draft-ietf-httpbis-http2-13.txt   draft-ietf-httpbis-http2-14.txt 
HTTPbis Working Group M. Belshe HTTPbis Working Group M. Belshe
Internet-Draft Twist Internet-Draft Twist
Intended status: Standards Track R. Peon Intended status: Standards Track R. Peon
Expires: December 19, 2014 Google, Inc Expires: January 31, 2015 Google, Inc
M. Thomson, Ed. M. Thomson, Ed.
Mozilla Mozilla
June 17, 2014 July 30, 2014
Hypertext Transfer Protocol version 2 Hypertext Transfer Protocol version 2
draft-ietf-httpbis-http2-13 draft-ietf-httpbis-http2-14
Abstract Abstract
This specification describes an optimized expression of the syntax of This specification describes an optimized expression of the syntax of
the Hypertext Transfer Protocol (HTTP). HTTP/2 enables a more the Hypertext Transfer Protocol (HTTP). HTTP/2 enables a more
efficient use of network resources and a reduced perception of efficient use of network resources and a reduced perception of
latency by introducing header field compression and allowing multiple latency by introducing header field compression and allowing multiple
concurrent messages on the same connection. It also introduces concurrent messages on the same connection. It also introduces
unsolicited push of representations from servers to clients. unsolicited push of representations from servers to clients.
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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 http://datatracker.ietf.org/drafts/current/. Drafts is at http://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 December 19, 2014. This Internet-Draft will expire on January 31, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 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
(http://trustee.ietf.org/license-info) in effect on the date of (http://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
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2.2. Conventions and Terminology . . . . . . . . . . . . . . . 6 2.2. Conventions and Terminology . . . . . . . . . . . . . . . 6
3. Starting HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . 7 3. Starting HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. HTTP/2 Version Identification . . . . . . . . . . . . . . 8 3.1. HTTP/2 Version Identification . . . . . . . . . . . . . . 8
3.2. Starting HTTP/2 for "http" URIs . . . . . . . . . . . . . 9 3.2. Starting HTTP/2 for "http" URIs . . . . . . . . . . . . . 9
3.2.1. HTTP2-Settings Header Field . . . . . . . . . . . . . 10 3.2.1. HTTP2-Settings Header Field . . . . . . . . . . . . . 10
3.3. Starting HTTP/2 for "https" URIs . . . . . . . . . . . . 11 3.3. Starting HTTP/2 for "https" URIs . . . . . . . . . . . . 11
3.4. Starting HTTP/2 with Prior Knowledge . . . . . . . . . . 11 3.4. Starting HTTP/2 with Prior Knowledge . . . . . . . . . . 11
3.5. HTTP/2 Connection Preface . . . . . . . . . . . . . . . . 11 3.5. HTTP/2 Connection Preface . . . . . . . . . . . . . . . . 11
4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 12 4. HTTP Frames . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Frame Format . . . . . . . . . . . . . . . . . . . . . . 12 4.1. Frame Format . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . 13 4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . 14
4.3. Header Compression and Decompression . . . . . . . . . . 14 4.3. Header Compression and Decompression . . . . . . . . . . 14
5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . 15 5. Streams and Multiplexing . . . . . . . . . . . . . . . . . . 15
5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 15 5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 16
5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . 20 5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . 20
5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . 21 5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . 21
5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . 21 5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . 22
5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 21 5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 22
5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 22 5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 23
5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 23 5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 23
5.3.1. Stream Dependencies . . . . . . . . . . . . . . . . . 24 5.3.1. Stream Dependencies . . . . . . . . . . . . . . . . . 24
5.3.2. Dependency Weighting . . . . . . . . . . . . . . . . 25 5.3.2. Dependency Weighting . . . . . . . . . . . . . . . . 25
5.3.3. Reprioritization . . . . . . . . . . . . . . . . . . 25 5.3.3. Reprioritization . . . . . . . . . . . . . . . . . . 25
5.3.4. Prioritization State Management . . . . . . . . . . . 26 5.3.4. Prioritization State Management . . . . . . . . . . . 26
5.3.5. Default Priorities . . . . . . . . . . . . . . . . . 27 5.3.5. Default Priorities . . . . . . . . . . . . . . . . . 27
5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 27 5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 27
5.4.1. Connection Error Handling . . . . . . . . . . . . . . 27 5.4.1. Connection Error Handling . . . . . . . . . . . . . . 28
5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 28 5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 28
5.4.3. Connection Termination . . . . . . . . . . . . . . . 28 5.4.3. Connection Termination . . . . . . . . . . . . . . . 29
5.5. Extending HTTP/2 . . . . . . . . . . . . . . . . . . . . 28 5.5. Extending HTTP/2 . . . . . . . . . . . . . . . . . . . . 29
6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 29 6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 30
6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 31 6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . 33 6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . 33
6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . 34 6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . 34
6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . 35 6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . 35
6.5.1. SETTINGS Format . . . . . . . . . . . . . . . . . . . 36 6.5.1. SETTINGS Format . . . . . . . . . . . . . . . . . . . 36
6.5.2. Defined SETTINGS Parameters . . . . . . . . . . . . . 36 6.5.2. Defined SETTINGS Parameters . . . . . . . . . . . . . 37
6.5.3. Settings Synchronization . . . . . . . . . . . . . . 37 6.5.3. Settings Synchronization . . . . . . . . . . . . . . 38
6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . 38 6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . 38
6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . 40 6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . 41 6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 43 6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 44
6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 44 6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 45
6.9.2. Initial Flow Control Window Size . . . . . . . . . . 45 6.9.2. Initial Flow Control Window Size . . . . . . . . . . 46
6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 46 6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 47
6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . 47 6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . 48
7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 47 7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 48
8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . 49 8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . 50
8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . 49 8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . 50
8.1.1. Informational Responses . . . . . . . . . . . . . . . 50 8.1.1. Upgrading From HTTP/2 . . . . . . . . . . . . . . . . 51
8.1.2. HTTP Header Fields . . . . . . . . . . . . . . . . . 51 8.1.2. HTTP Header Fields . . . . . . . . . . . . . . . . . 51
8.1.3. Examples . . . . . . . . . . . . . . . . . . . . . . 55 8.1.3. Examples . . . . . . . . . . . . . . . . . . . . . . 55
8.1.4. Request Reliability Mechanisms in HTTP/2 . . . . . . 58 8.1.4. Request Reliability Mechanisms in HTTP/2 . . . . . . 57
8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 59 8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 58
8.2.1. Push Requests . . . . . . . . . . . . . . . . . . . . 59 8.2.1. Push Requests . . . . . . . . . . . . . . . . . . . . 59
8.2.2. Push Responses . . . . . . . . . . . . . . . . . . . 60 8.2.2. Push Responses . . . . . . . . . . . . . . . . . . . 60
8.3. The CONNECT Method . . . . . . . . . . . . . . . . . . . 61 8.3. The CONNECT Method . . . . . . . . . . . . . . . . . . . 61
9. Additional HTTP Requirements/Considerations . . . . . . . . . 62 9. Additional HTTP Requirements/Considerations . . . . . . . . . 62
9.1. Connection Management . . . . . . . . . . . . . . . . . . 62 9.1. Connection Management . . . . . . . . . . . . . . . . . . 62
9.1.1. Connection Reuse . . . . . . . . . . . . . . . . . . 63 9.1.1. Connection Reuse . . . . . . . . . . . . . . . . . . 63
9.1.2. The 421 (Not Authoritative) Status Code . . . . . . . 64 9.1.2. The 421 (Not Authoritative) Status Code . . . . . . . 63
9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 64 9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 64
9.2.1. TLS Features . . . . . . . . . . . . . . . . . . . . 64 9.2.1. TLS Features . . . . . . . . . . . . . . . . . . . . 64
9.2.2. TLS Cipher Suites . . . . . . . . . . . . . . . . . . 65 9.2.2. TLS Cipher Suites . . . . . . . . . . . . . . . . . . 65
10. Security Considerations . . . . . . . . . . . . . . . . . . . 65 10. Security Considerations . . . . . . . . . . . . . . . . . . . 65
10.1. Server Authority . . . . . . . . . . . . . . . . . . . . 65 10.1. Server Authority . . . . . . . . . . . . . . . . . . . . 65
10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . 66 10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . 66
10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . 66 10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . 66
10.4. Cacheability of Pushed Responses . . . . . . . . . . . . 67 10.4. Cacheability of Pushed Responses . . . . . . . . . . . . 67
10.5. Denial of Service Considerations . . . . . . . . . . . . 67 10.5. Denial of Service Considerations . . . . . . . . . . . . 67
10.5.1. Limits on Header Block Size . . . . . . . . . . . . 68 10.5.1. Limits on Header Block Size . . . . . . . . . . . . 68
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11.1. Registration of HTTP/2 Identification Strings . . . . . 70 11.1. Registration of HTTP/2 Identification Strings . . . . . 70
11.2. Frame Type Registry . . . . . . . . . . . . . . . . . . 71 11.2. Frame Type Registry . . . . . . . . . . . . . . . . . . 71
11.3. Settings Registry . . . . . . . . . . . . . . . . . . . 72 11.3. Settings Registry . . . . . . . . . . . . . . . . . . . 72
11.4. Error Code Registry . . . . . . . . . . . . . . . . . . 72 11.4. Error Code Registry . . . . . . . . . . . . . . . . . . 72
11.5. HTTP2-Settings Header Field Registration . . . . . . . . 73 11.5. HTTP2-Settings Header Field Registration . . . . . . . . 73
11.6. PRI Method Registration . . . . . . . . . . . . . . . . 74 11.6. PRI Method Registration . . . . . . . . . . . . . . . . 74
11.7. The 421 Not Authoritative HTTP Status Code . . . . . . . 74 11.7. The 421 Not Authoritative HTTP Status Code . . . . . . . 74
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 74 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 74
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 75 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 75
13.1. Normative References . . . . . . . . . . . . . . . . . . 75 13.1. Normative References . . . . . . . . . . . . . . . . . . 75
13.2. Informative References . . . . . . . . . . . . . . . . . 76 13.2. Informative References . . . . . . . . . . . . . . . . . 77
13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 77 13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Appendix A. Change Log (to be removed by RFC Editor before Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 79
publication) . . . . . . . . . . . . . . . . . . . . 78 A.1. Since draft-ietf-httpbis-http2-13 . . . . . . . . . . . . 79
A.1. Since draft-ietf-httpbis-http2-12 . . . . . . . . . . . . 78 A.2. Since draft-ietf-httpbis-http2-12 . . . . . . . . . . . . 79
A.2. Since draft-ietf-httpbis-http2-11 . . . . . . . . . . . . 78 A.3. Since draft-ietf-httpbis-http2-11 . . . . . . . . . . . . 79
A.3. Since draft-ietf-httpbis-http2-10 . . . . . . . . . . . . 78 A.4. Since draft-ietf-httpbis-http2-10 . . . . . . . . . . . . 80
A.4. Since draft-ietf-httpbis-http2-09 . . . . . . . . . . . . 79 A.5. Since draft-ietf-httpbis-http2-09 . . . . . . . . . . . . 80
A.5. Since draft-ietf-httpbis-http2-08 . . . . . . . . . . . . 79 A.6. Since draft-ietf-httpbis-http2-08 . . . . . . . . . . . . 80
A.6. Since draft-ietf-httpbis-http2-07 . . . . . . . . . . . . 79 A.7. Since draft-ietf-httpbis-http2-07 . . . . . . . . . . . . 81
A.7. Since draft-ietf-httpbis-http2-06 . . . . . . . . . . . . 79 A.8. Since draft-ietf-httpbis-http2-06 . . . . . . . . . . . . 81
A.8. Since draft-ietf-httpbis-http2-05 . . . . . . . . . . . . 80 A.9. Since draft-ietf-httpbis-http2-05 . . . . . . . . . . . . 81
A.9. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 80 A.10. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 81
A.10. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 80 A.11. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 82
A.11. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 81 A.12. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 82
A.12. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 81 A.13. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 82
A.13. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 82 A.14. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 83
A.14. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 82 A.15. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 83
1. Introduction 1. Introduction
The Hypertext Transfer Protocol (HTTP) is a wildly successful The Hypertext Transfer Protocol (HTTP) is a wildly successful
protocol. However, the HTTP/1.1 message format ([RFC7230], protocol. However, the HTTP/1.1 message format ([RFC7230],
Section 3) was designed to be implemented with the tools at hand in Section 3) was designed to be implemented with the tools at hand in
the 1990s, not modern Web application performance. As such it has the 1990s, not modern Web application performance. As such it has
several characteristics that have a negative overall effect on several characteristics that have a negative overall effect on
application performance today. application performance today.
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The means by which support for HTTP/2 is determined is different for The means by which support for HTTP/2 is determined is different for
"http" and "https" URIs. Discovery for "http" URIs is described in "http" and "https" URIs. Discovery for "http" URIs is described in
Section 3.2. Discovery for "https" URIs is described in Section 3.3. Section 3.2. Discovery for "https" URIs is described in Section 3.3.
3.1. HTTP/2 Version Identification 3.1. HTTP/2 Version Identification
The protocol defined in this document has two identifiers. The protocol defined in this document has two identifiers.
o The string "h2" identifies the protocol where HTTP/2 uses TLS o The string "h2" identifies the protocol where HTTP/2 uses TLS
[TLS12]. This identifier is used in the TLS application layer [TLS12]. This identifier is used in the TLS application layer
protocol negotiation extension (ALPN) [TLSALPN] field and any protocol negotiation extension (ALPN) [TLS-ALPN] field and any
place that HTTP/2 over TLS is identified. place that HTTP/2 over TLS is identified.
The "h2" string is serialized into an ALPN protocol identifier as The "h2" string is serialized into an ALPN protocol identifier as
the two octet sequence: 0x68, 0x32. the two octet sequence: 0x68, 0x32.
o The string "h2c" identifies the protocol where HTTP/2 is run over o The string "h2c" identifies the protocol where HTTP/2 is run over
cleartext TCP. This identifier is used in the HTTP/1.1 Upgrade cleartext TCP. This identifier is used in the HTTP/1.1 Upgrade
header field and any place that HTTP/2 over TCP is identified. header field and any place that HTTP/2 over TCP is identified.
Negotiating "h2" or "h2c" implies the use of the transport, security, Negotiating "h2" or "h2c" implies the use of the transport, security,
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implicit acknowledgment. Providing these values in the Upgrade implicit acknowledgment. Providing these values in the Upgrade
request ensures that the protocol does not require default values for request ensures that the protocol does not require default values for
the above SETTINGS parameters, and gives a client an opportunity to the above SETTINGS parameters, and gives a client an opportunity to
provide other parameters prior to receiving any frames from the provide other parameters prior to receiving any frames from the
server. server.
3.3. Starting HTTP/2 for "https" URIs 3.3. Starting HTTP/2 for "https" URIs
A client that makes a request to an "https" URI without prior A client that makes a request to an "https" URI without prior
knowledge about support for HTTP/2 uses TLS [TLS12] with the knowledge about support for HTTP/2 uses TLS [TLS12] with the
application layer protocol negotiation extension [TLSALPN]. application layer protocol negotiation extension [TLS-ALPN].
HTTP/2 over TLS uses the "h2" application token. The "h2c" token HTTP/2 over TLS uses the "h2" application token. The "h2c" token
MUST NOT be sent by a client or selected by a server. MUST NOT be sent by a client or selected by a server.
Once TLS negotiation is complete, both the client and the server send Once TLS negotiation is complete, both the client and the server send
a connection preface (Section 3.5). a connection preface (Section 3.5).
3.4. Starting HTTP/2 with Prior Knowledge 3.4. Starting HTTP/2 with Prior Knowledge
A client can learn that a particular server supports HTTP/2 by other A client can learn that a particular server supports HTTP/2 by other
means. For example, [ALT-SVC] describes a mechanism for advertising means. For example, [ALT-SVC] describes a mechanism for advertising
this capability. this capability.
A client MAY immediately send HTTP/2 frames to a server that is known A client MAY immediately send HTTP/2 frames to a server that is known
to support HTTP/2, after the connection preface (Section 3.5). A to support HTTP/2, after the connection preface (Section 3.5). A
server can identify such a connection by the use of the "PRI" method server can identify such a connection by the use of the "PRI" method
in the connection preface. This only affects the establishment of in the connection preface. This only affects the establishment of
HTTP/2 connections over cleartext TCP; implementations that support HTTP/2 connections over cleartext TCP; implementations that support
HTTP/2 over TLS MUST use protocol negotiation in TLS [TLSALPN]. HTTP/2 over TLS MUST use protocol negotiation in TLS [TLS-ALPN].
Prior support for HTTP/2 is not a strong signal that a given server Prior support for HTTP/2 is not a strong signal that a given server
will support HTTP/2 for future connections. It is possible for will support HTTP/2 for future connections. It is possible for
server configurations to change; for configurations to differ between server configurations to change; for configurations to differ between
instances in clustered server; or network conditions to change. instances in clustered server; or network conditions to change.
3.5. HTTP/2 Connection Preface 3.5. HTTP/2 Connection Preface
Upon establishment of a TCP connection and determination that HTTP/2 Upon establishment of a TCP connection and determination that HTTP/2
will be used by both peers, each endpoint MUST send a connection will be used by both peers, each endpoint MUST send a connection
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SETTINGS frame (Section 6.5) that MUST be the first frame the server SETTINGS frame (Section 6.5) that MUST be the first frame the server
sends in the HTTP/2 connection. sends in the HTTP/2 connection.
To avoid unnecessary latency, clients are permitted to send To avoid unnecessary latency, clients are permitted to send
additional frames to the server immediately after sending the client additional frames to the server immediately after sending the client
connection preface, without waiting to receive the server connection connection preface, without waiting to receive the server connection
preface. It is important to note, however, that the server preface. It is important to note, however, that the server
connection preface SETTINGS frame might include parameters that connection preface SETTINGS frame might include parameters that
necessarily alter how a client is expected to communicate with the necessarily alter how a client is expected to communicate with the
server. Upon receiving the SETTINGS frame, the client is expected to server. Upon receiving the SETTINGS frame, the client is expected to
honor any parameters established. honor any parameters established. In some configurations, it is
possible for the server to transmit SETTINGS before the client,
providing an opportunity to avoid this issue.
Clients and servers MUST terminate the TCP connection if either peer Clients and servers MUST terminate the TCP connection if either peer
does not begin with a valid connection preface. A GOAWAY frame does not begin with a valid connection preface. A GOAWAY frame
(Section 6.8) can be omitted if it is clear that the peer is not (Section 6.8) can be omitted if it is clear that the peer is not
using HTTP/2. using HTTP/2.
4. HTTP Frames 4. HTTP Frames
Once the HTTP/2 connection is established, endpoints can begin Once the HTTP/2 connection is established, endpoints can begin
exchanging frames. exchanging frames.
4.1. Frame Format 4.1. Frame Format
All frames begin with a fixed 8-octet header followed by a payload of All frames begin with a fixed 9-octet header followed by a variable-
between 0 and 16,383 octets. length payload.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| R | Length (14) | Type (8) | Flags (8) | | Length (24) |
+---------------+---------------+---------------+
| Type (8) | Flags (8) |
+-+-+-----------+---------------+-------------------------------+ +-+-+-----------+---------------+-------------------------------+
|R| Stream Identifier (31) | |R| Stream Identifier (31) |
+=+=============================================================+ +=+=============================================================+
| Frame Payload (0...) ... | Frame Payload (0...) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Frame Layout Frame Layout
The fields of the frame header are defined as: The fields of the frame header are defined as:
R: A reserved 2-bit field. The semantics of these bits are undefined
and the bits MUST remain unset (0) when sending and MUST be
ignored when receiving.
Length: The length of the frame payload expressed as an unsigned Length: The length of the frame payload expressed as an unsigned
14-bit integer. The 8 octets of the frame header are not included 24-bit integer. Values greater than 2^14 (16,384) MUST NOT be
in this value. sent unless the receiver has set a larger value for
SETTINGS_MAX_FRAME_SIZE.
The 9 octets of the frame header are not included in this value.
Type: The 8-bit type of the frame. The frame type determines the Type: The 8-bit type of the frame. The frame type determines the
format and semantics of the frame. Implementations MUST ignore format and semantics of the frame. Implementations MUST ignore
and discard any frame that has a type that is unknown. and discard any frame that has a type that is unknown.
Flags: An 8-bit field reserved for frame-type specific boolean Flags: An 8-bit field reserved for frame-type specific boolean
flags. flags.
Flags are assigned semantics specific to the indicated frame type. Flags are assigned semantics specific to the indicated frame type.
Flags that have no defined semantics for a particular frame type Flags that have no defined semantics for a particular frame type
skipping to change at page 13, line 39 skipping to change at page 14, line 7
Stream Identifier: A 31-bit stream identifier (see Section 5.1.1). Stream Identifier: A 31-bit stream identifier (see Section 5.1.1).
The value 0 is reserved for frames that are associated with the The value 0 is reserved for frames that are associated with the
connection as a whole as opposed to an individual stream. connection as a whole as opposed to an individual stream.
The structure and content of the frame payload is dependent entirely The structure and content of the frame payload is dependent entirely
on the frame type. on the frame type.
4.2. Frame Size 4.2. Frame Size
The maximum size of a frame payload varies by frame type. The The size of a frame payload is limited by the maximum size that a
absolute maximum size of a frame payload is 2^14-1 (16,383) octets, receiver advertises in the SETTINGS_MAX_FRAME_SIZE setting. This
meaning that the maximum frame size is 16,391 octets. All setting can have any value between 2^14 (16,384) and 2^24-1
implementations MUST be capable of receiving and minimally processing (16,777,215) octets, inclusive.
frames up to this maximum size.
Certain frame types, such as PING (Section 6.7), impose additional All implementations MUST be capable of receiving and minimally
limits on the amount of payload data allowed. processing frames up to 2^14 octets in length, plus the 9 octet frame
header (Section 4.1). The size of the frame header is not included
when describing frame sizes.
Note: Certain frame types, such as PING (Section 6.7), impose
additional limits on the amount of payload data allowed.
If a frame size exceeds any defined limit, or is too small to contain If a frame size exceeds any defined limit, or is too small to contain
mandatory frame data, the endpoint MUST send a FRAME_SIZE_ERROR mandatory frame data, the endpoint MUST send a FRAME_SIZE_ERROR
error. A frame size error in a frame that could alter the state of error. A frame size error in a frame that could alter the state of
the entire connection MUST be treated as a connection error the entire connection MUST be treated as a connection error
(Section 5.4.1); this includes any frame carrying a header block (Section 5.4.1); this includes any frame carrying a header block
(Section 4.3) (that is, HEADERS, PUSH_PROMISE, and CONTINUATION), (Section 4.3) (that is, HEADERS, PUSH_PROMISE, and CONTINUATION),
SETTINGS, and any WINDOW_UPDATE frame with a stream identifier of 0. SETTINGS, and any WINDOW_UPDATE frame with a stream identifier of 0.
Endpoints are not obligated to use all available space in a frame.
Responsiveness can be improved by using frames that are smaller than
the permitted maximum size. Sending large frames can result in
delays in sending maintenance frames, such RST_STREAM, WINDOW_UPDATE,
or PRIORITY, which if blocked by the transmission of a large frame,
could affect performance.
4.3. Header Compression and Decompression 4.3. Header Compression and Decompression
A header field in HTTP/2 is a name with one or more associated A header field in HTTP/2 is a name with one or more associated
values. They are used within HTTP request and response messages as values. They are used within HTTP request and response messages as
well as server push operations (see Section 8.2). well as server push operations (see Section 8.2).
Header sets are collections of zero or more header fields. When Header lists are collections of zero or more header fields. When
transmitted over a connection, a header set is serialized into a transmitted over a connection, a header list is serialized into a
header block using HTTP Header Compression [COMPRESSION]. The header block using HTTP Header Compression [COMPRESSION]. The
serialized header block is then divided into one or more octet serialized header block is then divided into one or more octet
sequences, called header block fragments, and transmitted within the sequences, called header block fragments, and transmitted within the
payload of HEADERS (Section 6.2), PUSH_PROMISE (Section 6.6) or payload of HEADERS (Section 6.2), PUSH_PROMISE (Section 6.6) or
CONTINUATION (Section 6.10) frames. CONTINUATION (Section 6.10) frames.
HTTP Header Compression does not preserve the relative ordering of
header fields. Header fields with multiple values are encoded into a
single header field using a special delimiter (see Section 8.1.2.3),
this preserves the relative order of values for that header field.
The Cookie header field [COOKIE] is treated specially by the HTTP The Cookie header field [COOKIE] is treated specially by the HTTP
mapping (see Section 8.1.2.4). mapping (see Section 8.1.2.5).
A receiving endpoint reassembles the header block by concatenating A receiving endpoint reassembles the header block by concatenating
its fragments, then decompresses the block to reconstruct the header its fragments, then decompresses the block to reconstruct the header
set. list.
A complete header block consists of either: A complete header block consists of either:
o a single HEADERS or PUSH_PROMISE frame, with the END_HEADERS flag o a single HEADERS or PUSH_PROMISE frame, with the END_HEADERS flag
set, or set, or
o a HEADERS or PUSH_PROMISE frame with the END_HEADERS flag cleared o a HEADERS or PUSH_PROMISE frame with the END_HEADERS flag cleared
and one or more CONTINUATION frames, where the last CONTINUATION and one or more CONTINUATION frames, where the last CONTINUATION
frame has the END_HEADERS flag set. frame has the END_HEADERS flag set.
skipping to change at page 16, line 5 skipping to change at page 16, line 17
particular, the order of HEADERS, and DATA frames is semantically particular, the order of HEADERS, and DATA frames is semantically
significant. significant.
o Streams are identified by an integer. Stream identifiers are o Streams are identified by an integer. Stream identifiers are
assigned to streams by the endpoint initiating the stream. assigned to streams by the endpoint initiating the stream.
5.1. Stream States 5.1. Stream States
The lifecycle of a stream is shown in Figure 1. The lifecycle of a stream is shown in Figure 1.
+--------+ +--------+
PP | | PP PP | | PP
,--------| idle |--------. ,--------| idle |--------.
/ | | \ / | | \
v +--------+ v v +--------+ v
+----------+ | +----------+ +----------+ | +----------+
| | | H | | | | | H | |
,---| reserved | | | reserved |---. ,---| reserved | | | reserved |---.
| | (local) | v | (remote) | | | | (local) | v | (remote) | |
| +----------+ +--------+ +----------+ | | +----------+ +--------+ +----------+ |
| | ES | | ES | | | | ES | | ES | |
| | H ,-------| open |-------. | H | | | H ,-------| open |-------. | H |
| | / | | \ | | | | / | | \ | |
| v v +--------+ v v | | v v +--------+ v v |
| +----------+ | +----------+ | | +----------+ | +----------+ |
| | half | | | half | | | | half | | | half | |
| | closed | | R | closed | | | | closed | | R | closed | |
| | (remote) | | | (local) | | | | (remote) | | | (local) | |
| +----------+ | +----------+ | | +----------+ | +----------+ |
| | v | | | | v | |
| | ES / R +--------+ ES / R | | | | ES / R +--------+ ES / R | |
| `----------->| |<-----------' | | `----------->| |<-----------' |
| R | closed | R | | R | closed | R |
`-------------------->| |<--------------------' `-------------------->| |<--------------------'
+--------+ +--------+
H: HEADERS frame (with implied CONTINUATIONs) H: HEADERS frame (with implied CONTINUATIONs)
PP: PUSH_PROMISE frame (with implied CONTINUATIONs) PP: PUSH_PROMISE frame (with implied CONTINUATIONs)
ES: END_STREAM flag ES: END_STREAM flag
R: RST_STREAM frame R: RST_STREAM frame
Figure 1: Stream States Figure 1: Stream States
Note that this diagram shows stream state transitions and frames that Note that this diagram shows stream state transitions and frames that
affect those transitions only. In this regard, CONTINUATION frames affect those transitions only. In this regard, CONTINUATION frames
do not result in state transitions and are effectively part of the do not result in state transitions and are effectively part of the
HEADERS or PUSH_PROMISE that they follow. HEADERS or PUSH_PROMISE that they follow.
Both endpoints have a subjective view of the state of a stream that Both endpoints have a subjective view of the state of a stream that
could be different when frames are in transit. Endpoints do not could be different when frames are in transit. Endpoints do not
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A stream that is "half closed (remote)" is no longer being used by A stream that is "half closed (remote)" is no longer being used by
the peer to send frames. In this state, an endpoint is no longer the peer to send frames. In this state, an endpoint is no longer
obligated to maintain a receiver flow control window if it obligated to maintain a receiver flow control window if it
performs flow control. performs flow control.
If an endpoint receives additional frames for a stream that is in If an endpoint receives additional frames for a stream that is in
this state, other than WINDOW_UPDATE, PRIORITY or RST_STREAM, it this state, other than WINDOW_UPDATE, PRIORITY or RST_STREAM, it
MUST respond with a stream error (Section 5.4.2) of type MUST respond with a stream error (Section 5.4.2) of type
STREAM_CLOSED. STREAM_CLOSED.
A stream that is "half closed (remote)" can be used by the
endpoint to send frames of any type. In this state, the endpoint
continues to observe advertised stream level flow control limits
(Section 5.2).
A stream can transition from this state to "closed" by sending a A stream can transition from this state to "closed" by sending a
frame that contains an END_STREAM flag, or when either peer sends frame that contains an END_STREAM flag, or when either peer sends
a RST_STREAM frame. a RST_STREAM frame.
closed: closed:
The "closed" state is the terminal state. The "closed" state is the terminal state.
An endpoint MUST NOT send frames on a closed stream. An endpoint An endpoint MUST NOT send frames on a closed stream. An endpoint
that receives any frame other than PRIORITY after receiving a that receives any frame other than PRIORITY after receiving a
RST_STREAM MUST treat that as a stream error (Section 5.4.2) of RST_STREAM MUST treat that as a stream error (Section 5.4.2) of
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An endpoint might receive a PUSH_PROMISE frame after it sends An endpoint might receive a PUSH_PROMISE frame after it sends
RST_STREAM. PUSH_PROMISE causes a stream to become "reserved" RST_STREAM. PUSH_PROMISE causes a stream to become "reserved"
even if the associated stream has been reset. Therefore, a even if the associated stream has been reset. Therefore, a
RST_STREAM is needed to close an unwanted promised stream. RST_STREAM is needed to close an unwanted promised stream.
In the absence of more specific guidance elsewhere in this document, In the absence of more specific guidance elsewhere in this document,
implementations SHOULD treat the receipt of a message that is not implementations SHOULD treat the receipt of a message that is not
expressly permitted in the description of a state as a connection expressly permitted in the description of a state as a connection
error (Section 5.4.1) of type PROTOCOL_ERROR. error (Section 5.4.1) of type PROTOCOL_ERROR.
An example of the state transitions for an HTTP request/response
exchange can be found in Section 8.1. An example of the state
transitions for server push can be found in Section 8.2.1 and
Section 8.2.2.
5.1.1. Stream Identifiers 5.1.1. Stream Identifiers
Streams are identified with an unsigned 31-bit integer. Streams Streams are identified with an unsigned 31-bit integer. Streams
initiated by a client MUST use odd-numbered stream identifiers; those initiated by a client MUST use odd-numbered stream identifiers; those
initiated by the server MUST use even-numbered stream identifiers. A initiated by the server MUST use even-numbered stream identifiers. A
stream identifier of zero (0x0) is used for connection control stream identifier of zero (0x0) is used for connection control
messages; the stream identifier zero cannot be used to establish a messages; the stream identifier zero cannot be used to establish a
new stream. new stream.
HTTP/1.1 requests that are upgraded to HTTP/2 (see Section 3.2) are HTTP/1.1 requests that are upgraded to HTTP/2 (see Section 3.2) are
skipping to change at page 23, line 35 skipping to change at page 24, line 16
it would prefer its peer allocate resources when managing concurrent it would prefer its peer allocate resources when managing concurrent
streams. Most importantly, priority can be used to select streams streams. Most importantly, priority can be used to select streams
for transmitting frames when there is limited capacity for sending. for transmitting frames when there is limited capacity for sending.
Streams can be prioritized by marking them as dependent on the Streams can be prioritized by marking them as dependent on the
completion of other streams (Section 5.3.1). Each dependency is completion of other streams (Section 5.3.1). Each dependency is
assigned a relative weight, a number that is used to determine the assigned a relative weight, a number that is used to determine the
relative proportion of available resources that are assigned to relative proportion of available resources that are assigned to
streams dependent on the same stream. streams dependent on the same stream.
[[CREF2: Note that stream dependencies have not yet been validated in
practice. The theory might be fairly sound, but there are no
implementations currently sending these. If it turns out that they
are not useful, or actively harmful, implementations will be
requested to avoid creating stream dependencies.]]
Explicitly setting the priority for a stream is input to a Explicitly setting the priority for a stream is input to a
prioritization process. It does not guarantee any particular prioritization process. It does not guarantee any particular
processing or transmission order for the stream relative to any other processing or transmission order for the stream relative to any other
stream. An endpoint cannot force a peer to process concurrent stream. An endpoint cannot force a peer to process concurrent
streams in a particular order using priority. Expressing priority is streams in a particular order using priority. Expressing priority is
therefore only ever a suggestion. therefore only ever a suggestion.
Prioritization information can be specified explicitly for streams as Prioritization information can be specified explicitly for streams as
they are created using the HEADERS frame, or changed using the they are created using the HEADERS frame, or changed using the
PRIORITY frame. Providing prioritization information is optional, so PRIORITY frame. Providing prioritization information is optional, so
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Each stream can be given an explicit dependency on another stream. Each stream can be given an explicit dependency on another stream.
Including a dependency expresses a preference to allocate resources Including a dependency expresses a preference to allocate resources
to the identified stream rather than to the dependent stream. to the identified stream rather than to the dependent stream.
A stream that is not dependent on any other stream is given a stream A stream that is not dependent on any other stream is given a stream
dependency of 0x0. In other words, the non-existent stream 0 forms dependency of 0x0. In other words, the non-existent stream 0 forms
the root of the tree. the root of the tree.
A stream that depends on another stream is a dependent stream. The A stream that depends on another stream is a dependent stream. The
stream upon which a stream is dependent is a parent stream. stream upon which a stream is dependent is a parent stream. A
dependency on a stream that is not currently in the tree - such as a
stream in the "idle" state - results in the stream being given a
default priority (Section 5.3.5).
When assigning a dependency on another stream, the stream is added as When assigning a dependency on another stream, the stream is added as
a new dependency of the parent stream. Dependent streams that share a new dependency of the parent stream. Dependent streams that share
the same parent are not order with respect to each other. For the same parent are not ordered with respect to each other. For
example, if streams B and C are dependent on stream A, and if stream example, if streams B and C are dependent on stream A, and if stream
D is created with a dependency on stream A, this results in a D is created with a dependency on stream A, this results in a
dependency order of A followed by B, C, and D in any order. dependency order of A followed by B, C, and D in any order.
A A A A
/ \ ==> /|\ / \ ==> /|\
B C B D C B C B D C
Example of Default Dependency Creation Example of Default Dependency Creation
skipping to change at page 27, line 14 skipping to change at page 27, line 40
maintain state for at least as many streams as allowed by their maintain state for at least as many streams as allowed by their
setting for SETTINGS_MAX_CONCURRENT_STREAMS. setting for SETTINGS_MAX_CONCURRENT_STREAMS.
An endpoint receiving a PRIORITY frame that changes the priority of a An endpoint receiving a PRIORITY frame that changes the priority of a
closed stream SHOULD alter the dependencies of the streams that closed stream SHOULD alter the dependencies of the streams that
depend on it, if it has retained enough state to do so. depend on it, if it has retained enough state to do so.
5.3.5. Default Priorities 5.3.5. Default Priorities
Providing priority information is optional. Streams are assigned a Providing priority information is optional. Streams are assigned a
default dependency on stream 0x0. Pushed streams (Section 8.2) non-exclusive dependency on stream 0x0 by default. Pushed streams
initially depend on their associated stream. In both cases, streams (Section 8.2) initially depend on their associated stream. In both
are assigned a default weight of 16. cases, streams are assigned a default weight of 16.
5.4. Error Handling 5.4. Error Handling
HTTP/2 framing permits two classes of error: HTTP/2 framing permits two classes of error:
o An error condition that renders the entire connection unusable is o An error condition that renders the entire connection unusable is
a connection error. a connection error.
o An error in an individual stream is a stream error. o An error in an individual stream is a stream error.
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5.5. Extending HTTP/2 5.5. Extending HTTP/2
HTTP/2 permits extension of the protocol. Protocol extensions can be HTTP/2 permits extension of the protocol. Protocol extensions can be
used to provide additional services or alter any aspect of the used to provide additional services or alter any aspect of the
protocol, within the limitations described in this section. protocol, within the limitations described in this section.
Extensions are effective only within the scope of a single HTTP/2 Extensions are effective only within the scope of a single HTTP/2
connection. connection.
Extensions are permitted to use new frame types (Section 4.1), new Extensions are permitted to use new frame types (Section 4.1), new
settings (Section 6.5.2), new error codes (Section 7), or new header settings (Section 6.5.2), or new error codes (Section 7). Registries
fields that start with a colon (:). Of these, registries are are established for managing these extension points: frame types
established for frame types (Section 11.2), settings (Section 11.3) (Section 11.2), settings (Section 11.3) and error codes
and error codes (Section 11.4). (Section 11.4).
Implementations MUST ignore unknown or unsupported values in all Implementations MUST ignore unknown or unsupported values in all
extensible protocol elements. Implementations MUST discard frames extensible protocol elements. Implementations MUST discard frames
that have unknown or unsupported types. This means that any of these that have unknown or unsupported types. This means that any of these
extension points can be safely used by extensions without prior extension points can be safely used by extensions without prior
arrangement or negotiation. arrangement or negotiation.
However, extensions that could change the semantics of existing However, extensions that could change the semantics of existing
protocol components MUST be negotiated before being used. For protocol components MUST be negotiated before being used. For
example, an extension that changes the layout of the HEADERS frame example, an extension that changes the layout of the HEADERS frame
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Padding octets MUST be set to zero when sending and ignored when Padding octets MUST be set to zero when sending and ignored when
receiving. receiving.
The DATA frame defines the following flags: The DATA frame defines the following flags:
END_STREAM (0x1): Bit 1 being set indicates that this frame is the END_STREAM (0x1): Bit 1 being set indicates that this frame is the
last that the endpoint will send for the identified stream. last that the endpoint will send for the identified stream.
Setting this flag causes the stream to enter one of the "half Setting this flag causes the stream to enter one of the "half
closed" states or the "closed" state (Section 5.1). closed" states or the "closed" state (Section 5.1).
END_SEGMENT (0x2): Bit 2 being set indicates that this frame is the
last for the current segment. Intermediaries MUST NOT coalesce
frames across a segment boundary and MUST preserve segment
boundaries when forwarding frames.
PADDED (0x8): Bit 4 being set indicates that the Pad Length field is PADDED (0x8): Bit 4 being set indicates that the Pad Length field is
present. present.
DATA frames MUST be associated with a stream. If a DATA frame is DATA frames MUST be associated with a stream. If a DATA frame is
received whose stream identifier field is 0x0, the recipient MUST received whose stream identifier field is 0x0, the recipient MUST
respond with a connection error (Section 5.4.1) of type respond with a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
DATA frames are subject to flow control and can only be sent when a DATA frames are subject to flow control and can only be sent when a
stream is in the "open" or "half closed (remote)" states. The entire stream is in the "open" or "half closed (remote)" states. The entire
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END_STREAM (0x1): Bit 1 being set indicates that the header block END_STREAM (0x1): Bit 1 being set indicates that the header block
(Section 4.3) is the last that the endpoint will send for the (Section 4.3) is the last that the endpoint will send for the
identified stream. Setting this flag causes the stream to enter identified stream. Setting this flag causes the stream to enter
one of "half closed" states (Section 5.1). one of "half closed" states (Section 5.1).
A HEADERS frame that is followed by CONTINUATION frames carries A HEADERS frame that is followed by CONTINUATION frames carries
the END_STREAM flag that signals the end of a stream. A the END_STREAM flag that signals the end of a stream. A
CONTINUATION frame cannot be used to terminate a stream. CONTINUATION frame cannot be used to terminate a stream.
END_SEGMENT (0x2): Bit 2 being set indicates that this frame is the
last for the current segment. Intermediaries MUST NOT coalesce
frames across a segment boundary and MUST preserve segment
boundaries when forwarding frames.
END_HEADERS (0x4): Bit 3 being set indicates that this frame END_HEADERS (0x4): Bit 3 being set indicates that this frame
contains an entire header block (Section 4.3) and is not followed contains an entire header block (Section 4.3) and is not followed
by any CONTINUATION frames. by any CONTINUATION frames.
A HEADERS frame without the END_HEADERS flag set MUST be followed A HEADERS frame without the END_HEADERS flag set MUST be followed
by a CONTINUATION frame for the same stream. A receiver MUST by a CONTINUATION frame for the same stream. A receiver MUST
treat the receipt of any other type of frame or a frame on a treat the receipt of any other type of frame or a frame on a
different stream as a connection error (Section 5.4.1) of type different stream as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
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A value of 0 for SETTINGS_MAX_CONCURRENT_STREAMS SHOULD NOT be A value of 0 for SETTINGS_MAX_CONCURRENT_STREAMS SHOULD NOT be
treated as special by endpoints. A zero value does prevent the treated as special by endpoints. A zero value does prevent the
creation of new streams, however this can also happen for any creation of new streams, however this can also happen for any
limit that is exhausted with active streams. Servers SHOULD only limit that is exhausted with active streams. Servers SHOULD only
set a zero value for short durations; if a server does not wish to set a zero value for short durations; if a server does not wish to
accept requests, closing the connection could be preferable. accept requests, closing the connection could be preferable.
SETTINGS_INITIAL_WINDOW_SIZE (0x4): Indicates the sender's initial SETTINGS_INITIAL_WINDOW_SIZE (0x4): Indicates the sender's initial
window size (in bytes) for stream level flow control. The initial window size (in bytes) for stream level flow control. The initial
value is 65,535. value is 2^16-1 (65,535) octets.
This setting affects the window size of all streams, including This setting affects the window size of all streams, including
existing streams, see Section 6.9.2. existing streams, see Section 6.9.2.
Values above the maximum flow control window size of 2^31 - 1 MUST Values above the maximum flow control window size of 2^31-1 MUST
be treated as a connection error (Section 5.4.1) of type be treated as a connection error (Section 5.4.1) of type
FLOW_CONTROL_ERROR. FLOW_CONTROL_ERROR.
SETTINGS_MAX_FRAME_SIZE (0x5): Indicates the size of the largest
frame payload that a receiver is willing to accept.
The initial value is 2^14 (16,384) octets. The value advertised
by an endpoint MUST be between this initial value and the maximum
allowed frame size (2^24-1 or 16,777,215 octets), inclusive.
Values outside this range MUST be treated as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
SETTINGS_MAX_HEADER_LIST_SIZE (0x6): This advisory setting informs a
peer of the maximum size of header list that the sender is
prepared to accept. The value is based on the uncompressed size
of header fields, including the length of the name and value in
octets plus an overhead of 32 octets for each header field.
For any given request, a lower limit than what is advertised MAY
be enforced. The initial value of this setting is unlimited.
An endpoint that receives a SETTINGS frame with any unknown or An endpoint that receives a SETTINGS frame with any unknown or
unsupported identifier MUST ignore that setting. unsupported identifier MUST ignore that setting.
6.5.3. Settings Synchronization 6.5.3. Settings Synchronization
Most values in SETTINGS benefit from or require an understanding of Most values in SETTINGS benefit from or require an understanding of
when the peer has received and applied the changed the communicated when the peer has received and applied the changed parameter values.
parameter values. In order to provide such synchronization In order to provide such synchronization timepoints, the recipient of
timepoints, the recipient of a SETTINGS frame in which the ACK flag a SETTINGS frame in which the ACK flag is not set MUST apply the
is not set MUST apply the updated parameters as soon as possible upon updated parameters as soon as possible upon receipt.
receipt.
The values in the SETTINGS frame MUST be applied in the order they The values in the SETTINGS frame MUST be processed in the order they
appear, with no other frame processing between values. Once all appear, with no other frame processing between values. Unsupported
values have been applied, the recipient MUST immediately emit a parameters MUST be ignored. Once all values have been processed, the
SETTINGS frame with the ACK flag set. Upon receiving a SETTINGS recipient MUST immediately emit a SETTINGS frame with the ACK flag
frame with the ACK flag set, the sender of the altered parameters can set. Upon receiving a SETTINGS frame with the ACK flag set, the
rely upon their application. sender of the altered parameters can rely on the setting having been
applied.
If the sender of a SETTINGS frame does not receive an acknowledgement If the sender of a SETTINGS frame does not receive an acknowledgement
within a reasonable amount of time, it MAY issue a connection error within a reasonable amount of time, it MAY issue a connection error
(Section 5.4.1) of type SETTINGS_TIMEOUT. (Section 5.4.1) of type SETTINGS_TIMEOUT.
6.6. PUSH_PROMISE 6.6. PUSH_PROMISE
The PUSH_PROMISE frame (type=0x5) is used to notify the peer endpoint The PUSH_PROMISE frame (type=0x5) is used to notify the peer endpoint
in advance of streams the sender intends to initiate. The in advance of streams the sender intends to initiate. The
PUSH_PROMISE frame includes the unsigned 31-bit identifier of the PUSH_PROMISE frame includes the unsigned 31-bit identifier of the
skipping to change at page 41, line 22 skipping to change at page 42, line 14
streams on the connection, although a new connection can be streams on the connection, although a new connection can be
established for new streams. established for new streams.
The purpose of this frame is to allow an endpoint to gracefully stop The purpose of this frame is to allow an endpoint to gracefully stop
accepting new streams, while still finishing processing of previously accepting new streams, while still finishing processing of previously
established streams. This enables administrative actions, like established streams. This enables administrative actions, like
server maintainence. server maintainence.
There is an inherent race condition between an endpoint starting new There is an inherent race condition between an endpoint starting new
streams and the remote sending a GOAWAY frame. To deal with this streams and the remote sending a GOAWAY frame. To deal with this
case, the GOAWAY contains the stream identifier of the last stream case, the GOAWAY contains the stream identifier of the last peer-
which was or might be processed on the sending endpoint in this initiated stream which was or might be processed on the sending
connection. If the receiver of the GOAWAY has sent data on streams endpoint in this connection. For instance, if the server sends a
with a higher stream identifier than what is indicated in the GOAWAY GOAWAY frame, the identifed stream is the highest numbered stream
frame, those streams are not or will not be processed. The receiver initiated by the client.
of the GOAWAY frame can treat the streams as though they had never
been created at all, thereby allowing those streams to be retried If the receiver of the GOAWAY has sent data on streams with a higher
later on a new connection. stream identifier than what is indicated in the GOAWAY frame, those
streams are not or will not be processed. The receiver of the GOAWAY
frame can treat the streams as though they had never been created at
all, thereby allowing those streams to be retried later on a new
connection.
Endpoints SHOULD always send a GOAWAY frame before closing a Endpoints SHOULD always send a GOAWAY frame before closing a
connection so that the remote can know whether a stream has been connection so that the remote can know whether a stream has been
partially processed or not. For example, if an HTTP client sends a partially processed or not. For example, if an HTTP client sends a
POST at the same time that a server closes a connection, the client POST at the same time that a server closes a connection, the client
cannot know if the server started to process that POST request if the cannot know if the server started to process that POST request if the
server does not send a GOAWAY frame to indicate what streams it might server does not send a GOAWAY frame to indicate what streams it might
have acted on. have acted on.
An endpoint might choose to close a connection without sending GOAWAY An endpoint might choose to close a connection without sending GOAWAY
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| Window Size Increment (31) | |R| Window Size Increment (31) |
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
WINDOW_UPDATE Payload Format WINDOW_UPDATE Payload Format
The payload of a WINDOW_UPDATE frame is one reserved bit, plus an The payload of a WINDOW_UPDATE frame is one reserved bit, plus an
unsigned 31-bit integer indicating the number of bytes that the unsigned 31-bit integer indicating the number of bytes that the
sender can transmit in addition to the existing flow control window. sender can transmit in addition to the existing flow control window.
The legal range for the increment to the flow control window is 1 to The legal range for the increment to the flow control window is 1 to
2^31 - 1 (0x7fffffff) bytes. 2^31-1 (0x7fffffff) bytes.
The WINDOW_UPDATE frame does not define any flags. The WINDOW_UPDATE frame does not define any flags.
The WINDOW_UPDATE frame can be specific to a stream or to the entire The WINDOW_UPDATE frame can be specific to a stream or to the entire
connection. In the former case, the frame's stream identifier connection. In the former case, the frame's stream identifier
indicates the affected stream; in the latter, the value "0" indicates indicates the affected stream; in the latter, the value "0" indicates
that the entire connection is the subject of the frame. that the entire connection is the subject of the frame.
A receiver MUST treat the recipt of a WINDOW_UPDATE frame with an
flow control window increment of 0 as a stream error (Section 5.4.2)
of type PROTOCOL_ERROR; errors on the connection flow control window
MUST be treated as a connection error (Section 5.4.1).
WINDOW_UPDATE can be sent by a peer that has sent a frame bearing the WINDOW_UPDATE can be sent by a peer that has sent a frame bearing the
END_STREAM flag. This means that a receiver could receive a END_STREAM flag. This means that a receiver could receive a
WINDOW_UPDATE frame on a "half closed (remote)" or "closed" stream. WINDOW_UPDATE frame on a "half closed (remote)" or "closed" stream.
A receiver MUST NOT treat this as an error, see Section 5.1. A receiver MUST NOT treat this as an error, see Section 5.1.
A receiver that receives a flow controlled frame MUST always account A receiver that receives a flow controlled frame MUST always account
for its contribution against the connection flow control window, for its contribution against the connection flow control window,
unless the receiver treats this as a connection error unless the receiver treats this as a connection error
(Section 5.4.1). This is necessary even if the frame is in error. (Section 5.4.1). This is necessary even if the frame is in error.
Since the sender counts the frame toward the flow control window, if Since the sender counts the frame toward the flow control window, if
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available in both windows by the length of the transmitted frame. available in both windows by the length of the transmitted frame.
The receiver of a frame sends a WINDOW_UPDATE frame as it consumes The receiver of a frame sends a WINDOW_UPDATE frame as it consumes
data and frees up space in flow control windows. Separate data and frees up space in flow control windows. Separate
WINDOW_UPDATE frames are sent for the stream and connection level WINDOW_UPDATE frames are sent for the stream and connection level
flow control windows. flow control windows.
A sender that receives a WINDOW_UPDATE frame updates the A sender that receives a WINDOW_UPDATE frame updates the
corresponding window by the amount specified in the frame. corresponding window by the amount specified in the frame.
A sender MUST NOT allow a flow control window to exceed 2^31 - 1 A sender MUST NOT allow a flow control window to exceed 2^31-1 bytes.
bytes. If a sender receives a WINDOW_UPDATE that causes a flow If a sender receives a WINDOW_UPDATE that causes a flow control
control window to exceed this maximum it MUST terminate either the window to exceed this maximum it MUST terminate either the stream or
stream or the connection, as appropriate. For streams, the sender the connection, as appropriate. For streams, the sender sends a
sends a RST_STREAM with the error code of FLOW_CONTROL_ERROR code; RST_STREAM with the error code of FLOW_CONTROL_ERROR code; for the
for the connection, a GOAWAY frame with a FLOW_CONTROL_ERROR code. connection, a GOAWAY frame with a FLOW_CONTROL_ERROR code.
Flow controlled frames from the sender and WINDOW_UPDATE frames from Flow controlled frames from the sender and WINDOW_UPDATE frames from
the receiver are completely asynchronous with respect to each other. the receiver are completely asynchronous with respect to each other.
This property allows a receiver to aggressively update the window This property allows a receiver to aggressively update the window
size kept by the sender to prevent streams from stalling. size kept by the sender to prevent streams from stalling.
6.9.2. Initial Flow Control Window Size 6.9.2. Initial Flow Control Window Size
When an HTTP/2 connection is first established, new streams are When an HTTP/2 connection is first established, new streams are
created with an initial flow control window size of 65,535 bytes. created with an initial flow control window size of 65,535 bytes.
skipping to change at page 49, line 33 skipping to change at page 50, line 33
this protocol are defined in the sections below. this protocol are defined in the sections below.
8.1. HTTP Request/Response Exchange 8.1. HTTP Request/Response Exchange
A client sends an HTTP request on a new stream, using a previously A client sends an HTTP request on a new stream, using a previously
unused stream identifier (Section 5.1.1). A server sends an HTTP unused stream identifier (Section 5.1.1). A server sends an HTTP
response on the same stream as the request. response on the same stream as the request.
An HTTP message (request or response) consists of: An HTTP message (request or response) consists of:
1. one HEADERS frame (followed by zero or more CONTINUATION frames) 1. for a response only, zero or more HEADERS frames (each followed
by zero or more CONTINUATION frames) containing the message
headers of informational (1xx) HTTP responses (see [RFC7230],
Section 3.2 and [RFC7231], Section 6.2), and
2. one HEADERS frame (followed by zero or more CONTINUATION frames)
containing the message headers (see [RFC7230], Section 3.2), and containing the message headers (see [RFC7230], Section 3.2), and
2. zero or more DATA frames containing the message payload (see 3. zero or more DATA frames containing the message payload (see
[RFC7230], Section 3.3), and [RFC7230], Section 3.3), and
3. optionally, one HEADERS frame, followed by zero or more 4. optionally, one HEADERS frame, followed by zero or more
CONTINUATION frames containing the trailer-part, if present (see CONTINUATION frames containing the trailer-part, if present (see
[RFC7230], Section 4.1.2). [RFC7230], Section 4.1.2).
The last frame in the sequence bears an END_STREAM flag, noting that The last frame in the sequence bears an END_STREAM flag, noting that
a HEADERS frame bearing the END_STREAM flag can be followed by a HEADERS frame bearing the END_STREAM flag can be followed by
CONTINUATION frames that carry any remaining portions of the header CONTINUATION frames that carry any remaining portions of the header
block. block.
Other frames (from any stream) MUST NOT occur between either HEADERS Other frames (from any stream) MUST NOT occur between either HEADERS
frame and any CONTINUATION frames that might follow. frame and any CONTINUATION frames that might follow.
Otherwise, frames MAY be interspersed on the stream between these A HEADERS frame (and associated CONTINUATION frames) can only appear
frames, but those frames do not carry HTTP semantics. In particular, at the start or end of a stream. An endpoint that receives a second
HEADERS frames (and any CONTINUATION frames that follow) other than HEADERS frame without the END_STREAM flag set MUST treat the
the first and optional last frames in this sequence do not carry HTTP corresponding request or response as malformed (Section 8.1.2.6).
semantics.
Trailing header fields are carried in a header block that also Trailing header fields are carried in a header block that also
terminates the stream. That is, a sequence starting with a HEADERS terminates the stream. That is, a sequence starting with a HEADERS
frame, followed by zero or more CONTINUATION frames, where the frame, followed by zero or more CONTINUATION frames, where the
HEADERS frame bears an END_STREAM flag. Header blocks after the HEADERS frame bears an END_STREAM flag. Header blocks after the
first that do not terminate the stream are not part of an HTTP first that do not terminate the stream are not part of an HTTP
request or response. request or response.
An HTTP request/response exchange fully consumes a single stream. A An HTTP request/response exchange fully consumes a single stream. A
request starts with the HEADERS frame that puts the stream into an request starts with the HEADERS frame that puts the stream into an
"open" state and ends with a frame bearing END_STREAM, which causes "open" state. The request ends with a frame bearing END_STREAM,
the stream to become "half closed" for the client. A response starts which causes the stream to become "half closed (local)" for the
with a HEADERS frame and ends with a frame bearing END_STREAM, client and "half closed (remote)" for the server. A response starts
optionally followed by CONTINUATION frames, which places the stream with a HEADERS frame and ends with a frame bearing END_STREAM, which
in the "closed" state. places the stream in the "closed" state.
8.1.1. Informational Responses
The 1xx series of HTTP response status codes ([RFC7231], Section 6.2)
are not supported in HTTP/2.
The most common use case for 1xx is using an Expect header field with
a "100-continue" token (colloquially, "Expect/continue") to indicate
that the client expects a 100 (Continue) non-final response status
code, receipt of which indicates that the client should continue
sending the request body if it has not already done so.
Typically, Expect/continue is used by clients wishing to avoid
sending a large amount of data in a request body, only to have the
request rejected by the origin server, thereby leaving the connection
potentially unusable.
HTTP/2 does not enable the Expect/continue mechanism; if the server
sends a final status code to reject the request, it can do so without
making the underlying connection unusable.
Note that this means HTTP/2 clients sending requests with bodies may
waste at least one round trip of sent data when the request is
rejected. This can be mitigated by restricting the amount of data
sent for the first round trip by bandwidth-constrained clients, in
anticipation of a final status code.
Other defined 1xx status codes are not applicable to HTTP/2. For
example, the semantics of 101 (Switching Protocols) aren't suitable
to a multiplexed protocol. Likewise, 102 (Processing) [RFC2518] is
no longer necessary to ensure connection liveness, because HTTP/2 has
a separate means of keeping the connection alive. The use of the 102
(Processing) status code for progress reporting has since been
deprecated and is not retained.
This difference between protocol versions necessitates special
handling by intermediaries that translate between them:
o An intermediary that translates HTTP/1.1 requests to HTTP/2 MUST 8.1.1. Upgrading From HTTP/2
generate a 100 (Continue) response if a received request includes
and Expect header field with a "100-continue" token ([RFC7231],
Section 5.1.1), unless it can immediately generate a final status
code. It MUST NOT forward the "100-continue" expectation in the
request header fields.
o An intermediary that translates HTTP/2 to HTTP/1.1 MAY add an HTTP/2 removes support for the 101 (Switching Protocols)
Expect header field with a "100-continue" expectation when informational status code ([RFC7231], Section 6.2.2).
forwarding a request that has a body; see [RFC7231], Section 5.1.1
for specific requirements.
o An intermediary that gateways HTTP/2 to HTTP/1.1 MUST discard all The semantics of 101 (Switching Protocols) aren't applicable to a
other 1xx informational responses. multiplexed protocol. Alternative protocols are able to use the same
mechanisms that HTTP/2 uses to negotiate their use (see Section 3).
8.1.2. HTTP Header Fields 8.1.2. HTTP Header Fields
HTTP header fields carry information as a series of key-value pairs. HTTP header fields carry information as a series of key-value pairs.
For a listing of registered HTTP headers, see the Message Header For a listing of registered HTTP headers, see the Message Header
Field Registry maintained at [4]. Field Registry maintained at [4].
8.1.2.1. Pseudo-Header Fields
While HTTP/1.x used the message start-line (see [RFC7230], While HTTP/1.x used the message start-line (see [RFC7230],
Section 3.1) to convey the target URI and method of the request, and Section 3.1) to convey the target URI and method of the request, and
the status code for the response, HTTP/2 uses special pseudo-headers the status code for the response, HTTP/2 uses special pseudo-header
beginning with ':' character (ASCII 0x3a) for this purpose. fields beginning with ':' character (ASCII 0x3a) for this purpose.
Pseudo-header fields are only valid in the HTTP/2 context. These are
not HTTP header fields. Endpoints MUST NOT generate pseudo-header
fields other than those defined in this document.
Pseudo-header fields are only valid in the context in which they are
defined. Pseudo-header fields defined for requests MUST NOT appear
in responses; pseudo-header fields defined for responses MUST NOT
appear in requests. Pseudo-header fields MUST NOT appear in
trailers. Endpoints MUST treat a request or response that contains
undefined or invalid pseudo-header fields as malformed
(Section 8.1.2.6).
Just as in HTTP/1.x, header field names are strings of ASCII Just as in HTTP/1.x, header field names are strings of ASCII
characters that are compared in a case-insensitive fashion. However, characters that are compared in a case-insensitive fashion. However,
header field names MUST be converted to lowercase prior to their header field names MUST be converted to lowercase prior to their
encoding in HTTP/2. A request or response containing uppercase encoding in HTTP/2. A request or response containing uppercase
header field names MUST be treated as malformed (Section 8.1.2.5). header field names MUST be treated as malformed (Section 8.1.2.6).
All pseudo-header fields MUST appear in the header block before
regular header fields. Any request or response that contains a
pseudo-header field that appears in a header block after a regular
header field MUST be treated as malformed (Section 8.1.2.6).
8.1.2.2. Hop-by-Hop Header Fields
HTTP/2 does not use the Connection header field to indicate "hop-by- HTTP/2 does not use the Connection header field to indicate "hop-by-
hop" header fields; in this protocol, connection-specific metadata is hop" header fields; in this protocol, connection-specific metadata is
conveyed by other means. As such, a HTTP/2 message containing conveyed by other means. As such, a HTTP/2 message containing
Connection MUST be treated as malformed (Section 8.1.2.5). Connection MUST be treated as malformed (Section 8.1.2.6).
This means that an intermediary transforming an HTTP/1.x message to This means that an intermediary transforming an HTTP/1.x message to
HTTP/2 will need to remove any header fields nominated by the HTTP/2 will need to remove any header fields nominated by the
Connection header field, along with the Connection header field Connection header field, along with the Connection header field
itself. Such intermediaries SHOULD also remove other connection- itself. Such intermediaries SHOULD also remove other connection-
specific header fields, such as Keep-Alive, Proxy-Connection, specific header fields, such as Keep-Alive, Proxy-Connection,
Transfer-Encoding and Upgrade, even if they are not nominated by Transfer-Encoding and Upgrade, even if they are not nominated by
Connection. Connection.
One exception to this is the TE header field, which MAY be present in One exception to this is the TE header field, which MAY be present in
an HTTP/2 request, but when it is MUST NOT contain any value other an HTTP/2 request, but when it is MUST NOT contain any value other
than "trailers". than "trailers".
Note: HTTP/2 purposefully does not support upgrade to another Note: HTTP/2 purposefully does not support upgrade to another
protocol. The handshake methods described in Section 3 are protocol. The handshake methods described in Section 3 are
believed sufficient to negotiate the use of alternative protocols. believed sufficient to negotiate the use of alternative protocols.
8.1.2.1. Request Header Fields 8.1.2.3. Request Header Fields
HTTP/2 defines a number of pseudo header fields starting with a colon HTTP/2 defines a number of pseudo header fields starting with a colon
':' character that carry information about the request target: ':' character that carry information about the request target:
o The ":method" header field includes the HTTP method ([RFC7231], o The ":method" header field includes the HTTP method ([RFC7231],
Section 4). Section 4).
o The ":scheme" header field includes the scheme portion of the o The ":scheme" header field includes the scheme portion of the
target URI ([RFC3986], Section 3.1). target URI ([RFC3986], Section 3.1).
skipping to change at page 52, line 50 skipping to change at page 53, line 33
asterisk form (see [RFC7230], Section 5.3). Clients that generate asterisk form (see [RFC7230], Section 5.3). Clients that generate
HTTP/2 requests directly SHOULD instead omit the "Host" header HTTP/2 requests directly SHOULD instead omit the "Host" header
field. An intermediary that converts an HTTP/2 request to field. An intermediary that converts an HTTP/2 request to
HTTP/1.1 MUST create a "Host" header field if one is not present HTTP/1.1 MUST create a "Host" header field if one is not present
in a request by copying the value of the ":authority" header in a request by copying the value of the ":authority" header
field. field.
o The ":path" header field includes the path and query parts of the o The ":path" header field includes the path and query parts of the
target URI (the "path-absolute" production from [RFC3986] and target URI (the "path-absolute" production from [RFC3986] and
optionally a '?' character followed by the "query" production, see optionally a '?' character followed by the "query" production, see
[RFC3986], Section 3.3 and [RFC3986], Section 3.4). This field [RFC3986], Section 3.3 and [RFC3986], Section 3.4). A request in
MUST NOT be empty; URIs that do not contain a path component MUST asterisk form includes the value '*' for the ":path" header field.
include a value of '/', unless the request is an OPTIONS request
in asterisk form, in which case the ":path" header field MUST This field MUST NOT be empty for "http" or "https" URIs; "http" or
include '*'. "https" URIs that do not contain a path component MUST include a
value of '/'. The exception to this rule is an OPTIONS request
for an "http" or "https" URI that does not include a path
component; these MUST include a ":path" header field with a value
of '*' (see [RFC7230], Section 5.3.4).
All HTTP/2 requests MUST include exactly one valid value for the All HTTP/2 requests MUST include exactly one valid value for the
":method", ":scheme", and ":path" header fields, unless this is a ":method", ":scheme", and ":path" header fields, unless this is a
CONNECT request (Section 8.3). An HTTP request that omits mandatory CONNECT request (Section 8.3). An HTTP request that omits mandatory
header fields is malformed (Section 8.1.2.5). header fields is malformed (Section 8.1.2.6).
Header field names that start with a colon are only valid in the
HTTP/2 context. These are not HTTP header fields. Implementations
MUST NOT generate header fields that start with a colon, and they
MUST ignore and discard any header field that starts with a colon.
In particular, header fields with names starting with a colon MUST
NOT be exposed as HTTP header fields.
HTTP/2 does not define a way to carry the version identifier that is HTTP/2 does not define a way to carry the version identifier that is
included in the HTTP/1.1 request line. included in the HTTP/1.1 request line.
8.1.2.2. Response Header Fields 8.1.2.4. Response Header Fields
A single ":status" header field is defined that carries the HTTP A single ":status" header field is defined that carries the HTTP
status code field (see [RFC7231], Section 6). This header field MUST status code field (see [RFC7231], Section 6). This header field MUST
be included in all responses, otherwise the response is malformed be included in all responses, otherwise the response is malformed
(Section 8.1.2.5). (Section 8.1.2.6).
HTTP/2 does not define a way to carry the version or reason phrase HTTP/2 does not define a way to carry the version or reason phrase
that is included in an HTTP/1.1 status line. that is included in an HTTP/1.1 status line.
8.1.2.3. Header Field Ordering 8.1.2.5. Compressing the Cookie Header Field
HTTP Header Compression [COMPRESSION] does not preserve the order of
header fields, because the relative order of header fields with
different names is not important. However, the same header field can
be repeated to form a list (see [RFC7230], Section 3.2.2), where the
relative order of header field values is significant. This
repetition can occur either as a single header field with a comma-
separated list of values, or as several header fields with a single
value, or any combination thereof. Therefore, in the latter case,
ordering needs to be preserved before compression takes place.
To preserve the order of multiple occurrences of a header field with
the same name, its ordered values are concatenated into a single
value using a zero-valued octet (0x0) to delimit them.
After decompression, header fields that have values containing zero
octets (0x0) MUST be split into multiple header fields before being
processed.
For example, the following HTTP/1.x header block:
Content-Type: text/html
Cache-Control: max-age=60, private
Cache-Control: must-revalidate
contains three Cache-Control directives; two directives in the first
Cache-Control header field, and the third directive in the second
Cache-Control field. Before compression, they would need to be
converted to a form similar to this (with 0x0 represented as '\0'):
cache-control = max-age=60, private\0must-revalidate
content-type = text/html
Note here that the ordering between Content-Type and Cache-Control is
not preserved, but the relative ordering of the Cache-Control
directives - as well as the fact that the first two were comma-
separated, while the last was on a different line - is.
Header fields containing multiple values MUST be concatenated into a
single value unless the ordering of that header field is known to be
not significant.
The special case of "set-cookie" - which does not form a comma-
separated list, but can have multiple values - does not depend on
ordering. The "set-cookie" header field MAY be encoded as multiple
header field values, or as a single concatenated value.
8.1.2.4. Compressing the Cookie Header Field
The Cookie header field [COOKIE] can carry a significant amount of The Cookie header field [COOKIE] can carry a significant amount of
redundant data. redundant data.
The Cookie header field uses a semi-colon (";") to delimit cookie- The Cookie header field uses a semi-colon (";") to delimit cookie-
pairs (or "crumbs"). This header field doesn't follow the list pairs (or "crumbs"). This header field doesn't follow the list
construction rules in HTTP (see [RFC7230], Section 3.2.2), which construction rules in HTTP (see [RFC7230], Section 3.2.2), which
prevents cookie-pairs from being separated into different name-value prevents cookie-pairs from being separated into different name-value
pairs. This can significantly reduce compression efficiency as pairs. This can significantly reduce compression efficiency as
individual cookie-pairs are updated. individual cookie-pairs are updated.
To allow for better compression efficiency, the Cookie header field To allow for better compression efficiency, the Cookie header field
MAY be split into separate header fields, each with one or more MAY be split into separate header fields, each with one or more
cookie-pairs. If there are multiple Cookie header fields after cookie-pairs. If there are multiple Cookie header fields after
decompression, these MUST be concatenated into a single octet string decompression, these MUST be concatenated into a single octet string
using the two octet delimiter of 0x3B, 0x20 (the ASCII string "; "). using the two octet delimiter of 0x3B, 0x20 (the ASCII string "; ")
before being passed into a non-HTTP/2 context, such as an HTTP/1.1
The Cookie header field MAY be split using a zero octet (0x0), as connection, or a generic HTTP server application.
defined in Section 8.1.2.3. When decoding, zero octets MUST be
replaced with the cookie delimiter ("; ").
Therefore, the following sets of Cookie header fields are Therefore, the following two lists of Cookie header fields are
semantically equivalent, though the final form might appear in a semantically equivalent.
different order after compression and decompression.
cookie: a=b; c=d; e=f cookie: a=b; c=d; e=f
cookie: a=b\0c=d; e=f
cookie: a=b cookie: a=b
cookie: c=d cookie: c=d
cookie: e=f cookie: e=f
8.1.2.5. Malformed Messages 8.1.2.6. Malformed Requests and Responses
A malformed request or response is one that uses a valid sequence of A malformed request or response is one that is an otherwise valid
HTTP/2 frames, but is otherwise invalid due to the presence of sequence of HTTP/2 frames, but is otherwise invalid due to the
prohibited header fields, the absence of mandatory header fields, or presence of extraneous frames, prohibited header fields, the absence
the inclusion of uppercase header field names. of mandatory header fields, or the inclusion of uppercase header
field names.
A request or response that includes an entity body can include a A request or response that includes an entity body can include a
"content-length" header field. A request or response is also "content-length" header field. A request or response is also
malformed if the value of a "content-length" header field does not malformed if the value of a "content-length" header field does not
equal the sum of the DATA frame payload lengths that form the body. equal the sum of the DATA frame payload lengths that form the body,
with the exception of responses to HEAD requests, which always
contain no DATA frames.
Intermediaries that process HTTP requests or responses (i.e., any Intermediaries that process HTTP requests or responses (i.e., any
intermediary not acting as a tunnel) MUST NOT forward a malformed intermediary not acting as a tunnel) MUST NOT forward a malformed
request or response. request or response. Malformed requests or responses that are
detected MUST be treated as a stream error (Section 5.4.2) of type
PROTOCOL_ERROR.
Implementations that detect malformed requests or responses need to For malformed requests, a server MAY send an HTTP response prior to
ensure that the stream ends. For malformed requests, a server MAY closing or resetting the stream. Clients MUST NOT accept a malformed
send an HTTP response prior to closing or resetting the stream. response. Note that these requirements are intended to protect
Clients MUST NOT accept a malformed response. Note that these against several types of common attacks against HTTP; they are
requirements are intended to protect against several types of common deliberately strict, because being permissive can expose
attacks against HTTP; they are deliberately strict, because being implementations to these vulnerabilities.
permissive can expose implementations to these vulnerabilities.
8.1.3. Examples 8.1.3. Examples
This section shows HTTP/1.1 requests and responses, with This section shows HTTP/1.1 requests and responses, with
illustrations of equivalent HTTP/2 requests and responses. illustrations of equivalent HTTP/2 requests and responses.
An HTTP GET request includes request header fields and no body and is An HTTP GET request includes request header fields and no body and is
therefore transmitted as a single HEADERS frame, followed by zero or therefore transmitted as a single HEADERS frame, followed by zero or
more CONTINUATION frames containing the serialized block of request more CONTINUATION frames containing the serialized block of request
header fields. The HEADERS frame in the following has both the header fields. The HEADERS frame in the following has both the
skipping to change at page 58, line 22 skipping to change at page 57, line 38
0 0
Foo: bar DATA Foo: bar DATA
- END_STREAM - END_STREAM
{binary data} {binary data}
HEADERS HEADERS
+ END_STREAM + END_STREAM
+ END_HEADERS + END_HEADERS
foo = bar foo = bar
An informational response using a 1xx status code other than 101 is
transmitted as a HEADERS frame, followed by zero or more CONTINUATION
frames:
HTTP/1.1 103 BAR HEADERS
Extension-Field: bar ==> - END_STREAM
+ END_HEADERS
:status = 103
extension-field = bar
8.1.4. Request Reliability Mechanisms in HTTP/2 8.1.4. Request Reliability Mechanisms in HTTP/2
In HTTP/1.1, an HTTP client is unable to retry a non-idempotent In HTTP/1.1, an HTTP client is unable to retry a non-idempotent
request when an error occurs, because there is no means to determine request when an error occurs, because there is no means to determine
the nature of the error. It is possible that some server processing the nature of the error. It is possible that some server processing
occurred prior to the error, which could result in undesirable occurred prior to the error, which could result in undesirable
effects if the request were reattempted. effects if the request were reattempted.
HTTP/2 provides two mechanisms for providing a guarantee to a client HTTP/2 provides two mechanisms for providing a guarantee to a client
that a request has not been processed: that a request has not been processed:
skipping to change at page 60, line 13 skipping to change at page 59, line 36
includes a request body. includes a request body.
Pushed responses are always associated with an explicit request from Pushed responses are always associated with an explicit request from
the client. The PUSH_PROMISE frames sent by the server are sent on the client. The PUSH_PROMISE frames sent by the server are sent on
that explicit request's stream. The PUSH_PROMISE frame also includes that explicit request's stream. The PUSH_PROMISE frame also includes
a promised stream identifier, chosen from the stream identifiers a promised stream identifier, chosen from the stream identifiers
available to the server (see Section 5.1.1). available to the server (see Section 5.1.1).
The header fields in PUSH_PROMISE and any subsequent CONTINUATION The header fields in PUSH_PROMISE and any subsequent CONTINUATION
frames MUST be a valid and complete set of request header fields frames MUST be a valid and complete set of request header fields
(Section 8.1.2.1). The server MUST include a method in the ":method" (Section 8.1.2.3). The server MUST include a method in the ":method"
header field that is safe and cacheable. If a client receives a header field that is safe and cacheable. If a client receives a
PUSH_PROMISE that does not include a complete and valid set of header PUSH_PROMISE that does not include a complete and valid set of header
fields, or the ":method" header field identifies a method that is not fields, or the ":method" header field identifies a method that is not
safe, it MUST respond with a stream error (Section 5.4.2) of type safe, it MUST respond with a stream error (Section 5.4.2) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
The server SHOULD send PUSH_PROMISE (Section 6.6) frames prior to The server SHOULD send PUSH_PROMISE (Section 6.6) frames prior to
sending any frames that reference the promised responses. This sending any frames that reference the promised responses. This
avoids a race where clients issue requests prior to receiving any avoids a race where clients issue requests prior to receiving any
PUSH_PROMISE frames. PUSH_PROMISE frames.
skipping to change at page 60, line 35 skipping to change at page 60, line 10
For example, if the server receives a request for a document For example, if the server receives a request for a document
containing embedded links to multiple image files, and the server containing embedded links to multiple image files, and the server
chooses to push those additional images to the client, sending push chooses to push those additional images to the client, sending push
promises before the DATA frames that contain the image links ensures promises before the DATA frames that contain the image links ensures
that the client is able to see the promises before discovering that the client is able to see the promises before discovering
embedded links. Similarly, if the server pushes responses referenced embedded links. Similarly, if the server pushes responses referenced
by the header block (for instance, in Link header fields), sending by the header block (for instance, in Link header fields), sending
the push promises before sending the header block ensures that the push promises before sending the header block ensures that
clients do not request them. clients do not request them.
PUSH_PROMISE frames MUST NOT be sent by the client. PUSH_PROMISE PUSH_PROMISE frames MUST NOT be sent by the client.
frames can be sent by the server on any stream that was opened by the
client. They MUST be sent on a stream that is in either the "open" PUSH_PROMISE frames can be sent by the server in response to any
or "half closed (remote)" state to the server. PUSH_PROMISE frames client-initiated stream, but the stream MUST be in either the "open"
are interspersed with the frames that comprise a response, though or "half closed (remote)" state with respect to the server.
they cannot be interspersed with HEADERS and CONTINUATION frames that PUSH_PROMISE frames are interspersed with the frames that comprise a
comprise a single header block. response, though they cannot be interspersed with HEADERS and
CONTINUATION frames that comprise a single header block.
Sending a PUSH_PROMISE frame creates a new stream and puts the stream
into the "reserved (local)" state for the server and the "reserved
(remote)" state for the client.
8.2.2. Push Responses 8.2.2. Push Responses
After sending the PUSH_PROMISE frame, the server can begin delivering After sending the PUSH_PROMISE frame, the server can begin delivering
the pushed response as a response (Section 8.1.2.2) on a server- the pushed response as a response (Section 8.1.2.4) on a server-
initiated stream that uses the promised stream identifier. The initiated stream that uses the promised stream identifier. The
server uses this stream to transmit an HTTP response, using the same server uses this stream to transmit an HTTP response, using the same
sequence of frames as defined in Section 8.1. This stream becomes sequence of frames as defined in Section 8.1. This stream becomes
"half closed" to the client (Section 5.1) after the initial HEADERS "half closed" to the client (Section 5.1) after the initial HEADERS
frame is sent. frame is sent.
Once a client receives a PUSH_PROMISE frame and chooses to accept the Once a client receives a PUSH_PROMISE frame and chooses to accept the
pushed response, the client SHOULD NOT issue any requests for the pushed response, the client SHOULD NOT issue any requests for the
promised response until after the promised stream has closed. promised response until after the promised stream has closed.
skipping to change at page 61, line 29 skipping to change at page 61, line 11
streams. This does not prohibit a server from sending PUSH_PROMISE streams. This does not prohibit a server from sending PUSH_PROMISE
frames; clients need to reset any promised streams that are not frames; clients need to reset any promised streams that are not
wanted. wanted.
Clients receiving a pushed response MUST validate that the server is Clients receiving a pushed response MUST validate that the server is
authorized to provide the response, see Section 10.1. For example, a authorized to provide the response, see Section 10.1. For example, a
server that offers a certificate for only the "example.com" DNS-ID or server that offers a certificate for only the "example.com" DNS-ID or
Common Name is not permitted to push a response for Common Name is not permitted to push a response for
"https://www.example.org/doc". "https://www.example.org/doc".
The response for a PUSH_PROMISE stream begins with a HEADERS frame,
which immediately puts the stream into the "half closed (remote)"
state for the server and "half closed (local)" state for the client,
and ends with a frame bearing END_STREAM, which places the stream in
the "closed" state.
Note: The client never sends a frame with the END_STREAM flag for a
server push.
8.3. The CONNECT Method 8.3. The CONNECT Method
In HTTP/1.x, the pseudo-method CONNECT ([RFC7231], Section 4.3.6) is In HTTP/1.x, the pseudo-method CONNECT ([RFC7231], Section 4.3.6) is
used to convert an HTTP connection into a tunnel to a remote host. used to convert an HTTP connection into a tunnel to a remote host.
CONNECT is primarily used with HTTP proxies to establish a TLS CONNECT is primarily used with HTTP proxies to establish a TLS
session with an origin server for the purposes of interacting with session with an origin server for the purposes of interacting with
"https" resources. "https" resources.
In HTTP/2, the CONNECT method is used to establish a tunnel over a In HTTP/2, the CONNECT method is used to establish a tunnel over a
single HTTP/2 stream to a remote host, for similar purposes. The single HTTP/2 stream to a remote host, for similar purposes. The
HTTP header field mapping works as mostly as defined in Request HTTP header field mapping works as mostly as defined in Request
Header Fields (Section 8.1.2.1), with a few differences. Header Fields (Section 8.1.2.3), with a few differences.
Specifically: Specifically:
o The ":method" header field is set to "CONNECT". o The ":method" header field is set to "CONNECT".
o The ":scheme" and ":path" header fields MUST be omitted. o The ":scheme" and ":path" header fields MUST be omitted.
o The ":authority" header field contains the host and port to o The ":authority" header field contains the host and port to
connect to (equivalent to the authority-form of the request-target connect to (equivalent to the authority-form of the request-target
of CONNECT requests, see [RFC7230], Section 5.3). of CONNECT requests, see [RFC7230], Section 5.3).
skipping to change at page 63, line 49 skipping to change at page 63, line 40
result in requests being directed to the wrong origin server. For result in requests being directed to the wrong origin server. For
example, TLS termination might be performed by a middlebox that uses example, TLS termination might be performed by a middlebox that uses
the TLS Server Name Indication (SNI) [TLS-EXT] extension to select the TLS Server Name Indication (SNI) [TLS-EXT] extension to select
the an origin server. This means that it is possible for clients to the an origin server. This means that it is possible for clients to
send confidential information to servers that might not be the send confidential information to servers that might not be the
intended target for the request, even though the server has valid intended target for the request, even though the server has valid
authentication credentials. authentication credentials.
A server that does not wish clients to reuse connections can indicate A server that does not wish clients to reuse connections can indicate
that it is not authoritative for a request by sending a 421 (Not that it is not authoritative for a request by sending a 421 (Not
Authoritative) status code in response to request (see Authoritative) status code in response to the request (see
Section 9.1.2). Section 9.1.2).
9.1.2. The 421 (Not Authoritative) Status Code 9.1.2. The 421 (Not Authoritative) Status Code
The 421 (Not Authoritative) status code indicates that the current The 421 (Not Authoritative) status code indicates that the current
origin server is not authoritative for the requested resource, in the origin server is not authoritative for the requested resource, in the
sense of [RFC7230], Section 9.1 (see also Section 10.1). sense of [RFC7230], Section 9.1 (see also Section 10.1).
Clients receiving a 421 (Not Authoritative) response from a server Clients receiving a 421 (Not Authoritative) response from a server
MAY retry the request - whether the request method is idempotent or MAY retry the request - whether the request method is idempotent or
skipping to change at page 64, line 30 skipping to change at page 64, line 20
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 [RFC7234]). Section 4.2.2 of [RFC7234]).
9.2. Use of TLS Features 9.2. Use of TLS Features
Implementations of HTTP/2 MUST support TLS 1.2 [TLS12] for HTTP/2 Implementations of HTTP/2 MUST support TLS 1.2 [TLS12] for HTTP/2
over TLS. The general TLS usage guidance in [TLSBCP] SHOULD be over TLS. The general TLS usage guidance in [TLSBCP] SHOULD be
followed, with some additional restrictions that are specific to followed, with some additional restrictions that are specific to
HTTP/2. HTTP/2.
An implementation of HTTP/2 over TLS MUST use TLS 1.2 or higher with
the restrictions on feature set and cipher suite described in this
section. Due to implementation limitations, it might not be possible
to fail TLS negotiation. An endpoint MUST immediately terminate an
HTTP/2 connection that does not meet these minimum requirements with
a connection error (Section 5.4.1) of type INADEQUATE_SECURITY.
9.2.1. TLS Features 9.2.1. TLS Features
The TLS implementation MUST support the Server Name Indication (SNI) The TLS implementation MUST support the Server Name Indication (SNI)
[TLS-EXT] extension to TLS. HTTP/2 clients MUST indicate the target [TLS-EXT] extension to TLS. HTTP/2 clients MUST indicate the target
domain name when negotiating TLS. domain name when negotiating TLS.
The TLS implementation MUST disable compression. TLS compression can The TLS implementation MUST disable compression. TLS compression can
lead to the exposure of information that would not otherwise be lead to the exposure of information that would not otherwise be
revealed [RFC3749]. Generic compression is unnecessary since HTTP/2 revealed [RFC3749]. Generic compression is unnecessary since HTTP/2
provides compression features that are more aware of context and provides compression features that are more aware of context and
skipping to change at page 65, line 24 skipping to change at page 65, line 22
restricted. HTTP/2 MUST only be used with cipher suites that have restricted. HTTP/2 MUST only be used with cipher suites that have
ephemeral key exchange, such as the ephemeral Diffie-Hellman (DHE) ephemeral key exchange, such as the ephemeral Diffie-Hellman (DHE)
[TLS12] or the elliptic curve variant (ECDHE) [RFC4492]. Ephemeral [TLS12] or the elliptic curve variant (ECDHE) [RFC4492]. Ephemeral
key exchange MUST have a minimum size of 2048 bits for DHE or key exchange MUST have a minimum size of 2048 bits for DHE or
security level of 128 bits for ECDHE. Clients MUST accept DHE sizes security level of 128 bits for ECDHE. Clients MUST accept DHE sizes
of up to 4096 bits. HTTP MUST NOT be used with cipher suites that of up to 4096 bits. HTTP MUST NOT be used with cipher suites that
use stream or block ciphers. Authenticated Encryption with use stream or block ciphers. Authenticated Encryption with
Additional Data (AEAD) modes, such as the Galois Counter Model (GCM) Additional Data (AEAD) modes, such as the Galois Counter Model (GCM)
mode for AES [RFC5288] are acceptable. mode for AES [RFC5288] are acceptable.
Clients MAY advertise support of other cipher suites in order to The effect of these restrictions is that TLS 1.2 implementations
allow for connection to servers that do not support HTTP/2 to could have non-intersecting sets of available cipher suites, since
complete without the additional latency imposed by using a separate these prevent the use of the cipher suite that TLS 1.2 makes
connection for fallback. mandatory. To avoid this problem, implementations of HTTP/2 that use
TLS 1.2 MUST support TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
[TLS-ECDHE] with P256 [FIPS186].
An implementation SHOULD NOT negotiate a TLS connection for HTTP/2 Clients MAY advertise support of cipher suites that are prohibited by
without also negotiating a cipher suite that meets these the above restrictions in order to allow for connection to servers
requirements. Due to implementation limitations, it might not be that do not support HTTP/2. This enables a fallback to protocols
possible to fail TLS negotiation. An endpoint MUST immediately without these constraints without the additional latency imposed by
terminate an HTTP/2 connection that does not meet these minimum using a separate connection for fallback.
requirements with a connection error (Section 5.4.1) of type
INADEQUATE_SECURITY.
10. Security Considerations 10. Security Considerations
10.1. Server Authority 10.1. Server Authority
A client is only able to accept HTTP/2 responses from servers that A client is only able to accept HTTP/2 responses from servers that
are authoritative for those resources. This is particularly are authoritative for those resources. This is particularly
important for server push (Section 8.2), where the client validates important for server push (Section 8.2), where the client validates
the PUSH_PROMISE before accepting the response. the PUSH_PROMISE before accepting the response.
skipping to change at page 68, line 44 skipping to change at page 68, line 41
header fields that are critical to routing, such as ":authority", header fields that are critical to routing, such as ":authority",
":path", and ":scheme" are not guaranteed to be present early in the ":path", and ":scheme" are not guaranteed to be present early in the
header block. In particular, values that are in the reference set header block. In particular, values that are in the reference set
cannot be emitted until the header block ends. cannot be emitted until the header block ends.
This can prevent streaming of the header fields to their ultimate This can prevent streaming of the header fields to their ultimate
destination, and forces the endpoint to buffer the entire header destination, and forces the endpoint to buffer the entire header
block. Since there is no hard limit to the size of a header block, block. Since there is no hard limit to the size of a header block,
an endpoint could be forced to exhaust available memory. an endpoint could be forced to exhaust available memory.
An endpoint can use the SETTINGS_MAX_HEADER_LIST_SIZE to avise peers
of limits that might apply on the size of header blocks. This
setting is only advisory, so endpoints MAY choose to send header
blocks that exceed this limit and risk having the request or response
being treated as malformed. This setting is advertised hop-by-hop,
so any request or response could encounter a hop with a lower,
unknown limit. An intermediary can attempt to avoid this problem by
passing on values presented by different peers, but they are not
obligated to do so.
A server that receives a larger header block than it is willing to A server that receives a larger header block than it is willing to
handle can send an HTTP 431 (Request Header Fields Too Large) status handle can send an HTTP 431 (Request Header Fields Too Large) status
code [RFC6585]. A client can discard responses that it cannot code [RFC6585]. A client can discard responses that it cannot
process. The header block MUST be processed to ensure a consistent process. The header block MUST be processed to ensure a consistent
connection state, unless the connection is closed. connection state, unless the connection is closed.
10.6. Use of Compression 10.6. Use of Compression
HTTP/2 enables greater use of compression for both header fields HTTP/2 enables greater use of compression for both header fields
(Section 4.3) and entity bodies. Compression can allow an attacker (Section 4.3) and entity bodies. Compression can allow an attacker
skipping to change at page 70, line 27 skipping to change at page 70, line 31
features. features.
As far as this creates observable differences in behavior, they could As far as this creates observable differences in behavior, they could
be used as a basis for fingerprinting a specific client, as defined be used as a basis for fingerprinting a specific client, as defined
in Section 1.8 of [HTML5]. in Section 1.8 of [HTML5].
11. IANA Considerations 11. IANA Considerations
A string for identifying HTTP/2 is entered into the "Application A string for identifying HTTP/2 is entered into the "Application
Layer Protocol Negotiation (ALPN) Protocol IDs" registry established Layer Protocol Negotiation (ALPN) Protocol IDs" registry established
in [TLSALPN]. in [TLS-ALPN].
This document establishes a registry for frame types, settings, and This document establishes a registry for frame types, settings, and
error codes. These new registries are entered into a new "Hypertext error codes. These new registries are entered into a new "Hypertext
Transfer Protocol (HTTP) 2 Parameters" section. Transfer Protocol (HTTP) 2 Parameters" section.
This document registers the "HTTP2-Settings" header field for use in This document registers the "HTTP2-Settings" header field for use in
HTTP; and the 421 (Not Authoritative) status code. HTTP; and the 421 (Not Authoritative) status code.
This document registers the "PRI" method for use in HTTP, to avoid This document registers the "PRI" method for use in HTTP, to avoid
collisions with the connection preface (Section 3.5). collisions with the connection preface (Section 3.5).
11.1. Registration of HTTP/2 Identification Strings 11.1. Registration of HTTP/2 Identification Strings
This document creates two registrations for the identification of This document creates two registrations for the identification of
HTTP/2 in the "Application Layer Protocol Negotiation (ALPN) Protocol HTTP/2 in the "Application Layer Protocol Negotiation (ALPN) Protocol
IDs" registry established in [TLSALPN]. IDs" registry established in [TLS-ALPN].
The "h2" string identifies HTTP/2 when used over TLS: The "h2" string identifies HTTP/2 when used over TLS:
Protocol: HTTP/2 over TLS Protocol: HTTP/2 over TLS
Identification Sequence: 0x68 0x32 ("h2") Identification Sequence: 0x68 0x32 ("h2")
Specification: This document Specification: This document
The "h2c" string identifies HTTP/2 when used over cleartext TCP: The "h2c" string identifies HTTP/2 when used over cleartext TCP:
Protocol: HTTP/2 over TCP Protocol: HTTP/2 over TCP
Identification Sequence: 0x68 0x32 0x63 ("h2c") Identification Sequence: 0x68 0x32 0x63 ("h2c")
Specification: This document Specification: This document
11.2. Frame Type Registry 11.2. Frame Type Registry
skipping to change at page 72, line 35 skipping to change at page 72, line 35
An initial set of setting registrations can be found in An initial set of setting registrations can be found in
Section 6.5.2. Section 6.5.2.
+------------------------+------+---------------+---------------+ +------------------------+------+---------------+---------------+
| Name | Code | Initial Value | Specification | | Name | Code | Initial Value | Specification |
+------------------------+------+---------------+---------------+ +------------------------+------+---------------+---------------+
| HEADER_TABLE_SIZE | 0x1 | 4096 | Section 6.5.2 | | HEADER_TABLE_SIZE | 0x1 | 4096 | Section 6.5.2 |
| ENABLE_PUSH | 0x2 | 1 | Section 6.5.2 | | ENABLE_PUSH | 0x2 | 1 | Section 6.5.2 |
| MAX_CONCURRENT_STREAMS | 0x3 | (infinite) | Section 6.5.2 | | MAX_CONCURRENT_STREAMS | 0x3 | (infinite) | Section 6.5.2 |
| INITIAL_WINDOW_SIZE | 0x4 | 65535 | Section 6.5.2 | | INITIAL_WINDOW_SIZE | 0x4 | 65535 | Section 6.5.2 |
| MAX_FRAME_SIZE | 0x5 | 65536 | Section 6.5.2 |
| MAX_HEADER_LIST_SIZE | 0x6 | (infinite) | Section 6.5.2 |
+------------------------+------+---------------+---------------+ +------------------------+------+---------------+---------------+
11.4. Error Code Registry 11.4. Error Code Registry
This document establishes a registry for HTTP/2 error codes. The This document establishes a registry for HTTP/2 error codes. The
"HTTP/2 Error Code" registry manages a 32-bit space. The "HTTP/2 "HTTP/2 Error Code" registry manages a 32-bit space. The "HTTP/2
Error Code" registry operates under the "Expert Review" policy Error Code" registry operates under the "Expert Review" policy
[RFC5226]. [RFC5226].
Registrations for error codes are required to include a description Registrations for error codes are required to include a description
skipping to change at page 75, line 13 skipping to change at page 75, line 15
o Gabriel Montenegro and Willy Tarreau (Upgrade mechanism). o Gabriel Montenegro and Willy Tarreau (Upgrade mechanism).
o William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro, o William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro,
Jitu Padhye, Roberto Peon, Rob Trace (Flow control). Jitu Padhye, Roberto Peon, Rob Trace (Flow control).
o Mike Bishop (Extensibility). o Mike Bishop (Extensibility).
o Mark Nottingham, Julian Reschke, James Snell, Jeff Pinner, Mike o Mark Nottingham, Julian Reschke, James Snell, Jeff Pinner, Mike
Bishop, Herve Ruellan (Substantial editorial contributions). Bishop, Herve Ruellan (Substantial editorial contributions).
o Kari Hurtta, Tatsuhiro Tsujikawa, Greg Wilkins, Poul-Henning Kamp.
o Alexey Melnikov was an editor of this document during 2013. o Alexey Melnikov was an editor of this document during 2013.
o A substantial proportion of Martin's contribution was supported by o A substantial proportion of Martin's contribution was supported by
Microsoft during his employment there. Microsoft during his employment there.
13. References 13. References
13.1. Normative References 13.1. Normative References
[COMPRESSION] [COMPRESSION]
Ruellan, H. and R. Peon, "HPACK - Header Compression for Ruellan, H. and R. Peon, "HPACK - Header Compression for
HTTP/2", draft-ietf-httpbis-header-compression-08 (work in HTTP/2", draft-ietf-httpbis-header-compression-09 (work in
progress), June 2014. progress), July 2014.
[COOKIE] Barth, A., "HTTP State Management Mechanism", RFC 6265, [COOKIE] Barth, A., "HTTP State Management Mechanism", RFC 6265,
April 2011. April 2011.
[FIPS186] NIST, "Digital Signature Standard (DSS)", FIPS PUB 186-4,
July 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005. 3986, January 2005.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
skipping to change at page 76, line 27 skipping to change at page 76, line 34
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, June 2014. RFC 7234, June 2014.
[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, June 2014. Protocol (HTTP/1.1): Authentication", RFC 7235, June 2014.
[TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC [TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981. 793, September 1981.
[TLS-ALPN]
Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, July 2014.
[TLS-ECDHE]
Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
August 2008.
[TLS-EXT] Eastlake, D., "Transport Layer Security (TLS) Extensions: [TLS-EXT] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011. Extension Definitions", RFC 6066, January 2011.
[TLS12] Dierks, T. and E. Rescorla, "The Transport Layer Security [TLS12] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[TLSALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application Layer Protocol
Negotiation Extension", draft-ietf-tls-applayerprotoneg-05
(work in progress), March 2014.
13.2. Informative References 13.2. Informative References
[ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP [ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP
Alternative Services", draft-ietf-httpbis-alt-svc-01 (work Alternative Services", draft-ietf-httpbis-alt-svc-01 (work
in progress), April 2014. in progress), April 2014.
[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration [BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864, Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004. September 2004.
[BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the [BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the
CRIME Attack", July 2013, <http://breachattack.com/ CRIME Attack", July 2013,
resources/ <http://breachattack.com/resources/
BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>. BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>.
[HTML5] Berjon, R., Faulkner, S., Leithead, T., Doyle Navara, E., [HTML5] Berjon, R., Faulkner, S., Leithead, T., Doyle Navara, E.,
O'Connor, E., and S. Pfeiffer, "HTML5", W3C Candidate O'Connor, E., and S. Pfeiffer, "HTML5", W3C Candidate
Recommendation CR-html5-20140204, Febuary 2014, Recommendation CR-html5-20140204, Febuary 2014,
<http://www.w3.org/TR/2014/CR-html5-20140204/>. <http://www.w3.org/TR/2014/CR-html5-20140204/>.
Latest version available at [5]. Latest version available at [5].
[RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP Extensions [RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP Extensions
for High Performance", RFC 1323, May 1992. for High Performance", RFC 1323, May 1992.
[RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D.
Jensen, "HTTP Extensions for Distributed Authoring --
WEBDAV", RFC 2518, February 1999.
[RFC3749] Hollenbeck, S., "Transport Layer Security Protocol [RFC3749] Hollenbeck, S., "Transport Layer Security Protocol
Compression Methods", RFC 3749, May 2004. Compression Methods", RFC 3749, May 2004.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B. [RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, May 2006. for Transport Layer Security (TLS)", RFC 4492, May 2006.
[RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois [RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288, Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
August 2008. August 2008.
skipping to change at page 78, line 5 skipping to change at page 79, line 5
13.3. URIs 13.3. URIs
[1] https://www.iana.org/assignments/message-headers [1] https://www.iana.org/assignments/message-headers
[2] https://groups.google.com/forum/?fromgroups#!topic/spdy-dev/ [2] https://groups.google.com/forum/?fromgroups#!topic/spdy-dev/
cfUef2gL3iU cfUef2gL3iU
[3] https://tools.ietf.org/html/draft-montenegro-httpbis-http2-fc- [3] https://tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-
principles-01 principles-01
Appendix A. Change Log (to be removed by RFC Editor before publication) Appendix A. Change Log
A.1. Since draft-ietf-httpbis-http2-12 This section is to be removed by RFC Editor before publication.
A.1. Since draft-ietf-httpbis-http2-13
Pseudo-header fields are now required to appear strictly before
regular ones.
Restored 1xx series status codes, except 101.
Changed frame length field 24-bits. Expanded frame header to 9
octets. Added a setting to limit the damage.
Added a setting to advise peers of header set size limits.
Removed segments.
Made non-semantic-bearing HEADERS frames illegal in the HTTP mapping.
A.2. Since draft-ietf-httpbis-http2-12
Restored extensibility options. Restored extensibility options.
Restricting TLS cipher suites to AEAD only. Restricting TLS cipher suites to AEAD only.
Removing Content-Encoding requirements. Removing Content-Encoding requirements.
Permitting the use of PRIORITY after stream close. Permitting the use of PRIORITY after stream close.
Removed ALTSVC frame. Removed ALTSVC frame.
Removed BLOCKED frame. Removed BLOCKED frame.
Reducing the maximum padding size to 256 octets; removing padding Reducing the maximum padding size to 256 octets; removing padding
from CONTINUATION frames. from CONTINUATION frames.
Removed per-frame GZIP compression. Removed per-frame GZIP compression.
A.2. Since draft-ietf-httpbis-http2-11 A.3. Since draft-ietf-httpbis-http2-11
Added BLOCKED frame (at risk). Added BLOCKED frame (at risk).
Simplified priority scheme. Simplified priority scheme.
Added DATA per-frame GZIP compression. Added DATA per-frame GZIP compression.
A.3. Since draft-ietf-httpbis-http2-10 A.4. Since draft-ietf-httpbis-http2-10
Changed "connection header" to "connection preface" to avoid Changed "connection header" to "connection preface" to avoid
confusion. confusion.
Added dependency-based stream prioritization. Added dependency-based stream prioritization.
Added "h2c" identifier to distinguish between cleartext and secured Added "h2c" identifier to distinguish between cleartext and secured
HTTP/2. HTTP/2.
Adding missing padding to PUSH_PROMISE. Adding missing padding to PUSH_PROMISE.
Integrate ALTSVC frame and supporting text. Integrate ALTSVC frame and supporting text.
Dropping requirement on "deflate" Content-Encoding. Dropping requirement on "deflate" Content-Encoding.
Improving security considerations around use of compression. Improving security considerations around use of compression.
A.4. Since draft-ietf-httpbis-http2-09 A.5. Since draft-ietf-httpbis-http2-09
Adding padding for data frames. Adding padding for data frames.
Renumbering frame types, error codes, and settings. Renumbering frame types, error codes, and settings.
Adding INADEQUATE_SECURITY error code. Adding INADEQUATE_SECURITY error code.
Updating TLS usage requirements to 1.2; forbidding TLS compression. Updating TLS usage requirements to 1.2; forbidding TLS compression.
Removing extensibility for frames and settings. Removing extensibility for frames and settings.
skipping to change at page 79, line 30 skipping to change at page 80, line 48
Changing the protocol identification token to "h2". Changing the protocol identification token to "h2".
Changing the use of :authority to make it optional and to allow Changing the use of :authority to make it optional and to allow
userinfo in non-HTTP cases. userinfo in non-HTTP cases.
Allowing split on 0x0 for Cookie. Allowing split on 0x0 for Cookie.
Reserved PRI method in HTTP/1.1 to avoid possible future collisions. Reserved PRI method in HTTP/1.1 to avoid possible future collisions.
A.5. Since draft-ietf-httpbis-http2-08 A.6. Since draft-ietf-httpbis-http2-08
Added cookie crumbling for more efficient header compression. Added cookie crumbling for more efficient header compression.
Added header field ordering with the value-concatenation mechanism. Added header field ordering with the value-concatenation mechanism.
A.6. Since draft-ietf-httpbis-http2-07 A.7. Since draft-ietf-httpbis-http2-07
Marked draft for implementation. Marked draft for implementation.
A.7. Since draft-ietf-httpbis-http2-06 A.8. Since draft-ietf-httpbis-http2-06
Adding definition for CONNECT method. Adding definition for CONNECT method.
Constraining the use of push to safe, cacheable methods with no Constraining the use of push to safe, cacheable methods with no
request body. request body.
Changing from :host to :authority to remove any potential confusion. Changing from :host to :authority to remove any potential confusion.
Adding setting for header compression table size. Adding setting for header compression table size.
Adding settings acknowledgement. Adding settings acknowledgement.
Removing unnecessary and potentially problematic flags from Removing unnecessary and potentially problematic flags from
CONTINUATION. CONTINUATION.
Added denial of service considerations. Added denial of service considerations.
A.8. Since draft-ietf-httpbis-http2-05 A.9. Since draft-ietf-httpbis-http2-05
Marking the draft ready for implementation. Marking the draft ready for implementation.
Renumbering END_PUSH_PROMISE flag. Renumbering END_PUSH_PROMISE flag.
Editorial clarifications and changes. Editorial clarifications and changes.
A.9. Since draft-ietf-httpbis-http2-04 A.10. Since draft-ietf-httpbis-http2-04
Added CONTINUATION frame for HEADERS and PUSH_PROMISE. Added CONTINUATION frame for HEADERS and PUSH_PROMISE.
PUSH_PROMISE is no longer implicitly prohibited if PUSH_PROMISE is no longer implicitly prohibited if
SETTINGS_MAX_CONCURRENT_STREAMS is zero. SETTINGS_MAX_CONCURRENT_STREAMS is zero.
Push expanded to allow all safe methods without a request body. Push expanded to allow all safe methods without a request body.
Clarified the use of HTTP header fields in requests and responses. Clarified the use of HTTP header fields in requests and responses.
Prohibited HTTP/1.1 hop-by-hop header fields. Prohibited HTTP/1.1 hop-by-hop header fields.
skipping to change at page 80, line 43 skipping to change at page 82, line 12
Clarified requirements around handling different frames after stream Clarified requirements around handling different frames after stream
close, stream reset and GOAWAY. close, stream reset and GOAWAY.
Added more specific prohibitions for sending of different frame types Added more specific prohibitions for sending of different frame types
in various stream states. in various stream states.
Making the last received setting value the effective value. Making the last received setting value the effective value.
Clarified requirements on TLS version, extension and ciphers. Clarified requirements on TLS version, extension and ciphers.
A.10. Since draft-ietf-httpbis-http2-03 A.11. Since draft-ietf-httpbis-http2-03
Committed major restructuring atrocities. Committed major restructuring atrocities.
Added reference to first header compression draft. Added reference to first header compression draft.
Added more formal description of frame lifecycle. Added more formal description of frame lifecycle.
Moved END_STREAM (renamed from FINAL) back to HEADERS/DATA. Moved END_STREAM (renamed from FINAL) back to HEADERS/DATA.
Removed HEADERS+PRIORITY, added optional priority to HEADERS frame. Removed HEADERS+PRIORITY, added optional priority to HEADERS frame.
Added PRIORITY frame. Added PRIORITY frame.
A.11. Since draft-ietf-httpbis-http2-02 A.12. Since draft-ietf-httpbis-http2-02
Added continuations to frames carrying header blocks. Added continuations to frames carrying header blocks.
Replaced use of "session" with "connection" to avoid confusion with Replaced use of "session" with "connection" to avoid confusion with
other HTTP stateful concepts, like cookies. other HTTP stateful concepts, like cookies.
Removed "message". Removed "message".
Switched to TLS ALPN from NPN. Switched to TLS ALPN from NPN.
Editorial changes. Editorial changes.
A.12. Since draft-ietf-httpbis-http2-01 A.13. Since draft-ietf-httpbis-http2-01
Added IANA considerations section for frame types, error codes and Added IANA considerations section for frame types, error codes and
settings. settings.
Removed data frame compression. Removed data frame compression.
Added PUSH_PROMISE. Added PUSH_PROMISE.
Added globally applicable flags to framing. Added globally applicable flags to framing.
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Restructured frame header. Removed distinction between data and Restructured frame header. Removed distinction between data and
control frames. control frames.
Altered flow control properties to include session-level limits. Altered flow control properties to include session-level limits.
Added note on cacheability of pushed resources and multiple tenant Added note on cacheability of pushed resources and multiple tenant
servers. servers.
Changed protocol label form based on discussions. Changed protocol label form based on discussions.
A.13. Since draft-ietf-httpbis-http2-00 A.14. Since draft-ietf-httpbis-http2-00
Changed title throughout. Changed title throughout.
Removed section on Incompatibilities with SPDY draft#2. Removed section on Incompatibilities with SPDY draft#2.
Changed INTERNAL_ERROR on GOAWAY to have a value of 2 [6]. Changed INTERNAL_ERROR on GOAWAY to have a value of 2 [6].
Replaced abstract and introduction. Replaced abstract and introduction.
Added section on starting HTTP/2.0, including upgrade mechanism. Added section on starting HTTP/2.0, including upgrade mechanism.
Removed unused references. Removed unused references.
Added flow control principles (Section 5.2.1) based on [7]. Added flow control principles (Section 5.2.1) based on [7].
A.14. Since draft-mbelshe-httpbis-spdy-00 A.15. Since draft-mbelshe-httpbis-spdy-00
Adopted as base for draft-ietf-httpbis-http2. Adopted as base for draft-ietf-httpbis-http2.
Updated authors/editors list. Updated authors/editors list.
Added status note. Added status note.
Authors' Addresses Authors' Addresses
Mike Belshe Mike Belshe
 End of changes. 114 change blocks. 
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