draft-ietf-httpbis-http2-12.txt   draft-ietf-httpbis-http2-13.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: October 25, 2014 Google, Inc Expires: December 19, 2014 Google, Inc
M. Thomson, Ed. M. Thomson, Ed.
Mozilla Mozilla
April 23, 2014 June 17, 2014
Hypertext Transfer Protocol version 2 Hypertext Transfer Protocol version 2
draft-ietf-httpbis-http2-12 draft-ietf-httpbis-http2-13
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.
This document is an alternative to, but does not obsolete, the This specification is an alternative to, but does not obsolete, the
HTTP/1.1 message syntax. HTTP's existing semantics remain unchanged. HTTP/1.1 message syntax. HTTP's existing semantics remain unchanged.
Editorial Note (To be removed by RFC Editor) Editorial Note (To be removed by RFC Editor)
Discussion of this draft takes place on the HTTPBIS working group Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at [1].
<http://lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information can be found at Working Group information can be found at [2]; that specific to
<http://tools.ietf.org/wg/httpbis/>; that specific to HTTP/2 are at HTTP/2 are at [3].
<http://http2.github.io/>.
The changes in this draft are summarized in Appendix A. The changes in this draft are summarized in Appendix A.
This version of HTTP/2, identified as "h2-12" or "h2c-12", is
intended for implementation. An interoperability event will be
conducted 2014-06-05, see <https://github.com/http2/wg_materials/
blob/master/interim-14-06/agenda.md>.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at 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 October 25, 2014.
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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. HTTP/2 Protocol Overview . . . . . . . . . . . . . . . . . . . 5 2. HTTP/2 Protocol Overview . . . . . . . . . . . . . . . . . . 5
2.1. Document Organization . . . . . . . . . . . . . . . . . . 6 2.1. Document Organization . . . . . . . . . . . . . . . . . . 6
2.2. Conventions and Terminology . . . . . . . . . . . . . . . 7 2.2. Conventions and Terminology . . . . . . . . . . . . . . . 6
3. Starting HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . 8 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 . . . . . . . . . . . . . . . . . . . . . . . . 14 4.2. Frame Size . . . . . . . . . . . . . . . . . . . . . . . 13
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 . . . . . . . . . . . . . . . . . . . . . . 16 5.1. Stream States . . . . . . . . . . . . . . . . . . . . . . 15
5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . . 20 5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . 20
5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . . 20 5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . 21
5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . . 21 5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . 21
5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 21 5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 21
5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 22 5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 22
5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 23 5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 23
5.3.1. Stream Dependencies . . . . . . . . . . . . . . . . . 23 5.3.1. Stream Dependencies . . . . . . . . . . . . . . . . . 24
5.3.2. Dependency Weighting . . . . . . . . . . . . . . . . . 24 5.3.2. Dependency Weighting . . . . . . . . . . . . . . . . 25
5.3.3. Reprioritization . . . . . . . . . . . . . . . . . . . 24 5.3.3. Reprioritization . . . . . . . . . . . . . . . . . . 25
5.3.4. Prioritization State Management . . . . . . . . . . . 25 5.3.4. Prioritization State Management . . . . . . . . . . . 26
5.3.5. Default Priorities . . . . . . . . . . . . . . . . . . 26 5.3.5. Default Priorities . . . . . . . . . . . . . . . . . 27
5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . . 26 5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 27
5.4.1. Connection Error Handling . . . . . . . . . . . . . . 27 5.4.1. Connection Error Handling . . . . . . . . . . . . . . 27
5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 27 5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 28
5.4.3. Connection Termination . . . . . . . . . . . . . . . . 28 5.4.3. Connection Termination . . . . . . . . . . . . . . . 28
6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 28 5.5. Extending HTTP/2 . . . . . . . . . . . . . . . . . . . . 28
6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 29
6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 30 6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . . 32 6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . . 33 6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . 33
6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . 34 6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . 34
6.5.1. SETTINGS Format . . . . . . . . . . . . . . . . . . . 35 6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . 35
6.5.2. Defined SETTINGS Parameters . . . . . . . . . . . . . 35 6.5.1. SETTINGS Format . . . . . . . . . . . . . . . . . . . 36
6.5.3. Settings Synchronization . . . . . . . . . . . . . . . 37 6.5.2. Defined SETTINGS Parameters . . . . . . . . . . . . . 36
6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . . 37 6.5.3. Settings Synchronization . . . . . . . . . . . . . . 37
6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . 38
6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . . 40 6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . 40
6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 42 6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 43 6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 43
6.9.2. Initial Flow Control Window Size . . . . . . . . . . . 44 6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 44
6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 45 6.9.2. Initial Flow Control Window Size . . . . . . . . . . 45
6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . . 46 6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 46
6.11. ALTSVC . . . . . . . . . . . . . . . . . . . . . . . . . . 47 6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . 47
6.12. BLOCKED . . . . . . . . . . . . . . . . . . . . . . . . . 49 7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 47
7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 49 8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . 49
8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 51 8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . 49
8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . . 51 8.1.1. Informational Responses . . . . . . . . . . . . . . . 50
8.1.1. Informational Responses . . . . . . . . . . . . . . . 52 8.1.2. HTTP Header Fields . . . . . . . . . . . . . . . . . 51
8.1.2. Examples . . . . . . . . . . . . . . . . . . . . . . . 53 8.1.3. Examples . . . . . . . . . . . . . . . . . . . . . . 55
8.1.3. HTTP Header Fields . . . . . . . . . . . . . . . . . . 55 8.1.4. Request Reliability Mechanisms in HTTP/2 . . . . . . 58
8.1.4. Request Reliability Mechanisms in HTTP/2 . . . . . . . 59 8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 59
8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 60 8.2.1. Push Requests . . . . . . . . . . . . . . . . . . . . 59
8.2.1. Push Requests . . . . . . . . . . . . . . . . . . . . 61 8.2.2. Push Responses . . . . . . . . . . . . . . . . . . . 60
8.2.2. Push Responses . . . . . . . . . . . . . . . . . . . . 62 8.3. The CONNECT Method . . . . . . . . . . . . . . . . . . . 61
8.3. The CONNECT Method . . . . . . . . . . . . . . . . . . . . 63 9. Additional HTTP Requirements/Considerations . . . . . . . . . 62
9. Additional HTTP Requirements/Considerations . . . . . . . . . 64 9.1. Connection Management . . . . . . . . . . . . . . . . . . 62
9.1. Connection Management . . . . . . . . . . . . . . . . . . 64 9.1.1. Connection Reuse . . . . . . . . . . . . . . . . . . 63
9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 65 9.1.2. The 421 (Not Authoritative) Status Code . . . . . . . 64
9.3. GZip Content-Encoding . . . . . . . . . . . . . . . . . . 65 9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 64
10. Security Considerations . . . . . . . . . . . . . . . . . . . 66 9.2.1. TLS Features . . . . . . . . . . . . . . . . . . . . 64
10.1. Server Authority . . . . . . . . . . . . . . . . . . . . . 66 9.2.2. TLS Cipher Suites . . . . . . . . . . . . . . . . . . 65
10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 66 10. Security Considerations . . . . . . . . . . . . . . . . . . . 65
10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . . 67 10.1. Server Authority . . . . . . . . . . . . . . . . . . . . 65
10.4. Cacheability of Pushed Responses . . . . . . . . . . . . . 67 10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . 66
10.5. Denial of Service Considerations . . . . . . . . . . . . . 67 10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . 66
10.6. Use of Compression . . . . . . . . . . . . . . . . . . . . 68 10.4. Cacheability of Pushed Responses . . . . . . . . . . . . 67
10.7. Use of Padding . . . . . . . . . . . . . . . . . . . . . . 69 10.5. Denial of Service Considerations . . . . . . . . . . . . 67
10.8. Privacy Considerations . . . . . . . . . . . . . . . . . . 70 10.5.1. Limits on Header Block Size . . . . . . . . . . . . 68
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 70 10.6. Use of Compression . . . . . . . . . . . . . . . . . . . 69
11.1. Registration of HTTP/2 Identification Strings . . . . . . 70 10.7. Use of Padding . . . . . . . . . . . . . . . . . . . . . 69
11.2. Error Code Registry . . . . . . . . . . . . . . . . . . . 71 10.8. Privacy Considerations . . . . . . . . . . . . . . . . . 70
11.3. HTTP2-Settings Header Field Registration . . . . . . . . . 71 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 70
11.4. PRI Method Registration . . . . . . . . . . . . . . . . . 72 11.1. Registration of HTTP/2 Identification Strings . . . . . 70
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 72 11.2. Frame Type Registry . . . . . . . . . . . . . . . . . . 71
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 73 11.3. Settings Registry . . . . . . . . . . . . . . . . . . . 72
13.1. Normative References . . . . . . . . . . . . . . . . . . . 73 11.4. Error Code Registry . . . . . . . . . . . . . . . . . . 72
13.2. Informative References . . . . . . . . . . . . . . . . . . 74 11.5. HTTP2-Settings Header Field Registration . . . . . . . . 73
11.6. PRI Method Registration . . . . . . . . . . . . . . . . 74
11.7. The 421 Not Authoritative HTTP Status Code . . . . . . . 74
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 74
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 75
13.1. Normative References . . . . . . . . . . . . . . . . . . 75
13.2. Informative References . . . . . . . . . . . . . . . . . 76
13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Appendix A. Change Log (to be removed by RFC Editor before Appendix A. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 75 publication) . . . . . . . . . . . . . . . . . . . . 78
A.1. Since draft-ietf-httpbis-http2-11 . . . . . . . . . . . . 75 A.1. Since draft-ietf-httpbis-http2-12 . . . . . . . . . . . . 78
A.2. Since draft-ietf-httpbis-http2-10 . . . . . . . . . . . . 75 A.2. Since draft-ietf-httpbis-http2-11 . . . . . . . . . . . . 78
A.3. Since draft-ietf-httpbis-http2-09 . . . . . . . . . . . . 76 A.3. Since draft-ietf-httpbis-http2-10 . . . . . . . . . . . . 78
A.4. Since draft-ietf-httpbis-http2-08 . . . . . . . . . . . . 76 A.4. Since draft-ietf-httpbis-http2-09 . . . . . . . . . . . . 79
A.5. Since draft-ietf-httpbis-http2-07 . . . . . . . . . . . . 76 A.5. Since draft-ietf-httpbis-http2-08 . . . . . . . . . . . . 79
A.6. Since draft-ietf-httpbis-http2-06 . . . . . . . . . . . . 76 A.6. Since draft-ietf-httpbis-http2-07 . . . . . . . . . . . . 79
A.7. Since draft-ietf-httpbis-http2-05 . . . . . . . . . . . . 77 A.7. Since draft-ietf-httpbis-http2-06 . . . . . . . . . . . . 79
A.8. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 77 A.8. Since draft-ietf-httpbis-http2-05 . . . . . . . . . . . . 80
A.9. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 77 A.9. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 80
A.10. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 78 A.10. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 80
A.11. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 78 A.11. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 81
A.12. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 79 A.12. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 81
A.13. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 79 A.13. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 82
A.14. Since draft-mbelshe-httpbis-spdy-00 . . . . . . . . . . . 82
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 ([HTTP-p1], Section protocol. However, the HTTP/1.1 message format ([RFC7230],
3) was designed to be implemented with the tools at hand in the Section 3) was designed to be implemented with the tools at hand in
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.
In particular, HTTP/1.0 only allows one request to be outstanding at In particular, HTTP/1.0 only allows one request to be outstanding at
a time on a given connection. HTTP/1.1 pipelining only partially a time on a given connection. HTTP/1.1 pipelining only partially
addressed request concurrency and suffers from head-of-line blocking. addressed request concurrency and suffers from head-of-line blocking.
Therefore, clients that need to make many requests typically use Therefore, clients that need to make many requests typically use
multiple connections to a server in order to reduce latency. multiple connections to a server in order to reduce latency.
Furthermore, HTTP/1.1 header fields are often repetitive and verbose, Furthermore, HTTP/1.1 header fields are often repetitive and verbose,
which, in addition to generating more or larger network packets, can which, in addition to generating more or larger network packets, can
cause the small initial TCP congestion window to quickly fill. This cause the small initial TCP [TCP] congestion window to quickly fill.
can result in excessive latency when multiple requests are made on a This can result in excessive latency when multiple requests are made
single new TCP connection. on a single new TCP connection.
This document addresses these issues by defining an optimized mapping This specification addresses these issues by defining an optimized
of HTTP's semantics to an underlying connection. Specifically, it mapping of HTTP's semantics to an underlying connection.
allows interleaving of request and response messages on the same Specifically, it allows interleaving of request and response messages
connection and uses an efficient coding for HTTP header fields. It on the same connection and uses an efficient coding for HTTP header
also allows prioritization of requests, letting more important fields. It also allows prioritization of requests, letting more
requests complete more quickly, further improving performance. important requests complete more quickly, further improving
performance.
The resulting protocol is designed to be more friendly to the The resulting protocol is designed to be more friendly to the
network, because fewer TCP connections can be used in comparison to network, because fewer TCP connections can be used in comparison to
HTTP/1.x. This means less competition with other flows, and longer- HTTP/1.x. This means less competition with other flows, and longer-
lived connections, which in turn leads to better utilization of lived connections, which in turn leads to better utilization of
available network capacity. available network capacity.
Finally, this encapsulation also enables more scalable processing of Finally, this encapsulation also enables more efficient processing of
messages through use of binary message framing. messages through use of binary message framing.
2. HTTP/2 Protocol Overview 2. HTTP/2 Protocol Overview
HTTP/2 provides an optimized transport for HTTP semantics. HTTP/2 HTTP/2 provides an optimized transport for HTTP semantics. HTTP/2
supports all of the core features of HTTP/1.1, but aims to be more supports all of the core features of HTTP/1.1, but aims to be more
efficient in several ways. efficient in several ways.
The basic protocol unit in HTTP/2 is a frame (Section 4.1). Each The basic protocol unit in HTTP/2 is a frame (Section 4.1). Each
frame has a different type and purpose. For example, HEADERS and frame type serves a different purpose. For example, HEADERS and DATA
DATA frames form the basis of HTTP requests and responses frames form the basis of HTTP requests and responses (Section 8.1);
(Section 8.1); other frame types like SETTINGS, WINDOW_UPDATE, and other frame types like SETTINGS, WINDOW_UPDATE, and PUSH_PROMISE are
PUSH_PROMISE are used in support of other HTTP/2 features. used in support of other HTTP/2 features.
Multiplexing of requests is achieved by having each HTTP request- Multiplexing of requests is achieved by having each HTTP request-
response exchanged assigned to a single stream (Section 5). Streams response exchanged assigned to a single stream (Section 5). Streams
are largely independent of each other, so a blocked or stalled are largely independent of each other, so a blocked or stalled
request does not prevent progress on other requests. request does not prevent progress on other requests.
Flow control and prioritization ensure that it is possible to Flow control and prioritization ensure that it is possible to
properly use multiplexed streams. Flow control (Section 5.2) helps properly use multiplexed streams. Flow control (Section 5.2) helps
to ensure that only data that can be used by a receiver is to ensure that only data that can be used by a receiver is
transmitted. Prioritization (Section 5.3) ensures that limited transmitted. Prioritization (Section 5.3) ensures that limited
skipping to change at page 6, line 28 skipping to change at page 6, line 12
speculatively send a client data that the server anticipates the speculatively send a client data that the server anticipates the
client will need, trading off some network usage against a potential client will need, trading off some network usage against a potential
latency gain. The server does this by synthesizing a request, which latency gain. The server does this by synthesizing a request, which
it sends as a PUSH_PROMISE frame. The server is then able to send a it sends as a PUSH_PROMISE frame. The server is then able to send a
response to the synthetic request on a separate stream. response to the synthetic request on a separate stream.
Frames that contain HTTP header fields are compressed (Section 4.3). Frames that contain HTTP header fields are compressed (Section 4.3).
HTTP requests can be highly redundant, so compression can reduce the HTTP requests can be highly redundant, so compression can reduce the
size of requests and responses significantly. size of requests and responses significantly.
HTTP/2 also supports HTTP Alternative Services (see [ALT-SVC]) using
the ALTSVC frame type (Section 6.11), to allow servers more control
over traffic to them.
2.1. Document Organization 2.1. Document Organization
The HTTP/2 specification is split into four parts: The HTTP/2 specification is split into four parts:
o Starting HTTP/2 (Section 3) covers how an HTTP/2 connection is o Starting HTTP/2 (Section 3) covers how an HTTP/2 connection is
initiated. initiated.
o The framing (Section 4) and streams (Section 5) layers describe o The framing (Section 4) and streams (Section 5) layers describe
the way HTTP/2 frames are structured and formed into multiplexed the way HTTP/2 frames are structured and formed into multiplexed
streams. streams.
skipping to change at page 7, line 32 skipping to change at page 7, line 14
connection error: An error that affects the entire HTTP/2 connection error: An error that affects the entire HTTP/2
connection. connection.
endpoint: Either the client or server of the connection. endpoint: Either the client or server of the connection.
frame: The smallest unit of communication within an HTTP/2 frame: The smallest unit of communication within an HTTP/2
connection, consisting of a header and a variable-length sequence connection, consisting of a header and a variable-length sequence
of bytes structured according to the frame type. of bytes structured according to the frame type.
intermediary: A "proxy", "gateway" or other intermediary as defined
in Section 2.3 of [HTTP-p1].
peer: An endpoint. When discussing a particular endpoint, "peer" peer: An endpoint. When discussing a particular endpoint, "peer"
refers to the endpoint that is remote to the primary subject of refers to the endpoint that is remote to the primary subject of
discussion. discussion.
receiver: An endpoint that is receiving frames. receiver: An endpoint that is receiving frames.
sender: An endpoint that is transmitting frames. sender: An endpoint that is transmitting frames.
server: The endpoint which did not initiate the HTTP/2 connection. server: The endpoint which did not initiate the HTTP/2 connection.
stream: A bi-directional flow of frames across a virtual channel stream: A bi-directional flow of frames across a virtual channel
within the HTTP/2 connection. within the HTTP/2 connection.
stream error: An error on the individual HTTP/2 stream. stream error: An error on the individual HTTP/2 stream.
Finally, the terms "gateway", "intermediary", "proxy", and "tunnel"
are defined in Section 2.3 of [RFC7230].
3. Starting HTTP/2 3. Starting HTTP/2
An HTTP/2 connection is an application level protocol running on top An HTTP/2 connection is an application level protocol running on top
of a TCP connection ([TCP]). The client is the TCP connection of a TCP connection ([TCP]). The client is the TCP connection
initiator. initiator.
HTTP/2 uses the same "http" and "https" URI schemes used by HTTP/1.1. HTTP/2 uses the same "http" and "https" URI schemes used by HTTP/1.1.
HTTP/2 shares the same default port numbers: 80 for "http" URIs and HTTP/2 shares the same default port numbers: 80 for "http" URIs and
443 for "https" URIs. As a result, implementations processing 443 for "https" URIs. As a result, implementations processing
requests for target resource URIs like "http://example.org/foo" or requests for target resource URIs like "http://example.org/foo" or
skipping to change at page 8, line 29 skipping to change at page 8, line 11
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 [TLSALPN] field and any place that protocol negotiation extension (ALPN) [TLSALPN] field and any
HTTP/2 over TLS is identified. place that HTTP/2 over TLS is identified.
When serialised into an ALPN protocol identifier (which is a The "h2" string is serialized into an ALPN protocol identifier as
sequence of octets), the HTTP/2 protocol identifier string is the two octet sequence: 0x68, 0x32.
encoded using UTF-8 [UTF-8].
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,
framing and message semantics described in this document. framing and message semantics described in this document.
[[anchor3: RFC Editor's Note: please remove the remainder of this [[CREF1: RFC Editor's Note: please remove the remainder of this
section prior to the publication of a final version of this section prior to the publication of a final version of this
document.]] document.]]
Only implementations of the final, published RFC can identify Only implementations of the final, published RFC can identify
themselves as "h2" or "h2c". Until such an RFC exists, themselves as "h2" or "h2c". Until such an RFC exists,
implementations MUST NOT identify themselves using these strings. implementations MUST NOT identify themselves using these strings.
Examples and text throughout the rest of this document use "h2" as a Examples and text throughout the rest of this document use "h2" as a
matter of editorial convenience only. Implementations of draft matter of editorial convenience only. Implementations of draft
versions MUST NOT identify using this string. versions MUST NOT identify using this string.
skipping to change at page 9, line 16 skipping to change at page 8, line 46
Implementations of draft versions of the protocol MUST add the string Implementations of draft versions of the protocol MUST add the string
"-" and the corresponding draft number to the identifier. For "-" and the corresponding draft number to the identifier. For
example, draft-ietf-httpbis-http2-11 over TLS is identified using the example, draft-ietf-httpbis-http2-11 over TLS is identified using the
string "h2-11". string "h2-11".
Non-compatible experiments that are based on these draft versions Non-compatible experiments that are based on these draft versions
MUST append the string "-" and an experiment name to the identifier. MUST append the string "-" and an experiment name to the identifier.
For example, an experimental implementation of packet mood-based For example, an experimental implementation of packet mood-based
encoding based on draft-ietf-httpbis-http2-09 might identify itself encoding based on draft-ietf-httpbis-http2-09 might identify itself
as "h2-09-emo". Note that any label MUST conform to the "token" as "h2-09-emo". Note that any label MUST conform to the "token"
syntax defined in Section 3.2.6 of [HTTP-p1]. Experimenters are syntax defined in Section 3.2.6 of [RFC7230]. Experimenters are
encouraged to coordinate their experiments on the ietf-http-wg@w3.org encouraged to coordinate their experiments on the ietf-http-wg@w3.org
mailing list. mailing list.
3.2. Starting HTTP/2 for "http" URIs 3.2. Starting HTTP/2 for "http" URIs
A client that makes a request to an "http" URI without prior A client that makes a request to an "http" URI without prior
knowledge about support for HTTP/2 uses the HTTP Upgrade mechanism knowledge about support for HTTP/2 uses the HTTP Upgrade mechanism
(Section 6.7 of [HTTP-p1]). The client makes an HTTP/1.1 request (Section 6.7 of [RFC7230]). The client makes an HTTP/1.1 request
that includes an Upgrade header field identifying HTTP/2 with the that includes an Upgrade header field identifying HTTP/2 with the
"h2c" token. The HTTP/1.1 request MUST include exactly one HTTP2- "h2c" token. The HTTP/1.1 request MUST include exactly one
Settings (Section 3.2.1) header field. HTTP2-Settings (Section 3.2.1) header field.
For example: For example:
GET /default.htm HTTP/1.1 GET / HTTP/1.1
Host: server.example.com Host: server.example.com
Connection: Upgrade, HTTP2-Settings Connection: Upgrade, HTTP2-Settings
Upgrade: h2c Upgrade: h2c
HTTP2-Settings: <base64url encoding of HTTP/2 SETTINGS payload> HTTP2-Settings: <base64url encoding of HTTP/2 SETTINGS payload>
Requests that contain an entity body MUST be sent in their entirety Requests that contain an entity body MUST be sent in their entirety
before the client can send HTTP/2 frames. This means that a large before the client can send HTTP/2 frames. This means that a large
request entity can block the use of the connection until it is request entity can block the use of the connection until it is
completely sent. completely sent.
skipping to change at page 10, line 11 skipping to change at page 9, line 40
A server that does not support HTTP/2 can respond to the request as A server that does not support HTTP/2 can respond to the request as
though the Upgrade header field were absent: though the Upgrade header field were absent:
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Length: 243 Content-Length: 243
Content-Type: text/html Content-Type: text/html
... ...
A server MUST ignore a "h2" token in an Upgrade header field.
Presence of a token with "h2" implies HTTP/2 over TLS, which is
instead negotiated as described in Section 3.3.
A server that supports HTTP/2 can accept the upgrade with a 101 A server that supports HTTP/2 can accept the upgrade with a 101
(Switching Protocols) response. After the empty line that terminates (Switching Protocols) response. After the empty line that terminates
the 101 response, the server can begin sending HTTP/2 frames. These the 101 response, the server can begin sending HTTP/2 frames. These
frames MUST include a response to the request that initiated the frames MUST include a response to the request that initiated the
Upgrade. Upgrade.
HTTP/1.1 101 Switching Protocols HTTP/1.1 101 Switching Protocols
Connection: Upgrade Connection: Upgrade
Upgrade: h2c Upgrade: h2c
skipping to change at page 10, line 39 skipping to change at page 10, line 27
Stream 1 is implicitly half closed from the client toward the server, Stream 1 is implicitly half closed from the client toward the server,
since the request is completed as an HTTP/1.1 request. After since the request is completed as an HTTP/1.1 request. After
commencing the HTTP/2 connection, stream 1 is used for the response. commencing the HTTP/2 connection, stream 1 is used for the response.
3.2.1. HTTP2-Settings Header Field 3.2.1. HTTP2-Settings Header Field
A request that upgrades from HTTP/1.1 to HTTP/2 MUST include exactly A request that upgrades from HTTP/1.1 to HTTP/2 MUST include exactly
one "HTTP2-Settings" header field. The "HTTP2-Settings" header field one "HTTP2-Settings" header field. The "HTTP2-Settings" header field
is a hop-by-hop header field that includes parameters that govern the is a hop-by-hop header field that includes parameters that govern the
HTTP/2 connection, provided in anticipation of the server accepting HTTP/2 connection, provided in anticipation of the server accepting
the request to upgrade. A server MUST reject an attempt to upgrade the request to upgrade.
if this header field is not present.
HTTP2-Settings = token68 HTTP2-Settings = token68
A server MUST reject an attempt to upgrade if this header field is
not present. A server MUST NOT send this header field.
The content of the "HTTP2-Settings" header field is the payload of a The content of the "HTTP2-Settings" header field is the payload of a
SETTINGS frame (Section 6.5), encoded as a base64url string (that is, SETTINGS frame (Section 6.5), encoded as a base64url string (that is,
the URL- and filename-safe Base64 encoding described in Section 5 of the URL- and filename-safe Base64 encoding described in Section 5 of
[RFC4648], with any trailing '=' characters omitted). The ABNF [RFC4648], with any trailing '=' characters omitted). The ABNF
[RFC5234] production for "token68" is defined in Section 2.1 of [RFC5234] production for "token68" is defined in Section 2.1 of
[HTTP-p7]. [RFC7235].
As a hop-by-hop header field, the "Connection" header field MUST As a hop-by-hop header field, the "Connection" header field MUST
include a value of "HTTP2-Settings" in addition to "Upgrade" when include a value of "HTTP2-Settings" in addition to "Upgrade" when
upgrading to HTTP/2. upgrading to HTTP/2.
A server decodes and interprets these values as it would any other A server decodes and interprets these values as it would any other
SETTINGS frame. Acknowledgement of the SETTINGS parameters SETTINGS frame. Acknowledgement of the SETTINGS parameters
(Section 6.5.3) is not necessary, since a 101 response serves as (Section 6.5.3) is not necessary, since a 101 response serves as
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 [TLSALPN].
HTTP/2 over TLS uses the "h2" application token. The "h2c" token
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 in an HTTP header field; the ALTSVC frame this capability.
(Section 6.11) describes a similar mechanism in HTTP/2.
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 resolution of in the connection preface. This only affects the establishment of
"http" URIs; servers supporting HTTP/2 are required to support HTTP/2 connections over cleartext TCP; implementations that support
protocol negotiation in TLS [TLSALPN] for "https" URIs. HTTP/2 over TLS MUST use protocol negotiation in TLS [TLSALPN].
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
skipping to change at page 12, line 36 skipping to change at page 12, line 27
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.
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) MAY 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 an 8-octet header followed by a payload of All frames begin with a fixed 8-octet header followed by a payload of
between 0 and 16,383 octets. between 0 and 16,383 octets.
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) | | R | Length (14) | Type (8) | Flags (8) |
+-+-+-----------+---------------+-------------------------------+ +-+-+-----------+---------------+-------------------------------+
|R| Stream Identifier (31) | |R| Stream Identifier (31) |
+-+-------------------------------------------------------------+ +=+=============================================================+
| Frame Payload (0...) ... | Frame Payload (0...) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Frame Header 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 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 and the bits MUST remain unset (0) when sending and MUST be
ignored when receiving. ignored when receiving.
Length: The length of the frame payload expressed as an unsigned 14- Length: The length of the frame payload expressed as an unsigned
bit integer. The 8 octets of the frame header are not included in 14-bit integer. The 8 octets of the frame header are not included
this value. in this value.
Type: The 8-bit type of the frame. The frame type determines how Type: The 8-bit type of the frame. The frame type determines the
the remainder of the frame header and payload are interpreted. format and semantics of the frame. Implementations MUST ignore
Implementations MUST treat the receipt of an unknown frame type and discard any frame that has a type that is unknown.
(any frame types not defined in this document) as a connection
error (Section 5.4.1) of type PROTOCOL_ERROR.
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
MUST be ignored, and MUST be left unset (0) when sending. MUST be ignored, and MUST be left unset (0) when sending.
R: A reserved 1-bit field. The semantics of this bit are undefined R: A reserved 1-bit field. The semantics of this bit are undefined
and the bit MUST remain unset (0) when sending and MUST be ignored and the bit MUST remain unset (0) when sending and MUST be ignored
skipping to change at page 14, line 10 skipping to change at page 13, line 42
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 maximum size of a frame payload varies by frame type. The
absolute maximum size of a frame payload is 2^14-1 (16,383) octets, absolute maximum size of a frame payload is 2^14-1 (16,383) octets,
meaning that the maximum frame size is 16,391 octets. All meaning that the maximum frame size is 16,391 octets. All
implementations SHOULD be capable of receiving and minimally implementations MUST be capable of receiving and minimally processing
processing frames up to this maximum size. frames up to this maximum size.
Certain frame types, such as PING (see Section 6.7), impose Certain frame types, such as PING (Section 6.7), impose additional
additional limits on the amount of payload data allowed. Likewise, limits on the amount of payload data allowed.
additional size limits can be set by specific application uses (see
Section 9).
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.
4.3. Header Compression and Decompression 4.3. Header Compression and Decompression
A header field in HTTP/2 is a name-value pair with one or more A header field in HTTP/2 is a name with one or more associated
associated values. They are used within HTTP request and response values. They are used within HTTP request and response messages as
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 sets 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 set 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 HTTP Header Compression does not preserve the relative ordering of
header fields. Header fields with multiple values are encoded into a header fields. Header fields with multiple values are encoded into a
single header field using a special delimiter; see Section 8.1.3.3. 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 8.1.3.4. mapping (see Section 8.1.2.4).
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. set.
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
skipping to change at page 15, line 19 skipping to change at page 14, line 49
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.
Header compression is stateful, using a single compression context Header compression is stateful, using a single compression context
for the entire connection. Each header block is processed as a for the entire connection. Each header block is processed as a
discrete unit. Header blocks MUST be transmitted as a contiguous discrete unit. Header blocks MUST be transmitted as a contiguous
sequence of frames, with no interleaved frames of any other type or sequence of frames, with no interleaved frames of any other type or
from any other stream. The last frame in a sequence of HEADERS or from any other stream. The last frame in a sequence of HEADERS or
CONTINUATION frames MUST have the END_HEADERS flag set. The last CONTINUATION frames MUST have the END_HEADERS flag set. The last
frame in a sequence of PUSH_PROMISE or CONTINUATION frames MUST have frame in a sequence of PUSH_PROMISE or CONTINUATION frames MUST have
the END_HEADERS flag set. the END_HEADERS flag set. This allows a header block to be logically
equivalent to a single frame.
Header block fragments can only be sent as the payload of HEADERS, Header block fragments can only be sent as the payload of HEADERS,
PUSH_PROMISE or CONTINUATION frames, because these frames carry data PUSH_PROMISE or CONTINUATION frames, because these frames carry data
that can modify the compression context maintained by a receiver. An that can modify the compression context maintained by a receiver. An
endpoint receiving HEADERS, PUSH_PROMISE or CONTINUATION frames MUST endpoint receiving HEADERS, PUSH_PROMISE or CONTINUATION frames MUST
reassemble header blocks and perform decompression even if the frames reassemble header blocks and perform decompression even if the frames
are to be discarded. A receiver MUST terminate the connection with a are to be discarded. A receiver MUST terminate the connection with a
connection error (Section 5.4.1) of type COMPRESSION_ERROR if it does connection error (Section 5.4.1) of type COMPRESSION_ERROR if it does
not decompress a header block. not decompress a header block.
skipping to change at page 15, line 45 skipping to change at page 15, line 29
o A single HTTP/2 connection can contain multiple concurrently open o A single HTTP/2 connection can contain multiple concurrently open
streams, with either endpoint interleaving frames from multiple streams, with either endpoint interleaving frames from multiple
streams. streams.
o Streams can be established and used unilaterally or shared by o Streams can be established and used unilaterally or shared by
either the client or server. either the client or server.
o Streams can be closed by either endpoint. o Streams can be closed by either endpoint.
o The order in which frames are sent within a stream is significant. o The order in which frames are sent on a stream is significant.
Recipients process frames in the order they are received. Recipients process frames in the order they are received. In
particular, the order of HEADERS, and DATA frames is semantically
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
skipping to change at page 16, line 42 skipping to change at page 16, line 38
`-------------------->| |<--------------------' `-------------------->| |<--------------------'
+--------+ +--------+
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
affect those transitions only. In this regard, CONTINUATION frames
do not result in state transitions and are effectively part of the
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
coordinate the creation of streams; they are created unilaterally by coordinate the creation of streams; they are created unilaterally by
either endpoint. The negative consequences of a mismatch in states either endpoint. The negative consequences of a mismatch in states
are limited to the "closed" state after sending RST_STREAM, where are limited to the "closed" state after sending RST_STREAM, where
frames might be received for some time after closing. frames might be received for some time after closing.
Streams have the following states: Streams have the following states:
idle: idle:
skipping to change at page 18, line 29 skipping to change at page 18, line 26
open: open:
A stream in the "open" state may be used by both peers to send A stream in the "open" state may be used by both peers to send
frames of any type. In this state, sending peers observe frames of any type. In this state, sending peers observe
advertised stream level flow control limits (Section 5.2). advertised stream level flow control limits (Section 5.2).
From this state either endpoint can send a frame with an From this state either endpoint can send a frame with an
END_STREAM flag set, which causes the stream to transition into END_STREAM flag set, which causes the stream to transition into
one of the "half closed" states: an endpoint sending an END_STREAM one of the "half closed" states: an endpoint sending an END_STREAM
flag causes the stream state to become "half closed (local)"; an flag causes the stream state to become "half closed (local)"; an
endpoint receiving an END_STREAM flag causes the stream state to endpoint receiving an END_STREAM flag causes the stream state to
become "half closed (remote)". A HEADERS frame bearing an become "half closed (remote)".
END_STREAM flag can be followed by CONTINUATION frames.
Either endpoint can send a RST_STREAM frame from this state, Either endpoint can send a RST_STREAM frame from this state,
causing it to transition immediately to "closed". causing it to transition immediately to "closed".
half closed (local): half closed (local):
A stream that is in the "half closed (local)" state cannot be used A stream that is in the "half closed (local)" state cannot be used
for sending frames. for sending frames. Only WINDOW_UPDATE, PRIORITY and RST_STREAM
frames can be sent in this state.
A stream transitions from this state to "closed" when a frame that A stream transitions from this state to "closed" when a frame that
contains an END_STREAM flag is received, or when either peer sends contains an END_STREAM flag is received, or when either peer sends
a RST_STREAM frame. A HEADERS frame bearing an END_STREAM flag a RST_STREAM frame.
can be followed by CONTINUATION frames.
A receiver can ignore WINDOW_UPDATE or PRIORITY frames in this A receiver can ignore WINDOW_UPDATE frames in this state, which
state. These frame types might arrive for a short period after a might arrive for a short period after a frame bearing the
frame bearing the END_STREAM flag is sent. END_STREAM flag is sent.
PRIORITY frames received in this state are used to reprioritize
streams that depend on the current stream.
half closed (remote): half closed (remote):
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 CONTINUATION frames, it MUST respond with a this state, other than WINDOW_UPDATE, PRIORITY or RST_STREAM, it
stream error (Section 5.4.2) of type STREAM_CLOSED. MUST respond with a stream error (Section 5.4.2) of type
STREAM_CLOSED.
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 after receiving a RST_STREAM MUST treat that receives any frame other than PRIORITY after receiving a
that as a stream error (Section 5.4.2) of type STREAM_CLOSED. RST_STREAM MUST treat that as a stream error (Section 5.4.2) of
Similarly, an endpoint that receives any frames after receiving a type STREAM_CLOSED. Similarly, an endpoint that receives any
DATA frame with the END_STREAM flag set, or any frames except a frames after receiving a frame with the END_STREAM flag set MUST
CONTINUATION frame after receiving a HEADERS frame with an treat that as a connection error (Section 5.4.1) of type
END_STREAM flag set MUST treat that as a stream error STREAM_CLOSED, unless the frame is permitted as described below.
(Section 5.4.2) of type STREAM_CLOSED.
WINDOW_UPDATE, PRIORITY, or RST_STREAM frames can be received in WINDOW_UPDATE or RST_STREAM frames can be received in this state
this state for a short period after a DATA or HEADERS frame for a short period after a DATA or HEADERS frame containing an
containing an END_STREAM flag is sent. Until the remote peer END_STREAM flag is sent. Until the remote peer receives and
receives and processes the frame bearing the END_STREAM flag, it processes the frame bearing the END_STREAM flag, it might send
might send frame of any of these types. Endpoints MUST ignore frames of these types. Endpoints MUST ignore WINDOW_UPDATE or
WINDOW_UPDATE, PRIORITY, or RST_STREAM frames received in this RST_STREAM frames received in this state, though endpoints MAY
state, though endpoints MAY choose to treat frames that arrive a choose to treat frames that arrive a significant time after
significant time after sending END_STREAM as a connection error sending END_STREAM as a connection error (Section 5.4.1) of type
(Section 5.4.1) of type PROTOCOL_ERROR. PROTOCOL_ERROR.
PRIORITY frames can be sent on closed streams to prioritize
streams that are dependent on the closed stream. Endpoints SHOULD
process PRIORITY frame, though they can be ignored if the stream
has been removed from the dependency tree (see Section 5.3.4).
If this state is reached as a result of sending a RST_STREAM If this state is reached as a result of sending a RST_STREAM
frame, the peer that receives the RST_STREAM might have already frame, the peer that receives the RST_STREAM might have already
sent - or enqueued for sending - frames on the stream that cannot sent - or enqueued for sending - frames on the stream that cannot
be withdrawn. An endpoint MUST ignore frames that it receives on be withdrawn. An endpoint MUST ignore frames that it receives on
closed streams after it has sent a RST_STREAM frame. An endpoint closed streams after it has sent a RST_STREAM frame. An endpoint
MAY choose to limit the period over which it ignores frames and MAY choose to limit the period over which it ignores frames and
treat frames that arrive after this time as being in error. treat frames that arrive after this time as being in error.
Flow controlled frames (i.e., DATA) received after sending Flow controlled frames (i.e., DATA) received after sending
RST_STREAM are counted toward the connection flow control window. RST_STREAM are counted toward the connection flow control window.
Even though these frames might be ignored, because they are sent Even though these frames might be ignored, because they are sent
before the sender receives the RST_STREAM, the sender will before the sender receives the RST_STREAM, the sender will
consider the frames to count against the flow control window. consider the frames to count against the flow control window.
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 streams. 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.
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 MUST NOT 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
responded to with a stream identifier of one (0x1). After the responded to with a stream identifier of one (0x1). After the
upgrade completes, stream 0x1 is "half closed (local)" to the client. upgrade completes, stream 0x1 is "half closed (local)" to the client.
Therefore, stream 0x1 cannot be selected as a new stream identifier Therefore, stream 0x1 cannot be selected as a new stream identifier
by a client that upgrades from HTTP/1.1. by a client that upgrades from HTTP/1.1.
The identifier of a newly established stream MUST be numerically The identifier of a newly established stream MUST be numerically
greater than all streams that the initiating endpoint has opened or greater than all streams that the initiating endpoint has opened or
skipping to change at page 20, line 42 skipping to change at page 20, line 45
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
The first use of a new stream identifier implicitly closes all The first use of a new stream identifier implicitly closes all
streams in the "idle" state that might have been initiated by that streams in the "idle" state that might have been initiated by that
peer with a lower-valued stream identifier. For example, if a client peer with a lower-valued stream identifier. For example, if a client
sends a HEADERS frame on stream 7 without ever sending a frame on sends a HEADERS frame on stream 7 without ever sending a frame on
stream 5, then stream 5 transitions to the "closed" state when the stream 5, then stream 5 transitions to the "closed" state when the
first frame for stream 7 is sent or received. first frame for stream 7 is sent or received.
Stream identifiers cannot be reused. Long-lived connections can Stream identifiers cannot be reused. Long-lived connections can
result in endpoint exhausting the available range of stream result in an endpoint exhausting the available range of stream
identifiers. A client that is unable to establish a new stream identifiers. A client that is unable to establish a new stream
identifier can establish a new connection for new streams. identifier can establish a new connection for new streams. A server
that is unable to establish a new stream identifier can send a GOAWAY
frame so that the client is forced to open a new connection for new
streams.
5.1.2. Stream Concurrency 5.1.2. Stream Concurrency
A peer can limit the number of concurrently active streams using the A peer can limit the number of concurrently active streams using the
SETTINGS_MAX_CONCURRENT_STREAMS parameters within a SETTINGS frame. SETTINGS_MAX_CONCURRENT_STREAMS parameter (see Section 6.5.2) within
The maximum concurrent streams setting is specific to each endpoint a SETTINGS frame. The maximum concurrent streams setting is specific
and applies only to the peer that receives the setting. That is, to each endpoint and applies only to the peer that receives the
clients specify the maximum number of concurrent streams the server setting. That is, clients specify the maximum number of concurrent
can initiate, and servers specify the maximum number of concurrent streams the server can initiate, and servers specify the maximum
streams the client can initiate. Endpoints MUST NOT exceed the limit number of concurrent streams the client can initiate.
set by their peer.
Streams that are in the "open" state, or either of the "half closed" Streams that are in the "open" state, or either of the "half closed"
states count toward the maximum number of streams that an endpoint is states count toward the maximum number of streams that an endpoint is
permitted to open. Streams in any of these three states count toward permitted to open. Streams in any of these three states count toward
the limit advertised in the SETTINGS_MAX_CONCURRENT_STREAMS setting the limit advertised in the SETTINGS_MAX_CONCURRENT_STREAMS setting.
(see Section 6.5.2). Streams in either of the "reserved" states do not count toward the
stream limit.
An endpoint that receives a HEADERS frame that causes their
advertised concurrent stream limit to be exceeded MUST treat this as
a stream error (Section 5.4.2).
Streams in either of the "reserved" states do not count as open. Endpoints MUST NOT exceed the limit set by their peer. An endpoint
that receives a HEADERS frame that causes their advertised concurrent
stream limit to be exceeded MUST treat this as a stream error
(Section 5.4.2). An endpoint that wishes to reduce the value of
SETTINGS_MAX_CONCURRENT_STREAMS to a value that is below the current
number of open streams can either close streams that exceed the new
value or allow streams to complete.
5.2. Flow Control 5.2. Flow Control
Using streams for multiplexing introduces contention over use of the Using streams for multiplexing introduces contention over use of the
TCP connection, resulting in blocked streams. A flow control scheme TCP connection, resulting in blocked streams. A flow control scheme
ensures that streams on the same connection do not destructively ensures that streams on the same connection do not destructively
interfere with each other. Flow control is used for both individual interfere with each other. Flow control is used for both individual
streams and for the connection as a whole. streams and for the connection as a whole.
HTTP/2 provides for flow control through use of the WINDOW_UPDATE HTTP/2 provides for flow control through use of the WINDOW_UPDATE
frame type. frame (Section 6.9).
5.2.1. Flow Control Principles 5.2.1. Flow Control Principles
HTTP/2 stream flow control aims to allow for future improvements to HTTP/2 stream flow control aims to allow for future improvements to
flow control algorithms without requiring protocol changes. Flow flow control algorithms without requiring protocol changes. Flow
control in HTTP/2 has the following characteristics: control in HTTP/2 has the following characteristics:
1. Flow control is hop-by-hop, not end-to-end. 1. Flow control is hop-by-hop, not end-to-end.
2. Flow control is based on window update frames. Receivers 2. Flow control is based on window update frames. Receivers
skipping to change at page 22, line 17 skipping to change at page 22, line 25
5. The frame type determines whether flow control applies to a 5. The frame type determines whether flow control applies to a
frame. Of the frames specified in this document, only DATA frame. Of the frames specified in this document, only DATA
frames are subject to flow control; all other frame types do not frames are subject to flow control; all other frame types do not
consume space in the advertised flow control window. This consume space in the advertised flow control window. This
ensures that important control frames are not blocked by flow ensures that important control frames are not blocked by flow
control. control.
6. Flow control cannot be disabled. 6. Flow control cannot be disabled.
7. HTTP/2 standardizes only the format of the WINDOW_UPDATE frame 7. HTTP/2 defines only the format and semantics of the WINDOW_UPDATE
(Section 6.9). This does not stipulate how a receiver decides frame (Section 6.9). This document does not stipulate how a
when to send this frame or the value that it sends. Nor does it receiver decides when to send this frame or the value that it
specify how a sender chooses to send packets. Implementations sends. Nor does it specify how a sender chooses to send packets.
are able to select any algorithm that suits their needs. Implementations are able to select any algorithm that suits their
needs.
Implementations are also responsible for managing how requests and Implementations are also responsible for managing how requests and
responses are sent based on priority; choosing how to avoid head of responses are sent based on priority; choosing how to avoid head of
line blocking for requests; and managing the creation of new streams. line blocking for requests; and managing the creation of new streams.
Algorithm choices for these could interact with any flow control Algorithm choices for these could interact with any flow control
algorithm. algorithm.
5.2.2. Appropriate Use of Flow Control 5.2.2. Appropriate Use of Flow Control
Flow control is defined to protect endpoints that are operating under Flow control is defined to protect endpoints that are operating under
resource constraints. For example, a proxy needs to share memory resource constraints. For example, a proxy needs to share memory
between many connections, and also might have a slow upstream between many connections, and also might have a slow upstream
connection and a fast downstream one. Flow control addresses cases connection and a fast downstream one. Flow control addresses cases
where the receiver is unable process data on one stream, yet wants to where the receiver is unable process data on one stream, yet wants to
continue to process other streams in the same connection. continue to process other streams in the same connection.
Deployments that do not require this capability can advertise a flow Deployments that do not require this capability can advertise a flow
control window of the maximum size, incrementing the available space control window of the maximum size, incrementing the available space
when new data is received. Sending data is always subject to the when new data is received. This effectively disables flow control
for that receiver. Conversely, a sender is always subject to the
flow control window advertised by the receiver. flow control window advertised by the receiver.
Deployments with constrained resources (for example, memory) MAY Deployments with constrained resources (for example, memory) can
employ flow control to limit the amount of memory a peer can consume. employ flow control to limit the amount of memory a peer can consume.
Note, however, that this can lead to suboptimal use of available Note, however, that this can lead to suboptimal use of available
network resources if flow control is enabled without knowledge of the network resources if flow control is enabled without knowledge of the
bandwidth-delay product (see [RFC1323]). bandwidth-delay product (see [RFC1323]).
Even with full awareness of the current bandwidth-delay product, Even with full awareness of the current bandwidth-delay product,
implementation of flow control can be difficult. When using flow implementation of flow control can be difficult. When using flow
control, the receiver MUST read from the TCP receive buffer in a control, the receiver MUST read from the TCP receive buffer in a
timely fashion. Failure to do so could lead to a deadlock when timely fashion. Failure to do so could lead to a deadlock when
critical frames, such as WINDOW_UPDATE, are not available to HTTP/2. critical frames, such as WINDOW_UPDATE, are not read and acted upon.
However, flow control can ensure that constrained resources are
protected without any reduction in connection utilization.
5.3. Stream priority 5.3. Stream priority
A client can assign a priority for a new stream by including A client can assign a priority for a new stream by including
prioritization information in the HEADERS frame (Section 6.2) that prioritization information in the HEADERS frame (Section 6.2) that
opens the stream. For an existing stream, the PRIORITY frame opens the stream. For an existing stream, the PRIORITY frame
(Section 6.3) can be used to change the priority. (Section 6.3) can be used to change the priority.
The purpose of prioritization is to allow an endpoint to express how The purpose of prioritization is to allow an endpoint to express how
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
default values are used if no explicit indicator is provided default values are used if no explicit indicator is provided
(Section 5.3.5). (Section 5.3.5).
5.3.1. Stream Dependencies 5.3.1. Stream Dependencies
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 can given a stream A stream that is not dependent on any other stream is given a stream
dependency of 0x0. dependency of 0x0. In other words, the non-existent stream 0 forms
the root of the tree.
When assigning a dependency on another stream, by default, the stream A stream that depends on another stream is a dependent stream. The
is added as a new dependency of the stream it depends on. For stream upon which a stream is dependent is a parent stream.
When assigning a dependency on another stream, the stream is added as
a new dependency of the parent stream. Dependent streams that share
the same parent are not order 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. 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
An exclusive flag allows for the insertion of a new level of An exclusive flag allows for the insertion of a new level of
dependencies. The exclusive flag causes the stream to become the dependencies. The exclusive flag causes the stream to become the
sole dependency of the stream it depends on, causing other sole dependency of its parent stream, causing other dependencies to
dependencies to become dependencies of the stream. In the previous become dependent on the prioritized stream. In the previous example,
example, if stream D is created with an exclusive dependency on if stream D is created with an exclusive dependency on stream A, this
stream A, this results in a dependency order of A followed by D results in D becoming the dependency parent of B and C.
followed by B and C.
A A
A | A |
/ \ ==> D / \ ==> D
B C / \ B C / \
B C B C
Example of Exclusive Dependency Creation Example of Exclusive Dependency Creation
Inside the dependency tree, a dependent stream SHOULD only be Inside the dependency tree, a dependent stream SHOULD only be
allocated resources if the streams that it depends on are either allocated resources if all of the streams that it depends on (the
closed, or it is not possible to make progress on them. chain of parent streams up to 0x0) are either closed, or it is not
possible to make progress on them.
A stream cannot depend on itself. An endpoint MUST treat this as a
stream error (Section 5.4.2) of type PROTOCOL_ERROR.
5.3.2. Dependency Weighting 5.3.2. Dependency Weighting
Each dependency is allocated an integer weight between 1 to 256 All dependent streams are allocated an integer weight between 1 to
(inclusive). 256 (inclusive).
Streams with the same dependencies SHOULD be allocated resources Streams with the same parent SHOULD be allocated resources
proportionally based on their weight. Thus, if stream B depends on proportionally based on their weight. Thus, if stream B depends on
stream A with weight 4, and C depends on stream A with weight 12, and stream A with weight 4, and C depends on stream A with weight 12, and
if no progress can be made on A, stream B ideally receives one third if no progress can be made on A, stream B ideally receives one third
of the resources allocated to stream C. of the resources allocated to stream C.
A stream MUST NOT depend on itself. An endpoint MAY either treat
this as a stream error (Section 5.4.2) of type PROTOCOL_ERROR, or
assign default priority values (Section 5.3.5) to the stream.
5.3.3. Reprioritization 5.3.3. Reprioritization
Stream priorities are changed using the PRIORITY frame. Setting a Stream priorities are changed using the PRIORITY frame. Setting a
dependency causes a stream to become dependent on the identified dependency causes a stream to become dependent on the identified
stream. parent stream.
All streams that are dependent on a reprioritized stream move with Dependent streams move with their parent stream if the parent is
it. Setting a dependency with the exclusive flag for a reprioritized reprioritized. Setting a dependency with the exclusive flag for a
stream moves all the dependencies of the stream it depends on to reprioritized stream moves all the dependencies of the new parent
become dependencies of the reprioritized stream. stream to become dependent on the reprioritized stream.
If a stream is made dependent on one of its own dependencies, the If a stream is made dependent on one of its own dependencies, the
formerly dependent stream is first moved to be depedent on the formerly dependent stream is first moved to be dependent on the
reprioritized streams previous dependency, retaining its weight. reprioritized stream's previous parent. The moved dependency retains
its weight.
For example, for an original dependency tree where B and C depend on For example, consider an original dependency tree where B and C
A, D and E depend on C, and F depends on D; if A is made dependent on depend on A, D and E depend on C, and F depends on D. If A is made
D, then D takes the place of A with A dependent on D and all other dependent on D, then D takes the place of A. All other dependency
dependency relationships staying the same. relationships stay the same, except for F, which becomes dependent on
A if the reprioritization is exclusive.
0 ? ? ? ?
A / \ D D | / \ | |
/ \ D A / \ OR | A D A D D
B C ==> / / \ ==> F A ==> A / \ / / \ / \ |
/ \ F B C / \ /|\ B C ==> F B C ==> F A OR A
D E | B C B C F / \ | / \ /|\
| E | | D E E B C B C F
F E F | | |
F E E
(intermediate) (non-exclusive) (exclusive) (intermediate) (non-exclusive) (exclusive)
Example of Dependency Reordering Example of Dependency Reordering
5.3.4. Prioritization State Management 5.3.4. Prioritization State Management
When a stream is removed from the dependency tree, its dependencies When a stream is removed from the dependency tree, its dependencies
can be moved to become dependent on the stream the closed stream can be moved to become dependent on the parent of the closed stream.
depends on. The weights of new dependencies SHOULD be assigned by The weights of new dependencies are recalculated by distributing the
distributing the weight of the dependency of the closed stream weight of the dependency of the closed stream proportionally based on
proportionally based on the weights of its dependencies. the weights of its dependencies.
Streams that are removed from the dependency tree cause some Streams that are removed from the dependency tree cause some
prioritization information to be lost. Resources are shared between prioritization information to be lost. Resources are shared between
streams that depend on the same stream, which means that if a stream streams with the same parent stream, which means that if a stream in
in that set closes or becomes blocked, any spare capacity allocated that set closes or becomes blocked, any spare capacity allocated to a
to a stream is distributed to the immediate neighbors of the stream. stream is distributed to the immediate neighbors of the stream.
However, if the common dependency is removed from the tree, those However, if the common dependency is removed from the tree, those
streams share resources with streams at the next highest level. For streams share resources with streams at the next highest level.
example, assume streams A and B share a dependency, and C and D both
depend on A. Prior to the removal of A, if stream A and D are unable For example, assume streams A and B share a parent, and streams C and
to proceed, then C receives all the resources dedicated to A. If A is D both depend on stream A. Prior to the removal of stream A, if
removed from the tree, the weight of A is divided equally between D streams A and D are unable to proceed, then stream C receives all the
and E, which results in stream C receiving a reduced proportion of resources dedicated to stream A. If stream A is removed from the
resources (one third, rather than one half). tree, the weight of stream A is divided between streams C and D. If
stream D is still unable to proceed, this results in stream C
receiving a reduced proportion of resources. For equal starting
weights, C receives one third, rather than one half, of available
resources.
It is possible for a stream to become closed while prioritization It is possible for a stream to become closed while prioritization
information that creates a dependency on that stream is in transit. information that creates a dependency on that stream is in transit.
If a stream identified in a dependency has been closed and any If a stream identified in a dependency has had any associated
associated priority information destroyed then the dependent stream priority information destroyed, then the dependent stream is instead
is instead assigned a default priority. This potentially creates assigned a default priority. This potentially creates suboptimal
suboptimal prioritization, since the stream can be given an effective prioritization, since the stream could be given a priority that is
priority that is higher than expressed by a peer. higher than intended.
To avoid these problems, endpoints SHOULD maintain prioritization
state for closed streams for a period after streams close.
An endpoint SHOULD retain stream prioritization state for a period To avoid these problems, an endpoint SHOULD retain stream
after streams become closed. The longer state is retained, the lower prioritization state for a period after streams become closed. The
the chance that streams are assigned incorrect or default priority longer state is retained, the lower the chance that streams are
values. assigned incorrect or default priority values.
This could create a large state burden for an endpoint, so this state This could create a large state burden for an endpoint, so this state
MAY be limited. An endpoint MAY apply a fixed upper limit on the MAY be limited. An endpoint MAY apply a fixed upper limit on the
number of closed streams for which prioritization state is tracked to number of closed streams for which prioritization state is tracked to
limit state exposure. The amount of additional state an endpoint limit state exposure. The amount of additional state an endpoint
maintains could be dependent on load; under high load, prioritization maintains could be dependent on load; under high load, prioritization
state can be discarded to limit resource commitments. In extreme state can be discarded to limit resource commitments. In extreme
cases, an endpoint could even discard prioritization state for active cases, an endpoint could even discard prioritization state for active
or reserved streams. If a fixed limit is applied, endpoints SHOULD or reserved streams. If a fixed limit is applied, endpoints SHOULD
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
dependency on stream 0x0. Pushed streams (Section 8.2) initially default dependency on stream 0x0. Pushed streams (Section 8.2)
depend on their associated stream. In both cases, streams are initially depend on their associated stream. In both cases, streams
assigned a default weight of 16. 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.
skipping to change at page 27, line 19 skipping to change at page 27, line 43
An endpoint that encounters a connection error SHOULD first send a An endpoint that encounters a connection error SHOULD first send a
GOAWAY frame (Section 6.8) with the stream identifier of the last GOAWAY frame (Section 6.8) with the stream identifier of the last
stream that it successfully received from its peer. The GOAWAY frame stream that it successfully received from its peer. The GOAWAY frame
includes an error code that indicates why the connection is includes an error code that indicates why the connection is
terminating. After sending the GOAWAY frame, the endpoint MUST close terminating. After sending the GOAWAY frame, the endpoint MUST close
the TCP connection. the TCP connection.
It is possible that the GOAWAY will not be reliably received by the It is possible that the GOAWAY will not be reliably received by the
receiving endpoint. In the event of a connection error, GOAWAY only receiving endpoint. In the event of a connection error, GOAWAY only
provides a best-effort attempt to communicate with the peer about why provides a best effort attempt to communicate with the peer about why
the connection is being terminated. the connection is being terminated.
An endpoint can end a connection at any time. In particular, an An endpoint can end a connection at any time. In particular, an
endpoint MAY choose to treat a stream error as a connection error. endpoint MAY choose to treat a stream error as a connection error.
Endpoints SHOULD send a GOAWAY frame when ending a connection, as Endpoints SHOULD send a GOAWAY frame when ending a connection,
long as circumstances permit it. providing that circumstances permit it.
5.4.2. Stream Error Handling 5.4.2. Stream Error Handling
A stream error is an error related to a specific stream identifier A stream error is an error related to a specific stream that does not
that does not affect processing of other streams. affect processing of other streams.
An endpoint that detects a stream error sends a RST_STREAM frame An endpoint that detects a stream error sends a RST_STREAM frame
(Section 6.4) that contains the stream identifier of the stream where (Section 6.4) that contains the stream identifier of the stream where
the error occurred. The RST_STREAM frame includes an error code that the error occurred. The RST_STREAM frame includes an error code that
indicates the type of error. indicates the type of error.
A RST_STREAM is the last frame that an endpoint can send on a stream. A RST_STREAM is the last frame that an endpoint can send on a stream.
The peer that sends the RST_STREAM frame MUST be prepared to receive The peer that sends the RST_STREAM frame MUST be prepared to receive
any frames that were sent or enqueued for sending by the remote peer. any frames that were sent or enqueued for sending by the remote peer.
These frames can be ignored, except where they modify connection These frames can be ignored, except where they modify connection
state (such as the state maintained for header compression state (such as the state maintained for header compression
(Section 4.3)). (Section 4.3), or flow control).
Normally, an endpoint SHOULD NOT send more than one RST_STREAM frame Normally, an endpoint SHOULD NOT send more than one RST_STREAM frame
for any stream. However, an endpoint MAY send additional RST_STREAM for any stream. However, an endpoint MAY send additional RST_STREAM
frames if it receives frames on a closed stream after more than a frames if it receives frames on a closed stream after more than a
round-trip time. This behavior is permitted to deal with misbehaving round-trip time. This behavior is permitted to deal with misbehaving
implementations. implementations.
An endpoint MUST NOT send a RST_STREAM in response to an RST_STREAM An endpoint MUST NOT send a RST_STREAM in response to an RST_STREAM
frame, to avoid looping. frame, to avoid looping.
5.4.3. Connection Termination 5.4.3. Connection Termination
If the TCP connection is torn down while streams remain in open or If the TCP connection is torn down while streams remain in open or
half closed states, then the endpoint MUST assume that those streams half closed states, then the endpoint MUST assume that those streams
were abnormally interrupted and could be incomplete. were abnormally interrupted and could be incomplete.
5.5. Extending HTTP/2
HTTP/2 permits extension of the protocol. Protocol extensions can be
used to provide additional services or alter any aspect of the
protocol, within the limitations described in this section.
Extensions are effective only within the scope of a single HTTP/2
connection.
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
fields that start with a colon (:). Of these, registries are
established for frame types (Section 11.2), settings (Section 11.3)
and error codes (Section 11.4).
Implementations MUST ignore unknown or unsupported values in all
extensible protocol elements. Implementations MUST discard frames
that have unknown or unsupported types. This means that any of these
extension points can be safely used by extensions without prior
arrangement or negotiation.
However, extensions that could change the semantics of existing
protocol components MUST be negotiated before being used. For
example, an extension that changes the layout of the HEADERS frame
cannot be used until the peer has given a positive signal that this
is acceptable. In this case, it could also be necessary to
coordinate when the revised layout comes into effect. Note that
treating any frame other than DATA frames as flow controlled is such
a change in semantics, and can only be done through negotiation.
This document doesn't mandate a specific method for negotiating the
use of an extension, but notes that a setting (Section 6.5.2) could
be used for that purpose. If both peers set a value that indicates
willingness to use the extension, then the extension can be used. If
a setting is used for extension negotiation, the initial value MUST
be defined so that the extension is initially disabled.
6. Frame Definitions 6. Frame Definitions
This specification defines a number of frame types, each identified This specification defines a number of frame types, each identified
by a unique 8-bit type code. Each frame type serves a distinct by a unique 8-bit type code. Each frame type serves a distinct
purpose either in the establishment and management of the connection purpose either in the establishment and management of the connection
as a whole, or of individual streams. as a whole, or of individual streams.
The transmission of specific frame types can alter the state of a The transmission of specific frame types can alter the state of a
connection. If endpoints fail to maintain a synchronized view of the connection. If endpoints fail to maintain a synchronized view of the
connection state, successful communication within the connection will connection state, successful communication within the connection will
skipping to change at page 28, line 32 skipping to change at page 29, line 45
have a shared comprehension of how the state is affected by the use have a shared comprehension of how the state is affected by the use
any given frame. any given frame.
6.1. DATA 6.1. DATA
DATA frames (type=0x0) convey arbitrary, variable-length sequences of DATA frames (type=0x0) convey arbitrary, variable-length sequences of
octets associated with a stream. One or more DATA frames are used, octets associated with a stream. One or more DATA frames are used,
for instance, to carry HTTP request or response payloads. for instance, to carry HTTP request or response payloads.
DATA frames MAY also contain arbitrary padding. Padding can be added DATA frames MAY also contain arbitrary padding. Padding can be added
to DATA frames to hide the size of messages. to DATA frames to obscure the size of messages.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pad High? (8) | Pad Low? (8) | |Pad Length? (8)|
+---------------+---------------+-------------------------------+ +---------------+-----------------------------------------------+
| Data (*) ... | Data (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Padding (*) ... | Padding (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
DATA Frame Payload DATA Frame Payload
The DATA frame contains the following fields: The DATA frame contains the following fields:
Pad High: An 8-bit field containing an amount of padding in units of Pad Length: An 8-bit field containing the length of the frame
256 octets. This field is optional and is only present if the padding in units of octets. This field is optional and is only
PAD_HIGH flag is set. This field, in combination with Pad Low, present if the PADDED flag is set.
determines how much padding there is on a frame.
Pad Low: An 8-bit field containing an amount of padding in units of
single octets. This field is optional and is only present if the
PAD_LOW flag is set. This field, in combination with Pad High,
determines how much padding there is on a frame.
Data: Application data. The amount of data is the remainder of the Data: Application data. The amount of data is the remainder of the
frame payload after subtracting the length of the other fields frame payload after subtracting the length of the other fields
that are present. that are present.
Padding: Padding octets that contain no application semantic value. Padding: Padding octets that contain no application semantic value.
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:
skipping to change at page 29, line 30 skipping to change at page 30, line 43
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 END_SEGMENT (0x2): Bit 2 being set indicates that this frame is the
last for the current segment. Intermediaries MUST NOT coalesce last for the current segment. Intermediaries MUST NOT coalesce
frames across a segment boundary and MUST preserve segment frames across a segment boundary and MUST preserve segment
boundaries when forwarding frames. boundaries when forwarding frames.
PAD_LOW (0x8): Bit 4 being set indicates that the Pad Low field is PADDED (0x8): Bit 4 being set indicates that the Pad Length field is
present. present.
PAD_HIGH (0x10): Bit 5 being set indicates that the Pad High field
is present. This bit MUST NOT be set unless the PAD_LOW flag is
also set. Endpoints that receive a frame with PAD_HIGH set and
PAD_LOW cleared MUST treat this as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
COMPRESSED (0x20): Bit 6 being set indicates that the data in the
frame has been compressed with GZIP compression ([GZIP]).
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 optionally compressed using GZip compression [GZIP].
Each frame is individually compressed; the state of the compressor is
reset for each frame.
An endpoint MUST NOT send a DATA frame with the COMPRESSED flag set
unless the SETTINGS_COMPRESS_DATA setting is enabled, that is, set to
1. An endpoint that has not enabled DATA frame compression MUST
treat the receipt of a DATA frame with the COMPRESSED flag set as a
connection error (Section 5.4.1) of type 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. Padding is stream is in the "open" or "half closed (remote)" states. The entire
included in flow control. If a DATA frame is received whose stream DATA frame payload is included in flow control, including Pad Length
is not in "open" or "half closed (local)" state, the recipient MUST and Padding fields if present. If a DATA frame is received whose
respond with a stream error (Section 5.4.2) of type STREAM_CLOSED. stream is not in "open" or "half closed (local)" state, the recipient
MUST respond with a stream error (Section 5.4.2) of type
STREAM_CLOSED.
The total number of padding octets is determined by multiplying the The total number of padding octets is determined by the value of the
value of the Pad High field by 256 and adding the value of the Pad Pad Length field. If the length of the padding is greater than the
Low field. Both Pad High and Pad Low fields assume a value of zero length of the remainder of the frame payload, the recipient MUST
if absent. If the length of the padding is greater than the length treat this as a connection error (Section 5.4.1) of type
of the remainder of the frame payload, the recipient MUST treat this PROTOCOL_ERROR.
as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
Note: A frame can be increased in size by one octet by including a Note: A frame can be increased in size by one octet by including a
Pad Low field with a value of zero. Pad Length field with a value of zero.
Use of padding is a security feature; as such, its use demands some Use of padding is a security feature; as such, its use demands some
care, see Section 10.7. care, see Section 10.7.
6.2. HEADERS 6.2. HEADERS
The HEADERS frame (type=0x1) carries name-value pairs. It is used to The HEADERS frame (type=0x1) carries name-value pairs. It is used to
open a stream (Section 5.1). HEADERS frames can be sent on a stream open a stream (Section 5.1). HEADERS frames can be sent on a stream
in the "open" or "half closed (remote)" states. in the "open" or "half closed (remote)" states.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pad High? (8) | Pad Low? (8) | |Pad Length? (8)|
+-+-------------+---------------+-------------------------------+ +-+-------------+-----------------------------------------------+
|E| Stream Dependency? (31) | |E| Stream Dependency? (31) |
+-+-------------+-----------------------------------------------+ +-+-------------+-----------------------------------------------+
| Weight? (8) | | Weight? (8) |
+-+-------------+-----------------------------------------------+ +-+-------------+-----------------------------------------------+
| Header Block Fragment (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Padding (*) ... | Padding (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
HEADERS Frame Payload HEADERS Frame Payload
The HEADERS frame payload has the following fields: The HEADERS frame payload has the following fields:
Pad High: Padding size high bits. This field is only present if the Pad Length: An 8-bit field containing the length of the frame
PAD_HIGH flag is set. padding in units of octets. This field is optional and is only
present if the PADDED flag is set.
Pad Low: Padding size low bits. This field is only present if the
PAD_LOW flag is set.
E: A single bit flag indicates that the stream dependency is E: A single bit flag indicates that the stream dependency is
exclusive, see Section 5.3. This field is optional and is only exclusive, see Section 5.3. This field is optional and is only
present if the PRIORITY flag is set. present if the PRIORITY flag is set.
Stream Dependency: A 31-bit stream identifier for the stream that Stream Dependency: A 31-bit stream identifier for the stream that
this stream depends on, see Section 5.3. This field is optional this stream depends on, see Section 5.3. This field is optional
and is only present if the PRIORITY flag is set. and is only present if the PRIORITY flag is set.
Weight: An 8-bit weight for the stream, see Section 5.3. Add one to Weight: An 8-bit weight for the stream, see Section 5.3. Add one to
skipping to change at page 32, line 5 skipping to change at page 32, line 47
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.
PAD_LOW (0x8): Bit 4 being set indicates that the Pad Low field is PADDED (0x8): Bit 4 being set indicates that the Pad Length field is
present. present.
PAD_HIGH (0x10): Bit 5 being set indicates that the Pad High field
is present. This bit MUST NOT be set unless the PAD_LOW flag is
also set. Endpoints that receive a frame with PAD_HIGH set and
PAD_LOW cleared MUST treat this as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
PRIORITY (0x20): Bit 6 being set indicates that the Exclusive Flag PRIORITY (0x20): Bit 6 being set indicates that the Exclusive Flag
(E), Stream Dependency, and Weight fields are present; see (E), Stream Dependency, and Weight fields are present; see
Section 5.3. Section 5.3.
The payload of a HEADERS frame contains a header block fragment The payload of a HEADERS frame contains a header block fragment
(Section 4.3). A header block that does not fit within a HEADERS (Section 4.3). A header block that does not fit within a HEADERS
frame is continued in a CONTINUATION frame (Section 6.10). frame is continued in a CONTINUATION frame (Section 6.10).
HEADERS frames MUST be associated with a stream. If a HEADERS frame HEADERS frames MUST be associated with a stream. If a HEADERS frame
is received whose stream identifier field is 0x0, the recipient MUST is received whose stream identifier field is 0x0, the recipient MUST
skipping to change at page 32, line 37 skipping to change at page 33, line 24
The HEADERS frame changes the connection state as described in The HEADERS frame changes the connection state as described in
Section 4.3. Section 4.3.
The HEADERS frame includes optional padding. Padding fields and The HEADERS frame includes optional padding. Padding fields and
flags are identical to those defined for DATA frames (Section 6.1). flags are identical to those defined for DATA frames (Section 6.1).
6.3. PRIORITY 6.3. PRIORITY
The PRIORITY frame (type=0x2) specifies the sender-advised priority The PRIORITY frame (type=0x2) specifies the sender-advised priority
of a stream (Section 5.3). It can be sent at any time for an of a stream (Section 5.3). It can be sent at any time for an
existing stream. This enables reprioritization of existing streams. existing stream, including closed streams. This enables
reprioritization of existing streams.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| Stream Dependency (31) | |E| Stream Dependency (31) |
+-+-------------+-----------------------------------------------+ +-+-------------+-----------------------------------------------+
| Weight (8) | | Weight (8) |
+-+-------------+ +-+-------------+
PRIORITY Frame Payload PRIORITY Frame Payload
The payload of a PRIORITY frame contains the following fields: The payload of a PRIORITY frame contains the following fields:
skipping to change at page 33, line 23 skipping to change at page 34, line 8
and 256. and 256.
The PRIORITY frame does not define any flags. The PRIORITY frame does not define any flags.
The PRIORITY frame is associated with an existing stream. If a The PRIORITY frame is associated with an existing stream. If a
PRIORITY frame is received with a stream identifier of 0x0, the PRIORITY frame is received with a stream identifier of 0x0, the
recipient MUST respond with a connection error (Section 5.4.1) of recipient MUST respond with a connection error (Section 5.4.1) of
type PROTOCOL_ERROR. type PROTOCOL_ERROR.
The PRIORITY frame can be sent on a stream in any of the "reserved The PRIORITY frame can be sent on a stream in any of the "reserved
(remote)", "open", "half-closed (local)", or "half closed (remote)" (remote)", "open", "half closed (local)", "half closed (remote)", or
states, though it cannot be sent between consecutive frames that "closed" states, though it cannot be sent between consecutive frames
comprise a single header block (Section 4.3). Note that this frame that comprise a single header block (Section 4.3). Note that this
could arrive after processing or frame sending has completed, which frame could arrive after processing or frame sending has completed,
would cause it to have no effect. For a stream that is in the "half which would cause it to have no effect on the current stream. For a
closed (remote)" state, this frame can only affect processing of the stream that is in the "half closed (remote)" or "closed" - state,
stream and not frame transmission. this frame can only affect processing of the current stream and not
frame transmission.
The PRIORITY frame is the only frame that can be sent for a stream in
the "closed" state. This allows for the reprioritization of a group
of dependent streams by altering the priority of a parent stream,
which might be closed. However, a PRIORITY frame sent on a closed
stream risks being ignored due to the peer having discarded priority
state information for that stream.
6.4. RST_STREAM 6.4. RST_STREAM
The RST_STREAM frame (type=0x3) allows for abnormal termination of a The RST_STREAM frame (type=0x3) allows for abnormal termination of a
stream. When sent by the initiator of a stream, it indicates that stream. When sent by the initiator of a stream, it indicates that
they wish to cancel the stream or that an error condition has they wish to cancel the stream or that an error condition has
occurred. When sent by the receiver of a stream, it indicates that occurred. When sent by the receiver of a stream, it indicates that
either the receiver is rejecting the stream, requesting that the either the receiver is rejecting the stream, requesting that the
stream be cancelled or that an error condition has occurred. stream be cancelled, or that an error condition has occurred.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code (32) | | Error Code (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
RST_STREAM Frame Payload RST_STREAM Frame Payload
The RST_STREAM frame contains a single unsigned, 32-bit integer The RST_STREAM frame contains a single unsigned, 32-bit integer
identifying the error code (Section 7). The error code indicates why identifying the error code (Section 7). The error code indicates why
the stream is being terminated. the stream is being terminated.
skipping to change at page 34, line 25 skipping to change at page 35, line 19
treat this as a connection error (Section 5.4.1) of type treat this as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
RST_STREAM frames MUST NOT be sent for a stream in the "idle" state. RST_STREAM frames MUST NOT be sent for a stream in the "idle" state.
If a RST_STREAM frame identifying an idle stream is received, the If a RST_STREAM frame identifying an idle stream is received, the
recipient MUST treat this as a connection error (Section 5.4.1) of recipient MUST treat this as a connection error (Section 5.4.1) of
type PROTOCOL_ERROR. type PROTOCOL_ERROR.
6.5. SETTINGS 6.5. SETTINGS
The SETTINGS frame (type=0x4) conveys configuration parameters (such The SETTINGS frame (type=0x4) conveys configuration parameters that
as preferences and constraints on peer behavior) that affect how affect how endpoints communicate, such as preferences and constraints
endpoints communicate, and is also used to acknowledge the receipt of on peer behavior. The SETTINGS frame is also used to acknowledge the
those parameters. Individually, a SETTINGS parameter can also be receipt of those parameters. Individually, a SETTINGS parameter can
referred to as a "setting". also be referred to as a "setting".
SETTINGS parameters are not negotiated; they describe characteristics SETTINGS parameters are not negotiated; they describe characteristics
of the sending peer, which are used by the receiving peer. Different of the sending peer, which are used by the receiving peer. Different
values for the same parameter can be advertised by each peer. For values for the same parameter can be advertised by each peer. For
example, a client might set a high initial flow control window, example, a client might set a high initial flow control window,
whereas a server might set a lower value to conserve resources. whereas a server might set a lower value to conserve resources.
A SETTINGS frame MUST be sent by both endpoints at the start of a A SETTINGS frame MUST be sent by both endpoints at the start of a
connection, and MAY be sent at any other time by either endpoint over connection, and MAY be sent at any other time by either endpoint over
the lifetime of the connection. Implementations MUST support all of the lifetime of the connection. Implementations MUST support all of
skipping to change at page 35, line 14 skipping to change at page 36, line 8
ACK (0x1): Bit 1 being set indicates that this frame acknowledges ACK (0x1): Bit 1 being set indicates that this frame acknowledges
receipt and application of the peer's SETTINGS frame. When this receipt and application of the peer's SETTINGS frame. When this
bit is set, the payload of the SETTINGS frame MUST be empty. bit is set, the payload of the SETTINGS frame MUST be empty.
Receipt of a SETTINGS frame with the ACK flag set and a length Receipt of a SETTINGS frame with the ACK flag set and a length
field value other than 0 MUST be treated as a connection error field value other than 0 MUST be treated as a connection error
(Section 5.4.1) of type FRAME_SIZE_ERROR. For more info, see (Section 5.4.1) of type FRAME_SIZE_ERROR. For more info, see
Settings Synchronization (Section 6.5.3). Settings Synchronization (Section 6.5.3).
SETTINGS frames always apply to a connection, never a single stream. SETTINGS frames always apply to a connection, never a single stream.
The stream identifier for a SETTINGS frame MUST be zero. If an The stream identifier for a SETTINGS frame MUST be zero (0x0). If an
endpoint receives a SETTINGS frame whose stream identifier field is endpoint receives a SETTINGS frame whose stream identifier field is
anything other than 0x0, the endpoint MUST respond with a connection anything other than 0x0, the endpoint MUST respond with a connection
error (Section 5.4.1) of type PROTOCOL_ERROR. error (Section 5.4.1) of type PROTOCOL_ERROR.
The SETTINGS frame affects connection state. A badly formed or The SETTINGS frame affects connection state. A badly formed or
incomplete SETTINGS frame MUST be treated as a connection error incomplete SETTINGS frame MUST be treated as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
6.5.1. SETTINGS Format 6.5.1. SETTINGS Format
The payload of a SETTINGS frame consists of zero or more parameters, The payload of a SETTINGS frame consists of zero or more parameters,
each consisting of an unsigned 8-bit identifier and an unsigned 32- each consisting of an unsigned 16-bit setting identifier and an
bit value. unsigned 32-bit value.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier (8)| | Identifier (16) |
+---------------+-----------------------------------------------+ +-------------------------------+-------------------------------+
| Value (32) | | Value (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Setting Format Setting Format
6.5.2. Defined SETTINGS Parameters 6.5.2. Defined SETTINGS Parameters
The following parameters are defined: The following parameters are defined:
SETTINGS_HEADER_TABLE_SIZE (1): Allows the sender to inform the SETTINGS_HEADER_TABLE_SIZE (0x1): Allows the sender to inform the
remote endpoint of the size of the header compression table used remote endpoint of the maximum size of the header compression
to decode header blocks. The encoder can reduce this size by table used to decode header blocks. The encoder can select any
using signaling specific to the header compression format inside a size equal to or less than this value by using signaling specific
header block. The initial value is 4,096 bytes. to the header compression format inside a header block. The
initial value is 4,096 bytes.
SETTINGS_ENABLE_PUSH (2): This setting can be use to disable server SETTINGS_ENABLE_PUSH (0x2): This setting can be use to disable
push (Section 8.2). An endpoint MUST NOT send a PUSH_PROMISE server push (Section 8.2). An endpoint MUST NOT send a
frame if it receives this parameter set to a value of 0. An PUSH_PROMISE frame if it receives this parameter set to a value of
endpoint that has both set this parameter to 0 and had it 0. An endpoint that has both set this parameter to 0 and had it
acknowledged MUST treat the receipt of a PUSH_PROMISE frame as a acknowledged MUST treat the receipt of a PUSH_PROMISE frame as a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
The initial value is 1, which indicates that push is permitted. The initial value is 1, which indicates that server push is
Any value other than 0 or 1 MUST be treated as a connection error permitted. Any value other than 0 or 1 MUST be treated as a
(Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
SETTINGS_MAX_CONCURRENT_STREAMS (3): Indicates the maximum number of SETTINGS_MAX_CONCURRENT_STREAMS (0x3): Indicates the maximum number
concurrent streams that the sender will allow. This limit is of concurrent streams that the sender will allow. This limit is
directional: it applies to the number of streams that the sender directional: it applies to the number of streams that the sender
permits the receiver to create. Initially there is no limit to permits the receiver to create. Initially there is no limit to
this value. It is recommended that this value be no smaller than this value. It is recommended that this value be no smaller than
100, so as to not unnecessarily limit parallelism. 100, so as to not unnecessarily limit parallelism.
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 (4): 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 65,535.
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_COMPRESS_DATA (5): This setting is used to enable GZip An endpoint that receives a SETTINGS frame with any unknown or
compression of DATA frames. unsupported identifier MUST ignore that setting.
A value of 1 indicates that DATA frames MAY be compressed. A
value of 0 indicates that compression is not permitted. The
initial value is 0.
Values other than 0 or 1 are invalid. An endpoint MUST treat the
receipt of any other value as a connection error (Section 5.4.1)
of type PROTOCOL_ERROR.
An endpoint that receives a SETTINGS frame with any other identifier
MUST treat this as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
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 the communicated
parameter values. In order to provide such synchronization parameter values. In order to provide such synchronization
timepoints, the recipient of a SETTINGS frame in which the ACK flag timepoints, the recipient of a SETTINGS frame in which the ACK flag
is not set MUST apply the updated parameters as soon as possible upon is not set MUST apply the updated parameters as soon as possible upon
receipt. receipt.
skipping to change at page 37, line 34 skipping to change at page 38, line 18
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
stream the endpoint plans to create along with a set of headers that stream the endpoint plans to create along with a set of headers that
provide additional context for the stream. Section 8.2 contains a provide additional context for the stream. Section 8.2 contains a
thorough description of the use of PUSH_PROMISE frames. thorough description of the use of PUSH_PROMISE frames.
PUSH_PROMISE MUST NOT be sent if the SETTINGS_ENABLE_PUSH setting of 0 1 2 3
the peer endpoint is set to 0. 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
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pad High? (8) | Pad Low? (8) | |Pad Length? (8)|
+-+-------------+---------------+-------------------------------+ +-+-------------+-----------------------------------------------+
|R| Promised Stream ID (31) | |R| Promised Stream ID (31) |
+-+-----------------------------+-------------------------------+ +-+-----------------------------+-------------------------------+
| Header Block Fragment (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Padding (*) ... | Padding (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
PUSH_PROMISE Payload Format PUSH_PROMISE Payload Format
The PUSH_PROMISE frame payload has the following fields: The PUSH_PROMISE frame payload has the following fields:
Pad High: Padding size high bits. This field is only present if the Pad Length: An 8-bit field containing the length of the frame
PAD_HIGH flag is set. padding in units of octets. This field is optional and is only
present if the PADDED flag is set.
Pad Low: Padding size low bits. This field is only present if the
PAD_LOW flag is set.
R: A single reserved bit. R: A single reserved bit.
Promised Stream ID: This unsigned 31-bit integer identifies the Promised Stream ID: This unsigned 31-bit integer identifies the
stream the endpoint intends to start sending frames for. The stream the endpoint intends to start sending frames for. The
promised stream identifier MUST be a valid choice for the next promised stream identifier MUST be a valid choice for the next
stream sent by the sender (see new stream identifier stream sent by the sender (see new stream identifier
(Section 5.1.1)). (Section 5.1.1)).
Header Block Fragment: A header block fragment (Section 4.3) Header Block Fragment: A header block fragment (Section 4.3)
skipping to change at page 38, line 36 skipping to change at page 39, line 15
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 PUSH_PROMISE frame without the END_HEADERS flag set MUST be A PUSH_PROMISE frame without the END_HEADERS flag set MUST be
followed by a CONTINUATION frame for the same stream. A receiver followed 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 MUST 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.
PAD_LOW (0x8): Bit 4 being set indicates that the Pad Low field is PADDED (0x8): Bit 4 being set indicates that the Pad Length field is
present. present.
PAD_HIGH (0x10): Bit 5 being set indicates that the Pad High field
is present. This bit MUST NOT be set unless the PAD_LOW flag is
also set. Endpoints that receive a frame with PAD_HIGH set and
PAD_LOW cleared MUST treat this as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
PUSH_PROMISE frames MUST be associated with an existing, peer- PUSH_PROMISE frames MUST be associated with an existing, peer-
initiated stream. The stream identifier of a PUSH_PROMISE frame initiated stream. The stream identifier of a PUSH_PROMISE frame
indicates the stream it is associated with. If the stream identifier indicates the stream it is associated with. If the stream identifier
field specifies the value 0x0, a recipient MUST respond with a field specifies the value 0x0, a recipient MUST respond with a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
Promised streams are not required to be used in order promised. The Promised streams are not required to be used in the order they are
PUSH_PROMISE only reserves stream identifiers for later use. promised. The PUSH_PROMISE only reserves stream identifiers for
later use.
PUSH_PROMISE MUST NOT be sent if the SETTINGS_ENABLE_PUSH setting of
the peer endpoint is set to 0. An endpoint that has set this setting
and has received acknowledgement MUST treat the receipt of a
PUSH_PROMISE frame as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
Recipients of PUSH_PROMISE frames can choose to reject promised Recipients of PUSH_PROMISE frames can choose to reject promised
streams by returning a RST_STREAM referencing the promised stream streams by returning a RST_STREAM referencing the promised stream
identifier back to the sender of the PUSH_PROMISE. identifier back to the sender of the PUSH_PROMISE.
The PUSH_PROMISE frame modifies the connection state as defined in
Section 4.3.
A PUSH_PROMISE frame modifies the connection state in two ways. The A PUSH_PROMISE frame modifies the connection state in two ways. The
inclusion of a header block (Section 4.3) potentially modifies the inclusion of a header block (Section 4.3) potentially modifies the
state maintained for header compression. PUSH_PROMISE also reserves state maintained for header compression. PUSH_PROMISE also reserves
a stream for later use, causing the promised stream to enter the a stream for later use, causing the promised stream to enter the
"reserved" state. A sender MUST NOT send a PUSH_PROMISE on a stream "reserved" state. A sender MUST NOT send a PUSH_PROMISE on a stream
unless that stream is either "open" or "half closed (remote)"; the unless that stream is either "open" or "half closed (remote)"; the
sender MUST ensure that the promised stream is a valid choice for a sender MUST ensure that the promised stream is a valid choice for a
new stream identifier (Section 5.1.1) (that is, the promised stream new stream identifier (Section 5.1.1) (that is, the promised stream
MUST be in the "idle" state). MUST be in the "idle" state).
Since PUSH_PROMISE reserves a stream, ignoring a PUSH_PROMISE frame Since PUSH_PROMISE reserves a stream, ignoring a PUSH_PROMISE frame
causes the stream state to become indeterminate. A receiver MUST causes the stream state to become indeterminate. A receiver MUST
treat the receipt of a PUSH_PROMISE on a stream that is neither treat the receipt of a PUSH_PROMISE on a stream that is neither
"open" nor "half-closed (local)" as a connection error "open" nor "half closed (local)" as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. Similarly, a receiver MUST (Section 5.4.1) of type PROTOCOL_ERROR. Similarly, a receiver MUST
treat the receipt of a PUSH_PROMISE that promises an illegal stream treat the receipt of a PUSH_PROMISE that promises an illegal stream
identifier (Section 5.1.1) (that is, an identifier for a stream that identifier (Section 5.1.1) (that is, an identifier for a stream that
is not currently in the "idle" state) as a connection error is not currently in the "idle" state) as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
The PUSH_PROMISE frame includes optional padding. Padding fields and The PUSH_PROMISE frame includes optional padding. Padding fields and
flags are identical to those defined for DATA frames (Section 6.1). flags are identical to those defined for DATA frames (Section 6.1).
6.7. PING 6.7. PING
The PING frame (type=0x6) is a mechanism for measuring a minimal The PING frame (type=0x6) is a mechanism for measuring a minimal
round-trip time from the sender, as well as determining whether an round trip time from the sender, as well as determining whether an
idle connection is still functional. PING frames can be sent from idle connection is still functional. PING frames can be sent from
any endpoint. any endpoint.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| Opaque Data (64) | | Opaque Data (64) |
| | | |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
PING Payload Format PING Payload Format
In addition to the frame header, PING frames MUST contain 8 octets of In addition to the frame header, PING frames MUST contain 8 octets of
data in the payload. A sender can include any value it chooses and data in the payload. A sender can include any value it chooses and
skipping to change at page 40, line 31 skipping to change at page 41, line 9
(Section 5.4.1) of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
Receipt of a PING frame with a length field value other than 8 MUST Receipt of a PING frame with a length field value other than 8 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
FRAME_SIZE_ERROR. FRAME_SIZE_ERROR.
6.8. GOAWAY 6.8. GOAWAY
The GOAWAY frame (type=0x7) informs the remote peer to stop creating The GOAWAY frame (type=0x7) informs the remote peer to stop creating
streams on this connection. GOAWAY can be sent by either the client streams on this connection. GOAWAY can be sent by either the client
or the server. Once sent, the sender will ignore frames sent on new or the server. Once sent, the sender will ignore frames sent on any
streams for the remainder of the connection. Receivers of a GOAWAY new streams with identifiers higher than the included last stream
frame MUST NOT open additional streams on the connection, although a identifier. Receivers of a GOAWAY frame MUST NOT open additional
new connection can be established for new streams. The purpose of streams on the connection, although a new connection can be
this frame is to allow an endpoint to gracefully stop accepting new established for new streams.
streams (perhaps for a reboot or maintenance), while still finishing
processing of previously established streams. The purpose of this frame is to allow an endpoint to gracefully stop
accepting new streams, while still finishing processing of previously
established streams. This enables administrative actions, like
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 stream
which was processed on the sending endpoint in this connection. If which was or might be processed on the sending endpoint in this
the receiver of the GOAWAY used streams that are newer than the connection. If the receiver of the GOAWAY has sent data on streams
indicated stream identifier, they were not processed by the sender with a higher stream identifier than what is indicated in the GOAWAY
and the receiver may treat the streams as though they had never been frame, those streams are not or will not be processed. The receiver
created at all (hence the receiver may want to re-create the streams of the GOAWAY frame can treat the streams as though they had never
later on a new connection). 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 where it stopped server does not send a GOAWAY frame to indicate what streams it might
working. An endpoint might choose to close a connection without have acted on.
sending GOAWAY for misbehaving peers.
0 1 2 3 An endpoint might choose to close a connection without sending GOAWAY
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 for misbehaving peers.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| Last-Stream-ID (31) | |R| Last-Stream-ID (31) |
+-+-------------------------------------------------------------+ +-+-------------------------------------------------------------+
| Error Code (32) | | Error Code (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Additional Debug Data (*) | | Additional Debug Data (*) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
GOAWAY Payload Format GOAWAY Payload Format
The GOAWAY frame does not define any flags. The GOAWAY frame does not define any flags.
The GOAWAY frame applies to the connection, not a specific stream. The GOAWAY frame applies to the connection, not a specific stream.
An endpoint MUST treat a GOAWAY frame with a stream identifier other An endpoint MUST treat a GOAWAY frame with a stream identifier other
than 0x0 as a connection error (Section 5.4.1) of type than 0x0 as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
The last stream identifier in the GOAWAY frame contains the highest The last stream identifier in the GOAWAY frame contains the highest
numbered stream identifier for which the sender of the GOAWAY frame numbered stream identifier for which the sender of the GOAWAY frame
has received frames and might have taken some action on. All streams might have taken some action on, or might yet take action on. All
up to and including the identified stream might have been processed streams up to and including the identified stream might have been
in some way. The last stream identifier can be set to 0 if no processed in some way. The last stream identifier can be set to 0 if
streams were processed. no streams were processed.
Note: In this context, "processed" means that some data from the Note: In this context, "processed" means that some data from the
stream was passed to some higher layer of software that might have stream was passed to some higher layer of software that might have
taken some action as a result. taken some action as a result.
If a connection terminates without a GOAWAY frame, this value is If a connection terminates without a GOAWAY frame, the last stream
effectively the highest possible stream identifier. identifier is effectively the highest possible stream identifier.
On streams with lower or equal numbered identifiers that were not On streams with lower or equal numbered identifiers that were not
closed completely prior to the connection being closed, re-attempting closed completely prior to the connection being closed, re-attempting
requests, transactions, or any protocol activity is not possible requests, transactions, or any protocol activity is not possible,
(with the exception of idempotent actions like HTTP GET, PUT, or with the exception of idempotent actions like HTTP GET, PUT, or
DELETE). Any protocol activity that uses higher numbered streams can DELETE. Any protocol activity that uses higher numbered streams can
be safely retried using a new connection. be safely retried using a new connection.
Activity on streams numbered lower or equal to the last stream Activity on streams numbered lower or equal to the last stream
identifier might still complete successfully. The sender of a GOAWAY identifier might still complete successfully. The sender of a GOAWAY
frame might gracefully shut down a connection by sending a GOAWAY frame might gracefully shut down a connection by sending a GOAWAY
frame, maintaining the connection in an open state until all in- frame, maintaining the connection in an open state until all in-
progress streams complete. progress streams complete.
An endpoint MAY send multiple GOAWAY frames if circumstances change. An endpoint MAY send multiple GOAWAY frames if circumstances change.
For instance, an endpoint that sends GOAWAY with NO_ERROR during For instance, an endpoint that sends GOAWAY with NO_ERROR during
graceful shutdown could subsequently encounter an condition that graceful shutdown could subsequently encounter an condition that
requires immediate termination of the connection. The last stream requires immediate termination of the connection. The last stream
identifier from the last GOAWAY frame received applies. identifier from the last GOAWAY frame received indicates which
streams could have been acted upon. Endpoints MUST NOT increase the
value they send in the last stream identifier, since the peers might
already have retried unprocessed requests on another connection.
A client that is unable to retry requests loses all requests that are
in flight when the server closes the connection. This is especially
true for intermediaries that might not be serving clients using
HTTP/2. A server that is attempting to gracefully shut down a
connection SHOULD send an initial GOAWAY frame with the last stream
identifier set to 2^31-1 and a NO_ERROR code. This signals to the
client that a shutdown is imminent and that no further requests can
be initiated. After waiting at least one round trip time, the server
can send another GOAWAY frame with an updated last stream identifier.
This ensures that a connection can be cleanly shut down without
losing requests.
After sending a GOAWAY frame, the sender can discard frames for After sending a GOAWAY frame, the sender can discard frames for
streams with identifiers higher than the identified last stream. streams with identifiers higher than the identified last stream.
However, any frames that alter connection state cannot be completely However, any frames that alter connection state cannot be completely
ignored. For instance, HEADERS, PUSH_PROMISE and CONTINUATION frames ignored. For instance, HEADERS, PUSH_PROMISE and CONTINUATION frames
MUST be minimally processed to ensure the state maintained for header MUST be minimally processed to ensure the state maintained for header
compression is consistent (see Section 4.3); similarly DATA frames compression is consistent (see Section 4.3); similarly DATA frames
MUST be counted toward the connection flow control window. Failure MUST be counted toward the connection flow control window. Failure
to process these frames can cause flow control or header compression to process these frames can cause flow control or header compression
state to become unsynchronized. state to become unsynchronized.
skipping to change at page 42, line 50 skipping to change at page 43, line 47
the entire connection. the entire connection.
Both types of flow control are hop-by-hop; that is, only between the Both types of flow control are hop-by-hop; that is, only between the
two endpoints. Intermediaries do not forward WINDOW_UPDATE frames two endpoints. Intermediaries do not forward WINDOW_UPDATE frames
between dependent connections. However, throttling of data transfer between dependent connections. However, throttling of data transfer
by any receiver can indirectly cause the propagation of flow control by any receiver can indirectly cause the propagation of flow control
information toward the original sender. information toward the original sender.
Flow control only applies to frames that are identified as being Flow control only applies to frames that are identified as being
subject to flow control. Of the frame types defined in this subject to flow control. Of the frame types defined in this
document, this includes only DATA frame. Frames that are exempt from document, this includes only DATA frames. Frames that are exempt
flow control MUST be accepted and processed, unless the receiver is from flow control MUST be accepted and processed, unless the receiver
unable to assign resources to handling the frame. A receiver MAY is unable to assign resources to handling the frame. A receiver MAY
respond with a stream error (Section 5.4.2) or connection error respond with a stream error (Section 5.4.2) or connection error
(Section 5.4.1) of type FLOW_CONTROL_ERROR if it is unable to accept (Section 5.4.1) of type FLOW_CONTROL_ERROR if it is unable to accept
a frame. a frame.
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| 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
skipping to change at page 43, line 48 skipping to change at page 44, line 46
(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
the receiver does not, the flow control window at sender and receiver the receiver does not, the flow control window at sender and receiver
can become different. can become different.
6.9.1. The Flow Control Window 6.9.1. The Flow Control Window
Flow control in HTTP/2 is implemented using a window kept by each Flow control in HTTP/2 is implemented using a window kept by each
sender on every stream. The flow control window is a simple integer sender on every stream. The flow control window is a simple integer
value that indicates how many bytes of data the sender is permitted value that indicates how many bytes of data the sender is permitted
to transmit; as such, its size is a measure of the buffering to transmit; as such, its size is a measure of the buffering capacity
capability of the receiver. of the receiver.
Two flow control windows are applicable: the stream flow control Two flow control windows are applicable: the stream flow control
window and the connection flow control window. The sender MUST NOT window and the connection flow control window. The sender MUST NOT
send a flow controlled frame with a length that exceeds the space send a flow controlled frame with a length that exceeds the space
available in either of the flow control windows advertised by the available in either of the flow control windows advertised by the
receiver. Frames with zero length with the END_STREAM flag set (for receiver. Frames with zero length with the END_STREAM flag set (that
example, an empty data frame) MAY be sent if there is no available is, an empty DATA frame) MAY be sent if there is no available space
space in either flow control window. in either flow control window.
For flow control calculations, the 8 byte frame header is not For flow control calculations, the 8 byte frame header is not
counted. counted.
After sending a flow controlled frame, the sender reduces the space After sending a flow controlled frame, the sender reduces the space
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
skipping to change at page 44, line 37 skipping to change at page 45, line 35
control window to exceed this maximum it MUST terminate either the control window to exceed this maximum it MUST terminate either the
stream or the connection, as appropriate. For streams, the sender stream or the connection, as appropriate. For streams, the sender
sends a RST_STREAM with the error code of FLOW_CONTROL_ERROR code; sends a RST_STREAM with the error code of FLOW_CONTROL_ERROR code;
for the connection, a GOAWAY frame with a FLOW_CONTROL_ERROR code. for the 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.
A sender that is unable to send data on a stream due to either flow
control window being zero or lower MAY send a BLOCKED frame
(Section 6.12) in order to inform the receiver of a potential flow
control problem.
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.
The connection flow control window is 65,535 bytes. Both endpoints The connection flow control window is 65,535 bytes. Both endpoints
can adjust the initial window size for new streams by including a can adjust the initial window size for new streams by including a
value for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame that value for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame that
forms part of the connection preface. The connection flow control forms part of the connection preface. The connection flow control
window initial size cannot be changed. window can only be changed using WINDOW_UPDATE frames.
Prior to receiving a SETTINGS frame that sets a value for Prior to receiving a SETTINGS frame that sets a value for
SETTINGS_INITIAL_WINDOW_SIZE, an endpoint can only use the default SETTINGS_INITIAL_WINDOW_SIZE, an endpoint can only use the default
initial window size when sending flow controlled frames. Similarly, initial window size when sending flow controlled frames. Similarly,
the connection flow control window is set to the default initial the connection flow control window is set to the default initial
window size until a WINDOW_UPDATE frame is received. window size until a WINDOW_UPDATE frame is received.
A SETTINGS frame can alter the initial flow control window size for A SETTINGS frame can alter the initial flow control window size for
all current streams. When the value of SETTINGS_INITIAL_WINDOW_SIZE all current streams. When the value of SETTINGS_INITIAL_WINDOW_SIZE
changes, a receiver MUST adjust the size of all stream flow control changes, a receiver MUST adjust the size of all stream flow control
windows that it maintains by the difference between the new value and windows that it maintains by the difference between the new value and
the old value. A SETTINGS frame cannot alter the connection flow the old value.
control window.
An endpoint MUST treat a change to SETTINGS_INITIAL_WINDOW_SIZE that
causes any flow control window to exceed the maximum size as a
connection error (Section 5.4.1) of type FLOW_CONTROL_ERROR.
A change to SETTINGS_INITIAL_WINDOW_SIZE can cause the available A change to SETTINGS_INITIAL_WINDOW_SIZE can cause the available
space in a flow control window to become negative. A sender MUST space in a flow control window to become negative. A sender MUST
track the negative flow control window, and MUST NOT send new flow track the negative flow control window, and MUST NOT send new flow
controlled frames until it receives WINDOW_UPDATE frames that cause controlled frames until it receives WINDOW_UPDATE frames that cause
the flow control window to become positive. the flow control window to become positive.
For example, if the client sends 60KB immediately on connection For example, if the client sends 60KB immediately on connection
establishment, and the server sets the initial window size to be establishment, and the server sets the initial window size to be
16KB, the client will recalculate the available flow control window 16KB, the client will recalculate the available flow control window
to be -44KB on receipt of the SETTINGS frame. The client retains a to be -44KB on receipt of the SETTINGS frame. The client retains a
negative flow control window until WINDOW_UPDATE frames restore the negative flow control window until WINDOW_UPDATE frames restore the
window to being positive, after which the client can resume sending. window to being positive, after which the client can resume sending.
A SETTINGS frame cannot alter the connection flow control window.
An endpoint MUST treat a change to SETTINGS_INITIAL_WINDOW_SIZE that
causes any flow control window to exceed the maximum size as a
connection error (Section 5.4.1) of type FLOW_CONTROL_ERROR.
6.9.3. Reducing the Stream Window Size 6.9.3. Reducing the Stream Window Size
A receiver that wishes to use a smaller flow control window than the A receiver that wishes to use a smaller flow control window than the
current size can send a new SETTINGS frame. However, the receiver current size can send a new SETTINGS frame. However, the receiver
MUST be prepared to receive data that exceeds this window size, since MUST be prepared to receive data that exceeds this window size, since
the sender might send data that exceeds the lower limit prior to the sender might send data that exceeds the lower limit prior to
processing the SETTINGS frame. processing the SETTINGS frame.
After sending a SETTINGS frame that reduces the initial flow control After sending a SETTINGS frame that reduces the initial flow control
window size, a receiver has two options for handling streams that window size, a receiver has two options for handling streams that
skipping to change at page 46, line 13 skipping to change at page 47, line 13
consumes data. consumes data.
6.10. CONTINUATION 6.10. CONTINUATION
The CONTINUATION frame (type=0x9) is used to continue a sequence of The CONTINUATION frame (type=0x9) is used to continue a sequence of
header block fragments (Section 4.3). Any number of CONTINUATION header block fragments (Section 4.3). Any number of CONTINUATION
frames can be sent on an existing stream, as long as the preceding frames can be sent on an existing stream, as long as the preceding
frame is on the same stream and is a HEADERS, PUSH_PROMISE or frame is on the same stream and is a HEADERS, PUSH_PROMISE or
CONTINUATION frame without the END_HEADERS flag set. CONTINUATION frame without the END_HEADERS flag set.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pad High? (8) | Pad Low? (8) |
+---------------+---------------+-------------------------------+
| Header Block Fragment (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Padding (*) ...
+---------------------------------------------------------------+
CONTINUATION Frame Payload CONTINUATION Frame Payload
The CONTINUATION frame payload has the following fields: The CONTINUATION frame payload contains a header block fragment
(Section 4.3).
Pad High: Padding size high bits. This field is only present if the
PAD_HIGH flag is set.
Pad Low: Padding size low bits. This field is only present if the
PAD_LOW flag is set.
Header Block Fragment: A header block fragment (Section 4.3).
Padding: Padding octets.
The CONTINUATION frame defines the following flags: The CONTINUATION frame defines the following flag:
END_HEADERS (0x4): Bit 3 being set indicates that this frame ends a END_HEADERS (0x4): Bit 3 being set indicates that this frame ends a
header block (Section 4.3). header block (Section 4.3).
If the END_HEADERS bit is not set, this frame MUST be followed by If the END_HEADERS bit is not set, this frame MUST be followed by
another CONTINUATION frame. A receiver MUST treat the receipt of another CONTINUATION frame. A receiver MUST treat the receipt of
any other type of frame or a frame on a different stream as a any other type of frame or a frame on a different stream as a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
PAD_LOW (0x8): Bit 4 being set indicates that the Pad Low field is
present.
PAD_HIGH (0x10): Bit 5 being set indicates that the Pad High field
is present. This bit MUST NOT be set unless the PAD_LOW flag is
also set. Endpoints that receive a frame with PAD_HIGH set and
PAD_LOW cleared MUST treat this as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
The payload of a CONTINUATION frame contains a header block fragment
(Section 4.3).
The CONTINUATION frame changes the connection state as defined in The CONTINUATION frame changes the connection state as defined in
Section 4.3. Section 4.3.
CONTINUATION frames MUST be associated with a stream. If a CONTINUATION frames MUST be associated with a stream. If a
CONTINUATION frame is received whose stream identifier field is 0x0, CONTINUATION frame is received whose stream identifier field is 0x0,
the recipient MUST respond with a connection error (Section 5.4.1) of the recipient MUST respond with a connection error (Section 5.4.1) of
type PROTOCOL_ERROR. type PROTOCOL_ERROR.
A CONTINUATION frame MUST be preceded by a HEADERS, PUSH_PROMISE or A CONTINUATION frame MUST be preceded by a HEADERS, PUSH_PROMISE or
CONTINUATION frame without the END_HEADERS flag set. A recipient CONTINUATION frame without the END_HEADERS flag set. A recipient
that observes violation of this rule MUST respond with a connection that observes violation of this rule MUST respond with a connection
error (Section 5.4.1) of type PROTOCOL_ERROR. error (Section 5.4.1) of type PROTOCOL_ERROR.
The CONTINUATION frame includes optional padding. Padding fields and
flags are identical to those defined for DATA frames (Section 6.1).
6.11. ALTSVC
The ALTSVC frame (type=0xA) advertises the availability of an
alternative service to the client. It can be sent at any time for an
existing client-initiated stream or stream 0, and is intended to
allow servers to load balance or otherwise segment traffic; see
[ALT-SVC] for details (in particular, Section 2.4, which outlines
client handling of alternative services).
An ALTSVC frame on a client-initiated stream indicates that the
conveyed alternative service is associated with the origin of that
stream.
An ALTSVC frame on stream 0 indicates that the conveyed alternative
service is associated with the origin contained in the Origin field
of the frame. An association with an origin that the client does not
consider authoritative for the current connection MUST be ignored.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max-Age (32) |
+-------------------------------+---------------+---------------+
| Port (16) | Reserved (8) | Proto-Len (8) |
+-------------------------------+---------------+---------------+
| Protocol-ID (*) |
+---------------+-----------------------------------------------+
| Host-Len (8) | Host (*) ...
+---------------+-----------------------------------------------+
| Origin? (*) ...
+---------------------------------------------------------------+
ALTSVC Frame Payload
The ALTSVC frame contains the following fields:
Max-Age: An unsigned, 32-bit integer indicating the freshness
lifetime of the alternative service association, as per [ALT-SVC],
Section 2.2.
Port: An unsigned, 16-bit integer indicating the port that the
alternative service is available upon.
Reserved: For future use. Senders MUST set these bits to '0', and
recipients MUST ignore them.
Proto-Len: An unsigned, 8-bit integer indicating the length, in
octets, of the Protocol-ID field.
Protocol-ID: A sequence of bytes (length determined by "Proto-Len")
containing the ALPN protocol identifier of the alternative
service.
Host-Len: An unsigned, 8-bit integer indicating the length, in
octets, of the Host field.
Host: A sequence of characters (length determined by "Host-Len")
containing an ASCII string indicating the host that the
alternative service is available upon. An internationalized
domain name [IDNA] MUST be expressed using A-labels.
Origin: An optional sequence of characters (length determined by
subtracting the length of all preceding fields from the frame
length) containing the ASCII serialisation of an origin
([RFC6454], Section 6.2) that the alternate service is applicable
to.
The ALTSVC frame does not define any flags.
The ALTSVC frame is intended for receipt by clients; a server that
receives an ALTSVC frame MUST treat it as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR.
The ALTSVC frame is processed hop-by-hop. An intermediary MUST NOT
forward ALTSVC frames, though it can use the information contained in
ALTSVC frames in forming new ALTSVC frames to send to its own
clients.
6.12. BLOCKED
The BLOCKED frame (type=0xB) indicates that the sender is unable to
send data due to a closed flow control window.
[[anchor12: The BLOCKED frame is included in this draft version to
facilitate experimentation. If the results of the experiment do not
provide positive feedback, it could be removed.]]
The BLOCKED frame is used to provide feedback about the performance
of flow control for the purposes of performance tuning and debugging.
The BLOCKED frame can be sent by a peer when flow controlled data
cannot be sent due to the connection- or stream-level flow control.
This frame MUST NOT be sent if there are other reasons preventing
data from being sent, either a lack of available data, or the
underlying transport being blocked.
The BLOCKED frame is sent on the stream that is blocked, that is, the
stream with a non-positive number of bytes available in the flow
control window. A BLOCKED frame can be sent on stream 0x0 to
indicate that connection-level flow control is blocked.
An endpoint MUST NOT send any subsequent BLOCKED frames until the
affected flow control window becomes positive. This means that
WINDOW_UPDATE frames are received or SETTINGS_INITIAL_WINDOW_SIZE is
increased before more BLOCKED frames can be sent.
The BLOCKED frame defines no flags and contains no payload. A
receiver MUST treat the receipt of a BLOCKED frame with a payload as
a connection error (Section 5.4.1) of type FRAME_SIZE_ERROR.
7. Error Codes 7. Error Codes
Error codes are 32-bit fields that are used in RST_STREAM and GOAWAY Error codes are 32-bit fields that are used in RST_STREAM and GOAWAY
frames to convey the reasons for the stream or connection error. frames to convey the reasons for the stream or connection error.
Error codes share a common code space. Some error codes only apply Error codes share a common code space. Some error codes apply only
to specific conditions and have no defined semantics in certain frame to either streams or the entire connection and have no defined
types. semantics in the other context.
The following error codes are defined: The following error codes are defined:
NO_ERROR (0): The associated condition is not as a result of an NO_ERROR (0x0): The associated condition is not as a result of an
error. For example, a GOAWAY might include this code to indicate error. For example, a GOAWAY might include this code to indicate
graceful shutdown of a connection. graceful shutdown of a connection.
PROTOCOL_ERROR (1): The endpoint detected an unspecific protocol PROTOCOL_ERROR (0x1): The endpoint detected an unspecific protocol
error. This error is for use when a more specific error code is error. This error is for use when a more specific error code is
not available. not available.
INTERNAL_ERROR (2): The endpoint encountered an unexpected internal INTERNAL_ERROR (0x2): The endpoint encountered an unexpected
error. internal error.
FLOW_CONTROL_ERROR (3): The endpoint detected that its peer violated FLOW_CONTROL_ERROR (0x3): The endpoint detected that its peer
the flow control protocol. violated the flow control protocol.
SETTINGS_TIMEOUT (4): The endpoint sent a SETTINGS frame, but did SETTINGS_TIMEOUT (0x4): The endpoint sent a SETTINGS frame, but did
not receive a response in a timely manner. See Settings not receive a response in a timely manner. See Settings
Synchronization (Section 6.5.3). Synchronization (Section 6.5.3).
STREAM_CLOSED (5): The endpoint received a frame after a stream was STREAM_CLOSED (0x5): The endpoint received a frame after a stream
half closed. was half closed.
FRAME_SIZE_ERROR (6): The endpoint received a frame that was larger FRAME_SIZE_ERROR (0x6): The endpoint received a frame that was
than the maximum size that it supports. larger than the maximum size that it supports.
REFUSED_STREAM (7): The endpoint refuses the stream prior to REFUSED_STREAM (0x7): The endpoint refuses the stream prior to
performing any application processing, see Section 8.1.4 for performing any application processing, see Section 8.1.4 for
details. details.
CANCEL (8): Used by the endpoint to indicate that the stream is no CANCEL (0x8): Used by the endpoint to indicate that the stream is no
longer needed. longer needed.
COMPRESSION_ERROR (9): The endpoint is unable to maintain the COMPRESSION_ERROR (0x9): The endpoint is unable to maintain the
compression context for the connection. header compression context for the connection.
CONNECT_ERROR (10): The connection established in response to a CONNECT_ERROR (0xa): The connection established in response to a
CONNECT request (Section 8.3) was reset or abnormally closed. CONNECT request (Section 8.3) was reset or abnormally closed.
ENHANCE_YOUR_CALM (11): The endpoint detected that its peer is ENHANCE_YOUR_CALM (0xb): The endpoint detected that its peer is
exhibiting a behavior over a given amount of time that has caused exhibiting a behavior that might be generating excessive load.
it to refuse to process further frames.
INADEQUATE_SECURITY (12): The underlying transport has properties INADEQUATE_SECURITY (0xc): The underlying transport has properties
that do not meet the minimum requirements imposed by this document that do not meet minimum security requirements (see Section 9.2).
(see Section 9.2) or the endpoint.
Unknown or unsupported error codes MUST NOT trigger any special
behavior. These MAY be treated by an implementation as being
equivalent to INTERNAL_ERROR.
8. HTTP Message Exchanges 8. HTTP Message Exchanges
HTTP/2 is intended to be as compatible as possible with current uses HTTP/2 is intended to be as compatible as possible with current uses
of HTTP. This means that, from the perspective of the server and of HTTP. This means that, from the application perspective, the
client applications, the features of the protocol are unchanged. To features of the protocol are largely unchanged. To achieve this, all
achieve this, all request and response semantics are preserved, request and response semantics are preserved, although the syntax of
although the syntax of conveying those semantics has changed. conveying those semantics has changed.
Thus, the specification and requirements of HTTP/1.1 Semantics and Thus, the specification and requirements of HTTP/1.1 Semantics and
Content [HTTP-p2], Conditional Requests [HTTP-p4], Range Requests Content [RFC7231], Conditional Requests [RFC7232], Range Requests
[HTTP-p5], Caching [HTTP-p6] and Authentication [HTTP-p7] are [RFC7233], Caching [RFC7234] and Authentication [RFC7235] are
applicable to HTTP/2. Selected portions of HTTP/1.1 Message Syntax applicable to HTTP/2. Selected portions of HTTP/1.1 Message Syntax
and Routing [HTTP-p1], such as the HTTP and HTTPS URI schemes, are and Routing [RFC7230], such as the HTTP and HTTPS URI schemes, are
also applicable in HTTP/2, but the expression of those semantics for also applicable in HTTP/2, but the expression of those semantics for
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. one HEADERS frame (followed by zero or more CONTINUATION frames)
(containing the message headers; see [HTTP-p1], 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 2. zero or more DATA frames containing the message payload (see
[HTTP-p1], Section 3.3), and [RFC7230], Section 3.3), and
3. optionally, one HEADERS frame, followed by zero or more 3. 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
[HTTP-p1], Section 4.1.2). [RFC7230], Section 4.1.2).
The last frame in the sequence bears an END_STREAM flag, though a The last frame in the sequence bears an END_STREAM flag, noting that
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 the following CONTINUATION frames (if present), nor between frame and any CONTINUATION frames that might follow.
CONTINUATION frames.
Otherwise, frames MAY be interspersed on the stream between these Otherwise, frames MAY be interspersed on the stream between these
frames, but those frames do not carry HTTP semantics. In particular, frames, but those frames do not carry HTTP semantics. In particular,
HEADERS frames (and any CONTINUATION frames that follow) other than HEADERS frames (and any CONTINUATION frames that follow) other than
the first and optional last frames in this sequence do not carry HTTP the first and optional last frames in this sequence do not carry HTTP
semantics. 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
skipping to change at page 52, line 26 skipping to change at page 50, line 25
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 and ends with a frame bearing END_STREAM, which causes
the stream to become "half closed" for the client. A response starts the stream to become "half closed" for the client. A response starts
with a HEADERS frame and ends with a frame bearing END_STREAM, with a HEADERS frame and ends with a frame bearing END_STREAM,
optionally followed by CONTINUATION frames, which places the stream optionally followed by CONTINUATION frames, which places the stream
in the "closed" state. in the "closed" state.
8.1.1. Informational Responses 8.1.1. Informational Responses
The 1xx series of HTTP response status codes ([HTTP-p2], Section 6.2) The 1xx series of HTTP response status codes ([RFC7231], Section 6.2)
are not supported in HTTP/2. are not supported in HTTP/2.
The most common use case for 1xx is using an Expect header field with The most common use case for 1xx is using an Expect header field with
a "100-continue" token (colloquially, "Expect/continue") to indicate a "100-continue" token (colloquially, "Expect/continue") to indicate
that the client expects a 100 (Continue) non-final response status that the client expects a 100 (Continue) non-final response status
code, receipt of which indicates that the client should continue code, receipt of which indicates that the client should continue
sending the request body if it has not already done so. sending the request body if it has not already done so.
Typically, Expect/continue is used by clients wishing to avoid Typically, Expect/continue is used by clients wishing to avoid
sending a large amount of data in a request body, only to have the sending a large amount of data in a request body, only to have the
request rejected by the origin server (thus leaving the connection request rejected by the origin server, thereby leaving the connection
potentially unusable). potentially unusable.
HTTP/2 does not enable the Expect/continue mechanism; if the server 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 sends a final status code to reject the request, it can do so without
making the underlying connection unusable. making the underlying connection unusable.
Note that this means HTTP/2 clients sending requests with bodies may 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 waste at least one round trip of sent data when the request is
rejected. This can be mitigated by restricting the amount of data rejected. This can be mitigated by restricting the amount of data
sent for the first round trip by bandwidth-constrained clients, in sent for the first round trip by bandwidth-constrained clients, in
anticipation of a final status code. anticipation of a final status code.
Other defined 1xx status codes are not applicable to HTTP/2. For Other defined 1xx status codes are not applicable to HTTP/2. For
example, the semantics of 101 (Switching Protocols) aren't suitable example, the semantics of 101 (Switching Protocols) aren't suitable
to a multiplexed protocol. Likewise, 102 (Processing) is no longer to a multiplexed protocol. Likewise, 102 (Processing) [RFC2518] is
necessary, because HTTP/2 has a separate means of keeping the no longer necessary to ensure connection liveness, because HTTP/2 has
connection alive. 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 This difference between protocol versions necessitates special
handling by intermediaries that translate between them: handling by intermediaries that translate between them:
o An intermediary that gateways HTTP/1.1 to HTTP/2 MUST generate a o An intermediary that translates HTTP/1.1 requests to HTTP/2 MUST
100 (Continue) response if a received request includes and Expect generate a 100 (Continue) response if a received request includes
header field with a "100-continue" token ([HTTP-p2], Section and Expect header field with a "100-continue" token ([RFC7231],
5.1.1), unless it can immediately generate a final status code. Section 5.1.1), unless it can immediately generate a final status
It MUST NOT forward the "100-continue" expectation in the request code. It MUST NOT forward the "100-continue" expectation in the
header fields. request header fields.
o An intermediary that gateways HTTP/2 to HTTP/1.1 MAY add an Expect o An intermediary that translates HTTP/2 to HTTP/1.1 MAY add an
header field with a "100-continue" expectation when forwarding a Expect header field with a "100-continue" expectation when
request that has a body; see [HTTP-p2], Section 5.1.1 for specific forwarding a request that has a body; see [RFC7231], Section 5.1.1
requirements. for specific requirements.
o An intermediary that gateways HTTP/2 to HTTP/1.1 MUST discard all o An intermediary that gateways HTTP/2 to HTTP/1.1 MUST discard all
other 1xx informational responses. other 1xx informational responses.
8.1.2. Examples 8.1.2. HTTP Header Fields
This section shows HTTP/1.1 requests and responses, with
illustrations of equivalent HTTP/2 requests and responses.
An HTTP GET request includes request header fields and no body and is
therefore transmitted as a single HEADERS frame, followed by zero or
more CONTINUATION frames containing the serialized block of request
header fields. The HEADERS frame in the following has both the
END_HEADERS and END_STREAM flags set; no CONTINUATION frames are
sent:
GET /resource HTTP/1.1 HEADERS
Host: example.org ==> + END_STREAM
Accept: image/jpeg + END_HEADERS
:method = GET
:scheme = https
:path = /resource
host = example.org
accept = image/jpeg
Similarly, a response that includes only response header fields is
transmitted as a HEADERS frame (again, followed by zero or more
CONTINUATION frames) containing the serialized block of response
header fields.
HTTP/1.1 304 Not Modified HEADERS
ETag: "xyzzy" ==> + END_STREAM
Expires: Thu, 23 Jan ... + END_HEADERS
:status = 304
etag: "xyzzy"
expires: Thu, 23 Jan ...
An HTTP POST request that includes request header fields and payload
data is transmitted as one HEADERS frame, followed by zero or more
CONTINUATION frames containing the request header fields, followed by
one or more DATA frames, with the last CONTINUATION (or HEADERS)
frame having the END_HEADERS flag set and the final DATA frame having
the END_STREAM flag set:
POST /resource HTTP/1.1 HEADERS
Host: example.org ==> - END_STREAM
Content-Type: image/jpeg - END_HEADERS
Content-Length: 123 :method = POST
:path = /resource
{binary data} content-type = image/jpeg
CONTINUATION
+ END_HEADERS
:authority = example.org
:scheme = https
content-length = 123
DATA
+ END_STREAM
{binary data}
Note that data contributing to any given header field could be spread
between header block fragments. The allocation of header fields to
frames in this example is illustrative only.
A response that includes header fields and payload data is
transmitted as a HEADERS frame, followed by zero or more CONTINUATION
frames, followed by one or more DATA frames, with the last DATA frame
in the sequence having the END_STREAM flag set:
HTTP/1.1 200 OK HEADERS
Content-Type: image/jpeg ==> - END_STREAM
Content-Length: 123 + END_HEADERS
:status = 200
{binary data} content-type = image/jpeg
content-length = 123
DATA
+ END_STREAM
{binary data}
Trailing header fields are sent as a header block after both the
request or response header block and all the DATA frames have been
sent. The HEADERS frame starting the trailers header block has the
END_STREAM flag set.
HTTP/1.1 200 OK HEADERS
Content-Type: image/jpeg ==> - END_STREAM
Transfer-Encoding: chunked + END_HEADERS
Trailer: Foo :status = 200
content-length = 123
123 content-type = image/jpeg
{binary data} trailer = Foo
0
Foo: bar DATA
- END_STREAM
{binary data}
HEADERS
+ END_STREAM
+ END_HEADERS
foo: bar
8.1.3. 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 Field Registry maintained at [4].
<http://www.iana.org/assignments/message-headers>.
While HTTP/1.x used the message start-line (see [HTTP-p1], Section While HTTP/1.x used the message start-line (see [RFC7230],
3.1) to convey the target URI and method of the request, and the Section 3.1) to convey the target URI and method of the request, and
status code for the response, HTTP/2 uses special pseudo-headers the status code for the response, HTTP/2 uses special pseudo-headers
beginning with ":" for these tasks. beginning with ':' character (ASCII 0x3a) for this purpose.
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 8.1.3.5). header field names MUST be treated as malformed (Section 8.1.2.5).
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 8.1.3.5). Connection MUST be treated as malformed (Section 8.1.2.5).
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.
8.1.3.1. Request Header Fields 8.1.2.1. Request Header Fields
HTTP/2 defines a number of 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 ([HTTP-p2], 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).
":scheme" is not restricted to "http" and "https" schemed URIs. A ":scheme" is not restricted to "http" and "https" schemed URIs. A
proxy or gateway can translate requests for non-HTTP schemes, proxy or gateway can translate requests for non-HTTP schemes,
enabling the use of HTTP to interact with non-HTTP services. enabling the use of HTTP to interact with non-HTTP services.
o The ":authority" header field includes the authority portion of o The ":authority" header field includes the authority portion of
the target URI ([RFC3986], Section 3.2). The authority MUST NOT the target URI ([RFC3986], Section 3.2). The authority MUST NOT
include the deprecated "userinfo" subcomponent for "http" or include the deprecated "userinfo" subcomponent for "http" or
"https" schemed URIs. "https" schemed URIs.
To ensure that the HTTP/1.1 request line can be reproduced To ensure that the HTTP/1.1 request line can be reproduced
accurately, this header field MUST be omitted when translating accurately, this header field MUST be omitted when translating
from an HTTP/1.1 request that has a request target in origin or from an HTTP/1.1 request that has a request target in origin or
asterisk form (see [HTTP-p1], 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). This field
MUST NOT be empty; URIs that do not contain a path component MUST MUST NOT be empty; URIs that do not contain a path component MUST
include a value of '/', unless the request is an OPTIONS request include a value of '/', unless the request is an OPTIONS request
in asterisk form, in which case the ":path" header field MUST in asterisk form, in which case the ":path" header field MUST
include '*'. include '*'.
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 8.1.3.5). header fields is malformed (Section 8.1.2.5).
Header field names that start with a colon are only valid in the Header field names that start with a colon are only valid in the
HTTP/2 context. These are not HTTP header fields. Implementations HTTP/2 context. These are not HTTP header fields. Implementations
MUST NOT generate header fields that start with a colon, but they MUST NOT generate header fields that start with a colon, and they
MUST ignore any header field that starts with a colon. In MUST ignore and discard any header field that starts with a colon.
particular, header fields with names starting with a colon MUST NOT In particular, header fields with names starting with a colon MUST
be exposed as HTTP header fields. 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.
8.1.3.2. Response Header Fields 8.1.2.2. 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 [HTTP-p2], 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 8.1.3.5). (Section 8.1.2.5).
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.
8.1.3.3. Header Field Ordering 8.1.2.3. Header Field Ordering
HTTP Header Compression [COMPRESSION] does not preserve the order of HTTP Header Compression [COMPRESSION] does not preserve the order of
header fields, because the relative order of header fields with header fields, because the relative order of header fields with
different names is not important. However, the same header field can different names is not important. However, the same header field can
be repeated to form a list (see [HTTP-p1], Section 3.2.2), where the be repeated to form a list (see [RFC7230], Section 3.2.2), where the
relative order of header field values is significant. This relative order of header field values is significant. This
repetition can occur either as a single header field with a comma- repetition can occur either as a single header field with a comma-
separated list of values, or as several header fields with a single separated list of values, or as several header fields with a single
value, or any combination thereof. Therefore, in the latter case, value, or any combination thereof. Therefore, in the latter case,
ordering needs to be preserved before compression takes place. ordering needs to be preserved before compression takes place.
To preserve the order of multiple occurrences of a header field with To preserve the order of multiple occurrences of a header field with
the same name, its ordered values are concatenated into a single the same name, its ordered values are concatenated into a single
value using a zero-valued octet (0x0) to delimit them. value using a zero-valued octet (0x0) to delimit them.
After decompression, header fields that have values containing zero After decompression, header fields that have values containing zero
octets (0x0) MUST be split into multiple header fields before being octets (0x0) MUST be split into multiple header fields before being
processed. processed.
For example, the following HTTP/1.x header block: For example, the following HTTP/1.x header block:
Content-Type: text/html Content-Type: text/html
Cache-Control: max-age=60, private Cache-Control: max-age=60, private
Cache-Control: must-revalidate Cache-Control: must-revalidate
contains three Cache-Control directives; two in the first Cache- contains three Cache-Control directives; two directives in the first
Control header field, and the last one in the second Cache-Control Cache-Control header field, and the third directive in the second
field. Before compression, they would need to be converted to a form Cache-Control field. Before compression, they would need to be
similar to this (with 0x0 represented as "\0"): converted to a form similar to this (with 0x0 represented as '\0'):
cache-control: max-age=60, private\0must-revalidate cache-control = max-age=60, private\0must-revalidate
content-type: text/html content-type = text/html
Note here that the ordering between Content-Type and Cache-Control is Note here that the ordering between Content-Type and Cache-Control is
not preserved, but the relative ordering of the Cache-Control not preserved, but the relative ordering of the Cache-Control
directives -- as well as the fact that the first two were comma- directives - as well as the fact that the first two were comma-
separated, while the last was on a different line -- is. separated, while the last was on a different line - is.
Header fields containing multiple values MUST be concatenated into a Header fields containing multiple values MUST be concatenated into a
single value unless the ordering of that header field is known to be single value unless the ordering of that header field is known to be
insignificant. not significant.
The special case of "set-cookie" - which does not form a comma- The special case of "set-cookie" - which does not form a comma-
separated list, but can have multiple values - does not depend on separated list, but can have multiple values - does not depend on
ordering. The "set-cookie" header field MAY be encoded as multiple ordering. The "set-cookie" header field MAY be encoded as multiple
header field values, or as a single concatenated value. header field values, or as a single concatenated value.
8.1.3.4. Compressing the Cookie Header Field 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 [HTTP-p1], 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 "; ").
The Cookie header field MAY be split using a zero octet (0x0), as The Cookie header field MAY be split using a zero octet (0x0), as
defined in Section 8.1.3.3. When decoding, zero octets MUST be defined in Section 8.1.2.3. When decoding, zero octets MUST be
replaced with the cookie delimiter ("; "). replaced with the cookie delimiter ("; ").
8.1.3.5. Malformed Messages Therefore, the following sets of Cookie header fields are
semantically equivalent, though the final form might appear in a
different order after compression and decompression.
cookie: a=b; c=d; e=f
cookie: a=b\0c=d; e=f
cookie: a=b
cookie: c=d
cookie: e=f
8.1.2.5. Malformed Messages
A malformed request or response is one that uses a valid sequence of A malformed request or response is one that uses a valid sequence of
HTTP/2 frames, but is otherwise invalid due to the presence of HTTP/2 frames, but is otherwise invalid due to the presence of
prohibited header fields, the absence of mandatory header fields, or prohibited header fields, the absence of mandatory header fields, or
the inclusion of uppercase header field names. 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 uncompressed DATA frame payload lengths that equal the sum of the DATA frame payload lengths that form the body.
form the body.
Note: The "Content-Length" header field is set to the length of an
entity body. Compression of DATA frames is a function of HTTP/2
that does not alter entities.
Intermediaries that process HTTP requests or responses (i.e., all Intermediaries that process HTTP requests or responses (i.e., any
intermediaries other than those acting as tunnels) MUST NOT forward a intermediary not acting as a tunnel) MUST NOT forward a malformed
malformed request or response. request or response.
Implementations that detect malformed requests or responses need to Implementations that detect malformed requests or responses need to
ensure that the stream ends. For malformed requests, a server MAY ensure that the stream ends. For malformed requests, a server MAY
send an HTTP response prior to closing or resetting the stream. send an HTTP response prior to closing or resetting the stream.
Clients MUST NOT accept a malformed response. Note that these Clients MUST NOT accept a malformed response. Note that these
requirements are intended to protect against several types of common requirements are intended to protect against several types of common
attacks against HTTP; they are deliberately strict, because being attacks against HTTP; they are deliberately strict, because being
permissive can expose implementations to these vulnerabilites. permissive can expose implementations to these vulnerabilities.
8.1.3. Examples
This section shows HTTP/1.1 requests and responses, with
illustrations of equivalent HTTP/2 requests and responses.
An HTTP GET request includes request header fields and no body and is
therefore transmitted as a single HEADERS frame, followed by zero or
more CONTINUATION frames containing the serialized block of request
header fields. The HEADERS frame in the following has both the
END_HEADERS and END_STREAM flags set; no CONTINUATION frames are
sent:
GET /resource HTTP/1.1 HEADERS
Host: example.org ==> + END_STREAM
Accept: image/jpeg + END_HEADERS
:method = GET
:scheme = https
:path = /resource
host = example.org
accept = image/jpeg
Similarly, a response that includes only response header fields is
transmitted as a HEADERS frame (again, followed by zero or more
CONTINUATION frames) containing the serialized block of response
header fields.
HTTP/1.1 304 Not Modified HEADERS
ETag: "xyzzy" ==> + END_STREAM
Expires: Thu, 23 Jan ... + END_HEADERS
:status = 304
etag = "xyzzy"
expires = Thu, 23 Jan ...
An HTTP POST request that includes request header fields and payload
data is transmitted as one HEADERS frame, followed by zero or more
CONTINUATION frames containing the request header fields, followed by
one or more DATA frames, with the last CONTINUATION (or HEADERS)
frame having the END_HEADERS flag set and the final DATA frame having
the END_STREAM flag set:
POST /resource HTTP/1.1 HEADERS
Host: example.org ==> - END_STREAM
Content-Type: image/jpeg - END_HEADERS
Content-Length: 123 :method = POST
:path = /resource
{binary data} content-type = image/jpeg
CONTINUATION
+ END_HEADERS
host = example.org
:scheme = https
content-length = 123
DATA
+ END_STREAM
{binary data}
Note that data contributing to any given header field could be spread
between header block fragments. The allocation of header fields to
frames in this example is illustrative only.
A response that includes header fields and payload data is
transmitted as a HEADERS frame, followed by zero or more CONTINUATION
frames, followed by one or more DATA frames, with the last DATA frame
in the sequence having the END_STREAM flag set:
HTTP/1.1 200 OK HEADERS
Content-Type: image/jpeg ==> - END_STREAM
Content-Length: 123 + END_HEADERS
:status = 200
{binary data} content-type = image/jpeg
content-length = 123
DATA
+ END_STREAM
{binary data}
Trailing header fields are sent as a header block after both the
request or response header block and all the DATA frames have been
sent. The HEADERS frame starting the trailers header block has the
END_STREAM flag set.
HTTP/1.1 200 OK HEADERS
Content-Type: image/jpeg ==> - END_STREAM
Transfer-Encoding: chunked + END_HEADERS
Trailer: Foo :status = 200
content-length = 123
123 content-type = image/jpeg
{binary data} trailer = Foo
0
Foo: bar DATA
- END_STREAM
{binary data}
HEADERS
+ END_STREAM
+ END_HEADERS
foo = 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
skipping to change at page 61, line 10 skipping to change at page 59, line 34
Because pushing responses is effectively hop-by-hop, an intermediary Because pushing responses is effectively hop-by-hop, an intermediary
could receive pushed responses from the server and choose not to could receive pushed responses from the server and choose not to
forward those on to the client. In other words, how to make use of forward those on to the client. In other words, how to make use of
the pushed responses is up to that intermediary. Equally, the the pushed responses is up to that intermediary. Equally, the
intermediary might choose to push additional responses to the client, intermediary might choose to push additional responses to the client,
without any action taken by the server. without any action taken by the server.
A client cannot push. Thus, servers MUST treat the receipt of a A client cannot push. Thus, servers MUST treat the receipt of a
PUSH_PROMISE frame as a connection error (Section 5.4.1) of type PUSH_PROMISE frame as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. Clients MUST reject any attempt to change the PROTOCOL_ERROR. Clients MUST reject any attempt to change the
SETTINGS_ENABLE_PUSH setting to a value other than "0" by treating SETTINGS_ENABLE_PUSH setting to a value other than 0 by treating the
the message as a connection error (Section 5.4.1) of type message as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
PROTOCOL_ERROR.
A server can only push responses that are cacheable (see [HTTP-p6], A server can only push responses that are cacheable (see [RFC7234],
Section 3); promised requests MUST be safe (see [HTTP-p2], Section Section 3); promised requests MUST be safe (see [RFC7231],
4.2.1) and MUST NOT include a request body. Section 4.2.1) and MUST NOT include a request body.
8.2.1. Push Requests 8.2.1. Push Requests
Server push is semantically equivalent to a server responding to a Server push is semantically equivalent to a server responding to a
request; however, in this case that request is also sent by the request; however, in this case that request is also sent by the
server, as a PUSH_PROMISE frame. server, as a PUSH_PROMISE frame.
The PUSH_PROMISE frame includes a header block that contains a The PUSH_PROMISE frame includes a header block that contains a
complete set of request header fields that the server attributes to complete set of request header fields that the server attributes to
the request. It is not possible to push a response to a request that the request. It is not possible to push a response to a request that
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 8.1.3.1). The server MUST include a method in the ":method" (Section 8.1.2.1). 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 62, line 22 skipping to change at page 60, line 46
frames can be sent by the server on any stream that was opened by the 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" client. They MUST be sent on a stream that is in either the "open"
or "half closed (remote)" state to the server. PUSH_PROMISE frames or "half closed (remote)" state to the server. PUSH_PROMISE frames
are interspersed with the frames that comprise a response, though are interspersed with the frames that comprise a response, though
they cannot be interspersed with HEADERS and CONTINUATION frames that they cannot be interspersed with HEADERS and CONTINUATION frames that
comprise a single header block. comprise a single header block.
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 8.1.3.2) on a server- the pushed response as a response (Section 8.1.2.2) 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 63, line 7 skipping to change at page 61, line 31
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".
8.3. The CONNECT Method 8.3. The CONNECT Method
In HTTP/1.x, the pseudo-method CONNECT ([HTTP-p2], 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 8.1.3.1), with a few differences. Header Fields (Section 8.1.2.1), 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 [HTTP-p1], Section 5.3). of CONNECT requests, see [RFC7230], Section 5.3).
A proxy that supports CONNECT establishes a TCP connection [TCP] to A proxy that supports CONNECT establishes a TCP connection [TCP] to
the server identified in the ":authority" header field. Once this the server identified in the ":authority" header field. Once this
connection is successfully established, the proxy sends a HEADERS connection is successfully established, the proxy sends a HEADERS
frame containing a 2xx series status code to the client, as defined frame containing a 2xx series status code to the client, as defined
in [HTTP-p2], Section 4.3.6. in [RFC7231], Section 4.3.6.
After the initial HEADERS frame sent by each peer, all subsequent After the initial HEADERS frame sent by each peer, all subsequent
DATA frames correspond to data sent on the TCP connection. The DATA frames correspond to data sent on the TCP connection. The
payload of any DATA frames sent by the client are transmitted by the payload of any DATA frames sent by the client are transmitted by the
proxy to the TCP server; data received from the TCP server is proxy to the TCP server; data received from the TCP server is
assembled into DATA frames by the proxy. Frame types other than DATA assembled into DATA frames by the proxy. Frame types other than DATA
or stream management frames (RST_STREAM, WINDOW_UPDATE, and PRIORITY) or stream management frames (RST_STREAM, WINDOW_UPDATE, and PRIORITY)
MUST NOT be sent on a connected stream, and MUST be treated as a MUST NOT be sent on a connected stream, and MUST be treated as a
stream error (Section 5.4.2) if received. stream error (Section 5.4.2) if received.
skipping to change at page 64, line 25 skipping to change at page 62, line 49
9.1. Connection Management 9.1. Connection Management
HTTP/2 connections are persistent. For best performance, it is HTTP/2 connections are persistent. For best performance, it is
expected clients will not close connections until it is determined expected clients will not close connections until it is determined
that no further communication with a server is necessary (for that no further communication with a server is necessary (for
example, when a user navigates away from a particular web page), or example, when a user navigates away from a particular web page), or
until the server closes the connection. until the server closes the connection.
Clients SHOULD NOT open more than one HTTP/2 connection to a given Clients SHOULD NOT open more than one HTTP/2 connection to a given
destination, where a destination is the IP address and port that is host and port pair, where host is derived from a URI, a selected
derived from a URI, a selected alternative service [ALT-SVC], or a alternative service [ALT-SVC], or a configured proxy.
configured proxy. A client can create additional connections as
replacements, either to replace connections that are near to A client can create additional connections as replacements, either to
exhausting the available stream identifier space (Section 5.1.1), or replace connections that are near to exhausting the available stream
to replace connections that have encountered errors (Section 5.4.1). identifier space (Section 5.1.1), to refresh the keying material for
a TLS connection, or to replace connections that have encountered
errors (Section 5.4.1).
A client MAY open multiple connections to the same IP address and TCP A client MAY open multiple connections to the same IP address and TCP
port using different Server Name Indication [TLS-EXT] values or to port using different Server Name Indication [TLS-EXT] values or to
provide different TLS client certificates, but SHOULD avoid creating provide different TLS client certificates, but SHOULD avoid creating
multiple connections with the same configuration. [[anchor17: Need multiple connections with the same configuration.
more text on how client certificates relate here, see issue #363.]]
Clients MAY use a single server connection to send requests for URIs
with multiple different authority components as long as the server is
authoritative (Section 10.1).
Servers are encouraged to maintain open connections for as long as Servers are encouraged to maintain open connections for as long as
possible, but are permitted to terminate idle connections if possible, but are permitted to terminate idle connections if
necessary. When either endpoint chooses to close the transport-level necessary. When either endpoint chooses to close the transport-level
TCP connection, the terminating endpoint SHOULD first send a GOAWAY TCP connection, the terminating endpoint SHOULD first send a GOAWAY
(Section 6.8) frame so that both endpoints can reliably determine (Section 6.8) frame so that both endpoints can reliably determine
whether previously sent frames have been processed and gracefully whether previously sent frames have been processed and gracefully
complete or terminate any necessary remaining tasks. complete or terminate any necessary remaining tasks.
9.1.1. Connection Reuse
Clients MAY use a single server connection to send requests for URIs
with multiple different authority components as long as the server is
authoritative (Section 10.1). For "http" resources, this depends on
the host having resolved to the same IP address.
For "https" resources, connection reuse additionally depends on
having a certificate that is valid for the host in the URI. That is
the use of server certificate with multiple "subjectAltName"
attributes, or names with wildcards. For example, a certificate with
a "subjectAltName" of "*.example.com" might permit the use of the
same connection for "a.example.com" and "b.example.com".
In some deployments, reusing a connection for multiple origins can
result in requests being directed to the wrong origin server. For
example, TLS termination might be performed by a middlebox that uses
the TLS Server Name Indication (SNI) [TLS-EXT] extension to select
the an origin server. This means that it is possible for clients to
send confidential information to servers that might not be the
intended target for the request, even though the server has valid
authentication credentials.
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
Authoritative) status code in response to request (see
Section 9.1.2).
9.1.2. The 421 (Not Authoritative) Status Code
The 421 (Not Authoritative) status code indicates that the current
origin server is not authoritative for the requested resource, in the
sense of [RFC7230], Section 9.1 (see also Section 10.1).
Clients receiving a 421 (Not Authoritative) response from a server
MAY retry the request - whether the request method is idempotent or
not - over a different connection. This is possible if a connection
is reused (Section 9.1.1) or if an alternative service is selected
([ALT-SVC]).
This status code MUST NOT be generated by proxies.
A 421 response is cacheable by default; i.e., unless otherwise
indicated by the method definition or explicit cache controls (see
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]. The general Implementations of HTTP/2 MUST support TLS 1.2 [TLS12] for HTTP/2
TLS usage guidance in [TLSBCP] SHOULD be followed, with some over TLS. The general TLS usage guidance in [TLSBCP] SHOULD be
additional restrictions that are specific to HTTP/2. followed, with some additional restrictions that are specific to
HTTP/2.
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
therefore likely to be more appropriate for use for performance, therefore likely to be more appropriate for use for performance,
security or other reasons. security or other reasons.
Implementations MUST negotiate - and therefore use - ephemeral cipher The TLS implementation MUST disable renegotiation. An endpoint MUST
suites, such as ephemeral Diffie-Hellman (DHE) or the elliptic curve treat a TLS renegotiation as a connection error (Section 5.4.1) of
variant (ECDHE) with a minimum size of 2048 bits (DHE) or security type PROTOCOL_ERROR. Note that disabling renegotiation can result in
level of 128 bits (ECDHE). Clients MUST accept DHE sizes of up to long-lived connections becoming unusable due to limits on the number
4096 bits. of messages the underlying cipher suite can encipher.
Implementations are encouraged not to negotiate TLS cipher suites A client MAY use renegotiation to provide confidentiality protection
with known vulnerabilities, such as [RC4]. for client credentials offered in the handshake, but any
renegotiation MUST occur prior to sending the connection preface. A
server SHOULD request a client certificate if it sees a renegotiation
request immediately after establishing a connection.
An implementation that negotiates a TLS connection that does not meet This effectively prevents the use of renegotiation in response to a
the requirements in this section, or any policy-based constraints, request for a specific protected resource. A future specification
SHOULD NOT negotiate HTTP/2. Removing HTTP/2 protocols from might provide a way to support this use case.
consideration could result in the removal of all protocols from the
set of protocols offered by the client. This causes protocol
negotiation failure, as described in Section 3.2 of [TLSALPN].
Due to implementation limitations, it might not be possible to fail 9.2.2. TLS Cipher Suites
TLS negotiation based on all of these requirements. An endpoint MUST
terminate an HTTP/2 connection that is opened on a TLS session that
does not meet these minimum requirements with a connection error
(Section 5.4.1) of type INADEQUATE_SECURITY.
9.3. GZip Content-Encoding The set of TLS cipher suites that are permitted in HTTP/2 is
restricted. HTTP/2 MUST only be used with cipher suites that have
ephemeral key exchange, such as the ephemeral Diffie-Hellman (DHE)
[TLS12] or the elliptic curve variant (ECDHE) [RFC4492]. Ephemeral
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
of up to 4096 bits. HTTP MUST NOT be used with cipher suites that
use stream or block ciphers. Authenticated Encryption with
Additional Data (AEAD) modes, such as the Galois Counter Model (GCM)
mode for AES [RFC5288] are acceptable.
Clients MUST support gzip compression for HTTP response bodies. Clients MAY advertise support of other cipher suites in order to
Regardless of the value of the accept-encoding header field, a server allow for connection to servers that do not support HTTP/2 to
MAY send responses with gzip encoding. A compressed response MUST complete without the additional latency imposed by using a separate
still bear an appropriate content-encoding header field. connection for fallback.
This effectively changes the implicit value of the Accept-Encoding An implementation SHOULD NOT negotiate a TLS connection for HTTP/2
header field ([HTTP-p2], Section 5.3.4) from "identity" to "identity, without also negotiating a cipher suite that meets these
gzip", however gzip encoding cannot be suppressed by including requirements. Due to implementation limitations, it might not be
";q=0". Intermediaries that perform translation from HTTP/2 to possible to fail TLS negotiation. An endpoint MUST immediately
HTTP/1.1 MUST decompress payloads unless the request includes an terminate an HTTP/2 connection that does not meet these minimum
Accept-Encoding value that includes "gzip". 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.
HTTP/2 relies on the HTTP/1.1 definition of authority for determining HTTP/2 relies on the HTTP/1.1 definition of authority for determining
whether a server is authoritative in providing a given response, see whether a server is authoritative in providing a given response, see
[HTTP-p1], Section 9.1. This relies on local name resolution for the [RFC7230], Section 9.1. This relies on local name resolution for the
"http" URI scheme, and the offered server identity for the "https" "http" URI scheme, and the authenticated server identity for the
scheme (see [RFC2818], Section 3). "https" scheme (see [RFC2818], Section 3).
A client MUST NOT use, in any way, resources provided by a server A client MUST discard responses provided by a server that is not
that is not authoritative for those resources. authoritative for those resources.
10.2. Cross-Protocol Attacks 10.2. Cross-Protocol Attacks
In a cross-protocol attack, an attacker causes a client to initiate a In a cross-protocol attack, an attacker causes a client to initiate a
transaction in one protocol toward a server that understands a transaction in one protocol toward a server that understands a
different protocol. An attacker might be able to cause the different protocol. An attacker might be able to cause the
transaction to appear as valid transaction in the second protocol. transaction to appear as valid transaction in the second protocol.
In combination with the capabilities of the web context, this can be In combination with the capabilities of the web context, this can be
used to interact with poorly protected servers in private networks. used to interact with poorly protected servers in private networks.
Completing a TLS handshake with an ALPN identifier for HTTP/2 can be Completing a TLS handshake with an ALPN identifier for HTTP/2 can be
considered sufficient. ALPN provides a positive indication that a considered sufficient protection against cross protocol attacks.
server is willing to proceed with HTTP/2, which prevents attacks on ALPN provides a positive indication that a server is willing to
other TLS-based protocols. proceed with HTTP/2, which prevents attacks on other TLS-based
protocols.
The encryption in TLS makes it difficult for attackers to control the The encryption in TLS makes it difficult for attackers to control the
data which could be used in a cross-protocol attack on a cleartext data which could be used in a cross-protocol attack on a cleartext
protocol. protocol.
The cleartext version of HTTP/2 has minimal protection against cross- The cleartext version of HTTP/2 has minimal protection against cross-
protocol attacks. The connection preface (Section 3.5) contains a protocol attacks. The connection preface (Section 3.5) contains a
string that is designed to confuse HTTP/1.1 servers, but no special string that is designed to confuse HTTP/1.1 servers, but no special
protection is offered for other protocols. A server that is willing protection is offered for other protocols. A server that is willing
to ignore parts of an HTTP/1.1 request containing an Upgrade header to ignore parts of an HTTP/1.1 request containing an Upgrade header
field could be exposed to a cross-protocol attack. field in addition to the client connection preface could be exposed
to a cross-protocol attack.
10.3. Intermediary Encapsulation Attacks 10.3. Intermediary Encapsulation Attacks
HTTP/2 header field names and values are encoded as sequences of HTTP/2 header field names and values are encoded as sequences of
octets with a length prefix. This enables HTTP/2 to carry any string octets with a length prefix. This enables HTTP/2 to carry any string
of octets as the name or value of a header field. An intermediary of octets as the name or value of a header field. An intermediary
that translates HTTP/2 requests or responses into HTTP/1.1 directly that translates HTTP/2 requests or responses into HTTP/1.1 directly
could permit the creation of corrupted HTTP/1.1 messages. An could permit the creation of corrupted HTTP/1.1 messages. An
attacker might exploit this behavior to cause the intermediary to attacker might exploit this behavior to cause the intermediary to
create HTTP/1.1 messages with illegal header fields, extra header create HTTP/1.1 messages with illegal header fields, extra header
fields, or even new messages that are entirely falsified. fields, or even new messages that are entirely falsified.
Header field names or values that contain characters not permitted by Header field names or values that contain characters not permitted by
HTTP/1.1, including carriage return (U+000D) or line feed (U+000A) HTTP/1.1, including carriage return (ASCII 0xd) or line feed (ASCII
MUST NOT be translated verbatim by an intermediary, as stipulated in 0xa) MUST NOT be translated verbatim by an intermediary, as
[HTTP-p1], Section 3.2.4. stipulated in [RFC7230], Section 3.2.4.
Translation from HTTP/1.x to HTTP/2 does not produce the same Translation from HTTP/1.x to HTTP/2 does not produce the same
opportunity to an attacker. Intermediaries that perform translation opportunity to an attacker. Intermediaries that perform translation
to HTTP/2 MUST remove any instances of the "obs-fold" production from to HTTP/2 MUST remove any instances of the "obs-fold" production from
header field values. header field values.
10.4. Cacheability of Pushed Responses 10.4. Cacheability of Pushed Responses
Pushed responses do not have an explicit request from the client; the Pushed responses do not have an explicit request from the client; the
request is provided by the server in the PUSH_PROMISE frame. request is provided by the server in the PUSH_PROMISE frame.
skipping to change at page 68, line 5 skipping to change at page 67, line 35
Pushed responses for which an origin server is not authoritative (see Pushed responses for which an origin server is not authoritative (see
Section 10.1) are never cached or used. Section 10.1) are never cached or used.
10.5. Denial of Service Considerations 10.5. Denial of Service Considerations
An HTTP/2 connection can demand a greater commitment of resources to An HTTP/2 connection can demand a greater commitment of resources to
operate than a HTTP/1.1 connection. The use of header compression operate than a HTTP/1.1 connection. The use of header compression
and flow control depend on a commitment of resources for storing a and flow control depend on a commitment of resources for storing a
greater amount of state. Settings for these features ensure that greater amount of state. Settings for these features ensure that
memory commitments for these features are strictly bounded. memory commitments for these features are strictly bounded.
Processing capacity cannot be guarded in the same fashion.
The number of PUSH_PROMISE frames is not constrained in the same
fashion. A client that accepts server push SHOULD limit the number
of streams it allows to be in the "reserved (remote)" state.
Excessive number of server push streams can be treated as a stream
error (Section 5.4.2) of type ENHANCE_YOUR_CALM.
Processing capacity cannot be guarded as effectively as state
capacity.
The SETTINGS frame can be abused to cause a peer to expend additional The SETTINGS frame can be abused to cause a peer to expend additional
processing time. This might be done by pointlessly changing SETTINGS processing time. This might be done by pointlessly changing SETTINGS
parameters, setting multiple undefined parameters, or changing the parameters, setting multiple undefined parameters, or changing the
same setting multiple times in the same frame. WINDOW_UPDATE, same setting multiple times in the same frame. WINDOW_UPDATE or
PRIORITY, or BLOCKED frames can be abused to cause an unnecessary PRIORITY frames can be abused to cause an unnecessary waste of
waste of resources. A server might erroneously issue ALTSVC frames resources.
for origins on which it cannot be authoritative to generate excess
work for clients.
Large numbers of small or empty frames can be abused to cause a peer Large numbers of small or empty frames can be abused to cause a peer
to expend time processing frame headers. Note however that some uses to expend time processing frame headers. Note however that some uses
are entirely legitimate, such as the sending of an empty DATA frame are entirely legitimate, such as the sending of an empty DATA frame
to end a stream. to end a stream.
Header compression also offers some opportunities to waste processing Header compression also offers some opportunities to waste processing
resources; see [COMPRESSION] for more details on potential abuses. resources; see Section 8 of [COMPRESSION] for more details on
potential abuses.
Limits in SETTINGS parameters cannot be reduced instantaneously, Limits in SETTINGS parameters cannot be reduced instantaneously,
which leaves an endpoint exposed to behavior from a peer that could which leaves an endpoint exposed to behavior from a peer that could
exceed the new limits. In particular, immediately after establishing exceed the new limits. In particular, immediately after establishing
a connection, limits set by a server are not known to clients and a connection, limits set by a server are not known to clients and
could be exceeded without being an obvious protocol violation. could be exceeded without being an obvious protocol violation.
All these features - i.e., SETTINGS changes, small frames, header All these features - i.e., SETTINGS changes, small frames, header
compression - have legitimate uses. These features become a burden compression - have legitimate uses. These features become a burden
only when they are used unnecessarily or to excess. only when they are used unnecessarily or to excess.
An endpoint that doesn't monitor this behavior exposes itself to a An endpoint that doesn't monitor this behavior exposes itself to a
risk of denial of service attack. Implementations SHOULD track the risk of denial of service attack. Implementations SHOULD track the
use of these features and set limits on their use. An endpoint MAY use of these features and set limits on their use. An endpoint MAY
treat activity that is suspicious as a connection error treat activity that is suspicious as a connection error
(Section 5.4.1) of type ENHANCE_YOUR_CALM. (Section 5.4.1) of type ENHANCE_YOUR_CALM.
10.5.1. Limits on Header Block Size
A large header block (Section 4.3) can cause an implementation to
commit a large amount of state. In servers and intermediaries,
header fields that are critical to routing, such as ":authority",
":path", and ":scheme" are not guaranteed to be present early in the
header block. In particular, values that are in the reference set
cannot be emitted until the header block ends.
This can prevent streaming of the header fields to their ultimate
destination, and forces the endpoint to buffer the entire header
block. Since there is no hard limit to the size of a header block,
an endpoint could be forced to exhaust available memory.
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
code [RFC6585]. A client can discard responses that it cannot
process. The header block MUST be processed to ensure a consistent
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 response bodies (Section 9.3). Compression can (Section 4.3) and entity bodies. Compression can allow an attacker
allow an attacker to recover secret data when it is compressed in the to recover secret data when it is compressed in the same context as
same context as data under attacker control. data under attacker control.
There are demonstrable attacks on compression that exploit the There are demonstrable attacks on compression that exploit the
characteristics of the web (e.g., [BREACH]). The attacker induces characteristics of the web (e.g., [BREACH]). The attacker induces
multiple requests containing varying plaintext, observing the length multiple requests containing varying plaintext, observing the length
of the resulting ciphertext in each, which reveals a shorter length of the resulting ciphertext in each, which reveals a shorter length
when a guess about the secret is correct. when a guess about the secret is correct.
Implementations communicating on a secure channel MUST NOT compress Implementations communicating on a secure channel MUST NOT compress
content that includes both confidential and attacker-controlled data content that includes both confidential and attacker-controlled data
unless separate compression dictionaries are used for each source of unless separate compression dictionaries are used for each source of
data. Compression MUST NOT be used if the source of data cannot be data. Compression MUST NOT be used if the source of data cannot be
reliably determined. reliably determined.
Intermediaries MUST NOT alter the compression of DATA frames unless
additional information is available that allows the intermediary to
identify the source of data. In particular, frames that are not
compressed cannot be compressed, and frames that are separately
compressed cannot be merged into a single frame. Compressed frames
MAY be decompressed or split into multiple frames.
Further considerations regarding the compression of header fields are Further considerations regarding the compression of header fields are
described in [COMPRESSION]. described in [COMPRESSION].
10.7. Use of Padding 10.7. Use of Padding
Padding within HTTP/2 is not intended as a replacement for general Padding within HTTP/2 is not intended as a replacement for general
purpose padding, such as might be provided by TLS [TLS12]. Redundant purpose padding, such as might be provided by TLS [TLS12]. Redundant
padding could even be counterproductive. Correct application can padding could even be counterproductive. Correct application can
depend on having specific knowledge of the data that is being padded. depend on having specific knowledge of the data that is being padded.
To mitigate attacks that rely on compression, disabling compression To mitigate attacks that rely on compression, disabling or limiting
might be preferable to padding as a countermeasure. compression might be preferable to padding as a countermeasure.
Padding can be used to obscure the exact size of frame content, and Padding can be used to obscure the exact size of frame content, and
is provided to mitigate specific attacks within HTTP. For example, is provided to mitigate specific attacks within HTTP. For example,
attacks where compressed content includes both attacker-controlled attacks where compressed content includes both attacker-controlled
plaintext and secret data (see for example, [BREACH]). plaintext and secret data (see for example, [BREACH]).
Use of padding can result in less protection than might seem Use of padding can result in less protection than might seem
immediately obvious. At best, padding only makes it more difficult immediately obvious. At best, padding only makes it more difficult
for an attacker to infer length information by increasing the number for an attacker to infer length information by increasing the number
of frames an attacker has to observe. Incorrectly implemented of frames an attacker has to observe. Incorrectly implemented
padding schemes can be easily defeated. In particular, randomized padding schemes can be easily defeated. In particular, randomized
padding with a predictable distribution provides very little padding with a predictable distribution provides very little
protection; or padding payloads to a fixed size exposes information protection; similarly, padding payloads to a fixed size exposes
as payload sizes cross the fixed size boundary, which could be information as payload sizes cross the fixed size boundary, which
possible if an attacker can control plaintext. could be possible if an attacker can control plaintext.
Intermediaries SHOULD NOT remove padding, though an intermediary MAY Intermediaries SHOULD retain padding for DATA frames, but MAY drop
remove padding and add differing amounts if the intent is to improve padding for HEADERS and PUSH_PROMISE frames. A valid reason for an
the protections padding affords. intermediary to change the amount of padding of frames is to improve
the protections that padding provides.
10.8. Privacy Considerations 10.8. Privacy Considerations
Several characteristics of HTTP/2 provide an observer an opportunity Several characteristics of HTTP/2 provide an observer an opportunity
to correlate actions of a single client or server over time. This to correlate actions of a single client or server over time. This
includes the value of settings, the manner in which flow control includes the value of settings, the manner in which flow control
windows are managed, the way priorities are allocated to streams, windows are managed, the way priorities are allocated to streams,
timing of reactions to stimulus, and handling of any optional timing of reactions to stimulus, and handling of any optional
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 <http://www.w3.org/TR/html5/introduction.html#fingerprint>. 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 [TLSALPN].
This document establishes a registry for error codes. This new This document establishes a registry for frame types, settings, and
registry is entered into a new "Hypertext Transfer Protocol (HTTP) 2 error codes. These new registries are entered into a new "Hypertext
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. 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 [TLSALPN].
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 (RFCXXXX) 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 (RFCXXXX) Specification: This document
11.2. Error Code Registry 11.2. Frame Type Registry
This document establishes a registry for HTTP/2 frame types codes.
The "HTTP/2 Frame Type" registry manages an 8-bit space. The "HTTP/2
Frame Type" registry operates under either of the "IETF Review" or
"IESG Approval" policies [RFC5226] for values between 0x00 and 0xef,
with values between 0xf0 and 0xff being reserved for experimental
use.
New entries in this registry require the following information:
Frame Type: A name or label for the frame type.
Code: The 8-bit code assigned to the frame type.
Specification: A reference to a specification that includes a
description of the frame layout, it's semantics and flags that the
frame type uses, including any parts of the frame that are
conditionally present based on the value of flags.
The entries in the following table are registered by this document.
+---------------+------+--------------+
| Frame Type | Code | Section |
+---------------+------+--------------+
| DATA | 0x0 | Section 6.1 |
| HEADERS | 0x1 | Section 6.2 |
| PRIORITY | 0x2 | Section 6.3 |
| RST_STREAM | 0x3 | Section 6.4 |
| SETTINGS | 0x4 | Section 6.5 |
| PUSH_PROMISE | 0x5 | Section 6.6 |
| PING | 0x6 | Section 6.7 |
| GOAWAY | 0x7 | Section 6.8 |
| WINDOW_UPDATE | 0x8 | Section 6.9 |
| CONTINUATION | 0x9 | Section 6.10 |
+---------------+------+--------------+
11.3. Settings Registry
This document establishes a registry for HTTP/2 settings. The
"HTTP/2 Settings" registry manages a 16-bit space. The "HTTP/2
Settings" registry operates under the "Expert Review" policy
[RFC5226] for values in the range from 0x0000 to 0xefff, with values
between and 0xf000 and 0xffff being reserved for experimental use.
New registrations are advised to provide the following information:
Name: A symbolic name for the setting. Specifying a setting name is
optional.
Code: The 16-bit code assigned to the setting.
Initial Value: An initial value for the setting.
Specification: A stable reference to a specification that describes
the use of the setting.
An initial set of setting registrations can be found in
Section 6.5.2.
+------------------------+------+---------------+---------------+
| Name | Code | Initial Value | Specification |
+------------------------+------+---------------+---------------+
| HEADER_TABLE_SIZE | 0x1 | 4096 | Section 6.5.2 |
| ENABLE_PUSH | 0x2 | 1 | Section 6.5.2 |
| MAX_CONCURRENT_STREAMS | 0x3 | (infinite) | Section 6.5.2 |
| INITIAL_WINDOW_SIZE | 0x4 | 65535 | Section 6.5.2 |
+------------------------+------+---------------+---------------+
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
of the error code. An expert reviewer is advised to examine new of the error code. An expert reviewer is advised to examine new
registrations for possible duplication with existing error codes. registrations for possible duplication with existing error codes.
Use of existing registrations is to be encouraged, but not mandated. Use of existing registrations is to be encouraged, but not mandated.
New registrations are advised to provide the following information: New registrations are advised to provide the following information:
Error Code: The 32-bit error code value.
Name: A name for the error code. Specifying an error code name is Name: A name for the error code. Specifying an error code name is
optional. optional.
Description: A description of the conditions where the error code is Code: The 32-bit error code value.
applicable.
Description: A brief description of the error code semantics, longer
if no detailed specification is provided.
Specification: An optional reference for a specification that Specification: An optional reference for a specification that
defines the error code. defines the error code.
An initial set of error code registrations can be found in Section 7. The entries in the following table are registered by this document.
11.3. HTTP2-Settings Header Field Registration +---------------------+------+----------------------+---------------+
| Name | Code | Description | Specification |
+---------------------+------+----------------------+---------------+
| NO_ERROR | 0x0 | Graceful shutdown | Section 7 |
| PROTOCOL_ERROR | 0x1 | Protocol error | Section 7 |
| | | detected | |
| INTERNAL_ERROR | 0x2 | Implementation fault | Section 7 |
| FLOW_CONTROL_ERROR | 0x3 | Flow control limits | Section 7 |
| | | exceeded | |
| SETTINGS_TIMEOUT | 0x4 | Settings not | Section 7 |
| | | acknowledged | |
| STREAM_CLOSED | 0x5 | Frame received for | Section 7 |
| | | closed stream | |
| FRAME_SIZE_ERROR | 0x6 | Frame size incorrect | Section 7 |
| REFUSED_STREAM | 0x7 | Stream not processed | Section 7 |
| CANCEL | 0x8 | Stream cancelled | Section 7 |
| COMPRESSION_ERROR | 0x9 | Compression state | Section 7 |
| | | not updated | |
| CONNECT_ERROR | 0xa | TCP connection error | Section 7 |
| | | for CONNECT method | |
| ENHANCE_YOUR_CALM | 0xb | Processing capacity | Section 7 |
| | | exceeded | |
| INADEQUATE_SECURITY | 0xc | Negotiated TLS | Section 7 |
| | | parameters not | |
| | | acceptable | |
+---------------------+------+----------------------+---------------+
11.5. HTTP2-Settings Header Field Registration
This section registers the "HTTP2-Settings" header field in the This section registers the "HTTP2-Settings" header field in the
Permanent Message Header Field Registry [BCP90]. Permanent Message Header Field Registry [BCP90].
Header field name: HTTP2-Settings Header field name: HTTP2-Settings
Applicable protocol: http Applicable protocol: http
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): Section 3.2.1 of this document Specification document(s): Section 3.2.1 of this document
Related information: This header field is only used by an HTTP/2 Related information: This header field is only used by an HTTP/2
client for Upgrade-based negotiation. client for Upgrade-based negotiation.
11.4. PRI Method Registration 11.6. PRI Method Registration
This section registers the "PRI" method in the HTTP Method Registry This section registers the "PRI" method in the HTTP Method Registry
[HTTP-p2]. ([RFC7231], Section 8.1).
Method Name: PRI Method Name: PRI
Safe No Safe No
Idempotent No Idempotent No
Specification document(s) Section 3.5 of this document Specification document(s) Section 3.5 of this document
Related information: This method is never used by an actual client. Related information: This method is never used by an actual client.
This method will appear to be used when an HTTP/1.1 server or This method will appear to be used when an HTTP/1.1 server or
intermediary attempts to parse an HTTP/2 connection preface. intermediary attempts to parse an HTTP/2 connection preface.
11.7. The 421 Not Authoritative HTTP Status Code
This document registers the 421 (Not Authoritative) HTTP Status code
in the Hypertext Transfer Protocol (HTTP) Status Code Registry
([RFC7231], Section 8.2).
Status Code: 421
Short Description: Not Authoritative
Specification: Section 9.1.2 of this document
12. Acknowledgements 12. Acknowledgements
This document includes substantial input from the following This document includes substantial input from the following
individuals: individuals:
o Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa o Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa
Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam
Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay, Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay,
Paul Amer, Fan Yang, Jonathan Leighton (SPDY contributors). Paul Amer, Fan Yang, Jonathan Leighton (SPDY contributors).
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 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 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
[ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP [COMPRESSION]
Alternative Services", draft-ietf-httpbis-alt-svc-01 Ruellan, H. and R. Peon, "HPACK - Header Compression for
(work in progress), April 2014. HTTP/2", draft-ietf-httpbis-header-compression-08 (work in
progress), June 2014.
[COMPRESSION] Ruellan, H. and R. Peon, "HPACK - Header Compression [COOKIE] Barth, A., "HTTP State Management Mechanism", RFC 6265,
for HTTP/2", draft-ietf-httpbis-header-compression-07 April 2011.
(work in progress), April 2014.
[COOKIE] Barth, A., "HTTP State Management Mechanism", [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
RFC 6265, April 2011. Requirement Levels", BCP 14, RFC 2119, March 1997.
[GZIP] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
G. Randers-Pehrson, "GZIP file format specification
version 4.3", RFC 1952, May 1996.
[HTTP-p1] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Transfer Protocol (HTTP/1.1): Message Syntax and Resource Identifier (URI): Generic Syntax", STD 66, RFC
Routing", draft-ietf-httpbis-p1-messaging-26 (work in 3986, January 2005.
progress), February 2014.
[HTTP-p2] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Transfer Protocol (HTTP/1.1): Semantics and Content", Encodings", RFC 4648, October 2006.
draft-ietf-httpbis-p2-semantics-26 (work in progress),
February 2014.
[HTTP-p4] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
Transfer Protocol (HTTP/1.1): Conditional Requests", IANA Considerations Section in RFCs", BCP 26, RFC 5226,
draft-ietf-httpbis-p4-conditional-26 (work in May 2008.
progress), February 2014.
[HTTP-p5] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Range Specifications: ABNF", STD 68, RFC 5234, January 2008.
Requests", draft-ietf-httpbis-p5-range-26 (work in
progress), February 2014.
[HTTP-p6] Fielding, R., Ed., Nottingham, M., Ed., and J. [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Protocol (HTTP/1.1): Message Syntax and Routing", RFC
Caching", draft-ietf-httpbis-p6-cache-26 (work in 7230, June 2014.
progress), February 2014.
[HTTP-p7] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Transfer Protocol (HTTP/1.1): Authentication", Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
draft-ietf-httpbis-p7-auth-26 (work in progress), June 2014.
February 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Requirement Levels", BCP 14, RFC 2119, March 1997. Protocol (HTTP/1.1): Conditional Requests", RFC 7232, June
2014.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC7233] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"Hypertext Transfer Protocol (HTTP/1.1): Range Requests",
RFC 7233, June 2014.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
"Uniform Resource Identifier (URI): Generic Syntax", Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
STD 66, RFC 3986, January 2005. RFC 7234, June 2014.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Encodings", RFC 4648, October 2006. Protocol (HTTP/1.1): Authentication", RFC 7235, June 2014.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing [TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC
an IANA Considerations Section in RFCs", BCP 26, 793, September 1981.
RFC 5226, May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [TLS-EXT] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Specifications: ABNF", STD 68, RFC 5234, January 2008. Extension Definitions", RFC 6066, January 2011.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, [TLS12] Dierks, T. and E. Rescorla, "The Transport Layer Security
December 2011. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[TCP] Postel, J., "Transmission Control Protocol", STD 7, [TLSALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
RFC 793, September 1981. "Transport Layer Security (TLS) Application Layer Protocol
Negotiation Extension", draft-ietf-tls-applayerprotoneg-05
(work in progress), March 2014.
[TLS-EXT] Eastlake, D., "Transport Layer Security (TLS) 13.2. Informative References
Extensions: Extension Definitions", RFC 6066,
January 2011.
[TLS12] Dierks, T. and E. Rescorla, "The Transport Layer [ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP
Security (TLS) Protocol Version 1.2", RFC 5246, Alternative Services", draft-ietf-httpbis-alt-svc-01 (work
August 2008. in progress), April 2014.
[TLSALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan, [BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
"Transport Layer Security (TLS) Application Layer Procedures for Message Header Fields", BCP 90, RFC 3864,
Protocol Negotiation Extension", September 2004.
draft-ietf-tls-applayerprotoneg-05 (work in progress),
March 2014.
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO [BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the
10646", STD 63, RFC 3629, November 2003. CRIME Attack", July 2013, <http://breachattack.com/
resources/
BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>.
13.2. Informative References [HTML5] Berjon, R., Faulkner, S., Leithead, T., Doyle Navara, E.,
O'Connor, E., and S. Pfeiffer, "HTML5", W3C Candidate
Recommendation CR-html5-20140204, Febuary 2014,
<http://www.w3.org/TR/2014/CR-html5-20140204/>.
[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration Latest version available at [5].
Procedures for Message Header Fields", BCP 90,
RFC 3864, September 2004.
[BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving [RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP Extensions
the CRIME Attack", July 2013, <http:// for High Performance", RFC 1323, May 1992.
breachattack.com/resources/
BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>.
[IDNA] Klensin, J., "Internationalized Domain Names for [RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D.
Applications (IDNA): Definitions and Document Jensen, "HTTP Extensions for Distributed Authoring --
Framework", RFC 5890, August 2010. WEBDAV", RFC 2518, February 1999.
[RC4] Rivest, R., "The RC4 encryption algorithm", RSA Data [RFC3749] Hollenbeck, S., "Transport Layer Security Protocol
Security, Inc. , March 1992. Compression Methods", RFC 3749, May 2004.
[RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP [RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Extensions for High Performance", RFC 1323, May 1992. Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, May 2006.
[RFC3749] Hollenbeck, S., "Transport Layer Security Protocol [RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Compression Methods", RFC 3749, May 2004. Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
August 2008.
[TALKING] Huang, L-S., Chen, E., Barth, A., Rescorla, E., and C. [RFC6585] Nottingham, N. and R. Fielding, "Additional HTTP Status
Jackson, "Talking to Yourself for Fun and Profit", Codes", RFC 6585, April 2012.
2011, <http://w2spconf.com/2011/papers/websocket.pdf>.
[TLSBCP] Sheffer, Y., Holz, R., and P. Saint-Andre, [TALKING] Huang, L-S., Chen, E., Barth, A., Rescorla, E., and C.
"Recommendations for Secure Use of TLS and DTLS", Jackson, "Talking to Yourself for Fun and Profit", 2011,
draft-sheffer-tls-bcp-02 (work in progress), <http://w2spconf.com/2011/papers/websocket.pdf>.
February 2014.
[TLSBCP] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of TLS and DTLS", draft-
sheffer-tls-bcp-02 (work in progress), February 2014.
13.3. URIs
[1] https://www.iana.org/assignments/message-headers
[2] https://groups.google.com/forum/?fromgroups#!topic/spdy-dev/
cfUef2gL3iU
[3] https://tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-
principles-01
Appendix A. Change Log (to be removed by RFC Editor before publication) Appendix A. Change Log (to be removed by RFC Editor before publication)
A.1. Since draft-ietf-httpbis-http2-11 A.1. Since draft-ietf-httpbis-http2-12
Restored extensibility options.
Restricting TLS cipher suites to AEAD only.
Removing Content-Encoding requirements.
Permitting the use of PRIORITY after stream close.
Removed ALTSVC frame.
Removed BLOCKED frame.
Reducing the maximum padding size to 256 octets; removing padding
from CONTINUATION frames.
Removed per-frame GZIP compression.
A.2. 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.2. Since draft-ietf-httpbis-http2-10 A.3. 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.3. Since draft-ietf-httpbis-http2-09 A.4. 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 76, line 36 skipping to change at page 79, line 30
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.4. Since draft-ietf-httpbis-http2-08 A.5. 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.5. Since draft-ietf-httpbis-http2-07 A.6. Since draft-ietf-httpbis-http2-07
Marked draft for implementation. Marked draft for implementation.
A.6. Since draft-ietf-httpbis-http2-06 A.7. 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.7. Since draft-ietf-httpbis-http2-05 A.8. 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.8. Since draft-ietf-httpbis-http2-04 A.9. 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 77, line 49 skipping to change at page 80, line 43
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.9. Since draft-ietf-httpbis-http2-03 A.10. 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.10. Since draft-ietf-httpbis-http2-02 A.11. 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.11. Since draft-ietf-httpbis-http2-01 A.12. 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.
skipping to change at page 79, line 12 skipping to change at page 82, line 7
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.12. Since draft-ietf-httpbis-http2-00 A.13. 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 <https:// Changed INTERNAL_ERROR on GOAWAY to have a value of 2 [6].
groups.google.com/forum/?fromgroups#!topic/spdy-dev/cfUef2gL3iU>.
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 <http:// Added flow control principles (Section 5.2.1) based on [7].
tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01>.
A.13. Since draft-mbelshe-httpbis-spdy-00 A.14. 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
skipping to change at page 80, line 4 skipping to change at page 82, line 42
Mike Belshe Mike Belshe
Twist Twist
EMail: mbelshe@chromium.org EMail: mbelshe@chromium.org
Roberto Peon Roberto Peon
Google, Inc Google, Inc
EMail: fenix@google.com EMail: fenix@google.com
Martin Thomson (editor) Martin Thomson (editor)
Mozilla Mozilla
Suite 300 331 E Evelyn Street
650 Castro Street
Mountain View, CA 94041 Mountain View, CA 94041
US US
EMail: martin.thomson@gmail.com EMail: martin.thomson@gmail.com
 End of changes. 309 change blocks. 
1074 lines changed or deleted 1199 lines changed or added

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