (<https://github.com/httpwg/http- and also avoid lowercase "may" (<https://github.com/httpwg/http-
core/issues/224>) core/issues/224>)
o Move discussion of retries from [Messaging] into Section 7.2.2 o Move discussion of retries from [Messaging] into Section 8.2.2
(<https://github.com/httpwg/http-core/issues/230>) (<https://github.com/httpwg/http-core/issues/230>)
D.7. Since draft-ietf-httpbis-semantics-05 D.7. Since draft-ietf-httpbis-semantics-05
o Moved transport-independent part of the description of trailers o Moved transport-independent part of the description of trailers
into Section 4.6 (<https://github.com/httpwg/http-core/issues/16>) into Section 5.6 (<https://github.com/httpwg/http-core/issues/16>)
o Loosen requirements on retries based upon implementation behavior o Loosen requirements on retries based upon implementation behavior
(<https://github.com/httpwg/http-core/issues/27>) (<https://github.com/httpwg/http-core/issues/27>)
o In Section 12.9, update IANA port registry for TCP/UDP on ports 80 o In Section 13.9, update IANA port registry for TCP/UDP on ports 80
and 443 (<https://github.com/httpwg/http-core/issues/36>) and 443 (<https://github.com/httpwg/http-core/issues/36>)
o In Section 4.7, revise guidelines for new header field names o In Section 5.7, revise guidelines for new header field names
(<https://github.com/httpwg/http-core/issues/47>) (<https://github.com/httpwg/http-core/issues/47>)
o In Section 7.2.3, remove concept of "cacheable methods" in favor o In Section 8.2.3, remove concept of "cacheable methods" in favor
of prose (<https://github.com/httpwg/http-core/issues/54>, of prose (<https://github.com/httpwg/http-core/issues/54>,
<https://www.rfc-editor.org/errata/eid5300>) <https://www.rfc-editor.org/errata/eid5300>)
o In Section 11.1, mention that the concept of authority can be o In Section 12.1, mention that the concept of authority can be
modified by protocol extensions (<https://github.com/httpwg/http- modified by protocol extensions (<https://github.com/httpwg/http-
core/issues/143>) core/issues/143>)
o Create new subsection on payload body in Section 6.3.3, taken from o Create new subsection on payload body in Section 7.3.3, taken from
portions of message body (<https://github.com/httpwg/http-core/ portions of message body (<https://github.com/httpwg/http-core/
issues/159>) issues/159>)
o Moved definition of "Whitespace" into new container "Generic o Moved definition of "Whitespace" into new container "Generic
Syntax" (<https://github.com/httpwg/http-core/issues/162>) Syntax" (<https://github.com/httpwg/http-core/issues/162>)
o In Section 2.5, recommend minimum URI size support for o In Section 2.5, recommend minimum URI size support for
implementations (<https://github.com/httpwg/http-core/issues/169>) implementations (<https://github.com/httpwg/http-core/issues/169>)
o In Section 6.1.4, refactored the range-unit and ranges-specifier o In Section 7.1.4, refactored the range-unit and ranges-specifier
grammars (<https://github.com/httpwg/http-core/issues/196>, grammars (<https://github.com/httpwg/http-core/issues/196>,
<https://www.rfc-editor.org/errata/eid5620>) <https://www.rfc-editor.org/errata/eid5620>)
o In Section 7.3.1, caution against a request body more strongly o In Section 8.3.1, caution against a request body more strongly
(<https://github.com/httpwg/http-core/issues/202>) (<https://github.com/httpwg/http-core/issues/202>)
o Reorganized text in Section 4.7 (<https://github.com/httpwg/http- o Reorganized text in Section 5.7 (<https://github.com/httpwg/http-
core/issues/214>) core/issues/214>)
o In Section 9.5.4, replace "authorize" with "fulfill" o In Section 10.5.4, replace "authorize" with "fulfill"
(<https://github.com/httpwg/http-core/issues/218>) (<https://github.com/httpwg/http-core/issues/218>)
o In Section 7.3.7, removed a misleading statement about Content- o In Section 8.3.7, removed a misleading statement about Content-
Length (<https://github.com/httpwg/http-core/issues/235>, Length (<https://github.com/httpwg/http-core/issues/235>,
<https://www.rfc-editor.org/errata/eid5806>) <https://www.rfc-editor.org/errata/eid5806>)
o In Section 11.1, add text from RFC 2818 o In Section 12.1, add text from RFC 2818
(<https://github.com/httpwg/http-core/issues/236>) (<https://github.com/httpwg/http-core/issues/236>)
o Changed "cacheable by default" to "heuristically cacheable" o Changed "cacheable by default" to "heuristically cacheable"
throughout (<https://github.com/httpwg/http-core/issues/242>) throughout (<https://github.com/httpwg/http-core/issues/242>)
D.8. Since draft-ietf-httpbis-semantics-06 D.8. Since draft-ietf-httpbis-semantics-06
o In Section 5.7.1, simplify received-by grammar (and disallow comma o In Section 6.7.1, simplify received-by grammar (and disallow comma
character) (<https://github.com/httpwg/http-core/issues/24>) character) (<https://github.com/httpwg/http-core/issues/24>)
o In Section 4.3, give guidance on interoperable field names o In Section 5.3, give guidance on interoperable field names
(<https://github.com/httpwg/http-core/issues/30>) (<https://github.com/httpwg/http-core/issues/30>)
o In Section 1.2.1, define the semantics and possible replacement of o In Section 1.2.1, define the semantics and possible replacement of
whitespace when it is known to occur (<https://github.com/httpwg/ whitespace when it is known to occur (<https://github.com/httpwg/
http-core/issues/53>) http-core/issues/53>, <https://www.rfc-editor.org/errata/eid5163>)
o In Section 4, introduce field terminology and distinguish between o In Section 5, introduce field terminology and distinguish between
field line values and field values; use terminology consistently field line values and field values; use terminology consistently
throughout (<https://github.com/httpwg/http-core/issues/111>) throughout (<https://github.com/httpwg/http-core/issues/111>)
o Moved #rule definition into Section 4.4 and whitespace into o Moved #rule definition into Section 5.4 and whitespace into
Section 1.2 (<https://github.com/httpwg/http-core/issues/162>) Section 1.2 (<https://github.com/httpwg/http-core/issues/162>)
o In Section 6.1.4, explicitly call out range unit names as case- o In Section 7.1.4, explicitly call out range unit names as case-
insensitive, and encourage registration insensitive, and encourage registration
(<https://github.com/httpwg/http-core/issues/179>) (<https://github.com/httpwg/http-core/issues/179>)
o In Section 6.1.2, explicitly call out content codings as case- o In Section 7.1.2, explicitly call out content codings as case-
insensitive, and encourage registration insensitive, and encourage registration
(<https://github.com/httpwg/http-core/issues/179>) (<https://github.com/httpwg/http-core/issues/179>)
o In Section 4.3, explicitly call out field names as case- o In Section 5.3, explicitly call out field names as case-
insensitive (<https://github.com/httpwg/http-core/issues/179>) insensitive (<https://github.com/httpwg/http-core/issues/179>)
o In Section 11.11, cite [Bujlow] (<https://github.com/httpwg/http- o In Section 12.11, cite [Bujlow] (<https://github.com/httpwg/http-
core/issues/185>) core/issues/185>)
o In Section 9, formally define "final" and "interim" status codes o In Section 10, formally define "final" and "interim" status codes
(<https://github.com/httpwg/http-core/issues/245>) (<https://github.com/httpwg/http-core/issues/245>)
o In Section 7.3.5, caution against a request body more strongly o In Section 8.3.5, caution against a request body more strongly
(<https://github.com/httpwg/http-core/issues/258>) (<https://github.com/httpwg/http-core/issues/258>)
o In Section 10.2.3, note that Etag can be used in trailers o In Section 11.2.3, note that Etag can be used in trailers
(<https://github.com/httpwg/http-core/issues/262>) (<https://github.com/httpwg/http-core/issues/262>)
o In Section 12.4, consider reserved fields as well o In Section 13.4, consider reserved fields as well
(<https://github.com/httpwg/http-core/issues/273>) (<https://github.com/httpwg/http-core/issues/273>)
o In Section 2.5.4, be more correct about what was deprecated by RFC o In Section 2.5.4, be more correct about what was deprecated by RFC
3986 (<https://github.com/httpwg/http-core/issues/278>, 3986 (<https://github.com/httpwg/http-core/issues/278>,
<https://www.rfc-editor.org/errata/eid5964>) <https://www.rfc-editor.org/errata/eid5964>)
o In Section 4.1, recommend comma SP when combining field lines o In Section 5.1, recommend comma SP when combining field lines
(<https://github.com/httpwg/http-core/issues/148>) (<https://github.com/httpwg/http-core/issues/148>)
o In Section 5.6, make explicit requirements on origin server to use o In Section 6.6, make explicit requirements on origin server to use
authority from absolute-form when available authority from absolute-form when available
(<https://github.com/httpwg/http-core/issues/191>) (<https://github.com/httpwg/http-core/issues/191>)
o In Section 2.5.1, Section 2.5.2, Section 5.2, and Section 5.4, o In Section 2.5.1, Section 2.5.2, Section 6.2, and Section 6.4,
refactored schemes to define origin and authoritative access to an refactored schemes to define origin and authoritative access to an
origin server for both "http" and "https" URIs to account for origin server for both "http" and "https" URIs to account for
alternative services and secured connections that are not alternative services and secured connections that are not
necessarily based on TCP (<https://github.com/httpwg/http-core/ necessarily based on TCP (<https://github.com/httpwg/http-core/
issues/237>) issues/237>)
o In Section 1.1, reference RFC 8174 as well o In Section 1.1, reference RFC 8174 as well
(<https://github.com/httpwg/http-core/issues/303>) (<https://github.com/httpwg/http-core/issues/303>)
D.9. Since draft-ietf-httpbis-semantics-07 D.9. Since draft-ietf-httpbis-semantics-07
o In Section 8.3, explicitly reference the definition of o In Section 9.3, explicitly reference the definition of
representation data as including any content codings representation data as including any content codings
(<https://github.com/httpwg/http-core/issues/11>) (<https://github.com/httpwg/http-core/issues/11>)
o Move TE: trailers from [Messaging] into Section 4.6.2 o Move TE: trailers from [Messaging] into Section 5.6.2
(<https://github.com/httpwg/http-core/issues/18>) (<https://github.com/httpwg/http-core/issues/18>)
o In Section 6.2.4, adjust requirements for handling multiple o In Section 7.2.4, adjust requirements for handling multiple
content-length values (<https://github.com/httpwg/http-core/ content-length values (<https://github.com/httpwg/http-core/
issues/59>) issues/59>)
o In Section 8.2.3 and Section 8.2.4, clarified condition evaluation o In Section 9.2.3 and Section 9.2.4, clarified condition evaluation
(<https://github.com/httpwg/http-core/issues/72>) (<https://github.com/httpwg/http-core/issues/72>)
o In Section 4.4, remove concept of obs-fold, as that is o In Section 5.4, remove concept of obs-fold, as that is
HTTP/1-specific (<https://github.com/httpwg/http-core/issues/116>) HTTP/1-specific (<https://github.com/httpwg/http-core/issues/116>)
o In Section 6.4, introduce the concept of request payload o In Section 7.4, introduce the concept of request payload
negotiation (Section 6.4.3) and define for Accept-Encoding negotiation (Section 7.4.3) and define for Accept-Encoding
(<https://github.com/httpwg/http-core/issues/119>) (<https://github.com/httpwg/http-core/issues/119>)
o In Section 9.3.6, Section 9.5.9, and Section 9.5.14, remove o In Section 10.3.6, Section 10.5.9, and Section 10.5.14, remove
HTTP/1-specific, connection-related requirements HTTP/1-specific, connection-related requirements
(<https://github.com/httpwg/http-core/issues/144>) (<https://github.com/httpwg/http-core/issues/144>)
o In Section 7.3.6, correct language about what is forwarded o In Section 8.3.6, correct language about what is forwarded
(<https://github.com/httpwg/http-core/issues/170>) (<https://github.com/httpwg/http-core/issues/170>)
o Throughout, replace "effective request URI", "request-target" and o Throughout, replace "effective request URI", "request-target" and
similar with "target URI" (<https://github.com/httpwg/http-core/ similar with "target URI" (<https://github.com/httpwg/http-core/
issues/259>) issues/259>)
o In Section 4.7 and Section 9.7.2, describe how extensions should o In Section 5.7 and Section 10.7.2, describe how extensions should
consider scope of applicability (<https://github.com/httpwg/http- consider scope of applicability (<https://github.com/httpwg/http-
core/issues/265>) core/issues/265>)
o In Section 2.1, don't rely on the HTTP/1.1 Messaging specification o In Section 2.1, don't rely on the HTTP/1.1 Messaging specification
to define "message" (<https://github.com/httpwg/http-core/ to define "message" (<https://github.com/httpwg/http-core/
issues/311>) issues/311>)
o In Section 6.2.5 and Section 8.6.2, note that URL resolution is o In Section 7.2.5 and Section 9.6.2, note that URL resolution is
necessary (<https://github.com/httpwg/http-core/issues/321>) necessary (<https://github.com/httpwg/http-core/issues/321>)
o In Section 6, explicitly reference 206 as one of the status codes o In Section 7, explicitly reference 206 as one of the status codes
that provide representation data (<https://github.com/httpwg/http- that provide representation data (<https://github.com/httpwg/http-
core/issues/325>) core/issues/325>)
o In Section 8.2.6, refine requirements so that they don't apply to o In Section 9.2.6, refine requirements so that they don't apply to
resources without a concept of modification time resources without a concept of modification time
(<https://github.com/httpwg/http-core/issues/326>) (<https://github.com/httpwg/http-core/issues/326>)
o In Section 10.3.2, specify the scope as a request, not a target o In Section 11.3.2, specify the scope as a request, not a target
resource (<https://github.com/httpwg/http-core/issues/331>) resource (<https://github.com/httpwg/http-core/issues/331>)
o In Section 2.1, introduce concept of "complete" messages o In Section 2.1, introduce concept of "complete" messages
(<https://github.com/httpwg/http-core/issues/334>) (<https://github.com/httpwg/http-core/issues/334>)
o In Section 5.1, Section 7.3.6, and Section 7.3.7, refine use of o In Section 6.1, Section 8.3.6, and Section 8.3.7, refine use of
"request target" (<https://github.com/httpwg/http-core/ "request target" (<https://github.com/httpwg/http-core/
issues/340>) issues/340>)
o Throughout, remove "status-line" and "request-line", as these are o Throughout, remove "status-line" and "request-line", as these are
HTTP/1.1-specific (<https://github.com/httpwg/http-core/ HTTP/1.1-specific (<https://github.com/httpwg/http-core/
issues/361>) issues/361>)
D.10. Since draft-ietf-httpbis-semantics-08
o In Section 10.5.17, remove duplicate definition of what makes a
range satisfiable and refer instead to each range unit's
definition (<https://github.com/httpwg/http-core/issues/12>)
o In Section 7.1.4.2 and Section 9.3, clarify that a selected
representation of zero length can only be satisfiable as a suffix
range and that a server can still ignore Range for that case
(<https://github.com/httpwg/http-core/issues/12>)
o In Section 9.4.1 and Section 10.5.16, allow "Accept" as response
field (<https://github.com/httpwg/http-core/issues/48>)
o Appendix A now uses the sender variant of the "#" list expansion
(<https://github.com/httpwg/http-core/issues/192>)
o In Section 11.1.4, make the field list-based even when "*" is
present (<https://github.com/httpwg/http-core/issues/272>)
o In Section 5.3.2, add optional "Comments" entry
(<https://github.com/httpwg/http-core/issues/273>)
o In Section 5.8, reserve "*" as field name
(<https://github.com/httpwg/http-core/issues/274>)
o In Section 13.2, reserve "*" as method name
(<https://github.com/httpwg/http-core/issues/274>)
o In Section 9.2.3 and Section 9.2.4, state that multiple "*" is
unlikely to be interoperable (<https://github.com/httpwg/http-
core/issues/305>)
o In Section 9.4.1, avoid use of obsolete media type parameter on
text/html (<https://github.com/httpwg/http-core/issues/375>,
<https://www.rfc-editor.org/errata/eid6149>)
o Rephrase prose in Section 2.1 to become version-agnostic
(<https://github.com/httpwg/http-core/issues/372>)
o In Section 5.4, instruct recipients how to deal with control
characters in field values (<https://github.com/httpwg/http-core/
issues/377>)
o In Section 5.4, update note about field ABNF
(<https://github.com/httpwg/http-core/issues/380>)
o Add Section 4 about Extending and Versioning HTTP
(<https://github.com/httpwg/http-core/issues/384>)
o In Section 10.1, include status 308 in list of heuristically
cacheable status codes (<https://github.com/httpwg/http-core/
issues/385>)
o In Section 7.2.2, make it clearer that "identity" is not to be
included (<https://github.com/httpwg/http-core/issues/388>)
Index Index
1 1
100 Continue (status code) 123 100 Continue (status code) 127
100-continue (expect value) 90 100-continue (expect value) 93
101 Switching Protocols (status code) 123 101 Switching Protocols (status code) 127
1xx Informational (status code class) 123 1xx Informational (status code class) 126
2 2
200 OK (status code) 124 200 OK (status code) 127
201 Created (status code) 124 201 Created (status code) 128
202 Accepted (status code) 125 202 Accepted (status code) 128
203 Non-Authoritative Information (status code) 125 203 Non-Authoritative Information (status code) 129
204 No Content (status code) 125 204 No Content (status code) 129
205 Reset Content (status code) 126 205 Reset Content (status code) 130
206 Partial Content (status code) 127 206 Partial Content (status code) 130
2xx Successful (status code class) 124 2xx Successful (status code class) 127
3 3
300 Multiple Choices (status code) 131 300 Multiple Choices (status code) 135
301 Moved Permanently (status code) 132 301 Moved Permanently (status code) 136
302 Found (status code) 132 302 Found (status code) 136
303 See Other (status code) 133 303 See Other (status code) 137
304 Not Modified (status code) 133 304 Not Modified (status code) 137
305 Use Proxy (status code) 134 305 Use Proxy (status code) 138
306 (Unused) (status code) 134 306 (Unused) (status code) 138
307 Temporary Redirect (status code) 134 307 Temporary Redirect (status code) 138
308 Permanent Redirect (status code) 135 308 Permanent Redirect (status code) 139
3xx Redirection (status code class) 130 3xx Redirection (status code class) 133
4 4
400 Bad Request (status code) 135 400 Bad Request (status code) 139
401 Unauthorized (status code) 135 401 Unauthorized (status code) 139
402 Payment Required (status code) 136 402 Payment Required (status code) 140
403 Forbidden (status code) 136 403 Forbidden (status code) 140
404 Not Found (status code) 136 404 Not Found (status code) 140
405 Method Not Allowed (status code) 137 405 Method Not Allowed (status code) 141
406 Not Acceptable (status code) 137 406 Not Acceptable (status code) 141
407 Proxy Authentication Required (status code) 137 407 Proxy Authentication Required (status code) 141
408 Request Timeout (status code) 137 408 Request Timeout (status code) 141
409 Conflict (status code) 138 409 Conflict (status code) 142
410 Gone (status code) 138 410 Gone (status code) 142
411 Length Required (status code) 138 411 Length Required (status code) 142
412 Precondition Failed (status code) 139 412 Precondition Failed (status code) 143
413 Payload Too Large (status code) 139 413 Payload Too Large (status code) 143
414 URI Too Long (status code) 139 414 URI Too Long (status code) 143
415 Unsupported Media Type (status code) 139 415 Unsupported Media Type (status code) 143
416 Range Not Satisfiable (status code) 140 416 Range Not Satisfiable (status code) 144
417 Expectation Failed (status code) 140 417 Expectation Failed (status code) 144
418 (Unused) (status code) 140 418 (Unused) (status code) 145
422 Unprocessable Payload (status code) 141 422 Unprocessable Payload (status code) 145
426 Upgrade Required (status code) 141 426 Upgrade Required (status code) 145
4xx Client Error (status code class) 135 4xx Client Error (status code class) 139
5 5
500 Internal Server Error (status code) 142 500 Internal Server Error (status code) 146
501 Not Implemented (status code) 142 501 Not Implemented (status code) 146
502 Bad Gateway (status code) 142 502 Bad Gateway (status code) 146
503 Service Unavailable (status code) 142 503 Service Unavailable (status code) 146
504 Gateway Timeout (status code) 142 504 Gateway Timeout (status code) 146
505 HTTP Version Not Supported (status code) 142 505 HTTP Version Not Supported (status code) 147
5xx Server Error (status code class) 141 5xx Server Error (status code class) 145
A A
Accept header field 106 Accept header field 109
Accept-Charset header field 108 Accept-Charset header field 111
Accept-Encoding header field 108 Accept-Encoding header field 112
Accept-Language header field 110 Accept-Language header field 114
Accept-Ranges header field 163 Accept-Ranges header field 165
Allow header field 163 Allow header field 165
Authentication-Info header field 161 Authentication-Info header field 163
Authorization header field 114 Authorization header field 118
accelerator 14 accelerator 14
authoritative response 165 authoritative response 167
B B
browser 11 browser 11
C C
CONNECT method 85 CONNECT method 88
Canonical Root URI 113 Canonical Root URI 117
Content-Encoding header field 60 Content-Encoding header field 63
Content-Language header field 61 Content-Language header field 64
Content-Length header field 61 Content-Length header field 64
Content-Location header field 63 Content-Location header field 66
Content-MD5 header field 175 Content-MD5 header field 177
Content-Range header field 67 Content-Range header field 70
Content-Type header field 59 Content-Type header field 62
cache 15 cache 15
cacheable 16 cacheable 16
captive portal 15 captive portal 15
client 11 client 11
complete 12 complete 12
compress (Coding Format) 52 compress (Coding Format) 56
compress (content coding) 52 compress (content coding) 55
conditional request 93 conditional request 96
connection 11 connection 11
content coding 52 content coding 55
content negotiation 9 content negotiation 9
D D
DELETE method 84 DELETE method 87
Date header field 147 Date header field 149
Delimiters 30 Delimiters 31
deflate (Coding Format) 53 deflate (Coding Format) 56
deflate (content coding) 52 deflate (content coding) 55
downstream 14 downstream 14
E E
ETag field 155 ETag field 157
Expect header field 90 Expect header field 93
effective request URI 44 effective request URI 47
F F
Fields Fields
Accept 106 Accept 109
Accept-Charset 108 Accept-Charset 111
Accept-Encoding 108 Accept-Encoding 112
Accept-Language 110 Accept-Language 114
Accept-Ranges 163 Accept-Ranges 165
Allow 163 Allow 165
Authentication-Info 161 Authentication-Info 163
Authorization 114 Authorization 118
Content-Encoding 60 Content-Encoding 63
Content-Language 61 Content-Language 64
Content-Length 61 Content-Length 64
Content-Location 63 Content-Location 66
Content-MD5 175 Content-MD5 177
Content-Range 67 Content-Range 70
Content-Type 59 Content-Type 62
Date 147 Date 149
ETag 155 ETag 157
Expect 90 Expect 93
From 118 From 121
Host 44 Host 48
If-Match 97 If-Match 100
If-Modified-Since 99 If-Modified-Since 103
If-None-Match 98 If-None-Match 101
If-Range 102 If-Range 105
If-Unmodified-Since 101 If-Unmodified-Since 104
Last-Modified 153 Last-Modified 155
Location 148 Location 150
Max-Forwards 92 Max-Forwards 96
Proxy-Authenticate 161 Proxy-Authenticate 163
Proxy-Authentication-Info 162 Proxy-Authentication-Info 164
Proxy-Authorization 115 Proxy-Authorization 118
Range 103 Range 106
Referer 118 Referer 122
Retry-After 149 Retry-After 151
Server 164 Server 166
Trailer 34 Trailer 37
User-Agent 119 User-Agent 123
Vary 149 Vary 152
Via 46 Via 49
WWW-Authenticate 160 WWW-Authenticate 162
Fragment Identifiers 20 Fragment Identifiers 20
From header field 118 From header field 121
field 24 field 25
field line 25 field line 26
field line value 25 field line value 26
field name 25 field name 26
field value 25 field value 26
G G
GET method 79 GET method 82
Grammar Grammar
absolute-path 17 absolute-path 17
absolute-URI 17 absolute-URI 17
Accept 106 Accept 109
Accept-Charset 108 Accept-Charset 111
Accept-Encoding 108 Accept-Encoding 112
accept-ext 106 accept-ext 109
Accept-Language 110 Accept-Language 114
accept-params 106 accept-params 109
Accept-Ranges 163 Accept-Ranges 165
acceptable-ranges 163 acceptable-ranges 165
Allow 163 Allow 165
ALPHA 10 ALPHA 10
asctime-date 146 asctime-date 34
auth-param 112 auth-param 115
auth-scheme 112 auth-scheme 115
Authentication-Info 161 Authentication-Info 163
authority 17 authority 17
Authorization 114 Authorization 118
BWS 11 BWS 11
challenge 112 challenge 116
charset 50 charset 53
codings 108 codings 112
comment 31 comment 32
complete-length 67 complete-length 70
content-coding 52 content-coding 55
Content-Encoding 60 Content-Encoding 63
Content-Language 61 Content-Language 64
Content-Length 61 Content-Length 65
Content-Location 63 Content-Location 66
Content-Range 67 Content-Range 70
Content-Type 59 Content-Type 62
CR 10 CR 10
credentials 113 credentials 116
CRLF 10 CRLF 10
ctext 31 ctext 32
CTL 10 CTL 10
Date 147 Date 149
date1 146 date1 34
day 146 day 34
day-name 146 day-name 34
day-name-l 146 day-name-l 34
delay-seconds 149 delay-seconds 151
DIGIT 10 DIGIT 10
DQUOTE 10 DQUOTE 10
entity-tag 156 entity-tag 158
ETag 156 ETag 158
etagc 156 etagc 158
Expect 90 Expect 93
field-content 29 field-content 30
field-name 27, 34 field-name 28, 38
field-value 29 field-value 30
field-vchar 29 field-vchar 30
first-pos 55, 67 first-pos 58, 70
From 118 From 121
GMT 146 GMT 34
HEXDIG 10 HEXDIG 10
Host 44 Host 48
hour 146 hour 34
HTAB 10 HTAB 10
HTTP-date 145 HTTP-date 33
http-URI 18 http-URI 18
https-URI 19 https-URI 19
If-Match 97 If-Match 100
If-Modified-Since 99 If-Modified-Since 103
If-None-Match 98 If-None-Match 101
If-Range 102 If-Range 106
If-Unmodified-Since 101 If-Unmodified-Since 104
IMF-fixdate 146 IMF-fixdate 34
incl-range 67 incl-range 70
int-range 55 int-range 58
language-range 110 language-range 114
language-tag 54 language-tag 57
Last-Modified 153 Last-Modified 155
last-pos 55, 67 last-pos 58, 70
LF 10 LF 10
Location 148 Location 150
Max-Forwards 92 Max-Forwards 96
media-range 106 media-range 109
media-type 50 media-type 53
method 75 method 78
minute 146 minute 34
month 146 month 34
obs-date 146 obs-date 34
obs-text 31 obs-text 32
OCTET 10 OCTET 10
opaque-tag 156 opaque-tag 158
other-range 56 other-range 59
OWS 11 OWS 11
parameter 31 parameter 33
parameter-name 31 parameter-name 33
parameter-value 31 parameter-value 33
partial-URI 17 partial-URI 17
port 17 port 17
product 120 product 123
product-version 120 product-version 123
protocol-name 46 protocol-name 49
protocol-version 46 protocol-version 49
Proxy-Authenticate 161 Proxy-Authenticate 163
Proxy-Authentication-Info 162 Proxy-Authentication-Info 164
Proxy-Authorization 115 Proxy-Authorization 118
pseudonym 46 pseudonym 49
qdtext 31 qdtext 32
query 17 query 17
quoted-pair 31 quoted-pair 32
quoted-string 31 quoted-string 32
qvalue 74 qvalue 77
Range 103 Range 106
range-resp 67 range-resp 70
range-set 55 range-set 58
range-spec 55 range-spec 58
range-unit 54 range-unit 57
ranges-specifier 55 ranges-specifier 58
received-by 46 received-by 49
received-protocol 46 received-protocol 49
Referer 118 Referer 122
Retry-After 149 Retry-After 151
rfc850-date 146 rfc850-date 34
RWS 11 RWS 11
second 146 second 34
segment 17 segment 17
Server 164 Server 166
SP 10 SP 10
subtype 50 subtype 53
suffix-length 56 suffix-length 59
suffix-range 56 suffix-range 59
tchar 31 tchar 32
time-of-day 146 time-of-day 34
token 31 token 32
token68 112 token68 115
Trailer 34 Trailer 38
type 50 type 53
unsatisfied-range 67 unsatisfied-range 70
uri-host 17 uri-host 17
URI-reference 17 URI-reference 17
User-Agent 119 User-Agent 123
Vary 150 Vary 152
VCHAR 10 VCHAR 10
Via 46 Via 49
weak 156 weak 158
weight 74 weight 77
WWW-Authenticate 160 WWW-Authenticate 162
year 146 year 34
gateway 14 gateway 14
gzip (Coding Format) 53 gzip (Coding Format) 56
gzip (content coding) 52 gzip (content coding) 55
H H
HEAD method 80 HEAD method 83
Header Fields Header Fields
Accept 106 Accept 109
Accept-Charset 108 Accept-Charset 111
Accept-Encoding 108 Accept-Encoding 112
Accept-Language 110 Accept-Language 114
Accept-Ranges 163 Accept-Ranges 165
Allow 163 Allow 165
Authentication-Info 161 Authentication-Info 163
Authorization 114 Authorization 118
Content-Encoding 60 Content-Encoding 63
Content-Language 61 Content-Language 64
Content-Length 61 Content-Length 64
Content-Location 63 Content-Location 66
Content-MD5 175 Content-MD5 177
Content-Range 67 Content-Range 70
Content-Type 59 Content-Type 62
Date 147 Date 149
ETag 155 ETag 157
Expect 90 Expect 93
From 118 From 121
Host 44 Host 48
If-Match 97 If-Match 100
If-Modified-Since 99 If-Modified-Since 103
If-None-Match 98 If-None-Match 101
If-Range 102 If-Range 105
If-Unmodified-Since 101 If-Unmodified-Since 104
Last-Modified 153 Last-Modified 155
Location 148 Location 150
Max-Forwards 92 Max-Forwards 96
Proxy-Authenticate 161 Proxy-Authenticate 163
Proxy-Authentication-Info 162 Proxy-Authentication-Info 164
Proxy-Authorization 115 Proxy-Authorization 118
Range 103 Range 106
Referer 118 Referer 122
Retry-After 149 Retry-After 151
Server 164 Server 166
Trailer 34 Trailer 37
User-Agent 119 User-Agent 123
Vary 149 Vary 152
Via 46 Via 49
WWW-Authenticate 160 WWW-Authenticate 162
Host header field 48
Host header field 44 header section 25
header section 24
http URI scheme 18 http URI scheme 18
https URI scheme 18 https URI scheme 18
I I
If-Match header field 97 If-Match header field 100
If-Modified-Since header field 99 If-Modified-Since header field 103
If-None-Match header field 98 If-None-Match header field 101
If-Range header field 102 If-Range header field 105
If-Unmodified-Since header field 101 If-Unmodified-Since header field 104
idempotent 78 idempotent 81
inbound 14 inbound 14
incomplete 12 incomplete 12
interception proxy 15 interception proxy 15
intermediary 13 intermediary 13
L L
Last-Modified header field 153 Last-Modified header field 155
Location header field 148 Location header field 150
M M
Max-Forwards header field 92 Max-Forwards header field 96
Media Type Media Type
multipart/byteranges 69 multipart/byteranges 72
multipart/x-byteranges 69 multipart/x-byteranges 72
message 12 message 12
metadata 151 metadata 153
multipart/byteranges Media Type 69 multipart/byteranges Media Type 72
multipart/x-byteranges Media Type 69 multipart/x-byteranges Media Type 72
N N
non-transforming proxy 47 non-transforming proxy 51
O O
OPTIONS method 87 OPTIONS method 90
origin 38 origin 42
origin server 11 origin server 11
outbound 14 outbound 14
P P
POST method 81 POST method 84
PUT method 82 PUT method 85
Protection Space 113 Protection Space 117
Proxy-Authenticate header field 161 Proxy-Authenticate header field 163
Proxy-Authentication-Info header field 162 Proxy-Authentication-Info header field 164
Proxy-Authorization header field 115 Proxy-Authorization header field 118
payload 64 payload 68
phishing 165 phishing 167
proxy 14 proxy 14
R R
Range header field 103 Range header field 106
Realm 113 Realm 117
Referer header field 118 Referer header field 122
Retry-After header field 149 Retry-After header field 151
recipient 11 recipient 11
representation 49 representation 52
request 12 request 12
resource 16 resource 16
response 12 response 12
reverse proxy 14 reverse proxy 14
S S
Server header field 164 Server header field 166
Status Code 120 Status Code 124
Status Codes Status Codes
Final 121 Final 125
Informational 121 Informational 125
Interim 121 Interim 125
Status Codes Classes Status Codes Classes
1xx Informational 123 1xx Informational 126
2xx Successful 124 2xx Successful 127
3xx Redirection 130 3xx Redirection 133
4xx Client Error 135 4xx Client Error 139
5xx Server Error 141 5xx Server Error 145
safe 77 safe 80
secured 18 secured 18
selected representation 49, 93, 151 selected representation 52, 96, 153
sender 11 sender 11
server 11 server 11
spider 11 spider 11
T T
TRACE method 88 TRACE method 91
Trailer Fields Trailer Fields
ETag 155 ETag 157
Trailer header field 34 Trailer header field 37
target URI 38 target URI 41
target resource 38 target resource 41
trailer fields 33 trailer fields 36
trailer section 24 trailer section 25
trailers 33 trailers 36
transforming proxy 47 transforming proxy 51
transparent proxy 15 transparent proxy 15
tunnel 14 tunnel 15
U U
URI URI
origin 38 origin 42
URI scheme URI scheme
http 18 http 18
https 18 https 18
User-Agent header field 119 User-Agent header field 123
upstream 14 upstream 14
user agent 11 user agent 11
V V
Vary header field 149 Vary header field 152
Via header field 46 Via header field 49
validator 151 validator 153
strong 152 strong 154
weak 152 weak 154
W W
WWW-Authenticate header field 160 WWW-Authenticate header field 162
X X
x-compress (content coding) 52 x-compress (content coding) 55
x-gzip (content coding) 52 x-gzip (content coding) 55
Acknowledgments Acknowledgments
This edition of the HTTP specification builds on the many This edition of the HTTP specification builds on the many
contributions that went into RFC 1945, RFC 2068, RFC 2145, RFC 2616, contributions that went into RFC 1945, RFC 2068, RFC 2145, RFC 2616,
and RFC 2818, including substantial contributions made by the and RFC 2818, including substantial contributions made by the
previous authors, editors, and Working Group Chairs: Tim Berners-Lee, previous authors, editors, and Working Group Chairs: Tim Berners-Lee,
Ari Luotonen, Roy T. Fielding, Henrik Frystyk Nielsen, Jim Gettys, Ari Luotonen, Roy T. Fielding, Henrik Frystyk Nielsen, Jim Gettys,
Jeffrey C. Mogul, Larry Masinter, Paul J. Leach, Eric Rescorla, and Jeffrey C. Mogul, Larry Masinter, Paul J. Leach, Eric Rescorla, and
Yves Lafon. Yves Lafon.
 End of changes. 674 change blocks. 
1514 lines changed or deleted 1688 lines changed or added

This html diff was produced by rfcdiff 1.45. The latest version is available from http://tools.ietf.org/tools/rfcdiff/