draft-ietf-httpbis-semantics-00.txt   draft-ietf-httpbis-semantics-latest.txt 
HTTP Working Group R. Fielding, Ed. HTTP Working Group R. Fielding, Ed.
Internet-Draft Adobe Internet-Draft Adobe
Obsoletes: 7231 (if approved) M. Nottingham, Ed. Obsoletes: 7230,7231,7232,7233,7235 (if M. Nottingham, Ed.
Intended status: Standards Track Fastly approved) Fastly
Expires: October 5, 2018 J. Reschke, Ed. Intended status: Standards Track J. Reschke, Ed.
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April 3, 2018 May 26, 2018
Hypertext Transfer Protocol (HTTP): Semantics and Content HTTP Semantics
draft-ietf-httpbis-semantics-00 draft-ietf-httpbis-semantics-latest
Abstract Abstract
The Hypertext Transfer Protocol (HTTP) is a stateless application- The Hypertext Transfer Protocol (HTTP) is a stateless application-
level protocol for distributed, collaborative, hypertext information level protocol for distributed, collaborative, hypertext information
systems. This document defines the semantics of HTTP/1.1 messages, systems. This document defines the semantics of HTTP: its
as expressed by request methods, request header fields, response architecture, terminology, the "http" and "https" Uniform Resource
status codes, and response header fields, along with the payload of Identifier (URI) schemes, core request methods, request header
messages (metadata and body content) and mechanisms for content fields, response status codes, response header fields, and content
negotiation. negotiation.
This document obsoletes RFC 7231. This document obsoletes RFC 7231, RFC 7232, RFC 7233, RFC 7235, and
portions of RFC 7230.
Editorial Note Editorial Note
This note is to be removed before publishing as an RFC. This note is to be removed before publishing as an RFC.
Discussion of this draft takes place on the HTTP working group Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at
<http://lists.w3.org/Archives/Public/ietf-http-wg/>. <https://lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information can be found at <http://httpwg.github.io/>; Working Group information can be found at <https://httpwg.org/>;
source code and issues list for this draft can be found at source code and issues list for this draft can be found at
<https://github.com/httpwg/http-core>. <https://github.com/httpwg/http-core>.
The changes in this draft are summarized in Appendix E.1. The changes in this draft are summarized in Appendix G.2.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1. Conformance and Error Handling . . . . . . . . . . . . . 6 1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 9
1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6 1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 9
2. Resources . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 10
3. Representations . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Client/Server Messaging . . . . . . . . . . . . . . . . . 10
3.1. Representation Metadata . . . . . . . . . . . . . . . . . 7 2.2. Intermediaries . . . . . . . . . . . . . . . . . . . . . 11
3.1.1. Processing Representation Data . . . . . . . . . . . 8 2.3. Caches . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1.2. Encoding for Compression or Integrity . . . . . . . . 11 2.4. Uniform Resource Identifiers . . . . . . . . . . . . . . 14
3.1.3. Audience Language . . . . . . . . . . . . . . . . . . 12 2.5. Resources . . . . . . . . . . . . . . . . . . . . . . . . 15
3.1.4. Identification . . . . . . . . . . . . . . . . . . . 14 2.5.1. http URI Scheme . . . . . . . . . . . . . . . . . . . 16
3.2. Representation Data . . . . . . . . . . . . . . . . . . . 17 2.5.2. https URI Scheme . . . . . . . . . . . . . . . . . . 17
3.3. Payload Semantics . . . . . . . . . . . . . . . . . . . . 17 2.5.3. http and https URI Normalization and Comparison . . . 18
3.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 18
3.4.1. Proactive Negotiation . . . . . . . . . . . . . . . . 18 3. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.4.2. Reactive Negotiation . . . . . . . . . . . . . . . . 20 3.1. Implementation Diversity . . . . . . . . . . . . . . . . 18
4. Request Methods . . . . . . . . . . . . . . . . . . . . . . . 21 3.2. Role-based Requirements . . . . . . . . . . . . . . . . . 19
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 21 3.3. Parsing Elements . . . . . . . . . . . . . . . . . . . . 20
4.2. Common Method Properties . . . . . . . . . . . . . . . . 22 3.4. Error Handling . . . . . . . . . . . . . . . . . . . . . 20
4.2.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 22 3.5. Protocol Versioning . . . . . . . . . . . . . . . . . . . 21
4.2.2. Idempotent Methods . . . . . . . . . . . . . . . . . 23 4. Message Abstraction . . . . . . . . . . . . . . . . . . . . . 23
4.2.3. Cacheable Methods . . . . . . . . . . . . . . . . . . 24 4.1. Field Names . . . . . . . . . . . . . . . . . . . . . . . 23
4.3. Method Definitions . . . . . . . . . . . . . . . . . . . 24 4.1.1. Field Name Registry . . . . . . . . . . . . . . . . . 24
4.3.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 24 4.1.2. Field Extensibility . . . . . . . . . . . . . . . . . 25
4.3.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 25 4.1.3. Considerations for New Fields . . . . . . . . . . . . 25
4.3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . 25 4.2. Field Values . . . . . . . . . . . . . . . . . . . . . . 26
4.3.4. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 26 4.2.1. Field Order . . . . . . . . . . . . . . . . . . . . . 27
4.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . 29 4.2.2. Field Limits . . . . . . . . . . . . . . . . . . . . 28
4.3.6. CONNECT . . . . . . . . . . . . . . . . . . . . . . . 30 4.2.3. Field Value Components . . . . . . . . . . . . . . . 28
4.3.7. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . 31 4.2.4. Designing New Field Values . . . . . . . . . . . . . 29
4.3.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . 32 4.3. Whitespace . . . . . . . . . . . . . . . . . . . . . . . 30
5. Request Header Fields . . . . . . . . . . . . . . . . . . . . 33 4.4. Trailer . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.1. Controls . . . . . . . . . . . . . . . . . . . . . . . . 33 5. Message Routing . . . . . . . . . . . . . . . . . . . . . . . 31
5.1.1. Expect . . . . . . . . . . . . . . . . . . . . . . . 34 5.1. Identifying a Target Resource . . . . . . . . . . . . . . 31
5.1.2. Max-Forwards . . . . . . . . . . . . . . . . . . . . 36 5.2. Routing Inbound . . . . . . . . . . . . . . . . . . . . . 31
5.2. Conditionals . . . . . . . . . . . . . . . . . . . . . . 37 5.3. Effective Request URI . . . . . . . . . . . . . . . . . . 32
5.3. Content Negotiation . . . . . . . . . . . . . . . . . . . 37 5.4. Host . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.3.1. Quality Values . . . . . . . . . . . . . . . . . . . 38 5.5. Associating a Response to a Request . . . . . . . . . . . 34
5.3.2. Accept . . . . . . . . . . . . . . . . . . . . . . . 38 5.6. Message Forwarding . . . . . . . . . . . . . . . . . . . 34
5.3.3. Accept-Charset . . . . . . . . . . . . . . . . . . . 40 5.6.1. Via . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.3.4. Accept-Encoding . . . . . . . . . . . . . . . . . . . 41 5.6.2. Transformations . . . . . . . . . . . . . . . . . . . 36
5.3.5. Accept-Language . . . . . . . . . . . . . . . . . . . 43 6. Representations . . . . . . . . . . . . . . . . . . . . . . . 37
5.4. Authentication Credentials . . . . . . . . . . . . . . . 44 6.1. Representation Data . . . . . . . . . . . . . . . . . . . 38
5.5. Request Context . . . . . . . . . . . . . . . . . . . . . 44 6.1.1. Media Type . . . . . . . . . . . . . . . . . . . . . 38
5.5.1. From . . . . . . . . . . . . . . . . . . . . . . . . 44 6.1.2. Content Codings . . . . . . . . . . . . . . . . . . . 40
5.5.2. Referer . . . . . . . . . . . . . . . . . . . . . . . 45 6.1.3. Language Tags . . . . . . . . . . . . . . . . . . . . 42
5.5.3. User-Agent . . . . . . . . . . . . . . . . . . . . . 46 6.1.4. Range Units . . . . . . . . . . . . . . . . . . . . . 43
6. Response Status Codes . . . . . . . . . . . . . . . . . . . . 47 6.2. Representation Metadata . . . . . . . . . . . . . . . . . 46
6.1. Overview of Status Codes . . . . . . . . . . . . . . . . 48 6.2.1. Content-Type . . . . . . . . . . . . . . . . . . . . 46
6.2. Informational 1xx . . . . . . . . . . . . . . . . . . . . 50 6.2.2. Content-Encoding . . . . . . . . . . . . . . . . . . 47
6.2.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 50 6.2.3. Content-Language . . . . . . . . . . . . . . . . . . 48
6.2.2. 101 Switching Protocols . . . . . . . . . . . . . . . 50 6.2.4. Content-Length . . . . . . . . . . . . . . . . . . . 49
6.3. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 51 6.2.5. Content-Location . . . . . . . . . . . . . . . . . . 50
6.3.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 51 6.3. Payload . . . . . . . . . . . . . . . . . . . . . . . . . 52
6.3.2. 201 Created . . . . . . . . . . . . . . . . . . . . . 52 6.3.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 52
6.3.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 52 6.3.2. Identification . . . . . . . . . . . . . . . . . . . 53
6.3.4. 203 Non-Authoritative Information . . . . . . . . . . 52 6.3.3. Content-Range . . . . . . . . . . . . . . . . . . . . 54
6.3.5. 204 No Content . . . . . . . . . . . . . . . . . . . 53 6.3.4. Media Type multipart/byteranges . . . . . . . . . . . 55
6.3.6. 205 Reset Content . . . . . . . . . . . . . . . . . . 53 6.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 57
6.4. Redirection 3xx . . . . . . . . . . . . . . . . . . . . . 54 6.4.1. Proactive Negotiation . . . . . . . . . . . . . . . . 58
6.4.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 55 6.4.2. Reactive Negotiation . . . . . . . . . . . . . . . . 59
6.4.2. 301 Moved Permanently . . . . . . . . . . . . . . . . 56 7. Request Methods . . . . . . . . . . . . . . . . . . . . . . . 60
6.4.3. 302 Found . . . . . . . . . . . . . . . . . . . . . . 57 7.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 60
6.4.4. 303 See Other . . . . . . . . . . . . . . . . . . . . 57 7.2. Common Method Properties . . . . . . . . . . . . . . . . 62
6.4.5. 305 Use Proxy . . . . . . . . . . . . . . . . . . . . 58 7.2.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 62
6.4.6. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 58 7.2.2. Idempotent Methods . . . . . . . . . . . . . . . . . 63
6.4.7. 307 Temporary Redirect . . . . . . . . . . . . . . . 58 7.2.3. Cacheable Methods . . . . . . . . . . . . . . . . . . 63
6.5. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 58 7.3. Method Definitions . . . . . . . . . . . . . . . . . . . 64
6.5.1. 400 Bad Request . . . . . . . . . . . . . . . . . . . 59 7.3.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 64
6.5.2. 402 Payment Required . . . . . . . . . . . . . . . . 59 7.3.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 64
6.5.3. 403 Forbidden . . . . . . . . . . . . . . . . . . . . 59 7.3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . 65
6.5.4. 404 Not Found . . . . . . . . . . . . . . . . . . . . 59 7.3.4. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 66
6.5.5. 405 Method Not Allowed . . . . . . . . . . . . . . . 59 7.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . 68
6.5.6. 406 Not Acceptable . . . . . . . . . . . . . . . . . 60 7.3.6. CONNECT . . . . . . . . . . . . . . . . . . . . . . . 69
6.5.7. 408 Request Timeout . . . . . . . . . . . . . . . . . 60 7.3.7. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . 71
6.5.8. 409 Conflict . . . . . . . . . . . . . . . . . . . . 60 7.3.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . 72
6.5.9. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 61 7.4. Method Extensibility . . . . . . . . . . . . . . . . . . 73
6.5.10. 411 Length Required . . . . . . . . . . . . . . . . . 61 7.4.1. Method Registry . . . . . . . . . . . . . . . . . . . 73
6.5.11. 413 Payload Too Large . . . . . . . . . . . . . . . . 61 7.4.2. Considerations for New Methods . . . . . . . . . . . 73
6.5.12. 414 URI Too Long . . . . . . . . . . . . . . . . . . 62 8. Request Header Fields . . . . . . . . . . . . . . . . . . . . 74
6.5.13. 415 Unsupported Media Type . . . . . . . . . . . . . 62 8.1. Controls . . . . . . . . . . . . . . . . . . . . . . . . 74
6.5.14. 417 Expectation Failed . . . . . . . . . . . . . . . 62 8.1.1. Expect . . . . . . . . . . . . . . . . . . . . . . . 74
6.5.15. 426 Upgrade Required . . . . . . . . . . . . . . . . 62 8.1.2. Max-Forwards . . . . . . . . . . . . . . . . . . . . 77
6.6. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 63 8.2. Preconditions . . . . . . . . . . . . . . . . . . . . . . 77
6.6.1. 500 Internal Server Error . . . . . . . . . . . . . . 63 8.2.1. Evaluation . . . . . . . . . . . . . . . . . . . . . 78
6.6.2. 501 Not Implemented . . . . . . . . . . . . . . . . . 63 8.2.2. Precedence . . . . . . . . . . . . . . . . . . . . . 79
6.6.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . . 63 8.2.3. If-Match . . . . . . . . . . . . . . . . . . . . . . 80
6.6.4. 503 Service Unavailable . . . . . . . . . . . . . . . 64 8.2.4. If-None-Match . . . . . . . . . . . . . . . . . . . . 82
6.6.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . . 64 8.2.5. If-Modified-Since . . . . . . . . . . . . . . . . . . 83
6.6.6. 505 HTTP Version Not Supported . . . . . . . . . . . 64 8.2.6. If-Unmodified-Since . . . . . . . . . . . . . . . . . 84
7. Response Header Fields . . . . . . . . . . . . . . . . . . . 64 8.2.7. If-Range . . . . . . . . . . . . . . . . . . . . . . 85
7.1. Control Data . . . . . . . . . . . . . . . . . . . . . . 64 8.3. Range . . . . . . . . . . . . . . . . . . . . . . . . . . 86
7.1.1. Origination Date . . . . . . . . . . . . . . . . . . 65 8.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 88
7.1.2. Location . . . . . . . . . . . . . . . . . . . . . . 68 8.4.1. Quality Values . . . . . . . . . . . . . . . . . . . 89
7.1.3. Retry-After . . . . . . . . . . . . . . . . . . . . . 69 8.4.2. Accept . . . . . . . . . . . . . . . . . . . . . . . 89
7.1.4. Vary . . . . . . . . . . . . . . . . . . . . . . . . 70 8.4.3. Accept-Charset . . . . . . . . . . . . . . . . . . . 91
7.2. Validator Header Fields . . . . . . . . . . . . . . . . . 71 8.4.4. Accept-Encoding . . . . . . . . . . . . . . . . . . . 92
7.3. Authentication Challenges . . . . . . . . . . . . . . . . 72 8.4.5. Accept-Language . . . . . . . . . . . . . . . . . . . 93
7.4. Response Context . . . . . . . . . . . . . . . . . . . . 72 8.5. Authentication Credentials . . . . . . . . . . . . . . . 95
7.4.1. Allow . . . . . . . . . . . . . . . . . . . . . . . . 72 8.5.1. Challenge and Response . . . . . . . . . . . . . . . 95
7.4.2. Server . . . . . . . . . . . . . . . . . . . . . . . 73 8.5.2. Protection Space (Realm) . . . . . . . . . . . . . . 97
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 74 8.5.3. Authorization . . . . . . . . . . . . . . . . . . . . 98
8.1. Method Registry . . . . . . . . . . . . . . . . . . . . . 74 8.5.4. Proxy-Authorization . . . . . . . . . . . . . . . . . 98
8.1.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 74 8.5.5. Authentication Scheme Extensibility . . . . . . . . . 98
8.1.2. Considerations for New Methods . . . . . . . . . . . 74 8.6. Request Context . . . . . . . . . . . . . . . . . . . . . 101
8.1.3. Registrations . . . . . . . . . . . . . . . . . . . . 75 8.6.1. From . . . . . . . . . . . . . . . . . . . . . . . . 101
8.2. Status Code Registry . . . . . . . . . . . . . . . . . . 75 8.6.2. Referer . . . . . . . . . . . . . . . . . . . . . . . 101
8.2.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 75 8.6.3. User-Agent . . . . . . . . . . . . . . . . . . . . . 103
8.2.2. Considerations for New Status Codes . . . . . . . . . 76 9. Response Status Codes . . . . . . . . . . . . . . . . . . . . 104
8.2.3. Registrations . . . . . . . . . . . . . . . . . . . . 77 9.1. Overview of Status Codes . . . . . . . . . . . . . . . . 104
8.3. Header Field Registry . . . . . . . . . . . . . . . . . . 78 9.2. Informational 1xx . . . . . . . . . . . . . . . . . . . . 107
8.3.1. Considerations for New Header Fields . . . . . . . . 78 9.2.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 107
8.3.2. Registrations . . . . . . . . . . . . . . . . . . . . 80 9.2.2. 101 Switching Protocols . . . . . . . . . . . . . . . 107
8.4. Content Coding Registry . . . . . . . . . . . . . . . . . 81 9.3. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 108
8.4.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 81 9.3.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 108
8.4.2. Registrations . . . . . . . . . . . . . . . . . . . . 81 9.3.2. 201 Created . . . . . . . . . . . . . . . . . . . . . 109
9. Security Considerations . . . . . . . . . . . . . . . . . . . 81 9.3.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 109
9.1. Attacks Based on File and Path Names . . . . . . . . . . 82 9.3.4. 203 Non-Authoritative Information . . . . . . . . . . 109
9.2. Attacks Based on Command, Code, or Query Injection . . . 82 9.3.5. 204 No Content . . . . . . . . . . . . . . . . . . . 110
9.3. Disclosure of Personal Information . . . . . . . . . . . 83 9.3.6. 205 Reset Content . . . . . . . . . . . . . . . . . . 110
9.4. Disclosure of Sensitive Information in URIs . . . . . . . 83 9.3.7. 206 Partial Content . . . . . . . . . . . . . . . . . 111
9.5. Disclosure of Fragment after Redirects . . . . . . . . . 84 9.4. Redirection 3xx . . . . . . . . . . . . . . . . . . . . . 114
9.6. Disclosure of Product Information . . . . . . . . . . . . 84 9.4.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 115
9.7. Browser Fingerprinting . . . . . . . . . . . . . . . . . 84 9.4.2. 301 Moved Permanently . . . . . . . . . . . . . . . . 116
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 85 9.4.3. 302 Found . . . . . . . . . . . . . . . . . . . . . . 117
10.1. Normative References . . . . . . . . . . . . . . . . . . 85 9.4.4. 303 See Other . . . . . . . . . . . . . . . . . . . . 117
10.2. Informative References . . . . . . . . . . . . . . . . . 87 9.4.5. 304 Not Modified . . . . . . . . . . . . . . . . . . 118
Appendix A. Differences between HTTP and MIME . . . . . . . . . 90 9.4.6. 305 Use Proxy . . . . . . . . . . . . . . . . . . . . 118
A.1. MIME-Version . . . . . . . . . . . . . . . . . . . . . . 90 9.4.7. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 119
A.2. Conversion to Canonical Form . . . . . . . . . . . . . . 90 9.4.8. 307 Temporary Redirect . . . . . . . . . . . . . . . 119
A.3. Conversion of Date Formats . . . . . . . . . . . . . . . 91 9.5. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 119
A.4. Conversion of Content-Encoding . . . . . . . . . . . . . 91 9.5.1. 400 Bad Request . . . . . . . . . . . . . . . . . . . 119
A.5. Conversion of Content-Transfer-Encoding . . . . . . . . . 91 9.5.2. 401 Unauthorized . . . . . . . . . . . . . . . . . . 119
A.6. MHTML and Line Length Limitations . . . . . . . . . . . . 91 9.5.3. 402 Payment Required . . . . . . . . . . . . . . . . 120
Appendix B. Changes from RFC 7231 . . . . . . . . . . . . . . . 92 9.5.4. 403 Forbidden . . . . . . . . . . . . . . . . . . . . 120
Appendix C. Imported ABNF . . . . . . . . . . . . . . . . . . . 92 9.5.5. 404 Not Found . . . . . . . . . . . . . . . . . . . . 120
Appendix D. Collected ABNF . . . . . . . . . . . . . . . . . . . 92 9.5.6. 405 Method Not Allowed . . . . . . . . . . . . . . . 121
Appendix E. Change Log . . . . . . . . . . . . . . . . . . . . . 95 9.5.7. 406 Not Acceptable . . . . . . . . . . . . . . . . . 121
E.1. Since RFC 7231 . . . . . . . . . . . . . . . . . . . . . 95 9.5.8. 407 Proxy Authentication Required . . . . . . . . . . 121
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 9.5.9. 408 Request Timeout . . . . . . . . . . . . . . . . . 121
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 100 9.5.10. 409 Conflict . . . . . . . . . . . . . . . . . . . . 122
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 100 9.5.11. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 122
9.5.12. 411 Length Required . . . . . . . . . . . . . . . . . 122
9.5.13. 412 Precondition Failed . . . . . . . . . . . . . . . 123
9.5.14. 413 Payload Too Large . . . . . . . . . . . . . . . . 123
9.5.15. 414 URI Too Long . . . . . . . . . . . . . . . . . . 123
9.5.16. 415 Unsupported Media Type . . . . . . . . . . . . . 123
9.5.17. 416 Range Not Satisfiable . . . . . . . . . . . . . . 124
9.5.18. 417 Expectation Failed . . . . . . . . . . . . . . . 124
9.5.19. 426 Upgrade Required . . . . . . . . . . . . . . . . 124
9.6. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 125
9.6.1. 500 Internal Server Error . . . . . . . . . . . . . . 125
9.6.2. 501 Not Implemented . . . . . . . . . . . . . . . . . 125
9.6.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . . 125
9.6.4. 503 Service Unavailable . . . . . . . . . . . . . . . 126
9.6.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . . 126
9.6.6. 505 HTTP Version Not Supported . . . . . . . . . . . 126
9.7. Status Code Extensibility . . . . . . . . . . . . . . . . 126
9.7.1. Status Code Registry . . . . . . . . . . . . . . . . 126
9.7.2. Considerations for New Status Codes . . . . . . . . . 127
10. Response Header Fields . . . . . . . . . . . . . . . . . . . 128
10.1. Control Data . . . . . . . . . . . . . . . . . . . . . . 128
10.1.1. Origination Date . . . . . . . . . . . . . . . . . . 128
10.1.2. Location . . . . . . . . . . . . . . . . . . . . . . 132
10.1.3. Retry-After . . . . . . . . . . . . . . . . . . . . 133
10.1.4. Vary . . . . . . . . . . . . . . . . . . . . . . . . 134
10.2. Validators . . . . . . . . . . . . . . . . . . . . . . . 135
10.2.1. Weak versus Strong . . . . . . . . . . . . . . . . . 136
10.2.2. Last-Modified . . . . . . . . . . . . . . . . . . . 138
10.2.3. ETag . . . . . . . . . . . . . . . . . . . . . . . . 140
10.2.4. When to Use Entity-Tags and Last-Modified Dates . . 143
10.3. Authentication Challenges . . . . . . . . . . . . . . . 144
10.3.1. WWW-Authenticate . . . . . . . . . . . . . . . . . . 144
10.3.2. Proxy-Authenticate . . . . . . . . . . . . . . . . . 145
10.4. Response Context . . . . . . . . . . . . . . . . . . . . 145
10.4.1. Accept-Ranges . . . . . . . . . . . . . . . . . . . 146
10.4.2. Allow . . . . . . . . . . . . . . . . . . . . . . . 146
10.4.3. Server . . . . . . . . . . . . . . . . . . . . . . . 147
11. ABNF List Extension: #rule . . . . . . . . . . . . . . . . . 147
12. Security Considerations . . . . . . . . . . . . . . . . . . . 149
12.1. Establishing Authority . . . . . . . . . . . . . . . . . 149
12.2. Risks of Intermediaries . . . . . . . . . . . . . . . . 150
12.3. Attacks Based on File and Path Names . . . . . . . . . . 150
12.4. Attacks Based on Command, Code, or Query Injection . . . 151
12.5. Attacks via Protocol Element Length . . . . . . . . . . 152
12.6. Disclosure of Personal Information . . . . . . . . . . . 152
12.7. Privacy of Server Log Information . . . . . . . . . . . 152
12.8. Disclosure of Sensitive Information in URIs . . . . . . 153
12.9. Disclosure of Fragment after Redirects . . . . . . . . . 153
12.10. Disclosure of Product Information . . . . . . . . . . . 154
12.11. Browser Fingerprinting . . . . . . . . . . . . . . . . . 154
12.12. Validator Retention . . . . . . . . . . . . . . . . . . 155
12.13. Denial-of-Service Attacks Using Range . . . . . . . . . 155
12.14. Authentication Considerations . . . . . . . . . . . . . 156
12.14.1. Confidentiality of Credentials . . . . . . . . . . 156
12.14.2. Credentials and Idle Clients . . . . . . . . . . . 156
12.14.3. Protection Spaces . . . . . . . . . . . . . . . . . 157
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 157
13.1. URI Scheme Registration . . . . . . . . . . . . . . . . 158
13.2. Method Registration . . . . . . . . . . . . . . . . . . 158
13.3. Status Code Registration . . . . . . . . . . . . . . . . 158
13.4. Header Field Registration . . . . . . . . . . . . . . . 158
13.5. Authentication Scheme Registration . . . . . . . . . . . 158
13.6. Content Coding Registration . . . . . . . . . . . . . . 158
13.7. Range Unit Registration . . . . . . . . . . . . . . . . 158
13.8. Media Type Registration . . . . . . . . . . . . . . . . 159
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 159
14.1. Normative References . . . . . . . . . . . . . . . . . . 159
14.2. Informative References . . . . . . . . . . . . . . . . . 160
Appendix A. Collected ABNF . . . . . . . . . . . . . . . . . . . 166
Appendix B. Changes from RFC 7230 . . . . . . . . . . . . . . . 171
Appendix C. Changes from RFC 7231 . . . . . . . . . . . . . . . 171
Appendix D. Changes from RFC 7232 . . . . . . . . . . . . . . . 171
Appendix E. Changes from RFC 7233 . . . . . . . . . . . . . . . 171
Appendix F. Changes from RFC 7235 . . . . . . . . . . . . . . . 171
Appendix G. Change Log . . . . . . . . . . . . . . . . . . . . . 171
G.1. Between RFC723x and draft 00 . . . . . . . . . . . . . . 171
G.2. Since draft-ietf-httpbis-semantics-00 . . . . . . . . . . 172
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 180
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 180
1. Introduction 1. Introduction
Each Hypertext Transfer Protocol (HTTP) message is either a request The Hypertext Transfer Protocol (HTTP) is a stateless application-
or a response. A server listens on a connection for a request, level request/response protocol that uses extensible semantics and
parses each message received, interprets the message semantics in self-descriptive messages for flexible interaction with network-based
relation to the identified request target, and responds to that hypertext information systems. HTTP is defined by a series of
request with one or more response messages. A client constructs documents that collectively form the HTTP/1.1 specification:
request messages to communicate specific intentions, examines
received responses to see if the intentions were carried out, and o "HTTP Semantics" (this document)
determines how to interpret the results. This document defines
HTTP/1.1 request and response semantics in terms of the architecture o "HTTP Caching" [Caching]
defined in [MESSGNG].
o "HTTP/1.1 Messaging" [Messaging]
HTTP is a generic interface protocol for information systems. It is
designed to hide the details of how a service is implemented by
presenting a uniform interface to clients that is independent of the
types of resources provided. Likewise, servers do not need to be
aware of each client's purpose: an HTTP request can be considered in
isolation rather than being associated with a specific type of client
or a predetermined sequence of application steps. The result is a
protocol that can be used effectively in many different contexts and
for which implementations can evolve independently over time.
HTTP is also designed for use as an intermediation protocol for
translating communication to and from non-HTTP information systems.
HTTP proxies and gateways can provide access to alternative
information services by translating their diverse protocols into a
hypertext format that can be viewed and manipulated by clients in the
same way as HTTP services.
One consequence of this flexibility is that the protocol cannot be
defined in terms of what occurs behind the interface. Instead, we
are limited to defining the syntax of communication, the intent of
received communication, and the expected behavior of recipients. If
the communication is considered in isolation, then successful actions
ought to be reflected in corresponding changes to the observable
interface provided by servers. However, since multiple clients might
act in parallel and perhaps at cross-purposes, we cannot require that
such changes be observable beyond the scope of a single response.
Each HTTP message is either a request or a response. A server
listens on a connection for a request, parses each message received,
interprets the message semantics in relation to the identified
request target, and responds to that request with one or more
response messages. A client constructs request messages to
communicate specific intentions, examines received responses to see
if the intentions were carried out, and determines how to interpret
the results.
HTTP provides a uniform interface for interacting with a resource HTTP provides a uniform interface for interacting with a resource
(Section 2), regardless of its type, nature, or implementation, via (Section 2.5), regardless of its type, nature, or implementation, via
the manipulation and transfer of representations (Section 3). the manipulation and transfer of representations (Section 6).
HTTP semantics include the intentions defined by each request method This document defines semantics that are common to all versions of
(Section 4), extensions to those semantics that might be described in HTTP. HTTP semantics include the intentions defined by each request
request header fields (Section 5), the meaning of status codes to method (Section 7), extensions to those semantics that might be
indicate a machine-readable response (Section 6), and the meaning of described in request header fields (Section 8), the meaning of status
other control data and resource metadata that might be given in codes to indicate a machine-readable response (Section 9), and the
response header fields (Section 7). meaning of other control data and resource metadata that might be
given in response header fields (Section 10).
This document also defines representation metadata that describe how This document also defines representation metadata that describe how
a payload is intended to be interpreted by a recipient, the request a payload is intended to be interpreted by a recipient, the request
header fields that might influence content selection, and the various header fields that might influence content selection, and the various
selection algorithms that are collectively referred to as "content selection algorithms that are collectively referred to as "content
negotiation" (Section 3.4). negotiation" (Section 6.4).
This specification obsoletes RFC 7231, with the changes being This document defines HTTP/1.1 range requests, partial responses, and
summarized in Appendix B. the multipart/byteranges media type.
1.1. Conformance and Error Handling This document obsoletes the portions of RFC 7230 that are independent
of the HTTP/1.1 messaging syntax and connection management, with the
changes being summarized in Appendix B. The other parts of RFC 7230
are obsoleted by "HTTP/1.1 Messaging" [Messaging].
This document obsoletes RFC 7231, with the changes being summarized
in Appendix C.
This document obsoletes RFC 7232, with the changes being summarized
in Appendix D.
This document obsoletes RFC 7233, with the changes being summarized
in Appendix E.
This document obsoletes RFC 7235, with the changes being summarized
in Appendix F.
1.1. Requirements Notation
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 [RFC2119]. document are to be interpreted as described in [RFC2119].
Conformance criteria and considerations regarding error handling are Conformance criteria and considerations regarding error handling are
defined in Section 2.5 of [MESSGNG]. defined in Section 3.
1.2. Syntax Notation 1.2. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF) This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234] with a list extension, defined in Section 7 of notation of [RFC5234] with a list extension, defined in Section 11,
[MESSGNG], that allows for compact definition of comma-separated that allows for compact definition of comma-separated lists using a
lists using a '#' operator (similar to how the '*' operator indicates '#' operator (similar to how the '*' operator indicates repetition).
repetition). Appendix C describes rules imported from other Appendix A shows the collected grammar with all list operators
documents. Appendix D shows the collected grammar with all list expanded to standard ABNF notation.
operators expanded to standard ABNF notation.
As a convention, ABNF rule names prefixed with "obs-" denote
"obsolete" grammar rules that appear for historical reasons.
The following core rules are included by reference, as defined in
Appendix B.1 of [RFC5234]: ALPHA (letters), CR (carriage return),
CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double
quote), HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF
(line feed), OCTET (any 8-bit sequence of data), SP (space), and
VCHAR (any visible US-ASCII character). [[CREF1: Range also uses
CHAR, which is probably a bug.]]
The rules below are defined in [Messaging]:
obs-fold = <obs-fold, see [Messaging], Section 2.3.2>
protocol-name = <protocol-name, see [Messaging], Section 6.7>
protocol-version = <protocol-version, see [Messaging], Section 6.7>
request-target = <request-target, see [Messaging], Section 4>
This specification uses the terms "character", "character encoding This specification uses the terms "character", "character encoding
scheme", "charset", and "protocol element" as they are defined in scheme", "charset", and "protocol element" as they are defined in
[RFC6365]. [RFC6365].
2. Resources 2. Architecture
HTTP was created for the World Wide Web (WWW) architecture and has
evolved over time to support the scalability needs of a worldwide
hypertext system. Much of that architecture is reflected in the
terminology and syntax productions used to define HTTP.
2.1. Client/Server Messaging
HTTP is a stateless request/response protocol that operates by
exchanging messages (Section 2 of [Messaging]) across a reliable
transport- or session-layer "connection" (Section 6 of [Messaging]).
An HTTP "client" is a program that establishes a connection to a
server for the purpose of sending one or more HTTP requests. An HTTP
"server" is a program that accepts connections in order to service
HTTP requests by sending HTTP responses.
The terms "client" and "server" refer only to the roles that these
programs perform for a particular connection. The same program might
act as a client on some connections and a server on others. The term
"user agent" refers to any of the various client programs that
initiate a request, including (but not limited to) browsers, spiders
(web-based robots), command-line tools, custom applications, and
mobile apps. The term "origin server" refers to the program that can
originate authoritative responses for a given target resource. The
terms "sender" and "recipient" refer to any implementation that sends
or receives a given message, respectively.
HTTP relies upon the Uniform Resource Identifier (URI) standard
[RFC3986] to indicate the target resource (Section 5.1) and
relationships between resources.
Most HTTP communication consists of a retrieval request (GET) for a
representation of some resource identified by a URI. In the simplest
case, this might be accomplished via a single bidirectional
connection (===) between the user agent (UA) and the origin server
(O).
request >
UA ======================================= O
< response
A client sends an HTTP request to a server in the form of a request
message, beginning with a request-line that includes a method, URI,
and protocol version (Section 2.2.1 of [Messaging]), followed by
header fields containing request modifiers, client information, and
representation metadata (Section 2.3 of [Messaging]), an empty line
to indicate the end of the header section, and finally a message body
containing the payload body (if any, Section 2.4 of [Messaging]).
A server responds to a client's request by sending one or more HTTP
response messages, each beginning with a status line that includes
the protocol version, a success or error code, and textual reason
phrase (Section 2.2.2 of [Messaging]), possibly followed by header
fields containing server information, resource metadata, and
representation metadata (Section 2.3 of [Messaging]), an empty line
to indicate the end of the header section, and finally a message body
containing the payload body (if any, Section 2.4 of [Messaging]).
A connection might be used for multiple request/response exchanges,
as defined in Section 6.3 of [Messaging].
The following example illustrates a typical message exchange for a
GET request (Section 7.3.1) on the URI "http://www.example.com/
hello.txt":
Client request:
GET /hello.txt HTTP/1.1
User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com
Accept-Language: en, mi
Server response:
HTTP/1.1 200 OK
Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
ETag: "34aa387-d-1568eb00"
Accept-Ranges: bytes
Content-Length: 51
Vary: Accept-Encoding
Content-Type: text/plain
Hello World! My payload includes a trailing CRLF.
2.2. Intermediaries
HTTP enables the use of intermediaries to satisfy requests through a
chain of connections. There are three common forms of HTTP
intermediary: proxy, gateway, and tunnel. In some cases, a single
intermediary might act as an origin server, proxy, gateway, or
tunnel, switching behavior based on the nature of each request.
> > > >
UA =========== A =========== B =========== C =========== O
< < < <
The figure above shows three intermediaries (A, B, and C) between the
user agent and origin server. A request or response message that
travels the whole chain will pass through four separate connections.
Some HTTP communication options might apply only to the connection
with the nearest, non-tunnel neighbor, only to the endpoints of the
chain, or to all connections along the chain. Although the diagram
is linear, each participant might be engaged in multiple,
simultaneous communications. For example, B might be receiving
requests from many clients other than A, and/or forwarding requests
to servers other than C, at the same time that it is handling A's
request. Likewise, later requests might be sent through a different
path of connections, often based on dynamic configuration for load
balancing.
The terms "upstream" and "downstream" are used to describe
directional requirements in relation to the message flow: all
messages flow from upstream to downstream. The terms "inbound" and
"outbound" are used to describe directional requirements in relation
to the request route: "inbound" means toward the origin server and
"outbound" means toward the user agent.
A "proxy" is a message-forwarding agent that is selected by the
client, usually via local configuration rules, to receive requests
for some type(s) of absolute URI and attempt to satisfy those
requests via translation through the HTTP interface. Some
translations are minimal, such as for proxy requests for "http" URIs,
whereas other requests might require translation to and from entirely
different application-level protocols. Proxies are often used to
group an organization's HTTP requests through a common intermediary
for the sake of security, annotation services, or shared caching.
Some proxies are designed to apply transformations to selected
messages or payloads while they are being forwarded, as described in
Section 5.6.2.
A "gateway" (a.k.a. "reverse proxy") is an intermediary that acts as
an origin server for the outbound connection but translates received
requests and forwards them inbound to another server or servers.
Gateways are often used to encapsulate legacy or untrusted
information services, to improve server performance through
"accelerator" caching, and to enable partitioning or load balancing
of HTTP services across multiple machines.
All HTTP requirements applicable to an origin server also apply to
the outbound communication of a gateway. A gateway communicates with
inbound servers using any protocol that it desires, including private
extensions to HTTP that are outside the scope of this specification.
However, an HTTP-to-HTTP gateway that wishes to interoperate with
third-party HTTP servers ought to conform to user agent requirements
on the gateway's inbound connection.
A "tunnel" acts as a blind relay between two connections without
changing the messages. Once active, a tunnel is not considered a
party to the HTTP communication, though the tunnel might have been
initiated by an HTTP request. A tunnel ceases to exist when both
ends of the relayed connection are closed. Tunnels are used to
extend a virtual connection through an intermediary, such as when
Transport Layer Security (TLS, [RFC5246]) is used to establish
confidential communication through a shared firewall proxy.
The above categories for intermediary only consider those acting as
participants in the HTTP communication. There are also
intermediaries that can act on lower layers of the network protocol
stack, filtering or redirecting HTTP traffic without the knowledge or
permission of message senders. Network intermediaries are
indistinguishable (at a protocol level) from a man-in-the-middle
attack, often introducing security flaws or interoperability problems
due to mistakenly violating HTTP semantics.
For example, an "interception proxy" [RFC3040] (also commonly known
as a "transparent proxy" [RFC1919] or "captive portal") differs from
an HTTP proxy because it is not selected by the client. Instead, an
interception proxy filters or redirects outgoing TCP port 80 packets
(and occasionally other common port traffic). Interception proxies
are commonly found on public network access points, as a means of
enforcing account subscription prior to allowing use of non-local
Internet services, and within corporate firewalls to enforce network
usage policies.
HTTP is defined as a stateless protocol, meaning that each request
message can be understood in isolation. Many implementations depend
on HTTP's stateless design in order to reuse proxied connections or
dynamically load balance requests across multiple servers. Hence, a
server MUST NOT assume that two requests on the same connection are
from the same user agent unless the connection is secured and
specific to that agent. Some non-standard HTTP extensions (e.g.,
[RFC4559]) have been known to violate this requirement, resulting in
security and interoperability problems.
2.3. Caches
A "cache" is a local store of previous response messages and the
subsystem that controls its message storage, retrieval, and deletion.
A cache stores cacheable responses in order to reduce the response
time and network bandwidth consumption on future, equivalent
requests. Any client or server MAY employ a cache, though a cache
cannot be used by a server while it is acting as a tunnel.
The effect of a cache is that the request/response chain is shortened
if one of the participants along the chain has a cached response
applicable to that request. The following illustrates the resulting
chain if B has a cached copy of an earlier response from O (via C)
for a request that has not been cached by UA or A.
> >
UA =========== A =========== B - - - - - - C - - - - - - O
< <
A response is "cacheable" if a cache is allowed to store a copy of
the response message for use in answering subsequent requests. Even
when a response is cacheable, there might be additional constraints
placed by the client or by the origin server on when that cached
response can be used for a particular request. HTTP requirements for
cache behavior and cacheable responses are defined in Section 2 of
[Caching].
There is a wide variety of architectures and configurations of caches
deployed across the World Wide Web and inside large organizations.
These include national hierarchies of proxy caches to save
transoceanic bandwidth, collaborative systems that broadcast or
multicast cache entries, archives of pre-fetched cache entries for
use in off-line or high-latency environments, and so on.
2.4. Uniform Resource Identifiers
Uniform Resource Identifiers (URIs) [RFC3986] are used throughout
HTTP as the means for identifying resources (Section 2.5). URI
references are used to target requests, indicate redirects, and
define relationships.
The definitions of "URI-reference", "absolute-URI", "relative-part",
"authority", "port", "host", "path-abempty", "segment", "query", and
"fragment" are adopted from the URI generic syntax. An "absolute-
path" rule is defined for protocol elements that can contain a non-
empty path component. (This rule differs slightly from the path-
abempty rule of RFC 3986, which allows for an empty path to be used
in references, and path-absolute rule, which does not allow paths
that begin with "//".) A "partial-URI" rule is defined for protocol
elements that can contain a relative URI but not a fragment
component.
URI-reference = <URI-reference, see [RFC3986], Section 4.1>
absolute-URI = <absolute-URI, see [RFC3986], Section 4.3>
relative-part = <relative-part, see [RFC3986], Section 4.2>
authority = <authority, see [RFC3986], Section 3.2>
uri-host = <host, see [RFC3986], Section 3.2.2>
port = <port, see [RFC3986], Section 3.2.3>
path-abempty = <path-abempty, see [RFC3986], Section 3.3>
segment = <segment, see [RFC3986], Section 3.3>
query = <query, see [RFC3986], Section 3.4>
fragment = <fragment, see [RFC3986], Section 3.5>
absolute-path = 1*( "/" segment )
partial-URI = relative-part [ "?" query ]
Each protocol element in HTTP that allows a URI reference will
indicate in its ABNF production whether the element allows any form
of reference (URI-reference), only a URI in absolute form (absolute-
URI), only the path and optional query components, or some
combination of the above. Unless otherwise indicated, URI references
are parsed relative to the effective request URI (Section 5.3).
2.5. Resources
The target of an HTTP request is called a "resource". HTTP does not The target of an HTTP request is called a "resource". HTTP does not
limit the nature of a resource; it merely defines an interface that limit the nature of a resource; it merely defines an interface that
might be used to interact with resources. Each resource is might be used to interact with resources. Each resource is
identified by a Uniform Resource Identifier (URI), as described in identified by a Uniform Resource Identifier (URI), as described in
Section 2.7 of [MESSGNG]. Section 2.4.
When a client constructs an HTTP/1.1 request message, it sends the
target URI in one of various forms, as defined in (Section 5.3 of
[MESSGNG]). When a request is received, the server reconstructs an
effective request URI for the target resource (Section 5.5 of
[MESSGNG]).
One design goal of HTTP is to separate resource identification from One design goal of HTTP is to separate resource identification from
request semantics, which is made possible by vesting the request request semantics, which is made possible by vesting the request
semantics in the request method (Section 4) and a few request- semantics in the request method (Section 7) and a few request-
modifying header fields (Section 5). If there is a conflict between modifying header fields (Section 8). If there is a conflict between
the method semantics and any semantic implied by the URI itself, as the method semantics and any semantic implied by the URI itself, as
described in Section 4.2.1, the method semantics take precedence. described in Section 7.2.1, the method semantics take precedence.
3. Representations IANA maintains the registry of URI Schemes [BCP115] at
<https://www.iana.org/assignments/uri-schemes/>. [[CREF2: Although
requests might target any URI scheme, the following schemes are
inherent to HTTP servers:]]
+------------+------------------------------------+---------------+
| URI Scheme | Description | Reference |
+------------+------------------------------------+---------------+
| http | Hypertext Transfer Protocol | Section 2.5.1 |
| https | Hypertext Transfer Protocol Secure | Section 2.5.2 |
+------------+------------------------------------+---------------+
2.5.1. http URI Scheme
The "http" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening for
TCP ([RFC0793]) connections on a given port.
http-URI = "http:" "//" authority path-abempty [ "?" query ]
[ "#" fragment ]
The origin server for an "http" URI is identified by the authority
component, which includes a host identifier and optional TCP port
([RFC3986], Section 3.2.2). The hierarchical path component and
optional query component serve as an identifier for a potential
target resource within that origin server's name space. The optional
fragment component allows for indirect identification of a secondary
resource, independent of the URI scheme, as defined in Section 3.5 of
[RFC3986].
A sender MUST NOT generate an "http" URI with an empty host
identifier. A recipient that processes such a URI reference MUST
reject it as invalid.
If the host identifier is provided as an IP address, the origin
server is the listener (if any) on the indicated TCP port at that IP
address. If host is a registered name, the registered name is an
indirect identifier for use with a name resolution service, such as
DNS, to find an address for that origin server. If the port
subcomponent is empty or not given, TCP port 80 (the reserved port
for WWW services) is the default.
Note that the presence of a URI with a given authority component does
not imply that there is always an HTTP server listening for
connections on that host and port. Anyone can mint a URI. What the
authority component determines is who has the right to respond
authoritatively to requests that target the identified resource. The
delegated nature of registered names and IP addresses creates a
federated namespace, based on control over the indicated host and
port, whether or not an HTTP server is present. See Section 12.1 for
security considerations related to establishing authority.
When an "http" URI is used within a context that calls for access to
the indicated resource, a client MAY attempt access by resolving the
host to an IP address, establishing a TCP connection to that address
on the indicated port, and sending an HTTP request message (Section 2
of [Messaging]) containing the URI's identifying data to the server.
If the server responds to that request with a non-interim HTTP
response message, as described in Section 9, then that response is
considered an authoritative answer to the client's request.
Although HTTP is independent of the transport protocol, the "http"
scheme is specific to TCP-based services because the name delegation
process depends on TCP for establishing authority. An HTTP service
based on some other underlying connection protocol would presumably
be identified using a different URI scheme, just as the "https"
scheme (below) is used for resources that require an end-to-end
secured connection. Other protocols might also be used to provide
access to "http" identified resources -- it is only the authoritative
interface that is specific to TCP.
The URI generic syntax for authority also includes a deprecated
userinfo subcomponent ([RFC3986], Section 3.2.1) for including user
authentication information in the URI. Some implementations make use
of the userinfo component for internal configuration of
authentication information, such as within command invocation
options, configuration files, or bookmark lists, even though such
usage might expose a user identifier or password. A sender MUST NOT
generate the userinfo subcomponent (and its "@" delimiter) when an
"http" URI reference is generated within a message as a request
target or header field value. Before making use of an "http" URI
reference received from an untrusted source, a recipient SHOULD parse
for userinfo and treat its presence as an error; it is likely being
used to obscure the authority for the sake of phishing attacks.
2.5.2. https URI Scheme
The "https" URI scheme is hereby defined for the purpose of minting
identifiers according to their association with the hierarchical
namespace governed by a potential HTTP origin server listening to a
given TCP port for TLS-secured connections ([RFC5246]).
All of the requirements listed above for the "http" scheme are also
requirements for the "https" scheme, except that TCP port 443 is the
default if the port subcomponent is empty or not given, and the user
agent MUST ensure that its connection to the origin server is secured
through the use of strong encryption, end-to-end, prior to sending
the first HTTP request.
https-URI = "https:" "//" authority path-abempty [ "?" query ]
[ "#" fragment ]
Note that the "https" URI scheme depends on both TLS and TCP for
establishing authority. Resources made available via the "https"
scheme have no shared identity with the "http" scheme even if their
resource identifiers indicate the same authority (the same host
listening to the same TCP port). They are distinct namespaces and
are considered to be distinct origin servers. However, an extension
to HTTP that is defined to apply to entire host domains, such as the
Cookie protocol [RFC6265], can allow information set by one service
to impact communication with other services within a matching group
of host domains.
The process for authoritative access to an "https" identified
resource is defined in [RFC2818].
2.5.3. http and https URI Normalization and Comparison
Since the "http" and "https" schemes conform to the URI generic
syntax, such URIs are normalized and compared according to the
algorithm defined in Section 6 of [RFC3986], using the defaults
described above for each scheme.
If the port is equal to the default port for a scheme, the normal
form is to omit the port subcomponent. When not being used in
absolute form as the request target of an OPTIONS request, an empty
path component is equivalent to an absolute path of "/", so the
normal form is to provide a path of "/" instead. The scheme and host
are case-insensitive and normally provided in lowercase; all other
components are compared in a case-sensitive manner. Characters other
than those in the "reserved" set are equivalent to their percent-
encoded octets: the normal form is to not encode them (see Sections
2.1 and 2.2 of [RFC3986]).
For example, the following three URIs are equivalent:
http://example.com:80/~smith/home.html
http://EXAMPLE.com/%7Esmith/home.html
http://EXAMPLE.com:/%7esmith/home.html
3. Conformance
3.1. Implementation Diversity
When considering the design of HTTP, it is easy to fall into a trap
of thinking that all user agents are general-purpose browsers and all
origin servers are large public websites. That is not the case in
practice. Common HTTP user agents include household appliances,
stereos, scales, firmware update scripts, command-line programs,
mobile apps, and communication devices in a multitude of shapes and
sizes. Likewise, common HTTP origin servers include home automation
units, configurable networking components, office machines,
autonomous robots, news feeds, traffic cameras, ad selectors, and
video-delivery platforms.
The term "user agent" does not imply that there is a human user
directly interacting with the software agent at the time of a
request. In many cases, a user agent is installed or configured to
run in the background and save its results for later inspection (or
save only a subset of those results that might be interesting or
erroneous). Spiders, for example, are typically given a start URI
and configured to follow certain behavior while crawling the Web as a
hypertext graph.
The implementation diversity of HTTP means that not all user agents
can make interactive suggestions to their user or provide adequate
warning for security or privacy concerns. In the few cases where
this specification requires reporting of errors to the user, it is
acceptable for such reporting to only be observable in an error
console or log file. Likewise, requirements that an automated action
be confirmed by the user before proceeding might be met via advance
configuration choices, run-time options, or simple avoidance of the
unsafe action; confirmation does not imply any specific user
interface or interruption of normal processing if the user has
already made that choice.
3.2. Role-based Requirements
This specification targets conformance criteria according to the role
of a participant in HTTP communication. Hence, HTTP requirements are
placed on senders, recipients, clients, servers, user agents,
intermediaries, origin servers, proxies, gateways, or caches,
depending on what behavior is being constrained by the requirement.
Additional (social) requirements are placed on implementations,
resource owners, and protocol element registrations when they apply
beyond the scope of a single communication.
The verb "generate" is used instead of "send" where a requirement
differentiates between creating a protocol element and merely
forwarding a received element downstream.
An implementation is considered conformant if it complies with all of
the requirements associated with the roles it partakes in HTTP.
Conformance includes both the syntax and semantics of protocol
elements. A sender MUST NOT generate protocol elements that convey a
meaning that is known by that sender to be false. A sender MUST NOT
generate protocol elements that do not match the grammar defined by
the corresponding ABNF rules. Within a given message, a sender MUST
NOT generate protocol elements or syntax alternatives that are only
allowed to be generated by participants in other roles (i.e., a role
that the sender does not have for that message).
3.3. Parsing Elements
When a received protocol element is parsed, the recipient MUST be
able to parse any value of reasonable length that is applicable to
the recipient's role and that matches the grammar defined by the
corresponding ABNF rules. Note, however, that some received protocol
elements might not be parsed. For example, an intermediary
forwarding a message might parse a header-field into generic field-
name and field-value components, but then forward the header field
without further parsing inside the field-value.
HTTP does not have specific length limitations for many of its
protocol elements because the lengths that might be appropriate will
vary widely, depending on the deployment context and purpose of the
implementation. Hence, interoperability between senders and
recipients depends on shared expectations regarding what is a
reasonable length for each protocol element. Furthermore, what is
commonly understood to be a reasonable length for some protocol
elements has changed over the course of the past two decades of HTTP
use and is expected to continue changing in the future.
At a minimum, a recipient MUST be able to parse and process protocol
element lengths that are at least as long as the values that it
generates for those same protocol elements in other messages. For
example, an origin server that publishes very long URI references to
its own resources needs to be able to parse and process those same
references when received as a request target.
3.4. Error Handling
A recipient MUST interpret a received protocol element according to
the semantics defined for it by this specification, including
extensions to this specification, unless the recipient has determined
(through experience or configuration) that the sender incorrectly
implements what is implied by those semantics. For example, an
origin server might disregard the contents of a received Accept-
Encoding header field if inspection of the User-Agent header field
indicates a specific implementation version that is known to fail on
receipt of certain content codings.
Unless noted otherwise, a recipient MAY attempt to recover a usable
protocol element from an invalid construct. HTTP does not define
specific error handling mechanisms except when they have a direct
impact on security, since different applications of the protocol
require different error handling strategies. For example, a Web
browser might wish to transparently recover from a response where the
Location header field doesn't parse according to the ABNF, whereas a
systems control client might consider any form of error recovery to
be dangerous.
3.5. Protocol Versioning
HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
of the protocol. This specification defines version "1.1". The
protocol version as a whole indicates the sender's conformance with
the set of requirements laid out in that version's corresponding
specification of HTTP.
The version of an HTTP message is indicated by an HTTP-version field
in the first line of the message. HTTP-version is case-sensitive.
HTTP-version = HTTP-name "/" DIGIT "." DIGIT
HTTP-name = %x48.54.54.50 ; "HTTP", case-sensitive
The HTTP version number consists of two decimal digits separated by a
"." (period or decimal point). The first digit ("major version")
indicates the HTTP messaging syntax, whereas the second digit ("minor
version") indicates the highest minor version within that major
version to which the sender is conformant and able to understand for
future communication. The minor version advertises the sender's
communication capabilities even when the sender is only using a
backwards-compatible subset of the protocol, thereby letting the
recipient know that more advanced features can be used in response
(by servers) or in future requests (by clients).
When an HTTP/1.1 message is sent to an HTTP/1.0 recipient [RFC1945]
or a recipient whose version is unknown, the HTTP/1.1 message is
constructed such that it can be interpreted as a valid HTTP/1.0
message if all of the newer features are ignored. This specification
places recipient-version requirements on some new features so that a
conformant sender will only use compatible features until it has
determined, through configuration or the receipt of a message, that
the recipient supports HTTP/1.1.
The interpretation of a header field does not change between minor
versions of the same major HTTP version, though the default behavior
of a recipient in the absence of such a field can change. Unless
specified otherwise, header fields defined in HTTP/1.1 are defined
for all versions of HTTP/1.x. In particular, the Host and Connection
header fields ought to be implemented by all HTTP/1.x implementations
whether or not they advertise conformance with HTTP/1.1.
New header fields can be introduced without changing the protocol
version if their defined semantics allow them to be safely ignored by
recipients that do not recognize them. Header field extensibility is
discussed in Section 4.1.2.
Intermediaries that process HTTP messages (i.e., all intermediaries
other than those acting as tunnels) MUST send their own HTTP-version
in forwarded messages. In other words, they are not allowed to
blindly forward the first line of an HTTP message without ensuring
that the protocol version in that message matches a version to which
that intermediary is conformant for both the receiving and sending of
messages. Forwarding an HTTP message without rewriting the HTTP-
version might result in communication errors when downstream
recipients use the message sender's version to determine what
features are safe to use for later communication with that sender.
A client SHOULD send a request version equal to the highest version
to which the client is conformant and whose major version is no
higher than the highest version supported by the server, if this is
known. A client MUST NOT send a version to which it is not
conformant.
A client MAY send a lower request version if it is known that the
server incorrectly implements the HTTP specification, but only after
the client has attempted at least one normal request and determined
from the response status code or header fields (e.g., Server) that
the server improperly handles higher request versions.
A server SHOULD send a response version equal to the highest version
to which the server is conformant that has a major version less than
or equal to the one received in the request. A server MUST NOT send
a version to which it is not conformant. A server can send a 505
(HTTP Version Not Supported) response if it wishes, for any reason,
to refuse service of the client's major protocol version.
A server MAY send an HTTP/1.0 response to a request if it is known or
suspected that the client incorrectly implements the HTTP
specification and is incapable of correctly processing later version
responses, such as when a client fails to parse the version number
correctly or when an intermediary is known to blindly forward the
HTTP-version even when it doesn't conform to the given minor version
of the protocol. Such protocol downgrades SHOULD NOT be performed
unless triggered by specific client attributes, such as when one or
more of the request header fields (e.g., User-Agent) uniquely match
the values sent by a client known to be in error.
The intention of HTTP's versioning design is that the major number
will only be incremented if an incompatible message syntax is
introduced, and that the minor number will only be incremented when
changes made to the protocol have the effect of adding to the message
semantics or implying additional capabilities of the sender.
However, the minor version was not incremented for the changes
introduced between [RFC2068] and [RFC2616], and this revision has
specifically avoided any such changes to the protocol.
When an HTTP message is received with a major version number that the
recipient implements, but a higher minor version number than what the
recipient implements, the recipient SHOULD process the message as if
it were in the highest minor version within that major version to
which the recipient is conformant. A recipient can assume that a
message with a higher minor version, when sent to a recipient that
has not yet indicated support for that higher version, is
sufficiently backwards-compatible to be safely processed by any
implementation of the same major version.
4. Message Abstraction
[[CREF3: Each major version of HTTP defines its own syntax for the
inclusion of information in messages. Nevertheless, a common
abstraction is that a message includes some form of envelope/framing,
a potential set of named data fields, and a potential body. This
section defines the abstraction for message fields as field-name and
field-value pairs. ]]
4.1. Field Names
Header fields are key:value pairs that can be used to communicate
data about the message, its payload, the target resource, or the
connection (i.e., control data).
The requirements for header field names are defined in [BCP90].
The field-name token labels the corresponding field-value as having
the semantics defined by that header field. For example, the Date
header field is defined in Section 10.1.1.2 as containing the
origination timestamp for the message in which it appears.
field-name = token
The following field names are defined by this document:
+---------------------+----------+----------+-------------------+
| Header Field Name | Protocol | Status | Reference |
+---------------------+----------+----------+-------------------+
| Accept | http | standard | Section 8.4.2 |
| Accept-Charset | http | standard | Section 8.4.3 |
| Accept-Encoding | http | standard | Section 8.4.4 |
| Accept-Language | http | standard | Section 8.4.5 |
| Accept-Ranges | http | standard | Section 10.4.1 |
| Allow | http | standard | Section 10.4.2 |
| Authorization | http | standard | Section 8.5.3 |
| Content-Encoding | http | standard | Section 6.2.2 |
| Content-Language | http | standard | Section 6.2.3 |
| Content-Length | http | standard | Section 6.2.4 |
| Content-Location | http | standard | Section 6.2.5 |
| Content-Range | http | standard | Section 6.3.3 |
| Content-Type | http | standard | Section 6.2.1 |
| Date | http | standard | Section 10.1.1.2 |
| ETag | http | standard | Section 10.2.3 |
| Expect | http | standard | Section 8.1.1 |
| From | http | standard | Section 8.6.1 |
| Host | http | standard | Section 5.4 |
| If-Match | http | standard | Section 8.2.3 |
| If-Modified-Since | http | standard | Section 8.2.5 |
| If-None-Match | http | standard | Section 8.2.4 |
| If-Range | http | standard | Section 8.2.7 |
| If-Unmodified-Since | http | standard | Section 8.2.6 |
| Last-Modified | http | standard | Section 10.2.2 |
| Location | http | standard | Section 10.1.2 |
| Max-Forwards | http | standard | Section 8.1.2 |
| Proxy-Authenticate | http | standard | Section 10.3.2 |
| Proxy-Authorization | http | standard | Section 8.5.4 |
| Range | http | standard | Section 8.3 |
| Referer | http | standard | Section 8.6.2 |
| Retry-After | http | standard | Section 10.1.3 |
| Server | http | standard | Section 10.4.3 |
| Trailer | http | standard | Section 4.4 |
| User-Agent | http | standard | Section 8.6.3 |
| Vary | http | standard | Section 10.1.4 |
| Via | http | standard | Section 5.6.1 |
| WWW-Authenticate | http | standard | Section 10.3.1 |
+---------------------+----------+----------+-------------------+
4.1.1. Field Name Registry
HTTP header fields are registered within the "Message Headers"
registry located at <https://www.iana.org/assignments/message-
headers>, as defined by [BCP90], with the protocol "http".
4.1.2. Field Extensibility
Header fields are fully extensible: there is no limit on the
introduction of new field names, each presumably defining new
semantics, nor on the number of header fields used in a given
message. Existing fields are defined in each part of this
specification and in many other specifications outside this document
set.
New header fields can be defined such that, when they are understood
by a recipient, they might override or enhance the interpretation of
previously defined header fields, define preconditions on request
evaluation, or refine the meaning of responses.
A proxy MUST forward unrecognized header fields unless the field-name
is listed in the Connection header field (Section 6.1 of [Messaging])
or the proxy is specifically configured to block, or otherwise
transform, such fields. Other recipients SHOULD ignore unrecognized
header fields. These requirements allow HTTP's functionality to be
enhanced without requiring prior update of deployed intermediaries.
All defined header fields ought to be registered with IANA in the
"Message Headers" registry.
4.1.3. Considerations for New Fields
Authors of specifications defining new fields are advised to keep the
name as short as practical and not to prefix the name with "X-"
unless the header field will never be used on the Internet. (The
"X-" prefix idiom has been extensively misused in practice; it was
intended to only be used as a mechanism for avoiding name collisions
inside proprietary software or intranet processing, since the prefix
would ensure that private names never collide with a newly registered
Internet name; see [BCP178] for further information).
Authors of specifications defining new header fields are advised to
consider documenting:
o Whether the field is a single value or whether it can be a list
(delimited by commas; see Section 2.3 of [Messaging]).
If it does not use the list syntax, document how to treat messages
where the field occurs multiple times (a sensible default would be
to ignore the field, but this might not always be the right
choice).
Note that intermediaries and software libraries might combine
multiple header field instances into a single one, despite the
field's definition not allowing the list syntax. A robust format
enables recipients to discover these situations (good example:
"Content-Type", as the comma can only appear inside quoted
strings; bad example: "Location", as a comma can occur inside a
URI).
o Under what conditions the header field can be used; e.g., only in
responses or requests, in all messages, only on responses to a
particular request method, etc.
o Whether the field should be stored by origin servers that
understand it upon a PUT request.
o Whether the field semantics are further refined by the context,
such as by existing request methods or status codes.
o Whether it is appropriate to list the field-name in the Connection
header field (i.e., if the header field is to be hop-by-hop; see
Section 6.1 of [Messaging]).
o Under what conditions intermediaries are allowed to insert,
delete, or modify the field's value.
o Whether it is appropriate to list the field-name in a Vary
response header field (e.g., when the request header field is used
by an origin server's content selection algorithm; see
Section 10.1.4).
o Whether the header field is useful or allowable in trailers (see
Section 3.1 of [Messaging]).
o Whether the header field ought to be preserved across redirects.
o Whether it introduces any additional security considerations, such
as disclosure of privacy-related data.
4.2. Field Values
This specification does not use ABNF rules to define each "Field-
Name: Field Value" pair, as was done in earlier editions. Instead,
this specification uses ABNF rules that are named according to each
registered field name, wherein the rule defines the valid grammar for
that field's corresponding field values (i.e., after the field-value
has been extracted by a generic field parser).
field-value = *( field-content / obs-fold )
field-content = field-vchar [ 1*( SP / HTAB ) field-vchar ]
field-vchar = VCHAR / obs-text
Historically, HTTP header field values could be extended over
multiple lines by preceding each extra line with at least one space
or horizontal tab (obs-fold). [[CREF4: This document assumes that
any such]] [obs-fold has been replaced with one or more SP octets
prior to interpreting the field value, as described in Section 2.3.2
of [Messaging].]
Historically, HTTP has allowed field content with text in the
ISO-8859-1 charset [ISO-8859-1], supporting other charsets only
through use of [RFC2047] encoding. In practice, most HTTP header
field values use only a subset of the US-ASCII charset [USASCII].
Newly defined header fields SHOULD limit their field values to
US-ASCII octets. A recipient SHOULD treat other octets in field
content (obs-text) as opaque data.
4.2.1. Field Order
The order in which header fields with differing field names are
received is not significant. However, it is good practice to send
header fields that contain control data first, such as Host on
requests and Date on responses, so that implementations can decide
when not to handle a message as early as possible. A server MUST NOT
apply a request to the target resource until the entire request
header section is received, since later header fields might include
conditionals, authentication credentials, or deliberately misleading
duplicate header fields that would impact request processing.
A sender MUST NOT generate multiple header fields with the same field
name in a message unless either the entire field value for that
header field is defined as a comma-separated list [i.e., #(values)]
or the header field is a well-known exception (as noted below).
A recipient MAY combine multiple header fields with the same field
name into one "field-name: field-value" pair, without changing the
semantics of the message, by appending each subsequent field value to
the combined field value in order, separated by a comma. The order
in which header fields with the same field name are received is
therefore significant to the interpretation of the combined field
value; a proxy MUST NOT change the order of these field values when
forwarding a message.
Note: In practice, the "Set-Cookie" header field ([RFC6265]) often
appears multiple times in a response message and does not use the
list syntax, violating the above requirements on multiple header
fields with the same name. Since it cannot be combined into a
single field-value, recipients ought to handle "Set-Cookie" as a
special case while processing header fields. (See Appendix A.2.3
of [Kri2001] for details.)
4.2.2. Field Limits
HTTP does not place a predefined limit on the length of each header
field or on the length of the header section as a whole, as described
in Section 3. Various ad hoc limitations on individual header field
length are found in practice, often depending on the specific field
semantics.
A server that receives a request header field, or set of fields,
larger than it wishes to process MUST respond with an appropriate 4xx
(Client Error) status code. Ignoring such header fields would
increase the server's vulnerability to request smuggling attacks
(Section 8.2 of [Messaging]).
A client MAY discard or truncate received header fields that are
larger than the client wishes to process if the field semantics are
such that the dropped value(s) can be safely ignored without changing
the message framing or response semantics.
4.2.3. Field Value Components
Most HTTP header field values are defined using common syntax
components (token, quoted-string, and comment) separated by
whitespace or specific delimiting characters. Delimiters are chosen
from the set of US-ASCII visual characters not allowed in a token
(DQUOTE and "(),/:;<=>?@[\]{}").
token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*"
/ "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
/ DIGIT / ALPHA
; any VCHAR, except delimiters
A string of text is parsed as a single value if it is quoted using
double-quote marks.
quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
qdtext = HTAB / SP /%x21 / %x23-5B / %x5D-7E / obs-text
obs-text = %x80-FF
Comments can be included in some HTTP header fields by surrounding
the comment text with parentheses. Comments are only allowed in
fields containing "comment" as part of their field value definition.
comment = "(" *( ctext / quoted-pair / comment ) ")"
ctext = HTAB / SP / %x21-27 / %x2A-5B / %x5D-7E / obs-text
The backslash octet ("\") can be used as a single-octet quoting
mechanism within quoted-string and comment constructs. Recipients
that process the value of a quoted-string MUST handle a quoted-pair
as if it were replaced by the octet following the backslash.
quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
A sender SHOULD NOT generate a quoted-pair in a quoted-string except
where necessary to quote DQUOTE and backslash octets occurring within
that string. A sender SHOULD NOT generate a quoted-pair in a comment
except where necessary to quote parentheses ["(" and ")"] and
backslash octets occurring within that comment.
4.2.4. Designing New Field Values
New header field values typically have their syntax defined using
ABNF ([RFC5234]), using the extension defined in Section 11 as
necessary, and are usually constrained to the range of US-ASCII
characters. Header fields needing a greater range of characters can
use an encoding such as the one defined in [RFC5987].
Leading and trailing whitespace in raw field values is removed upon
field parsing (Section 2.3.1 of [Messaging]). Field definitions
where leading or trailing whitespace in values is significant will
have to use a container syntax such as quoted-string (Section 4.2.3).
Because commas (",") are used as a generic delimiter between field-
values, they need to be treated with care if they are allowed in the
field-value. Typically, components that might contain a comma are
protected with double-quotes using the quoted-string ABNF production.
For example, a textual date and a URI (either of which might contain
a comma) could be safely carried in field-values like these:
Example-URI-Field: "http://example.com/a.html,foo",
"http://without-a-comma.example.com/"
Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
Note that double-quote delimiters almost always are used with the
quoted-string production; using a different syntax inside double-
quotes will likely cause unnecessary confusion.
Many header fields use a format including (case-insensitively) named
parameters (for instance, Content-Type, defined in Section 6.2.1).
Allowing both unquoted (token) and quoted (quoted-string) syntax for
the parameter value enables recipients to use existing parser
components. When allowing both forms, the meaning of a parameter
value ought to be independent of the syntax used for it (for an
example, see the notes on parameter handling for media types in
Section 6.1.1).
4.3. Whitespace
This specification uses three rules to denote the use of linear
whitespace: OWS (optional whitespace), RWS (required whitespace), and
BWS ("bad" whitespace).
The OWS rule is used where zero or more linear whitespace octets
might appear. For protocol elements where optional whitespace is
preferred to improve readability, a sender SHOULD generate the
optional whitespace as a single SP; otherwise, a sender SHOULD NOT
generate optional whitespace except as needed to white out invalid or
unwanted protocol elements during in-place message filtering.
The RWS rule is used when at least one linear whitespace octet is
required to separate field tokens. A sender SHOULD generate RWS as a
single SP.
The BWS rule is used where the grammar allows optional whitespace
only for historical reasons. A sender MUST NOT generate BWS in
messages. A recipient MUST parse for such bad whitespace and remove
it before interpreting the protocol element.
OWS = *( SP / HTAB )
; optional whitespace
RWS = 1*( SP / HTAB )
; required whitespace
BWS = OWS
; "bad" whitespace
4.4. Trailer
[[CREF5: The "Trailer" header field in a message indicates fields
that the sender anticipates sending after the message header block
(i.e., during or after the payload is sent). This is typically used
to supply metadata that might be dynamically generated while the data
is sent, such as a message integrity check, digital signature, or
post-processing status. ]]
Trailer = 1#field-name
[[CREF6: How, where, and when trailer fields might be sent depends on
both the protocol in use (HTTP version and/or transfer coding) and
the semantics of each named header field. Many header fields cannot
be processed outside the header section because their evaluation is
necessary for message routing, authentication, or configuration prior
to receiving the representation data. ]]
5. Message Routing
HTTP request message routing is determined by each client based on
the target resource, the client's proxy configuration, and
establishment or reuse of an inbound connection. The corresponding
response routing follows the same connection chain back to the
client.
5.1. Identifying a Target Resource
HTTP is used in a wide variety of applications, ranging from general-
purpose computers to home appliances. In some cases, communication
options are hard-coded in a client's configuration. However, most
HTTP clients rely on the same resource identification mechanism and
configuration techniques as general-purpose Web browsers.
HTTP communication is initiated by a user agent for some purpose.
The purpose is a combination of request semantics and a target
resource upon which to apply those semantics. A URI reference
(Section 2.4) is typically used as an identifier for the "target
resource", which a user agent would resolve to its absolute form in
order to obtain the "target URI". The target URI excludes the
reference's fragment component, if any, since fragment identifiers
are reserved for client-side processing ([RFC3986], Section 3.5).
5.2. Routing Inbound
Once the target URI is determined, a client needs to decide whether a
network request is necessary to accomplish the desired semantics and,
if so, where that request is to be directed.
If the client has a cache [Caching] and the request can be satisfied
by it, then the request is usually directed there first.
If the request is not satisfied by a cache, then a typical client
will check its configuration to determine whether a proxy is to be
used to satisfy the request. Proxy configuration is implementation-
dependent, but is often based on URI prefix matching, selective
authority matching, or both, and the proxy itself is usually
identified by an "http" or "https" URI. If a proxy is applicable,
the client connects inbound by establishing (or reusing) a connection
to that proxy.
If no proxy is applicable, a typical client will invoke a handler
routine, usually specific to the target URI's scheme, to connect
directly to an authority for the target resource. How that is
accomplished is dependent on the target URI scheme and defined by its
associated specification, similar to how this specification defines
origin server access for resolution of the "http" (Section 2.5.1) and
"https" (Section 2.5.2) schemes.
HTTP requirements regarding connection management are defined in
Section 6 of [Messaging].
5.3. Effective Request URI
Once an inbound connection is obtained, the client sends an HTTP
request message (Section 2 of [Messaging]).
[[CREF7: Depending on the nature of the request, the client's target
URI might be split into components and transmitted (or implied)
within various parts of a request message. These parts are
recombined by each recipient, in accordance with their local
configuration and incoming connection context,]] [to form an
"effective request URI" for identifying the intended target resource
with respect to that server. Section 5 of [Messaging] defines how a
server determines the effective request URI for an HTTP/1.1 request.]
For a user agent, the effective request URI is the target URI.
Once the effective request URI has been constructed, an origin server
needs to decide whether or not to provide service for that URI via
the connection in which the request was received. For example, the
request might have been misdirected, deliberately or accidentally,
such that the information within a received request-target or Host
header field differs from the host or port upon which the connection
has been made. If the connection is from a trusted gateway, that
inconsistency might be expected; otherwise, it might indicate an
attempt to bypass security filters, trick the server into delivering
non-public content, or poison a cache. See Section 12 for security
considerations regarding message routing.
5.4. Host
The "Host" header field in a request provides the host and port
information from the target URI, enabling the origin server to
distinguish among resources while servicing requests for multiple
host names on a single IP address.
Host = uri-host [ ":" port ] ; Section 2.4
A client MUST send a Host header field in all HTTP/1.1 request
messages. If the target URI includes an authority component, then a
client MUST send a field-value for Host that is identical to that
authority component, excluding any userinfo subcomponent and its "@"
delimiter (Section 2.5.1). If the authority component is missing or
undefined for the target URI, then a client MUST send a Host header
field with an empty field-value.
Since the Host field-value is critical information for handling a
request, a user agent SHOULD generate Host as the first header field
following the request-line.
For example, a GET request to the origin server for
<http://www.example.org/pub/WWW/> would begin with:
GET /pub/WWW/ HTTP/1.1
Host: www.example.org
A client MUST send a Host header field in an HTTP/1.1 request even if
the request-target is in the absolute-form, since this allows the
Host information to be forwarded through ancient HTTP/1.0 proxies
that might not have implemented Host.
When a proxy receives a request with an absolute-form of request-
target, the proxy MUST ignore the received Host header field (if any)
and instead replace it with the host information of the request-
target. A proxy that forwards such a request MUST generate a new
Host field-value based on the received request-target rather than
forward the received Host field-value.
Since the Host header field acts as an application-level routing
mechanism, it is a frequent target for malware seeking to poison a
shared cache or redirect a request to an unintended server. An
interception proxy is particularly vulnerable if it relies on the
Host field-value for redirecting requests to internal servers, or for
use as a cache key in a shared cache, without first verifying that
the intercepted connection is targeting a valid IP address for that
host.
A server MUST respond with a 400 (Bad Request) status code to any
HTTP/1.1 request message that lacks a Host header field and to any
request message that contains more than one Host header field or a
Host header field with an invalid field-value.
5.5. Associating a Response to a Request
HTTP does not include a request identifier for associating a given
request message with its corresponding one or more response messages.
Hence, it relies on the order of response arrival to correspond
exactly to the order in which requests are made on the same
connection. More than one response message per request only occurs
when one or more informational responses (1xx, see Section 9.2)
precede a final response to the same request.
A client that has more than one outstanding request on a connection
MUST maintain a list of outstanding requests in the order sent and
MUST associate each received response message on that connection to
the highest ordered request that has not yet received a final (non-
1xx) response.
5.6. Message Forwarding
As described in Section 2.2, intermediaries can serve a variety of
roles in the processing of HTTP requests and responses. Some
intermediaries are used to improve performance or availability.
Others are used for access control or to filter content. Since an
HTTP stream has characteristics similar to a pipe-and-filter
architecture, there are no inherent limits to the extent an
intermediary can enhance (or interfere) with either direction of the
stream.
An intermediary not acting as a tunnel MUST implement the Connection
header field, as specified in Section 6.1 of [Messaging], and exclude
fields from being forwarded that are only intended for the incoming
connection.
An intermediary MUST NOT forward a message to itself unless it is
protected from an infinite request loop. In general, an intermediary
ought to recognize its own server names, including any aliases, local
variations, or literal IP addresses, and respond to such requests
directly.
An HTTP message can be parsed as a stream for incremental processing
or forwarding downstream. However, recipients cannot rely on
incremental delivery of partial messages, since some implementations
will buffer or delay message forwarding for the sake of network
efficiency, security checks, or payload transformations.
5.6.1. Via
The "Via" header field indicates the presence of intermediate
protocols and recipients between the user agent and the server (on
requests) or between the origin server and the client (on responses),
similar to the "Received" header field in email (Section 3.6.7 of
[RFC5322]). Via can be used for tracking message forwards, avoiding
request loops, and identifying the protocol capabilities of senders
along the request/response chain.
Via = 1#( received-protocol RWS received-by [ RWS comment ] )
received-protocol = [ protocol-name "/" ] protocol-version
; see [Messaging], Section 6.7
received-by = ( uri-host [ ":" port ] ) / pseudonym
pseudonym = token
Multiple Via field values represent each proxy or gateway that has
forwarded the message. Each intermediary appends its own information
about how the message was received, such that the end result is
ordered according to the sequence of forwarding recipients.
A proxy MUST send an appropriate Via header field, as described
below, in each message that it forwards. An HTTP-to-HTTP gateway
MUST send an appropriate Via header field in each inbound request
message and MAY send a Via header field in forwarded response
messages.
For each intermediary, the received-protocol indicates the protocol
and protocol version used by the upstream sender of the message.
Hence, the Via field value records the advertised protocol
capabilities of the request/response chain such that they remain
visible to downstream recipients; this can be useful for determining
what backwards-incompatible features might be safe to use in
response, or within a later request, as described in Section 3.5.
For brevity, the protocol-name is omitted when the received protocol
is HTTP.
The received-by portion of the field value is normally the host and
optional port number of a recipient server or client that
subsequently forwarded the message. However, if the real host is
considered to be sensitive information, a sender MAY replace it with
a pseudonym. If a port is not provided, a recipient MAY interpret
that as meaning it was received on the default TCP port, if any, for
the received-protocol.
A sender MAY generate comments in the Via header field to identify
the software of each recipient, analogous to the User-Agent and
Server header fields. However, all comments in the Via field are
optional, and a recipient MAY remove them prior to forwarding the
message.
For example, a request message could be sent from an HTTP/1.0 user
agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
forward the request to a public proxy at p.example.net, which
completes the request by forwarding it to the origin server at
www.example.com. The request received by www.example.com would then
have the following Via header field:
Via: 1.0 fred, 1.1 p.example.net
An intermediary used as a portal through a network firewall SHOULD
NOT forward the names and ports of hosts within the firewall region
unless it is explicitly enabled to do so. If not enabled, such an
intermediary SHOULD replace each received-by host of any host behind
the firewall by an appropriate pseudonym for that host.
An intermediary MAY combine an ordered subsequence of Via header
field entries into a single such entry if the entries have identical
received-protocol values. For example,
Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
could be collapsed to
Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
A sender SHOULD NOT combine multiple entries unless they are all
under the same organizational control and the hosts have already been
replaced by pseudonyms. A sender MUST NOT combine entries that have
different received-protocol values.
5.6.2. Transformations
Some intermediaries include features for transforming messages and
their payloads. A proxy might, for example, convert between image
formats in order to save cache space or to reduce the amount of
traffic on a slow link. However, operational problems might occur
when these transformations are applied to payloads intended for
critical applications, such as medical imaging or scientific data
analysis, particularly when integrity checks or digital signatures
are used to ensure that the payload received is identical to the
original.
An HTTP-to-HTTP proxy is called a "transforming proxy" if it is
designed or configured to modify messages in a semantically
meaningful way (i.e., modifications, beyond those required by normal
HTTP processing, that change the message in a way that would be
significant to the original sender or potentially significant to
downstream recipients). For example, a transforming proxy might be
acting as a shared annotation server (modifying responses to include
references to a local annotation database), a malware filter, a
format transcoder, or a privacy filter. Such transformations are
presumed to be desired by whichever client (or client organization)
selected the proxy.
If a proxy receives a request-target with a host name that is not a
fully qualified domain name, it MAY add its own domain to the host
name it received when forwarding the request. A proxy MUST NOT
change the host name if the request-target contains a fully qualified
domain name.
A proxy MUST NOT modify the "absolute-path" and "query" parts of the
received request-target when forwarding it to the next inbound
server, except as noted above to replace an empty path with "/" or
"*".
A proxy MAY modify the message body through application or removal of
a transfer coding (Section 3 of [Messaging]).
A proxy MUST NOT transform the payload (Section 6.3) of a message
that contains a no-transform cache-control directive (Section 5.2 of
[Caching]).
A proxy MAY transform the payload of a message that does not contain
a no-transform cache-control directive. A proxy that transforms a
payload MUST add a Warning header field with the warn-code of 214
("Transformation Applied") if one is not already in the message (see
Section 5.5 of [Caching]). A proxy that transforms the payload of a
200 (OK) response can further inform downstream recipients that a
transformation has been applied by changing the response status code
to 203 (Non-Authoritative Information) (Section 9.3.4).
A proxy SHOULD NOT modify header fields that provide information
about the endpoints of the communication chain, the resource state,
or the selected representation (other than the payload) unless the
field's definition specifically allows such modification or the
modification is deemed necessary for privacy or security.
6. Representations
Considering that a resource could be anything, and that the uniform Considering that a resource could be anything, and that the uniform
interface provided by HTTP is similar to a window through which one interface provided by HTTP is similar to a window through which one
can observe and act upon such a thing only through the communication can observe and act upon such a thing only through the communication
of messages to some independent actor on the other side, an of messages to some independent actor on the other side, an
abstraction is needed to represent ("take the place of") the current abstraction is needed to represent ("take the place of") the current
or desired state of that thing in our communications. That or desired state of that thing in our communications. That
abstraction is called a representation [REST]. abstraction is called a representation [REST].
For the purposes of HTTP, a "representation" is information that is For the purposes of HTTP, a "representation" is information that is
skipping to change at page 7, line 42 skipping to change at page 38, line 21
resource, in a format that can be readily communicated via the resource, in a format that can be readily communicated via the
protocol, and that consists of a set of representation metadata and a protocol, and that consists of a set of representation metadata and a
potentially unbounded stream of representation data. potentially unbounded stream of representation data.
An origin server might be provided with, or be capable of generating, An origin server might be provided with, or be capable of generating,
multiple representations that are each intended to reflect the multiple representations that are each intended to reflect the
current state of a target resource. In such cases, some algorithm is current state of a target resource. In such cases, some algorithm is
used by the origin server to select one of those representations as used by the origin server to select one of those representations as
most applicable to a given request, usually based on content most applicable to a given request, usually based on content
negotiation. This "selected representation" is used to provide the negotiation. This "selected representation" is used to provide the
data and metadata for evaluating conditional requests [CONDTNL] and data and metadata for evaluating conditional requests Section 8.2 and
constructing the payload for 200 (OK) and 304 (Not Modified) constructing the payload for 200 (OK) and 304 (Not Modified)
responses to GET (Section 4.3.1). responses to GET (Section 7.3.1).
3.1. Representation Metadata
Representation header fields provide metadata about the 6.1. Representation Data
representation. When a message includes a payload body, the
representation header fields describe how to interpret the
representation data enclosed in the payload body. In a response to a
HEAD request, the representation header fields describe the
representation data that would have been enclosed in the payload body
if the same request had been a GET.
The following header fields convey representation metadata: The representation data associated with an HTTP message is either
provided as the payload body of the message or referred to by the
message semantics and the effective request URI. The representation
data is in a format and encoding defined by the representation
metadata header fields.
+-------------------+-----------------+ The data type of the representation data is determined via the header
| Header Field Name | Defined in... | fields Content-Type and Content-Encoding. These define a two-layer,
+-------------------+-----------------+ ordered encoding model:
| Content-Type | Section 3.1.1.5 |
| Content-Encoding | Section 3.1.2.2 |
| Content-Language | Section 3.1.3.2 |
| Content-Location | Section 3.1.4.2 |
+-------------------+-----------------+
3.1.1. Processing Representation Data representation-data := Content-Encoding( Content-Type( bits ) )
3.1.1.1. Media Type 6.1.1. Media Type
HTTP uses Internet media types [RFC2046] in the Content-Type HTTP uses media types [RFC2046] in the Content-Type (Section 6.2.1)
(Section 3.1.1.5) and Accept (Section 5.3.2) header fields in order and Accept (Section 8.4.2) header fields in order to provide open and
to provide open and extensible data typing and type negotiation. extensible data typing and type negotiation. Media types define both
Media types define both a data format and various processing models: a data format and various processing models: how to process that data
how to process that data in accordance with each context in which it in accordance with each context in which it is received.
is received.
media-type = type "/" subtype *( OWS ";" OWS parameter ) media-type = type "/" subtype *( OWS ";" OWS parameter )
type = token type = token
subtype = token subtype = token
The type/subtype MAY be followed by parameters in the form of The type/subtype MAY be followed by parameters in the form of
name=value pairs. name=value pairs.
parameter = token "=" ( token / quoted-string ) parameter = token "=" ( token / quoted-string )
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transmitted either as a token or within a quoted-string. The quoted transmitted either as a token or within a quoted-string. The quoted
and unquoted values are equivalent. For example, the following and unquoted values are equivalent. For example, the following
examples are all equivalent, but the first is preferred for examples are all equivalent, but the first is preferred for
consistency: consistency:
text/html;charset=utf-8 text/html;charset=utf-8
text/html;charset=UTF-8 text/html;charset=UTF-8
Text/HTML;Charset="utf-8" Text/HTML;Charset="utf-8"
text/html; charset="utf-8" text/html; charset="utf-8"
Internet media types ought to be registered with IANA according to Media types ought to be registered with IANA according to the
the procedures defined in [BCP13]. procedures defined in [BCP13].
Note: Unlike some similar constructs in other header fields, media Note: Unlike some similar constructs in other header fields, media
type parameters do not allow whitespace (even "bad" whitespace) type parameters do not allow whitespace (even "bad" whitespace)
around the "=" character. around the "=" character.
3.1.1.2. Charset 6.1.1.1. Charset
HTTP uses charset names to indicate or negotiate the character HTTP uses charset names to indicate or negotiate the character
encoding scheme of a textual representation [RFC6365]. A charset is encoding scheme of a textual representation [RFC6365]. A charset is
identified by a case-insensitive token. identified by a case-insensitive token.
charset = token charset = token
Charset names ought to be registered in the IANA "Character Sets" Charset names ought to be registered in the IANA "Character Sets"
registry (<http://www.iana.org/assignments/character-sets>) according registry (<https://www.iana.org/assignments/character-sets>)
to the procedures defined in [RFC2978]. according to the procedures defined in [RFC2978].
3.1.1.3. Canonicalization and Text Defaults 6.1.1.2. Canonicalization and Text Defaults
Internet media types are registered with a canonical form in order to Media types are registered with a canonical form in order to be
be interoperable among systems with varying native encoding formats. interoperable among systems with varying native encoding formats.
Representations selected or transferred via HTTP ought to be in Representations selected or transferred via HTTP ought to be in
canonical form, for many of the same reasons described by the canonical form, for many of the same reasons described by the
Multipurpose Internet Mail Extensions (MIME) [RFC2045]. However, the Multipurpose Internet Mail Extensions (MIME) [RFC2045]. However, the
performance characteristics of email deployments (i.e., store and performance characteristics of email deployments (i.e., store and
forward messages to peers) are significantly different from those forward messages to peers) are significantly different from those
common to HTTP and the Web (server-based information services). common to HTTP and the Web (server-based information services).
Furthermore, MIME's constraints for the sake of compatibility with Furthermore, MIME's constraints for the sake of compatibility with
older mail transfer protocols do not apply to HTTP (see Appendix A). older mail transfer protocols do not apply to HTTP (see Appendix B of
[Messaging]).
MIME's canonical form requires that media subtypes of the "text" type MIME's canonical form requires that media subtypes of the "text" type
use CRLF as the text line break. HTTP allows the transfer of text use CRLF as the text line break. HTTP allows the transfer of text
media with plain CR or LF alone representing a line break, when such media with plain CR or LF alone representing a line break, when such
line breaks are consistent for an entire representation. An HTTP line breaks are consistent for an entire representation. An HTTP
sender MAY generate, and a recipient MUST be able to parse, line sender MAY generate, and a recipient MUST be able to parse, line
breaks in text media that consist of CRLF, bare CR, or bare LF. In breaks in text media that consist of CRLF, bare CR, or bare LF. In
addition, text media in HTTP is not limited to charsets that use addition, text media in HTTP is not limited to charsets that use
octets 13 and 10 for CR and LF, respectively. This flexibility octets 13 and 10 for CR and LF, respectively. This flexibility
regarding line breaks applies only to text within a representation regarding line breaks applies only to text within a representation
that has been assigned a "text" media type; it does not apply to that has been assigned a "text" media type; it does not apply to
"multipart" types or HTTP elements outside the payload body (e.g., "multipart" types or HTTP elements outside the payload body (e.g.,
header fields). header fields).
If a representation is encoded with a content-coding, the underlying If a representation is encoded with a content-coding, the underlying
data ought to be in a form defined above prior to being encoded. data ought to be in a form defined above prior to being encoded.
3.1.1.4. Multipart Types 6.1.1.3. Multipart Types
MIME provides for a number of "multipart" types -- encapsulations of MIME provides for a number of "multipart" types -- encapsulations of
one or more representations within a single message body. All one or more representations within a single message body. All
multipart types share a common syntax, as defined in Section 5.1.1 of multipart types share a common syntax, as defined in Section 5.1.1 of
[RFC2046], and include a boundary parameter as part of the media type [RFC2046], and include a boundary parameter as part of the media type
value. The message body is itself a protocol element; a sender MUST value. The message body is itself a protocol element; a sender MUST
generate only CRLF to represent line breaks between body parts. generate only CRLF to represent line breaks between body parts.
HTTP message framing does not use the multipart boundary as an HTTP message framing does not use the multipart boundary as an
indicator of message body length, though it might be used by indicator of message body length, though it might be used by
implementations that generate or process the payload. For example, implementations that generate or process the payload. For example,
the "multipart/form-data" type is often used for carrying form data the "multipart/form-data" type is often used for carrying form data
in a request, as described in [RFC2388], and the "multipart/ in a request, as described in [RFC2388], and the "multipart/
byteranges" type is defined by this specification for use in some 206 byteranges" type is defined by this specification for use in some 206
(Partial Content) responses [RANGERQ]. (Partial Content) responses Section 9.3.7.
3.1.1.5. Content-Type 6.1.2. Content Codings
Content coding values indicate an encoding transformation that has
been or can be applied to a representation. Content codings are
primarily used to allow a representation to be compressed or
otherwise usefully transformed without losing the identity of its
underlying media type and without loss of information. Frequently,
the representation is stored in coded form, transmitted directly, and
only decoded by the final recipient.
content-coding = token
Content-coding values are used in the Accept-Encoding (Section 8.4.4)
and Content-Encoding (Section 6.2.2) header fields.
The following content-coding values are defined by this
specification:
+------------+------------------------------------------+-----------+
| Name | Description | Reference |
+------------+------------------------------------------+-----------+
| compress | UNIX "compress" data format [Welch] | Section 6 |
| | | .1.2.1 |
| deflate | "deflate" compressed data ([RFC1951]) | Section 6 |
| | inside the "zlib" data format | .1.2.2 |
| | ([RFC1950]) | |
| gzip | GZIP file format [RFC1952] | Section 6 |
| | | .1.2.3 |
| identity | Reserved (synonym for "no encoding" in | Section 8 |
| | Accept-Encoding) | .4.4 |
| x-compress | Deprecated (alias for compress) | Section 6 |
| | | .1.2.1 |
| x-gzip | Deprecated (alias for gzip) | Section 6 |
| | | .1.2.3 |
+------------+------------------------------------------+-----------+
6.1.2.1. Compress Coding
The "compress" coding is an adaptive Lempel-Ziv-Welch (LZW) coding
[Welch] that is commonly produced by the UNIX file compression
program "compress". A recipient SHOULD consider "x-compress" to be
equivalent to "compress".
6.1.2.2. Deflate Coding
The "deflate" coding is a "zlib" data format [RFC1950] containing a
"deflate" compressed data stream [RFC1951] that uses a combination of
the Lempel-Ziv (LZ77) compression algorithm and Huffman coding.
Note: Some non-conformant implementations send the "deflate"
compressed data without the zlib wrapper.
6.1.2.3. Gzip Coding
The "gzip" coding is an LZ77 coding with a 32-bit Cyclic Redundancy
Check (CRC) that is commonly produced by the gzip file compression
program [RFC1952]. A recipient SHOULD consider "x-gzip" to be
equivalent to "gzip".
6.1.2.4. Content Coding Extensibility
Additional content codings, outside the scope of this specification,
have been specified for use in HTTP. All such content codings ought
to be registered within the "HTTP Content Coding Registry".
6.1.2.4.1. Content Coding Registry
The "HTTP Content Coding Registry", maintained by IANA at
<https://www.iana.org/assignments/http-parameters/>, registers
content-coding names.
Content coding registrations MUST include the following fields:
o Name
o Description
o Pointer to specification text
Names of content codings MUST NOT overlap with names of transfer
codings (Section 3 of [Messaging]), unless the encoding
transformation is identical (as is the case for the compression
codings defined in Section 6.1.2).
Values to be added to this namespace require IETF Review (see
Section 4.1 of [RFC5226]) and MUST conform to the purpose of content
coding defined in Section 6.1.2.
6.1.3. Language Tags
A language tag, as defined in [RFC5646], identifies a natural
language spoken, written, or otherwise conveyed by human beings for
communication of information to other human beings. Computer
languages are explicitly excluded.
HTTP uses language tags within the Accept-Language and Content-
Language header fields. Accept-Language uses the broader language-
range production defined in Section 8.4.5, whereas Content-Language
uses the language-tag production defined below.
language-tag = <Language-Tag, see [RFC5646], Section 2.1>
A language tag is a sequence of one or more case-insensitive subtags,
each separated by a hyphen character ("-", %x2D). In most cases, a
language tag consists of a primary language subtag that identifies a
broad family of related languages (e.g., "en" = English), which is
optionally followed by a series of subtags that refine or narrow that
language's range (e.g., "en-CA" = the variety of English as
communicated in Canada). Whitespace is not allowed within a language
tag. Example tags include:
fr, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
See [RFC5646] for further information.
6.1.4. Range Units
A representation can be partitioned into subranges according to
various structural units, depending on the structure inherent in the
representation's media type. This "range unit" is used in the
Accept-Ranges (Section 10.4.1) response header field to advertise
support for range requests, the Range (Section 8.3) request header
field to delineate the parts of a representation that are requested,
and the Content-Range (Section 6.3.3) payload header field to
describe which part of a representation is being transferred.
range-unit = bytes-unit / other-range-unit
The following range unit names are defined by this document:
+-------------+---------------------------------------+-------------+
| Range Unit | Description | Reference |
| Name | | |
+-------------+---------------------------------------+-------------+
| bytes | a range of octets | Section 6.1 |
| | | .4.1 |
| none | reserved as keyword, indicating no | Section 10. |
| | ranges are supported | 4.1 |
+-------------+---------------------------------------+-------------+
6.1.4.1. Byte Ranges
Since representation data is transferred in payloads as a sequence of
octets, a byte range is a meaningful substructure for any
representation transferable over HTTP (Section 6). The "bytes" range
unit is defined for expressing subranges of the data's octet
sequence.
bytes-unit = "bytes"
A byte-range request can specify a single range of bytes or a set of
ranges within a single representation.
byte-ranges-specifier = bytes-unit "=" byte-range-set
byte-range-set = 1#( byte-range-spec / suffix-byte-range-spec )
byte-range-spec = first-byte-pos "-" [ last-byte-pos ]
first-byte-pos = 1*DIGIT
last-byte-pos = 1*DIGIT
The first-byte-pos value in a byte-range-spec gives the byte-offset
of the first byte in a range. The last-byte-pos value gives the
byte-offset of the last byte in the range; that is, the byte
positions specified are inclusive. Byte offsets start at zero.
Examples of byte-ranges-specifier values:
o The first 500 bytes (byte offsets 0-499, inclusive):
bytes=0-499
o The second 500 bytes (byte offsets 500-999, inclusive):
bytes=500-999
A byte-range-spec is invalid if the last-byte-pos value is present
and less than the first-byte-pos.
A client can limit the number of bytes requested without knowing the
size of the selected representation. If the last-byte-pos value is
absent, or if the value is greater than or equal to the current
length of the representation data, the byte range is interpreted as
the remainder of the representation (i.e., the server replaces the
value of last-byte-pos with a value that is one less than the current
length of the selected representation).
A client can request the last N bytes of the selected representation
using a suffix-byte-range-spec.
suffix-byte-range-spec = "-" suffix-length
suffix-length = 1*DIGIT
If the selected representation is shorter than the specified suffix-
length, the entire representation is used.
Additional examples, assuming a representation of length 10000:
o The final 500 bytes (byte offsets 9500-9999, inclusive):
bytes=-500
Or:
bytes=9500-
o The first and last bytes only (bytes 0 and 9999):
bytes=0-0,-1
o Other valid (but not canonical) specifications of the second 500
bytes (byte offsets 500-999, inclusive):
bytes=500-600,601-999
bytes=500-700,601-999
If a valid byte-range-set includes at least one byte-range-spec with
a first-byte-pos that is less than the current length of the
representation, or at least one suffix-byte-range-spec with a non-
zero suffix-length, then the byte-range-set is satisfiable.
Otherwise, the byte-range-set is unsatisfiable.
In the byte-range syntax, first-byte-pos, last-byte-pos, and suffix-
length are expressed as decimal number of octets. Since there is no
predefined limit to the length of a payload, recipients MUST
anticipate potentially large decimal numerals and prevent parsing
errors due to integer conversion overflows.
6.1.4.2. Other Range Units
Range units are intended to be extensible. New range units ought to
be registered with IANA, as defined in Section 6.1.4.3.
other-range-unit = token
6.1.4.3. Range Unit Registry
The "HTTP Range Unit Registry" defines the namespace for the range
unit names and refers to their corresponding specifications. It is
maintained at <https://www.iana.org/assignments/http-parameters>.
Registration of an HTTP Range Unit MUST include the following fields:
o Name
o Description
o Pointer to specification text
Values to be added to this namespace require IETF Review (see
[RFC5226], Section 4.1).
6.2. Representation Metadata
Representation header fields provide metadata about the
representation. When a message includes a payload body, the
representation header fields describe how to interpret the
representation data enclosed in the payload body. In a response to a
HEAD request, the representation header fields describe the
representation data that would have been enclosed in the payload body
if the same request had been a GET.
The following header fields convey representation metadata:
+-------------------+---------------+
| Header Field Name | Defined in... |
+-------------------+---------------+
| Content-Type | Section 6.2.1 |
| Content-Encoding | Section 6.2.2 |
| Content-Language | Section 6.2.3 |
| Content-Length | Section 6.2.4 |
| Content-Location | Section 6.2.5 |
+-------------------+---------------+
6.2.1. Content-Type
The "Content-Type" header field indicates the media type of the The "Content-Type" header field indicates the media type of the
associated representation: either the representation enclosed in the associated representation: either the representation enclosed in the
message payload or the selected representation, as determined by the message payload or the selected representation, as determined by the
message semantics. The indicated media type defines both the data message semantics. The indicated media type defines both the data
format and how that data is intended to be processed by a recipient, format and how that data is intended to be processed by a recipient,
within the scope of the received message semantics, after any content within the scope of the received message semantics, after any content
codings indicated by Content-Encoding are decoded. codings indicated by Content-Encoding are decoded.
Content-Type = media-type Content-Type = media-type
Media types are defined in Section 3.1.1.1. An example of the field Media types are defined in Section 6.1.1. An example of the field is
is
Content-Type: text/html; charset=ISO-8859-4 Content-Type: text/html; charset=ISO-8859-4
A sender that generates a message containing a payload body SHOULD A sender that generates a message containing a payload body SHOULD
generate a Content-Type header field in that message unless the generate a Content-Type header field in that message unless the
intended media type of the enclosed representation is unknown to the intended media type of the enclosed representation is unknown to the
sender. If a Content-Type header field is not present, the recipient sender. If a Content-Type header field is not present, the recipient
MAY either assume a media type of "application/octet-stream" MAY either assume a media type of "application/octet-stream"
([RFC2046], Section 4.5.1) or examine the data to determine its type. ([RFC2046], Section 4.5.1) or examine the data to determine its type.
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origin server to provide the correct Content-Type for a given origin server to provide the correct Content-Type for a given
representation, with the result that some clients will examine a representation, with the result that some clients will examine a
payload's content and override the specified type. Clients that do payload's content and override the specified type. Clients that do
so risk drawing incorrect conclusions, which might expose additional so risk drawing incorrect conclusions, which might expose additional
security risks (e.g., "privilege escalation"). Furthermore, it is security risks (e.g., "privilege escalation"). Furthermore, it is
impossible to determine the sender's intent by examining the data impossible to determine the sender's intent by examining the data
format: many data formats match multiple media types that differ only format: many data formats match multiple media types that differ only
in processing semantics. Implementers are encouraged to provide a in processing semantics. Implementers are encouraged to provide a
means of disabling such "content sniffing" when it is used. means of disabling such "content sniffing" when it is used.
3.1.2. Encoding for Compression or Integrity 6.2.2. Content-Encoding
3.1.2.1. Content Codings
Content coding values indicate an encoding transformation that has
been or can be applied to a representation. Content codings are
primarily used to allow a representation to be compressed or
otherwise usefully transformed without losing the identity of its
underlying media type and without loss of information. Frequently,
the representation is stored in coded form, transmitted directly, and
only decoded by the final recipient.
content-coding = token
All content-coding values are case-insensitive and ought to be
registered within the "HTTP Content Coding Registry", as defined in
Section 8.4. They are used in the Accept-Encoding (Section 5.3.4)
and Content-Encoding (Section 3.1.2.2) header fields.
The following content-coding values are defined by this
specification:
compress (and x-compress): See Section 4.2.1 of [MESSGNG].
deflate: See Section 4.2.2 of [MESSGNG].
gzip (and x-gzip): See Section 4.2.3 of [MESSGNG].
3.1.2.2. Content-Encoding
The "Content-Encoding" header field indicates what content codings The "Content-Encoding" header field indicates what content codings
have been applied to the representation, beyond those inherent in the have been applied to the representation, beyond those inherent in the
media type, and thus what decoding mechanisms have to be applied in media type, and thus what decoding mechanisms have to be applied in
order to obtain data in the media type referenced by the Content-Type order to obtain data in the media type referenced by the Content-Type
header field. Content-Encoding is primarily used to allow a header field. Content-Encoding is primarily used to allow a
representation's data to be compressed without losing the identity of representation's data to be compressed without losing the identity of
its underlying media type. its underlying media type.
Content-Encoding = 1#content-coding Content-Encoding = 1#content-coding
skipping to change at page 12, line 18 skipping to change at page 47, line 41
Content-Encoding: gzip Content-Encoding: gzip
If one or more encodings have been applied to a representation, the If one or more encodings have been applied to a representation, the
sender that applied the encodings MUST generate a Content-Encoding sender that applied the encodings MUST generate a Content-Encoding
header field that lists the content codings in the order in which header field that lists the content codings in the order in which
they were applied. Additional information about the encoding they were applied. Additional information about the encoding
parameters can be provided by other header fields not defined by this parameters can be provided by other header fields not defined by this
specification. specification.
Unlike Transfer-Encoding (Section 3.3.1 of [MESSGNG]), the codings Unlike Transfer-Encoding (Section 2.4.1 of [Messaging]), the codings
listed in Content-Encoding are a characteristic of the listed in Content-Encoding are a characteristic of the
representation; the representation is defined in terms of the coded representation; the representation is defined in terms of the coded
form, and all other metadata about the representation is about the form, and all other metadata about the representation is about the
coded form unless otherwise noted in the metadata definition. coded form unless otherwise noted in the metadata definition.
Typically, the representation is only decoded just prior to rendering Typically, the representation is only decoded just prior to rendering
or analogous usage. or analogous usage.
If the media type includes an inherent encoding, such as a data If the media type includes an inherent encoding, such as a data
format that is always compressed, then that encoding would not be format that is always compressed, then that encoding would not be
restated in Content-Encoding even if it happens to be the same restated in Content-Encoding even if it happens to be the same
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choose to publish the same data as multiple representations that choose to publish the same data as multiple representations that
differ only in whether the coding is defined as part of Content-Type differ only in whether the coding is defined as part of Content-Type
or Content-Encoding, since some user agents will behave differently or Content-Encoding, since some user agents will behave differently
in their handling of each response (e.g., open a "Save as ..." dialog in their handling of each response (e.g., open a "Save as ..." dialog
instead of automatic decompression and rendering of content). instead of automatic decompression and rendering of content).
An origin server MAY respond with a status code of 415 (Unsupported An origin server MAY respond with a status code of 415 (Unsupported
Media Type) if a representation in the request message has a content Media Type) if a representation in the request message has a content
coding that is not acceptable. coding that is not acceptable.
3.1.3. Audience Language 6.2.3. Content-Language
3.1.3.1. Language Tags
A language tag, as defined in [RFC5646], identifies a natural
language spoken, written, or otherwise conveyed by human beings for
communication of information to other human beings. Computer
languages are explicitly excluded.
HTTP uses language tags within the Accept-Language and Content-
Language header fields. Accept-Language uses the broader language-
range production defined in Section 5.3.5, whereas Content-Language
uses the language-tag production defined below.
language-tag = <Language-Tag, see [RFC5646], Section 2.1>
A language tag is a sequence of one or more case-insensitive subtags,
each separated by a hyphen character ("-", %x2D). In most cases, a
language tag consists of a primary language subtag that identifies a
broad family of related languages (e.g., "en" = English), which is
optionally followed by a series of subtags that refine or narrow that
language's range (e.g., "en-CA" = the variety of English as
communicated in Canada). Whitespace is not allowed within a language
tag. Example tags include:
fr, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
See [RFC5646] for further information.
3.1.3.2. Content-Language
The "Content-Language" header field describes the natural language(s) The "Content-Language" header field describes the natural language(s)
of the intended audience for the representation. Note that this of the intended audience for the representation. Note that this
might not be equivalent to all the languages used within the might not be equivalent to all the languages used within the
representation. representation.
Content-Language = 1#language-tag Content-Language = 1#language-tag
Language tags are defined in Section 3.1.3.1. The primary purpose of Language tags are defined in Section 6.1.3. The primary purpose of
Content-Language is to allow a user to identify and differentiate Content-Language is to allow a user to identify and differentiate
representations according to the users' own preferred language. representations according to the users' own preferred language.
Thus, if the content is intended only for a Danish-literate audience, Thus, if the content is intended only for a Danish-literate audience,
the appropriate field is the appropriate field is
Content-Language: da Content-Language: da
If no Content-Language is specified, the default is that the content If no Content-Language is specified, the default is that the content
is intended for all language audiences. This might mean that the is intended for all language audiences. This might mean that the
sender does not consider it to be specific to any natural language, sender does not consider it to be specific to any natural language,
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However, just because multiple languages are present within a However, just because multiple languages are present within a
representation does not mean that it is intended for multiple representation does not mean that it is intended for multiple
linguistic audiences. An example would be a beginner's language linguistic audiences. An example would be a beginner's language
primer, such as "A First Lesson in Latin", which is clearly intended primer, such as "A First Lesson in Latin", which is clearly intended
to be used by an English-literate audience. In this case, the to be used by an English-literate audience. In this case, the
Content-Language would properly only include "en". Content-Language would properly only include "en".
Content-Language MAY be applied to any media type -- it is not Content-Language MAY be applied to any media type -- it is not
limited to textual documents. limited to textual documents.
3.1.4. Identification 6.2.4. Content-Length
3.1.4.1. Identifying a Representation [[CREF8: The "Content-Length" header field indicates the number of
data octets (body length) for the representation. In some cases,
Content-Length is used to define or estimate message framing. ]]
When a complete or partial representation is transferred in a message Content-Length = 1*DIGIT
payload, it is often desirable for the sender to supply, or the
recipient to determine, an identifier for a resource corresponding to
that representation.
For a request message: An example is
o If the request has a Content-Location header field, then the Content-Length: 3495
sender asserts that the payload is a representation of the
resource identified by the Content-Location field-value. However,
such an assertion cannot be trusted unless it can be verified by
other means (not defined by this specification). The information
might still be useful for revision history links.
o Otherwise, the payload is unidentified. A sender MUST NOT send a Content-Length header field in any message
that contains a Transfer-Encoding header field.
For a response message, the following rules are applied in order A user agent SHOULD send a Content-Length in a request message when
until a match is found: no Transfer-Encoding is sent and the request method defines a meaning
for an enclosed payload body. For example, a Content-Length header
field is normally sent in a POST request even when the value is 0
(indicating an empty payload body). A user agent SHOULD NOT send a
Content-Length header field when the request message does not contain
a payload body and the method semantics do not anticipate such a
body.
1. If the request method is GET or HEAD and the response status code A server MAY send a Content-Length header field in a response to a
is 200 (OK), 204 (No Content), 206 (Partial Content), or 304 (Not HEAD request (Section 7.3.2); a server MUST NOT send Content-Length
Modified), the payload is a representation of the resource in such a response unless its field-value equals the decimal number
identified by the effective request URI (Section 5.5 of of octets that would have been sent in the payload body of a response
[MESSGNG]). if the same request had used the GET method.
2. If the request method is GET or HEAD and the response status code A server MAY send a Content-Length header field in a 304 (Not
is 203 (Non-Authoritative Information), the payload is a Modified) response to a conditional GET request (Section 9.4.5); a
potentially modified or enhanced representation of the target server MUST NOT send Content-Length in such a response unless its
resource as provided by an intermediary. field-value equals the decimal number of octets that would have been
sent in the payload body of a 200 (OK) response to the same request.
3. If the response has a Content-Location header field and its A server MUST NOT send a Content-Length header field in any response
field-value is a reference to the same URI as the effective with a status code of 1xx (Informational) or 204 (No Content). A
request URI, the payload is a representation of the resource server MUST NOT send a Content-Length header field in any 2xx
identified by the effective request URI. (Successful) response to a CONNECT request (Section 7.3.6).
4. If the response has a Content-Location header field and its Aside from the cases defined above, in the absence of Transfer-
field-value is a reference to a URI different from the effective Encoding, an origin server SHOULD send a Content-Length header field
request URI, then the sender asserts that the payload is a when the payload body size is known prior to sending the complete
representation of the resource identified by the Content-Location header section. This will allow downstream recipients to measure
field-value. However, such an assertion cannot be trusted unless transfer progress, know when a received message is complete, and
it can be verified by other means (not defined by this potentially reuse the connection for additional requests.
specification).
5. Otherwise, the payload is unidentified. Any Content-Length field value greater than or equal to zero is
valid. Since there is no predefined limit to the length of a
payload, a recipient MUST anticipate potentially large decimal
numerals and prevent parsing errors due to integer conversion
overflows (Section 12.5).
3.1.4.2. Content-Location If a message is received that has multiple Content-Length header
fields with field-values consisting of the same decimal value, or a
single Content-Length header field with a field value containing a
list of identical decimal values (e.g., "Content-Length: 42, 42"),
indicating that duplicate Content-Length header fields have been
generated or combined by an upstream message processor, then the
recipient MUST either reject the message as invalid or replace the
duplicated field-values with a single valid Content-Length field
containing that decimal value prior to determining the message body
length or forwarding the message.
6.2.5. Content-Location
The "Content-Location" header field references a URI that can be used The "Content-Location" header field references a URI that can be used
as an identifier for a specific resource corresponding to the as an identifier for a specific resource corresponding to the
representation in this message's payload. In other words, if one representation in this message's payload. In other words, if one
were to perform a GET request on this URI at the time of this were to perform a GET request on this URI at the time of this
message's generation, then a 200 (OK) response would contain the same message's generation, then a 200 (OK) response would contain the same
representation that is enclosed as payload in this message. representation that is enclosed as payload in this message.
Content-Location = absolute-URI / partial-URI Content-Location = absolute-URI / partial-URI
The Content-Location value is not a replacement for the effective The Content-Location value is not a replacement for the effective
Request URI (Section 5.5 of [MESSGNG]). It is representation Request URI (Section 5.3). It is representation metadata. It has
metadata. It has the same syntax and semantics as the header field the same syntax and semantics as the header field of the same name
of the same name defined for MIME body parts in Section 4 of defined for MIME body parts in Section 4 of [RFC2557]. However, its
[RFC2557]. However, its appearance in an HTTP message has some appearance in an HTTP message has some special implications for HTTP
special implications for HTTP recipients. recipients.
If Content-Location is included in a 2xx (Successful) response If Content-Location is included in a 2xx (Successful) response
message and its value refers (after conversion to absolute form) to a message and its value refers (after conversion to absolute form) to a
URI that is the same as the effective request URI, then the recipient URI that is the same as the effective request URI, then the recipient
MAY consider the payload to be a current representation of that MAY consider the payload to be a current representation of that
resource at the time indicated by the message origination date. For resource at the time indicated by the message origination date. For
a GET (Section 4.3.1) or HEAD (Section 4.3.2) request, this is the a GET (Section 7.3.1) or HEAD (Section 7.3.2) request, this is the
same as the default semantics when no Content-Location is provided by same as the default semantics when no Content-Location is provided by
the server. For a state-changing request like PUT (Section 4.3.4) or the server. For a state-changing request like PUT (Section 7.3.4) or
POST (Section 4.3.3), it implies that the server's response contains POST (Section 7.3.3), it implies that the server's response contains
the new representation of that resource, thereby distinguishing it the new representation of that resource, thereby distinguishing it
from representations that might only report about the action (e.g., from representations that might only report about the action (e.g.,
"It worked!"). This allows authoring applications to update their "It worked!"). This allows authoring applications to update their
local copies without the need for a subsequent GET request. local copies without the need for a subsequent GET request.
If Content-Location is included in a 2xx (Successful) response If Content-Location is included in a 2xx (Successful) response
message and its field-value refers to a URI that differs from the message and its field-value refers to a URI that differs from the
effective request URI, then the origin server claims that the URI is effective request URI, then the origin server claims that the URI is
an identifier for a different resource corresponding to the enclosed an identifier for a different resource corresponding to the enclosed
representation. Such a claim can only be trusted if both identifiers representation. Such a claim can only be trusted if both identifiers
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For example, if a client makes a PUT request on a negotiated resource For example, if a client makes a PUT request on a negotiated resource
and the origin server accepts that PUT (without redirection), then and the origin server accepts that PUT (without redirection), then
the new state of that resource is expected to be consistent with the the new state of that resource is expected to be consistent with the
one representation supplied in that PUT; the Content-Location cannot one representation supplied in that PUT; the Content-Location cannot
be used as a form of reverse content selection identifier to update be used as a form of reverse content selection identifier to update
only one of the negotiated representations. If the user agent had only one of the negotiated representations. If the user agent had
wanted the latter semantics, it would have applied the PUT directly wanted the latter semantics, it would have applied the PUT directly
to the Content-Location URI. to the Content-Location URI.
3.2. Representation Data 6.3. Payload
The representation data associated with an HTTP message is either
provided as the payload body of the message or referred to by the
message semantics and the effective request URI. The representation
data is in a format and encoding defined by the representation
metadata header fields.
The data type of the representation data is determined via the header
fields Content-Type and Content-Encoding. These define a two-layer,
ordered encoding model:
representation-data := Content-Encoding( Content-Type( bits ) )
3.3. Payload Semantics
Some HTTP messages transfer a complete or partial representation as Some HTTP messages transfer a complete or partial representation as
the message "payload". In some cases, a payload might contain only the message "payload". In some cases, a payload might contain only
the associated representation's header fields (e.g., responses to the associated representation's header fields (e.g., responses to
HEAD) or only some part(s) of the representation data (e.g., the 206 HEAD) or only some part(s) of the representation data (e.g., the 206
(Partial Content) status code). (Partial Content) status code).
Header fields that specifically describe the payload, rather than the
associated representation, are referred to as "payload header
fields". Payload header fields are defined in other parts of this
specification, due to their impact on message parsing.
+-------------------+------------------------------+
| Header Field Name | Defined in... |
+-------------------+------------------------------+
| Content-Range | Section 6.3.3 |
| Trailer | Section 4.4 |
| Transfer-Encoding | Section 2.4.1 of [Messaging] |
+-------------------+------------------------------+
6.3.1. Purpose
The purpose of a payload in a request is defined by the method The purpose of a payload in a request is defined by the method
semantics. For example, a representation in the payload of a PUT semantics. For example, a representation in the payload of a PUT
request (Section 4.3.4) represents the desired state of the target request (Section 7.3.4) represents the desired state of the target
resource if the request is successfully applied, whereas a resource if the request is successfully applied, whereas a
representation in the payload of a POST request (Section 4.3.3) representation in the payload of a POST request (Section 7.3.3)
represents information to be processed by the target resource. represents information to be processed by the target resource.
In a response, the payload's purpose is defined by both the request In a response, the payload's purpose is defined by both the request
method and the response status code. For example, the payload of a method and the response status code. For example, the payload of a
200 (OK) response to GET (Section 4.3.1) represents the current state 200 (OK) response to GET (Section 7.3.1) represents the current state
of the target resource, as observed at the time of the message of the target resource, as observed at the time of the message
origination date (Section 7.1.1.2), whereas the payload of the same origination date (Section 10.1.1.2), whereas the payload of the same
status code in a response to POST might represent either the status code in a response to POST might represent either the
processing result or the new state of the target resource after processing result or the new state of the target resource after
applying the processing. Response messages with an error status code applying the processing. Response messages with an error status code
usually contain a payload that represents the error condition, such usually contain a payload that represents the error condition, such
that it describes the error state and what next steps are suggested that it describes the error state and what next steps are suggested
for resolving it. for resolving it.
Header fields that specifically describe the payload, rather than the 6.3.2. Identification
associated representation, are referred to as "payload header
fields". Payload header fields are defined in other parts of this
specification, due to their impact on message parsing.
+-------------------+----------------------------+ When a complete or partial representation is transferred in a message
| Header Field Name | Defined in... | payload, it is often desirable for the sender to supply, or the
+-------------------+----------------------------+ recipient to determine, an identifier for a resource corresponding to
| Content-Length | Section 3.3.2 of [MESSGNG] | that representation.
| Content-Range | Section 4.2 of [RANGERQ] |
| Trailer | Section 4.4 of [MESSGNG] |
| Transfer-Encoding | Section 3.3.1 of [MESSGNG] |
+-------------------+----------------------------+
3.4. Content Negotiation For a request message:
o If the request has a Content-Location header field, then the
sender asserts that the payload is a representation of the
resource identified by the Content-Location field-value. However,
such an assertion cannot be trusted unless it can be verified by
other means (not defined by this specification). The information
might still be useful for revision history links.
o Otherwise, the payload is unidentified.
For a response message, the following rules are applied in order
until a match is found:
1. If the request method is GET or HEAD and the response status code
is 200 (OK), 204 (No Content), 206 (Partial Content), or 304 (Not
Modified), the payload is a representation of the resource
identified by the effective request URI (Section 5.3).
2. If the request method is GET or HEAD and the response status code
is 203 (Non-Authoritative Information), the payload is a
potentially modified or enhanced representation of the target
resource as provided by an intermediary.
3. If the response has a Content-Location header field and its
field-value is a reference to the same URI as the effective
request URI, the payload is a representation of the resource
identified by the effective request URI.
4. If the response has a Content-Location header field and its
field-value is a reference to a URI different from the effective
request URI, then the sender asserts that the payload is a
representation of the resource identified by the Content-Location
field-value. However, such an assertion cannot be trusted unless
it can be verified by other means (not defined by this
specification).
5. Otherwise, the payload is unidentified.
6.3.3. Content-Range
The "Content-Range" header field is sent in a single part 206
(Partial Content) response to indicate the partial range of the
selected representation enclosed as the message payload, sent in each
part of a multipart 206 response to indicate the range enclosed
within each body part, and sent in 416 (Range Not Satisfiable)
responses to provide information about the selected representation.
Content-Range = byte-content-range
/ other-content-range
byte-content-range = bytes-unit SP
( byte-range-resp / unsatisfied-range )
byte-range-resp = byte-range "/" ( complete-length / "*" )
byte-range = first-byte-pos "-" last-byte-pos
unsatisfied-range = "*/" complete-length
complete-length = 1*DIGIT
other-content-range = other-range-unit SP other-range-resp
other-range-resp = *CHAR
If a 206 (Partial Content) response contains a Content-Range header
field with a range unit (Section 6.1.4) that the recipient does not
understand, the recipient MUST NOT attempt to recombine it with a
stored representation. A proxy that receives such a message SHOULD
forward it downstream.
For byte ranges, a sender SHOULD indicate the complete length of the
representation from which the range has been extracted, unless the
complete length is unknown or difficult to determine. An asterisk
character ("*") in place of the complete-length indicates that the
representation length was unknown when the header field was
generated.
The following example illustrates when the complete length of the
selected representation is known by the sender to be 1234 bytes:
Content-Range: bytes 42-1233/1234
and this second example illustrates when the complete length is
unknown:
Content-Range: bytes 42-1233/*
A Content-Range field value is invalid if it contains a byte-range-
resp that has a last-byte-pos value less than its first-byte-pos
value, or a complete-length value less than or equal to its last-
byte-pos value. The recipient of an invalid Content-Range MUST NOT
attempt to recombine the received content with a stored
representation.
A server generating a 416 (Range Not Satisfiable) response to a byte-
range request SHOULD send a Content-Range header field with an
unsatisfied-range value, as in the following example:
Content-Range: bytes */1234
The complete-length in a 416 response indicates the current length of
the selected representation.
The Content-Range header field has no meaning for status codes that
do not explicitly describe its semantic. For this specification,
only the 206 (Partial Content) and 416 (Range Not Satisfiable) status
codes describe a meaning for Content-Range.
The following are examples of Content-Range values in which the
selected representation contains a total of 1234 bytes:
o The first 500 bytes:
Content-Range: bytes 0-499/1234
o The second 500 bytes:
Content-Range: bytes 500-999/1234
o All except for the first 500 bytes:
Content-Range: bytes 500-1233/1234
o The last 500 bytes:
Content-Range: bytes 734-1233/1234
6.3.4. Media Type multipart/byteranges
When a 206 (Partial Content) response message includes the content of
multiple ranges, they are transmitted as body parts in a multipart
message body ([RFC2046], Section 5.1) with the media type of
"multipart/byteranges".
The multipart/byteranges media type includes one or more body parts,
each with its own Content-Type and Content-Range fields. The
required boundary parameter specifies the boundary string used to
separate each body part.
Implementation Notes:
1. Additional CRLFs might precede the first boundary string in the
body.
2. Although [RFC2046] permits the boundary string to be quoted, some
existing implementations handle a quoted boundary string
incorrectly.
3. A number of clients and servers were coded to an early draft of
the byteranges specification that used a media type of multipart/
x-byteranges, which is almost (but not quite) compatible with
this type.
Despite the name, the "multipart/byteranges" media type is not
limited to byte ranges. The following example uses an "exampleunit"
range unit:
HTTP/1.1 206 Partial Content
Date: Tue, 14 Nov 1995 06:25:24 GMT
Last-Modified: Tue, 14 July 04:58:08 GMT
Content-Length: 2331785
Content-Type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
--THIS_STRING_SEPARATES
Content-Type: video/example
Content-Range: exampleunit 1.2-4.3/25
...the first range...
--THIS_STRING_SEPARATES
Content-Type: video/example
Content-Range: exampleunit 11.2-14.3/25
...the second range
--THIS_STRING_SEPARATES--
The following information serves as the registration form for the
multipart/byteranges media type.
Type name: multipart
Subtype name: byteranges
Required parameters: boundary
Optional parameters: N/A
Encoding considerations: only "7bit", "8bit", or "binary" are
permitted
Security considerations: see Section 12
Interoperability considerations: N/A
Published specification: This specification (see Section 6.3.4).
Applications that use this media type: HTTP components supporting
multiple ranges in a single request.
Fragment identifier considerations: N/A
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): N/A
Macintosh file type code(s): N/A
Person and email address to contact for further information: See Aut
hors' Addresses section.
Intended usage: COMMON
Restrictions on usage: N/A
Author: See Authors' Addresses section.
Change controller: IESG
6.4. Content Negotiation
When responses convey payload information, whether indicating a When responses convey payload information, whether indicating a
success or an error, the origin server often has different ways of success or an error, the origin server often has different ways of
representing that information; for example, in different formats, representing that information; for example, in different formats,
languages, or encodings. Likewise, different users or user agents languages, or encodings. Likewise, different users or user agents
might have differing capabilities, characteristics, or preferences might have differing capabilities, characteristics, or preferences
that could influence which representation, among those available, that could influence which representation, among those available,
would be best to deliver. For this reason, HTTP provides mechanisms would be best to deliver. For this reason, HTTP provides mechanisms
for content negotiation. for content negotiation.
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practicality. practicality.
Note that, in all cases, HTTP is not aware of the resource semantics. Note that, in all cases, HTTP is not aware of the resource semantics.
The consistency with which an origin server responds to requests, The consistency with which an origin server responds to requests,
over time and over the varying dimensions of content negotiation, and over time and over the varying dimensions of content negotiation, and
thus the "sameness" of a resource's observed representations over thus the "sameness" of a resource's observed representations over
time, is determined entirely by whatever entity or algorithm selects time, is determined entirely by whatever entity or algorithm selects
or generates those responses. HTTP pays no attention to the man or generates those responses. HTTP pays no attention to the man
behind the curtain. behind the curtain.
3.4.1. Proactive Negotiation 6.4.1. Proactive Negotiation
When content negotiation preferences are sent by the user agent in a When content negotiation preferences are sent by the user agent in a
request to encourage an algorithm located at the server to select the request to encourage an algorithm located at the server to select the
preferred representation, it is called proactive negotiation (a.k.a., preferred representation, it is called proactive negotiation (a.k.a.,
server-driven negotiation). Selection is based on the available server-driven negotiation). Selection is based on the available
representations for a response (the dimensions over which it might representations for a response (the dimensions over which it might
vary, such as language, content-coding, etc.) compared to various vary, such as language, content-coding, etc.) compared to various
information supplied in the request, including both the explicit information supplied in the request, including both the explicit
negotiation fields of Section 5.3 and implicit characteristics, such negotiation fields of Section 8.4 and implicit characteristics, such
as the client's network address or parts of the User-Agent field. as the client's network address or parts of the User-Agent field.
Proactive negotiation is advantageous when the algorithm for Proactive negotiation is advantageous when the algorithm for
selecting from among the available representations is difficult to selecting from among the available representations is difficult to
describe to a user agent, or when the server desires to send its describe to a user agent, or when the server desires to send its
"best guess" to the user agent along with the first response (hoping "best guess" to the user agent along with the first response (hoping
to avoid the round trip delay of a subsequent request if the "best to avoid the round trip delay of a subsequent request if the "best
guess" is good enough for the user). In order to improve the guess" is good enough for the user). In order to improve the
server's guess, a user agent MAY send request header fields that server's guess, a user agent MAY send request header fields that
describe its preferences. describe its preferences.
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algorithms for generating responses to a request; and, algorithms for generating responses to a request; and,
o It limits the reusability of responses for shared caching. o It limits the reusability of responses for shared caching.
A user agent cannot rely on proactive negotiation preferences being A user agent cannot rely on proactive negotiation preferences being
consistently honored, since the origin server might not implement consistently honored, since the origin server might not implement
proactive negotiation for the requested resource or might decide that proactive negotiation for the requested resource or might decide that
sending a response that doesn't conform to the user agent's sending a response that doesn't conform to the user agent's
preferences is better than sending a 406 (Not Acceptable) response. preferences is better than sending a 406 (Not Acceptable) response.
A Vary header field (Section 7.1.4) is often sent in a response A Vary header field (Section 10.1.4) is often sent in a response
subject to proactive negotiation to indicate what parts of the subject to proactive negotiation to indicate what parts of the
request information were used in the selection algorithm. request information were used in the selection algorithm.
3.4.2. Reactive Negotiation 6.4.2. Reactive Negotiation
With reactive negotiation (a.k.a., agent-driven negotiation), With reactive negotiation (a.k.a., agent-driven negotiation),
selection of the best response representation (regardless of the selection of the best response representation (regardless of the
status code) is performed by the user agent after receiving an status code) is performed by the user agent after receiving an
initial response from the origin server that contains a list of initial response from the origin server that contains a list of
resources for alternative representations. If the user agent is not resources for alternative representations. If the user agent is not
satisfied by the initial response representation, it can perform a satisfied by the initial response representation, it can perform a
GET request on one or more of the alternative resources, selected GET request on one or more of the alternative resources, selected
based on metadata included in the list, to obtain a different form of based on metadata included in the list, to obtain a different form of
representation for that response. Selection of alternatives might be representation for that response. Selection of alternatives might be
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caches are used to distribute server load and reduce network usage. caches are used to distribute server load and reduce network usage.
Reactive negotiation suffers from the disadvantages of transmitting a Reactive negotiation suffers from the disadvantages of transmitting a
list of alternatives to the user agent, which degrades user-perceived list of alternatives to the user agent, which degrades user-perceived
latency if transmitted in the header section, and needing a second latency if transmitted in the header section, and needing a second
request to obtain an alternate representation. Furthermore, this request to obtain an alternate representation. Furthermore, this
specification does not define a mechanism for supporting automatic specification does not define a mechanism for supporting automatic
selection, though it does not prevent such a mechanism from being selection, though it does not prevent such a mechanism from being
developed as an extension. developed as an extension.
4. Request Methods 7. Request Methods
4.1. Overview 7.1. Overview
The request method token is the primary source of request semantics; The request method token is the primary source of request semantics;
it indicates the purpose for which the client has made this request it indicates the purpose for which the client has made this request
and what is expected by the client as a successful result. and what is expected by the client as a successful result.
The request method's semantics might be further specialized by the The request method's semantics might be further specialized by the
semantics of some header fields when present in a request (Section 5) semantics of some header fields when present in a request (Section 8)
if those additional semantics do not conflict with the method. For if those additional semantics do not conflict with the method. For
example, a client can send conditional request header fields example, a client can send conditional request header fields
(Section 5.2) to make the requested action conditional on the current (Section 8.2) to make the requested action conditional on the current
state of the target resource ([CONDTNL]). state of the target resource.
method = token method = token
HTTP was originally designed to be usable as an interface to HTTP was originally designed to be usable as an interface to
distributed object systems. The request method was envisioned as distributed object systems. The request method was envisioned as
applying semantics to a target resource in much the same way as applying semantics to a target resource in much the same way as
invoking a defined method on an identified object would apply invoking a defined method on an identified object would apply
semantics. The method token is case-sensitive because it might be semantics. The method token is case-sensitive because it might be
used as a gateway to object-based systems with case-sensitive method used as a gateway to object-based systems with case-sensitive method
names. names.
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whether those semantics are implemented or allowed. whether those semantics are implemented or allowed.
This specification defines a number of standardized methods that are This specification defines a number of standardized methods that are
commonly used in HTTP, as outlined by the following table. By commonly used in HTTP, as outlined by the following table. By
convention, standardized methods are defined in all-uppercase US- convention, standardized methods are defined in all-uppercase US-
ASCII letters. ASCII letters.
+---------+-------------------------------------------------+-------+ +---------+-------------------------------------------------+-------+
| Method | Description | Sec. | | Method | Description | Sec. |
+---------+-------------------------------------------------+-------+ +---------+-------------------------------------------------+-------+
| GET | Transfer a current representation of the target | 4.3.1 | | GET | Transfer a current representation of the target | 7.3.1 |
| | resource. | | | | resource. | |
| HEAD | Same as GET, but only transfer the status line | 4.3.2 | | HEAD | Same as GET, but only transfer the status line | 7.3.2 |
| | and header section. | | | | and header section. | |
| POST | Perform resource-specific processing on the | 4.3.3 | | POST | Perform resource-specific processing on the | 7.3.3 |
| | request payload. | | | | request payload. | |
| PUT | Replace all current representations of the | 4.3.4 | | PUT | Replace all current representations of the | 7.3.4 |
| | target resource with the request payload. | | | | target resource with the request payload. | |
| DELETE | Remove all current representations of the | 4.3.5 | | DELETE | Remove all current representations of the | 7.3.5 |
| | target resource. | | | | target resource. | |
| CONNECT | Establish a tunnel to the server identified by | 4.3.6 | | CONNECT | Establish a tunnel to the server identified by | 7.3.6 |
| | the target resource. | | | | the target resource. | |
| OPTIONS | Describe the communication options for the | 4.3.7 | | OPTIONS | Describe the communication options for the | 7.3.7 |
| | target resource. | | | | target resource. | |
| TRACE | Perform a message loop-back test along the path | 4.3.8 | | TRACE | Perform a message loop-back test along the path | 7.3.8 |
| | to the target resource. | | | | to the target resource. | |
+---------+-------------------------------------------------+-------+ +---------+-------------------------------------------------+-------+
All general-purpose servers MUST support the methods GET and HEAD. All general-purpose servers MUST support the methods GET and HEAD.
All other methods are OPTIONAL. All other methods are OPTIONAL.
Additional methods, outside the scope of this specification, have
been standardized for use in HTTP. All such methods ought to be
registered within the "Hypertext Transfer Protocol (HTTP) Method
Registry" maintained by IANA, as defined in Section 8.1.
The set of methods allowed by a target resource can be listed in an The set of methods allowed by a target resource can be listed in an
Allow header field (Section 7.4.1). However, the set of allowed Allow header field (Section 10.4.2). However, the set of allowed
methods can change dynamically. When a request method is received methods can change dynamically. When a request method is received
that is unrecognized or not implemented by an origin server, the that is unrecognized or not implemented by an origin server, the
origin server SHOULD respond with the 501 (Not Implemented) status origin server SHOULD respond with the 501 (Not Implemented) status
code. When a request method is received that is known by an origin code. When a request method is received that is known by an origin
server but not allowed for the target resource, the origin server server but not allowed for the target resource, the origin server
SHOULD respond with the 405 (Method Not Allowed) status code. SHOULD respond with the 405 (Method Not Allowed) status code.
4.2. Common Method Properties 7.2. Common Method Properties
4.2.1. Safe Methods +---------+------+------------+----------------+
| Method | Safe | Idempotent | Reference |
+---------+------+------------+----------------+
| CONNECT | no | no | Section 7.3.6 |
| DELETE | no | yes | Section 7.3.5 |
| GET | yes | yes | Section 7.3.1 |
| HEAD | yes | yes | Section 7.3.2 |
| OPTIONS | yes | yes | Section 7.3.7 |
| POST | no | no | Section 7.3.3 |
| PUT | no | yes | Section 7.3.4 |
| TRACE | yes | yes | Section 7.3.8 |
+---------+------+------------+----------------+
7.2.1. Safe Methods
Request methods are considered "safe" if their defined semantics are Request methods are considered "safe" if their defined semantics are
essentially read-only; i.e., the client does not request, and does essentially read-only; i.e., the client does not request, and does
not expect, any state change on the origin server as a result of not expect, any state change on the origin server as a result of
applying a safe method to a target resource. Likewise, reasonable applying a safe method to a target resource. Likewise, reasonable
use of a safe method is not expected to cause any harm, loss of use of a safe method is not expected to cause any harm, loss of
property, or unusual burden on the origin server. property, or unusual burden on the origin server.
This definition of safe methods does not prevent an implementation This definition of safe methods does not prevent an implementation
from including behavior that is potentially harmful, that is not from including behavior that is potentially harmful, that is not
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consistent with the request method semantics. For example, it is consistent with the request method semantics. For example, it is
common for Web-based content editing software to use actions within common for Web-based content editing software to use actions within
query parameters, such as "page?do=delete". If the purpose of such a query parameters, such as "page?do=delete". If the purpose of such a
resource is to perform an unsafe action, then the resource owner MUST resource is to perform an unsafe action, then the resource owner MUST
disable or disallow that action when it is accessed using a safe disable or disallow that action when it is accessed using a safe
request method. Failure to do so will result in unfortunate side request method. Failure to do so will result in unfortunate side
effects when automated processes perform a GET on every URI reference effects when automated processes perform a GET on every URI reference
for the sake of link maintenance, pre-fetching, building a search for the sake of link maintenance, pre-fetching, building a search
index, etc. index, etc.
4.2.2. Idempotent Methods 7.2.2. Idempotent Methods
A request method is considered "idempotent" if the intended effect on A request method is considered "idempotent" if the intended effect on
the server of multiple identical requests with that method is the the server of multiple identical requests with that method is the
same as the effect for a single such request. Of the request methods same as the effect for a single such request. Of the request methods
defined by this specification, PUT, DELETE, and safe request methods defined by this specification, PUT, DELETE, and safe request methods
are idempotent. are idempotent.
Like the definition of safe, the idempotent property only applies to Like the definition of safe, the idempotent property only applies to
what has been requested by the user; a server is free to log each what has been requested by the user; a server is free to log each
request separately, retain a revision control history, or implement request separately, retain a revision control history, or implement
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Idempotent methods are distinguished because the request can be Idempotent methods are distinguished because the request can be
repeated automatically if a communication failure occurs before the repeated automatically if a communication failure occurs before the
client is able to read the server's response. For example, if a client is able to read the server's response. For example, if a
client sends a PUT request and the underlying connection is closed client sends a PUT request and the underlying connection is closed
before any response is received, then the client can establish a new before any response is received, then the client can establish a new
connection and retry the idempotent request. It knows that repeating connection and retry the idempotent request. It knows that repeating
the request will have the same intended effect, even if the original the request will have the same intended effect, even if the original
request succeeded, though the response might differ. request succeeded, though the response might differ.
4.2.3. Cacheable Methods 7.2.3. Cacheable Methods
Request methods can be defined as "cacheable" to indicate that Request methods can be defined as "cacheable" to indicate that
responses to them are allowed to be stored for future reuse; for responses to them are allowed to be stored for future reuse; for
specific requirements see [CACHING]. In general, safe methods that specific requirements see [Caching]. In general, safe methods that
do not depend on a current or authoritative response are defined as do not depend on a current or authoritative response are defined as
cacheable; this specification defines GET, HEAD, and POST as cacheable; this specification defines GET, HEAD, and POST as
cacheable, although the overwhelming majority of cache cacheable, although the overwhelming majority of cache
implementations only support GET and HEAD. implementations only support GET and HEAD.
4.3. Method Definitions 7.3. Method Definitions
4.3.1. GET 7.3.1. GET
The GET method requests transfer of a current selected representation The GET method requests transfer of a current selected representation
for the target resource. GET is the primary mechanism of information for the target resource. GET is the primary mechanism of information
retrieval and the focus of almost all performance optimizations. retrieval and the focus of almost all performance optimizations.
Hence, when people speak of retrieving some identifiable information Hence, when people speak of retrieving some identifiable information
via HTTP, they are generally referring to making a GET request. via HTTP, they are generally referring to making a GET request.
It is tempting to think of resource identifiers as remote file system It is tempting to think of resource identifiers as remote file system
pathnames and of representations as being a copy of the contents of pathnames and of representations as being a copy of the contents of
such files. In fact, that is how many resources are implemented (see such files. In fact, that is how many resources are implemented (see
Section 9.1 for related security considerations). However, there are Section 12.3 for related security considerations). However, there
no such limitations in practice. The HTTP interface for a resource are no such limitations in practice. The HTTP interface for a
is just as likely to be implemented as a tree of content objects, a resource is just as likely to be implemented as a tree of content
programmatic view on various database records, or a gateway to other objects, a programmatic view on various database records, or a
information systems. Even when the URI mapping mechanism is tied to gateway to other information systems. Even when the URI mapping
a file system, an origin server might be configured to execute the mechanism is tied to a file system, an origin server might be
files with the request as input and send the output as the configured to execute the files with the request as input and send
representation rather than transfer the files directly. Regardless, the output as the representation rather than transfer the files
only the origin server needs to know how each of its resource directly. Regardless, only the origin server needs to know how each
identifiers corresponds to an implementation and how each of its resource identifiers corresponds to an implementation and how
implementation manages to select and send a current representation of each implementation manages to select and send a current
the target resource in a response to GET. representation of the target resource in a response to GET.
A client can alter the semantics of GET to be a "range request", A client can alter the semantics of GET to be a "range request",
requesting transfer of only some part(s) of the selected requesting transfer of only some part(s) of the selected
representation, by sending a Range header field in the request representation, by sending a Range header field in the request
([RANGERQ]). (Section 8.3).
A payload within a GET request message has no defined semantics; A payload within a GET request message has no defined semantics;
sending a payload body on a GET request might cause some existing sending a payload body on a GET request might cause some existing
implementations to reject the request. implementations to reject the request.
The response to a GET request is cacheable; a cache MAY use it to The response to a GET request is cacheable; a cache MAY use it to
satisfy subsequent GET and HEAD requests unless otherwise indicated satisfy subsequent GET and HEAD requests unless otherwise indicated
by the Cache-Control header field (Section 5.2 of [CACHING]). by the Cache-Control header field (Section 5.2 of [Caching]).
4.3.2. HEAD 7.3.2. HEAD
The HEAD method is identical to GET except that the server MUST NOT The HEAD method is identical to GET except that the server MUST NOT
send a message body in the response (i.e., the response terminates at send a message body in the response (i.e., the response terminates at
the end of the header section). The server SHOULD send the same the end of the header section). The server SHOULD send the same
header fields in response to a HEAD request as it would have sent if header fields in response to a HEAD request as it would have sent if
the request had been a GET, except that the payload header fields the request had been a GET, except that the payload header fields
(Section 3.3) MAY be omitted. This method can be used for obtaining (Section 6.3) MAY be omitted. This method can be used for obtaining
metadata about the selected representation without transferring the metadata about the selected representation without transferring the
representation data and is often used for testing hypertext links for representation data and is often used for testing hypertext links for
validity, accessibility, and recent modification. validity, accessibility, and recent modification.
A payload within a HEAD request message has no defined semantics; A payload within a HEAD request message has no defined semantics;
sending a payload body on a HEAD request might cause some existing sending a payload body on a HEAD request might cause some existing
implementations to reject the request. implementations to reject the request.
The response to a HEAD request is cacheable; a cache MAY use it to The response to a HEAD request is cacheable; a cache MAY use it to
satisfy subsequent HEAD requests unless otherwise indicated by the satisfy subsequent HEAD requests unless otherwise indicated by the
Cache-Control header field (Section 5.2 of [CACHING]). A HEAD Cache-Control header field (Section 5.2 of [Caching]). A HEAD
response might also have an effect on previously cached responses to response might also have an effect on previously cached responses to
GET; see Section 4.3.5 of [CACHING]. GET; see Section 4.3.5 of [Caching].
4.3.3. POST 7.3.3. POST
The POST method requests that the target resource process the The POST method requests that the target resource process the
representation enclosed in the request according to the resource's representation enclosed in the request according to the resource's
own specific semantics. For example, POST is used for the following own specific semantics. For example, POST is used for the following
functions (among others): functions (among others):
o Providing a block of data, such as the fields entered into an HTML o Providing a block of data, such as the fields entered into an HTML
form, to a data-handling process; form, to a data-handling process;
o Posting a message to a bulletin board, newsgroup, mailing list, o Posting a message to a bulletin board, newsgroup, mailing list,
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appropriate status code depending on the result of processing the appropriate status code depending on the result of processing the
POST request; almost all of the status codes defined by this POST request; almost all of the status codes defined by this
specification might be received in a response to POST (the exceptions specification might be received in a response to POST (the exceptions
being 206 (Partial Content), 304 (Not Modified), and 416 (Range Not being 206 (Partial Content), 304 (Not Modified), and 416 (Range Not
Satisfiable)). Satisfiable)).
If one or more resources has been created on the origin server as a If one or more resources has been created on the origin server as a
result of successfully processing a POST request, the origin server result of successfully processing a POST request, the origin server
SHOULD send a 201 (Created) response containing a Location header SHOULD send a 201 (Created) response containing a Location header
field that provides an identifier for the primary resource created field that provides an identifier for the primary resource created
(Section 7.1.2) and a representation that describes the status of the (Section 10.1.2) and a representation that describes the status of
request while referring to the new resource(s). the request while referring to the new resource(s).
Responses to POST requests are only cacheable when they include Responses to POST requests are only cacheable when they include
explicit freshness information (see Section 4.2.1 of [CACHING]). explicit freshness information (see Section 4.2.1 of [Caching]).
However, POST caching is not widely implemented. For cases where an However, POST caching is not widely implemented. For cases where an
origin server wishes the client to be able to cache the result of a origin server wishes the client to be able to cache the result of a
POST in a way that can be reused by a later GET, the origin server POST in a way that can be reused by a later GET, the origin server
MAY send a 200 (OK) response containing the result and a Content- MAY send a 200 (OK) response containing the result and a Content-
Location header field that has the same value as the POST's effective Location header field that has the same value as the POST's effective
request URI (Section 3.1.4.2). request URI (Section 6.2.5).
If the result of processing a POST would be equivalent to a If the result of processing a POST would be equivalent to a
representation of an existing resource, an origin server MAY redirect representation of an existing resource, an origin server MAY redirect
the user agent to that resource by sending a 303 (See Other) response the user agent to that resource by sending a 303 (See Other) response
with the existing resource's identifier in the Location field. This with the existing resource's identifier in the Location field. This
has the benefits of providing the user agent a resource identifier has the benefits of providing the user agent a resource identifier
and transferring the representation via a method more amenable to and transferring the representation via a method more amenable to
shared caching, though at the cost of an extra request if the user shared caching, though at the cost of an extra request if the user
agent does not already have the representation cached. agent does not already have the representation cached.
4.3.4. PUT 7.3.4. PUT
The PUT method requests that the state of the target resource be The PUT method requests that the state of the target resource be
created or replaced with the state defined by the representation created or replaced with the state defined by the representation
enclosed in the request message payload. A successful PUT of a given enclosed in the request message payload. A successful PUT of a given
representation would suggest that a subsequent GET on that same representation would suggest that a subsequent GET on that same
target resource will result in an equivalent representation being target resource will result in an equivalent representation being
sent in a 200 (OK) response. However, there is no guarantee that sent in a 200 (OK) response. However, there is no guarantee that
such a state change will be observable, since the target resource such a state change will be observable, since the target resource
might be acted upon by other user agents in parallel, or might be might be acted upon by other user agents in parallel, or might be
subject to dynamic processing by the origin server, before any subject to dynamic processing by the origin server, before any
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agent request and the semantics of the origin server response. It agent request and the semantics of the origin server response. It
does not define what a resource might be, in any sense of that word, does not define what a resource might be, in any sense of that word,
beyond the interface provided via HTTP. It does not define how beyond the interface provided via HTTP. It does not define how
resource state is "stored", nor how such storage might change as a resource state is "stored", nor how such storage might change as a
result of a change in resource state, nor how the origin server result of a change in resource state, nor how the origin server
translates resource state into representations. Generally speaking, translates resource state into representations. Generally speaking,
all implementation details behind the resource interface are all implementation details behind the resource interface are
intentionally hidden by the server. intentionally hidden by the server.
An origin server MUST NOT send a validator header field An origin server MUST NOT send a validator header field
(Section 7.2), such as an ETag or Last-Modified field, in a (Section 10.2), such as an ETag or Last-Modified field, in a
successful response to PUT unless the request's representation data successful response to PUT unless the request's representation data
was saved without any transformation applied to the body (i.e., the was saved without any transformation applied to the body (i.e., the
resource's new representation data is identical to the representation resource's new representation data is identical to the representation
data received in the PUT request) and the validator field value data received in the PUT request) and the validator field value
reflects the new representation. This requirement allows a user reflects the new representation. This requirement allows a user
agent to know when the representation body it has in memory remains agent to know when the representation body it has in memory remains
current as a result of the PUT, thus not in need of being retrieved current as a result of the PUT, thus not in need of being retrieved
again from the origin server, and that the new validator(s) received again from the origin server, and that the new validator(s) received
in the response can be used for future conditional requests in order in the response can be used for future conditional requests in order
to prevent accidental overwrites (Section 5.2). to prevent accidental overwrites (Section 8.2).
The fundamental difference between the POST and PUT methods is The fundamental difference between the POST and PUT methods is
highlighted by the different intent for the enclosed representation. highlighted by the different intent for the enclosed representation.
The target resource in a POST request is intended to handle the The target resource in a POST request is intended to handle the
enclosed representation according to the resource's own semantics, enclosed representation according to the resource's own semantics,
whereas the enclosed representation in a PUT request is defined as whereas the enclosed representation in a PUT request is defined as
replacing the state of the target resource. Hence, the intent of PUT replacing the state of the target resource. Hence, the intent of PUT
is idempotent and visible to intermediaries, even though the exact is idempotent and visible to intermediaries, even though the exact
effect is only known by the origin server. effect is only known by the origin server.
Proper interpretation of a PUT request presumes that the user agent Proper interpretation of a PUT request presumes that the user agent
knows which target resource is desired. A service that selects a knows which target resource is desired. A service that selects a
proper URI on behalf of the client, after receiving a state-changing proper URI on behalf of the client, after receiving a state-changing
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identifying "the current version" (a resource) that is separate from identifying "the current version" (a resource) that is separate from
the URIs identifying each particular version (different resources the URIs identifying each particular version (different resources
that at one point shared the same state as the current version that at one point shared the same state as the current version
resource). A successful PUT request on "the current version" URI resource). A successful PUT request on "the current version" URI
might therefore create a new version resource in addition to changing might therefore create a new version resource in addition to changing
the state of the target resource, and might also cause links to be the state of the target resource, and might also cause links to be
added between the related resources. added between the related resources.
An origin server that allows PUT on a given target resource MUST send An origin server that allows PUT on a given target resource MUST send
a 400 (Bad Request) response to a PUT request that contains a a 400 (Bad Request) response to a PUT request that contains a
Content-Range header field (Section 4.2 of [RANGERQ]), since the Content-Range header field (Section 6.3.3), since the payload is
payload is likely to be partial content that has been mistakenly PUT likely to be partial content that has been mistakenly PUT as a full
as a full representation. Partial content updates are possible by representation. Partial content updates are possible by targeting a
targeting a separately identified resource with state that overlaps a separately identified resource with state that overlaps a portion of
portion of the larger resource, or by using a different method that the larger resource, or by using a different method that has been
has been specifically defined for partial updates (for example, the specifically defined for partial updates (for example, the PATCH
PATCH method defined in [RFC5789]). method defined in [RFC5789]).
Responses to the PUT method are not cacheable. If a successful PUT Responses to the PUT method are not cacheable. If a successful PUT
request passes through a cache that has one or more stored responses request passes through a cache that has one or more stored responses
for the effective request URI, those stored responses will be for the effective request URI, those stored responses will be
invalidated (see Section 4.4 of [CACHING]). invalidated (see Section 4.4 of [Caching]).
4.3.5. DELETE 7.3.5. DELETE
The DELETE method requests that the origin server remove the The DELETE method requests that the origin server remove the
association between the target resource and its current association between the target resource and its current
functionality. In effect, this method is similar to the rm command functionality. In effect, this method is similar to the rm command
in UNIX: it expresses a deletion operation on the URI mapping of the in UNIX: it expresses a deletion operation on the URI mapping of the
origin server rather than an expectation that the previously origin server rather than an expectation that the previously
associated information be deleted. associated information be deleted.
If the target resource has one or more current representations, they If the target resource has one or more current representations, they
might or might not be destroyed by the origin server, and the might or might not be destroyed by the origin server, and the
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or a 200 (OK) status code if the action has been enacted and the or a 200 (OK) status code if the action has been enacted and the
response message includes a representation describing the status. response message includes a representation describing the status.
A payload within a DELETE request message has no defined semantics; A payload within a DELETE request message has no defined semantics;
sending a payload body on a DELETE request might cause some existing sending a payload body on a DELETE request might cause some existing
implementations to reject the request. implementations to reject the request.
Responses to the DELETE method are not cacheable. If a DELETE Responses to the DELETE method are not cacheable. If a DELETE
request passes through a cache that has one or more stored responses request passes through a cache that has one or more stored responses
for the effective request URI, those stored responses will be for the effective request URI, those stored responses will be
invalidated (see Section 4.4 of [CACHING]). invalidated (see Section 4.4 of [Caching]).
4.3.6. CONNECT 7.3.6. CONNECT
The CONNECT method requests that the recipient establish a tunnel to The CONNECT method requests that the recipient establish a tunnel to
the destination origin server identified by the request-target and, the destination origin server identified by the request-target and,
if successful, thereafter restrict its behavior to blind forwarding if successful, thereafter restrict its behavior to blind forwarding
of packets, in both directions, until the tunnel is closed. Tunnels of packets, in both directions, until the tunnel is closed. Tunnels
are commonly used to create an end-to-end virtual connection, through are commonly used to create an end-to-end virtual connection, through
one or more proxies, which can then be secured using TLS (Transport one or more proxies, which can then be secured using TLS (Transport
Layer Security, [RFC5246]). Layer Security, [RFC5246]).
CONNECT is intended only for use in requests to a proxy. An origin CONNECT is intended only for use in requests to a proxy. An origin
server that receives a CONNECT request for itself MAY respond with a server that receives a CONNECT request for itself MAY respond with a
2xx (Successful) status code to indicate that a connection is 2xx (Successful) status code to indicate that a connection is
established. However, most origin servers do not implement CONNECT. established. However, most origin servers do not implement CONNECT.
A client sending a CONNECT request MUST send the authority form of A client sending a CONNECT request MUST send the authority form of
request-target (Section 5.3 of [MESSGNG]); i.e., the request-target request-target (Section 4 of [Messaging]); i.e., the request-target
consists of only the host name and port number of the tunnel consists of only the host name and port number of the tunnel
destination, separated by a colon. For example, destination, separated by a colon. For example,
CONNECT server.example.com:80 HTTP/1.1 CONNECT server.example.com:80 HTTP/1.1
Host: server.example.com:80 Host: server.example.com:80
The recipient proxy can establish a tunnel either by directly The recipient proxy can establish a tunnel either by directly
connecting to the request-target or, if configured to use another connecting to the request-target or, if configured to use another
proxy, by forwarding the CONNECT request to the next inbound proxy. proxy, by forwarding the CONNECT request to the next inbound proxy.
Any 2xx (Successful) response indicates that the sender (and all Any 2xx (Successful) response indicates that the sender (and all
inbound proxies) will switch to tunnel mode immediately after the inbound proxies) will switch to tunnel mode immediately after the
blank line that concludes the successful response's header section; blank line that concludes the successful response's header section;
data received after that blank line is from the server identified by data received after that blank line is from the server identified by
the request-target. Any response other than a successful response the request-target. Any response other than a successful response
indicates that the tunnel has not yet been formed and that the indicates that the tunnel has not yet been formed and that the
connection remains governed by HTTP. connection remains governed by HTTP.
A tunnel is closed when a tunnel intermediary detects that either A tunnel is closed when a tunnel intermediary detects that either
side has closed its connection: the intermediary MUST attempt to send side has closed its connection: the intermediary MUST attempt to send
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fields in a 2xx (Successful) response to CONNECT. A client MUST fields in a 2xx (Successful) response to CONNECT. A client MUST
ignore any Content-Length or Transfer-Encoding header fields received ignore any Content-Length or Transfer-Encoding header fields received
in a successful response to CONNECT. in a successful response to CONNECT.
A payload within a CONNECT request message has no defined semantics; A payload within a CONNECT request message has no defined semantics;
sending a payload body on a CONNECT request might cause some existing sending a payload body on a CONNECT request might cause some existing
implementations to reject the request. implementations to reject the request.
Responses to the CONNECT method are not cacheable. Responses to the CONNECT method are not cacheable.
4.3.7. OPTIONS 7.3.7. OPTIONS
The OPTIONS method requests information about the communication The OPTIONS method requests information about the communication
options available for the target resource, at either the origin options available for the target resource, at either the origin
server or an intervening intermediary. This method allows a client server or an intervening intermediary. This method allows a client
to determine the options and/or requirements associated with a to determine the options and/or requirements associated with a
resource, or the capabilities of a server, without implying a resource, or the capabilities of a server, without implying a
resource action. resource action.
An OPTIONS request with an asterisk ("*") as the request-target An OPTIONS request with an asterisk ("*") as the request-target
(Section 5.3 of [MESSGNG]) applies to the server in general rather (Section 4 of [Messaging]) applies to the server in general rather
than to a specific resource. Since a server's communication options than to a specific resource. Since a server's communication options
typically depend on the resource, the "*" request is only useful as a typically depend on the resource, the "*" request is only useful as a
"ping" or "no-op" type of method; it does nothing beyond allowing the "ping" or "no-op" type of method; it does nothing beyond allowing the
client to test the capabilities of the server. For example, this can client to test the capabilities of the server. For example, this can
be used to test a proxy for HTTP/1.1 conformance (or lack thereof). be used to test a proxy for HTTP/1.1 conformance (or lack thereof).
If the request-target is not an asterisk, the OPTIONS request applies If the request-target is not an asterisk, the OPTIONS request applies
to the options that are available when communicating with the target to the options that are available when communicating with the target
resource. resource.
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including potential extensions not defined by this specification. including potential extensions not defined by this specification.
The response payload, if any, might also describe the communication The response payload, if any, might also describe the communication
options in a machine or human-readable representation. A standard options in a machine or human-readable representation. A standard
format for such a representation is not defined by this format for such a representation is not defined by this
specification, but might be defined by future extensions to HTTP. A specification, but might be defined by future extensions to HTTP. A
server MUST generate a Content-Length field with a value of "0" if no server MUST generate a Content-Length field with a value of "0" if no
payload body is to be sent in the response. payload body is to be sent in the response.
A client MAY send a Max-Forwards header field in an OPTIONS request A client MAY send a Max-Forwards header field in an OPTIONS request
to target a specific recipient in the request chain (see to target a specific recipient in the request chain (see
Section 5.1.2). A proxy MUST NOT generate a Max-Forwards header Section 8.1.2). A proxy MUST NOT generate a Max-Forwards header
field while forwarding a request unless that request was received field while forwarding a request unless that request was received
with a Max-Forwards field. with a Max-Forwards field.
A client that generates an OPTIONS request containing a payload body A client that generates an OPTIONS request containing a payload body
MUST send a valid Content-Type header field describing the MUST send a valid Content-Type header field describing the
representation media type. Although this specification does not representation media type. Although this specification does not
define any use for such a payload, future extensions to HTTP might define any use for such a payload, future extensions to HTTP might
use the OPTIONS body to make more detailed queries about the target use the OPTIONS body to make more detailed queries about the target
resource. resource.
Responses to the OPTIONS method are not cacheable. Responses to the OPTIONS method are not cacheable.
4.3.8. TRACE 7.3.8. TRACE
The TRACE method requests a remote, application-level loop-back of The TRACE method requests a remote, application-level loop-back of
the request message. The final recipient of the request SHOULD the request message. The final recipient of the request SHOULD
reflect the message received, excluding some fields described below, reflect the message received, excluding some fields described below,
back to the client as the message body of a 200 (OK) response with a back to the client as the message body of a 200 (OK) response with a
Content-Type of "message/http" (Section 8.3.1 of [MESSGNG]). The Content-Type of "message/http" (Section 7.1 of [Messaging]). The
final recipient is either the origin server or the first server to final recipient is either the origin server or the first server to
receive a Max-Forwards value of zero (0) in the request receive a Max-Forwards value of zero (0) in the request
(Section 5.1.2). (Section 8.1.2).
A client MUST NOT generate header fields in a TRACE request A client MUST NOT generate header fields in a TRACE request
containing sensitive data that might be disclosed by the response. containing sensitive data that might be disclosed by the response.
For example, it would be foolish for a user agent to send stored user For example, it would be foolish for a user agent to send stored user
credentials [AUTHFRM] or cookies [RFC6265] in a TRACE request. The credentials Section 8.5 or cookies [RFC6265] in a TRACE request. The
final recipient of the request SHOULD exclude any request header final recipient of the request SHOULD exclude any request header
fields that are likely to contain sensitive data when that recipient fields that are likely to contain sensitive data when that recipient
generates the response body. generates the response body.
TRACE allows the client to see what is being received at the other TRACE allows the client to see what is being received at the other
end of the request chain and use that data for testing or diagnostic end of the request chain and use that data for testing or diagnostic
information. The value of the Via header field (Section 5.7.1 of information. The value of the Via header field (Section 5.6.1) is of
[MESSGNG]) is of particular interest, since it acts as a trace of the particular interest, since it acts as a trace of the request chain.
request chain. Use of the Max-Forwards header field allows the Use of the Max-Forwards header field allows the client to limit the
client to limit the length of the request chain, which is useful for length of the request chain, which is useful for testing a chain of
testing a chain of proxies forwarding messages in an infinite loop. proxies forwarding messages in an infinite loop.
A client MUST NOT send a message body in a TRACE request. A client MUST NOT send a message body in a TRACE request.
Responses to the TRACE method are not cacheable. Responses to the TRACE method are not cacheable.
5. Request Header Fields 7.4. Method Extensibility
Additional methods, outside the scope of this specification, have
been specified for use in HTTP. All such methods ought to be
registered within the "Hypertext Transfer Protocol (HTTP) Method
Registry".
7.4.1. Method Registry
The "Hypertext Transfer Protocol (HTTP) Method Registry", maintained
by IANA at <https://www.iana.org/assignments/http-methods>, registers
method names.
HTTP method registrations MUST include the following fields:
o Method Name (see Section 7)
o Safe ("yes" or "no", see Section 7.2.1)
o Idempotent ("yes" or "no", see Section 7.2.2)
o Pointer to specification text
Values to be added to this namespace require IETF Review (see
[RFC5226], Section 4.1).
7.4.2. Considerations for New Methods
Standardized methods are generic; that is, they are potentially
applicable to any resource, not just one particular media type, kind
of resource, or application. As such, it is preferred that new
methods be registered in a document that isn't specific to a single
application or data format, since orthogonal technologies deserve
orthogonal specification.
Since message parsing (Section 2.4 of [Messaging]) needs to be
independent of method semantics (aside from responses to HEAD),
definitions of new methods cannot change the parsing algorithm or
prohibit the presence of a message body on either the request or the
response message. Definitions of new methods can specify that only a
zero-length message body is allowed by requiring a Content-Length
header field with a value of "0".
A new method definition needs to indicate whether it is safe
(Section 7.2.1), idempotent (Section 7.2.2), cacheable
(Section 7.2.3), what semantics are to be associated with the payload
body if any is present in the request and what refinements the method
makes to header field or status code semantics. If the new method is
cacheable, its definition ought to describe how, and under what
conditions, a cache can store a response and use it to satisfy a
subsequent request. The new method ought to describe whether it can
be made conditional (Section 8.2) and, if so, how a server responds
when the condition is false. Likewise, if the new method might have
some use for partial response semantics (Section 8.3), it ought to
document this, too.
Note: Avoid defining a method name that starts with "M-", since
that prefix might be misinterpreted as having the semantics
assigned to it by [RFC2774].
8. Request Header Fields
A client sends request header fields to provide more information A client sends request header fields to provide more information
about the request context, make the request conditional based on the about the request context, make the request conditional based on the
target resource state, suggest preferred formats for the response, target resource state, suggest preferred formats for the response,
supply authentication credentials, or modify the expected request supply authentication credentials, or modify the expected request
processing. These fields act as request modifiers, similar to the processing. These fields act as request modifiers, similar to the
parameters on a programming language method invocation. parameters on a programming language method invocation.
5.1. Controls 8.1. Controls
Controls are request header fields that direct specific handling of Controls are request header fields that direct specific handling of
the request. the request.
+-------------------+--------------------------+ +-------------------+----------------------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+--------------------------+ +-------------------+----------------------------+
| Cache-Control | Section 5.2 of [CACHING] | | Cache-Control | Section 5.2 of [Caching] |
| Expect | Section 5.1.1 | | Expect | Section 8.1.1 |
| Host | Section 5.4 of [MESSGNG] | | Host | Section 5.4 |
| Max-Forwards | Section 5.1.2 | | Max-Forwards | Section 8.1.2 |
| Pragma | Section 5.4 of [CACHING] | | Pragma | Section 5.4 of [Caching] |
| Range | Section 3.1 of [RANGERQ] | | TE | Section 3.4 of [Messaging] |
| TE | Section 4.3 of [MESSGNG] | +-------------------+----------------------------+
+-------------------+--------------------------+
5.1.1. Expect 8.1.1. Expect
The "Expect" header field in a request indicates a certain set of The "Expect" header field in a request indicates a certain set of
behaviors (expectations) that need to be supported by the server in behaviors (expectations) that need to be supported by the server in
order to properly handle this request. The only such expectation order to properly handle this request. The only such expectation
defined by this specification is 100-continue. defined by this specification is 100-continue.
Expect = "100-continue" Expect = "100-continue"
The Expect field-value is case-insensitive. The Expect field-value is case-insensitive.
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corresponding request, or if the framing indicates that there is corresponding request, or if the framing indicates that there is
no message body. no message body.
o A server that sends a 100 (Continue) response MUST ultimately send o A server that sends a 100 (Continue) response MUST ultimately send
a final status code, once the message body is received and a final status code, once the message body is received and
processed, unless the connection is closed prematurely. processed, unless the connection is closed prematurely.
o A server that responds with a final status code before reading the o A server that responds with a final status code before reading the
entire message body SHOULD indicate in that response whether it entire message body SHOULD indicate in that response whether it
intends to close the connection or continue reading and discarding intends to close the connection or continue reading and discarding
the request message (see Section 6.6 of [MESSGNG]). the request message (see Section 6.6 of [Messaging]).
An origin server MUST, upon receiving an HTTP/1.1 (or later) request- An origin server MUST, upon receiving an HTTP/1.1 (or later) request-
line and a complete header section that contains a 100-continue line and a complete header section that contains a 100-continue
expectation and indicates a request message body will follow, either expectation and indicates a request message body will follow, either
send an immediate response with a final status code, if that status send an immediate response with a final status code, if that status
can be determined by examining just the request-line and header can be determined by examining just the request-line and header
fields, or send an immediate 100 (Continue) response to encourage the fields, or send an immediate 100 (Continue) response to encourage the
client to send the request's message body. The origin server MUST client to send the request's message body. The origin server MUST
NOT wait for the message body before sending the 100 (Continue) NOT wait for the message body before sending the 100 (Continue)
response. response.
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Note: The Expect header field was added after the original Note: The Expect header field was added after the original
publication of HTTP/1.1 [RFC2068] as both the means to request an publication of HTTP/1.1 [RFC2068] as both the means to request an
interim 100 (Continue) response and the general mechanism for interim 100 (Continue) response and the general mechanism for
indicating must-understand extensions. However, the extension indicating must-understand extensions. However, the extension
mechanism has not been used by clients and the must-understand mechanism has not been used by clients and the must-understand
requirements have not been implemented by many servers, rendering requirements have not been implemented by many servers, rendering
the extension mechanism useless. This specification has removed the extension mechanism useless. This specification has removed
the extension mechanism in order to simplify the definition and the extension mechanism in order to simplify the definition and
processing of 100-continue. processing of 100-continue.
5.1.2. Max-Forwards 8.1.2. Max-Forwards
The "Max-Forwards" header field provides a mechanism with the TRACE The "Max-Forwards" header field provides a mechanism with the TRACE
(Section 4.3.8) and OPTIONS (Section 4.3.7) request methods to limit (Section 7.3.8) and OPTIONS (Section 7.3.7) request methods to limit
the number of times that the request is forwarded by proxies. This the number of times that the request is forwarded by proxies. This
can be useful when the client is attempting to trace a request that can be useful when the client is attempting to trace a request that
appears to be failing or looping mid-chain. appears to be failing or looping mid-chain.
Max-Forwards = 1*DIGIT Max-Forwards = 1*DIGIT
The Max-Forwards value is a decimal integer indicating the remaining The Max-Forwards value is a decimal integer indicating the remaining
number of times this request message can be forwarded. number of times this request message can be forwarded.
Each intermediary that receives a TRACE or OPTIONS request containing Each intermediary that receives a TRACE or OPTIONS request containing
skipping to change at page 37, line 12 skipping to change at page 77, line 36
intermediary MUST NOT forward the request; instead, the intermediary intermediary MUST NOT forward the request; instead, the intermediary
MUST respond as the final recipient. If the received Max-Forwards MUST respond as the final recipient. If the received Max-Forwards
value is greater than zero, the intermediary MUST generate an updated value is greater than zero, the intermediary MUST generate an updated
Max-Forwards field in the forwarded message with a field-value that Max-Forwards field in the forwarded message with a field-value that
is the lesser of a) the received value decremented by one (1) or b) is the lesser of a) the received value decremented by one (1) or b)
the recipient's maximum supported value for Max-Forwards. the recipient's maximum supported value for Max-Forwards.
A recipient MAY ignore a Max-Forwards header field received with any A recipient MAY ignore a Max-Forwards header field received with any
other request methods. other request methods.
5.2. Conditionals 8.2. Preconditions
The HTTP conditional request header fields [CONDTNL] allow a client A conditional request is an HTTP request with one or more request
to place a precondition on the state of the target resource, so that header fields that indicate a precondition to be tested before
the action corresponding to the method semantics will not be applied applying the request method to the target resource. Section 8.2.1
if the precondition evaluates to false. Each precondition defined by defines when preconditions are applied. Section 8.2.2 defines the
this specification consists of a comparison between a set of order of evaluation when more than one precondition is present.
validators obtained from prior representations of the target resource
to the current state of validators for the selected representation
(Section 7.2). Hence, these preconditions evaluate whether the state
of the target resource has changed since a given state known by the
client. The effect of such an evaluation depends on the method
semantics and choice of conditional, as defined in Section 5 of
[CONDTNL].
+---------------------+--------------------------+ Conditional GET requests are the most efficient mechanism for HTTP
| Header Field Name | Defined in... | cache updates [Caching]. Conditionals can also be applied to state-
+---------------------+--------------------------+ changing methods, such as PUT and DELETE, to prevent the "lost
| If-Match | Section 3.1 of [CONDTNL] | update" problem: one client accidentally overwriting the work of
| If-None-Match | Section 3.2 of [CONDTNL] | another client that has been acting in parallel.
| If-Modified-Since | Section 3.3 of [CONDTNL] |
| If-Unmodified-Since | Section 3.4 of [CONDTNL] |
| If-Range | Section 3.2 of [RANGERQ] |
+---------------------+--------------------------+
5.3. Content Negotiation Conditional request preconditions are based on the state of the
target resource as a whole (its current value set) or the state as
observed in a previously obtained representation (one value in that
set). A resource might have multiple current representations, each
with its own observable state. The conditional request mechanisms
assume that the mapping of requests to a "selected representation"
(Section 6) will be consistent over time if the server intends to
take advantage of conditionals. Regardless, if the mapping is
inconsistent and the server is unable to select the appropriate
representation, then no harm will result when the precondition
evaluates to false.
The following request header fields allow a client to place a
precondition on the state of the target resource, so that the action
corresponding to the method semantics will not be applied if the
precondition evaluates to false. Each precondition defined by this
specification consists of a comparison between a set of validators
obtained from prior representations of the target resource to the
current state of validators for the selected representation
(Section 10.2). Hence, these preconditions evaluate whether the
state of the target resource has changed since a given state known by
the client. The effect of such an evaluation depends on the method
semantics and choice of conditional, as defined in Section 8.2.1.
+---------------------+---------------+
| Header Field Name | Defined in... |
+---------------------+---------------+
| If-Match | Section 8.2.3 |
| If-None-Match | Section 8.2.4 |
| If-Modified-Since | Section 8.2.5 |
| If-Unmodified-Since | Section 8.2.6 |
| If-Range | Section 8.2.7 |
+---------------------+---------------+
8.2.1. Evaluation
Except when excluded below, a recipient cache or origin server MUST
evaluate received request preconditions after it has successfully
performed its normal request checks and just before it would perform
the action associated with the request method. A server MUST ignore
all received preconditions if its response to the same request
without those conditions would have been a status code other than a
2xx (Successful) or 412 (Precondition Failed). In other words,
redirects and failures take precedence over the evaluation of
preconditions in conditional requests.
A server that is not the origin server for the target resource and
cannot act as a cache for requests on the target resource MUST NOT
evaluate the conditional request header fields defined by this
specification, and it MUST forward them if the request is forwarded,
since the generating client intends that they be evaluated by a
server that can provide a current representation. Likewise, a server
MUST ignore the conditional request header fields defined by this
specification when received with a request method that does not
involve the selection or modification of a selected representation,
such as CONNECT, OPTIONS, or TRACE.
Conditional request header fields that are defined by extensions to
HTTP might place conditions on all recipients, on the state of the
target resource in general, or on a group of resources. For
instance, the "If" header field in WebDAV can make a request
conditional on various aspects of multiple resources, such as locks,
if the recipient understands and implements that field ([RFC4918],
Section 10.4).
Although conditional request header fields are defined as being
usable with the HEAD method (to keep HEAD's semantics consistent with
those of GET), there is no point in sending a conditional HEAD
because a successful response is around the same size as a 304 (Not
Modified) response and more useful than a 412 (Precondition Failed)
response.
8.2.2. Precedence
When more than one conditional request header field is present in a
request, the order in which the fields are evaluated becomes
important. In practice, the fields defined in this document are
consistently implemented in a single, logical order, since "lost
update" preconditions have more strict requirements than cache
validation, a validated cache is more efficient than a partial
response, and entity tags are presumed to be more accurate than date
validators.
A recipient cache or origin server MUST evaluate the request
preconditions defined by this specification in the following order:
1. When recipient is the origin server and If-Match is present,
evaluate the If-Match precondition:
* if true, continue to step 3
* if false, respond 412 (Precondition Failed) unless it can be
determined that the state-changing request has already
succeeded (see Section 8.2.3)
2. When recipient is the origin server, If-Match is not present, and
If-Unmodified-Since is present, evaluate the If-Unmodified-Since
precondition:
* if true, continue to step 3
* if false, respond 412 (Precondition Failed) unless it can be
determined that the state-changing request has already
succeeded (see Section 8.2.6)
3. When If-None-Match is present, evaluate the If-None-Match
precondition:
* if true, continue to step 5
* if false for GET/HEAD, respond 304 (Not Modified)
* if false for other methods, respond 412 (Precondition Failed)
4. When the method is GET or HEAD, If-None-Match is not present, and
If-Modified-Since is present, evaluate the If-Modified-Since
precondition:
* if true, continue to step 5
* if false, respond 304 (Not Modified)
5. When the method is GET and both Range and If-Range are present,
evaluate the If-Range precondition:
* if the validator matches and the Range specification is
applicable to the selected representation, respond 206
(Partial Content)
6. Otherwise,
* all conditions are met, so perform the requested action and
respond according to its success or failure.
Any extension to HTTP/1.1 that defines additional conditional request
header fields ought to define its own expectations regarding the
order for evaluating such fields in relation to those defined in this
document and other conditionals that might be found in practice.
8.2.3. If-Match
The "If-Match" header field makes the request method conditional on
the recipient origin server either having at least one current
representation of the target resource, when the field-value is "*",
or having a current representation of the target resource that has an
entity-tag matching a member of the list of entity-tags provided in
the field-value.
An origin server MUST use the strong comparison function when
comparing entity-tags for If-Match (Section 10.2.3.2), since the
client intends this precondition to prevent the method from being
applied if there have been any changes to the representation data.
If-Match = "*" / 1#entity-tag
Examples:
If-Match: "xyzzy"
If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
If-Match: *
If-Match is most often used with state-changing methods (e.g., POST,
PUT, DELETE) to prevent accidental overwrites when multiple user
agents might be acting in parallel on the same resource (i.e., to
prevent the "lost update" problem). It can also be used with safe
methods to abort a request if the selected representation does not
match one already stored (or partially stored) from a prior request.
An origin server that receives an If-Match header field MUST evaluate
the condition prior to performing the method (Section 8.2.1). If the
field-value is "*", the condition is false if the origin server does
not have a current representation for the target resource. If the
field-value is a list of entity-tags, the condition is false if none
of the listed tags match the entity-tag of the selected
representation.
An origin server MUST NOT perform the requested method if a received
If-Match condition evaluates to false; instead, the origin server
MUST respond with either a) the 412 (Precondition Failed) status code
or b) one of the 2xx (Successful) status codes if the origin server
has verified that a state change is being requested and the final
state is already reflected in the current state of the target
resource (i.e., the change requested by the user agent has already
succeeded, but the user agent might not be aware of it, perhaps
because the prior response was lost or a compatible change was made
by some other user agent). In the latter case, the origin server
MUST NOT send a validator header field in the response unless it can
verify that the request is a duplicate of an immediately prior change
made by the same user agent.
The If-Match header field can be ignored by caches and intermediaries
because it is not applicable to a stored response.
8.2.4. If-None-Match
The "If-None-Match" header field makes the request method conditional
on a recipient cache or origin server either not having any current
representation of the target resource, when the field-value is "*",
or having a selected representation with an entity-tag that does not
match any of those listed in the field-value.
A recipient MUST use the weak comparison function when comparing
entity-tags for If-None-Match (Section 10.2.3.2), since weak entity-
tags can be used for cache validation even if there have been changes
to the representation data.
If-None-Match = "*" / 1#entity-tag
Examples:
If-None-Match: "xyzzy"
If-None-Match: W/"xyzzy"
If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"
If-None-Match: *
If-None-Match is primarily used in conditional GET requests to enable
efficient updates of cached information with a minimum amount of
transaction overhead. When a client desires to update one or more
stored responses that have entity-tags, the client SHOULD generate an
If-None-Match header field containing a list of those entity-tags
when making a GET request; this allows recipient servers to send a
304 (Not Modified) response to indicate when one of those stored
responses matches the selected representation.
If-None-Match can also be used with a value of "*" to prevent an
unsafe request method (e.g., PUT) from inadvertently modifying an
existing representation of the target resource when the client
believes that the resource does not have a current representation
(Section 7.2.1). This is a variation on the "lost update" problem
that might arise if more than one client attempts to create an
initial representation for the target resource.
An origin server that receives an If-None-Match header field MUST
evaluate the condition prior to performing the method
(Section 8.2.1). If the field-value is "*", the condition is false
if the origin server has a current representation for the target
resource. If the field-value is a list of entity-tags, the condition
is false if one of the listed tags match the entity-tag of the
selected representation.
An origin server MUST NOT perform the requested method if the
condition evaluates to false; instead, the origin server MUST respond
with either a) the 304 (Not Modified) status code if the request
method is GET or HEAD or b) the 412 (Precondition Failed) status code
for all other request methods.
Requirements on cache handling of a received If-None-Match header
field are defined in Section 4.3.2 of [Caching].
8.2.5. If-Modified-Since
The "If-Modified-Since" header field makes a GET or HEAD request
method conditional on the selected representation's modification date
being more recent than the date provided in the field-value.
Transfer of the selected representation's data is avoided if that
data has not changed.
If-Modified-Since = HTTP-date
An example of the field is:
If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
A recipient MUST ignore If-Modified-Since if the request contains an
If-None-Match header field; the condition in If-None-Match is
considered to be a more accurate replacement for the condition in If-
Modified-Since, and the two are only combined for the sake of
interoperating with older intermediaries that might not implement If-
None-Match.
A recipient MUST ignore the If-Modified-Since header field if the
received field-value is not a valid HTTP-date, or if the request
method is neither GET nor HEAD.
A recipient MUST interpret an If-Modified-Since field-value's
timestamp in terms of the origin server's clock.
If-Modified-Since is typically used for two distinct purposes: 1) to
allow efficient updates of a cached representation that does not have
an entity-tag and 2) to limit the scope of a web traversal to
resources that have recently changed.
When used for cache updates, a cache will typically use the value of
the cached message's Last-Modified field to generate the field value
of If-Modified-Since. This behavior is most interoperable for cases
where clocks are poorly synchronized or when the server has chosen to
only honor exact timestamp matches (due to a problem with Last-
Modified dates that appear to go "back in time" when the origin
server's clock is corrected or a representation is restored from an
archived backup). However, caches occasionally generate the field
value based on other data, such as the Date header field of the
cached message or the local clock time that the message was received,
particularly when the cached message does not contain a Last-Modified
field.
When used for limiting the scope of retrieval to a recent time
window, a user agent will generate an If-Modified-Since field value
based on either its own local clock or a Date header field received
from the server in a prior response. Origin servers that choose an
exact timestamp match based on the selected representation's Last-
Modified field will not be able to help the user agent limit its data
transfers to only those changed during the specified window.
An origin server that receives an If-Modified-Since header field
SHOULD evaluate the condition prior to performing the method
(Section 8.2.1). The origin server SHOULD NOT perform the requested
method if the selected representation's last modification date is
earlier than or equal to the date provided in the field-value;
instead, the origin server SHOULD generate a 304 (Not Modified)
response, including only those metadata that are useful for
identifying or updating a previously cached response.
Requirements on cache handling of a received If-Modified-Since header
field are defined in Section 4.3.2 of [Caching].
8.2.6. If-Unmodified-Since
The "If-Unmodified-Since" header field makes the request method
conditional on the selected representation's last modification date
being earlier than or equal to the date provided in the field-value.
This field accomplishes the same purpose as If-Match for cases where
the user agent does not have an entity-tag for the representation.
If-Unmodified-Since = HTTP-date
An example of the field is:
If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
A recipient MUST ignore If-Unmodified-Since if the request contains
an If-Match header field; the condition in If-Match is considered to
be a more accurate replacement for the condition in If-Unmodified-
Since, and the two are only combined for the sake of interoperating
with older intermediaries that might not implement If-Match.
A recipient MUST ignore the If-Unmodified-Since header field if the
received field-value is not a valid HTTP-date.
A recipient MUST interpret an If-Unmodified-Since field-value's
timestamp in terms of the origin server's clock.
If-Unmodified-Since is most often used with state-changing methods
(e.g., POST, PUT, DELETE) to prevent accidental overwrites when
multiple user agents might be acting in parallel on a resource that
does not supply entity-tags with its representations (i.e., to
prevent the "lost update" problem). It can also be used with safe
methods to abort a request if the selected representation does not
match one already stored (or partially stored) from a prior request.
An origin server that receives an If-Unmodified-Since header field
MUST evaluate the condition prior to performing the method
(Section 8.2.1). The origin server MUST NOT perform the requested
method if the selected representation's last modification date is
more recent than the date provided in the field-value; instead the
origin server MUST respond with either a) the 412 (Precondition
Failed) status code or b) one of the 2xx (Successful) status codes if
the origin server has verified that a state change is being requested
and the final state is already reflected in the current state of the
target resource (i.e., the change requested by the user agent has
already succeeded, but the user agent might not be aware of that
because the prior response message was lost or a compatible change
was made by some other user agent). In the latter case, the origin
server MUST NOT send a validator header field in the response unless
it can verify that the request is a duplicate of an immediately prior
change made by the same user agent.
The If-Unmodified-Since header field can be ignored by caches and
intermediaries because it is not applicable to a stored response.
8.2.7. If-Range
The "If-Range" header field provides a special conditional request
mechanism that is similar to the If-Match and If-Unmodified-Since
header fields but that instructs the recipient to ignore the Range
header field if the validator doesn't match, resulting in transfer of
the new selected representation instead of a 412 (Precondition
Failed) response.
If a client has a partial copy of a representation and wishes to have
an up-to-date copy of the entire representation, it could use the
Range header field with a conditional GET (using either or both of
If-Unmodified-Since and If-Match.) However, if the precondition
fails because the representation has been modified, the client would
then have to make a second request to obtain the entire current
representation.
The "If-Range" header field allows a client to "short-circuit" the
second request. Informally, its meaning is as follows: if the
representation is unchanged, send me the part(s) that I am requesting
in Range; otherwise, send me the entire representation.
If-Range = entity-tag / HTTP-date
A client MUST NOT generate an If-Range header field in a request that
does not contain a Range header field. A server MUST ignore an If-
Range header field received in a request that does not contain a
Range header field. An origin server MUST ignore an If-Range header
field received in a request for a target resource that does not
support Range requests.
A client MUST NOT generate an If-Range header field containing an
entity-tag that is marked as weak. A client MUST NOT generate an If-
Range header field containing an HTTP-date unless the client has no
entity-tag for the corresponding representation and the date is a
strong validator in the sense defined by Section 10.2.2.2.
A server that evaluates an If-Range precondition MUST use the strong
comparison function when comparing entity-tags (Section 10.2.3.2) and
MUST evaluate the condition as false if an HTTP-date validator is
provided that is not a strong validator in the sense defined by
Section 10.2.2.2. A valid entity-tag can be distinguished from a
valid HTTP-date by examining the first two characters for a DQUOTE.
If the validator given in the If-Range header field matches the
current validator for the selected representation of the target
resource, then the server SHOULD process the Range header field as
requested. If the validator does not match, the server MUST ignore
the Range header field. Note that this comparison by exact match,
including when the validator is an HTTP-date, differs from the
"earlier than or equal to" comparison used when evaluating an If-
Unmodified-Since conditional.
8.3. Range
The "Range" header field on a GET request modifies the method
semantics to request transfer of only one or more subranges of the
selected representation data, rather than the entire selected
representation data.
Range = byte-ranges-specifier / other-ranges-specifier
other-ranges-specifier = other-range-unit "=" other-range-set
other-range-set = 1*VCHAR
Clients often encounter interrupted data transfers as a result of
canceled requests or dropped connections. When a client has stored a
partial representation, it is desirable to request the remainder of
that representation in a subsequent request rather than transfer the
entire representation. Likewise, devices with limited local storage
might benefit from being able to request only a subset of a larger
representation, such as a single page of a very large document, or
the dimensions of an embedded image.
Range requests are an OPTIONAL feature of HTTP, designed so that
recipients not implementing this feature (or not supporting it for
the target resource) can respond as if it is a normal GET request
without impacting interoperability. Partial responses are indicated
by a distinct status code to not be mistaken for full responses by
caches that might not implement the feature.
A server MAY ignore the Range header field. However, origin servers
and intermediate caches ought to support byte ranges when possible,
since Range supports efficient recovery from partially failed
transfers and partial retrieval of large representations. A server
MUST ignore a Range header field received with a request method other
than GET.
Although the range request mechanism is designed to allow for
extensible range types, this specification only defines requests for
byte ranges.
An origin server MUST ignore a Range header field that contains a
range unit it does not understand. A proxy MAY discard a Range
header field that contains a range unit it does not understand.
A server that supports range requests MAY ignore or reject a Range
header field that consists of more than two overlapping ranges, or a
set of many small ranges that are not listed in ascending order,
since both are indications of either a broken client or a deliberate
denial-of-service attack (Section 12.13). A client SHOULD NOT
request multiple ranges that are inherently less efficient to process
and transfer than a single range that encompasses the same data.
A client that is requesting multiple ranges SHOULD list those ranges
in ascending order (the order in which they would typically be
received in a complete representation) unless there is a specific
need to request a later part earlier. For example, a user agent
processing a large representation with an internal catalog of parts
might need to request later parts first, particularly if the
representation consists of pages stored in reverse order and the user
agent wishes to transfer one page at a time.
The Range header field is evaluated after evaluating the precondition
header fields defined in Section 8.2, and only if the result in
absence of the Range header field would be a 200 (OK) response. In
other words, Range is ignored when a conditional GET would result in
a 304 (Not Modified) response.
The If-Range header field (Section 8.2.7) can be used as a
precondition to applying the Range header field.
If all of the preconditions are true, the server supports the Range
header field for the target resource, and the specified range(s) are
valid and satisfiable (as defined in Section 6.1.4.1), the server
SHOULD send a 206 (Partial Content) response with a payload
containing one or more partial representations that correspond to the
satisfiable ranges requested.
If all of the preconditions are true, the server supports the Range
header field for the target resource, and the specified range(s) are
invalid or unsatisfiable, the server SHOULD send a 416 (Range Not
Satisfiable) response.
8.4. Content Negotiation
The following request header fields are sent by a user agent to The following request header fields are sent by a user agent to
engage in proactive negotiation of the response content, as defined engage in proactive negotiation of the response content, as defined
in Section 3.4.1. The preferences sent in these fields apply to any in Section 6.4.1. The preferences sent in these fields apply to any
content in the response, including representations of the target content in the response, including representations of the target
resource, representations of error or processing status, and resource, representations of error or processing status, and
potentially even the miscellaneous text strings that might appear potentially even the miscellaneous text strings that might appear
within the protocol. within the protocol.
+-------------------+---------------+ +-------------------+---------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+---------------+ +-------------------+---------------+
| Accept | Section 5.3.2 | | Accept | Section 8.4.2 |
| Accept-Charset | Section 5.3.3 | | Accept-Charset | Section 8.4.3 |
| Accept-Encoding | Section 5.3.4 | | Accept-Encoding | Section 8.4.4 |
| Accept-Language | Section 5.3.5 | | Accept-Language | Section 8.4.5 |
+-------------------+---------------+ +-------------------+---------------+
5.3.1. Quality Values 8.4.1. Quality Values
Many of the request header fields for proactive negotiation use a Many of the request header fields for proactive negotiation use a
common parameter, named "q" (case-insensitive), to assign a relative common parameter, named "q" (case-insensitive), to assign a relative
"weight" to the preference for that associated kind of content. This "weight" to the preference for that associated kind of content. This
weight is referred to as a "quality value" (or "qvalue") because the weight is referred to as a "quality value" (or "qvalue") because the
same parameter name is often used within server configurations to same parameter name is often used within server configurations to
assign a weight to the relative quality of the various assign a weight to the relative quality of the various
representations that can be selected for a resource. representations that can be selected for a resource.
The weight is normalized to a real number in the range 0 through 1, The weight is normalized to a real number in the range 0 through 1,
skipping to change at page 38, line 37 skipping to change at page 89, line 28
the default weight is 1. the default weight is 1.
weight = OWS ";" OWS "q=" qvalue weight = OWS ";" OWS "q=" qvalue
qvalue = ( "0" [ "." 0*3DIGIT ] ) qvalue = ( "0" [ "." 0*3DIGIT ] )
/ ( "1" [ "." 0*3("0") ] ) / ( "1" [ "." 0*3("0") ] )
A sender of qvalue MUST NOT generate more than three digits after the A sender of qvalue MUST NOT generate more than three digits after the
decimal point. User configuration of these values ought to be decimal point. User configuration of these values ought to be
limited in the same fashion. limited in the same fashion.
5.3.2. Accept 8.4.2. Accept
The "Accept" header field can be used by user agents to specify The "Accept" header field can be used by user agents to specify
response media types that are acceptable. Accept header fields can response media types that are acceptable. Accept header fields can
be used to indicate that the request is specifically limited to a be used to indicate that the request is specifically limited to a
small set of desired types, as in the case of a request for an in- small set of desired types, as in the case of a request for an in-
line image. line image.
Accept = #( media-range [ accept-params ] ) Accept = #( media-range [ accept-params ] )
media-range = ( "*/*" media-range = ( "*/*"
skipping to change at page 39, line 12 skipping to change at page 89, line 52
accept-params = weight *( accept-ext ) accept-params = weight *( accept-ext )
accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ] accept-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
The asterisk "*" character is used to group media types into ranges, The asterisk "*" character is used to group media types into ranges,
with "*/*" indicating all media types and "type/*" indicating all with "*/*" indicating all media types and "type/*" indicating all
subtypes of that type. The media-range can include media type subtypes of that type. The media-range can include media type
parameters that are applicable to that range. parameters that are applicable to that range.
Each media-range might be followed by zero or more applicable media Each media-range might be followed by zero or more applicable media
type parameters (e.g., charset), an optional "q" parameter for type parameters (e.g., charset), an optional "q" parameter for
indicating a relative weight (Section 5.3.1), and then zero or more indicating a relative weight (Section 8.4.1), and then zero or more
extension parameters. The "q" parameter is necessary if any extension parameters. The "q" parameter is necessary if any
extensions (accept-ext) are present, since it acts as a separator extensions (accept-ext) are present, since it acts as a separator
between the two parameter sets. between the two parameter sets.
Note: Use of the "q" parameter name to separate media type Note: Use of the "q" parameter name to separate media type
parameters from Accept extension parameters is due to historical parameters from Accept extension parameters is due to historical
practice. Although this prevents any media type parameter named practice. Although this prevents any media type parameter named
"q" from being used with a media range, such an event is believed "q" from being used with a media range, such an event is believed
to be unlikely given the lack of any "q" parameters in the IANA to be unlikely given the lack of any "q" parameters in the IANA
media type registry and the rare usage of any media type media type registry and the rare usage of any media type
skipping to change at page 40, line 46 skipping to change at page 91, line 35
| image/jpeg | 0.5 | | image/jpeg | 0.5 |
| text/html;level=2 | 0.4 | | text/html;level=2 | 0.4 |
| text/html;level=3 | 0.7 | | text/html;level=3 | 0.7 |
+-------------------+---------------+ +-------------------+---------------+
Note: A user agent might be provided with a default set of quality Note: A user agent might be provided with a default set of quality
values for certain media ranges. However, unless the user agent is a values for certain media ranges. However, unless the user agent is a
closed system that cannot interact with other rendering agents, this closed system that cannot interact with other rendering agents, this
default set ought to be configurable by the user. default set ought to be configurable by the user.
5.3.3. Accept-Charset 8.4.3. Accept-Charset
The "Accept-Charset" header field can be sent by a user agent to The "Accept-Charset" header field can be sent by a user agent to
indicate what charsets are acceptable in textual response content. indicate what charsets are acceptable in textual response content.
This field allows user agents capable of understanding more This field allows user agents capable of understanding more
comprehensive or special-purpose charsets to signal that capability comprehensive or special-purpose charsets to signal that capability
to an origin server that is capable of representing information in to an origin server that is capable of representing information in
those charsets. those charsets.
Accept-Charset = 1#( ( charset / "*" ) [ weight ] ) Accept-Charset = 1#( ( charset / "*" ) [ weight ] )
Charset names are defined in Section 3.1.1.2. A user agent MAY Charset names are defined in Section 6.1.1.1. A user agent MAY
associate a quality value with each charset to indicate the user's associate a quality value with each charset to indicate the user's
relative preference for that charset, as defined in Section 5.3.1. relative preference for that charset, as defined in Section 8.4.1.
An example is An example is
Accept-Charset: iso-8859-5, unicode-1-1;q=0.8 Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
The special value "*", if present in the Accept-Charset field, The special value "*", if present in the Accept-Charset field,
matches every charset that is not mentioned elsewhere in the Accept- matches every charset that is not mentioned elsewhere in the Accept-
Charset field. If no "*" is present in an Accept-Charset field, then Charset field. If no "*" is present in an Accept-Charset field, then
any charsets not explicitly mentioned in the field are considered any charsets not explicitly mentioned in the field are considered
"not acceptable" to the client. "not acceptable" to the client.
A request without any Accept-Charset header field implies that the A request without any Accept-Charset header field implies that the
user agent will accept any charset in response. Most general-purpose user agent will accept any charset in response. Most general-purpose
user agents do not send Accept-Charset, unless specifically user agents do not send Accept-Charset, unless specifically
configured to do so, because a detailed list of supported charsets configured to do so, because a detailed list of supported charsets
makes it easier for a server to identify an individual by virtue of makes it easier for a server to identify an individual by virtue of
the user agent's request characteristics (Section 9.7). the user agent's request characteristics (Section 12.11).
If an Accept-Charset header field is present in a request and none of If an Accept-Charset header field is present in a request and none of
the available representations for the response has a charset that is the available representations for the response has a charset that is
listed as acceptable, the origin server can either honor the header listed as acceptable, the origin server can either honor the header
field, by sending a 406 (Not Acceptable) response, or disregard the field, by sending a 406 (Not Acceptable) response, or disregard the
header field by treating the resource as if it is not subject to header field by treating the resource as if it is not subject to
content negotiation. content negotiation.
5.3.4. Accept-Encoding 8.4.4. Accept-Encoding
The "Accept-Encoding" header field can be used by user agents to The "Accept-Encoding" header field can be used by user agents to
indicate what response content-codings (Section 3.1.2.1) are indicate what response content-codings (Section 6.1.2) are acceptable
acceptable in the response. An "identity" token is used as a synonym in the response. An "identity" token is used as a synonym for "no
for "no encoding" in order to communicate when no encoding is encoding" in order to communicate when no encoding is preferred.
preferred.
Accept-Encoding = #( codings [ weight ] ) Accept-Encoding = #( codings [ weight ] )
codings = content-coding / "identity" / "*" codings = content-coding / "identity" / "*"
Each codings value MAY be given an associated quality value Each codings value MAY be given an associated quality value
representing the preference for that encoding, as defined in representing the preference for that encoding, as defined in
Section 5.3.1. The asterisk "*" symbol in an Accept-Encoding field Section 8.4.1. The asterisk "*" symbol in an Accept-Encoding field
matches any available content-coding not explicitly listed in the matches any available content-coding not explicitly listed in the
header field. header field.
For example, For example,
Accept-Encoding: compress, gzip Accept-Encoding: compress, gzip
Accept-Encoding: Accept-Encoding:
Accept-Encoding: * Accept-Encoding: *
Accept-Encoding: compress;q=0.5, gzip;q=1.0 Accept-Encoding: compress;q=0.5, gzip;q=1.0
Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0 Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
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is considered acceptable by the user agent. is considered acceptable by the user agent.
2. If the representation has no content-coding, then it is 2. If the representation has no content-coding, then it is
acceptable by default unless specifically excluded by the Accept- acceptable by default unless specifically excluded by the Accept-
Encoding field stating either "identity;q=0" or "*;q=0" without a Encoding field stating either "identity;q=0" or "*;q=0" without a
more specific entry for "identity". more specific entry for "identity".
3. If the representation's content-coding is one of the content- 3. If the representation's content-coding is one of the content-
codings listed in the Accept-Encoding field, then it is codings listed in the Accept-Encoding field, then it is
acceptable unless it is accompanied by a qvalue of 0. (As acceptable unless it is accompanied by a qvalue of 0. (As
defined in Section 5.3.1, a qvalue of 0 means "not acceptable".) defined in Section 8.4.1, a qvalue of 0 means "not acceptable".)
4. If multiple content-codings are acceptable, then the acceptable 4. If multiple content-codings are acceptable, then the acceptable
content-coding with the highest non-zero qvalue is preferred. content-coding with the highest non-zero qvalue is preferred.
An Accept-Encoding header field with a combined field-value that is An Accept-Encoding header field with a combined field-value that is
empty implies that the user agent does not want any content-coding in empty implies that the user agent does not want any content-coding in
response. If an Accept-Encoding header field is present in a request response. If an Accept-Encoding header field is present in a request
and none of the available representations for the response have a and none of the available representations for the response have a
content-coding that is listed as acceptable, the origin server SHOULD content-coding that is listed as acceptable, the origin server SHOULD
send a response without any content-coding. send a response without any content-coding.
Note: Most HTTP/1.0 applications do not recognize or obey qvalues Note: Most HTTP/1.0 applications do not recognize or obey qvalues
associated with content-codings. This means that qvalues might associated with content-codings. This means that qvalues might
not work and are not permitted with x-gzip or x-compress. not work and are not permitted with x-gzip or x-compress.
5.3.5. Accept-Language 8.4.5. Accept-Language
The "Accept-Language" header field can be used by user agents to The "Accept-Language" header field can be used by user agents to
indicate the set of natural languages that are preferred in the indicate the set of natural languages that are preferred in the
response. Language tags are defined in Section 3.1.3.1. response. Language tags are defined in Section 6.1.3.
Accept-Language = 1#( language-range [ weight ] ) Accept-Language = 1#( language-range [ weight ] )
language-range = language-range =
<language-range, see [RFC4647], Section 2.1> <language-range, see [RFC4647], Section 2.1>
Each language-range can be given an associated quality value Each language-range can be given an associated quality value
representing an estimate of the user's preference for the languages representing an estimate of the user's preference for the languages
specified by that range, as defined in Section 5.3.1. For example, specified by that range, as defined in Section 8.4.1. For example,
Accept-Language: da, en-gb;q=0.8, en;q=0.7 Accept-Language: da, en-gb;q=0.8, en;q=0.7
would mean: "I prefer Danish, but will accept British English and would mean: "I prefer Danish, but will accept British English and
other types of English". other types of English".
A request without any Accept-Language header field implies that the A request without any Accept-Language header field implies that the
user agent will accept any language in response. If the header field user agent will accept any language in response. If the header field
is present in a request and none of the available representations for is present in a request and none of the available representations for
the response have a matching language tag, the origin server can the response have a matching language tag, the origin server can
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found in Section 2.3 of [RFC4647]. found in Section 2.3 of [RFC4647].
For matching, Section 3 of [RFC4647] defines several matching For matching, Section 3 of [RFC4647] defines several matching
schemes. Implementations can offer the most appropriate matching schemes. Implementations can offer the most appropriate matching
scheme for their requirements. The "Basic Filtering" scheme scheme for their requirements. The "Basic Filtering" scheme
([RFC4647], Section 3.3.1) is identical to the matching scheme that ([RFC4647], Section 3.3.1) is identical to the matching scheme that
was previously defined for HTTP in Section 14.4 of [RFC2616]. was previously defined for HTTP in Section 14.4 of [RFC2616].
It might be contrary to the privacy expectations of the user to send It might be contrary to the privacy expectations of the user to send
an Accept-Language header field with the complete linguistic an Accept-Language header field with the complete linguistic
preferences of the user in every request (Section 9.7). preferences of the user in every request (Section 12.11).
Since intelligibility is highly dependent on the individual user, Since intelligibility is highly dependent on the individual user,
user agents need to allow user control over the linguistic preference user agents need to allow user control over the linguistic preference
(either through configuration of the user agent itself or by (either through configuration of the user agent itself or by
defaulting to a user controllable system setting). A user agent that defaulting to a user controllable system setting). A user agent that
does not provide such control to the user MUST NOT send an Accept- does not provide such control to the user MUST NOT send an Accept-
Language header field. Language header field.
Note: User agents ought to provide guidance to users when setting Note: User agents ought to provide guidance to users when setting
a preference, since users are rarely familiar with the details of a preference, since users are rarely familiar with the details of
language matching as described above. For example, users might language matching as described above. For example, users might
assume that on selecting "en-gb", they will be served any kind of assume that on selecting "en-gb", they will be served any kind of
English document if British English is not available. A user English document if British English is not available. A user
agent might suggest, in such a case, to add "en" to the list for agent might suggest, in such a case, to add "en" to the list for
better matching behavior. better matching behavior.
5.4. Authentication Credentials 8.5. Authentication Credentials
Two header fields are used for carrying authentication credentials, HTTP provides a general framework for access control and
as defined in [AUTHFRM]. Note that various custom mechanisms for authentication, via an extensible set of challenge-response
user authentication use the Cookie header field for this purpose, as authentication schemes, which can be used by a server to challenge a
defined in [RFC6265]. client request and by a client to provide authentication information.
+---------------------+--------------------------+ Two header fields are used for carrying authentication credentials.
| Header Field Name | Defined in... | Note that various custom mechanisms for user authentication use the
+---------------------+--------------------------+ Cookie header field for this purpose, as defined in [RFC6265].
| Authorization | Section 4.2 of [AUTHFRM] |
| Proxy-Authorization | Section 4.4 of [AUTHFRM] |
+---------------------+--------------------------+
5.5. Request Context +---------------------+---------------+
| Header Field Name | Defined in... |
+---------------------+---------------+
| Authorization | Section 8.5.3 |
| Proxy-Authorization | Section 8.5.4 |
+---------------------+---------------+
8.5.1. Challenge and Response
HTTP provides a simple challenge-response authentication framework
that can be used by a server to challenge a client request and by a
client to provide authentication information. It uses a case-
insensitive token as a means to identify the authentication scheme,
followed by additional information necessary for achieving
authentication via that scheme. The latter can be either a comma-
separated list of parameters or a single sequence of characters
capable of holding base64-encoded information.
Authentication parameters are name=value pairs, where the name token
is matched case-insensitively, and each parameter name MUST only
occur once per challenge.
auth-scheme = token
auth-param = token BWS "=" BWS ( token / quoted-string )
token68 = 1*( ALPHA / DIGIT /
"-" / "." / "_" / "~" / "+" / "/" ) *"="
The token68 syntax allows the 66 unreserved URI characters
([RFC3986]), plus a few others, so that it can hold a base64,
base64url (URL and filename safe alphabet), base32, or base16 (hex)
encoding, with or without padding, but excluding whitespace
([RFC4648]).
A 401 (Unauthorized) response message is used by an origin server to
challenge the authorization of a user agent, including a WWW-
Authenticate header field containing at least one challenge
applicable to the requested resource.
A 407 (Proxy Authentication Required) response message is used by a
proxy to challenge the authorization of a client, including a Proxy-
Authenticate header field containing at least one challenge
applicable to the proxy for the requested resource.
challenge = auth-scheme [ 1*SP ( token68 / #auth-param ) ]
Note: Many clients fail to parse a challenge that contains an
unknown scheme. A workaround for this problem is to list well-
supported schemes (such as "basic") first.
A user agent that wishes to authenticate itself with an origin server
-- usually, but not necessarily, after receiving a 401 (Unauthorized)
-- can do so by including an Authorization header field with the
request.
A client that wishes to authenticate itself with a proxy -- usually,
but not necessarily, after receiving a 407 (Proxy Authentication
Required) -- can do so by including a Proxy-Authorization header
field with the request.
Both the Authorization field value and the Proxy-Authorization field
value contain the client's credentials for the realm of the resource
being requested, based upon a challenge received in a response
(possibly at some point in the past). When creating their values,
the user agent ought to do so by selecting the challenge with what it
considers to be the most secure auth-scheme that it understands,
obtaining credentials from the user as appropriate. Transmission of
credentials within header field values implies significant security
considerations regarding the confidentiality of the underlying
connection, as described in Section 12.14.1.
credentials = auth-scheme [ 1*SP ( token68 / #auth-param ) ]
Upon receipt of a request for a protected resource that omits
credentials, contains invalid credentials (e.g., a bad password) or
partial credentials (e.g., when the authentication scheme requires
more than one round trip), an origin server SHOULD send a 401
(Unauthorized) response that contains a WWW-Authenticate header field
with at least one (possibly new) challenge applicable to the
requested resource.
Likewise, upon receipt of a request that omits proxy credentials or
contains invalid or partial proxy credentials, a proxy that requires
authentication SHOULD generate a 407 (Proxy Authentication Required)
response that contains a Proxy-Authenticate header field with at
least one (possibly new) challenge applicable to the proxy.
A server that receives valid credentials that are not adequate to
gain access ought to respond with the 403 (Forbidden) status code
(Section 9.5.4).
HTTP does not restrict applications to this simple challenge-response
framework for access authentication. Additional mechanisms can be
used, such as authentication at the transport level or via message
encapsulation, and with additional header fields specifying
authentication information. However, such additional mechanisms are
not defined by this specification.
8.5.2. Protection Space (Realm)
The "realm" authentication parameter is reserved for use by
authentication schemes that wish to indicate a scope of protection.
A protection space is defined by the canonical root URI (the scheme
and authority components of the effective request URI; see
Section 5.3) of the server being accessed, in combination with the
realm value if present. These realms allow the protected resources
on a server to be partitioned into a set of protection spaces, each
with its own authentication scheme and/or authorization database.
The realm value is a string, generally assigned by the origin server,
that can have additional semantics specific to the authentication
scheme. Note that a response can have multiple challenges with the
same auth-scheme but with different realms.
The protection space determines the domain over which credentials can
be automatically applied. If a prior request has been authorized,
the user agent MAY reuse the same credentials for all other requests
within that protection space for a period of time determined by the
authentication scheme, parameters, and/or user preferences (such as a
configurable inactivity timeout). Unless specifically allowed by the
authentication scheme, a single protection space cannot extend
outside the scope of its server.
For historical reasons, a sender MUST only generate the quoted-string
syntax. Recipients might have to support both token and quoted-
string syntax for maximum interoperability with existing clients that
have been accepting both notations for a long time.
8.5.3. Authorization
The "Authorization" header field allows a user agent to authenticate
itself with an origin server -- usually, but not necessarily, after
receiving a 401 (Unauthorized) response. Its value consists of
credentials containing the authentication information of the user
agent for the realm of the resource being requested.
Authorization = credentials
If a request is authenticated and a realm specified, the same
credentials are presumed to be valid for all other requests within
this realm (assuming that the authentication scheme itself does not
require otherwise, such as credentials that vary according to a
challenge value or using synchronized clocks).
A proxy forwarding a request MUST NOT modify any Authorization fields
in that request. See Section 3.2 of [Caching] for details of and
requirements pertaining to handling of the Authorization field by
HTTP caches.
8.5.4. Proxy-Authorization
The "Proxy-Authorization" header field allows the client to identify
itself (or its user) to a proxy that requires authentication. Its
value consists of credentials containing the authentication
information of the client for the proxy and/or realm of the resource
being requested.
Proxy-Authorization = credentials
Unlike Authorization, the Proxy-Authorization header field applies
only to the next inbound proxy that demanded authentication using the
Proxy-Authenticate field. When multiple proxies are used in a chain,
the Proxy-Authorization header field is consumed by the first inbound
proxy that was expecting to receive credentials. A proxy MAY relay
the credentials from the client request to the next proxy if that is
the mechanism by which the proxies cooperatively authenticate a given
request.
8.5.5. Authentication Scheme Extensibility
Aside from the general framework, this document does not specify any
authentication schemes. New and existing authentication schemes are
specified independently and ought to be registered within the
"Hypertext Transfer Protocol (HTTP) Authentication Scheme Registry".
For example, the "basic" and "digest" authentication schemes are
defined by RFC 7617 and RFC 7616, respectively.
8.5.5.1. Authentication Scheme Registry
The "Hypertext Transfer Protocol (HTTP) Authentication Scheme
Registry" defines the namespace for the authentication schemes in
challenges and credentials. It is maintained at
<https://www.iana.org/assignments/http-authschemes>.
Registrations MUST include the following fields:
o Authentication Scheme Name
o Pointer to specification text
o Notes (optional)
Values to be added to this namespace require IETF Review (see
[RFC5226], Section 4.1).
8.5.5.2. Considerations for New Authentication Schemes
There are certain aspects of the HTTP Authentication framework that
put constraints on how new authentication schemes can work:
o HTTP authentication is presumed to be stateless: all of the
information necessary to authenticate a request MUST be provided
in the request, rather than be dependent on the server remembering
prior requests. Authentication based on, or bound to, the
underlying connection is outside the scope of this specification
and inherently flawed unless steps are taken to ensure that the
connection cannot be used by any party other than the
authenticated user (see Section 2.2).
o The authentication parameter "realm" is reserved for defining
protection spaces as described in Section 8.5.2. New schemes MUST
NOT use it in a way incompatible with that definition.
o The "token68" notation was introduced for compatibility with
existing authentication schemes and can only be used once per
challenge or credential. Thus, new schemes ought to use the auth-
param syntax instead, because otherwise future extensions will be
impossible.
o The parsing of challenges and credentials is defined by this
specification and cannot be modified by new authentication
schemes. When the auth-param syntax is used, all parameters ought
to support both token and quoted-string syntax, and syntactical
constraints ought to be defined on the field value after parsing
(i.e., quoted-string processing). This is necessary so that
recipients can use a generic parser that applies to all
authentication schemes.
Note: The fact that the value syntax for the "realm" parameter is
restricted to quoted-string was a bad design choice not to be
repeated for new parameters.
o Definitions of new schemes ought to define the treatment of
unknown extension parameters. In general, a "must-ignore" rule is
preferable to a "must-understand" rule, because otherwise it will
be hard to introduce new parameters in the presence of legacy
recipients. Furthermore, it's good to describe the policy for
defining new parameters (such as "update the specification" or
"use this registry").
o Authentication schemes need to document whether they are usable in
origin-server authentication (i.e., using WWW-Authenticate), and/
or proxy authentication (i.e., using Proxy-Authenticate).
o The credentials carried in an Authorization header field are
specific to the user agent and, therefore, have the same effect on
HTTP caches as the "private" Cache-Control response directive
(Section 5.2.2.6 of [Caching]), within the scope of the request in
which they appear.
Therefore, new authentication schemes that choose not to carry
credentials in the Authorization header field (e.g., using a newly
defined header field) will need to explicitly disallow caching, by
mandating the use of either Cache-Control request directives
(e.g., "no-store", Section 5.2.1.5 of [Caching]) or response
directives (e.g., "private").
8.6. Request Context
The following request header fields provide additional information The following request header fields provide additional information
about the request context, including information about the user, user about the request context, including information about the user, user
agent, and resource behind the request. agent, and resource behind the request.
+-------------------+---------------+ +-------------------+---------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+---------------+ +-------------------+---------------+
| From | Section 5.5.1 | | From | Section 8.6.1 |
| Referer | Section 5.5.2 | | Referer | Section 8.6.2 |
| User-Agent | Section 5.5.3 | | User-Agent | Section 8.6.3 |
+-------------------+---------------+ +-------------------+---------------+
5.5.1. From 8.6.1. From
The "From" header field contains an Internet email address for a The "From" header field contains an Internet email address for a
human user who controls the requesting user agent. The address ought human user who controls the requesting user agent. The address ought
to be machine-usable, as defined by "mailbox" in Section 3.4 of to be machine-usable, as defined by "mailbox" in Section 3.4 of
[RFC5322]: [RFC5322]:
From = mailbox From = mailbox
mailbox = <mailbox, see [RFC5322], Section 3.4> mailbox = <mailbox, see [RFC5322], Section 3.4>
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A robotic user agent SHOULD send a valid From header field so that A robotic user agent SHOULD send a valid From header field so that
the person responsible for running the robot can be contacted if the person responsible for running the robot can be contacted if
problems occur on servers, such as if the robot is sending excessive, problems occur on servers, such as if the robot is sending excessive,
unwanted, or invalid requests. unwanted, or invalid requests.
A server SHOULD NOT use the From header field for access control or A server SHOULD NOT use the From header field for access control or
authentication, since most recipients will assume that the field authentication, since most recipients will assume that the field
value is public information. value is public information.
5.5.2. Referer 8.6.2. Referer
The "Referer" [sic] header field allows the user agent to specify a The "Referer" [sic] header field allows the user agent to specify a
URI reference for the resource from which the target URI was obtained URI reference for the resource from which the target URI was obtained
(i.e., the "referrer", though the field name is misspelled). A user (i.e., the "referrer", though the field name is misspelled). A user
agent MUST NOT include the fragment and userinfo components of the agent MUST NOT include the fragment and userinfo components of the
URI reference [RFC3986], if any, when generating the Referer field URI reference [RFC3986], if any, when generating the Referer field
value. value.
Referer = absolute-URI / partial-URI Referer = absolute-URI / partial-URI
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The Referer field has the potential to reveal information about the The Referer field has the potential to reveal information about the
request context or browsing history of the user, which is a privacy request context or browsing history of the user, which is a privacy
concern if the referring resource's identifier reveals personal concern if the referring resource's identifier reveals personal
information (such as an account name) or a resource that is supposed information (such as an account name) or a resource that is supposed
to be confidential (such as behind a firewall or internal to a to be confidential (such as behind a firewall or internal to a
secured service). Most general-purpose user agents do not send the secured service). Most general-purpose user agents do not send the
Referer header field when the referring resource is a local "file" or Referer header field when the referring resource is a local "file" or
"data" URI. A user agent MUST NOT send a Referer header field in an "data" URI. A user agent MUST NOT send a Referer header field in an
unsecured HTTP request if the referring page was received with a unsecured HTTP request if the referring page was received with a
secure protocol. See Section 9.4 for additional security secure protocol. See Section 12.8 for additional security
considerations. considerations.
Some intermediaries have been known to indiscriminately remove Some intermediaries have been known to indiscriminately remove
Referer header fields from outgoing requests. This has the Referer header fields from outgoing requests. This has the
unfortunate side effect of interfering with protection against CSRF unfortunate side effect of interfering with protection against CSRF
attacks, which can be far more harmful to their users. attacks, which can be far more harmful to their users.
Intermediaries and user agent extensions that wish to limit Intermediaries and user agent extensions that wish to limit
information disclosure in Referer ought to restrict their changes to information disclosure in Referer ought to restrict their changes to
specific edits, such as replacing internal domain names with specific edits, such as replacing internal domain names with
pseudonyms or truncating the query and/or path components. An pseudonyms or truncating the query and/or path components. An
intermediary SHOULD NOT modify or delete the Referer header field intermediary SHOULD NOT modify or delete the Referer header field
when the field value shares the same scheme and host as the request when the field value shares the same scheme and host as the request
target. target.
5.5.3. User-Agent 8.6.3. User-Agent
The "User-Agent" header field contains information about the user The "User-Agent" header field contains information about the user
agent originating the request, which is often used by servers to help agent originating the request, which is often used by servers to help
identify the scope of reported interoperability problems, to work identify the scope of reported interoperability problems, to work
around or tailor responses to avoid particular user agent around or tailor responses to avoid particular user agent
limitations, and for analytics regarding browser or operating system limitations, and for analytics regarding browser or operating system
use. A user agent SHOULD send a User-Agent field in each request use. A user agent SHOULD send a User-Agent field in each request
unless specifically configured not to do so. unless specifically configured not to do so.
User-Agent = product *( RWS ( product / comment ) ) User-Agent = product *( RWS ( product / comment ) )
The User-Agent field-value consists of one or more product The User-Agent field-value consists of one or more product
identifiers, each followed by zero or more comments (Section 3.2 of identifiers, each followed by zero or more comments (Section 2.3 of
[MESSGNG]), which together identify the user agent software and its [Messaging]), which together identify the user agent software and its
significant subproducts. By convention, the product identifiers are significant subproducts. By convention, the product identifiers are
listed in decreasing order of their significance for identifying the listed in decreasing order of their significance for identifying the
user agent software. Each product identifier consists of a name and user agent software. Each product identifier consists of a name and
optional version. optional version.
product = token ["/" product-version] product = token ["/" product-version]
product-version = token product-version = token
A sender SHOULD limit generated product identifiers to what is A sender SHOULD limit generated product identifiers to what is
necessary to identify the product; a sender MUST NOT generate necessary to identify the product; a sender MUST NOT generate
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identified against their wishes ("fingerprinting"). identified against their wishes ("fingerprinting").
Likewise, implementations are encouraged not to use the product Likewise, implementations are encouraged not to use the product
tokens of other implementations in order to declare compatibility tokens of other implementations in order to declare compatibility
with them, as this circumvents the purpose of the field. If a user with them, as this circumvents the purpose of the field. If a user
agent masquerades as a different user agent, recipients can assume agent masquerades as a different user agent, recipients can assume
that the user intentionally desires to see responses tailored for that the user intentionally desires to see responses tailored for
that identified user agent, even if they might not work as well for that identified user agent, even if they might not work as well for
the actual user agent being used. the actual user agent being used.
6. Response Status Codes 9. Response Status Codes
The status-code element is a three-digit integer code giving the The status-code element is a three-digit integer code giving the
result of the attempt to understand and satisfy the request. result of the attempt to understand and satisfy the request.
HTTP status codes are extensible. HTTP clients are not required to HTTP status codes are extensible. HTTP clients are not required to
understand the meaning of all registered status codes, though such understand the meaning of all registered status codes, though such
understanding is obviously desirable. However, a client MUST understanding is obviously desirable. However, a client MUST
understand the class of any status code, as indicated by the first understand the class of any status code, as indicated by the first
digit, and treat an unrecognized status code as being equivalent to digit, and treat an unrecognized status code as being equivalent to
the x00 status code of that class, with the exception that a the x00 status code of that class, with the exception that a
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o 3xx (Redirection): Further action needs to be taken in order to o 3xx (Redirection): Further action needs to be taken in order to
complete the request complete the request
o 4xx (Client Error): The request contains bad syntax or cannot be o 4xx (Client Error): The request contains bad syntax or cannot be
fulfilled fulfilled
o 5xx (Server Error): The server failed to fulfill an apparently o 5xx (Server Error): The server failed to fulfill an apparently
valid request valid request
6.1. Overview of Status Codes 9.1. Overview of Status Codes
The status codes listed below are defined in this specification, The status codes listed below are defined in this specification. The
Section 4 of [CONDTNL], Section 4 of [RANGERQ], and Section 3 of reason phrases listed here are only recommendations -- they can be
[AUTHFRM]. The reason phrases listed here are only recommendations replaced by local equivalents without affecting the protocol.
-- they can be replaced by local equivalents without affecting the
protocol.
Responses with status codes that are defined as cacheable by default Responses with status codes that are defined as cacheable by default
(e.g., 200, 203, 204, 206, 300, 301, 404, 405, 410, 414, and 501 in (e.g., 200, 203, 204, 206, 300, 301, 404, 405, 410, 414, and 501 in
this specification) can be reused by a cache with heuristic this specification) can be reused by a cache with heuristic
expiration unless otherwise indicated by the method definition or expiration unless otherwise indicated by the method definition or
explicit cache controls [CACHING]; all other status codes are not explicit cache controls [Caching]; all other status codes are not
cacheable by default. cacheable by default.
+------+-------------------------------+--------------------------+ +-------+-------------------------------+-----------------+
| Code | Reason-Phrase | Defined in... | | Value | Description | Reference |
+------+-------------------------------+--------------------------+ +-------+-------------------------------+-----------------+
| 100 | Continue | Section 6.2.1 | | 100 | Continue | Section 9.2.1 |
| 101 | Switching Protocols | Section 6.2.2 | | 101 | Switching Protocols | Section 9.2.2 |
| 200 | OK | Section 6.3.1 | | 200 | OK | Section 9.3.1 |
| 201 | Created | Section 6.3.2 | | 201 | Created | Section 9.3.2 |
| 202 | Accepted | Section 6.3.3 | | 202 | Accepted | Section 9.3.3 |
| 203 | Non-Authoritative Information | Section 6.3.4 | | 203 | Non-Authoritative Information | Section 9.3.4 |
| 204 | No Content | Section 6.3.5 | | 204 | No Content | Section 9.3.5 |
| 205 | Reset Content | Section 6.3.6 | | 205 | Reset Content | Section 9.3.6 |
| 206 | Partial Content | Section 4.1 of [RANGERQ] | | 206 | Partial Content | Section 9.3.7 |
| 300 | Multiple Choices | Section 6.4.1 | | 300 | Multiple Choices | Section 9.4.1 |
| 301 | Moved Permanently | Section 6.4.2 | | 301 | Moved Permanently | Section 9.4.2 |
| 302 | Found | Section 6.4.3 | | 302 | Found | Section 9.4.3 |
| 303 | See Other | Section 6.4.4 | | 303 | See Other | Section 9.4.4 |
| 304 | Not Modified | Section 4.1 of [CONDTNL] | | 304 | Not Modified | Section 9.4.5 |
| 305 | Use Proxy | Section 6.4.5 | | 305 | Use Proxy | Section 9.4.6 |
| 307 | Temporary Redirect | Section 6.4.7 | | 306 | (Unused) | Section 9.4.7 |
| 400 | Bad Request | Section 6.5.1 | | 307 | Temporary Redirect | Section 9.4.8 |
| 401 | Unauthorized | Section 3.1 of [AUTHFRM] | | 400 | Bad Request | Section 9.5.1 |
| 402 | Payment Required | Section 6.5.2 | | 401 | Unauthorized | Section 9.5.2 |
| 403 | Forbidden | Section 6.5.3 | | 402 | Payment Required | Section 9.5.3 |
| 404 | Not Found | Section 6.5.4 | | 403 | Forbidden | Section 9.5.4 |
| 405 | Method Not Allowed | Section 6.5.5 | | 404 | Not Found | Section 9.5.5 |
| 406 | Not Acceptable | Section 6.5.6 | | 405 | Method Not Allowed | Section 9.5.6 |
| 407 | Proxy Authentication Required | Section 3.2 of [AUTHFRM] | | 406 | Not Acceptable | Section 9.5.7 |
| 408 | Request Timeout | Section 6.5.7 | | 407 | Proxy Authentication Required | Section 9.5.8 |
| 409 | Conflict | Section 6.5.8 | | 408 | Request Timeout | Section 9.5.9 |
| 410 | Gone | Section 6.5.9 | | 409 | Conflict | Section 9.5.10 |
| 411 | Length Required | Section 6.5.10 | | 410 | Gone | Section 9.5.11 |
| 412 | Precondition Failed | Section 4.2 of [CONDTNL] | | 411 | Length Required | Section 9.5.12 |
| 413 | Payload Too Large | Section 6.5.11 | | 412 | Precondition Failed | Section 9.5.13 |
| 414 | URI Too Long | Section 6.5.12 | | 413 | Payload Too Large | Section 9.5.14 |
| 415 | Unsupported Media Type | Section 6.5.13 | | 414 | URI Too Long | Section 9.5.15 |
| 416 | Range Not Satisfiable | Section 4.4 of [RANGERQ] | | 415 | Unsupported Media Type | Section 9.5.16 |
| 417 | Expectation Failed | Section 6.5.14 | | 416 | Range Not Satisfiable | Section 9.5.17 |
| 426 | Upgrade Required | Section 6.5.15 | | 417 | Expectation Failed | Section 9.5.18 |
| 500 | Internal Server Error | Section 6.6.1 | | 426 | Upgrade Required | Section 9.5.19 |
| 501 | Not Implemented | Section 6.6.2 | | 500 | Internal Server Error | Section 9.6.1 |
| 502 | Bad Gateway | Section 6.6.3 | | 501 | Not Implemented | Section 9.6.2 |
| 503 | Service Unavailable | Section 6.6.4 | | 502 | Bad Gateway | Section 9.6.3 |
| 504 | Gateway Timeout | Section 6.6.5 | | 503 | Service Unavailable | Section 9.6.4 |
| 505 | HTTP Version Not Supported | Section 6.6.6 | | 504 | Gateway Timeout | Section 9.6.5 |
+------+-------------------------------+--------------------------+ | 505 | HTTP Version Not Supported | Section 9.6.6 |
+-------+-------------------------------+-----------------+
Note that this list is not exhaustive -- it does not include Note that this list is not exhaustive -- it does not include
extension status codes defined in other specifications. The complete extension status codes defined in other specifications (Section 9.7).
list of status codes is maintained by IANA. See Section 8.2 for
details.
6.2. Informational 1xx 9.2. Informational 1xx
The 1xx (Informational) class of status code indicates an interim The 1xx (Informational) class of status code indicates an interim
response for communicating connection status or request progress response for communicating connection status or request progress
prior to completing the requested action and sending a final prior to completing the requested action and sending a final
response. 1xx responses are terminated by the first empty line after response. 1xx responses are terminated by the first empty line after
the status-line (the empty line signaling the end of the header the status-line (the empty line signaling the end of the header
section). Since HTTP/1.0 did not define any 1xx status codes, a section). Since HTTP/1.0 did not define any 1xx status codes, a
server MUST NOT send a 1xx response to an HTTP/1.0 client. server MUST NOT send a 1xx response to an HTTP/1.0 client.
A client MUST be able to parse one or more 1xx responses received A client MUST be able to parse one or more 1xx responses received
prior to a final response, even if the client does not expect one. A prior to a final response, even if the client does not expect one. A
user agent MAY ignore unexpected 1xx responses. user agent MAY ignore unexpected 1xx responses.
A proxy MUST forward 1xx responses unless the proxy itself requested A proxy MUST forward 1xx responses unless the proxy itself requested
the generation of the 1xx response. For example, if a proxy adds an the generation of the 1xx response. For example, if a proxy adds an
"Expect: 100-continue" field when it forwards a request, then it need "Expect: 100-continue" field when it forwards a request, then it need
not forward the corresponding 100 (Continue) response(s). not forward the corresponding 100 (Continue) response(s).
6.2.1. 100 Continue 9.2.1. 100 Continue
The 100 (Continue) status code indicates that the initial part of a The 100 (Continue) status code indicates that the initial part of a
request has been received and has not yet been rejected by the request has been received and has not yet been rejected by the
server. The server intends to send a final response after the server. The server intends to send a final response after the
request has been fully received and acted upon. request has been fully received and acted upon.
When the request contains an Expect header field that includes a When the request contains an Expect header field that includes a
100-continue expectation, the 100 response indicates that the server 100-continue expectation, the 100 response indicates that the server
wishes to receive the request payload body, as described in wishes to receive the request payload body, as described in
Section 5.1.1. The client ought to continue sending the request and Section 8.1.1. The client ought to continue sending the request and
discard the 100 response. discard the 100 response.
If the request did not contain an Expect header field containing the If the request did not contain an Expect header field containing the
100-continue expectation, the client can simply discard this interim 100-continue expectation, the client can simply discard this interim
response. response.
6.2.2. 101 Switching Protocols 9.2.2. 101 Switching Protocols
The 101 (Switching Protocols) status code indicates that the server The 101 (Switching Protocols) status code indicates that the server
understands and is willing to comply with the client's request, via understands and is willing to comply with the client's request, via
the Upgrade header field (Section 6.7 of [MESSGNG]), for a change in the Upgrade header field (Section 6.7 of [Messaging]), for a change
the application protocol being used on this connection. The server in the application protocol being used on this connection. The
MUST generate an Upgrade header field in the response that indicates server MUST generate an Upgrade header field in the response that
which protocol(s) will be switched to immediately after the empty indicates which protocol(s) will be switched to immediately after the
line that terminates the 101 response. empty line that terminates the 101 response.
It is assumed that the server will only agree to switch protocols It is assumed that the server will only agree to switch protocols
when it is advantageous to do so. For example, switching to a newer when it is advantageous to do so. For example, switching to a newer
version of HTTP might be advantageous over older versions, and version of HTTP might be advantageous over older versions, and
switching to a real-time, synchronous protocol might be advantageous switching to a real-time, synchronous protocol might be advantageous
when delivering resources that use such features. when delivering resources that use such features.
6.3. Successful 2xx 9.3. Successful 2xx
The 2xx (Successful) class of status code indicates that the client's The 2xx (Successful) class of status code indicates that the client's
request was successfully received, understood, and accepted. request was successfully received, understood, and accepted.
6.3.1. 200 OK 9.3.1. 200 OK
The 200 (OK) status code indicates that the request has succeeded. The 200 (OK) status code indicates that the request has succeeded.
The payload sent in a 200 response depends on the request method. The payload sent in a 200 response depends on the request method.
For the methods defined by this specification, the intended meaning For the methods defined by this specification, the intended meaning
of the payload can be summarized as: of the payload can be summarized as:
GET a representation of the target resource; GET a representation of the target resource;
HEAD the same representation as GET, but without the representation HEAD the same representation as GET, but without the representation
data; data;
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Aside from responses to CONNECT, a 200 response always has a payload, Aside from responses to CONNECT, a 200 response always has a payload,
though an origin server MAY generate a payload body of zero length. though an origin server MAY generate a payload body of zero length.
If no payload is desired, an origin server ought to send 204 (No If no payload is desired, an origin server ought to send 204 (No
Content) instead. For CONNECT, no payload is allowed because the Content) instead. For CONNECT, no payload is allowed because the
successful result is a tunnel, which begins immediately after the 200 successful result is a tunnel, which begins immediately after the 200
response header section. response header section.
A 200 response is cacheable by default; i.e., unless otherwise A 200 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 [CACHING]). Section 4.2.2 of [Caching]).
6.3.2. 201 Created 9.3.2. 201 Created
The 201 (Created) status code indicates that the request has been The 201 (Created) status code indicates that the request has been
fulfilled and has resulted in one or more new resources being fulfilled and has resulted in one or more new resources being
created. The primary resource created by the request is identified created. The primary resource created by the request is identified
by either a Location header field in the response or, if no Location by either a Location header field in the response or, if no Location
field is received, by the effective request URI. field is received, by the effective request URI.
The 201 response payload typically describes and links to the The 201 response payload typically describes and links to the
resource(s) created. See Section 7.2 for a discussion of the meaning resource(s) created. See Section 10.2 for a discussion of the
and purpose of validator header fields, such as ETag and Last- meaning and purpose of validator header fields, such as ETag and
Modified, in a 201 response. Last-Modified, in a 201 response.
6.3.3. 202 Accepted 9.3.3. 202 Accepted
The 202 (Accepted) status code indicates that the request has been The 202 (Accepted) status code indicates that the request has been
accepted for processing, but the processing has not been completed. accepted for processing, but the processing has not been completed.
The request might or might not eventually be acted upon, as it might The request might or might not eventually be acted upon, as it might
be disallowed when processing actually takes place. There is no be disallowed when processing actually takes place. There is no
facility in HTTP for re-sending a status code from an asynchronous facility in HTTP for re-sending a status code from an asynchronous
operation. operation.
The 202 response is intentionally noncommittal. Its purpose is to The 202 response is intentionally noncommittal. Its purpose is to
allow a server to accept a request for some other process (perhaps a allow a server to accept a request for some other process (perhaps a
batch-oriented process that is only run once per day) without batch-oriented process that is only run once per day) without
requiring that the user agent's connection to the server persist requiring that the user agent's connection to the server persist
until the process is completed. The representation sent with this until the process is completed. The representation sent with this
response ought to describe the request's current status and point to response ought to describe the request's current status and point to
(or embed) a status monitor that can provide the user with an (or embed) a status monitor that can provide the user with an
estimate of when the request will be fulfilled. estimate of when the request will be fulfilled.
6.3.4. 203 Non-Authoritative Information 9.3.4. 203 Non-Authoritative Information
The 203 (Non-Authoritative Information) status code indicates that The 203 (Non-Authoritative Information) status code indicates that
the request was successful but the enclosed payload has been modified the request was successful but the enclosed payload has been modified
from that of the origin server's 200 (OK) response by a transforming from that of the origin server's 200 (OK) response by a transforming
proxy (Section 5.7.2 of [MESSGNG]). This status code allows the proxy (Section 5.6.2). This status code allows the proxy to notify
proxy to notify recipients when a transformation has been applied, recipients when a transformation has been applied, since that
since that knowledge might impact later decisions regarding the knowledge might impact later decisions regarding the content. For
content. For example, future cache validation requests for the example, future cache validation requests for the content might only
content might only be applicable along the same request path (through be applicable along the same request path (through the same proxies).
the same proxies).
The 203 response is similar to the Warning code of 214 Transformation The 203 response is similar to the Warning code of 214 Transformation
Applied (Section 5.5 of [CACHING]), which has the advantage of being Applied (Section 5.5 of [Caching]), which has the advantage of being
applicable to responses with any status code. applicable to responses with any status code.
A 203 response is cacheable by default; i.e., unless otherwise A 203 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 [CACHING]). Section 4.2.2 of [Caching]).
6.3.5. 204 No Content 9.3.5. 204 No Content
The 204 (No Content) status code indicates that the server has The 204 (No Content) status code indicates that the server has
successfully fulfilled the request and that there is no additional successfully fulfilled the request and that there is no additional
content to send in the response payload body. Metadata in the content to send in the response payload body. Metadata in the
response header fields refer to the target resource and its selected response header fields refer to the target resource and its selected
representation after the requested action was applied. representation after the requested action was applied.
For example, if a 204 status code is received in response to a PUT For example, if a 204 status code is received in response to a PUT
request and the response contains an ETag header field, then the PUT request and the response contains an ETag header field, then the PUT
was successful and the ETag field-value contains the entity-tag for was successful and the ETag field-value contains the entity-tag for
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interfaces corresponding to a "save" action, such that the document interfaces corresponding to a "save" action, such that the document
being saved remains available to the user for editing. It is also being saved remains available to the user for editing. It is also
frequently used with interfaces that expect automated data transfers frequently used with interfaces that expect automated data transfers
to be prevalent, such as within distributed version control systems. to be prevalent, such as within distributed version control systems.
A 204 response is terminated by the first empty line after the header A 204 response is terminated by the first empty line after the header
fields because it cannot contain a message body. fields because it cannot contain a message body.
A 204 response is cacheable by default; i.e., unless otherwise A 204 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 [CACHING]). Section 4.2.2 of [Caching]).
6.3.6. 205 Reset Content 9.3.6. 205 Reset Content
The 205 (Reset Content) status code indicates that the server has The 205 (Reset Content) status code indicates that the server has
fulfilled the request and desires that the user agent reset the fulfilled the request and desires that the user agent reset the
"document view", which caused the request to be sent, to its original "document view", which caused the request to be sent, to its original
state as received from the origin server.