draft-ietf-httpbis-http2-14.txt   draft-ietf-httpbis-http2-latest.txt 
HTTPbis Working Group M. Belshe HTTPbis Working Group M. Belshe
Internet-Draft Twist Internet-Draft BitGo
Intended status: Standards Track R. Peon Intended status: Standards Track R. Peon
Expires: January 31, 2015 Google, Inc Expires: November 2, 2015 Google, Inc
M. Thomson, Ed. M. Thomson, Ed.
Mozilla Mozilla
July 30, 2014 May 2015
Hypertext Transfer Protocol version 2 Hypertext Transfer Protocol Version 2 (HTTP/2)
draft-ietf-httpbis-http2-14 draft-ietf-httpbis-http2-latest
Abstract Abstract
This specification describes an optimized expression of the syntax of This specification describes an optimized expression of the semantics
the Hypertext Transfer Protocol (HTTP). HTTP/2 enables a more of the Hypertext Transfer Protocol (HTTP), referred to as HTTP
efficient use of network resources and a reduced perception of version 2 (HTTP/2). HTTP/2 enables a more efficient use of network
latency by introducing header field compression and allowing multiple resources and a reduced perception of latency by introducing header
concurrent messages on the same connection. It also introduces field compression and allowing multiple concurrent exchanges on the
unsolicited push of representations from servers to clients. same connection. It also introduces unsolicited push of
representations from servers to clients.
This specification 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)
Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at
<https://lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information can be found at
<https://tools.ietf.org/wg/httpbis/>; that specific to HTTP/2 are at
<https://http2.github.io/>.
The changes in this draft are summarized in Appendix A.
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-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on January 31, 2015. This Internet-Draft will expire on November 2, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
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 . . . . . . . . . . . . . . . 7
3. Starting HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . 7 3. Starting HTTP/2 . . . . . . . . . . . . . . . . . . . . . . . 8
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 . . . . . . . . . . . . . 8
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 . . . . . . . . . . . . . . . . . . . . . . 16
5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . . 20 5.1.1. Stream Identifiers . . . . . . . . . . . . . . . . . . 21
5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . . 21 5.1.2. Stream Concurrency . . . . . . . . . . . . . . . . . . 22
5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . . 22 5.2. Flow Control . . . . . . . . . . . . . . . . . . . . . . . 22
5.2.1. Flow Control Principles . . . . . . . . . . . . . . . 22 5.2.1. Flow-Control Principles . . . . . . . . . . . . . . . 22
5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 23 5.2.2. Appropriate Use of Flow Control . . . . . . . . . . . 23
5.3. Stream priority . . . . . . . . . . . . . . . . . . . . . 23 5.3. Stream Priority . . . . . . . . . . . . . . . . . . . . . 24
5.3.1. Stream Dependencies . . . . . . . . . . . . . . . . . 24 5.3.1. Stream Dependencies . . . . . . . . . . . . . . . . . 25
5.3.2. Dependency Weighting . . . . . . . . . . . . . . . . . 25 5.3.2. Dependency Weighting . . . . . . . . . . . . . . . . . 26
5.3.3. Reprioritization . . . . . . . . . . . . . . . . . . . 25 5.3.3. Reprioritization . . . . . . . . . . . . . . . . . . . 26
5.3.4. Prioritization State Management . . . . . . . . . . . 26 5.3.4. Prioritization State Management . . . . . . . . . . . 27
5.3.5. Default Priorities . . . . . . . . . . . . . . . . . . 27 5.3.5. Default Priorities . . . . . . . . . . . . . . . . . . 28
5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . . 27 5.4. Error Handling . . . . . . . . . . . . . . . . . . . . . . 28
5.4.1. Connection Error Handling . . . . . . . . . . . . . . 27 5.4.1. Connection Error Handling . . . . . . . . . . . . . . 29
5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 28 5.4.2. Stream Error Handling . . . . . . . . . . . . . . . . 29
5.4.3. Connection Termination . . . . . . . . . . . . . . . . 28 5.4.3. Connection Termination . . . . . . . . . . . . . . . . 30
5.5. Extending HTTP/2 . . . . . . . . . . . . . . . . . . . . . 29 5.5. Extending HTTP/2 . . . . . . . . . . . . . . . . . . . . . 30
6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 29 6. Frame Definitions . . . . . . . . . . . . . . . . . . . . . . 31
6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 6.1. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 31 6.2. HEADERS . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . . 33 6.3. PRIORITY . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . . 34 6.4. RST_STREAM . . . . . . . . . . . . . . . . . . . . . . . . 35
6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . 35 6.5. SETTINGS . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.5.1. SETTINGS Format . . . . . . . . . . . . . . . . . . . 36 6.5.1. SETTINGS Format . . . . . . . . . . . . . . . . . . . 37
6.5.2. Defined SETTINGS Parameters . . . . . . . . . . . . . 36 6.5.2. Defined SETTINGS Parameters . . . . . . . . . . . . . 38
6.5.3. Settings Synchronization . . . . . . . . . . . . . . . 38 6.5.3. Settings Synchronization . . . . . . . . . . . . . . . 39
6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . . 38 6.6. PUSH_PROMISE . . . . . . . . . . . . . . . . . . . . . . . 40
6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 6.7. PING . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . . 41 6.8. GOAWAY . . . . . . . . . . . . . . . . . . . . . . . . . . 43
6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 44 6.9. WINDOW_UPDATE . . . . . . . . . . . . . . . . . . . . . . 45
6.9.1. The Flow Control Window . . . . . . . . . . . . . . . 45 6.9.1. The Flow-Control Window . . . . . . . . . . . . . . . 47
6.9.2. Initial Flow Control Window Size . . . . . . . . . . . 46 6.9.2. Initial Flow-Control Window Size . . . . . . . . . . . 48
6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 47 6.9.3. Reducing the Stream Window Size . . . . . . . . . . . 48
6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . . 47 6.10. CONTINUATION . . . . . . . . . . . . . . . . . . . . . . . 49
7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 48 7. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 50
8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 49 8. HTTP Message Exchanges . . . . . . . . . . . . . . . . . . . . 51
8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . . 50 8.1. HTTP Request/Response Exchange . . . . . . . . . . . . . . 51
8.1.1. Upgrading From HTTP/2 . . . . . . . . . . . . . . . . 51 8.1.1. Upgrading from HTTP/2 . . . . . . . . . . . . . . . . 53
8.1.2. HTTP Header Fields . . . . . . . . . . . . . . . . . . 51 8.1.2. HTTP Header Fields . . . . . . . . . . . . . . . . . . 53
8.1.3. Examples . . . . . . . . . . . . . . . . . . . . . . . 55 8.1.3. Examples . . . . . . . . . . . . . . . . . . . . . . . 57
8.1.4. Request Reliability Mechanisms in HTTP/2 . . . . . . . 57 8.1.4. Request Reliability Mechanisms in HTTP/2 . . . . . . . 59
8.2. Server Push . . . . . . . . . . . . . . . . . . . . . . . 58 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 9.1.1. Connection Reuse . . . . . . . . . . . . . . . . . . . 65
9.1.2. The 421 (Not Authoritative) Status Code . . . . . . . 63 9.1.2. The 421 (Misdirected Request) Status Code . . . . . . 66
9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 64 9.2. Use of TLS Features . . . . . . . . . . . . . . . . . . . 66
9.2.1. TLS Features . . . . . . . . . . . . . . . . . . . . . 64 9.2.1. TLS 1.2 Features . . . . . . . . . . . . . . . . . . . 66
9.2.2. TLS Cipher Suites . . . . . . . . . . . . . . . . . . 64 9.2.2. TLS 1.2 Cipher Suites . . . . . . . . . . . . . . . . 67
10. Security Considerations . . . . . . . . . . . . . . . . . . . 65 10. Security Considerations . . . . . . . . . . . . . . . . . . . 68
10.1. Server Authority . . . . . . . . . . . . . . . . . . . . . 65 10.1. Server Authority . . . . . . . . . . . . . . . . . . . . . 68
10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 65 10.2. Cross-Protocol Attacks . . . . . . . . . . . . . . . . . . 68
10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . . 66 10.3. Intermediary Encapsulation Attacks . . . . . . . . . . . . 69
10.4. Cacheability of Pushed Responses . . . . . . . . . . . . . 66 10.4. Cacheability of Pushed Responses . . . . . . . . . . . . . 69
10.5. Denial of Service Considerations . . . . . . . . . . . . . 67 10.5. Denial-of-Service Considerations . . . . . . . . . . . . . 70
10.5.1. Limits on Header Block Size . . . . . . . . . . . . . 68 10.5.1. Limits on Header Block Size . . . . . . . . . . . . . 71
10.6. Use of Compression . . . . . . . . . . . . . . . . . . . . 68 10.5.2. CONNECT Issues . . . . . . . . . . . . . . . . . . . . 71
10.7. Use of Padding . . . . . . . . . . . . . . . . . . . . . . 69 10.6. Use of Compression . . . . . . . . . . . . . . . . . . . . 71
10.8. Privacy Considerations . . . . . . . . . . . . . . . . . . 70 10.7. Use of Padding . . . . . . . . . . . . . . . . . . . . . . 72
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 70 10.8. Privacy Considerations . . . . . . . . . . . . . . . . . . 73
11.1. Registration of HTTP/2 Identification Strings . . . . . . 70 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 73
11.2. Frame Type Registry . . . . . . . . . . . . . . . . . . . 71 11.1. Registration of HTTP/2 Identification Strings . . . . . . 73
11.3. Settings Registry . . . . . . . . . . . . . . . . . . . . 71 11.2. Frame Type Registry . . . . . . . . . . . . . . . . . . . 74
11.4. Error Code Registry . . . . . . . . . . . . . . . . . . . 72 11.3. Settings Registry . . . . . . . . . . . . . . . . . . . . 75
11.5. HTTP2-Settings Header Field Registration . . . . . . . . . 73 11.4. Error Code Registry . . . . . . . . . . . . . . . . . . . 76
11.6. PRI Method Registration . . . . . . . . . . . . . . . . . 74 11.5. HTTP2-Settings Header Field Registration . . . . . . . . . 77
11.7. The 421 Not Authoritative HTTP Status Code . . . . . . . . 74 11.6. PRI Method Registration . . . . . . . . . . . . . . . . . 77
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 74 11.7. The 421 (Misdirected Request) HTTP Status Code . . . . . . 78
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 75 11.8. The h2c Upgrade Token . . . . . . . . . . . . . . . . . . 78
13.1. Normative References . . . . . . . . . . . . . . . . . . . 75 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 78
13.2. Informative References . . . . . . . . . . . . . . . . . . 77 12.1. Normative References . . . . . . . . . . . . . . . . . . . 78
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 78 12.2. Informative References . . . . . . . . . . . . . . . . . . 80
A.1. Since draft-ietf-httpbis-http2-13 . . . . . . . . . . . . 78 Appendix A. TLS 1.2 Cipher Suite Black List . . . . . . . . . . . 81
A.2. Since draft-ietf-httpbis-http2-12 . . . . . . . . . . . . 78 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 93
A.3. Since draft-ietf-httpbis-http2-11 . . . . . . . . . . . . 78
A.4. Since draft-ietf-httpbis-http2-10 . . . . . . . . . . . . 79
A.5. Since draft-ietf-httpbis-http2-09 . . . . . . . . . . . . 79
A.6. Since draft-ietf-httpbis-http2-08 . . . . . . . . . . . . 80
A.7. Since draft-ietf-httpbis-http2-07 . . . . . . . . . . . . 80
A.8. Since draft-ietf-httpbis-http2-06 . . . . . . . . . . . . 80
A.9. Since draft-ietf-httpbis-http2-05 . . . . . . . . . . . . 80
A.10. Since draft-ietf-httpbis-http2-04 . . . . . . . . . . . . 80
A.11. Since draft-ietf-httpbis-http2-03 . . . . . . . . . . . . 81
A.12. Since draft-ietf-httpbis-http2-02 . . . . . . . . . . . . 81
A.13. Since draft-ietf-httpbis-http2-01 . . . . . . . . . . . . 81
A.14. Since draft-ietf-httpbis-http2-00 . . . . . . . . . . . . 82
A.15. 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 ([RFC7230], Section protocol. However, the way HTTP/1.1 uses the underlying transport
3) was designed to be implemented with the tools at hand in the ([RFC7230], Section 6) has several characteristics that have a
1990s, not modern Web application performance. As such it has negative overall effect on application performance today.
several characteristics that have a negative overall effect on
application performance today.
In particular, HTTP/1.0 only allows one request to be outstanding at In particular, HTTP/1.0 allowed only one request to be outstanding at
a time on a given connection. HTTP/1.1 pipelining only partially a time on a given TCP connection. HTTP/1.1 added request pipelining,
addressed request concurrency and suffers from head-of-line blocking. but this only partially addressed request concurrency and still
Therefore, clients that need to make many requests typically use suffers from head-of-line blocking. Therefore, HTTP/1.0 and HTTP/1.1
multiple connections to a server in order to reduce latency. clients that need to make many requests use multiple connections to a
server in order to achieve concurrency and thereby reduce latency.
Furthermore, HTTP/1.1 header fields are often repetitive and verbose, Furthermore, HTTP header fields are often repetitive and verbose,
which, in addition to generating more or larger network packets, can causing unnecessary network traffic as well as causing the initial
cause the small initial TCP [TCP] congestion window to quickly fill. TCP [TCP] congestion window to quickly fill. This can result in
This can result in excessive latency when multiple requests are made excessive latency when multiple requests are made on a new TCP
on a single new TCP connection. connection.
This specification addresses these issues by defining an optimized HTTP/2 addresses these issues by defining an optimized mapping of
mapping of HTTP's semantics to an underlying connection. HTTP's semantics to an underlying connection. Specifically, it
Specifically, it allows interleaving of request and response messages allows interleaving of request and response messages on the same
on the same connection and uses an efficient coding for HTTP header connection and uses an efficient coding for HTTP header fields. It
fields. It also allows prioritization of requests, letting more also allows prioritization of requests, letting more important
important requests complete more quickly, further improving requests complete more quickly, further improving performance.
performance.
The resulting protocol is designed to be more friendly to the The resulting protocol is more friendly to the network because fewer
network, because fewer TCP connections can be used in comparison to TCP connections can be used in comparison to HTTP/1.x. This means
HTTP/1.x. This means less competition with other flows, and longer- less competition with other flows and longer-lived connections, which
lived connections, which in turn leads to better utilization of in turn lead to better utilization of available network capacity.
available network capacity.
Finally, this encapsulation also enables more efficient processing of Finally, HTTP/2 also enables more efficient processing of messages
messages through use of binary message framing. 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 type serves a different purpose. For example, HEADERS and DATA frame type serves a different purpose. For example, HEADERS and DATA
frames form the basis of HTTP requests and responses (Section 8.1); frames form the basis of HTTP requests and responses (Section 8.1);
other frame types like SETTINGS, WINDOW_UPDATE, and PUSH_PROMISE are other frame types like SETTINGS, WINDOW_UPDATE, and 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 exchange associated with its own stream (Section 5).
are largely independent of each other, so a blocked or stalled Streams are largely independent of each other, so a blocked or
request does not prevent progress on other requests. stalled request or response does not prevent progress on other
streams.
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 efficiently use multiplexed streams. Flow control (Section 5.2)
to ensure that only data that can be used by a receiver is helps 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
resources can be directed to the most important requests first. resources can be directed to the most important streams first.
HTTP/2 adds a new interaction mode, whereby a server can push HTTP/2 adds a new interaction mode whereby a server can push
responses to a client (Section 8.2). Server push allows a server to responses to a client (Section 8.2). Server push allows a server to
speculatively send a client data that the server anticipates the speculatively send data to a client 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). Because HTTP header fields used in a connection can contain large
HTTP requests can be highly redundant, so compression can reduce the amounts of redundant data, frames that contain them are compressed
size of requests and responses significantly. (Section 4.3). This has especially advantageous impact upon request
sizes in the common case, allowing many requests to be compressed
into one packet.
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 frame (Section 4) and stream (Section 5) layers describe the
the way HTTP/2 frames are structured and formed into multiplexed way HTTP/2 frames are structured and formed into multiplexed
streams. streams.
o Frame (Section 6) and error (Section 7) definitions include o Frame (Section 6) and error (Section 7) definitions include
details of the frame and error types used in HTTP/2. details of the frame and error types used in HTTP/2.
o HTTP mappings (Section 8) and additional requirements (Section 9) o HTTP mappings (Section 8) and additional requirements (Section 9)
describe how HTTP semantics are expressed using frames and describe how HTTP semantics are expressed using frames and
streams. streams.
While some of the frame and stream layer concepts are isolated from While some of the frame and stream layer concepts are isolated from
HTTP, the intent is not to define a completely generic framing layer. HTTP, this specification does not define a completely generic frame
The framing and streams layers are tailored to the needs of the HTTP layer. The frame and stream layers are tailored to the needs of the
protocol and server push. HTTP protocol and server push.
2.2. Conventions and Terminology 2.2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
All numeric values are in network byte order. Values are unsigned All numeric values are in network byte order. Values are unsigned
unless otherwise indicated. Literal values are provided in decimal unless otherwise indicated. Literal values are provided in decimal
or hexadecimal as appropriate. Hexadecimal literals are prefixed or hexadecimal as appropriate. Hexadecimal literals are prefixed
with "0x" to distinguish them from decimal literals. with "0x" to distinguish them from decimal literals.
The following terms are used: The following terms are used:
client: The endpoint initiating the HTTP/2 connection. client: The endpoint that initiates an HTTP/2 connection. Clients
send HTTP requests and receive HTTP responses.
connection: A transport-level connection between two endpoints. connection: A transport-layer connection between two endpoints.
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 octets structured according to the frame type.
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 that accepts an HTTP/2 connection. Servers
receive HTTP requests and send HTTP responses.
stream: A bi-directional flow of frames across a virtual channel stream: A bidirectional flow of frames 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" Finally, the terms "gateway", "intermediary", "proxy", and "tunnel"
are defined in Section 2.3 of [RFC7230]. are defined in Section 2.3 of [RFC7230]. Intermediaries act as both
client and server at different times.
The term "payload body" is defined in Section 3.3 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-layer 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
"https://example.com/bar" are required to first discover whether the "https://example.com/bar" are required to first discover whether the
upstream server (the immediate peer to which the client wishes to upstream server (the immediate peer to which the client wishes to
establish a connection) supports HTTP/2. establish a connection) supports HTTP/2.
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
[TLS12]. This identifier is used in the TLS application layer Transport Layer Security (TLS) [TLS12]. This identifier is used
protocol negotiation extension (ALPN) [TLS-ALPN] field and any in the TLS application-layer protocol negotiation (ALPN) extension
place that HTTP/2 over TLS is identified. [TLS-ALPN] field and in any place where HTTP/2 over TLS is
identified.
The "h2" string is serialized into an ALPN protocol identifier as The "h2" string is serialized into an ALPN protocol identifier as
the two octet sequence: 0x68, 0x32. the two-octet sequence: 0x68, 0x32.
o The string "h2c" identifies the protocol where HTTP/2 is run over o The string "h2c" identifies the protocol where HTTP/2 is run over
cleartext TCP. This identifier is used in the HTTP/1.1 Upgrade cleartext TCP. This identifier is used in the HTTP/1.1 Upgrade
header field and any place that HTTP/2 over TCP is identified. header field and in any place where HTTP/2 over TCP is identified.
Negotiating "h2" or "h2c" implies the use of the transport, security,
framing and message semantics described in this document.
[[anchor3: RFC Editor's Note: please remove the remainder of this
section prior to the publication of a final version of this
document.]]
Only implementations of the final, published RFC can identify
themselves as "h2" or "h2c". Until such an RFC exists,
implementations MUST NOT identify themselves using these strings.
Examples and text throughout the rest of this document use "h2" as a
matter of editorial convenience only. Implementations of draft
versions MUST NOT identify using this string.
Implementations of draft versions of the protocol MUST add the string The "h2c" string is reserved from the ALPN identifier space but
"-" and the corresponding draft number to the identifier. For describes a protocol that does not use TLS.
example, draft-ietf-httpbis-http2-11 over TLS is identified using the
string "h2-11".
Non-compatible experiments that are based on these draft versions Negotiating "h2" or "h2c" implies the use of the transport, security,
MUST append the string "-" and an experiment name to the identifier. framing, and message semantics described in this document.
For example, an experimental implementation of packet mood-based
encoding based on draft-ietf-httpbis-http2-09 might identify itself
as "h2-09-emo". Note that any label MUST conform to the "token"
syntax defined in Section 3.2.6 of [RFC7230]. Experimenters are
encouraged to coordinate their experiments on the ietf-http-wg@w3.org
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 for an "http" URI without prior
knowledge about support for HTTP/2 uses the HTTP Upgrade mechanism knowledge about support for HTTP/2 on the next hop uses the HTTP
(Section 6.7 of [RFC7230]). The client makes an HTTP/1.1 request Upgrade mechanism (Section 6.7 of [RFC7230]). The client does so by
that includes an Upgrade header field identifying HTTP/2 with the making an HTTP/1.1 request that includes an Upgrade header field with
"h2c" token. The HTTP/1.1 request MUST include exactly one HTTP2- the "h2c" token. Such an 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 / 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 a payload 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 can block the use of the connection until it is completely
completely sent. sent.
If concurrency of an initial request with subsequent requests is If concurrency of an initial request with subsequent requests is
important, a small request can be used to perform the upgrade to important, an OPTIONS request can be used to perform the upgrade to
HTTP/2, at the cost of an additional round-trip. HTTP/2, at the cost of an additional round trip.
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. A server MUST ignore an "h2" token in an Upgrade header field.
Presence of a token with "h2" implies HTTP/2 over TLS, which is Presence of a token with "h2" implies HTTP/2 over TLS, which is
instead negotiated as described in Section 3.3. 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 accepts 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.
For example:
HTTP/1.1 101 Switching Protocols HTTP/1.1 101 Switching Protocols
Connection: Upgrade Connection: Upgrade
Upgrade: h2c Upgrade: h2c
[ HTTP/2 connection ... [ HTTP/2 connection ...
The first HTTP/2 frame sent by the server is a SETTINGS frame The first HTTP/2 frame sent by the server MUST be a server connection
(Section 6.5). Upon receiving the 101 response, the client sends a preface (Section 3.5) consisting of a SETTINGS frame (Section 6.5).
connection preface (Section 3.5), which includes a SETTINGS frame. Upon receiving the 101 response, the client MUST send a connection
preface (Section 3.5), which includes a SETTINGS frame.
The HTTP/1.1 request that is sent prior to upgrade is assigned stream The HTTP/1.1 request that is sent prior to upgrade is assigned a
identifier 1 and is assigned default priority values (Section 5.3.5). stream identifier of 1 (see Section 5.1.1) with default priority
Stream 1 is implicitly half closed from the client toward the server, values (Section 5.3.5). Stream 1 is implicitly "half-closed" from
since the request is completed as an HTTP/1.1 request. After the client toward the server (see Section 5.1), since the request is
commencing the HTTP/2 connection, stream 1 is used for the response. completed as an HTTP/1.1 request. After 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 connection-specific header field that includes parameters that
HTTP/2 connection, provided in anticipation of the server accepting govern the HTTP/2 connection, provided in anticipation of the server
the request to upgrade. accepting the request to upgrade.
HTTP2-Settings = token68 HTTP2-Settings = token68
A server MUST reject an attempt to upgrade if this header field is A server MUST NOT upgrade the connection to HTTP/2 if this header
not present. A server MUST NOT send this header field. field is not present or if more than one is 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
[RFC7235]. [RFC7235].
As a hop-by-hop header field, the "Connection" header field MUST Since the upgrade is only intended to apply to the immediate
include a value of "HTTP2-Settings" in addition to "Upgrade" when connection, a client sending the HTTP2-Settings header field MUST
upgrading to HTTP/2. also send "HTTP2-Settings" as a connection option in the Connection
header field to prevent it from being forwarded (see Section 6.1 of
[RFC7230]).
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. Explicit acknowledgement of these settings
(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 acknowledgement. Providing these values in the upgrade
request ensures that the protocol does not require default values for request gives a client an opportunity to provide parameters prior to
the above SETTINGS parameters, and gives a client an opportunity to receiving any frames from the server.
provide other parameters prior to receiving any frames from the
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 uses TLS [TLS12] with
knowledge about support for HTTP/2 uses TLS [TLS12] with the the application-layer protocol negotiation (ALPN) extension
application layer protocol negotiation extension [TLS-ALPN]. [TLS-ALPN].
HTTP/2 over TLS uses the "h2" application token. The "h2c" token HTTP/2 over TLS uses the "h2" protocol identifier. The "h2c"
MUST NOT be sent by a client or selected by a server. protocol identifier MUST NOT be sent by a client or selected by a
server; the "h2c" protocol identifier describes a protocol that does
not use TLS.
Once TLS negotiation is complete, both the client and the server send Once TLS negotiation is complete, both the client and the server MUST
a connection preface (Section 3.5). send a connection preface (Section 3.5).
3.4. Starting HTTP/2 with Prior Knowledge 3.4. Starting HTTP/2 with Prior Knowledge
A client can learn that a particular server supports HTTP/2 by other A client can learn that a particular server supports HTTP/2 by other
means. For example, [ALT-SVC] describes a mechanism for advertising means. For example, [ALT-SVC] describes a mechanism for advertising
this capability. this capability.
A client MAY immediately send HTTP/2 frames to a server that is known A client MUST send the connection preface (Section 3.5) and then MAY
to support HTTP/2, after the connection preface (Section 3.5). A immediately send HTTP/2 frames to such a server; servers can identify
server can identify such a connection by the use of the "PRI" method these connections by the presence of the connection preface. This
in the connection preface. This only affects the establishment of only affects the establishment of HTTP/2 connections over cleartext
HTTP/2 connections over cleartext TCP; implementations that support TCP; implementations that support HTTP/2 over TLS MUST use protocol
HTTP/2 over TLS MUST use protocol negotiation in TLS [TLS-ALPN]. negotiation in TLS [TLS-ALPN].
Prior support for HTTP/2 is not a strong signal that a given server Likewise, the server MUST send a connection preface (Section 3.5).
will support HTTP/2 for future connections. It is possible for
server configurations to change; for configurations to differ between Without additional information, prior support for HTTP/2 is not a
instances in clustered server; or network conditions to change. strong signal that a given server will support HTTP/2 for future
connections. For example, it is possible for server configurations
to change, for configurations to differ between instances in
clustered servers, or for 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 In HTTP/2, each endpoint is required to send a connection preface as
will be used by both peers, each endpoint MUST send a connection a final confirmation of the protocol in use and to establish the
preface as a final confirmation and to establish the initial SETTINGS initial settings for the HTTP/2 connection. The client and server
parameters for the HTTP/2 connection. each send a different connection preface.
The client connection preface starts with a sequence of 24 octets, The client connection preface starts with a sequence of 24 octets,
which in hex notation are: which in hex notation is:
0x505249202a20485454502f322e300d0a0d0a534d0d0a0d0a 0x505249202a20485454502f322e300d0a0d0a534d0d0a0d0a
(the string "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"). This sequence is That is, the connection preface starts with the string "PRI *
followed by a SETTINGS frame (Section 6.5). The SETTINGS frame MAY HTTP/2.0\r\n\r\nSM\r\n\r\n"). This sequence MUST be followed by a
be empty. The client sends the client connection preface immediately SETTINGS frame (Section 6.5), which MAY be empty. The client sends
upon receipt of a 101 Switching Protocols response (indicating a the client connection preface immediately upon receipt of a 101
successful upgrade), or as the first application data octets of a TLS (Switching Protocols) response (indicating a successful upgrade) or
connection. If starting an HTTP/2 connection with prior knowledge of as the first application data octets of a TLS connection. If
server support for the protocol, the client connection preface is starting an HTTP/2 connection with prior knowledge of server support
sent upon connection establishment. for the protocol, the client connection preface is sent upon
connection establishment.
The client connection preface is selected so that a large Note: The client connection preface is selected so that a large
proportion of HTTP/1.1 or HTTP/1.0 servers and intermediaries do proportion of HTTP/1.1 or HTTP/1.0 servers and intermediaries do
not attempt to process further frames. Note that this does not not attempt to process further frames. Note that this does not
address the concerns raised in [TALKING]. address the concerns raised in [TALKING].
The server connection preface consists of a potentially empty The server connection preface consists of a potentially empty
SETTINGS frame (Section 6.5) that MUST be the first frame the server SETTINGS frame (Section 6.5) that MUST be the first frame the server
sends in the HTTP/2 connection. sends in the HTTP/2 connection.
The SETTINGS frames received from a peer as part of the connection
preface MUST be acknowledged (see Section 6.5.3) after sending the
connection preface.
To avoid unnecessary latency, clients are permitted to send To avoid unnecessary latency, clients are permitted to send
additional frames to the server immediately after sending the client additional frames to the server immediately after sending the client
connection preface, without waiting to receive the server connection connection preface, without waiting to receive the server connection
preface. It is important to note, however, that the server preface. It is important to note, however, that the server
connection preface SETTINGS frame might include parameters that connection preface SETTINGS frame might include parameters that
necessarily alter how a client is expected to communicate with the necessarily alter how a client is expected to communicate with the
server. Upon receiving the SETTINGS frame, the client is expected to server. Upon receiving the SETTINGS frame, the client is expected to
honor any parameters established. In some configurations, it is honor any parameters established. In some configurations, it is
possible for the server to transmit SETTINGS before the client, possible for the server to transmit SETTINGS before the client sends
providing an opportunity to avoid this issue. additional frames, providing an opportunity to avoid this issue.
Clients and servers MUST terminate the TCP connection if either peer Clients and servers MUST treat an invalid connection preface as a
does not begin with a valid connection preface. A GOAWAY frame connection error (Section 5.4.1) of type PROTOCOL_ERROR. A GOAWAY
(Section 6.8) can be omitted if it is clear that the peer is not frame (Section 6.8) MAY be omitted in this case, since an invalid
using HTTP/2. preface indicates that the peer is not using HTTP/2.
4. HTTP Frames 4. HTTP Frames
Once the HTTP/2 connection is established, endpoints can begin Once the HTTP/2 connection is established, endpoints can begin
exchanging frames. exchanging frames.
4.1. Frame Format 4.1. Frame Format
All frames begin with a fixed 9-octet header followed by a variable- All frames begin with a fixed 9-octet header followed by a variable-
length payload. length payload.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (24) | | Length (24) |
+---------------+---------------+---------------+ +---------------+---------------+---------------+
| Type (8) | Flags (8) | | Type (8) | Flags (8) |
+-+-+-----------+---------------+-------------------------------+ +-+-------------+---------------+-------------------------------+
|R| Stream Identifier (31) | |R| Stream Identifier (31) |
+=+=============================================================+ +=+=============================================================+
| Frame Payload (0...) ... | Frame Payload (0...) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Frame Layout Figure 1: Frame Layout
The fields of the frame header are defined as: The fields of the frame header are defined as:
Length: The length of the frame payload expressed as an unsigned 24- Length: The length of the frame payload expressed as an unsigned 24-
bit integer. Values greater than 2^14 (16,384) MUST NOT be sent bit integer. Values greater than 2^14 (16,384) MUST NOT be sent
unless the receiver has set a larger value for unless the receiver has set a larger value for
SETTINGS_MAX_FRAME_SIZE. SETTINGS_MAX_FRAME_SIZE.
The 9 octets of the frame header are not included in this value. The 9 octets of the frame header are not included in this value.
Type: The 8-bit type of the frame. The frame type determines the Type: The 8-bit type of the frame. The frame type determines the
format and semantics of the frame. Implementations MUST ignore format and semantics of the frame. Implementations MUST ignore
and discard any frame that has a type that is unknown. and discard any frame that has a type that is unknown.
Flags: An 8-bit field reserved for frame-type specific boolean Flags: An 8-bit field reserved for boolean flags specific to the
flags. frame type.
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 (0x0) 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 (0x0) when sending and MUST be
when receiving. ignored when receiving.
Stream Identifier: A 31-bit stream identifier (see Section 5.1.1). Stream Identifier: A stream identifier (see Section 5.1.1) expressed
The value 0 is reserved for frames that are associated with the as an unsigned 31-bit integer. The value 0x0 is reserved for
connection as a whole as opposed to an individual stream. frames that are associated with the 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 size of a frame payload is limited by the maximum size that a The size of a frame payload is limited by the maximum size that a
receiver advertises in the SETTINGS_MAX_FRAME_SIZE setting. This receiver advertises in the SETTINGS_MAX_FRAME_SIZE setting. This
setting can have any value between 2^14 (16,384) and 2^24-1 setting can have any value between 2^14 (16,384) and 2^24-1
(16,777,215) octets, inclusive. (16,777,215) octets, inclusive.
All implementations MUST be capable of receiving and minimally All implementations MUST be capable of receiving and minimally
processing frames up to 2^14 octets in length, plus the 9 octet frame processing frames up to 2^14 octets in length, plus the 9-octet frame
header (Section 4.1). The size of the frame header is not included header (Section 4.1). The size of the frame header is not included
when describing frame sizes. when describing frame sizes.
Note: Certain frame types, such as PING (Section 6.7), impose Note: Certain frame types, such as PING (Section 6.7), impose
additional limits on the amount of payload data allowed. additional limits on the amount of payload data allowed.
If a frame size exceeds any defined limit, or is too small to contain An endpoint MUST send an error code of FRAME_SIZE_ERROR if a frame
mandatory frame data, the endpoint MUST send a FRAME_SIZE_ERROR exceeds the size defined in SETTINGS_MAX_FRAME_SIZE, exceeds any
error. A frame size error in a frame that could alter the state of limit defined for the frame type, or is too small to contain
the entire connection MUST be treated as a connection error mandatory frame data. A frame size error in a frame that could alter
(Section 5.4.1); this includes any frame carrying a header block the state of the entire connection MUST be treated as a connection
(Section 4.3) (that is, HEADERS, PUSH_PROMISE, and CONTINUATION), error (Section 5.4.1); this includes any frame carrying a header
SETTINGS, and any WINDOW_UPDATE frame with a stream identifier of 0. block (Section 4.3) (that is, HEADERS, PUSH_PROMISE, and
CONTINUATION), SETTINGS, and any frame with a stream identifier of 0.
Endpoints are not obligated to use all available space in a frame. Endpoints are not obligated to use all available space in a frame.
Responsiveness can be improved by using frames that are smaller than Responsiveness can be improved by using frames that are smaller than
the permitted maximum size. Sending large frames can result in the permitted maximum size. Sending large frames can result in
delays in sending maintenance frames, such RST_STREAM, WINDOW_UPDATE, delays in sending time-sensitive frames (such as RST_STREAM,
or PRIORITY, which if blocked by the transmission of a large frame, WINDOW_UPDATE, or PRIORITY), which, if blocked by the transmission of
could affect performance. a large frame, could affect performance.
4.3. Header Compression and Decompression 4.3. Header Compression and Decompression
A header field in HTTP/2 is a name with one or more associated Just as in HTTP/1, a header field in HTTP/2 is a name with one or
values. They are used within HTTP request and response messages as more associated values. Header fields are used within HTTP request
well as server push operations (see Section 8.2). and response messages as well as in server push operations (see
Section 8.2).
Header lists are collections of zero or more header fields. When Header lists are collections of zero or more header fields. When
transmitted over a connection, a header list is serialized into a transmitted over a connection, a header list is serialized into a
header block using HTTP Header Compression [COMPRESSION]. The header block using HTTP header compression [COMPRESSION]. The
serialized header block is then divided into one or more octet serialized header block is then divided into one or more octet
sequences, called header block fragments, and transmitted within the sequences, called header block fragments, and transmitted within the
payload of HEADERS (Section 6.2), PUSH_PROMISE (Section 6.6) or payload of HEADERS (Section 6.2), PUSH_PROMISE (Section 6.6), or
CONTINUATION (Section 6.10) frames. CONTINUATION (Section 6.10) frames.
The Cookie header field [COOKIE] is treated specially by the HTTP The Cookie header field [COOKIE] is treated specially by the HTTP
mapping (see Section 8.1.2.5). mapping (see Section 8.1.2.5).
A receiving endpoint reassembles the header block by concatenating A receiving endpoint reassembles the header block by concatenating
its fragments, then decompresses the block to reconstruct the header its fragments and then decompresses the block to reconstruct the
list. header list.
A complete header block consists of either: A complete header block consists of either:
o a single HEADERS or PUSH_PROMISE frame, with the END_HEADERS flag o a single HEADERS or PUSH_PROMISE frame, with the END_HEADERS flag
set, or set, or
o a HEADERS or PUSH_PROMISE frame with the END_HEADERS flag cleared o a HEADERS or PUSH_PROMISE frame with the END_HEADERS flag cleared
and one or more CONTINUATION frames, where the last CONTINUATION and one or more CONTINUATION frames, where the last CONTINUATION
frame has the END_HEADERS flag set. frame has the END_HEADERS flag set.
Header compression is stateful, using a single compression context Header compression is stateful. One compression context and one
for the entire connection. Each header block is processed as a decompression context are used for the entire connection. A decoding
discrete unit. Header blocks MUST be transmitted as a contiguous error in a header block MUST be treated as a connection error
sequence of frames, with no interleaved frames of any other type or (Section 5.4.1) of type COMPRESSION_ERROR.
from any other stream. The last frame in a sequence of HEADERS or
CONTINUATION frames MUST have the END_HEADERS flag set. The last Each header block is processed as a discrete unit. Header blocks
frame in a sequence of PUSH_PROMISE or CONTINUATION frames MUST have MUST be transmitted as a contiguous sequence of frames, with no
the END_HEADERS flag set. This allows a header block to be logically interleaved frames of any other type or from any other stream. The
equivalent to a single frame. last frame in a sequence of HEADERS or CONTINUATION frames has the
END_HEADERS flag set. The last frame in a sequence of PUSH_PROMISE
or CONTINUATION frames has 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
reassemble header blocks and perform decompression even if the frames needs to reassemble header blocks and perform decompression even if
are to be discarded. A receiver MUST terminate the connection with a the frames are to be discarded. A receiver MUST terminate the
connection error (Section 5.4.1) of type COMPRESSION_ERROR if it does connection with a connection error (Section 5.4.1) of type
not decompress a header block. COMPRESSION_ERROR if it does not decompress a header block.
5. Streams and Multiplexing 5. Streams and Multiplexing
A "stream" is an independent, bi-directional sequence of frames A "stream" is an independent, bidirectional sequence of frames
exchanged between the client and server within an HTTP/2 connection. exchanged between the client and server within an HTTP/2 connection.
Streams have several important characteristics: Streams have several important characteristics:
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 on 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. In Recipients process frames in the order they are received. In
particular, the order of HEADERS, and DATA frames is semantically particular, the order of HEADERS and DATA frames is semantically
significant. significant.
o Streams are identified by an integer. Stream identifiers are o Streams are identified by an integer. Stream identifiers are
assigned to streams by the endpoint initiating the stream. assigned to streams by the endpoint initiating the stream.
5.1. Stream States 5.1. Stream States
The lifecycle of a stream is shown in Figure 1. The lifecycle of a stream is shown in Figure 2.
+--------+ +--------+
PP | | PP send PP | | recv PP
,--------| idle |--------. ,--------| idle |--------.
/ | | \ / | | \
v +--------+ v v +--------+ v
+----------+ | +----------+ +----------+ | +----------+
| | | H | | | | | send H / | |
,---| reserved | | | reserved |---. ,------| reserved | | recv H | reserved |------.
| | (local) | v | (remote) | | | | (local) | | | (remote) | |
| +----------+ +--------+ +----------+ | | +----------+ v +----------+ |
| | ES | | ES | | | | +--------+ | |
| | H ,-------| open |-------. | H | | | recv ES | | send ES | |
| | / | | \ | | | send H | ,-------| open |-------. | recv H |
| v v +--------+ v v | | | / | | \ | |
| +----------+ | +----------+ | | v v +--------+ v v |
| | half | | | half | | | +----------+ | +----------+ |
| | closed | | R | closed | | | | half | | | half | |
| | (remote) | | | (local) | | | | closed | | send R / | closed | |
| +----------+ | +----------+ | | | (remote) | | recv R | (local) | |
| | v | | | +----------+ | +----------+ |
| | ES / R +--------+ ES / R | | | | | | |
| `----------->| |<-----------' | | | send ES / | recv ES / | |
| R | closed | R | | | send R / v send R / | |
`-------------------->| |<--------------------' | | recv R +--------+ recv R | |
+--------+ | send R / `----------->| |<-----------' send R / |
| recv R | closed | recv R |
`----------------------->| |<----------------------'
+--------+
send: endpoint sends this frame
recv: endpoint receives this frame
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 2: Stream States
Figure 1: Stream States Note that this diagram shows stream state transitions and the frames
and flags that affect those transitions only. In this regard,
Note that this diagram shows stream state transitions and frames that CONTINUATION frames do not result in state transitions; they are
affect those transitions only. In this regard, CONTINUATION frames effectively part of the HEADERS or PUSH_PROMISE that they follow.
do not result in state transitions and are effectively part of the For the purpose of state transitions, the END_STREAM flag is
HEADERS or PUSH_PROMISE that they follow. processed as a separate event to the frame that bears it; a HEADERS
frame with the END_STREAM flag set can cause two state transitions.
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:
All streams start in the "idle" state. In this state, no frames All streams start in the "idle" state.
have been exchanged.
The following transitions are valid from this state: The following transitions are valid from this state:
* Sending or receiving a HEADERS frame causes the stream to * Sending or receiving a HEADERS frame causes the stream to
become "open". The stream identifier is selected as described become "open". The stream identifier is selected as described
in Section 5.1.1. The same HEADERS frame can also cause a in Section 5.1.1. The same HEADERS frame can also cause a
stream to immediately become "half closed". stream to immediately become "half-closed".
* Sending a PUSH_PROMISE frame marks the associated stream for * Sending a PUSH_PROMISE frame on another stream reserves the
later use. The stream state for the reserved stream idle stream that is identified for later use. The stream state
transitions to "reserved (local)". for the reserved stream transitions to "reserved (local)".
* Receiving a PUSH_PROMISE frame marks the associated stream as * Receiving a PUSH_PROMISE frame on another stream reserves an
reserved by the remote peer. The state of the stream becomes idle stream that is identified for later use. The stream state
"reserved (remote)". for the reserved stream transitions to "reserved (remote)".
* Note that the PUSH_PROMISE frame is not sent on the idle stream
but references the newly reserved stream in the Promised Stream
ID field.
Receiving any frame other than HEADERS or PRIORITY on a stream in
this state MUST be treated as a connection error (Section 5.4.1)
of type PROTOCOL_ERROR.
reserved (local): reserved (local):
A stream in the "reserved (local)" state is one that has been A stream in the "reserved (local)" state is one that has been
promised by sending a PUSH_PROMISE frame. A PUSH_PROMISE frame promised by sending a PUSH_PROMISE frame. A PUSH_PROMISE frame
reserves an idle stream by associating the stream with an open reserves an idle stream by associating the stream with an open
stream that was initiated by the remote peer (see Section 8.2). stream that was initiated by the remote peer (see Section 8.2).
In this state, only the following transitions are possible: In this state, only the following transitions are possible:
* The endpoint can send a HEADERS frame. This causes the stream * The endpoint can send a HEADERS frame. This causes the stream
to open in a "half closed (remote)" state. to open in a "half-closed (remote)" state.
* Either endpoint can send a RST_STREAM frame to cause the stream * Either endpoint can send a RST_STREAM frame to cause the stream
to become "closed". This releases the stream reservation. to become "closed". This releases the stream reservation.
An endpoint MUST NOT send frames other than HEADERS or RST_STREAM An endpoint MUST NOT send any type of frame other than HEADERS,
in this state. RST_STREAM, or PRIORITY in this state.
A PRIORITY frame MAY be received in this state. Receiving any A PRIORITY or WINDOW_UPDATE frame MAY be received in this state.
frames other than RST_STREAM, or PRIORITY MUST be treated as a Receiving any type of frame other than RST_STREAM, PRIORITY, or
WINDOW_UPDATE on a stream in this state MUST be treated as a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
reserved (remote): reserved (remote):
A stream in the "reserved (remote)" state has been reserved by a A stream in the "reserved (remote)" state has been reserved by a
remote peer. remote peer.
In this state, only the following transitions are possible: In this state, only the following transitions are possible:
* Receiving a HEADERS frame causes the stream to transition to * Receiving a HEADERS frame causes the stream to transition to
"half closed (local)". "half-closed (local)".
* Either endpoint can send a RST_STREAM frame to cause the stream * Either endpoint can send a RST_STREAM frame to cause the stream
to become "closed". This releases the stream reservation. to become "closed". This releases the stream reservation.
An endpoint MAY send a PRIORITY frame in this state to An endpoint MAY send a PRIORITY frame in this state to
reprioritize the reserved stream. An endpoint MUST NOT send any reprioritize the reserved stream. An endpoint MUST NOT send any
other type of frame other than RST_STREAM or PRIORITY. type of frame other than RST_STREAM, WINDOW_UPDATE, or PRIORITY in
this state.
Receiving any other type of frame other than HEADERS or RST_STREAM Receiving any type of frame other than HEADERS, RST_STREAM, or
MUST be treated as a connection error (Section 5.4.1) of type PRIORITY on a stream in this state MUST be treated as a connection
PROTOCOL_ERROR. error (Section 5.4.1) of type PROTOCOL_ERROR.
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
flag causes the stream state to become "half closed (local)"; an END_STREAM flag causes the stream state to become "half-closed
endpoint receiving an END_STREAM flag causes the stream state to (local)"; an endpoint receiving an END_STREAM flag causes the
become "half closed (remote)". stream state to become "half-closed (remote)".
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. Only WINDOW_UPDATE, PRIORITY and RST_STREAM for sending frames other than WINDOW_UPDATE, PRIORITY, and
frames can be sent in this state. RST_STREAM.
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 RST_STREAM frame.
A receiver can ignore WINDOW_UPDATE frames in this state, which An endpoint can receive any type of frame in this state.
might arrive for a short period after a frame bearing the Providing flow-control credit using WINDOW_UPDATE frames is
END_STREAM flag is sent. necessary to continue receiving flow-controlled frames. In this
state, a receiver can ignore WINDOW_UPDATE frames, which might
arrive for a short period after a frame bearing the END_STREAM
flag is sent.
PRIORITY frames received in this state are used to reprioritize PRIORITY frames received in this state are used to reprioritize
streams that depend on the current stream. streams that depend on the identified 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.
performs flow control.
If an endpoint receives additional frames for a stream that is in If an endpoint receives additional frames, other than
this state, other than WINDOW_UPDATE, PRIORITY or RST_STREAM, it WINDOW_UPDATE, PRIORITY, or RST_STREAM, for a stream that is in
MUST respond with a stream error (Section 5.4.2) of type this state, it MUST respond with a stream error (Section 5.4.2) of
STREAM_CLOSED. type STREAM_CLOSED.
A stream that is "half closed (remote)" can be used by the A stream that is "half-closed (remote)" can be used by the
endpoint to send frames of any type. In this state, the endpoint endpoint to send frames of any type. In this state, the endpoint
continues to observe advertised stream level flow control limits continues to observe advertised stream-level flow-control limits
(Section 5.2). (Section 5.2).
A stream can transition from this state to "closed" by sending a A stream can transition from this state to "closed" by sending a
frame that contains an END_STREAM flag, or when either peer sends frame that contains an END_STREAM flag or when either peer sends a
a RST_STREAM frame. 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 other than PRIORITY on a closed
that receives any frame other than PRIORITY after receiving a stream. An endpoint that receives any frame other than PRIORITY
RST_STREAM MUST treat that as a stream error (Section 5.4.2) of after receiving a RST_STREAM MUST treat that as a stream error
type STREAM_CLOSED. Similarly, an endpoint that receives any (Section 5.4.2) of type STREAM_CLOSED. Similarly, an endpoint
frames after receiving a frame with the END_STREAM flag set MUST that receives any frames after receiving a frame with the
treat that as a connection error (Section 5.4.1) of type END_STREAM flag set MUST treat that as a connection error
STREAM_CLOSED, unless the frame is permitted as described below. (Section 5.4.1) of type STREAM_CLOSED, unless the frame is
permitted as described below.
WINDOW_UPDATE or RST_STREAM frames can be received in this state WINDOW_UPDATE or RST_STREAM frames can be received in this state
for a short period after a DATA or HEADERS frame containing an for a short period after a DATA or HEADERS frame containing an
END_STREAM flag is sent. Until the remote peer receives and END_STREAM flag is sent. Until the remote peer receives and
processes the frame bearing the END_STREAM flag, it might send processes RST_STREAM or the frame bearing the END_STREAM flag, it
frames of these types. Endpoints MUST ignore WINDOW_UPDATE or might send frames of these types. Endpoints MUST ignore
RST_STREAM frames received in this state, though endpoints MAY WINDOW_UPDATE or RST_STREAM frames received in this state, though
choose to treat frames that arrive a significant time after endpoints MAY choose to treat frames that arrive a significant
sending END_STREAM as a connection error (Section 5.4.1) of type time after sending END_STREAM as a connection error
PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
PRIORITY frames can be sent on closed streams to prioritize PRIORITY frames can be sent on closed streams to prioritize
streams that are dependent on the closed stream. Endpoints SHOULD streams that are dependent on the closed stream. Endpoints SHOULD
process PRIORITY frame, though they can be ignored if the stream process PRIORITY frames, though they can be ignored if the stream
has been removed from the dependency tree (see Section 5.3.4). 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
be withdrawn. An endpoint MUST ignore frames that it receives on cannot be withdrawn. An endpoint MUST ignore frames that it
closed streams after it has sent a RST_STREAM frame. An endpoint receives on closed streams after it has sent a RST_STREAM frame.
MAY choose to limit the period over which it ignores frames and An endpoint MAY choose to limit the period over which it ignores
treat frames that arrive after this time as being in error. frames and 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 stream. RST_STREAM is needed to close an unwanted promised stream.
In the absence of more specific guidance elsewhere in this document, In the absence of more specific guidance elsewhere in this document,
implementations SHOULD treat the receipt of a message that is not implementations SHOULD treat the receipt of a frame 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. Note that PRIORITY can
be sent and received in any stream state. Frames of unknown types
are ignored.
An example of the state transitions for an HTTP request/response An example of the state transitions for an HTTP request/response
exchange can be found in Section 8.1. An example of the state exchange can be found in Section 8.1. An example of the state
transitions for server push can be found in Section 8.2.1 and transitions for server push can be found in Sections 8.2.1 and 8.2.2.
Section 8.2.2.
5.1.1. Stream Identifiers 5.1.1. Stream Identifiers
Streams are identified with an unsigned 31-bit integer. Streams Streams are identified with an unsigned 31-bit integer. Streams
initiated by a client MUST use odd-numbered stream identifiers; those initiated by a client MUST use odd-numbered stream identifiers; those
initiated by the server MUST use even-numbered stream identifiers. A initiated by the server MUST use even-numbered stream identifiers. A
stream identifier of zero (0x0) is used for connection control stream identifier of zero (0x0) is used for connection control
messages; the stream identifier zero cannot be used to establish a messages; the stream identifier of 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
reserved. This governs streams that are opened using a HEADERS frame reserved. This governs streams that are opened using a HEADERS frame
and streams that are reserved using PUSH_PROMISE. An endpoint that and streams that are reserved using PUSH_PROMISE. An endpoint that
receives an unexpected stream identifier MUST respond with a receives an unexpected stream identifier MUST respond with a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
skipping to change at page 21, line 37 skipping to change at page 22, line 17
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 parameter (see Section 6.5.2) within SETTINGS_MAX_CONCURRENT_STREAMS parameter (see Section 6.5.2) within
a SETTINGS frame. The maximum concurrent streams setting is specific a SETTINGS frame. The maximum concurrent streams setting is specific
to each endpoint and applies only to the peer that receives the to each endpoint and applies only to the peer that receives the
setting. That is, clients specify the maximum number of concurrent setting. That is, clients specify the maximum number of concurrent
streams the server can initiate, and servers specify the maximum streams the server can initiate, and servers specify the maximum
number of concurrent streams the client can initiate. number of concurrent streams the client can initiate.
Streams that are in the "open" state, or either of the "half closed" Streams that are in the "open" state or in either of the "half-
states count toward the maximum number of streams that an endpoint is closed" states count toward the maximum number of streams that an
permitted to open. Streams in any of these three states count toward endpoint is permitted to open. Streams in any of these three states
the limit advertised in the SETTINGS_MAX_CONCURRENT_STREAMS setting. count toward the limit advertised in the
Streams in either of the "reserved" states do not count toward the SETTINGS_MAX_CONCURRENT_STREAMS setting. Streams in either of the
stream limit. "reserved" states do not count toward the stream limit.
Endpoints MUST NOT exceed the limit set by their peer. An endpoint Endpoints MUST NOT exceed the limit set by their peer. An endpoint
that receives a HEADERS frame that causes their advertised concurrent that receives a HEADERS frame that causes its advertised concurrent
stream limit to be exceeded MUST treat this as a stream error 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 (Section 5.4.2) of type PROTOCOL_ERROR or REFUSED_STREAM. The choice
of error code determines whether the endpoint wishes to enable
automatic retry (see Section 8.1.4) for details).
An endpoint that wishes to reduce the value of
SETTINGS_MAX_CONCURRENT_STREAMS to a value that is below the current SETTINGS_MAX_CONCURRENT_STREAMS to a value that is below the current
number of open streams can either close streams that exceed the new number of open streams can either close streams that exceed the new
value or allow streams to complete. 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 (Section 6.9). 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 a variety of flow-control
flow control algorithms without requiring protocol changes. Flow algorithms to be used 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 specific to a connection. Both types of flow
control are between the endpoints of a single hop and not over
the entire end-to-end path.
2. Flow control is based on window update frames. Receivers 2. Flow control is based on WINDOW_UPDATE frames. Receivers
advertise how many bytes they are prepared to receive on a stream advertise how many octets they are prepared to receive on a
and for the entire connection. This is a credit-based scheme. stream and for the entire connection. This is a credit-based
scheme.
3. Flow control is directional with overall control provided by the 3. Flow control is directional with overall control provided by the
receiver. A receiver MAY choose to set any window size that it receiver. A receiver MAY choose to set any window size that it
desires for each stream and for the entire connection. A sender desires for each stream and for the entire connection. A sender
MUST respect flow control limits imposed by a receiver. Clients, MUST respect flow-control limits imposed by a receiver. Clients,
servers and intermediaries all independently advertise their flow servers, and intermediaries all independently advertise their
control window as a receiver and abide by the flow control limits flow-control window as a receiver and abide by the flow-control
set by their peer when sending. limits set by their peer when sending.
4. The initial value for the flow control window is 65,535 bytes for 4. The initial value for the flow-control window is 65,535 octets
both new streams and the overall connection. for both new streams and the overall connection.
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 defines only the format and semantics of the WINDOW_UPDATE 7. HTTP/2 defines only the format and semantics of the WINDOW_UPDATE
frame (Section 6.9). This document does not stipulate how a frame (Section 6.9). This document does not stipulate how a
receiver decides when to send this frame or the value that it receiver decides when to send this frame or the value that it
sends. Nor does it specify how a sender chooses to send packets. sends, nor does it specify how a sender chooses to send packets.
Implementations are able to select any algorithm that suits their Implementations are able to select any algorithm that suits their
needs. 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 to process data on one stream yet wants
continue to process other streams in the same connection. to 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 (2^31-1) and can maintain this
when new data is received. This effectively disables flow control window by sending a WINDOW_UPDATE frame when any data is received.
for that receiver. Conversely, a sender is always subject to the This effectively disables flow control for that receiver.
flow control window advertised by the receiver. Conversely, a sender is always subject to the flow-control window
advertised by the receiver.
Deployments with constrained resources (for example, memory) can 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 [RFC7323]).
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 read and acted upon. critical frames, such as WINDOW_UPDATE, are not read and acted upon.
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. At any other time, the PRIORITY frame
(Section 6.3) can be used to change the priority. (Section 6.3) can be used to change the priority of a stream.
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 to allocate resources when managing
streams. Most importantly, priority can be used to select streams concurrent streams. Most importantly, priority can be used to select
for transmitting frames when there is limited capacity for sending. streams 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.
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 a suggestion.
Prioritization information can be specified explicitly for streams as Prioritization information can be omitted from messages. Defaults
they are created using the HEADERS frame, or changed using the are used prior to any explicit values being provided (Section 5.3.5).
PRIORITY frame. Providing prioritization information is optional, so
default values are used if no explicit indicator is provided
(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 is given a stream A stream that is not dependent on any other stream is given a stream
dependency of 0x0. In other words, the non-existent stream 0 forms dependency of 0x0. In other words, the non-existent stream 0 forms
the root of the tree. the root of the tree.
A stream that depends on another stream is a dependent stream. The A stream that depends on another stream is a dependent stream. The
stream upon which a stream is dependent is a parent stream. A stream upon which a stream is dependent is a parent stream. A
dependency on a stream that is not currently in the tree - such as a dependency on a stream that is not currently in the tree -- such as a
stream in the "idle" state - results in the stream being given a stream in the "idle" state -- results in that stream being given a
default priority (Section 5.3.5). default priority (Section 5.3.5).
When assigning a dependency on another stream, the stream is added as When assigning a dependency on another stream, the stream is added as
a new dependency of the parent stream. Dependent streams that share a new dependency of the parent stream. Dependent streams that share
the same parent are not ordered with respect to each other. For the same parent are not ordered with respect to each other. For
example, if streams B and C are dependent on stream A, and if stream example, if streams B and C are dependent on stream A, and if stream
D is created with a dependency on stream A, this results in a D is created with a dependency on stream A, this results in a
dependency order of A followed by B, C, and D in any order. dependency order of A followed by B, C, and D in any order.
A A A A
/ \ ==> /|\ / \ ==> /|\
B C B D C B C B D C
Example of Default Dependency Creation Figure 3: 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 its parent stream, causing other dependencies to sole dependency of its parent stream, causing other dependencies to
become dependent on the prioritized stream. In the previous example, become dependent on the exclusive stream. In the previous example,
if stream D is created with an exclusive dependency on stream A, this if stream D is created with an exclusive dependency on stream A, this
results in D becoming the dependency parent of B and C. results in D becoming the dependency parent of B and C.
A A
A | A |
/ \ ==> D / \ ==> D
B C / \ B C / \
B C B C
Example of Exclusive Dependency Creation Figure 4: 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 all of the streams that it depends on (the allocated resources if either all of the streams that it depends on
chain of parent streams up to 0x0) are either closed, or it is not (the chain of parent streams up to 0x0) are closed or it is not
possible to make progress on them. possible to make progress on them.
A stream cannot depend on itself. An endpoint MUST treat this as a A stream cannot depend on itself. An endpoint MUST treat this as a
stream error (Section 5.4.2) of type PROTOCOL_ERROR. stream error (Section 5.4.2) of type PROTOCOL_ERROR.
5.3.2. Dependency Weighting 5.3.2. Dependency Weighting
All dependent streams are allocated an integer weight between 1 to All dependent streams are allocated an integer weight between 1 and
256 (inclusive). 256 (inclusive).
Streams with the same parent 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, stream C depends on stream A with weight 12,
if no progress can be made on A, stream B ideally receives one third and no progress can be made on stream A, stream B ideally receives
of the resources allocated to stream C. one-third of the resources allocated to stream C.
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
parent stream. parent stream.
Dependent streams move with their parent stream if the parent is Dependent streams move with their parent stream if the parent is
reprioritized. Setting a dependency with the exclusive flag for a reprioritized. Setting a dependency with the exclusive flag for a
reprioritized stream moves all the dependencies of the new parent reprioritized stream causes all the dependencies of the new parent
stream to become dependent on 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 dependent on the formerly dependent stream is first moved to be dependent on the
reprioritized stream's previous parent. The moved dependency retains reprioritized stream's previous parent. The moved dependency retains
its weight. its weight.
For example, consider an original dependency tree where B and C For example, consider an original dependency tree where B and C
depend on A, D and E depend on C, and F depends on D. If A is made depend on A, D and E depend on C, and F depends on D. If A is made
dependent on D, then D takes the place of A. All other dependency dependent on D, then D takes the place of A. All other dependency
relationships stay the same, except for F, which becomes dependent on relationships stay the same, except for F, which becomes dependent on
A if the reprioritization is exclusive. A if the reprioritization is exclusive.
? ? ? ? x x x x
| / \ | | | / \ | |
A D A D D A D A D D
/ \ / / \ / \ | / \ / / \ / \ |
B C ==> F B C ==> F A OR A B C ==> F B C ==> F A OR A
/ \ | / \ /|\ / \ | / \ /|\
D E E B C B C F D E E B C B C F
| | | | | |
F E E F E E
(intermediate) (non-exclusive) (exclusive) (intermediate) (non-exclusive) (exclusive)
Example of Dependency Reordering Figure 5: 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 parent of the closed stream. can be moved to become dependent on the parent of the closed stream.
The weights of new dependencies are recalculated by distributing the The weights of new dependencies are recalculated by distributing the
weight of the dependency of the closed stream proportionally based on weight of the dependency of the closed stream 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
skipping to change at page 26, line 52 skipping to change at page 27, line 46
streams A and D are unable to proceed, then stream C receives all the streams A and D are unable to proceed, then stream C receives all the
resources dedicated to stream A. If stream A is removed from the resources dedicated to stream A. If stream A is removed from the
tree, the weight of stream A is divided between streams C and D. If 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 stream D is still unable to proceed, this results in stream C
receiving a reduced proportion of resources. For equal starting receiving a reduced proportion of resources. For equal starting
weights, C receives one third, rather than one half, of available weights, C receives one third, rather than one half, of available
resources. 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 had any associated If a stream identified in a dependency has no associated priority
priority information destroyed, then the dependent stream is instead information, then the dependent stream is instead assigned a default
assigned a default priority. This potentially creates suboptimal priority (Section 5.3.5). This potentially creates suboptimal
prioritization, since the stream could be given a priority that is prioritization, since the stream could be given a priority that is
higher than intended. different from what is intended.
To avoid these problems, an endpoint SHOULD retain stream To avoid these problems, an endpoint SHOULD retain stream
prioritization state for a period after streams become closed. The prioritization state for a period after streams become closed. The
longer state is retained, the lower the chance that streams are longer state is retained, the lower the chance that streams are
assigned incorrect or default priority values. assigned incorrect or default priority values.
This could create a large state burden for an endpoint, so this state Similarly, streams that are in the "idle" state can be assigned
MAY be limited. An endpoint MAY apply a fixed upper limit on the priority or become a parent of other streams. This allows for the
number of closed streams for which prioritization state is tracked to creation of a grouping node in the dependency tree, which enables
limit state exposure. The amount of additional state an endpoint more flexible expressions of priority. Idle streams begin with a
maintains could be dependent on load; under high load, prioritization default priority (Section 5.3.5).
state can be discarded to limit resource commitments. In extreme
cases, an endpoint could even discard prioritization state for active
or reserved streams. If a fixed limit is applied, endpoints SHOULD
maintain state for at least as many streams as allowed by their
setting for SETTINGS_MAX_CONCURRENT_STREAMS.
An endpoint receiving a PRIORITY frame that changes the priority of a The retention of priority information for streams that are not
closed stream SHOULD alter the dependencies of the streams that counted toward the limit set by SETTINGS_MAX_CONCURRENT_STREAMS could
depend on it, if it has retained enough state to do so. create a large state burden for an endpoint. Therefore, the amount
of prioritization state that is retained MAY be limited.
The amount of additional state an endpoint maintains for
prioritization could be dependent on load; under high load,
prioritization state can be discarded to limit resource commitments.
In extreme cases, an endpoint could even discard prioritization state
for active or reserved streams. If a limit is applied, endpoints
SHOULD maintain state for at least as many streams as allowed by
their setting for SETTINGS_MAX_CONCURRENT_STREAMS. Implementations
SHOULD also attempt to retain state for streams that are in active
use in the priority tree.
If it has retained enough state to do so, an endpoint receiving a
PRIORITY frame that changes the priority of a closed stream SHOULD
alter the dependencies of the streams that depend on it.
5.3.5. Default Priorities 5.3.5. Default Priorities
Providing priority information is optional. Streams are assigned a All streams are initially assigned a non-exclusive dependency on
non-exclusive dependency on stream 0x0 by default. Pushed streams stream 0x0. Pushed streams (Section 8.2) initially depend on their
(Section 8.2) initially depend on their associated stream. In both associated stream. In both cases, streams are assigned a default
cases, streams are assigned a default weight of 16. 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.
A list of error codes is included in Section 7. A list of error codes is included in Section 7.
5.4.1. Connection Error Handling 5.4.1. Connection Error Handling
A connection error is any error which prevents further processing of A connection error is any error that prevents further processing of
the framing layer, or which corrupts any connection state. the frame layer or corrupts any connection state.
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 for an error condition,
the TCP connection. the endpoint MUST close 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 ([RFC7230], Section 6.6 describes how an immediate
provides a best effort attempt to communicate with the peer about why connection close can result in data loss). In the event of a
the connection is being terminated. connection error, GOAWAY only provides a best-effort attempt to
communicate with the peer about why 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, Endpoints SHOULD send a GOAWAY frame when ending a connection,
providing that 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 that does not A stream error is an error related to a specific stream that does not
affect processing of other streams. affect processing of other streams.
skipping to change at page 28, line 37 skipping to change at page 29, line 44
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), or flow control). (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 To avoid looping, an endpoint MUST NOT send a RST_STREAM in response
frame, to avoid looping. to a RST_STREAM frame.
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 closed or reset while streams remain in
half closed states, then the endpoint MUST assume that those streams "open" or "half-closed" state, then the affected streams cannot be
were abnormally interrupted and could be incomplete. automatically retried (see Section 8.1.4 for details).
5.5. Extending HTTP/2 5.5. Extending HTTP/2
HTTP/2 permits extension of the protocol. Protocol extensions can be HTTP/2 permits extension of the protocol. Within the limitations
used to provide additional services or alter any aspect of the described in this section, protocol extensions can be used to provide
protocol, within the limitations described in this section. additional services or alter any aspect of the protocol. Extensions
Extensions are effective only within the scope of a single HTTP/2 are effective only within the scope of a single HTTP/2 connection.
connection.
This applies to the protocol elements defined in this document. This
does not affect the existing options for extending HTTP, such as
defining new methods, status codes, or header fields.
Extensions are permitted to use new frame types (Section 4.1), new Extensions are permitted to use new frame types (Section 4.1), new
settings (Section 6.5.2), or new error codes (Section 7). Registries settings (Section 6.5.2), or new error codes (Section 7). Registries
are established for managing these extension points: frame types are established for managing these extension points: frame types
(Section 11.2), settings (Section 11.3) and error codes (Section 11.2), settings (Section 11.3), and error codes
(Section 11.4). (Section 11.4).
Implementations MUST ignore unknown or unsupported values in all Implementations MUST ignore unknown or unsupported values in all
extensible protocol elements. Implementations MUST discard frames extensible protocol elements. Implementations MUST discard frames
that have unknown or unsupported types. This means that any of these that have unknown or unsupported types. This means that any of these
extension points can be safely used by extensions without prior extension points can be safely used by extensions without prior
arrangement or negotiation. arrangement or negotiation. However, extension frames that appear in
the middle of a header block (Section 4.3) are not permitted; these
MUST be treated as a connection error (Section 5.4.1) of type
PROTOCOL_ERROR.
However, extensions that could change the semantics of existing Extensions that could change the semantics of existing protocol
protocol components MUST be negotiated before being used. For components MUST be negotiated before being used. For example, an
example, an extension that changes the layout of the HEADERS frame extension that changes the layout of the HEADERS frame cannot be used
cannot be used until the peer has given a positive signal that this until the peer has given a positive signal that this is acceptable.
is acceptable. In this case, it could also be necessary to In this case, it could also be necessary to coordinate when the
coordinate when the revised layout comes into effect. Note that revised layout comes into effect. Note that treating any frames
treating any frame other than DATA frames as flow controlled is such other than DATA frames as flow controlled is such a change in
a change in semantics, and can only be done through negotiation. semantics and can only be done through negotiation.
This document doesn't mandate a specific method for negotiating the 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 use of an extension but notes that a setting (Section 6.5.2) could be
be used for that purpose. If both peers set a value that indicates used for that purpose. If both peers set a value that indicates
willingness to use the extension, then the extension can be used. If willingness to use the extension, then the extension can be used. If
a setting is used for extension negotiation, the initial value MUST a setting is used for extension negotiation, the initial value MUST
be defined so that the extension is initially disabled. be defined in such a fashion 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 in the establishment and management either 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
no longer be possible. Therefore, it is important that endpoints no longer be possible. Therefore, it is important that endpoints
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 padding. Padding can be added to DATA
to DATA frames to obscure the size of messages. frames to obscure the size of messages. Padding is a security
feature; see Section 10.7.
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 Length? (8)| |Pad Length? (8)|
+---------------+-----------------------------------------------+ +---------------+-----------------------------------------------+
| Data (*) ... | Data (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
| Padding (*) ... | Padding (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
DATA Frame Payload Figure 6: DATA Frame Payload
The DATA frame contains the following fields: The DATA frame contains the following fields:
Pad Length: An 8-bit field containing the length of the frame Pad Length: An 8-bit field containing the length of the frame
padding in units of octets. This field is optional and is only padding in units of octets. This field is conditional (as
present if the PADDED flag is set. signified by a "?" in the diagram) and is only present if the
PADDED flag is set.
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. A receiver is
receiving. not obligated to verify padding but MAY treat non-zero padding as
a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
The DATA frame defines the following flags: The DATA frame defines the following flags:
END_STREAM (0x1): Bit 1 being set indicates that this frame is the END_STREAM (0x1): When set, bit 0 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).
PADDED (0x8): Bit 4 being set indicates that the Pad Length field is PADDED (0x8): When set, bit 3 indicates that the Pad Length field
present. and any padding that it describes are present.
DATA frames MUST be associated with a stream. If a DATA frame is DATA frames MUST be associated with a stream. If a DATA frame is
received whose stream identifier field is 0x0, the recipient MUST received whose stream identifier field is 0x0, the recipient MUST
respond with a connection error (Section 5.4.1) of type respond with a connection error (Section 5.4.1) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
DATA frames are subject to flow control and can only be sent when a DATA frames are subject to flow control and can only be sent when a
stream is in the "open" or "half closed (remote)" states. The entire stream is in the "open" or "half-closed (remote)" state. The entire
DATA frame payload is included in flow control, including Pad Length DATA frame payload is included in flow control, including the Pad
and Padding fields if present. If a DATA frame is received whose Length and Padding fields if present. If a DATA frame is received
stream is not in "open" or "half closed (local)" state, the recipient whose stream is not in "open" or "half-closed (local)" state, the
MUST respond with a stream error (Section 5.4.2) of type recipient MUST respond with a stream error (Section 5.4.2) of type
STREAM_CLOSED. STREAM_CLOSED.
The total number of padding octets is determined by the value of the The total number of padding octets is determined by the value of the
Pad Length field. If the length of the padding is greater than the Pad Length field. If the length of the padding is the length of the
length of the remainder of the frame payload, the recipient MUST frame payload or greater, the recipient MUST treat this as a
treat this as a connection error (Section 5.4.1) of type connection error (Section 5.4.1) of type PROTOCOL_ERROR.
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 Length 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
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) is used to open a stream (Section 5.1),
open a stream (Section 5.1). HEADERS frames can be sent on a stream and additionally carries a header block fragment. HEADERS frames can
in the "open" or "half closed (remote)" states. be sent on a stream in the "idle", "reserved (local)", "open", or
"half-closed (remote)" state.
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 Length? (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 Figure 7: HEADERS Frame Payload
The HEADERS frame payload has the following fields: The HEADERS frame payload has the following fields:
Pad Length: An 8-bit field containing the length of the frame Pad Length: An 8-bit field containing the length of the frame
padding in units of octets. This field is optional and is only padding in units of octets. This field is only present if the
present if the PADDED flag is set. PADDED flag is set.
E: A single bit flag indicates that the stream dependency is E: A single-bit flag indicating 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 only present if the
present if the PRIORITY flag is set. 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 only
and is only present if the PRIORITY flag is set. present if the PRIORITY flag is set.
Weight: An 8-bit weight for the stream, see Section 5.3. Add one to Weight: An unsigned 8-bit integer representing a priority weight for
the value to obtain a weight between 1 and 256. This field is the stream (see Section 5.3). Add one to the value to obtain a
optional and is only present if the PRIORITY flag is set. weight between 1 and 256. This field is only present if the
PRIORITY flag is set.
Header Block Fragment: A header block fragment (Section 4.3). Header Block Fragment: A header block fragment (Section 4.3).
Padding: Padding octets. Padding: Padding octets.
The HEADERS frame defines the following flags: The HEADERS frame defines the following flags:
END_STREAM (0x1): Bit 1 being set indicates that the header block END_STREAM (0x1): When set, bit 0 indicates that the header block
(Section 4.3) is the last that the endpoint will send for the (Section 4.3) is the last that the endpoint will send for the
identified stream. Setting this flag causes the stream to enter identified stream.
one of "half closed" states (Section 5.1).
A HEADERS frame that is followed by CONTINUATION frames carries A HEADERS frame carries the END_STREAM flag that signals the end
the END_STREAM flag that signals the end of a stream. A of a stream. However, a HEADERS frame with the END_STREAM flag
CONTINUATION frame cannot be used to terminate a stream. set can be followed by CONTINUATION frames on the same stream.
Logically, the CONTINUATION frames are part of the HEADERS frame.
END_HEADERS (0x4): Bit 3 being set indicates that this frame END_HEADERS (0x4): When set, bit 2 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.
PADDED (0x8): Bit 4 being set indicates that the Pad Length field is PADDED (0x8): When set, bit 3 indicates that the Pad Length field
present. and any padding that it describes are present.
PRIORITY (0x20): Bit 6 being set indicates that the Exclusive Flag PRIORITY (0x20): When set, bit 5 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
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.
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 can include padding. Padding fields and flags are
flags are identical to those defined for DATA frames (Section 6.1). identical to those defined for DATA frames (Section 6.1). Padding
that exceeds the size remaining for the header block fragment MUST be
treated as a PROTOCOL_ERROR.
Prioritization information in a HEADERS frame is logically equivalent
to a separate PRIORITY frame, but inclusion in HEADERS avoids the
potential for churn in stream prioritization when new streams are
created. Prioritization fields in HEADERS frames subsequent to the
first on a stream reprioritize the stream (Section 5.3.3).
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 in any stream state,
existing stream, including closed streams. This enables including idle or closed streams.
reprioritization of existing streams.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| Stream Dependency (31) | |E| Stream Dependency (31) |
+-+-------------+-----------------------------------------------+ +-+-------------+-----------------------------------------------+
| Weight (8) | | Weight (8) |
+-+-------------+ +-+-------------+
PRIORITY Frame Payload Figure 8: PRIORITY Frame Payload
The payload of a PRIORITY frame contains the following fields: The payload of a PRIORITY frame contains the following fields:
E: A single bit flag indicates that the stream dependency is E: A single-bit flag indicating that the stream dependency is
exclusive, see Section 5.3. exclusive (see Section 5.3).
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 stream depends on (see Section 5.3).
Weight: An 8-bit weight for the identified stream dependency, see Weight: An unsigned 8-bit integer representing a priority weight for
Section 5.3. Add one to the value to obtain a weight between 1 the stream (see Section 5.3). Add one to the value to obtain a
and 256. weight between 1 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 always identifies a stream. If a PRIORITY frame
PRIORITY frame is received with a stream identifier of 0x0, the is received with a stream identifier of 0x0, the recipient MUST
recipient MUST respond with a connection error (Section 5.4.1) of respond with a connection error (Section 5.4.1) of type
type PROTOCOL_ERROR. 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 state, though it
(remote)", "open", "half closed (local)", "half closed (remote)", or cannot be sent between consecutive frames that comprise a single
"closed" states, though it cannot be sent between consecutive frames header block (Section 4.3). Note that this frame could arrive after
that comprise a single header block (Section 4.3). Note that this processing or frame sending has completed, which would cause it to
frame could arrive after processing or frame sending has completed, have no effect on the identified stream. For a stream that is in the
which would cause it to have no effect on the current stream. For a "half-closed (remote)" or "closed" state, this frame can only affect
stream that is in the "half closed (remote)" or "closed" - state, processing of the identified stream and its dependent streams; it
this frame can only affect processing of the current stream and not does not affect frame transmission on that stream.
frame transmission.
The PRIORITY frame is the only frame that can be sent for a stream in The PRIORITY frame can be sent for a stream in the "idle" or "closed"
the "closed" state. This allows for the reprioritization of a group state. This allows for the reprioritization of a group of dependent
of dependent streams by altering the priority of a parent stream, streams by altering the priority of an unused or closed parent
which might be closed. However, a PRIORITY frame sent on a closed stream.
stream risks being ignored due to the peer having discarded priority
state information for that stream. A PRIORITY frame with a length other than 5 octets MUST be treated as
a stream error (Section 5.4.2) of type FRAME_SIZE_ERROR.
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 immediate termination of a
stream. When sent by the initiator of a stream, it indicates that stream. RST_STREAM is sent to request cancellation of a stream or to
they wish to cancel the stream or that an error condition has indicate that an error condition has occurred.
occurred. When sent by the receiver of a stream, it indicates that
either the receiver is rejecting the stream, requesting that the
stream be cancelled, or that an error condition has occurred.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code (32) | | Error Code (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
RST_STREAM Frame Payload Figure 9: 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.
The RST_STREAM frame does not define any flags. The RST_STREAM frame does not define any flags.
The RST_STREAM frame fully terminates the referenced stream and The RST_STREAM frame fully terminates the referenced stream and
causes it to enter the closed state. After receiving a RST_STREAM on causes it to enter the "closed" state. After receiving a RST_STREAM
a stream, the receiver MUST NOT send additional frames for that on a stream, the receiver MUST NOT send additional frames for that
stream. However, after sending the RST_STREAM, the sending endpoint stream, with the exception of PRIORITY. However, after sending the
MUST be prepared to receive and process additional frames sent on the RST_STREAM, the sending endpoint MUST be prepared to receive and
stream that might have been sent by the peer prior to the arrival of process additional frames sent on the stream that might have been
the RST_STREAM. sent by the peer prior to the arrival of the RST_STREAM.
RST_STREAM frames MUST be associated with a stream. If a RST_STREAM RST_STREAM frames MUST be associated with a stream. If a RST_STREAM
frame is received with a stream identifier of 0x0, the recipient MUST frame is received with a stream identifier of 0x0, the recipient MUST
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.
A RST_STREAM frame with a length other than 4 octets MUST be treated
as a connection error (Section 5.4.1) of type FRAME_SIZE_ERROR.
6.5. SETTINGS 6.5. SETTINGS
The SETTINGS frame (type=0x4) conveys configuration parameters that The SETTINGS frame (type=0x4) conveys configuration parameters that
affect how endpoints communicate, such as preferences and constraints affect how endpoints communicate, such as preferences and constraints
on peer behavior. The SETTINGS frame is also used to acknowledge the on peer behavior. The SETTINGS frame is also used to acknowledge the
receipt of those parameters. Individually, a SETTINGS parameter can receipt of those parameters. Individually, a SETTINGS parameter can
also be 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
the parameters defined by this specification. the parameters defined by this specification.
Each parameter in a SETTINGS frame replaces any existing value for Each parameter in a SETTINGS frame replaces any existing value for
that parameter. Parameters are processed in the order in which they that parameter. Parameters are processed in the order in which they
appear, and a receiver of a SETTINGS frame does not need to maintain appear, and a receiver of a SETTINGS frame does not need to maintain
any state other than the current value of its parameters. Therefore, any state other than the current value of its parameters. Therefore,
the value of a SETTINGS parameter is the last value that is seen by a the value of a SETTINGS parameter is the last value that is seen by a
receiver. receiver.
SETTINGS parameters are acknowledged by the receiving peer. To SETTINGS parameters are acknowledged by the receiving peer. To
enable this, the SETTINGS frame defines the following flag: enable this, the SETTINGS frame defines the following flag:
ACK (0x1): Bit 1 being set indicates that this frame acknowledges ACK (0x1): When set, bit 0 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 information,
Settings Synchronization (Section 6.5.3). see Section 6.5.3 ("Settings Synchronization").
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 (0x0). 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.
A SETTINGS frame with a length other than a multiple of 6 octets MUST
be treated as a connection error (Section 5.4.1) of type
FRAME_SIZE_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 16-bit setting identifier and an each consisting of an unsigned 16-bit setting identifier and an
unsigned 32-bit value. unsigned 32-bit value.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier (16) | | Identifier (16) |
+-------------------------------+-------------------------------+ +-------------------------------+-------------------------------+
| Value (32) | | Value (32) |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Setting Format Figure 10: 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 (0x1): Allows the sender to inform the SETTINGS_HEADER_TABLE_SIZE (0x1): Allows the sender to inform the
remote endpoint of the maximum size of the header compression remote endpoint of the maximum size of the header compression
table used to decode header blocks. The encoder can select any table used to decode header blocks, in octets. The encoder can
size equal to or less than this value by using signaling specific select any size equal to or less than this value by using
to the header compression format inside a header block. The signaling specific to the header compression format inside a
initial value is 4,096 bytes. header block (see [COMPRESSION]). The initial value is 4,096
octets.
SETTINGS_ENABLE_PUSH (0x2): This setting can be use to disable SETTINGS_ENABLE_PUSH (0x2): This setting can be used to disable
server push (Section 8.2). An endpoint MUST NOT send a server push (Section 8.2). An endpoint MUST NOT send a
PUSH_PROMISE frame if it receives this parameter set to a value of PUSH_PROMISE frame if it receives this parameter set to a value of
0. An 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 server push is The initial value is 1, which indicates that server push is
permitted. Any value other than 0 or 1 MUST be treated as a permitted. Any value other than 0 or 1 MUST be treated as a
connection error (Section 5.4.1) of type PROTOCOL_ERROR. connection error (Section 5.4.1) of type PROTOCOL_ERROR.
SETTINGS_MAX_CONCURRENT_STREAMS (0x3): Indicates the maximum number SETTINGS_MAX_CONCURRENT_STREAMS (0x3): Indicates the maximum number
of 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 is more appropriate.
SETTINGS_INITIAL_WINDOW_SIZE (0x4): Indicates the sender's initial SETTINGS_INITIAL_WINDOW_SIZE (0x4): Indicates the sender's initial
window size (in bytes) for stream level flow control. The initial window size (in octets) for stream-level flow control. The
value is 2^16-1 (65,535) octets. initial value is 2^16-1 (65,535) octets.
This setting affects the window size of all streams, including This setting affects the window size of all streams (see
existing streams, see Section 6.9.2. Section 6.9.2).
Values above the maximum flow control window size of 2^31-1 MUST Values above the maximum flow-control window size of 2^31-1 MUST
be treated as a connection error (Section 5.4.1) of type be treated as a connection error (Section 5.4.1) of type
FLOW_CONTROL_ERROR. FLOW_CONTROL_ERROR.
SETTINGS_MAX_FRAME_SIZE (0x5): Indicates the size of the largest SETTINGS_MAX_FRAME_SIZE (0x5): Indicates the size of the largest
frame payload that a receiver is willing to accept. frame payload that the sender is willing to receive, in octets.
The initial value is 2^14 (16,384) octets. The value advertised The initial value is 2^14 (16,384) octets. The value advertised
by an endpoint MUST be between this initial value and the maximum by an endpoint MUST be between this initial value and the maximum
allowed frame size (2^24-1 or 16,777,215 octets), inclusive. allowed frame size (2^24-1 or 16,777,215 octets), inclusive.
Values outside this range MUST be treated as a connection error Values outside this range MUST be treated as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. (Section 5.4.1) of type PROTOCOL_ERROR.
SETTINGS_MAX_HEADER_LIST_SIZE (0x6): This advisory setting informs a SETTINGS_MAX_HEADER_LIST_SIZE (0x6): This advisory setting informs a
peer of the maximum size of header list that the sender is peer of the maximum size of header list that the sender is
prepared to accept. The value is based on the uncompressed size prepared to accept, in octets. The value is based on the
of header fields, including the length of the name and value in uncompressed size of header fields, including the length of the
octets plus an overhead of 32 octets for each header field. name and value in octets plus an overhead of 32 octets for each
header field.
For any given request, a lower limit than what is advertised MAY For any given request, a lower limit than what is advertised MAY
be enforced. The initial value of this setting is unlimited. be enforced. The initial value of this setting is unlimited.
An endpoint that receives a SETTINGS frame with any unknown or An endpoint that receives a SETTINGS frame with any unknown or
unsupported identifier MUST ignore that setting. unsupported identifier MUST ignore that setting.
6.5.3. Settings Synchronization 6.5.3. Settings Synchronization
Most values in SETTINGS benefit from or require an understanding of Most values in SETTINGS benefit from or require an understanding of
skipping to change at page 38, line 34 skipping to change at page 40, 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.
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 Length? (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 Figure 11: PUSH_PROMISE Payload Format
The PUSH_PROMISE frame payload has the following fields: The PUSH_PROMISE frame payload has the following fields:
Pad Length: An 8-bit field containing the length of the frame Pad Length: An 8-bit field containing the length of the frame
padding in units of octets. This field is optional and is only padding in units of octets. This field is only present if the
present if the PADDED flag is set. PADDED 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: An unsigned 31-bit integer that identifies the
stream the endpoint intends to start sending frames for. The stream that is reserved by the PUSH_PROMISE. The promised stream
promised stream identifier MUST be a valid choice for the next identifier MUST be a valid choice for the next stream sent by the
stream sent by the sender (see new stream identifier sender (see "new stream identifier" in 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)
containing request header fields. containing request header fields.
Padding: Padding octets. Padding: Padding octets.
The PUSH_PROMISE frame defines the following flags: The PUSH_PROMISE frame defines the following flags:
END_HEADERS (0x4): Bit 3 being set indicates that this frame END_HEADERS (0x4): When set, bit 2 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.
PADDED (0x8): Bit 4 being set indicates that the Pad Length field is PADDED (0x8): When set, bit 3 indicates that the Pad Length field
present. and any padding that it describes are present.
PUSH_PROMISE frames MUST be associated with an existing, peer- PUSH_PROMISE frames MUST only be sent on a peer-initiated stream that
initiated stream. The stream identifier of a PUSH_PROMISE frame is in either the "open" or "half-closed (remote)" state. The stream
indicates the stream it is associated with. If the stream identifier identifier of a PUSH_PROMISE frame indicates the stream it is
field specifies the value 0x0, a recipient MUST respond with a associated with. If the stream identifier field specifies the value
connection error (Section 5.4.1) of type PROTOCOL_ERROR. 0x0, a recipient MUST respond with a connection error (Section 5.4.1)
of type PROTOCOL_ERROR.
Promised streams are not required to be used in the order they are Promised streams are not required to be used in the order they are
promised. The PUSH_PROMISE only reserves stream identifiers for promised. The PUSH_PROMISE only reserves stream identifiers for
later use. later use.
PUSH_PROMISE MUST NOT be sent if the SETTINGS_ENABLE_PUSH setting of 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 the peer endpoint is set to 0. An endpoint that has set this setting
and has received acknowledgement MUST treat the receipt of a and has received acknowledgement 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. 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.
A PUSH_PROMISE frame modifies the connection state in two ways. The A PUSH_PROMISE frame modifies the connection state in two ways.
inclusion of a header block (Section 4.3) potentially modifies the First, the inclusion of a header block (Section 4.3) potentially
state maintained for header compression. PUSH_PROMISE also reserves modifies the state maintained for header compression. Second,
a stream for later use, causing the promised stream to enter the PUSH_PROMISE also reserves a stream for later use, causing the
"reserved" state. A sender MUST NOT send a PUSH_PROMISE on a stream promised stream to enter the "reserved" state. A sender MUST NOT
unless that stream is either "open" or "half closed (remote)"; the send a PUSH_PROMISE on a stream unless that stream is either "open"
sender MUST ensure that the promised stream is a valid choice for a or "half-closed (remote)"; the sender MUST ensure that the promised
new stream identifier (Section 5.1.1) (that is, the promised stream stream is a valid choice for a new stream identifier (Section 5.1.1)
MUST be in the "idle" state). (that is, the promised stream 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. However, an endpoint that
treat the receipt of a PUSH_PROMISE that promises an illegal stream has sent RST_STREAM on the associated stream MUST handle PUSH_PROMISE
identifier (Section 5.1.1) (that is, an identifier for a stream that frames that might have been created before the RST_STREAM frame is
is not currently in the "idle" state) as a connection error received and processed.
(Section 5.4.1) of type PROTOCOL_ERROR.
The PUSH_PROMISE frame includes optional padding. Padding fields and A receiver MUST treat the receipt of a PUSH_PROMISE that promises an
flags are identical to those defined for DATA frames (Section 6.1). illegal stream identifier (Section 5.1.1) as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. Note that an illegal stream
identifier is an identifier for a stream that is not currently in the
"idle" state.
The PUSH_PROMISE frame can include padding. Padding fields and 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 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 Figure 12: 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 opaque data in the payload. A sender can include any value it
use those bytes in any fashion. chooses and use those octets in any fashion.
Receivers of a PING frame that does not include an ACK flag MUST send Receivers of a PING frame that does not include an ACK flag MUST send
a PING frame with the ACK flag set in response, with an identical a PING frame with the ACK flag set in response, with an identical
payload. PING responses SHOULD be given higher priority than any payload. PING responses SHOULD be given higher priority than any
other frame. other frame.
The PING frame defines the following flags: The PING frame defines the following flags:
ACK (0x1): Bit 1 being set indicates that this PING frame is a PING ACK (0x1): When set, bit 0 indicates that this PING frame is a PING
response. An endpoint MUST set this flag in PING responses. An response. An endpoint MUST set this flag in PING responses. An
endpoint MUST NOT respond to PING frames containing this flag. endpoint MUST NOT respond to PING frames containing this flag.
PING frames are not associated with any individual stream. If a PING PING frames are not associated with any individual stream. If a PING
frame is received with a stream identifier field value other than frame is received with a stream identifier field value other than
0x0, the recipient MUST respond with a connection error 0x0, the recipient MUST respond with a connection error
(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) is used to initiate shutdown of a
streams on this connection. GOAWAY can be sent by either the client connection or to signal serious error conditions. GOAWAY allows an
or the server. Once sent, the sender will ignore frames sent on any endpoint to gracefully stop accepting new streams while still
new streams with identifiers higher than the included last stream finishing processing of previously established streams. This enables
identifier. Receivers of a GOAWAY frame MUST NOT open additional administrative actions, like server maintenance.
streams on the connection, although a new connection can be
established for new 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 peer- case, the GOAWAY contains the stream identifier of the last peer-
initiated stream which was or might be processed on the sending initiated stream that was or might be processed on the sending
endpoint in this connection. For instance, if the server sends a endpoint in this connection. For instance, if the server sends a
GOAWAY frame, the identifed stream is the highest numbered stream GOAWAY frame, the identified stream is the highest-numbered stream
initiated by the client. initiated by the client.
Once sent, the sender will ignore frames sent on streams initiated by
the receiver if the stream has an identifier higher than the included
last stream identifier. Receivers of a GOAWAY frame MUST NOT open
additional streams on the connection, although a new connection can
be established for new streams.
If the receiver of the GOAWAY has sent data on streams with a higher If the receiver of the GOAWAY has sent data on streams with a higher
stream identifier than what is indicated in the GOAWAY frame, those stream identifier than what is indicated in the GOAWAY frame, those
streams are not or will not be processed. The receiver of the GOAWAY streams are not or will not be processed. The receiver of the GOAWAY
frame can treat the streams as though they had never been created at frame can treat the streams as though they had never been created at
all, thereby allowing those streams to be retried later on a new all, thereby allowing those streams to be retried later on a new
connection. 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 peer can know whether a stream has been
partially processed or not. For example, if an HTTP client sends a partially processed or not. For example, if an HTTP client sends a
POST at the same time that a server closes a connection, the client POST at the same time that a server closes a connection, the client
cannot know if the server started to process that POST request if the cannot know if the server started to process that POST request if the
server does not send a GOAWAY frame to indicate what streams it might server does not send a GOAWAY frame to indicate what streams it might
have acted on. have acted on.
An endpoint might choose to close a connection without sending GOAWAY An endpoint might choose to close a connection without sending a
for misbehaving peers. GOAWAY for misbehaving peers.
0 1 2 3 A GOAWAY frame might not immediately precede closing of the
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 connection; a receiver of a GOAWAY that has no more use for the
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ connection SHOULD still send a GOAWAY frame before terminating the
connection.
+-+-------------------------------------------------------------+
|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 Figure 13: 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
might have taken some action on, or might yet take action on. All might have taken some action on or might yet take action on. All
streams up to and including the identified stream might have been streams up to and including the identified stream might have been
processed in some way. The last stream identifier can be set to 0 if processed in some way. The last stream identifier can be set to 0 if
no 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, the last stream If a connection terminates without a GOAWAY frame, the last stream
identifier is 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, reattempting
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 a 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 indicates which identifier from the last GOAWAY frame received indicates which
streams could have been acted upon. Endpoints MUST NOT increase the streams could have been acted upon. Endpoints MUST NOT increase the
value they send in the last stream identifier, since the peers might value they send in the last stream identifier, since the peers might
already have retried unprocessed requests on another connection. already have retried unprocessed requests on another connection.
A client that is unable to retry requests loses all requests that are A client that is unable to retry requests loses all requests that are
in flight when the server closes the connection. This is especially in flight when the server closes the connection. This is especially
true for intermediaries that might not be serving clients using true for intermediaries that might not be serving clients using
HTTP/2. A server that is attempting to gracefully shut down a HTTP/2. A server that is attempting to gracefully shut down a
connection SHOULD send an initial GOAWAY frame with the last stream 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 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 client that a shutdown is imminent and that initiating further
be initiated. After waiting at least one round trip time, the server requests is prohibited. After allowing time for any in-flight stream
can send another GOAWAY frame with an updated last stream identifier. creation (at least one round-trip time), the server can send another
This ensures that a connection can be cleanly shut down without GOAWAY frame with an updated last stream identifier. This ensures
losing requests. 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 initiated by the receiver with identifiers higher than the
However, any frames that alter connection state cannot be completely identified last stream. However, any frames that alter connection
ignored. For instance, HEADERS, PUSH_PROMISE and CONTINUATION frames state cannot be completely ignored. For instance, HEADERS,
MUST be minimally processed to ensure the state maintained for header PUSH_PROMISE, and CONTINUATION frames MUST be minimally processed to
compression is consistent (see Section 4.3); similarly DATA frames ensure the state maintained for header compression is consistent (see
MUST be counted toward the connection flow control window. Failure Section 4.3); similarly, DATA frames MUST be counted toward the
to process these frames can cause flow control or header compression connection flow-control window. Failure to process these frames can
state to become unsynchronized. cause flow control or header compression state to become
unsynchronized.
The GOAWAY frame also contains a 32-bit error code (Section 7) that The GOAWAY frame also contains a 32-bit error code (Section 7) that
contains the reason for closing the connection. contains the reason for closing the connection.
Endpoints MAY append opaque data to the payload of any GOAWAY frame. Endpoints MAY append opaque data to the payload of any GOAWAY frame.
Additional debug data is intended for diagnostic purposes only and Additional debug data is intended for diagnostic purposes only and
carries no semantic value. Debug information could contain security- carries no semantic value. Debug information could contain security-
or privacy-sensitive data. Logged or otherwise persistently stored or privacy-sensitive data. Logged or otherwise persistently stored
debug data MUST have adequate safeguards to prevent unauthorized debug data MUST have adequate safeguards to prevent unauthorized
access. access.
6.9. WINDOW_UPDATE 6.9. WINDOW_UPDATE
The WINDOW_UPDATE frame (type=0x8) is used to implement flow control; The WINDOW_UPDATE frame (type=0x8) is used to implement flow control;
see Section 5.2 for an overview. see Section 5.2 for an overview.
Flow control operates at two levels: on each individual stream and on Flow control operates at two levels: on each individual stream and on
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 frames. Frames that are exempt document, this includes only DATA frames. Frames that are exempt
from flow control MUST be accepted and processed, unless the receiver from flow control MUST be accepted and processed, unless the receiver
is 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 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 Figure 14: 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 octets that the
sender can transmit in addition to the existing flow control window. sender can transmit in addition to the existing flow-control window.
The legal range for the increment to the flow control window is 1 to The legal range for the increment to the flow-control window is 1 to
2^31-1 (0x7fffffff) bytes. 2^31-1 (2,147,483,647) octets.
The WINDOW_UPDATE frame does not define any flags. The WINDOW_UPDATE frame does not define any flags.
The WINDOW_UPDATE frame can be specific to a stream or to the entire The WINDOW_UPDATE frame can be specific to a stream or to the entire
connection. In the former case, the frame's stream identifier connection. In the former case, the frame's stream identifier
indicates the affected stream; in the latter, the value "0" indicates indicates the affected stream; in the latter, the value "0" indicates
that the entire connection is the subject of the frame. that the entire connection is the subject of the frame.
A receiver MUST treat the recipt of a WINDOW_UPDATE frame with an A receiver MUST treat the receipt of a WINDOW_UPDATE frame with an
flow control window increment of 0 as a stream error (Section 5.4.2) flow-control window increment of 0 as a stream error (Section 5.4.2)
of type PROTOCOL_ERROR; errors on the connection flow control window of type PROTOCOL_ERROR; errors on the connection flow-control window
MUST be treated as a connection error (Section 5.4.1). MUST be treated as a connection error (Section 5.4.1).
WINDOW_UPDATE can be sent by a peer that has sent a frame bearing the WINDOW_UPDATE can be sent by a peer that has sent a frame bearing the
END_STREAM flag. This means that a receiver could receive a END_STREAM flag. This means that a receiver could receive a
WINDOW_UPDATE frame on a "half closed (remote)" or "closed" stream. WINDOW_UPDATE frame on a "half-closed (remote)" or "closed" stream.
A receiver MUST NOT treat this as an error, see Section 5.1. A receiver MUST NOT treat this as an error (see Section 5.1).
A receiver that receives a flow controlled frame MUST always account A receiver that receives a flow-controlled frame MUST always account
for its contribution against the connection flow control window, for its contribution against the connection flow-control window,
unless the receiver treats this as a connection error unless the receiver treats this as a connection error
(Section 5.4.1). This is necessary even if the frame is in error. (Section 5.4.1). This is necessary even if the frame is in error.
Since the sender counts the frame toward the flow control window, if The sender counts the frame toward the flow-control window, but if
the receiver does not, the flow control window at sender and receiver the receiver does not, the flow-control window at the sender and
can become different. receiver can become different.
6.9.1. The Flow Control Window A WINDOW_UPDATE frame with a length other than 4 octets MUST be
treated as a connection error (Section 5.4.1) of type
FRAME_SIZE_ERROR.
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 octets of data the sender is permitted
to transmit; as such, its size is a measure of the buffering capacity to transmit; as such, its size is a measure of the buffering capacity
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 (that receiver. Frames with zero length with the END_STREAM flag set (that
is, an empty DATA frame) MAY be sent if there is no available space is, an empty DATA frame) MAY be sent if there is no available 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 9-octet 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
flow control windows. flow-control windows.
A sender that receives a WINDOW_UPDATE frame updates the A sender that receives a WINDOW_UPDATE frame updates the
corresponding window by the amount specified in the frame. corresponding window by the amount specified in the frame.
A sender MUST NOT allow a flow control window to exceed 2^31-1 bytes. A sender MUST NOT allow a flow-control window to exceed 2^31-1
If a sender receives a WINDOW_UPDATE that causes a flow control octets. If a sender receives a WINDOW_UPDATE that causes a flow-
window to exceed this maximum it MUST terminate either the stream or control window to exceed this maximum, it MUST terminate either the
the connection, as appropriate. For streams, the sender sends a stream or the connection, as appropriate. For streams, the sender
RST_STREAM with the error code of FLOW_CONTROL_ERROR code; for the sends a RST_STREAM with an error code of FLOW_CONTROL_ERROR; for the
connection, a GOAWAY frame with a FLOW_CONTROL_ERROR code. connection, a GOAWAY frame with an error code of FLOW_CONTROL_ERROR
is sent.
Flow controlled frames from the sender and WINDOW_UPDATE frames from Flow-controlled frames from the sender and WINDOW_UPDATE frames from
the receiver are completely asynchronous with respect to each other. the receiver are completely asynchronous with respect to each other.
This property allows a receiver to aggressively update the window This property allows a receiver to aggressively update the window
size kept by the sender to prevent streams from stalling. size kept by the sender to prevent streams from stalling.
6.9.2. Initial Flow Control Window Size 6.9.2. Initial Flow-Control Window Size
When an HTTP/2 connection is first established, new streams are When an HTTP/2 connection is first established, new streams are
created with an initial flow control window size of 65,535 bytes. created with an initial flow-control window size of 65,535 octets.
The connection flow control window is 65,535 bytes. Both endpoints The connection flow-control window is also 65,535 octets. Both
can adjust the initial window size for new streams by including a endpoints can adjust the initial window size for new streams by
value for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame that including a value for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS
forms part of the connection preface. The connection flow control frame that forms part of the connection preface. The connection
window can only be changed using WINDOW_UPDATE frames. flow-control 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 In addition to changing the flow-control window for streams that are
all current streams. When the value of SETTINGS_INITIAL_WINDOW_SIZE not yet active, a SETTINGS frame can alter the initial flow-control
changes, a receiver MUST adjust the size of all stream flow control window size for streams with active flow-control windows (that is,
windows that it maintains by the difference between the new value and streams in the "open" or "half-closed (remote)" state). When the
the old value. value of SETTINGS_INITIAL_WINDOW_SIZE changes, a receiver MUST adjust
the size of all stream flow-control windows that it maintains by the
difference between the new value and the old value.
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 60 KB 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 16
16KB, the client will recalculate the available flow control window KB, the client will recalculate the available flow-control window to
to be -44KB on receipt of the SETTINGS frame. The client retains a be -44 KB 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. A SETTINGS frame cannot alter the connection flow-control window.
An endpoint MUST treat a change to SETTINGS_INITIAL_WINDOW_SIZE that An endpoint MUST treat a change to SETTINGS_INITIAL_WINDOW_SIZE that
causes any flow control window to exceed the maximum size as a causes any flow-control window to exceed the maximum size as a
connection error (Section 5.4.1) of type FLOW_CONTROL_ERROR. 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 MAY continue to process streams that exceed
exceed flow control limits: flow-control limits. Allowing streams to continue does not allow the
receiver to immediately reduce the space it reserves for flow-control
1. The receiver can immediately send RST_STREAM with windows. Progress on these streams can also stall, since
FLOW_CONTROL_ERROR error code for the affected streams. WINDOW_UPDATE frames are needed to allow the sender to resume
sending. The receiver MAY instead send a RST_STREAM with an error
2. The receiver can accept the streams and tolerate the resulting code of FLOW_CONTROL_ERROR for the affected streams.
head of line blocking, sending WINDOW_UPDATE frames as it
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, as long as the preceding frame is on the same
frame is on the same stream and is a HEADERS, PUSH_PROMISE or stream and is a HEADERS, PUSH_PROMISE, or CONTINUATION frame without
CONTINUATION frame without the END_HEADERS flag set. the END_HEADERS flag set.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Block Fragment (*) ... | Header Block Fragment (*) ...
+---------------------------------------------------------------+ +---------------------------------------------------------------+
CONTINUATION Frame Payload Figure 15: CONTINUATION Frame Payload
The CONTINUATION frame payload contains a header block fragment The CONTINUATION frame payload contains a header block fragment
(Section 4.3). (Section 4.3).
The CONTINUATION frame defines the following flag: The CONTINUATION frame defines the following flag:
END_HEADERS (0x4): Bit 3 being set indicates that this frame ends a END_HEADERS (0x4): When set, bit 2 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.
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.
skipping to change at page 48, line 32 skipping to change at page 50, line 19
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 apply only Error codes share a common code space. Some error codes apply only
to either streams or the entire connection and have no defined to either streams or the entire connection and have no defined
semantics in the other context. semantics in the other context.
The following error codes are defined: The following error codes are defined:
NO_ERROR (0x0): The associated condition is not as a result of an NO_ERROR (0x0): The associated condition is not 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 (0x1): 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 (0x2): The endpoint encountered an unexpected INTERNAL_ERROR (0x2): The endpoint encountered an unexpected
internal error. internal error.
FLOW_CONTROL_ERROR (0x3): The endpoint detected that its peer FLOW_CONTROL_ERROR (0x3): The endpoint detected that its peer
violated the flow control protocol. violated the flow-control protocol.
SETTINGS_TIMEOUT (0x4): 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 Section 6.5.3
Synchronization (Section 6.5.3). ("Settings Synchronization").
STREAM_CLOSED (0x5): The endpoint received a frame after a stream STREAM_CLOSED (0x5): The endpoint received a frame after a stream
was half closed. was half-closed.
FRAME_SIZE_ERROR (0x6): The endpoint received a frame that was FRAME_SIZE_ERROR (0x6): The endpoint received a frame with an
larger than the maximum size that it supports. invalid size.
REFUSED_STREAM (0x7): The endpoint refuses the stream prior to REFUSED_STREAM (0x7): The endpoint refused 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 (0x8): 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 (0x9): The endpoint is unable to maintain the COMPRESSION_ERROR (0x9): The endpoint is unable to maintain the
header compression context for the connection. header compression context for the connection.
CONNECT_ERROR (0xa): 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 (0xb): The endpoint detected that its peer is ENHANCE_YOUR_CALM (0xb): The endpoint detected that its peer is
exhibiting a behavior that might be generating excessive load. exhibiting a behavior that might be generating excessive load.
INADEQUATE_SECURITY (0xc): The underlying transport has properties INADEQUATE_SECURITY (0xc): The underlying transport has properties
that do not meet minimum security requirements (see Section 9.2). that do not meet minimum security requirements (see Section 9.2).
HTTP_1_1_REQUIRED (0xd): The endpoint requires that HTTP/1.1 be used
instead of HTTP/2.
Unknown or unsupported error codes MUST NOT trigger any special Unknown or unsupported error codes MUST NOT trigger any special
behavior. These MAY be treated by an implementation as being behavior. These MAY be treated by an implementation as being
equivalent to INTERNAL_ERROR. 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 application perspective, the of HTTP. This means that, from the application perspective, the
features of the protocol are largely unchanged. To achieve this, all features of the protocol are largely unchanged. To achieve this, all
request and response semantics are preserved, although the syntax of request and response semantics are preserved, 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 [RFC7231], Conditional Requests [RFC7232], Range Requests Content [RFC7231], Conditional Requests [RFC7232], Range Requests
[RFC7233], Caching [RFC7234] and Authentication [RFC7235] 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 [RFC7230], 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. for a response only, zero or more HEADERS frames (each followed 1. for a response only, zero or more HEADERS frames (each followed
by zero or more CONTINUATION frames) containing the message by zero or more CONTINUATION frames) containing the message
headers of informational (1xx) HTTP responses (see [RFC7230], headers of informational (1xx) HTTP responses (see [RFC7230],
Section 3.2 and [RFC7231], Section 6.2), and Section 3.2 and [RFC7231], Section 6.2),
2. one HEADERS frame (followed by zero or more CONTINUATION frames) 2. one HEADERS frame (followed by zero or more CONTINUATION frames)
containing the message headers (see [RFC7230], Section 3.2), and containing the message headers (see [RFC7230], Section 3.2),
3. zero or more DATA frames containing the message payload (see 3. zero or more DATA frames containing the payload body (see
[RFC7230], Section 3.3), and [RFC7230], Section 3.3), and
4. optionally, one HEADERS frame, followed by zero or more 4. optionally, one HEADERS frame, followed by zero or more
CONTINUATION frames containing the trailer-part, if present (see CONTINUATION frames containing the trailer-part, if present (see
[RFC7230], Section 4.1.2). [RFC7230], Section 4.1.2).
The last frame in the sequence bears an END_STREAM flag, noting that The last frame in the sequence bears an END_STREAM flag, noting that
a HEADERS frame bearing the END_STREAM flag can be followed by a HEADERS frame bearing the END_STREAM flag can be followed by
CONTINUATION frames that carry any remaining portions of the header CONTINUATION frames that carry any remaining portions of the header
block. block.
Other frames (from any stream) MUST NOT occur between either HEADERS Other frames (from any stream) MUST NOT occur between the HEADERS
frame and any CONTINUATION frames that might follow. frame and any CONTINUATION frames that might follow.
A HEADERS frame (and associated CONTINUATION frames) can only appear HTTP/2 uses DATA frames to carry message payloads. The "chunked"
at the start or end of a stream. An endpoint that receives a second transfer encoding defined in Section 4.1 of [RFC7230] MUST NOT be
HEADERS frame without the END_STREAM flag set MUST treat the used in HTTP/2.
corresponding request or response as malformed (Section 8.1.2.6).
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. Such a header block is a sequence starting
frame, followed by zero or more CONTINUATION frames, where the with a HEADERS frame, followed by zero or more CONTINUATION frames,
HEADERS frame bears an END_STREAM flag. Header blocks after the where the HEADERS frame bears an END_STREAM flag. Header blocks
first that do not terminate the stream are not part of an HTTP after the first that do not terminate the stream are not part of an
request or response. HTTP request or response.
A HEADERS frame (and associated CONTINUATION frames) can only appear
at the start or end of a stream. An endpoint that receives a HEADERS
frame without the END_STREAM flag set after receiving a final (non-
informational) status code MUST treat the corresponding request or
response as malformed (Section 8.1.2.6).
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. The request ends with a frame bearing END_STREAM, "open" state. The request ends with a frame bearing END_STREAM,
which causes the stream to become "half closed (local)" for the which causes the stream to become "half-closed (local)" for the
client and "half closed (remote)" for the server. A response starts client and "half-closed (remote)" for the server. A response starts
with a HEADERS frame and ends with a frame bearing END_STREAM, which with a HEADERS frame and ends with a frame bearing END_STREAM, which
places the stream in the "closed" state. places the stream in the "closed" state.
8.1.1. Upgrading From HTTP/2 An HTTP response is complete after the server sends -- or the client
receives -- a frame with the END_STREAM flag set (including any
CONTINUATION frames needed to complete a header block). A server can
send a complete response prior to the client sending an entire
request if the response does not depend on any portion of the request
that has not been sent and received. When this is true, a server MAY
request that the client abort transmission of a request without error
by sending a RST_STREAM with an error code of NO_ERROR after sending
a complete response (i.e., a frame with the END_STREAM flag).
Clients MUST NOT discard responses as a result of receiving such a
RST_STREAM, though clients can always discard responses at their
discretion for other reasons.
8.1.1. Upgrading from HTTP/2
HTTP/2 removes support for the 101 (Switching Protocols) HTTP/2 removes support for the 101 (Switching Protocols)
informational status code ([RFC7231], Section 6.2.2). informational status code ([RFC7231], Section 6.2.2).
The semantics of 101 (Switching Protocols) aren't applicable to a The semantics of 101 (Switching Protocols) aren't applicable to a
multiplexed protocol. Alternative protocols are able to use the same multiplexed protocol. Alternative protocols are able to use the same
mechanisms that HTTP/2 uses to negotiate their use (see Section 3). mechanisms that HTTP/2 uses to negotiate their use (see Section 3).
8.1.2. HTTP Header Fields 8.1.2. HTTP Header Fields
HTTP header fields carry information as a series of key-value pairs. HTTP header fields carry information as a series of key-value pairs.
For a listing of registered HTTP headers, see the Message Header For a listing of registered HTTP headers, see the "Message Header
Field Registry maintained at Field" registry maintained at
<https://www.iana.org/assignments/message-headers>. <https://www.iana.org/assignments/message-headers>.
Just as in HTTP/1.x, header field names are strings of ASCII
characters that are compared in a case-insensitive fashion. However,
header field names MUST be converted to lowercase prior to their
encoding in HTTP/2. A request or response containing uppercase
header field names MUST be treated as malformed (Section 8.1.2.6).
8.1.2.1. Pseudo-Header Fields 8.1.2.1. Pseudo-Header Fields
While HTTP/1.x used the message start-line (see [RFC7230], Section While HTTP/1.x used the message start-line (see [RFC7230], Section
3.1) to convey the target URI and method of the request, and the 3.1) to convey the target URI, the method of the request, and the
status code for the response, HTTP/2 uses special pseudo-header status code for the response, HTTP/2 uses special pseudo-header
fields beginning with ':' character (ASCII 0x3a) for this purpose. fields beginning with ':' character (ASCII 0x3a) for this purpose.
Pseudo-header fields are only valid in the HTTP/2 context. These are Pseudo-header fields are not HTTP header fields. Endpoints MUST NOT
not HTTP header fields. Endpoints MUST NOT generate pseudo-header generate pseudo-header fields other than those defined in this
fields other than those defined in this document. document.
Pseudo-header fields are only valid in the context in which they are Pseudo-header fields are only valid in the context in which they are
defined. Pseudo-header fields defined for requests MUST NOT appear defined. Pseudo-header fields defined for requests MUST NOT appear
in responses; pseudo-header fields defined for responses MUST NOT in responses; pseudo-header fields defined for responses MUST NOT
appear in requests. Pseudo-header fields MUST NOT appear in appear in requests. Pseudo-header fields MUST NOT appear in
trailers. Endpoints MUST treat a request or response that contains trailers. Endpoints MUST treat a request or response that contains
undefined or invalid pseudo-header fields as malformed undefined or invalid pseudo-header fields as malformed
(Section 8.1.2.6). (Section 8.1.2.6).
Just as in HTTP/1.x, header field names are strings of ASCII
characters that are compared in a case-insensitive fashion. However,
header field names MUST be converted to lowercase prior to their
encoding in HTTP/2. A request or response containing uppercase
header field names MUST be treated as malformed (Section 8.1.2.6).
All pseudo-header fields MUST appear in the header block before All pseudo-header fields MUST appear in the header block before
regular header fields. Any request or response that contains a regular header fields. Any request or response that contains a
pseudo-header field that appears in a header block after a regular pseudo-header field that appears in a header block after a regular
header field MUST be treated as malformed (Section 8.1.2.6). header field MUST be treated as malformed (Section 8.1.2.6).
8.1.2.2. Hop-by-Hop Header Fields 8.1.2.2. Connection-Specific Header Fields
HTTP/2 does not use the Connection header field to indicate "hop-by- HTTP/2 does not use the Connection header field to indicate
hop" header fields; in this protocol, connection-specific metadata is connection-specific header fields; in this protocol, connection-
conveyed by other means. As such, a HTTP/2 message containing specific metadata is conveyed by other means. An endpoint MUST NOT
Connection MUST be treated as malformed (Section 8.1.2.6). generate an HTTP/2 message containing connection-specific header
fields; any message containing connection-specific header fields MUST
be treated as malformed (Section 8.1.2.6).
The only exception to this is the TE header field, which MAY be
present in an HTTP/2 request; when it is, it MUST NOT contain any
value other than "trailers".
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 the
Connection. Connection header field.
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
than "trailers".
Note: HTTP/2 purposefully does not support upgrade to another Note: HTTP/2 purposefully does not support upgrade to another
protocol. The handshake methods described in Section 3 are protocol. The handshake methods described in Section 3 are
believed sufficient to negotiate the use of alternative protocols. believed sufficient to negotiate the use of alternative protocols.
8.1.2.3. Request Header Fields 8.1.2.3. Request Pseudo-Header Fields
HTTP/2 defines a number of pseudo header fields starting with a colon The following pseudo-header fields are defined for HTTP/2 requests:
':' character that carry information about the request target:
o The ":method" header field includes the HTTP method ([RFC7231], o The ":method" pseudo-header field includes the HTTP method
Section 4). ([RFC7231], Section 4).
o The ":scheme" header field includes the scheme portion of the o The ":scheme" pseudo-header field includes the scheme portion of
target URI ([RFC3986], Section 3.1). the 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" pseudo-header field includes the authority
the target URI ([RFC3986], Section 3.2). The authority MUST NOT portion of the target URI ([RFC3986], Section 3.2). The authority
include the deprecated "userinfo" subcomponent for "http" or MUST NOT include the deprecated "userinfo" subcomponent for "http"
"https" schemed URIs. or "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 pseudo-header field MUST be omitted when
from an HTTP/1.1 request that has a request target in origin or translating from an HTTP/1.1 request that has a request target in
asterisk form (see [RFC7230], Section 5.3). Clients that generate origin or asterisk form (see [RFC7230], Section 5.3). Clients
HTTP/2 requests directly SHOULD instead omit the "Host" header that generate HTTP/2 requests directly SHOULD use the ":authority"
field. An intermediary that converts an HTTP/2 request to pseudo-header field instead of the Host header field. An
HTTP/1.1 MUST create a "Host" header field if one is not present intermediary that converts an HTTP/2 request to HTTP/1.1 MUST
in a request by copying the value of the ":authority" header create a Host header field if one is not present in a request by
field. copying the value of the ":authority" pseudo-header field.
o The ":path" header field includes the path and query parts of the o The ":path" pseudo-header field includes the path and query parts
target URI (the "path-absolute" production from [RFC3986] and of the target URI (the "path-absolute" production and optionally a
optionally a '?' character followed by the "query" production, see '?' character followed by the "query" production (see Sections 3.3
[RFC3986], Section 3.3 and [RFC3986], Section 3.4). A request in and 3.4 of [RFC3986]). A request in asterisk form includes the
asterisk form includes the value '*' for the ":path" header field. value '*' for the ":path" pseudo-header field.
This field MUST NOT be empty for "http" or "https" URIs; "http" or This pseudo-header field MUST NOT be empty for "http" or "https"
"https" URIs that do not contain a path component MUST include a URIs; "http" or "https" URIs that do not contain a path component
value of '/'. The exception to this rule is an OPTIONS request MUST include a value of '/'. The exception to this rule is an
for an "http" or "https" URI that does not include a path OPTIONS request for an "http" or "https" URI that does not include
component; these MUST include a ":path" header field with a value a path component; these MUST include a ":path" pseudo-header field
of '*' (see [RFC7230], Section 5.3.4). with a value of '*' (see [RFC7230], Section 5.3.4).
All HTTP/2 requests MUST include exactly one valid value for the All HTTP/2 requests MUST include exactly one valid value for the
":method", ":scheme", and ":path" header fields, unless this is a ":method", ":scheme", and ":path" pseudo-header fields, unless it is
CONNECT request (Section 8.3). An HTTP request that omits mandatory a CONNECT request (Section 8.3). An HTTP request that omits
header fields is malformed (Section 8.1.2.6). mandatory pseudo-header fields is malformed (Section 8.1.2.6).
HTTP/2 does not define a way to carry the version identifier that is HTTP/2 does not define a way to carry the version identifier that is
included in the HTTP/1.1 request line. included in the HTTP/1.1 request line.
8.1.2.4. Response Header Fields 8.1.2.4. Response Pseudo-Header Fields
A single ":status" header field is defined that carries the HTTP For HTTP/2 responses, a single ":status" pseudo-header field is
status code field (see [RFC7231], Section 6). This header field MUST defined that carries the HTTP status code field (see [RFC7231],
be included in all responses, otherwise the response is malformed Section 6). This pseudo-header field MUST be included in all
(Section 8.1.2.6). responses; otherwise, the response is malformed (Section 8.1.2.6).
HTTP/2 does not define a way to carry the version or reason phrase HTTP/2 does not define a way to carry the version or reason phrase
that is included in an HTTP/1.1 status line. that is included in an HTTP/1.1 status line.
8.1.2.5. Compressing the Cookie Header Field 8.1.2.5. Compressing the Cookie Header Field
The Cookie header field [COOKIE] can carry a significant amount of The Cookie header field [COOKIE] uses a semi-colon (";") to delimit
redundant data. cookie-pairs (or "crumbs"). This header field doesn't follow the
list construction rules in HTTP (see [RFC7230], Section 3.2.2), which
The Cookie header field uses a semi-colon (";") to delimit cookie-
pairs (or "crumbs"). This header field doesn't follow the list
construction rules in HTTP (see [RFC7230], Section 3.2.2), which
prevents cookie-pairs from being separated into different name-value prevents cookie-pairs from being separated into different name-value
pairs. This can significantly reduce compression efficiency as pairs. This can significantly reduce compression efficiency as
individual cookie-pairs are updated. individual cookie-pairs are updated.
To allow for better compression efficiency, the Cookie header field To allow for better compression efficiency, the Cookie header field
MAY be split into separate header fields, each with one or more MAY be split into separate header fields, each with one or more
cookie-pairs. If there are multiple Cookie header fields after cookie-pairs. If there are multiple Cookie header fields after
decompression, these MUST be concatenated into a single octet string decompression, these MUST be concatenated into a single octet string
using the two octet delimiter of 0x3B, 0x20 (the ASCII string "; ") using the two-octet delimiter of 0x3B, 0x20 (the ASCII string "; ")
before being passed into a non-HTTP/2 context, such as an HTTP/1.1 before being passed into a non-HTTP/2 context, such as an HTTP/1.1
connection, or a generic HTTP server application. connection, or a generic HTTP server application.
Therefore, the following two lists of Cookie header fields are Therefore, the following two lists of Cookie header fields are
semantically equivalent. semantically equivalent.
cookie: a=b; c=d; e=f cookie: a=b; c=d; e=f
cookie: a=b cookie: a=b
cookie: c=d cookie: c=d
cookie: e=f cookie: e=f
8.1.2.6. Malformed Requests and Responses 8.1.2.6. Malformed Requests and Responses
A malformed request or response is one that is an otherwise valid A malformed request or response is one that is an otherwise valid
sequence of HTTP/2 frames, but is otherwise invalid due to the sequence of HTTP/2 frames but is invalid due to the presence of
presence of extraneous frames, prohibited header fields, the absence extraneous frames, prohibited header fields, the absence of mandatory
of mandatory header fields, or the inclusion of uppercase header header fields, or the inclusion of uppercase header field names.
field names.
A request or response that includes an entity body can include a A request or response that includes a payload 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
malformed if the value of a "content-length" header field does not if the value of a content-length header field does not equal the sum
equal the sum of the DATA frame payload lengths that form the body, of the DATA frame payload lengths that form the body. A response
with the exception of responses to HEAD requests, which always that is defined to have no payload, as described in [RFC7230],
contain no DATA frames. Section 3.3.2, can have a non-zero content-length header field, even
though no content is included in DATA frames.
Intermediaries that process HTTP requests or responses (i.e., any Intermediaries that process HTTP requests or responses (i.e., any
intermediary not acting as a tunnel) MUST NOT forward a malformed intermediary not acting as a tunnel) MUST NOT forward a malformed
request or response. Malformed requests or responses that are request or response. Malformed requests or responses that are
detected MUST be treated as a stream error (Section 5.4.2) of type detected MUST be treated as a stream error (Section 5.4.2) of type
PROTOCOL_ERROR. PROTOCOL_ERROR.
For malformed requests, a server MAY send an HTTP response prior to For malformed requests, a server MAY send an HTTP response prior to
closing or resetting the stream. Clients MUST NOT accept a malformed closing or resetting the stream. Clients MUST NOT accept a malformed
response. Note that these requirements are intended to protect response. Note that these requirements are intended to protect
against several types of common attacks against HTTP; they are against several types of common attacks against HTTP; they are
deliberately strict, because being permissive can expose deliberately strict because being permissive can expose
implementations to these vulnerabilities. implementations to these vulnerabilities.
8.1.3. Examples 8.1.3. Examples
This section shows HTTP/1.1 requests and responses, with This section shows HTTP/1.1 requests and responses, with
illustrations of equivalent HTTP/2 requests and responses. illustrations of equivalent HTTP/2 requests and responses.
An HTTP GET request includes request header fields and no body and is An HTTP GET request includes request header fields and no payload
therefore transmitted as a single HEADERS frame, followed by zero or body and is therefore transmitted as a single HEADERS frame, followed
more CONTINUATION frames containing the serialized block of request by zero or more CONTINUATION frames containing the serialized block
header fields. The HEADERS frame in the following has both the of request header fields. The HEADERS frame in the following has
END_HEADERS and END_STREAM flags set; no CONTINUATION frames are both the END_HEADERS and END_STREAM flags set; no CONTINUATION frames
sent: are sent.
GET /resource HTTP/1.1 HEADERS GET /resource HTTP/1.1 HEADERS
Host: example.org ==> + END_STREAM Host: example.org ==> + END_STREAM
Accept: image/jpeg + END_HEADERS Accept: image/jpeg + END_HEADERS
:method = GET :method = GET
:scheme = https :scheme = https
:path = /resource :path = /resource
host = example.org host = example.org
accept = image/jpeg accept = image/jpeg
skipping to change at page 56, line 10 skipping to change at page 58, line 10
CONTINUATION frames containing the request header fields, followed by CONTINUATION frames containing the request header fields, followed by
one or more DATA frames, with the last CONTINUATION (or HEADERS) one or more DATA frames, with the last CONTINUATION (or HEADERS)
frame having the END_HEADERS flag set and the final DATA frame having frame having the END_HEADERS flag set and the final DATA frame having
the END_STREAM flag set: the END_STREAM flag set:
POST /resource HTTP/1.1 HEADERS POST /resource HTTP/1.1 HEADERS
Host: example.org ==> - END_STREAM Host: example.org ==> - END_STREAM
Content-Type: image/jpeg - END_HEADERS Content-Type: image/jpeg - END_HEADERS
Content-Length: 123 :method = POST Content-Length: 123 :method = POST
:path = /resource :path = /resource
{binary data} content-type = image/jpeg {binary data} :scheme = https
CONTINUATION CONTINUATION
+ END_HEADERS + END_HEADERS
content-type = image/jpeg
host = example.org host = example.org
:scheme = https
content-length = 123 content-length = 123
DATA DATA
+ END_STREAM + END_STREAM
{binary data} {binary data}
Note that data contributing to any given header field could be spread Note that data contributing to any given header field could be spread
between header block fragments. The allocation of header fields to between header block fragments. The allocation of header fields to
frames in this example is illustrative only. frames in this example is illustrative only.
skipping to change at page 56, line 42 skipping to change at page 58, line 42
Content-Type: image/jpeg ==> - END_STREAM Content-Type: image/jpeg ==> - END_STREAM
Content-Length: 123 + END_HEADERS Content-Length: 123 + END_HEADERS
:status = 200 :status = 200
{binary data} content-type = image/jpeg {binary data} content-type = image/jpeg
content-length = 123 content-length = 123
DATA DATA
+ END_STREAM + END_STREAM
{binary data} {binary data}
An informational response using a 1xx status code other than 101 is
transmitted as a HEADERS frame, followed by zero or more CONTINUATION
frames.
Trailing header fields are sent as a header block after both the Trailing header fields are sent as a header block after both the
request or response header block and all the DATA frames have been request or response header block and all the DATA frames have been
sent. The HEADERS frame starting the trailers header block has the sent. The HEADERS frame starting the trailers header block has the
END_STREAM flag set. END_STREAM flag set.
The following example includes both a 100 (Continue) status code,
which is sent in response to a request containing a "100-continue"
token in the Expect header field, and trailing header fields:
HTTP/1.1 100 Continue HEADERS
Extension-Field: bar ==> - END_STREAM
+ END_HEADERS
:status = 100
extension-field = bar
HTTP/1.1 200 OK HEADERS HTTP/1.1 200 OK HEADERS
Content-Type: image/jpeg ==> - END_STREAM Content-Type: image/jpeg ==> - END_STREAM
Transfer-Encoding: chunked + END_HEADERS Transfer-Encoding: chunked + END_HEADERS
Trailer: Foo :status = 200 Trailer: Foo :status = 200
content-length = 123 content-length = 123
123 content-type = image/jpeg 123 content-type = image/jpeg
{binary data} trailer = Foo {binary data} trailer = Foo
0 0
Foo: bar DATA Foo: bar DATA
- END_STREAM - END_STREAM
{binary data} {binary data}
HEADERS HEADERS
+ END_STREAM + END_STREAM
+ END_HEADERS + END_HEADERS
foo = bar foo = bar
An informational response using a 1xx status code other than 101 is
transmitted as a HEADERS frame, followed by zero or more CONTINUATION
frames:
HTTP/1.1 103 BAR HEADERS
Extension-Field: bar ==> - END_STREAM
+ END_HEADERS
:status = 103
extension-field = bar
8.1.4. Request Reliability Mechanisms in HTTP/2 8.1.4. Request Reliability Mechanisms in HTTP/2
In HTTP/1.1, an HTTP client is unable to retry a non-idempotent In HTTP/1.1, an HTTP client is unable to retry a non-idempotent
request when an error occurs, because there is no means to determine request when an error occurs because there is no means to determine
the nature of the error. It is possible that some server processing the nature of the error. It is possible that some server processing
occurred prior to the error, which could result in undesirable occurred prior to the error, which could result in undesirable
effects if the request were reattempted. effects if the request were reattempted.
HTTP/2 provides two mechanisms for providing a guarantee to a client HTTP/2 provides two mechanisms for providing a guarantee to a client
that a request has not been processed: that a request has not been processed:
o The GOAWAY frame indicates the highest stream number that might o The GOAWAY frame indicates the highest stream number that might
have been processed. Requests on streams with higher numbers are have been processed. Requests on streams with higher numbers are
therefore guaranteed to be safe to retry. therefore guaranteed to be safe to retry.
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A server MUST NOT indicate that a stream has not been processed A server MUST NOT indicate that a stream has not been processed
unless it can guarantee that fact. If frames that are on a stream unless it can guarantee that fact. If frames that are on a stream
are passed to the application layer for any stream, then are passed to the application layer for any stream, then
REFUSED_STREAM MUST NOT be used for that stream, and a GOAWAY frame REFUSED_STREAM MUST NOT be used for that stream, and a GOAWAY frame
MUST include a stream identifier that is greater than or equal to the MUST include a stream identifier that is greater than or equal to the
given stream identifier. given stream identifier.
In addition to these mechanisms, the PING frame provides a way for a In addition to these mechanisms, the PING frame provides a way for a
client to easily test a connection. Connections that remain idle can client to easily test a connection. Connections that remain idle can
become broken as some middleboxes (for instance, network address become broken as some middleboxes (for instance, network address
translators, or load balancers) silently discard connection bindings. translators or load balancers) silently discard connection bindings.
The PING frame allows a client to safely test whether a connection is The PING frame allows a client to safely test whether a connection is
still active without sending a request. still active without sending a request.
8.2. Server Push 8.2. Server Push
HTTP/2 enables a server to pre-emptively send (or "push") one or more HTTP/2 allows a server to pre-emptively send (or "push") responses
associated responses to a client in response to a single request. (along with corresponding "promised" requests) to a client in
This feature becomes particularly helpful when the server knows the association with a previous client-initiated request. This can be
client will need to have those responses available in order to fully useful when the server knows the client will need to have those
process the response to the original request. responses available in order to fully process the response to the
original request.
Pushing additional responses is optional, and is negotiated between A client can request that server push be disabled, though this is
individual endpoints. The SETTINGS_ENABLE_PUSH setting can be set to negotiated for each hop independently. The SETTINGS_ENABLE_PUSH
0 to indicate that server push is disabled. setting can be set to 0 to indicate that server push is disabled.
Because pushing responses is effectively hop-by-hop, an intermediary Promised requests MUST be cacheable (see [RFC7231], Section 4.2.3),
could receive pushed responses from the server and choose not to MUST be safe (see [RFC7231], Section 4.2.1), and MUST NOT include a
forward those on to the client. In other words, how to make use of request body. Clients that receive a promised request that is not
the pushed responses is up to that intermediary. Equally, the cacheable, that is not known to be safe, or that indicates the
intermediary might choose to push additional responses to the client, presence of a request body MUST reset the promised stream with a
stream error (Section 5.4.2) of type PROTOCOL_ERROR. Note this could
result in the promised stream being reset if the client does not
recognize a newly defined method as being safe.
Pushed responses that are cacheable (see [RFC7234], Section 3) can be
stored by the client, if it implements an HTTP cache. Pushed
responses are considered successfully validated on the origin server
(e.g., if the "no-cache" cache response directive is present
([RFC7234], Section 5.2.2)) while the stream identified by the
promised stream ID is still open.
Pushed responses that are not cacheable MUST NOT be stored by any
HTTP cache. They MAY be made available to the application
separately.
The server MUST include a value in the ":authority" pseudo-header
field for which the server is authoritative (see Section 10.1). A
client MUST treat a PUSH_PROMISE for which the server is not
authoritative as a stream error (Section 5.4.2) of type
PROTOCOL_ERROR.
An intermediary can receive pushes from the server and choose not to
forward them on to the client. In other words, how to make use of
the pushed information is up to that intermediary. Equally, the
intermediary might choose to make additional pushes 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 the SETTINGS_ENABLE_PUSH setting to a value other than 0 by treating the
message as a connection error (Section 5.4.1) of type PROTOCOL_ERROR. message as a connection error (Section 5.4.1) of type PROTOCOL_ERROR.
A server can only push responses that are cacheable (see [RFC7234],
Section 3); promised requests MUST be safe (see [RFC7231], 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 8.1.2.3). The server MUST include a method in the ":method" (Section 8.1.2.3). The server MUST include a method in the ":method"
header field that is safe and cacheable. If a client receives a pseudo-header field that is safe and cacheable. If a client receives
PUSH_PROMISE that does not include a complete and valid set of header a PUSH_PROMISE that does not include a complete and valid set of
fields, or the ":method" header field identifies a method that is not header fields or the ":method" pseudo-header field identifies a
safe, it MUST respond with a stream error (Section 5.4.2) of type method that is not safe, it MUST respond with a stream error
PROTOCOL_ERROR. (Section 5.4.2) of type 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.
For example, if the server receives a request for a document For example, if the server receives a request for a document
containing embedded links to multiple image files, and the server containing embedded links to multiple image files and the server
chooses to push those additional images to the client, sending push chooses to push those additional images to the client, sending
promises before the DATA frames that contain the image links ensures PUSH_PROMISE frames before the DATA frames that contain the image
that the client is able to see the promises before discovering links ensures that the client is able to see that a resource will be
embedded links. Similarly, if the server pushes responses referenced pushed before discovering embedded links. Similarly, if the server
by the header block (for instance, in Link header fields), sending pushes responses referenced by the header block (for instance, in
the push promises before sending the header block ensures that Link header fields), sending a PUSH_PROMISE before sending the header
clients do not request them. block ensures that clients do not request those resources.
PUSH_PROMISE frames MUST NOT be sent by the client. PUSH_PROMISE frames MUST NOT be sent by the client.
PUSH_PROMISE frames can be sent by the server in response to any PUSH_PROMISE frames can be sent by the server in response to any
client-initiated stream, but the stream MUST be in either the "open" client-initiated stream, but the stream MUST be in either the "open"
or "half closed (remote)" state with respect to the server. or "half-closed (remote)" state with respect to the server.
PUSH_PROMISE frames are interspersed with the frames that comprise a PUSH_PROMISE frames are interspersed with the frames that comprise a
response, though they cannot be interspersed with HEADERS and response, though they cannot be interspersed with HEADERS and
CONTINUATION frames that comprise a single header block. CONTINUATION frames that comprise a single header block.
Sending a PUSH_PROMISE frame creates a new stream and puts the stream Sending a PUSH_PROMISE frame creates a new stream and puts the stream
into the "reserved (local)" state for the server and the "reserved into the "reserved (local)" state for the server and the "reserved
(remote)" state for the client. (remote)" state for the client.
8.2.2. Push Responses 8.2.2. Push Responses
After sending the PUSH_PROMISE frame, the server can begin delivering After sending the PUSH_PROMISE frame, the server can begin delivering
the pushed response as a response (Section 8.1.2.4) on a server- the pushed response as a response (Section 8.1.2.4) on a server-
initiated stream that uses the promised stream identifier. The initiated stream that uses the promised stream identifier. The
server uses this stream to transmit an HTTP response, using the same server uses this stream to transmit an HTTP response, using the same
sequence of frames as defined in Section 8.1. This stream becomes sequence of frames as defined in Section 8.1. This stream becomes
"half closed" to the client (Section 5.1) after the initial HEADERS "half-closed" to the client (Section 5.1) after the initial HEADERS
frame is sent. frame is sent.
Once a client receives a PUSH_PROMISE frame and chooses to accept the Once a client receives a PUSH_PROMISE frame and chooses to accept the
pushed response, the client SHOULD NOT issue any requests for the pushed response, the client SHOULD NOT issue any requests for the
promised response until after the promised stream has closed. promised response until after the promised stream has closed.
If the client determines, for any reason, that it does not wish to If the client determines, for any reason, that it does not wish to
receive the pushed response from the server, or if the server takes receive the pushed response from the server or if the server takes
too long to begin sending the promised response, the client can send too long to begin sending the promised response, the client can send
an RST_STREAM frame, using either the CANCEL or REFUSED_STREAM codes, a RST_STREAM frame, using either the CANCEL or REFUSED_STREAM code
and referencing the pushed stream's identifier. and referencing the pushed stream's identifier.
A client can use the SETTINGS_MAX_CONCURRENT_STREAMS setting to limit A client can use the SETTINGS_MAX_CONCURRENT_STREAMS setting to limit
the number of responses that can be concurrently pushed by a server. the number of responses that can be concurrently pushed by a server.
Advertising a SETTINGS_MAX_CONCURRENT_STREAMS value of zero disables Advertising a SETTINGS_MAX_CONCURRENT_STREAMS value of zero disables
server push by preventing the server from creating the necessary server push by preventing the server from creating the necessary
streams. This does not prohibit a server from sending PUSH_PROMISE streams. This does not prohibit a server from sending PUSH_PROMISE
frames; clients need to reset any promised streams that are not frames; clients need to reset any promised streams that are not
wanted. wanted.
Clients receiving a pushed response MUST validate that the server is Clients receiving a pushed response MUST validate that either the
authorized to provide the response, see Section 10.1. For example, a server is authoritative (see Section 10.1) or the proxy that provided
server that offers a certificate for only the "example.com" DNS-ID or the pushed response is configured for the corresponding request. For
Common Name is not permitted to push a response for example, a server that offers a certificate for only the
"https://www.example.org/doc". "example.com" DNS-ID or Common Name is not permitted to push a
response for "https://www.example.org/doc".
The response for a PUSH_PROMISE stream begins with a HEADERS frame, The response for a PUSH_PROMISE stream begins with a HEADERS frame,
which immediately puts the stream into the "half closed (remote)" which immediately puts the stream into the "half-closed (remote)"
state for the server and "half closed (local)" state for the client, state for the server and "half-closed (local)" state for the client,
and ends with a frame bearing END_STREAM, which places the stream in and ends with a frame bearing END_STREAM, which places the stream in
the "closed" state. the "closed" state.
Note: The client never sends a frame with the END_STREAM flag for a Note: The client never sends a frame with the END_STREAM flag for
server push. a server push.
8.3. The CONNECT Method 8.3. The CONNECT Method
In HTTP/1.x, the pseudo-method CONNECT ([RFC7231], Section 4.3.6) is In HTTP/1.x, the pseudo-method CONNECT ([RFC7231], Section 4.3.6) is
used to convert an HTTP connection into a tunnel to a remote host. used to convert an HTTP connection into a tunnel to a remote host.
CONNECT is primarily used with HTTP proxies to establish a TLS CONNECT is primarily used with HTTP proxies to establish a TLS
session with an origin server for the purposes of interacting with session with an origin server for the purposes of interacting with
"https" resources. "https" resources.
In HTTP/2, the CONNECT method is used to establish a tunnel over a In HTTP/2, the CONNECT method is used to establish a tunnel over a
single HTTP/2 stream to a remote host, for similar purposes. The single HTTP/2 stream to a remote host for similar purposes. The HTTP
HTTP header field mapping works as mostly as defined in Request header field mapping works as defined in Section 8.1.2.3 ("Request
Header Fields (Section 8.1.2.3), with a few differences. Pseudo-Header Fields"), with a few differences. Specifically:
Specifically:
o The ":method" header field is set to "CONNECT". o The ":method" pseudo-header field is set to "CONNECT".
o The ":scheme" and ":path" header fields MUST be omitted. o The ":scheme" and ":path" pseudo-header fields MUST be omitted.
o The ":authority" header field contains the host and port to o The ":authority" pseudo-header field contains the host and port to
connect to (equivalent to the authority-form of the request-target connect to (equivalent to the authority-form of the request-target
of CONNECT requests, see [RFC7230], Section 5.3). of CONNECT requests (see [RFC7230], Section 5.3)).
A CONNECT request that does not conform to these restrictions is
malformed (Section 8.1.2.6).
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" pseudo-header field. Once
connection is successfully established, the proxy sends a HEADERS this connection is successfully established, the proxy sends a
frame containing a 2xx series status code to the client, as defined HEADERS frame containing a 2xx series status code to the client, as
in [RFC7231], Section 4.3.6. defined 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 is 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.
The TCP connection can be closed by either peer. The END_STREAM flag The TCP connection can be closed by either peer. The END_STREAM flag
on a DATA frame is treated as being equivalent to the TCP FIN bit. A on a DATA frame is treated as being equivalent to the TCP FIN bit. A
client is expected to send a DATA frame with the END_STREAM flag set client is expected to send a DATA frame with the END_STREAM flag set
after receiving a frame bearing the END_STREAM flag. A proxy that after receiving a frame bearing the END_STREAM flag. A proxy that
receives a DATA frame with the END_STREAM flag set sends the attached receives a DATA frame with the END_STREAM flag set sends the attached
data with the FIN bit set on the last TCP segment. A proxy that data with the FIN bit set on the last TCP segment. A proxy that
receives a TCP segment with the FIN bit set sends a DATA frame with receives a TCP segment with the FIN bit set sends a DATA frame with
the END_STREAM flag set. Note that the final TCP segment or DATA the END_STREAM flag set. Note that the final TCP segment or DATA
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9. Additional HTTP Requirements/Considerations 9. Additional HTTP Requirements/Considerations
This section outlines attributes of the HTTP protocol that improve This section outlines attributes of the HTTP protocol that improve
interoperability, reduce exposure to known security vulnerabilities, interoperability, reduce exposure to known security vulnerabilities,
or reduce the potential for implementation variation. or reduce the potential for implementation variation.
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 that clients will not close connections until it is
that no further communication with a server is necessary (for determined that no further communication with a server is necessary
example, when a user navigates away from a particular web page), or (for example, when a user navigates away from a particular web page)
until the server closes the connection. or 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
host and port pair, where host is derived from a URI, a selected host and port pair, where the host is derived from a URI, a selected
alternative service [ALT-SVC], or a configured proxy. alternative service [ALT-SVC], or a configured proxy.
A client can create additional connections as replacements, either to A client can create additional connections as replacements, either to
replace connections that are near to exhausting the available stream replace connections that are near to exhausting the available stream
identifier space (Section 5.1.1), to refresh the keying material for identifier space (Section 5.1.1), to refresh the keying material for
a TLS connection, or to replace connections that have encountered a TLS connection, or to replace connections that have encountered
errors (Section 5.4.1). 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. multiple connections with the same configuration.
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-layer
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 9.1.1. Connection Reuse
Clients MAY use a single server connection to send requests for URIs Connections that are made to an origin server, either directly or
with multiple different authority components as long as the server is through a tunnel created using the CONNECT method (Section 8.3), MAY
authoritative (Section 10.1). For "http" resources, this depends on be reused for requests with multiple different URI authority
the host having resolved to the same IP address. components. A connection can be reused as long as the origin server
is authoritative (Section 10.1). For TCP connections without TLS,
this depends on the host having resolved to the same IP address.
For "https" resources, connection reuse additionally depends on For "https" resources, connection reuse additionally depends on
having a certificate that is valid for the host in the URI. That is having a certificate that is valid for the host in the URI. The
the use of server certificate with multiple "subjectAltName" certificate presented by the server MUST satisfy any checks that the
attributes, or names with wildcards. For example, a certificate with client would perform when forming a new TLS connection for the host
in the URI.
An origin server might offer a certificate with multiple
"subjectAltName" attributes or names with wildcards, one of which is
valid for the authority in the URI. For example, a certificate with
a "subjectAltName" of "*.example.com" might permit the use of the a "subjectAltName" of "*.example.com" might permit the use of the
same connection for "a.example.com" and "b.example.com". same connection for requests to URIs starting with
"https://a.example.com/" and "https://b.example.com/".
In some deployments, reusing a connection for multiple origins can In some deployments, reusing a connection for multiple origins can
result in requests being directed to the wrong origin server. For result in requests being directed to the wrong origin server. For
example, TLS termination might be performed by a middlebox that uses example, TLS termination might be performed by a middlebox that uses
the TLS Server Name Indication (SNI) [TLS-EXT] extension to select the TLS Server Name Indication (SNI) [TLS-EXT] extension to select an
the an origin server. This means that it is possible for clients to origin server. This means that it is possible for clients to send
send confidential information to servers that might not be the confidential information to servers that might not be the intended
intended target for the request, even though the server has valid target for the request, even though the server is otherwise
authentication credentials. authoritative.
A server that does not wish clients to reuse connections can indicate A server that does not wish clients to reuse connections can indicate
that it is not authoritative for a request by sending a 421 (Not that it is not authoritative for a request by sending a 421
Authoritative) status code in response to the request (see (Misdirected Request) status code in response to the request (see
Section 9.1.2). Section 9.1.2).
9.1.2. The 421 (Not Authoritative) Status Code A client that is configured to use a proxy over HTTP/2 directs
requests to that proxy through a single connection. That is, all
requests sent via a proxy reuse the connection to the proxy.
The 421 (Not Authoritative) status code indicates that the current 9.1.2. The 421 (Misdirected Request) Status Code
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 The 421 (Misdirected Request) status code indicates that the request
MAY retry the request - whether the request method is idempotent or was directed at a server that is not able to produce a response.
not - over a different connection. This is possible if a connection This can be sent by a server that is not configured to produce
responses for the combination of scheme and authority that are
included in the request URI.
Clients receiving a 421 (Misdirected Request) 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 is reused (Section 9.1.1) or if an alternative service is selected
([ALT-SVC]). [ALT-SVC].
This status code MUST NOT be generated by proxies. This status code MUST NOT be generated by proxies.
A 421 response is cacheable by default; i.e., unless otherwise A 421 response is cacheable by default, i.e., unless otherwise
indicated by the method definition or explicit cache controls (see indicated by the method definition or explicit cache controls (see
Section 4.2.2 of [RFC7234]). Section 4.2.2 of [RFC7234]).
9.2. Use of TLS Features 9.2. Use of TLS Features
Implementations of HTTP/2 MUST support TLS 1.2 [TLS12] for HTTP/2 Implementations of HTTP/2 MUST use TLS version 1.2 [TLS12] or higher
over TLS. The general TLS usage guidance in [TLSBCP] SHOULD be for HTTP/2 over TLS. The general TLS usage guidance in [TLSBCP]
followed, with some additional restrictions that are specific to SHOULD be followed, with some additional restrictions that are
HTTP/2. specific to HTTP/2.
An implementation of HTTP/2 over TLS MUST use TLS 1.2 or higher with
the restrictions on feature set and cipher suite described in this
section. Due to implementation limitations, it might not be possible
to fail TLS negotiation. An endpoint MUST immediately terminate an
HTTP/2 connection that does not meet these minimum requirements with
a connection error (Section 5.4.1) of type INADEQUATE_SECURITY.
9.2.1. TLS Features
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 Deployments of HTTP/2 that negotiate TLS 1.3 or higher need only
lead to the exposure of information that would not otherwise be support and use the SNI extension; deployments of TLS 1.2 are subject
revealed [RFC3749]. Generic compression is unnecessary since HTTP/2 to the requirements in the following sections. Implementations are
provides compression features that are more aware of context and encouraged to provide defaults that comply, but it is recognized that
therefore likely to be more appropriate for use for performance, deployments are ultimately responsible for compliance.
security or other reasons.
The TLS implementation MUST disable renegotiation. An endpoint MUST 9.2.1. TLS 1.2 Features
treat a TLS renegotiation as a connection error (Section 5.4.1) of
type PROTOCOL_ERROR. Note that disabling renegotiation can result in
long-lived connections becoming unusable due to limits on the number
of messages the underlying cipher suite can encipher.
A client MAY use renegotiation to provide confidentiality protection This section describes restrictions on the TLS 1.2 feature set that
for client credentials offered in the handshake, but any can be used with HTTP/2. Due to deployment limitations, it might not
be possible to fail TLS negotiation when these restrictions are not
met. An endpoint MAY immediately terminate an HTTP/2 connection that
does not meet these TLS requirements with a connection error
(Section 5.4.1) of type INADEQUATE_SECURITY.
A deployment of HTTP/2 over TLS 1.2 MUST disable compression. TLS
compression can lead to the exposure of information that would not
otherwise be revealed [RFC3749]. Generic compression is unnecessary
since HTTP/2 provides compression features that are more aware of
context and therefore likely to be more appropriate for use for
performance, security, or other reasons.
A deployment of HTTP/2 over TLS 1.2 MUST disable renegotiation. An
endpoint MUST treat a TLS renegotiation as a connection error
(Section 5.4.1) of type PROTOCOL_ERROR. Note that disabling
renegotiation can result in long-lived connections becoming unusable
due to limits on the number of messages the underlying cipher suite
can encipher.
An endpoint MAY use renegotiation to provide confidentiality
protection for client credentials offered in the handshake, but any
renegotiation MUST occur prior to sending the connection preface. A renegotiation MUST occur prior to sending the connection preface. A
server SHOULD request a client certificate if it sees a renegotiation server SHOULD request a client certificate if it sees a renegotiation
request immediately after establishing a connection. request immediately after establishing a connection.
This effectively prevents the use of renegotiation in response to a This effectively prevents the use of renegotiation in response to a
request for a specific protected resource. A future specification request for a specific protected resource. A future specification
might provide a way to support this use case. might provide a way to support this use case. Alternatively, a
server might use an error (Section 5.4) of type HTTP_1_1_REQUIRED to
request the client use a protocol that supports renegotiation.
9.2.2. TLS Cipher Suites Implementations MUST support ephemeral key exchange sizes of at least
2048 bits for cipher suites that use ephemeral finite field Diffie-
Hellman (DHE) [TLS12] and 224 bits for cipher suites that use
ephemeral elliptic curve Diffie-Hellman (ECDHE) [RFC4492]. Clients
MUST accept DHE sizes of up to 4096 bits. Endpoints MAY treat
negotiation of key sizes smaller than the lower limits as a
connection error (Section 5.4.1) of type INADEQUATE_SECURITY.
The set of TLS cipher suites that are permitted in HTTP/2 is 9.2.2. TLS 1.2 Cipher Suites
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 A deployment of HTTP/2 over TLS 1.2 SHOULD NOT use any of the cipher
key exchange MUST have a minimum size of 2048 bits for DHE or suites that are listed in the cipher suite black list (Appendix A).
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.
The effect of these restrictions is that TLS 1.2 implementations Endpoints MAY choose to generate a connection error (Section 5.4.1)
could have non-intersecting sets of available cipher suites, since of type INADEQUATE_SECURITY if one of the cipher suites from the
these prevent the use of the cipher suite that TLS 1.2 makes black list is negotiated. A deployment that chooses to use a black-
mandatory. To avoid this problem, implementations of HTTP/2 that use listed cipher suite risks triggering a connection error unless the
TLS 1.2 MUST support TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 set of potential peers is known to accept that cipher suite.
[TLS-ECDHE] with P256 [FIPS186].
Clients MAY advertise support of cipher suites that are prohibited by Implementations MUST NOT generate this error in reaction to the
the above restrictions in order to allow for connection to servers negotiation of a cipher suite that is not on the black list.
that do not support HTTP/2. This enables a fallback to protocols Consequently, when clients offer a cipher suite that is not on the
without these constraints without the additional latency imposed by black list, they have to be prepared to use that cipher suite with
using a separate connection for fallback. HTTP/2.
The black list includes the cipher suite that TLS 1.2 makes
mandatory, which means that TLS 1.2 deployments could have non-
intersecting sets of permitted cipher suites. To avoid this problem
causing TLS handshake failures, deployments of HTTP/2 that use TLS
1.2 MUST support TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 [TLS-ECDHE]
with the P-256 elliptic curve [FIPS186].
Note that clients might advertise support of cipher suites that are
on the black list in order to allow for connection to servers that do
not support HTTP/2. This allows servers to select HTTP/1.1 with a
cipher suite that is on the HTTP/2 black list. However, this can
result in HTTP/2 being negotiated with a black-listed cipher suite if
the application protocol and cipher suite are independently selected.
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
are authoritative for those resources. This is particularly
important for server push (Section 8.2), where the client validates
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
[RFC7230], Section 9.1. This relies on local name resolution for the [RFC7230], Section 9.1). This relies on local name resolution for
"http" URI scheme, and the authenticated server identity for the the "http" URI scheme and the authenticated server identity for the
"https" scheme (see [RFC2818], Section 3). "https" scheme (see [RFC2818], Section 3).
A client MUST discard responses provided by a server that is not
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 a 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 protection against cross protocol attacks. considered sufficient protection against cross-protocol attacks.
ALPN provides a positive indication that a server is willing to ALPN provides a positive indication that a server is willing to
proceed with HTTP/2, which prevents attacks on other TLS-based proceed with HTTP/2, which prevents attacks on other TLS-based
protocols. 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 that 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 in addition to the client connection preface could be exposed field in addition to the client connection preface could be exposed
to a cross-protocol attack. 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 The HTTP/2 header field encoding allows the expression of names that
octets with a length prefix. This enables HTTP/2 to carry any string are not valid field names in the Internet Message Syntax used by
of octets as the name or value of a header field. An intermediary HTTP/1.1. Requests or responses containing invalid header field
that translates HTTP/2 requests or responses into HTTP/1.1 directly names MUST be treated as malformed (Section 8.1.2.6). An
could permit the creation of corrupted HTTP/1.1 messages. An intermediary therefore cannot translate an HTTP/2 request or response
attacker might exploit this behavior to cause the intermediary to containing an invalid field name into an HTTP/1.1 message.
create HTTP/1.1 messages with illegal header fields, extra header
fields, or even new messages that are entirely falsified.
Header field names or values that contain characters not permitted by
HTTP/1.1, including carriage return (ASCII 0xd) or line feed (ASCII
0xa) MUST NOT be translated verbatim by an intermediary, as
stipulated in [RFC7230], Section 3.2.4.
Translation from HTTP/1.x to HTTP/2 does not produce the same Similarly, HTTP/2 allows header field values that are not valid.
opportunity to an attacker. Intermediaries that perform translation While most of the values that can be encoded will not alter header
to HTTP/2 MUST remove any instances of the "obs-fold" production from field parsing, carriage return (CR, ASCII 0xd), line feed (LF, ASCII
header field values. 0xa), and the zero character (NUL, ASCII 0x0) might be exploited by
an attacker if they are translated verbatim. Any request or response
that contains a character not permitted in a header field value MUST
be treated as malformed (Section 8.1.2.6). Valid characters are
defined by the "field-content" ABNF rule in Section 3.2 of [RFC7230].
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.
Caching responses that are pushed is possible based on the guidance Caching responses that are pushed is possible based on the guidance
provided by the origin server in the Cache-Control header field. provided by the origin server in the Cache-Control header field.
However, this can cause issues if a single server hosts more than one However, this can cause issues if a single server hosts more than one
tenant. For example, a server might offer multiple users each a tenant. For example, a server might offer multiple users each a
small portion of its URI space. small portion of its URI space.
Where multiple tenants share space on the same server, that server Where multiple tenants share space on the same server, that server
MUST ensure that tenants are not able to push representations of MUST ensure that tenants are not able to push representations of
resources that they do not have authority over. Failure to enforce resources that they do not have authority over. Failure to enforce
this would allow a tenant to provide a representation that would be this would allow a tenant to provide a representation that would be
served out of cache, overriding the actual representation that the served out of cache, overriding the actual representation that the
authoritative tenant provides. authoritative tenant provides.
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) MUST NOT be used or cached.
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 an 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.
The number of PUSH_PROMISE frames is not constrained in the same The number of PUSH_PROMISE frames is not constrained in the same
fashion. A client that accepts server push SHOULD limit the number fashion. A client that accepts server push SHOULD limit the number
of streams it allows to be in the "reserved (remote)" state. of streams it allows to be in the "reserved (remote)" state. An
Excessive number of server push streams can be treated as a stream excessive number of server push streams can be treated as a stream
error (Section 5.4.2) of type ENHANCE_YOUR_CALM. error (Section 5.4.2) of type ENHANCE_YOUR_CALM.
Processing capacity cannot be guarded as effectively as state Processing capacity cannot be guarded as effectively as state
capacity. 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 or same setting multiple times in the same frame. WINDOW_UPDATE or
PRIORITY frames can be abused to cause an unnecessary waste of PRIORITY frames can be abused to cause an unnecessary waste of
resources. resources.
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
are entirely legitimate, such as the sending of an empty DATA frame uses are entirely legitimate, such as the sending of an empty DATA or
to end a stream. CONTINUATION frame at the end of a stream.
Header compression also offers some opportunities to waste processing Header compression also offers some opportunities to waste processing
resources; see Section 8 of [COMPRESSION] for more details on resources; see Section 7 of [COMPRESSION] for more details on
potential abuses. 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 10.5.1. Limits on Header Block Size
A large header block (Section 4.3) can cause an implementation to A large header block (Section 4.3) can cause an implementation to
commit a large amount of state. In servers and intermediaries, commit a large amount of state. Header fields that are critical for
header fields that are critical to routing, such as ":authority", routing can appear toward the end of a header block, which prevents
":path", and ":scheme" are not guaranteed to be present early in the streaming of header fields to their ultimate destination. This
header block. In particular, values that are in the reference set ordering and other reasons, such as ensuring cache correctness, mean
cannot be emitted until the header block ends. that an endpoint might need to buffer the entire header block. Since
there is no hard limit to the size of a header block, some endpoints
This can prevent streaming of the header fields to their ultimate could be forced to commit a large amount of available memory for
destination, and forces the endpoint to buffer the entire header header fields.
block. Since there is no hard limit to the size of a header block,
an endpoint could be forced to exhaust available memory.
An endpoint can use the SETTINGS_MAX_HEADER_LIST_SIZE to avise peers An endpoint can use the SETTINGS_MAX_HEADER_LIST_SIZE to advise peers
of limits that might apply on the size of header blocks. This of limits that might apply on the size of header blocks. This
setting is only advisory, so endpoints MAY choose to send header setting is only advisory, so endpoints MAY choose to send header
blocks that exceed this limit and risk having the request or response blocks that exceed this limit and risk having the request or response
being treated as malformed. This setting is advertised hop-by-hop, being treated as malformed. This setting is specific to a
so any request or response could encounter a hop with a lower, connection, so any request or response could encounter a hop with a
unknown limit. An intermediary can attempt to avoid this problem by lower, unknown limit. An intermediary can attempt to avoid this
passing on values presented by different peers, but they are not problem by passing on values presented by different peers, but they
obligated to do so. are not obligated to do so.
A server that receives a larger header block than it is willing to A server that receives a larger header block than it is willing to
handle can send an HTTP 431 (Request Header Fields Too Large) status handle can send an HTTP 431 (Request Header Fields Too Large) status
code [RFC6585]. A client can discard responses that it cannot code [RFC6585]. A client can discard responses that it cannot
process. The header block MUST be processed to ensure a consistent process. The header block MUST be processed to ensure a consistent
connection state, unless the connection is closed. connection state, unless the connection is closed.
10.5.2. CONNECT Issues
The CONNECT method can be used to create disproportionate load on an
proxy, since stream creation is relatively inexpensive when compared
to the creation and maintenance of a TCP connection. A proxy might
also maintain some resources for a TCP connection beyond the closing
of the stream that carries the CONNECT request, since the outgoing
TCP connection remains in the TIME_WAIT state. Therefore, a proxy
cannot rely on SETTINGS_MAX_CONCURRENT_STREAMS alone to limit the
resources consumed by CONNECT requests.
10.6. Use of Compression 10.6. Use of Compression
HTTP/2 enables greater use of compression for both header fields Compression can allow an attacker to recover secret data when it is
(Section 4.3) and entity bodies. Compression can allow an attacker compressed in the same context as data under attacker control.
to recover secret data when it is compressed in the same context as HTTP/2 enables compression of header fields (Section 4.3); the
data under attacker control. following concerns also apply to the use of HTTP compressed content-
codings ([RFC7231], Section 3.1.2.1).
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. Generic stream compression, such as that
provided by TLS, MUST NOT be used with HTTP/2 (see Section 9.2).
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 or limiting To mitigate attacks that rely on compression, disabling or limiting
compression 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
is provided to mitigate specific attacks within HTTP. For example, 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 (e.g., [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; similarly, padding payloads to a fixed size exposes protection; similarly, padding payloads to a fixed size exposes
information as payload sizes cross the fixed size boundary, which information as payload sizes cross the fixed-sized boundary, which
could be possible if an attacker can control plaintext. could be possible if an attacker can control plaintext.
Intermediaries SHOULD retain padding for DATA frames, but MAY drop Intermediaries SHOULD retain padding for DATA frames but MAY drop
padding for HEADERS and PUSH_PROMISE frames. A valid reason for an padding for HEADERS and PUSH_PROMISE frames. A valid reason for an
intermediary to change the amount of padding of frames is to improve intermediary to change the amount of padding of frames is to improve
the protections that padding provides. 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. These
includes the value of settings, the manner in which flow control include 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, the
timing of reactions to stimulus, and handling of any optional timing of reactions to stimulus, and the handling of any features
features. that are controlled by settings.
As far as this creates observable differences in behavior, they could As far as these create observable differences in behavior, they could
be used as a basis for fingerprinting a specific client, as defined be used as a basis for fingerprinting a specific client, as defined
in Section 1.8 of [HTML5]. in Section 1.8 of [HTML5].
HTTP/2's preference for using a single TCP connection allows
correlation of a user's activity on a site. Reusing connections for
different origins allows tracking across those origins.
Because the PING and SETTINGS frames solicit immediate responses,
they can be used by an endpoint to measure latency to their peer.
This might have privacy implications in certain scenarios.
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 [TLS-ALPN]. in [TLS-ALPN].
This document establishes a registry for frame types, settings, and This document establishes a registry for frame types, settings, and
error codes. These new registries are entered into a new "Hypertext error codes. These new registries appear in the new "Hypertext
Transfer Protocol (HTTP) 2 Parameters" section. Transfer Protocol version 2 (HTTP/2) Parameters" section.
This document registers the "HTTP2-Settings" header field for use in This document registers the HTTP2-Settings header field for use in
HTTP; and the 421 (Not Authoritative) status code. HTTP; it also registers the 421 (Misdirected Request) 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 (see Section 3.3) in the "Application-Layer Protocol
IDs" registry established in [TLS-ALPN]. Negotiation (ALPN) Protocol IDs" registry established in [TLS-ALPN].
The "h2" string identifies HTTP/2 when used over TLS: The "h2" string identifies HTTP/2 when used over TLS:
Protocol: HTTP/2 over TLS Protocol: HTTP/2 over TLS
Identification Sequence: 0x68 0x32 ("h2") Identification Sequence: 0x68 0x32 ("h2")
Specification: This document Specification: This document
The "h2c" string identifies HTTP/2 when used over cleartext TCP: The "h2c" string identifies HTTP/2 when used over cleartext TCP:
Protocol: HTTP/2 over TCP Protocol: HTTP/2 over TCP
Identification Sequence: 0x68 0x32 0x63 ("h2c") Identification Sequence: 0x68 0x32 0x63 ("h2c")
Specification: This document Specification: This document
11.2. Frame Type Registry 11.2. Frame Type Registry
This document establishes a registry for HTTP/2 frame types codes. This document establishes a registry for HTTP/2 frame type codes.
The "HTTP/2 Frame Type" registry manages an 8-bit space. The "HTTP/2 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 Frame Type" registry operates under either of the "IETF Review" or
"IESG Approval" policies [RFC5226] for values between 0x00 and 0xef, "IESG Approval" policies [RFC5226] for values between 0x00 and 0xef,
with values between 0xf0 and 0xff being reserved for experimental with values between 0xf0 and 0xff being reserved for Experimental
use. Use.
New entries in this registry require the following information: New entries in this registry require the following information:
Frame Type: A name or label for the frame type. Frame Type: A name or label for the frame type.
Code: The 8-bit code assigned to the frame type. Code: The 8-bit code assigned to the frame type.
Specification: A reference to a specification that includes a Specification: A reference to a specification that includes a
description of the frame layout, it's semantics and flags that the description of the frame layout, its semantics, and flags that the
frame type uses, including any parts of the frame that are frame type uses, including any parts of the frame that are
conditionally present based on the value of flags. conditionally present based on the value of flags.
The entries in the following table are registered by this document. The entries in the following table are registered by this document.
+---------------+------+--------------+ +---------------+------+--------------+
| Frame Type | Code | Section | | Frame Type | Code | Section |
+---------------+------+--------------+ +---------------+------+--------------+
| DATA | 0x0 | Section 6.1 | | DATA | 0x0 | Section 6.1 |
| HEADERS | 0x1 | Section 6.2 | | HEADERS | 0x1 | Section 6.2 |
skipping to change at page 72, line 4 skipping to change at page 75, line 25
| GOAWAY | 0x7 | Section 6.8 | | GOAWAY | 0x7 | Section 6.8 |
| WINDOW_UPDATE | 0x8 | Section 6.9 | | WINDOW_UPDATE | 0x8 | Section 6.9 |
| CONTINUATION | 0x9 | Section 6.10 | | CONTINUATION | 0x9 | Section 6.10 |
+---------------+------+--------------+ +---------------+------+--------------+
11.3. Settings Registry 11.3. Settings Registry
This document establishes a registry for HTTP/2 settings. The This document establishes a registry for HTTP/2 settings. The
"HTTP/2 Settings" registry manages a 16-bit space. The "HTTP/2 "HTTP/2 Settings" registry manages a 16-bit space. The "HTTP/2
Settings" registry operates under the "Expert Review" policy Settings" registry operates under the "Expert Review" policy
[RFC5226] for values in the range from 0x0000 to 0xefff, with values [RFC5226] for values in the range from 0x0000 to 0xefff, with values
between and 0xf000 and 0xffff being reserved for experimental use. between and 0xf000 and 0xffff being reserved for Experimental Use.
New registrations are advised to provide the following information: New registrations are advised to provide the following information:
Name: A symbolic name for the setting. Specifying a setting name is Name: A symbolic name for the setting. Specifying a setting name is
optional. optional.
Code: The 16-bit code assigned to the setting. Code: The 16-bit code assigned to the setting.
Initial Value: An initial value for the setting. Initial Value: An initial value for the setting.
Specification: A stable reference to a specification that describes Specification: An optional reference to a specification that
the use of the setting. describes the use of the setting.
An initial set of setting registrations can be found in The entries in the following table are registered by this document.
Section 6.5.2.
+------------------------+------+---------------+---------------+ +------------------------+------+---------------+---------------+
| Name | Code | Initial Value | Specification | | Name | Code | Initial Value | Specification |
+------------------------+------+---------------+---------------+ +------------------------+------+---------------+---------------+
| HEADER_TABLE_SIZE | 0x1 | 4096 | Section 6.5.2 | | HEADER_TABLE_SIZE | 0x1 | 4096 | Section 6.5.2 |
| ENABLE_PUSH | 0x2 | 1 | Section 6.5.2 | | ENABLE_PUSH | 0x2 | 1 | Section 6.5.2 |
| MAX_CONCURRENT_STREAMS | 0x3 | (infinite) | Section 6.5.2 | | MAX_CONCURRENT_STREAMS | 0x3 | (infinite) | Section 6.5.2 |
| INITIAL_WINDOW_SIZE | 0x4 | 65535 | Section 6.5.2 | | INITIAL_WINDOW_SIZE | 0x4 | 65535 | Section 6.5.2 |
| MAX_FRAME_SIZE | 0x5 | 65536 | Section 6.5.2 | | MAX_FRAME_SIZE | 0x5 | 16384 | Section 6.5.2 |
| MAX_HEADER_LIST_SIZE | 0x6 | (infinite) | Section 6.5.2 | | MAX_HEADER_LIST_SIZE | 0x6 | (infinite) | Section 6.5.2 |
+------------------------+------+---------------+---------------+ +------------------------+------+---------------+---------------+
11.4. Error Code Registry 11.4. Error Code Registry
This document establishes a registry for HTTP/2 error codes. The This document establishes a registry for HTTP/2 error codes. The
"HTTP/2 Error Code" registry manages a 32-bit space. The "HTTP/2 "HTTP/2 Error Code" registry manages a 32-bit space. The "HTTP/2
Error Code" registry operates under the "Expert Review" policy Error Code" registry operates under the "Expert Review" policy
[RFC5226]. [RFC5226].
skipping to change at page 73, line 22 skipping to change at page 76, line 39
The entries in the following table are registered by this document. The entries in the following table are registered by this document.
+---------------------+------+----------------------+---------------+ +---------------------+------+----------------------+---------------+
| Name | Code | Description | Specification | | Name | Code | Description | Specification |
+---------------------+------+----------------------+---------------+ +---------------------+------+----------------------+---------------+
| NO_ERROR | 0x0 | Graceful shutdown | Section 7 | | NO_ERROR | 0x0 | Graceful shutdown | Section 7 |
| PROTOCOL_ERROR | 0x1 | Protocol error | Section 7 | | PROTOCOL_ERROR | 0x1 | Protocol error | Section 7 |
| | | detected | | | | | detected | |
| INTERNAL_ERROR | 0x2 | Implementation fault | Section 7 | | INTERNAL_ERROR | 0x2 | Implementation fault | Section 7 |
| FLOW_CONTROL_ERROR | 0x3 | Flow control limits | Section 7 | | FLOW_CONTROL_ERROR | 0x3 | Flow-control limits | Section 7 |
| | | exceeded | | | | | exceeded | |
| SETTINGS_TIMEOUT | 0x4 | Settings not | Section 7 | | SETTINGS_TIMEOUT | 0x4 | Settings not | Section 7 |
| | | acknowledged | | | | | acknowledged | |
| STREAM_CLOSED | 0x5 | Frame received for | Section 7 | | STREAM_CLOSED | 0x5 | Frame received for | Section 7 |
| | | closed stream | | | | | closed stream | |
| FRAME_SIZE_ERROR | 0x6 | Frame size incorrect | Section 7 | | FRAME_SIZE_ERROR | 0x6 | Frame size incorrect | Section 7 |
| REFUSED_STREAM | 0x7 | Stream not processed | Section 7 | | REFUSED_STREAM | 0x7 | Stream not processed | Section 7 |
| CANCEL | 0x8 | Stream cancelled | Section 7 | | CANCEL | 0x8 | Stream cancelled | Section 7 |
| COMPRESSION_ERROR | 0x9 | Compression state | Section 7 | | COMPRESSION_ERROR | 0x9 | Compression state | Section 7 |
| | | not updated | | | | | not updated | |
| CONNECT_ERROR | 0xa | TCP connection error | Section 7 | | CONNECT_ERROR | 0xa | TCP connection error | Section 7 |
| | | for CONNECT method | | | | | for CONNECT method | |
| ENHANCE_YOUR_CALM | 0xb | Processing capacity | Section 7 | | ENHANCE_YOUR_CALM | 0xb | Processing capacity | Section 7 |
| | | exceeded | | | | | exceeded | |
| INADEQUATE_SECURITY | 0xc | Negotiated TLS | Section 7 | | INADEQUATE_SECURITY | 0xc | Negotiated TLS | Section 7 |
| | | parameters not | | | | | parameters not | |
| | | acceptable | | | | | acceptable | |
| HTTP_1_1_REQUIRED | 0xd | Use HTTP/1.1 for the | Section 7 |
| | | request | |
+---------------------+------+----------------------+---------------+ +---------------------+------+----------------------+---------------+
11.5. HTTP2-Settings Header Field Registration 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 Names" 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.
11.6. 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"
([RFC7231], Section 8.1). ([RFC7231], Section 8.1).
Method Name: PRI Method Name: PRI
Safe No Safe: Yes
Idempotent No Idempotent: Yes
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 11.7. The 421 (Misdirected Request) HTTP Status Code
This document registers the 421 (Not Authoritative) HTTP Status code This document registers the 421 (Misdirected Request) HTTP status
in the Hypertext Transfer Protocol (HTTP) Status Code Registry code in the "HTTP Status Codes" registry ([RFC7231], Section 8.2).
([RFC7231], Section 8.2).
Status Code: 421 Status Code: 421
Short Description: Not Authoritative Short Description: Misdirected Request
Specification: Section 9.1.2 of this document Specification: Section 9.1.2 of this document
12. Acknowledgements 11.8. The h2c Upgrade Token
This document includes substantial input from the following
individuals:
o Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa
Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam
Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay,
Paul Amer, Fan Yang, Jonathan Leighton (SPDY contributors).
o Gabriel Montenegro and Willy Tarreau (Upgrade mechanism).
o William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro,
Jitu Padhye, Roberto Peon, Rob Trace (Flow control).
o Mike Bishop (Extensibility). This document registers the "h2c" upgrade token in the "HTTP Upgrade
Tokens" registry ([RFC7230], Section 8.6).
o Mark Nottingham, Julian Reschke, James Snell, Jeff Pinner, Mike Value: h2c
Bishop, Herve Ruellan (Substantial editorial contributions).
o Kari Hurtta, Tatsuhiro Tsujikawa, Greg Wilkins, Poul-Henning Kamp. Description: Hypertext Transfer Protocol version 2 (HTTP/2)
o Alexey Melnikov was an editor of this document during 2013. Expected Version Tokens: None
o A substantial proportion of Martin's contribution was supported by Reference: Section 3.2 of this document
Microsoft during his employment there.
13. References 12. References
13.1. Normative References 12.1. Normative References
[COMPRESSION] Ruellan, H. and R. Peon, "HPACK - Header Compression [COMPRESSION] Peon, R. and H. Ruellan, "HPACK: Header Compression
for HTTP/2", draft-ietf-httpbis-header-compression-09 for HTTP/2", RFC 7541, DOI 10.17487/RFC7541, May 2015,
(work in progress), July 2014. <http://www.rfc-editor.org/info/rfc7541>.
[COOKIE] Barth, A., "HTTP State Management Mechanism", [COOKIE] Barth, A., "HTTP State Management Mechanism",
RFC 6265, April 2011. RFC 6265, DOI 10.17487/RFC6265, April 2011,
<http://www.rfc-editor.org/info/rfc6265>.
[FIPS186] NIST, "Digital Signature Standard (DSS)", FIPS PUB [FIPS186] NIST, "Digital Signature Standard (DSS)", FIPS PUB
186-4, July 2013. 186-4, July 2013,
<http://dx.doi.org/10.6028/NIST.FIPS.186-4>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, DOI 10.17487/
RFC2818, May 2000,
<http://www.rfc-editor.org/info/rfc2818>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic Syntax", "Uniform Resource Identifier (URI): Generic Syntax",
STD 66, RFC 3986, January 2005. STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006. Encodings", RFC 4648, DOI 10.17487/RFC4648,
October 2006,
<http://www.rfc-editor.org/info/rfc4648>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, an IANA Considerations Section in RFCs", BCP 26,
RFC 5226, May 2008. RFC 5226, DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for
Specifications: ABNF", STD 68, RFC 5234, January 2008. Syntax Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Message Syntax and Transfer Protocol (HTTP/1.1): Message Syntax and
Routing", RFC 7230, June 2014. Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Semantics and Content", Transfer Protocol (HTTP/1.1): Semantics and Content",
RFC 7231, June 2014. RFC 7231, DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
[RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Conditional Requests", Transfer Protocol (HTTP/1.1): Conditional Requests",
RFC 7232, June 2014. RFC 7232, DOI 10.17487/RFC7232, June 2014,
<http://www.rfc-editor.org/info/rfc7232>.
[RFC7233] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, [RFC7233] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Range Ed., "Hypertext Transfer Protocol (HTTP/1.1): Range
Requests", RFC 7233, June 2014. Requests", RFC 7233, DOI 10.17487/RFC7233, June 2014,
<http://www.rfc-editor.org/info/rfc7233>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J.
Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1):
Caching", RFC 7234, June 2014. Caching", RFC 7234, DOI 10.17487/RFC7234, June 2014,
<http://www.rfc-editor.org/info/rfc7234>.
[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext [RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Authentication", Transfer Protocol (HTTP/1.1): Authentication",
RFC 7235, June 2014. RFC 7235, DOI 10.17487/RFC7235, June 2014,
<http://www.rfc-editor.org/info/rfc7235>.
[TCP] Postel, J., "Transmission Control Protocol", STD 7, [TCP] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981. RFC 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
[TLS-ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan, [TLS-ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer "Transport Layer Security (TLS) Application-Layer
Protocol Negotiation Extension", RFC 7301, July 2014. Protocol Negotiation Extension", RFC 7301,
DOI 10.17487/RFC7301, July 2014,
<http://www.rfc-editor.org/info/rfc7301>.
[TLS-ECDHE] Rescorla, E., "TLS Elliptic Curve Cipher Suites with [TLS-ECDHE] Rescorla, E., "TLS Elliptic Curve Cipher Suites with
SHA-256/384 and AES Galois Counter Mode (GCM)", SHA-256/384 and AES Galois Counter Mode (GCM)",
RFC 5289, August 2008. RFC 5289, DOI 10.17487/RFC5289, August 2008,
<http://www.rfc-editor.org/info/rfc5289>.
[TLS-EXT] Eastlake, D., "Transport Layer Security (TLS) [TLS-EXT] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, Extensions: Extension Definitions", RFC 6066,
January 2011. DOI 10.17487/RFC6066, January 2011,
<http://www.rfc-editor.org/info/rfc6066>.
[TLS12] Dierks, T. and E. Rescorla, "The Transport Layer [TLS12] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246, Security (TLS) Protocol Version 1.2", RFC 5246,
August 2008. DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
13.2. Informative References 12.2. Informative References
[ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP [ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP
Alternative Services", draft-ietf-httpbis-alt-svc-01 Alternative Services", draft-ietf-httpbis-alt-svc-06
(work in progress), April 2014. (work in progress), February 2015.
[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration [BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, Procedures for Message Header Fields", BCP 90,
RFC 3864, September 2004. RFC 3864, September 2004,
<http://www.rfc-editor.org/info/bcp90>.
[BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving [BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving
the CRIME Attack", July 2013, <http:// the CRIME Attack", July 2013, <http://
breachattack.com/resources/ breachattack.com/resources/
BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>. BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>.
[HTML5] Berjon, R., Faulkner, S., Leithead, T., Doyle Navara, [HTML5] Hickson, I., Berjon, R., Faulkner, S., Leithead, T.,
E., O'Connor, E., and S. Pfeiffer, "HTML5", W3C Doyle Navara, E., O'Connor, E., and S. Pfeiffer,
Candidate Recommendation CR-html5-20140204, "HTML5", W3C Recommendation REC-html5-20141028,
Febuary 2014, October 2014,
<http://www.w3.org/TR/2014/CR-html5-20140204/>. <http://www.w3.org/TR/2014/REC-html5-20141028/>.
Latest version available at
<http://www.w3.org/TR/html5/>.
[RFC1323] Jacobson, V., Braden, B., and D. Borman, "TCP
Extensions for High Performance", RFC 1323, May 1992.
[RFC3749] Hollenbeck, S., "Transport Layer Security Protocol [RFC3749] Hollenbeck, S., "Transport Layer Security Protocol
Compression Methods", RFC 3749, May 2004. Compression Methods", RFC 3749, DOI 10.17487/RFC3749,
May 2004, <http://www.rfc-editor.org/info/rfc3749>.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., [RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C.,
and B. Moeller, "Elliptic Curve Cryptography (ECC) and B. Moeller, "Elliptic Curve Cryptography (ECC)
Cipher Suites for Transport Layer Security (TLS)", Cipher Suites for Transport Layer Security (TLS)",
RFC 4492, May 2006. RFC 4492, DOI 10.17487/RFC4492, May 2006,
<http://www.rfc-editor.org/info/rfc4492>.
[RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288, Status Codes", RFC 6585, DOI 10.17487/RFC6585,
August 2008. April 2012, <http://www.rfc-editor.org/info/rfc6585>.
[RFC6585] Nottingham, N. and R. Fielding, "Additional HTTP [RFC7323] Borman, D., Braden, B., Jacobson, V., and R.
Status Codes", RFC 6585, April 2012. Scheffenegger, Ed., "TCP Extensions for High
Performance", RFC 7323, DOI 10.17487/RFC7323,
September 2014,
<http://www.rfc-editor.org/info/rfc7323>.
[TALKING] Huang, L-S., Chen, E., Barth, A., Rescorla, E., and C. [TALKING] Huang, L., Chen, E., Barth, A., Rescorla, E., and C.
Jackson, "Talking to Yourself for Fun and Profit", Jackson, "Talking to Yourself for Fun and Profit",
2011, <http://w2spconf.com/2011/papers/websocket.pdf>. 2011, <http://w2spconf.com/2011/papers/websocket.pdf>.
[TLSBCP] Sheffer, Y., Holz, R., and P. Saint-Andre, [TLSBCP] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of TLS and DTLS", "Recommendations for Secure Use of Transport Layer
draft-sheffer-tls-bcp-02 (work in progress), Security (TLS) and Datagram Transport Layer Security
February 2014. (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525,
May 2015, <http://www.rfc-editor.org/info/rfc7525>.
Appendix A. Change Log Appendix A. TLS 1.2 Cipher Suite Black List
This section is to be removed by RFC Editor before publication. An HTTP/2 implementation MAY treat the negotiation of any of the
following cipher suites with TLS 1.2 as a connection error
(Section 5.4.1) of type INADEQUATE_SECURITY:
A.1. Since draft-ietf-httpbis-http2-13 o TLS_NULL_WITH_NULL_NULL
Pseudo-header fields are now required to appear strictly before o TLS_RSA_WITH_NULL_MD5
regular ones.
Restored 1xx series status codes, except 101. o TLS_RSA_WITH_NULL_SHA
Changed frame length field 24-bits. Expanded frame header to 9 o TLS_RSA_EXPORT_WITH_RC4_40_MD5
octets. Added a setting to limit the damage.
Added a setting to advise peers of header set size limits. o TLS_RSA_WITH_RC4_128_MD5
Removed segments. o TLS_RSA_WITH_RC4_128_SHA
o TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5
Made non-semantic-bearing HEADERS frames illegal in the HTTP mapping. o TLS_RSA_WITH_IDEA_CBC_SHA
A.2. Since draft-ietf-httpbis-http2-12 o TLS_RSA_EXPORT_WITH_DES40_CBC_SHA
Restored extensibility options. o TLS_RSA_WITH_DES_CBC_SHA
Restricting TLS cipher suites to AEAD only. o TLS_RSA_WITH_3DES_EDE_CBC_SHA
Removing Content-Encoding requirements. o TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA
Permitting the use of PRIORITY after stream close. o TLS_DH_DSS_WITH_DES_CBC_SHA
Removed ALTSVC frame. o TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA
Removed BLOCKED frame. o TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA
Reducing the maximum padding size to 256 octets; removing padding o TLS_DH_RSA_WITH_DES_CBC_SHA
from CONTINUATION frames.
Removed per-frame GZIP compression. o TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA
A.3. Since draft-ietf-httpbis-http2-11 o TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA
Added BLOCKED frame (at risk). o TLS_DHE_DSS_WITH_DES_CBC_SHA
Simplified priority scheme. o TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA
Added DATA per-frame GZIP compression. o TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA
A.4. Since draft-ietf-httpbis-http2-10 o TLS_DHE_RSA_WITH_DES_CBC_SHA
Changed "connection header" to "connection preface" to avoid o TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA
confusion.
Added dependency-based stream prioritization. o TLS_DH_anon_EXPORT_WITH_RC4_40_MD5
Added "h2c" identifier to distinguish between cleartext and secured o TLS_DH_anon_WITH_RC4_128_MD5
HTTP/2.
Adding missing padding to PUSH_PROMISE. o TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA
Integrate ALTSVC frame and supporting text. o TLS_DH_anon_WITH_DES_CBC_SHA
Dropping requirement on "deflate" Content-Encoding. o TLS_DH_anon_WITH_3DES_EDE_CBC_SHA
Improving security considerations around use of compression. o TLS_KRB5_WITH_DES_CBC_SHA
A.5. Since draft-ietf-httpbis-http2-09 o TLS_KRB5_WITH_3DES_EDE_CBC_SHA
o TLS_KRB5_WITH_RC4_128_SHA
Adding padding for data frames. o TLS_KRB5_WITH_IDEA_CBC_SHA
Renumbering frame types, error codes, and settings. o TLS_KRB5_WITH_DES_CBC_MD5
Adding INADEQUATE_SECURITY error code. o TLS_KRB5_WITH_3DES_EDE_CBC_MD5
Updating TLS usage requirements to 1.2; forbidding TLS compression. o TLS_KRB5_WITH_RC4_128_MD5
Removing extensibility for frames and settings. o TLS_KRB5_WITH_IDEA_CBC_MD5
Changing setting identifier size. o TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA
Removing the ability to disable flow control. o TLS_KRB5_EXPORT_WITH_RC2_CBC_40_SHA
Changing the protocol identification token to "h2". o TLS_KRB5_EXPORT_WITH_RC4_40_SHA
Changing the use of :authority to make it optional and to allow o TLS_KRB5_EXPORT_WITH_DES_CBC_40_MD5
userinfo in non-HTTP cases.
Allowing split on 0x0 for Cookie. o TLS_KRB5_EXPORT_WITH_RC2_CBC_40_MD5
Reserved PRI method in HTTP/1.1 to avoid possible future collisions. o TLS_KRB5_EXPORT_WITH_RC4_40_MD5
A.6. Since draft-ietf-httpbis-http2-08 o TLS_PSK_WITH_NULL_SHA
Added cookie crumbling for more efficient header compression. o TLS_DHE_PSK_WITH_NULL_SHA
Added header field ordering with the value-concatenation mechanism. o TLS_RSA_PSK_WITH_NULL_SHA
A.7. Since draft-ietf-httpbis-http2-07 o TLS_RSA_WITH_AES_128_CBC_SHA
Marked draft for implementation. o TLS_DH_DSS_WITH_AES_128_CBC_SHA
A.8. Since draft-ietf-httpbis-http2-06 o TLS_DH_RSA_WITH_AES_128_CBC_SHA
Adding definition for CONNECT method. o TLS_DHE_DSS_WITH_AES_128_CBC_SHA
Constraining the use of push to safe, cacheable methods with no o TLS_DHE_RSA_WITH_AES_128_CBC_SHA
request body.
Changing from :host to :authority to remove any potential confusion. o TLS_DH_anon_WITH_AES_128_CBC_SHA
Adding setting for header compression table size. o TLS_RSA_WITH_AES_256_CBC_SHA
Adding settings acknowledgement. o TLS_DH_DSS_WITH_AES_256_CBC_SHA
Removing unnecessary and potentially problematic flags from o TLS_DH_RSA_WITH_AES_256_CBC_SHA
CONTINUATION. o TLS_DHE_DSS_WITH_AES_256_CBC_SHA
Added denial of service considerations. o TLS_DHE_RSA_WITH_AES_256_CBC_SHA
A.9. Since draft-ietf-httpbis-http2-05 o TLS_DH_anon_WITH_AES_256_CBC_SHA
Marking the draft ready for implementation. o TLS_RSA_WITH_NULL_SHA256
Renumbering END_PUSH_PROMISE flag. o TLS_RSA_WITH_AES_128_CBC_SHA256
Editorial clarifications and changes. o TLS_RSA_WITH_AES_256_CBC_SHA256
A.10. Since draft-ietf-httpbis-http2-04 o TLS_DH_DSS_WITH_AES_128_CBC_SHA256
Added CONTINUATION frame for HEADERS and PUSH_PROMISE. o TLS_DH_RSA_WITH_AES_128_CBC_SHA256
PUSH_PROMISE is no longer implicitly prohibited if o TLS_DHE_DSS_WITH_AES_128_CBC_SHA256
SETTINGS_MAX_CONCURRENT_STREAMS is zero.
Push expanded to allow all safe methods without a request body. o TLS_RSA_WITH_CAMELLIA_128_CBC_SHA
Clarified the use of HTTP header fields in requests and responses. o TLS_DH_DSS_WITH_CAMELLIA_128_CBC_SHA
Prohibited HTTP/1.1 hop-by-hop header fields.
Requiring that intermediaries not forward requests with missing or o TLS_DH_RSA_WITH_CAMELLIA_128_CBC_SHA
illegal routing :-headers.
Clarified requirements around handling different frames after stream o TLS_DHE_DSS_WITH_CAMELLIA_128_CBC_SHA
close, stream reset and GOAWAY.
Added more specific prohibitions for sending of different frame types o TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA
in various stream states.
Making the last received setting value the effective value. o TLS_DH_anon_WITH_CAMELLIA_128_CBC_SHA
Clarified requirements on TLS version, extension and ciphers. o TLS_DHE_RSA_WITH_AES_128_CBC_SHA256
A.11. Since draft-ietf-httpbis-http2-03 o TLS_DH_DSS_WITH_AES_256_CBC_SHA256
Committed major restructuring atrocities. o TLS_DH_RSA_WITH_AES_256_CBC_SHA256
Added reference to first header compression draft. o TLS_DHE_DSS_WITH_AES_256_CBC_SHA256
Added more formal description of frame lifecycle. o TLS_DHE_RSA_WITH_AES_256_CBC_SHA256
Moved END_STREAM (renamed from FINAL) back to HEADERS/DATA. o TLS_DH_anon_WITH_AES_128_CBC_SHA256
Removed HEADERS+PRIORITY, added optional priority to HEADERS frame. o TLS_DH_anon_WITH_AES_256_CBC_SHA256
Added PRIORITY frame. o TLS_RSA_WITH_CAMELLIA_256_CBC_SHA
A.12. Since draft-ietf-httpbis-http2-02 o TLS_DH_DSS_WITH_CAMELLIA_256_CBC_SHA
o TLS_DH_RSA_WITH_CAMELLIA_256_CBC_SHA
Added continuations to frames carrying header blocks. o TLS_DHE_DSS_WITH_CAMELLIA_256_CBC_SHA
Replaced use of "session" with "connection" to avoid confusion with o TLS_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA
other HTTP stateful concepts, like cookies.
Removed "message". o TLS_DH_anon_WITH_CAMELLIA_256_CBC_SHA
Switched to TLS ALPN from NPN. o TLS_PSK_WITH_RC4_128_SHA
Editorial changes. o TLS_PSK_WITH_3DES_EDE_CBC_SHA
A.13. Since draft-ietf-httpbis-http2-01 o TLS_PSK_WITH_AES_128_CBC_SHA
Added IANA considerations section for frame types, error codes and o TLS_PSK_WITH_AES_256_CBC_SHA
settings.
Removed data frame compression. o TLS_DHE_PSK_WITH_RC4_128_SHA
Added PUSH_PROMISE. o TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA
Added globally applicable flags to framing. o TLS_DHE_PSK_WITH_AES_128_CBC_SHA
Removed zlib-based header compression mechanism. o TLS_DHE_PSK_WITH_AES_256_CBC_SHA
Updated references. o TLS_RSA_PSK_WITH_RC4_128_SHA
Clarified stream identifier reuse. o TLS_RSA_PSK_WITH_3DES_EDE_CBC_SHA
Removed CREDENTIALS frame and associated mechanisms. o TLS_RSA_PSK_WITH_AES_128_CBC_SHA
Added advice against naive implementation of flow control. o TLS_RSA_PSK_WITH_AES_256_CBC_SHA
Added session header section. o TLS_RSA_WITH_SEED_CBC_SHA
Restructured frame header. Removed distinction between data and o TLS_DH_DSS_WITH_SEED_CBC_SHA
control frames.
Altered flow control properties to include session-level limits. o TLS_DH_RSA_WITH_SEED_CBC_SHA
Added note on cacheability of pushed resources and multiple tenant o TLS_DHE_DSS_WITH_SEED_CBC_SHA
servers.
Changed protocol label form based on discussions. o TLS_DHE_RSA_WITH_SEED_CBC_SHA
A.14. Since draft-ietf-httpbis-http2-00 o TLS_DH_anon_WITH_SEED_CBC_SHA
Changed title throughout. o TLS_RSA_WITH_AES_128_GCM_SHA256
Removed section on Incompatibilities with SPDY draft#2. o TLS_RSA_WITH_AES_256_GCM_SHA384
o TLS_DH_RSA_WITH_AES_128_GCM_SHA256
Changed INTERNAL_ERROR on GOAWAY to have a value of 2 <https:// o TLS_DH_RSA_WITH_AES_256_GCM_SHA384
groups.google.com/forum/?fromgroups#!topic/spdy-dev/cfUef2gL3iU>.
Replaced abstract and introduction. o TLS_DH_DSS_WITH_AES_128_GCM_SHA256
Added section on starting HTTP/2.0, including upgrade mechanism. o TLS_DH_DSS_WITH_AES_256_GCM_SHA384
Removed unused references. o TLS_DH_anon_WITH_AES_128_GCM_SHA256
Added flow control principles (Section 5.2.1) based on <https:// o TLS_DH_anon_WITH_AES_256_GCM_SHA384
tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01>.
A.15. Since draft-mbelshe-httpbis-spdy-00 o TLS_PSK_WITH_AES_128_GCM_SHA256
Adopted as base for draft-ietf-httpbis-http2. o TLS_PSK_WITH_AES_256_GCM_SHA384
Updated authors/editors list. o TLS_RSA_PSK_WITH_AES_128_GCM_SHA256
Added status note. o TLS_RSA_PSK_WITH_AES_256_GCM_SHA384
o TLS_PSK_WITH_AES_128_CBC_SHA256
o TLS_PSK_WITH_AES_256_CBC_SHA384
o TLS_PSK_WITH_NULL_SHA256
o TLS_PSK_WITH_NULL_SHA384
o TLS_DHE_PSK_WITH_AES_128_CBC_SHA256
o TLS_DHE_PSK_WITH_AES_256_CBC_SHA384
o TLS_DHE_PSK_WITH_NULL_SHA256
o TLS_DHE_PSK_WITH_NULL_SHA384
o TLS_RSA_PSK_WITH_AES_128_CBC_SHA256
o TLS_RSA_PSK_WITH_AES_256_CBC_SHA384
o TLS_RSA_PSK_WITH_NULL_SHA256
o TLS_RSA_PSK_WITH_NULL_SHA384
o TLS_RSA_WITH_CAMELLIA_128_CBC_SHA256
o TLS_DH_DSS_WITH_CAMELLIA_128_CBC_SHA256
o TLS_DH_RSA_WITH_CAMELLIA_128_CBC_SHA256
o TLS_DHE_DSS_WITH_CAMELLIA_128_CBC_SHA256
o TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA256
o TLS_DH_anon_WITH_CAMELLIA_128_CBC_SHA256
o TLS_RSA_WITH_CAMELLIA_256_CBC_SHA256
o TLS_DH_DSS_WITH_CAMELLIA_256_CBC_SHA256
o TLS_DH_RSA_WITH_CAMELLIA_256_CBC_SHA256
o TLS_DHE_DSS_WITH_CAMELLIA_256_CBC_SHA256
o TLS_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA256
o TLS_DH_anon_WITH_CAMELLIA_256_CBC_SHA256
o TLS_EMPTY_RENEGOTIATION_INFO_SCSV
o TLS_ECDH_ECDSA_WITH_NULL_SHA
o TLS_ECDH_ECDSA_WITH_RC4_128_SHA
o TLS_ECDH_ECDSA_WITH_3DES_EDE_CBC_SHA
o TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA
o TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA
o TLS_ECDHE_ECDSA_WITH_NULL_SHA
o TLS_ECDHE_ECDSA_WITH_RC4_128_SHA
o TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA
o TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA
o TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA
o TLS_ECDH_RSA_WITH_NULL_SHA
o TLS_ECDH_RSA_WITH_RC4_128_SHA
o TLS_ECDH_RSA_WITH_3DES_EDE_CBC_SHA
o TLS_ECDH_RSA_WITH_AES_128_CBC_SHA
o TLS_ECDH_RSA_WITH_AES_256_CBC_SHA
o TLS_ECDHE_RSA_WITH_NULL_SHA
o TLS_ECDHE_RSA_WITH_RC4_128_SHA
o TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA
o TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA
o TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA
o TLS_ECDH_anon_WITH_NULL_SHA
o TLS_ECDH_anon_WITH_RC4_128_SHA
o TLS_ECDH_anon_WITH_3DES_EDE_CBC_SHA
o TLS_ECDH_anon_WITH_AES_128_CBC_SHA
o TLS_ECDH_anon_WITH_AES_256_CBC_SHA
o TLS_SRP_SHA_WITH_3DES_EDE_CBC_SHA
o TLS_SRP_SHA_RSA_WITH_3DES_EDE_CBC_SHA
o TLS_SRP_SHA_DSS_WITH_3DES_EDE_CBC_SHA
o TLS_SRP_SHA_WITH_AES_128_CBC_SHA
o TLS_SRP_SHA_RSA_WITH_AES_128_CBC_SHA
o TLS_SRP_SHA_DSS_WITH_AES_128_CBC_SHA
o TLS_SRP_SHA_WITH_AES_256_CBC_SHA
o TLS_SRP_SHA_RSA_WITH_AES_256_CBC_SHA
o TLS_SRP_SHA_DSS_WITH_AES_256_CBC_SHA
o TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256
o TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384
o TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA256
o TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA384
o TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256
o TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384
o TLS_ECDH_RSA_WITH_AES_128_CBC_SHA256
o TLS_ECDH_RSA_WITH_AES_256_CBC_SHA384
o TLS_ECDH_ECDSA_WITH_AES_128_GCM_SHA256
o TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384
o TLS_ECDH_RSA_WITH_AES_128_GCM_SHA256
o TLS_ECDH_RSA_WITH_AES_256_GCM_SHA384
o TLS_ECDHE_PSK_WITH_RC4_128_SHA
o TLS_ECDHE_PSK_WITH_3DES_EDE_CBC_SHA
o TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA
o TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA
o TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA256
o TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA384
o TLS_ECDHE_PSK_WITH_NULL_SHA
o TLS_ECDHE_PSK_WITH_NULL_SHA256
o TLS_ECDHE_PSK_WITH_NULL_SHA384
o TLS_RSA_WITH_ARIA_128_CBC_SHA256
o TLS_RSA_WITH_ARIA_256_CBC_SHA384
o TLS_DH_DSS_WITH_ARIA_128_CBC_SHA256
o TLS_DH_DSS_WITH_ARIA_256_CBC_SHA384
o TLS_DH_RSA_WITH_ARIA_128_CBC_SHA256
o TLS_DH_RSA_WITH_ARIA_256_CBC_SHA384
o TLS_DHE_DSS_WITH_ARIA_128_CBC_SHA256
o TLS_DHE_DSS_WITH_ARIA_256_CBC_SHA384
o TLS_DHE_RSA_WITH_ARIA_128_CBC_SHA256
o TLS_DHE_RSA_WITH_ARIA_256_CBC_SHA384
o TLS_DH_anon_WITH_ARIA_128_CBC_SHA256
o TLS_DH_anon_WITH_ARIA_256_CBC_SHA384
o TLS_ECDHE_ECDSA_WITH_ARIA_128_CBC_SHA256
o TLS_ECDHE_ECDSA_WITH_ARIA_256_CBC_SHA384
o TLS_ECDH_ECDSA_WITH_ARIA_128_CBC_SHA256
o TLS_ECDH_ECDSA_WITH_ARIA_256_CBC_SHA384
o TLS_ECDHE_RSA_WITH_ARIA_128_CBC_SHA256
o TLS_ECDHE_RSA_WITH_ARIA_256_CBC_SHA384
o TLS_ECDH_RSA_WITH_ARIA_128_CBC_SHA256
o TLS_ECDH_RSA_WITH_ARIA_256_CBC_SHA384
o TLS_RSA_WITH_ARIA_128_GCM_SHA256
o TLS_RSA_WITH_ARIA_256_GCM_SHA384
o TLS_DH_RSA_WITH_ARIA_128_GCM_SHA256
o TLS_DH_RSA_WITH_ARIA_256_GCM_SHA384
o TLS_DH_DSS_WITH_ARIA_128_GCM_SHA256
o TLS_DH_DSS_WITH_ARIA_256_GCM_SHA384
o TLS_DH_anon_WITH_ARIA_128_GCM_SHA256
o TLS_DH_anon_WITH_ARIA_256_GCM_SHA384
o TLS_ECDH_ECDSA_WITH_ARIA_128_GCM_SHA256
o TLS_ECDH_ECDSA_WITH_ARIA_256_GCM_SHA384
o TLS_ECDH_RSA_WITH_ARIA_128_GCM_SHA256
o TLS_ECDH_RSA_WITH_ARIA_256_GCM_SHA384
o TLS_PSK_WITH_ARIA_128_CBC_SHA256
o TLS_PSK_WITH_ARIA_256_CBC_SHA384
o TLS_DHE_PSK_WITH_ARIA_128_CBC_SHA256
o TLS_DHE_PSK_WITH_ARIA_256_CBC_SHA384
o TLS_RSA_PSK_WITH_ARIA_128_CBC_SHA256
o TLS_RSA_PSK_WITH_ARIA_256_CBC_SHA384
o TLS_PSK_WITH_ARIA_128_GCM_SHA256
o TLS_PSK_WITH_ARIA_256_GCM_SHA384
o TLS_RSA_PSK_WITH_ARIA_128_GCM_SHA256
o TLS_RSA_PSK_WITH_ARIA_256_GCM_SHA384
o TLS_ECDHE_PSK_WITH_ARIA_128_CBC_SHA256
o TLS_ECDHE_PSK_WITH_ARIA_256_CBC_SHA384
o TLS_ECDHE_ECDSA_WITH_CAMELLIA_128_CBC_SHA256
o TLS_ECDHE_ECDSA_WITH_CAMELLIA_256_CBC_SHA384
o TLS_ECDH_ECDSA_WITH_CAMELLIA_128_CBC_SHA256
o TLS_ECDH_ECDSA_WITH_CAMELLIA_256_CBC_SHA384
o TLS_ECDHE_RSA_WITH_CAMELLIA_128_CBC_SHA256
o TLS_ECDHE_RSA_WITH_CAMELLIA_256_CBC_SHA384
o TLS_ECDH_RSA_WITH_CAMELLIA_128_CBC_SHA256
o TLS_ECDH_RSA_WITH_CAMELLIA_256_CBC_SHA384
o TLS_RSA_WITH_CAMELLIA_128_GCM_SHA256
o TLS_RSA_WITH_CAMELLIA_256_GCM_SHA384
o TLS_DH_RSA_WITH_CAMELLIA_128_GCM_SHA256
o TLS_DH_RSA_WITH_CAMELLIA_256_GCM_SHA384
o TLS_DH_DSS_WITH_CAMELLIA_128_GCM_SHA256
o TLS_DH_DSS_WITH_CAMELLIA_256_GCM_SHA384
o TLS_DH_anon_WITH_CAMELLIA_128_GCM_SHA256
o TLS_DH_anon_WITH_CAMELLIA_256_GCM_SHA384
o TLS_ECDH_ECDSA_WITH_CAMELLIA_128_GCM_SHA256
o TLS_ECDH_ECDSA_WITH_CAMELLIA_256_GCM_SHA384
o TLS_ECDH_RSA_WITH_CAMELLIA_128_GCM_SHA256
o TLS_ECDH_RSA_WITH_CAMELLIA_256_GCM_SHA384
o TLS_PSK_WITH_CAMELLIA_128_GCM_SHA256
o TLS_PSK_WITH_CAMELLIA_256_GCM_SHA384
o TLS_RSA_PSK_WITH_CAMELLIA_128_GCM_SHA256
o TLS_RSA_PSK_WITH_CAMELLIA_256_GCM_SHA384
o TLS_PSK_WITH_CAMELLIA_128_CBC_SHA256
o TLS_PSK_WITH_CAMELLIA_256_CBC_SHA384
o TLS_DHE_PSK_WITH_CAMELLIA_128_CBC_SHA256
o TLS_DHE_PSK_WITH_CAMELLIA_256_CBC_SHA384
o TLS_RSA_PSK_WITH_CAMELLIA_128_CBC_SHA256
o TLS_RSA_PSK_WITH_CAMELLIA_256_CBC_SHA384
o TLS_ECDHE_PSK_WITH_CAMELLIA_128_CBC_SHA256
o TLS_ECDHE_PSK_WITH_CAMELLIA_256_CBC_SHA384
o TLS_RSA_WITH_AES_128_CCM
o TLS_RSA_WITH_AES_256_CCM
o TLS_RSA_WITH_AES_128_CCM_8
o TLS_RSA_WITH_AES_256_CCM_8
o TLS_PSK_WITH_AES_128_CCM
o TLS_PSK_WITH_AES_256_CCM
o TLS_PSK_WITH_AES_128_CCM_8
o TLS_PSK_WITH_AES_256_CCM_8
Note: This list was assembled from the set of registered TLS
cipher suites at the time of writing. This list includes those
cipher suites that do not offer an ephemeral key exchange and
those that are based on the TLS null, stream, or block cipher type
(as defined in Section 6.2.3 of [TLS12]). Additional cipher
suites with these properties could be defined; these would not be
explicitly prohibited.
Appendix B. Acknowledgements
This document includes substantial input from the following
individuals:
o Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa
Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam
Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay,
Paul Amer, Fan Yang, and Jonathan Leighton (SPDY contributors).
o Gabriel Montenegro and Willy Tarreau (Upgrade mechanism).
o William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro,
Jitu Padhye, Roberto Peon, and Rob Trace (Flow control).
o Mike Bishop (Extensibility).
o Mark Nottingham, Julian Reschke, James Snell, Jeff Pinner, Mike
Bishop, and Herve Ruellan (Substantial editorial contributions).
o Kari Hurtta, Tatsuhiro Tsujikawa, Greg Wilkins, Poul-Henning Kamp,
and Jonathan Thackray.
o Alexey Melnikov, who was an editor of this document in 2013.
A substantial proportion of Martin's contribution was supported by
Microsoft during his employment there.
The Japanese HTTP/2 community provided invaluable contributions,
including a number of implementations as well as numerous technical
and editorial contributions.
Authors' Addresses Authors' Addresses
Mike Belshe Mike Belshe
Twist BitGo
EMail: mbelshe@chromium.org EMail: mike@belshe.com
Roberto Peon Roberto Peon
Google, Inc Google, Inc
EMail: fenix@google.com EMail: fenix@google.com
Martin Thomson (editor) Martin Thomson (editor)
Mozilla Mozilla
331 E Evelyn Street 331 E Evelyn Street
Mountain View, CA 94041 Mountain View, CA 94041
US United States
EMail: martin.thomson@gmail.com EMail: martin.thomson@gmail.com
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