RFC 7540 Hypertext Transfer Protocol Version 2 HTTP/2
Internet Engineering Task Force (IETF) M. Belshe
Request for Comments: 7540 BitGo
Category: Standards TrackR. Peon
ISSN: 2070-1721Google, Inc
M. Thomson, Ed.
Mozilla
May 2015
Hypertext Transfer Protocol Version 2 (HTTP/2)
Abstract
This specification describes an optimized expression of the semantics
of the Hypertext Transfer Protocol (HTTP), referred to as HTTP
version 2 (HTTP/2).HTTP/2 enables a more efficient use of network
resources and a reduced perception of latency by introducing header
field compression and allowing multiple concurrent exchanges on the
same connection.It also introduces unsolicited push of
representations from servers to clients.
This specification is an alternative to, but does not obsolete, the
HTTP/1.1 message syntax.HTTPs existing semantics remain unchanged.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF).It represents the consensus of the IETF community.It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG).Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7540.
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors.All rights reserved.
This document is subject to BCP 78 and the IETF Trusts Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document.Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction .4
2. HTTP/2 Protocol Overview .5
2.1. Document Organization ..6
2.2. Conventions and Terminology ..6
3. Starting HTTP/2 .7
3.1. HTTP/2 Version Identification 8
3.2. Starting HTTP/2 for http URIs .8
3.2.1. HTTP2-Settings Header Field .9
3.3. Starting HTTP/2 for https URIs ..10
3.4. Starting HTTP/2 with Prior Knowledge .10
3.5. HTTP/2 Connection Preface 11
4. HTTP Frames .12
4.1. Frame Format .12
4.2. Frame Size 13
4.3. Header Compression and Decompression .14
5. Streams and Multiplexing 15
5.1. Stream States 16
5.1.1. Stream Identifiers 21
5.1.2. Stream Concurrency 22
5.2. Flow Control .22
5.2.1. Flow-Control Principles .23
5.2.2. Appropriate Use of Flow Control ..24
5.3. Stream Priority .24
5.3.1. Stream Dependencies ..25
5.3.2. Dependency Weighting .26
5.3.3. Reprioritization ..26
5.3.4. Prioritization State Management ..27
5.3.5. Default Priorities 28
5.4. Error Handling ..28
5.4.1. Connection Error Handling ..29
5.4.2. Stream Error Handling 29
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5.4.3. Connection Termination ..30
5.5. Extending HTTP/2 30
6. Frame Definitions .31
6.1. DATA 31
6.2. HEADERS 32
6.3. PRIORITY ..34
6.4. RST_STREAM 36
6.5. SETTINGS ..36
6.5.1. SETTINGS Format 38
6.5.2. Defined SETTINGS Parameters 38
6.5.3. Settings Synchronization 39
6.6. PUSH_PROMISE .40
6.7. PING 42
6.8. GOAWAY .43
6.9. WINDOW_UPDATE 46
6.9.1. The Flow-Control Window .47
6.9.2. Initial Flow-Control Window Size .48
6.9.3. Reducing the Stream Window Size ..49
6.10. CONTINUATION 49
7. Error Codes .50
8. HTTP Message Exchanges ..51
8.1. HTTP Request/Response Exchange .52
8.1.1. Upgrading from HTTP/2 53
8.1.2. HTTP Header Fields 53
8.1.3. Examples .57
8.1.4. Request Reliability Mechanisms in HTTP/2 ..60
8.2. Server Push ..60
8.2.1. Push Requests ..61
8.2.2. Push Responses .63
8.3. The CONNECT Method .64
9. Additional HTTP Requirements/Considerations ..65
9.1. Connection Management .65
9.1.1. Connection Reuse ..66
9.1.2. The 421 (Misdirected Request) Status Code .66
9.2. Use of TLS Features 67
9.2.1. TLS 1.2 Features ..67
9.2.2. TLS 1.2 Cipher Suites 68
10. Security Considerations 69
10.1. Server Authority ..69
10.2. Cross-Protocol Attacks ..69
10.3. Intermediary Encapsulation Attacks ..70
10.4. Cacheability of Pushed Responses .70
10.5. Denial-of-Service Considerations .70
10.5.1. Limits on Header Block Size ..71
10.5.2. CONNECT Issues 72
10.6. Use of Compression 72
10.7. Use of Padding .73
10.8. Privacy Considerations ..73
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11. IANA Considerations .74
11.1. Registration of HTTP/2 Identification Strings 74
11.2. Frame Type Registry ..75
11.3. Settings Registry .75
11.4. Error Code Registry ..76
11.5. HTTP2-Settings Header Field Registration ..77
11.6. PRI Method Registration .78
11.7. The 421 (Misdirected Request) HTTP Status Code ..78
11.8. The h2c Upgrade Token 78
12. References .79
12.1. Normative References .79
12.2. Informative References ..81
Appendix A. TLS 1.2 Cipher Suite Black List ..83
Acknowledgements ..
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