< draft-ietf-httpbis-p2-semantics-21.txt   draft-ietf-httpbis-p2-semantics-22.txt >
HTTPbis Working Group R. Fielding, Ed. HTTPbis Working Group R. Fielding, Ed.
Internet-Draft Adobe Internet-Draft Adobe
Obsoletes: 2616 (if approved) J. Reschke, Ed. Obsoletes: 2616 (if approved) J. Reschke, Ed.
Updates: 2817 (if approved) greenbytes Updates: 2817 (if approved) greenbytes
Intended status: Standards Track October 4, 2012 Intended status: Standards Track February 23, 2013
Expires: April 7, 2013 Expires: August 27, 2013
Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content
draft-ietf-httpbis-p2-semantics-21 draft-ietf-httpbis-p2-semantics-22
Abstract Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypertext information 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/1.1 messages,
as expressed by request methods, request header fields, response as expressed by request methods, request header fields, response
status codes, and response header fields, along with the payload of status codes, and response header fields, along with the payload of
messages (metadata and body content) and mechanisms for content messages (metadata and body content) and mechanisms for content
negotiation. negotiation.
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Discussion of this draft takes place on the HTTPBIS working group Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at
<http://lists.w3.org/Archives/Public/ietf-http-wg/>. <http://lists.w3.org/Archives/Public/ietf-http-wg/>.
The current issues list is at The current issues list is at
<http://tools.ietf.org/wg/httpbis/trac/report/3> and related <http://tools.ietf.org/wg/httpbis/trac/report/3> and related
documents (including fancy diffs) can be found at documents (including fancy diffs) can be found at
<http://tools.ietf.org/wg/httpbis/>. <http://tools.ietf.org/wg/httpbis/>.
The changes in this draft are summarized in Appendix F.41. The changes in this draft are summarized in Appendix E.2.
Status of This Memo Status of This Memo
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Conformance and Error Handling . . . . . . . . . . . . . 7 1.1. Conformance and Error Handling . . . . . . . . . . . . . . 6
1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 7 1.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6
2. Resource . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2. Resources . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Representation . . . . . . . . . . . . . . . . . . . . . . . 8 3. Representations . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Representation Metadata . . . . . . . . . . . . . . . . . 8 3.1. Representation Metadata . . . . . . . . . . . . . . . . . 8
3.1.1. Data Type . . . . . . . . . . . . . . . . . . . . . . 9 3.1.1. Processing the Data . . . . . . . . . . . . . . . . . 8
3.1.2. Data Encoding . . . . . . . . . . . . . . . . . . . . 12 3.1.2. Encoding for Compression or Integrity . . . . . . . . 11
3.1.3. Audience Language . . . . . . . . . . . . . . . . . . 14 3.1.3. Audience Language . . . . . . . . . . . . . . . . . . 13
3.1.4. Identification . . . . . . . . . . . . . . . . . . . 15 3.1.4. Identification . . . . . . . . . . . . . . . . . . . . 14
3.2. Representation Data . . . . . . . . . . . . . . . . . . . 18 3.2. Representation Data . . . . . . . . . . . . . . . . . . . 17
3.3. Payload Semantics . . . . . . . . . . . . . . . . . . . . 18 3.3. Payload Semantics . . . . . . . . . . . . . . . . . . . . 17
3.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 19 3.4. Content Negotiation . . . . . . . . . . . . . . . . . . . 18
3.4.1. Proactive Negotiation . . . . . . . . . . . . . . . . 20 3.4.1. Proactive Negotiation . . . . . . . . . . . . . . . . 18
3.4.2. Reactive Negotiation . . . . . . . . . . . . . . . . 21 3.4.2. Reactive Negotiation . . . . . . . . . . . . . . . . . 19
4. Product Tokens . . . . . . . . . . . . . . . . . . . . . . . 22 4. Request Methods . . . . . . . . . . . . . . . . . . . . . . . 20
5. Request Methods . . . . . . . . . . . . . . . . . . . . . . . 22 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 22 4.2. Common Method Properties . . . . . . . . . . . . . . . . . 22
5.2. Common Method Properties . . . . . . . . . . . . . . . . 24 4.2.1. Safe Methods . . . . . . . . . . . . . . . . . . . . . 22
5.2.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 24 4.2.2. Idempotent Methods . . . . . . . . . . . . . . . . . . 23
5.2.2. Idempotent Methods . . . . . . . . . . . . . . . . . 25 4.2.3. Cacheable Methods . . . . . . . . . . . . . . . . . . 23
5.2.3. Cacheable Methods . . . . . . . . . . . . . . . . . . 25 4.3. Method Definitions . . . . . . . . . . . . . . . . . . . . 23
5.3. Method Definitions . . . . . . . . . . . . . . . . . . . 25 4.3.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.3.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 25 4.3.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.3.2. HEAD . . . . . . . . . . . . . . . . . . . . . . . . 26 4.3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . 27 4.3.4. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.3.4. PUT . . . . . . . . . . . . . . . . . . . . . . . . . 28 4.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . . 28
5.3.5. DELETE . . . . . . . . . . . . . . . . . . . . . . . 30 4.3.6. CONNECT . . . . . . . . . . . . . . . . . . . . . . . 29
5.3.6. CONNECT . . . . . . . . . . . . . . . . . . . . . . . 30 4.3.7. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . 31
5.3.7. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . 32 4.3.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . 32
5.3.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . 33 5. Request Header Fields . . . . . . . . . . . . . . . . . . . . 32
6. Request Header Fields . . . . . . . . . . . . . . . . . . . . 33 5.1. Controls . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.1. Controls . . . . . . . . . . . . . . . . . . . . . . . . 33 5.1.1. Expect . . . . . . . . . . . . . . . . . . . . . . . . 33
6.1.1. Max-Forwards . . . . . . . . . . . . . . . . . . . . 34 5.1.2. Max-Forwards . . . . . . . . . . . . . . . . . . . . . 36
6.1.2. Expect . . . . . . . . . . . . . . . . . . . . . . . 34 5.2. Conditionals . . . . . . . . . . . . . . . . . . . . . . . 36
6.2. Conditionals . . . . . . . . . . . . . . . . . . . . . . 37 5.3. Content Negotiation . . . . . . . . . . . . . . . . . . . 37
6.3. Content Negotiation . . . . . . . . . . . . . . . . . . . 38 5.3.1. Quality Values . . . . . . . . . . . . . . . . . . . . 37
6.3.1. Quality Values . . . . . . . . . . . . . . . . . . . 38 5.3.2. Accept . . . . . . . . . . . . . . . . . . . . . . . . 38
6.3.2. Accept . . . . . . . . . . . . . . . . . . . . . . . 38 5.3.3. Accept-Charset . . . . . . . . . . . . . . . . . . . . 40
6.3.3. Accept-Charset . . . . . . . . . . . . . . . . . . . 41 5.3.4. Accept-Encoding . . . . . . . . . . . . . . . . . . . 41
6.3.4. Accept-Encoding . . . . . . . . . . . . . . . . . . . 41 5.3.5. Accept-Language . . . . . . . . . . . . . . . . . . . 42
6.3.5. Accept-Language . . . . . . . . . . . . . . . . . . . 42 5.4. Authentication Credentials . . . . . . . . . . . . . . . . 43
6.4. Authentication Credentials . . . . . . . . . . . . . . . 44 5.5. Request Context . . . . . . . . . . . . . . . . . . . . . 43
6.5. Context . . . . . . . . . . . . . . . . . . . . . . . . . 44 5.5.1. From . . . . . . . . . . . . . . . . . . . . . . . . . 44
6.5.1. From . . . . . . . . . . . . . . . . . . . . . . . . 44 5.5.2. Referer . . . . . . . . . . . . . . . . . . . . . . . 44
6.5.2. Referer . . . . . . . . . . . . . . . . . . . . . . . 45 5.5.3. User-Agent . . . . . . . . . . . . . . . . . . . . . . 45
6.5.3. User-Agent . . . . . . . . . . . . . . . . . . . . . 45 6. Response Status Codes . . . . . . . . . . . . . . . . . . . . 46
7. Response Status Codes . . . . . . . . . . . . . . . . . . . . 46 6.1. Overview of Status Codes . . . . . . . . . . . . . . . . . 47
7.1. Overview of Status Codes . . . . . . . . . . . . . . . . 47 6.2. Informational 1xx . . . . . . . . . . . . . . . . . . . . 49
7.2. Informational 1xx . . . . . . . . . . . . . . . . . . . . 49 6.2.1. 100 Continue . . . . . . . . . . . . . . . . . . . . . 49
7.2.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 49 6.2.2. 101 Switching Protocols . . . . . . . . . . . . . . . 50
7.2.2. 101 Switching Protocols . . . . . . . . . . . . . . . 49 6.3. Successful 2xx . . . . . . . . . . . . . . . . . . . . . . 50
7.3. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 50 6.3.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . . 50
7.3.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 50 6.3.2. 201 Created . . . . . . . . . . . . . . . . . . . . . 51
7.3.2. 201 Created . . . . . . . . . . . . . . . . . . . . . 50 6.3.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . . 51
7.3.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 51 6.3.4. 203 Non-Authoritative Information . . . . . . . . . . 51
7.3.4. 203 Non-Authoritative Information . . . . . . . . . . 51 6.3.5. 204 No Content . . . . . . . . . . . . . . . . . . . . 52
7.3.5. 204 No Content . . . . . . . . . . . . . . . . . . . 51 6.3.6. 205 Reset Content . . . . . . . . . . . . . . . . . . 52
7.3.6. 205 Reset Content . . . . . . . . . . . . . . . . . . 52 6.4. Redirection 3xx . . . . . . . . . . . . . . . . . . . . . 53
7.4. Redirection 3xx . . . . . . . . . . . . . . . . . . . . . 52 6.4.1. 300 Multiple Choices . . . . . . . . . . . . . . . . . 54
7.4.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 54 6.4.2. 301 Moved Permanently . . . . . . . . . . . . . . . . 55
7.4.2. 301 Moved Permanently . . . . . . . . . . . . . . . . 54 6.4.3. 302 Found . . . . . . . . . . . . . . . . . . . . . . 55
7.4.3. 302 Found . . . . . . . . . . . . . . . . . . . . . . 55 6.4.4. 303 See Other . . . . . . . . . . . . . . . . . . . . 56
7.4.4. 303 See Other . . . . . . . . . . . . . . . . . . . . 55 6.4.5. 305 Use Proxy . . . . . . . . . . . . . . . . . . . . 56
7.4.5. 305 Use Proxy . . . . . . . . . . . . . . . . . . . . 56 6.4.6. 306 (Unused) . . . . . . . . . . . . . . . . . . . . . 56
7.4.6. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 56 6.4.7. 307 Temporary Redirect . . . . . . . . . . . . . . . . 57
7.4.7. 307 Temporary Redirect . . . . . . . . . . . . . . . 56 6.5. Client Error 4xx . . . . . . . . . . . . . . . . . . . . . 57
7.5. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 56 6.5.1. 400 Bad Request . . . . . . . . . . . . . . . . . . . 57
7.5.1. 400 Bad Request . . . . . . . . . . . . . . . . . . . 56 6.5.2. 402 Payment Required . . . . . . . . . . . . . . . . . 57
7.5.2. 402 Payment Required . . . . . . . . . . . . . . . . 56 6.5.3. 403 Forbidden . . . . . . . . . . . . . . . . . . . . 57
7.5.3. 403 Forbidden . . . . . . . . . . . . . . . . . . . . 57 6.5.4. 404 Not Found . . . . . . . . . . . . . . . . . . . . 58
7.5.4. 404 Not Found . . . . . . . . . . . . . . . . . . . . 57 6.5.5. 405 Method Not Allowed . . . . . . . . . . . . . . . . 58
7.5.5. 405 Method Not Allowed . . . . . . . . . . . . . . . 57 6.5.6. 406 Not Acceptable . . . . . . . . . . . . . . . . . . 58
7.5.6. 406 Not Acceptable . . . . . . . . . . . . . . . . . 57 6.5.7. 408 Request Timeout . . . . . . . . . . . . . . . . . 59
7.5.7. 408 Request Timeout . . . . . . . . . . . . . . . . . 58 6.5.8. 409 Conflict . . . . . . . . . . . . . . . . . . . . . 59
7.5.8. 409 Conflict . . . . . . . . . . . . . . . . . . . . 58 6.5.9. 410 Gone . . . . . . . . . . . . . . . . . . . . . . . 59
7.5.9. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 58 6.5.10. 411 Length Required . . . . . . . . . . . . . . . . . 60
7.5.10. 411 Length Required . . . . . . . . . . . . . . . . . 59 6.5.11. 413 Payload Too Large . . . . . . . . . . . . . . . . 60
7.5.11. 413 Request Representation Too Large . . . . . . . . 59 6.5.12. 414 URI Too Long . . . . . . . . . . . . . . . . . . . 60
7.5.12. 414 URI Too Long . . . . . . . . . . . . . . . . . . 59 6.5.13. 415 Unsupported Media Type . . . . . . . . . . . . . . 60
7.5.13. 415 Unsupported Media Type . . . . . . . . . . . . . 59 6.5.14. 417 Expectation Failed . . . . . . . . . . . . . . . . 61
7.5.14. 417 Expectation Failed . . . . . . . . . . . . . . . 60 6.5.15. 426 Upgrade Required . . . . . . . . . . . . . . . . . 61
7.5.15. 426 Upgrade Required . . . . . . . . . . . . . . . . 60 6.6. Server Error 5xx . . . . . . . . . . . . . . . . . . . . . 61
7.6. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 60 6.6.1. 500 Internal Server Error . . . . . . . . . . . . . . 61
7.6.1. 500 Internal Server Error . . . . . . . . . . . . . . 60 6.6.2. 501 Not Implemented . . . . . . . . . . . . . . . . . 61
7.6.2. 501 Not Implemented . . . . . . . . . . . . . . . . . 60 6.6.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . . 62
7.6.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . . 61 6.6.4. 503 Service Unavailable . . . . . . . . . . . . . . . 62
7.6.4. 503 Service Unavailable . . . . . . . . . . . . . . . 61 6.6.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . . 62
7.6.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . . 61 6.6.6. 505 HTTP Version Not Supported . . . . . . . . . . . . 62
7.6.6. 505 HTTP Version Not Supported . . . . . . . . . . . 61 7. Response Header Fields . . . . . . . . . . . . . . . . . . . . 62
8. Response Header Fields . . . . . . . . . . . . . . . . . . . 61 7.1. Control Data . . . . . . . . . . . . . . . . . . . . . . . 63
8.1. Control Data . . . . . . . . . . . . . . . . . . . . . . 62 7.1.1. Origination Date . . . . . . . . . . . . . . . . . . . 63
8.1.1. Origination Date . . . . . . . . . . . . . . . . . . 62 7.1.2. Location . . . . . . . . . . . . . . . . . . . . . . . 66
8.1.2. Location . . . . . . . . . . . . . . . . . . . . . . 65 7.1.3. Retry-After . . . . . . . . . . . . . . . . . . . . . 68
8.1.3. Retry-After . . . . . . . . . . . . . . . . . . . . . 66 7.1.4. Vary . . . . . . . . . . . . . . . . . . . . . . . . . 68
8.2. Selected Representation Header Fields . . . . . . . . . . 67 7.2. Validator Header Fields . . . . . . . . . . . . . . . . . 69
8.2.1. Vary . . . . . . . . . . . . . . . . . . . . . . . . 67 7.3. Authentication Challenges . . . . . . . . . . . . . . . . 70
8.3. Authentication Challenges . . . . . . . . . . . . . . . . 68 7.4. Response Context . . . . . . . . . . . . . . . . . . . . . 70
8.4. Informative . . . . . . . . . . . . . . . . . . . . . . . 68 7.4.1. Allow . . . . . . . . . . . . . . . . . . . . . . . . 71
8.4.1. Allow . . . . . . . . . . . . . . . . . . . . . . . . 69 7.4.2. Server . . . . . . . . . . . . . . . . . . . . . . . . 71
8.4.2. Server . . . . . . . . . . . . . . . . . . . . . . . 69 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 72
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 70 8.1. Method Registry . . . . . . . . . . . . . . . . . . . . . 72
9.1. Method Registry . . . . . . . . . . . . . . . . . . . . . 70 8.1.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 72
9.1.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 70 8.1.2. Considerations for New Methods . . . . . . . . . . . . 72
9.1.2. Considerations for New Methods . . . . . . . . . . . 70 8.1.3. Registrations . . . . . . . . . . . . . . . . . . . . 73
9.1.3. Registrations . . . . . . . . . . . . . . . . . . . . 71 8.2. Status Code Registry . . . . . . . . . . . . . . . . . . . 73
9.2. Status Code Registry . . . . . . . . . . . . . . . . . . 71 8.2.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 73
9.2.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 71 8.2.2. Considerations for New Status Codes . . . . . . . . . 73
9.2.2. Considerations for New Status Codes . . . . . . . . . 71 8.2.3. Registrations . . . . . . . . . . . . . . . . . . . . 74
9.2.3. Registrations . . . . . . . . . . . . . . . . . . . . 72 8.3. Header Field Registry . . . . . . . . . . . . . . . . . . 75
9.3. Header Field Registry . . . . . . . . . . . . . . . . . . 73 8.3.1. Considerations for New Header Fields . . . . . . . . . 76
9.3.1. Considerations for New Header Fields . . . . . . . . 74 8.3.2. Registrations . . . . . . . . . . . . . . . . . . . . 78
9.3.2. Registrations . . . . . . . . . . . . . . . . . . . . 75 8.4. Content Coding Registry . . . . . . . . . . . . . . . . . 78
8.4.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 78
9.4. Content Coding Registry . . . . . . . . . . . . . . . . . 76 8.4.2. Registrations . . . . . . . . . . . . . . . . . . . . 79
9.4.1. Procedure . . . . . . . . . . . . . . . . . . . . . . 76 9. Security Considerations . . . . . . . . . . . . . . . . . . . 79
9.4.2. Registrations . . . . . . . . . . . . . . . . . . . . 77 9.1. Attacks Based On File and Path Names . . . . . . . . . . . 79
10. Security Considerations . . . . . . . . . . . . . . . . . . . 77 9.2. Personal Information . . . . . . . . . . . . . . . . . . . 80
10.1. Transfer of Sensitive Information . . . . . . . . . . . . 77 9.3. Sensitive Information in URIs . . . . . . . . . . . . . . 80
10.2. Encoding Sensitive Information in URIs . . . . . . . . . 78 9.4. Product Information . . . . . . . . . . . . . . . . . . . 81
10.3. Location Header Fields: Spoofing and Information 9.5. Fragment after Redirects . . . . . . . . . . . . . . . . . 81
Leakage . . . . . . . . . . . . . . . . . . . . . . . . . 79 9.6. Browser Fingerprinting . . . . . . . . . . . . . . . . . . 81
10.4. Security Considerations for CONNECT . . . . . . . . . . . 79 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 82
10.5. Privacy Issues Connected to Accept Header Fields . . . . 79 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 82
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 80 11.1. Normative References . . . . . . . . . . . . . . . . . . . 82
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 80 11.2. Informative References . . . . . . . . . . . . . . . . . . 84
12.1. Normative References . . . . . . . . . . . . . . . . . . 80 Appendix A. Differences between HTTP and MIME . . . . . . . . . . 85
12.2. Informative References . . . . . . . . . . . . . . . . . 81 A.1. MIME-Version . . . . . . . . . . . . . . . . . . . . . . . 86
Appendix A. Differences between HTTP and MIME . . . . . . . . . 83 A.2. Conversion to Canonical Form . . . . . . . . . . . . . . . 86
A.1. MIME-Version . . . . . . . . . . . . . . . . . . . . . . 84 A.3. Conversion of Date Formats . . . . . . . . . . . . . . . . 86
A.2. Conversion to Canonical Form . . . . . . . . . . . . . . 84 A.4. Conversion of Content-Encoding . . . . . . . . . . . . . . 87
A.3. Conversion of Date Formats . . . . . . . . . . . . . . . 84 A.5. Conversion of Content-Transfer-Encoding . . . . . . . . . 87
A.4. Introduction of Content-Encoding . . . . . . . . . . . . 85 A.6. MHTML and Line Length Limitations . . . . . . . . . . . . 87
A.5. No Content-Transfer-Encoding . . . . . . . . . . . . . . 85 Appendix B. Changes from RFC 2616 . . . . . . . . . . . . . . . . 87
A.6. MHTML and Line Length Limitations . . . . . . . . . . . . 85 Appendix C. Imported ABNF . . . . . . . . . . . . . . . . . . . . 90
Appendix B. Additional Features . . . . . . . . . . . . . . . . 85 Appendix D. Collected ABNF . . . . . . . . . . . . . . . . . . . 90
Appendix C. Changes from RFC 2616 . . . . . . . . . . . . . . . 86 Appendix E. Change Log (to be removed by RFC Editor before
Appendix D. Imported ABNF . . . . . . . . . . . . . . . . . . . 88 publication) . . . . . . . . . . . . . . . . . . . . 93
Appendix E. Collected ABNF . . . . . . . . . . . . . . . . . . . 88 E.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . . 93
Appendix F. Change Log (to be removed by RFC Editor before E.2. Since draft-ietf-httpbis-p2-semantics-21 . . . . . . . . . 94
publication) . . . . . . . . . . . . . . . . . . . . 91 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
F.1. Since RFC 2616 . . . . . . . . . . . . . . . . . . . . . 91
F.2. Since draft-ietf-httpbis-p2-semantics-00 . . . . . . . . 91
F.3. Since draft-ietf-httpbis-p3-payload-00 . . . . . . . . . 92
F.4. Since draft-ietf-httpbis-p2-semantics-01 . . . . . . . . 93
F.5. Since draft-ietf-httpbis-p3-payload-01 . . . . . . . . . 93
F.6. Since draft-ietf-httpbis-p2-semantics-02 . . . . . . . . 93
F.7. Since draft-ietf-httpbis-p3-payload-02 . . . . . . . . . 94
F.8. Since draft-ietf-httpbis-p2-semantics-03 . . . . . . . . 95
F.9. Since draft-ietf-httpbis-p3-payload-03 . . . . . . . . . 95
F.10. Since draft-ietf-httpbis-p2-semantics-04 . . . . . . . . 95
F.11. Since draft-ietf-httpbis-p3-payload-04 . . . . . . . . . 96
F.12. Since draft-ietf-httpbis-p2-semantics-05 . . . . . . . . 96
F.13. Since draft-ietf-httpbis-p3-payload-05 . . . . . . . . . 96
F.14. Since draft-ietf-httpbis-p2-semantics-06 . . . . . . . . 97
F.15. Since draft-ietf-httpbis-p3-payload-06 . . . . . . . . . 97
F.16. Since draft-ietf-httpbis-p2-semantics-07 . . . . . . . . 97
F.17. Since draft-ietf-httpbis-p3-payload-07 . . . . . . . . . 98
F.18. Since draft-ietf-httpbis-p2-semantics-08 . . . . . . . . 99
F.19. Since draft-ietf-httpbis-p3-payload-08 . . . . . . . . . 99
F.20. Since draft-ietf-httpbis-p2-semantics-09 . . . . . . . . 99
F.21. Since draft-ietf-httpbis-p3-payload-09 . . . . . . . . . 99
F.22. Since draft-ietf-httpbis-p2-semantics-10 . . . . . . . . 100
F.23. Since draft-ietf-httpbis-p3-payload-10 . . . . . . . . . 100
F.24. Since draft-ietf-httpbis-p2-semantics-11 . . . . . . . . 101
F.25. Since draft-ietf-httpbis-p3-payload-11 . . . . . . . . . 101
F.26. Since draft-ietf-httpbis-p2-semantics-12 . . . . . . . . 101
F.27. Since draft-ietf-httpbis-p3-payload-12 . . . . . . . . . 103
F.28. Since draft-ietf-httpbis-p2-semantics-13 . . . . . . . . 103
F.29. Since draft-ietf-httpbis-p3-payload-13 . . . . . . . . . 103
F.30. Since draft-ietf-httpbis-p2-semantics-14 . . . . . . . . 103
F.31. Since draft-ietf-httpbis-p3-payload-14 . . . . . . . . . 104
F.32. Since draft-ietf-httpbis-p2-semantics-15 . . . . . . . . 104
F.33. Since draft-ietf-httpbis-p3-payload-15 . . . . . . . . . 104
F.34. Since draft-ietf-httpbis-p2-semantics-16 . . . . . . . . 104
F.35. Since draft-ietf-httpbis-p3-payload-16 . . . . . . . . . 104
F.36. Since draft-ietf-httpbis-p2-semantics-17 . . . . . . . . 105
F.37. Since draft-ietf-httpbis-p3-payload-17 . . . . . . . . . 105
F.38. Since draft-ietf-httpbis-p2-semantics-18 . . . . . . . . 105
F.39. Since draft-ietf-httpbis-p3-payload-18 . . . . . . . . . 106
F.40. Since draft-ietf-httpbis-p2-semantics-19 and
draft-ietf-httpbis-p3-payload-19 . . . . . . . . . . . . 106
F.41. Since draft-ietf-httpbis-p2-semantics-20 . . . . . . . . 107
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
1. Introduction 1. Introduction
Each Hypertext Transfer Protocol (HTTP) message is either a request Each Hypertext Transfer Protocol (HTTP) message is either a request
or a response. A server listens on a connection for a request, or a response. A server listens on a connection for a request,
parses each message received, interprets the message semantics in parses each message received, interprets the message semantics in
relation to the identified request target, and responds to that relation to the identified request target, and responds to that
request with one or more response messages. A client constructs request with one or more response messages. A client constructs
request messages to communicate specific intentions, and examines request messages to communicate specific intentions, and examines
received responses to see if the intentions were carried out and received responses to see if the intentions were carried out and
determine how to interpret the results. This document defines determine how to interpret the results. This document defines
HTTP/1.1 request and response semantics in terms of the architecture HTTP/1.1 request and response semantics in terms of the architecture
defined in [Part1]. defined in [Part1].
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, and (Section 2), regardless of its type, nature, or implementation, via
for transferring content in message payloads in the form of a the manipulation and transfer of representations (Section 3).
representation (Section 3).
HTTP semantics include the intentions defined by each request method HTTP semantics include the intentions defined by each request method
(Section 5), extensions to those semantics that might be described in (Section 4), extensions to those semantics that might be described in
request header fields (Section 6), the meaning of status codes to request header fields (Section 5), the meaning of status codes to
indicate a machine-readable response (Section 7), and the meaning of indicate a machine-readable response (Section 6), and the meaning of
other control data and resource metadata that might be given in other control data and resource metadata that might be given in
response header fields (Section 8). response header fields (Section 7).
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 3.4).
1.1. Conformance and Error Handling 1.1. Conformance and Error Handling
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 [Part1]. defined in Section 2.5 of [Part1].
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 the list rule extension defined in Section notation of [RFC5234] with the list rule extension defined in Section
1.2 of [Part1]. Appendix D describes rules imported from other 1.2 of [Part1]. Appendix C describes rules imported from other
documents. Appendix E shows the collected ABNF with the list rule documents. Appendix D shows the collected ABNF with the list rule
expanded. expanded.
2. Resource This specification uses the terms "character", "character encoding
scheme", "charset", and "protocol element" as they are defined in
[RFC6365].
2. Resources
The target of each HTTP request is called a resource. HTTP does not The target of each 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 [Part1]. Section 2.7 of [Part1].
When a client constructs an HTTP/1.1 request message, it sends the 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 target URI in one of various forms, as defined in (Section 5.3 of
[Part1]). When a request is received, the server reconstructs an [Part1]). When a request is received, the server reconstructs an
"effective request URI" for the target resource (Section 5.5 of effective request URI for the target resource (Section 5.5 of
[Part1]). [Part1]).
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 5) and a few request- semantics in the request method (Section 4) and a few request-
modifying header fields (Section 6). Resource owners SHOULD NOT modifying header fields (Section 5). Resource owners SHOULD NOT
include request semantics within a URI, such as by specifying an include request semantics within a URI, such as by specifying an
action to invoke within the path or query components of the effective action to invoke within the path or query components of the effective
request URI, unless those semantics are disabled when they are request URI, unless those semantics are disabled when they are
inconsistent with the request method. inconsistent with the request method.
3. Representation 3. Representations
If we consider that a resource could be anything, and that the If we consider that a resource could be anything, and that the
uniform interface provided by HTTP is similar to a window through uniform interface provided by HTTP is similar to a window through
which one can observe and act upon such a thing only through the which one can observe and act upon such a thing only through the
communication of messages to some independent actor on the other communication of messages to some independent actor on the other
side, then we need an abstraction to represent ("take the place of") side, then we need an abstraction to represent ("take the place of")
the current or desired state of that thing in our communications. We the current or desired state of that thing in our communications. We
call that abstraction a "representation" [REST]. call that abstraction a representation [REST].
For the purposes of HTTP, a representation is information that For the purposes of HTTP, a "representation" is information that is
reflects the current or desired state of a given resource, in a intended to reflect a past, current, or desired state of a given
format that can be readily communicated via the protocol, consisting resource, in a format that can be readily communicated via the
of a set of representation metadata and a potentially unbounded protocol, and that consists of a set of representation metadata and a
stream of representation data. potentially unbounded stream of representation data.
An origin server might be provided with, or capable of generating,
multiple representations that are each intended to reflect the
current state of a target resource. In such cases, some algorithm is
used by the origin server to select one of those representations as
most applicable to a given request, usually based on content
negotiation. We refer to that one representation as the "selected
representation" and use its particular data and metadata for
evaluating conditional requests [Part4] and constructing the payload
for 200 (OK) and 304 (Not Modified) responses to GET (Section 4.3.1).
3.1. Representation Metadata 3.1. Representation Metadata
Representation header fields provide metadata about the Representation header fields provide metadata about the
representation. When a message includes a payload body, the representation. When a message includes a payload body, the
representation header fields describe how to interpret the representation header fields describe how to interpret the
representation data enclosed in the payload body. In a response to a representation data enclosed in the payload body. In a response to a
HEAD request, the representation header fields describe the HEAD request, the representation header fields describe the
representation data that would have been enclosed in the payload body representation data that would have been enclosed in the payload body
if the same request had been a GET. if the same request had been a GET.
The following header fields are defined to convey representation The following header fields are defined to convey representation
metadata: metadata:
+-------------------+------------------------+ +-------------------+-----------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+------------------------+ +-------------------+-----------------+
| Content-Type | Section 3.1.1.5 | | Content-Type | Section 3.1.1.5 |
| Content-Encoding | Section 3.1.2.2 | | Content-Encoding | Section 3.1.2.2 |
| Content-Language | Section 3.1.3.2 | | Content-Language | Section 3.1.3.2 |
| Content-Location | Section 3.1.4.2 | | Content-Location | Section 3.1.4.2 |
| Expires | Section 7.3 of [Part6] | +-------------------+-----------------+
+-------------------+------------------------+
3.1.1. Data Type 3.1.1. Processing the Data
3.1.1.1. Media Types 3.1.1.1. Media Type
HTTP uses Internet Media Types [RFC2046] in the Content-Type HTTP uses Internet Media Types [RFC2046] in the Content-Type
(Section 3.1.1.5) and Accept (Section 6.3.2) header fields in order (Section 3.1.1.5) and Accept (Section 5.3.2) header fields in order
to provide open and extensible data typing and type negotiation. to provide open and extensible data typing and type negotiation.
Media types define both a data format and various processing models:
how to process that data in accordance with each context in which it
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
attribute/value pairs. attribute/value pairs.
parameter = attribute "=" value parameter = attribute "=" value
attribute = token attribute = token
skipping to change at page 9, line 46 skipping to change at page 9, line 14
The type, subtype, and parameter attribute names are case- The type, subtype, and parameter attribute names are case-
insensitive. Parameter values might or might not be case-sensitive, insensitive. Parameter values might or might not be case-sensitive,
depending on the semantics of the parameter name. The presence or depending on the semantics of the parameter name. The presence or
absence of a parameter might be significant to the processing of a absence of a parameter might be significant to the processing of a
media-type, depending on its definition within the media type media-type, depending on its definition within the media type
registry. registry.
A parameter value that matches the token production can be A parameter value that matches the token production can be
transmitted as either a token or within a quoted-string. The quoted transmitted as either a token or within a quoted-string. The quoted
and unquoted values are equivalent. and unquoted values are equivalent. For example, the following
examples are all equivalent, but the first is preferred for
consistency:
Media-type values are registered with the Internet Assigned Number text/html;charset=utf-8
Authority (IANA). The media type registration process is outlined in text/html;charset=UTF-8
[RFC4288]. Use of non-registered media types is discouraged. Text/HTML;Charset="utf-8"
text/html; charset="utf-8"
3.1.1.2. Character Encodings (charset) Internet media types ought to be registered with IANA according to
the procedures defined in [BCP13].
HTTP uses charset names to indicate the character encoding of a 3.1.1.2. Charset
textual representation.
A character encoding is identified by a case-insensitive token. The HTTP uses charset names to indicate or negotiate the character
complete set of tokens is defined by the IANA Character Set registry encoding scheme of a textual representation [RFC6365]. A charset is
(<http://www.iana.org/assignments/character-sets>). identified by a case-insensitive token.
charset = token charset = token
Although HTTP allows an arbitrary token to be used as a charset Charset names ought to be registered in IANA Character Set registry
value, any token that has a predefined value within the IANA (<http://www.iana.org/assignments/character-sets>) according to the
Character Set registry MUST represent the character encoding defined procedures defined in [RFC2978].
by that registry. Applications SHOULD limit their use of character
encodings to those defined within the IANA registry.
HTTP uses charset in two contexts: within an Accept-Charset request
header field (in which the charset value is an unquoted token) and as
the value of a parameter in a Content-Type header field (within a
request or response), in which case the parameter value of the
charset parameter can be quoted.
Implementers need to be aware of IETF character set requirements
[RFC3629] [RFC2277].
3.1.1.3. Canonicalization and Text Defaults 3.1.1.3. Canonicalization and Text Defaults
Internet media types are registered with a canonical form. A Internet media types are registered with a canonical form in order to
representation transferred via HTTP messages MUST be in the be interoperable among systems with varying native encoding formats.
appropriate canonical form prior to its transmission except for Representations selected or transferred via HTTP ought to be in
"text" types, as defined in the next paragraph. canonical form, for many of the same reasons described by the
Multipurpose Internet Mail Extensions (MIME) [RFC2045]. However, the
performance characteristics of email deployments (i.e., store and
forward messages to peers) are significantly different from those
common to HTTP and the Web (server-based information services).
Furthermore, MIME's constraints for the sake of compatibility with
older mail transfer protocols do not apply to HTTP (see Appendix A).
When in canonical form, media subtypes of the "text" type use CRLF as MIME's canonical form requires that media subtypes of the "text" type
the text line break. HTTP relaxes this requirement and allows the use CRLF as the text line break. HTTP allows the transfer of text
transport of text media with plain CR or LF alone representing a line media with plain CR or LF alone representing a line break, when such
break when it is done consistently for an entire representation. line breaks are consistent for an entire representation. HTTP
HTTP applications MUST accept CRLF, bare CR, and bare LF as senders MAY generate, and recipients MUST be able to parse, line
indicating a line break in text media received via HTTP. In breaks in text media that consist of CRLF, bare CR, or bare LF. In
addition, if the text is in a character encoding that does not use addition, text media in HTTP is not limited to charsets that use
octets 13 and 10 for CR and LF respectively, as is the case for some octets 13 and 10 for CR and LF, respectively. This flexibility
multi-byte character encodings, HTTP allows the use of whatever octet regarding line breaks applies only to text within a representation
sequences are defined by that character encoding to represent the that has been assigned a "text" media type; it does not apply to
equivalent of CR and LF for line breaks. This flexibility regarding "multipart" types or HTTP elements outside the payload body (e.g.,
line breaks applies only to text media in the payload body; a bare CR header fields).
or LF MUST NOT be substituted for CRLF within any of the HTTP control
structures (such as header fields and multipart boundaries).
If a representation is encoded with a content-coding, the underlying If a representation is encoded with a content-coding, the underlying
data MUST 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 3.1.1.4. 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.
In general, HTTP treats a multipart message body no differently than
any other media type: strictly as payload. HTTP does not use the
multipart boundary as an indicator of message body length. In all
other respects, an HTTP user agent SHOULD follow the same or similar
behavior as a MIME user agent would upon receipt of a multipart type.
The MIME header fields within each body-part of a multipart message
body do not have any significance to HTTP beyond that defined by
their MIME semantics.
A recipient MUST treat an unrecognized multipart subtype as being
equivalent to "multipart/mixed".
Note: The "multipart/form-data" type has been specifically defined HTTP message framing does not use the multipart boundary as an
for carrying form data suitable for processing via the POST indicator of message body length, though it might be used by
request method, as described in [RFC2388]. implementations that generate or process the payload. For example,
the "multipart/form-data" type is often used for carrying form data
in a request, as described in [RFC2388], and the "multipart/
byteranges" type is defined by this specification for use in some 206
(Partial Content) responses [Part5].
3.1.1.5. Content-Type 3.1.1.5. Content-Type
The "Content-Type" header field indicates the media type of the The "Content-Type" header field indicates the media type of the
representation, which defines both the data format and how that data associated representation: either the representation enclosed in the
SHOULD be processed by the recipient (within the scope of the request message payload or the selected representation, as determined by the
method semantics) after any Content-Encoding is decoded. For message semantics. The indicated media type defines both the data
responses to the HEAD method, the media type is that which would have format and how that data is intended to be processed by a recipient,
been sent had the request been a GET. within the scope of the received message semantics, after any content
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 3.1.1.1. 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 SHOULD include a Content-Type header field in a message A sender that generates a message containing a payload body SHOULD
containing a payload body, defining the media type of the enclosed generate a Content-Type header field in that message unless the
representation, unless the intended media type 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, recipients sender. If a Content-Type header field is not present, recipients
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 representation data to ([RFC2046], Section 4.5.1) or examine the data to determine its type.
determine its type.
In practice, resource owners do not always properly configure their In practice, resource owners do not always properly configure their
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. Data Encoding 3.1.2. Encoding for Compression or Integrity
3.1.2.1. Content Codings 3.1.2.1. Content Codings
Content coding values indicate an encoding transformation that has Content coding values indicate an encoding transformation that has
been or can be applied to a representation. Content codings are been or can be applied to a representation. Content codings are
primarily used to allow a representation to be compressed or primarily used to allow a representation to be compressed or
otherwise usefully transformed without losing the identity of its otherwise usefully transformed without losing the identity of its
underlying media type and without loss of information. Frequently, underlying media type and without loss of information. Frequently,
the representation is stored in coded form, transmitted directly, and the representation is stored in coded form, transmitted directly, and
only decoded by the recipient. only decoded by the recipient.
content-coding = token content-coding = token
All content-coding values are case-insensitive and SHOULD be All content-coding values are case-insensitive and ought to be
registered within the HTTP Content Coding registry, as defined in registered within the HTTP Content Coding registry, as defined in
Section 9.4. They are used in the Accept-Encoding (Section 6.3.4) Section 8.4. They are used in the Accept-Encoding (Section 5.3.4)
and Content-Encoding (Section 3.1.2.2) header fields. and Content-Encoding (Section 3.1.2.2) header fields.
The following content-coding values are defined by this The following content-coding values are defined by this
specification: specification:
compress (and x-compress): See Section 4.2.1 of [Part1]. compress (and x-compress): See Section 4.2.1 of [Part1].
deflate: See Section 4.2.2 of [Part1]. deflate: See Section 4.2.2 of [Part1].
gzip (and x-gzip): See Section 4.2.3 of [Part1]. gzip (and x-gzip): See Section 4.2.3 of [Part1].
skipping to change at page 13, line 28 skipping to change at page 12, line 34
provided by other header fields not defined by this specification. provided by other header fields not defined by this specification.
Unlike Transfer-Encoding (Section 3.3.1 of [Part1]), the codings Unlike Transfer-Encoding (Section 3.3.1 of [Part1]), 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.
A transforming proxy MAY modify the content coding if the new coding
is known to be acceptable to the recipient, unless the "no-transform"
cache-control directive is present in the message.
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 as a Content-Encoding even if it happens to be the same restated in Content-Encoding even if it happens to be the same
algorithm as one of the content codings. Such a content coding would algorithm as one of the content codings. Such a content coding would
only be listed if, for some bizarre reason, it is applied a second only be listed if, for some bizarre reason, it is applied a second
time to form the representation. Likewise, an origin server might time to form the representation. Likewise, an origin server might
choose to publish the same payload data as multiple representations choose to publish the same data as multiple representations that
that differ only in whether the coding is defined as part of Content- differ only in whether the coding is defined as part of Content-Type
Type or Content-Encoding, since some user agents will behave or Content-Encoding, since some user agents will behave differently
differently in their handling of each response (e.g., open a "Save as in their handling of each response (e.g., open a "Save as ..." dialog
..." dialog instead of automatic decompression and rendering of instead of automatic decompression and rendering of content).
content).
If the content-coding of a representation in a request message is not An origin server MAY respond with a status code of 415 (Unsupported
acceptable to the origin server, the server SHOULD respond with a Media Type) if a representation in the request message has a content
status code of 415 (Unsupported Media Type). coding that is not acceptable.
3.1.3. Audience Language 3.1.3. Audience Language
3.1.3.1. Language Tags 3.1.3.1. Language Tags
A language tag, as defined in [RFC5646], identifies a natural A language tag, as defined in [RFC5646], identifies a natural
language spoken, written, or otherwise conveyed by human beings for language spoken, written, or otherwise conveyed by human beings for
communication of information to other human beings. Computer communication of information to other human beings. Computer
languages are explicitly excluded. HTTP uses language tags within languages are explicitly excluded. HTTP uses language tags within
the Accept-Language and Content-Language fields. the Accept-Language and Content-Language fields.
In summary, a language tag is composed of one or more parts: A
primary language subtag followed by a possibly empty series of
subtags:
language-tag = <Language-Tag, defined in [RFC5646], Section 2.1> language-tag = <Language-Tag, defined in [RFC5646], Section 2.1>
White space is not allowed within the tag and all tags are case- A language tag is composed of one or more parts: a primary language
insensitive. The name space of language subtags is administered by subtag followed by a possibly empty series of subtags. White space
the IANA (see is not allowed within the tag and all tags are case-insensitive.
<http://www.iana.org/assignments/language-subtag-registry>).
Example tags include: Example tags include:
en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN
See [RFC5646] for further information. See [RFC5646] for further information.
3.1.3.2. Content-Language 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 3.1.3.1. 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 user's 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,
or that the sender does not know for which language it is intended. or that the sender does not know for which language it is intended.
skipping to change at page 15, line 31 skipping to change at page 14, line 25
3.1.4. Identification 3.1.4. Identification
3.1.4.1. Identifying a Representation 3.1.4.1. Identifying a Representation
When a complete or partial representation is transferred in a message When a complete or partial representation is transferred in a message
payload, it is often desirable for the sender to supply, or the payload, it is often desirable for the sender to supply, or the
recipient to determine, an identifier for a resource corresponding to recipient to determine, an identifier for a resource corresponding to
that representation. that representation.
The following rules are used to determine such a URI for the payload For a request message:
of a request message:
o If the request has a Content-Location header field, then the o If the request has a Content-Location header field, then the
sender asserts that the payload is a representation of the sender asserts that the payload is a representation of the
resource identified by the Content-Location field-value. However, resource identified by the Content-Location field-value. However,
such an assertion cannot be trusted unless it can be verified by such an assertion cannot be trusted unless it can be verified by
other means (not defined by HTTP). The information might still be other means (not defined by HTTP). The information might still be
useful for revision history links. useful for revision history links.
o Otherwise, the payload is unidentified. o Otherwise, the payload is unidentified.
The following rules, to be applied in order until a match is found, For a response message, the following rules are applied in order
are used to determine such a URI for the payload of a response until a match is found:
message:
1. If the request is GET or HEAD and the response status code is 200 1. If the request is GET or HEAD and the response status code is 200
(OK), 204 (No Content), 206 (Partial Content), or 304 (Not (OK), 204 (No Content), 206 (Partial Content), or 304 (Not
Modified), the payload's identifier is the effective request URI Modified), the payload is a representation of the resource
(Section 5.5 of [Part1]). identified by the effective request URI (Section 5.5 of [Part1]).
2. If the request is GET or HEAD and the response status code is 203 2. If the request is GET or HEAD and the response status code is 203
(Non-Authoritative Information), the payload is a potentially (Non-Authoritative Information), the payload is a potentially
modified representation of the target resource; as such, the modified or enhanced representation of the target resource as
effective request URI might only act as an identifier for the provided by an intermediary.
payload's representation when a request is made via the same
chain of intermediaries.
3. If the response has a Content-Location header field and its 3. If the response has a Content-Location header field and its
field-value is a reference to the same URI as the effective field-value is a reference to the same URI as the effective
request URI, the payload's identifier is the effective request request URI, the payload is a representation of the resource
URI. identified by the effective request URI.
4. If the response has a Content-Location header field and its 4. If the response has a Content-Location header field and its
field-value is a reference to a URI different from the effective field-value is a reference to a URI different from the effective
request URI, then the sender asserts that the payload is a request URI, then the sender asserts that the payload is a
representation of the resource identified by the Content-Location representation of the resource identified by the Content-Location
field-value. However, such an assertion cannot be trusted unless field-value. However, such an assertion cannot be trusted unless
it can be verified by other means (not defined by HTTP). it can be verified by other means (not defined by HTTP).
5. Otherwise, the payload is unidentified. 5. Otherwise, the payload is unidentified.
3.1.4.2. Content-Location 3.1.4.2. 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 a specific identifier for the representation in this message as an identifier for a specific resource corresponding to the
payload. In other words, if one were to perform a GET on this URI at representation in this message's payload. In other words, if one
the time of this message's generation, then a 200 (OK) response would were to perform a GET request on this URI at the time of this
contain the same representation that is enclosed as payload in this message's generation, then a 200 (OK) response would contain the same
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 [Part1]). It is representation metadata. Request URI (Section 5.5 of [Part1]). It is representation metadata.
It has the same syntax and semantics as the header field of the same It has the same syntax and semantics as the header field of the same
name defined for MIME body parts in Section 4 of [RFC2557]. However, name defined for MIME body parts in Section 4 of [RFC2557]. However,
its appearance in an HTTP message has some special implications for its appearance in an HTTP message has some special implications for
HTTP recipients. HTTP 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 response URI that is the same as the effective request URI, then the recipient
payload SHOULD be considered a current representation of that MAY consider the payload to be a current representation of that
resource. For a GET or HEAD request, this is the same as the default resource at the time indicated by the message origination date. For
semantics when no Content-Location is provided by the server. For a a GET or HEAD request, this is the same as the default semantics when
state-changing request like PUT or POST, it implies that the server's no Content-Location is provided by the server. For a state-changing
response contains the new representation of that resource, thereby request like PUT or POST, it implies that the server's response
contains the new representation of that resource, thereby
distinguishing it from representations that might only report about distinguishing it from representations that might only report about
the action (e.g., "It worked!"). This allows authoring applications the action (e.g., "It worked!"). This allows authoring applications
to update their local copies without the need for a subsequent GET to update their local copies without the need for a subsequent GET
request. 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 field- effective request URI, then the origin server claims that the URI is
value is an identifier for the payload's representation. Such a an identifier for a different resource corresponding to the enclosed
claim can only be trusted if both identifiers share the same resource representation. Such a claim can only be trusted if both identifiers
owner, which cannot be programmatically determined via HTTP. share the same resource owner, which cannot be programmatically
determined via HTTP.
o For a response to a GET or HEAD request, this is an indication o For a response to a GET or HEAD request, this is an indication
that the effective request URI identifies a resource that is that the effective request URI refers to a resource that is
subject to content negotiation and the Content-Location field- subject to content negotiation and the Content-Location field-
value is a more specific identifier for the selected value is a more specific identifier for the selected
representation. representation.
o For a 201 (Created) response to a state-changing method, a o For a 201 (Created) response to a state-changing method, a
Content-Location field-value that is identical to the Location Content-Location field-value that is identical to the Location
field-value indicates that this payload is a current field-value indicates that this payload is a current
representation of the newly created resource. representation of the newly created resource.
o Otherwise, such a Content-Location indicates that this payload is o Otherwise, such a Content-Location indicates that this payload is
a representation reporting on the requested action's status and a representation reporting on the requested action's status and
that the same report is available (for future access with GET) at that the same report is available (for future access with GET) at
the given URI. For example, a purchase transaction made via a the given URI. For example, a purchase transaction made via a
POST request might include a receipt document as the payload of POST request might include a receipt document as the payload of
the 200 (OK) response; the Content-Location field-value provides the 200 (OK) response; the Content-Location field-value provides
an identifier for retrieving a copy of that same receipt in the an identifier for retrieving a copy of that same receipt in the
future. future.
If Content-Location is included in a request message, then it MAY be A user agent that sends Content-Location in a request message is
interpreted by the origin server as an indication of where the user stating that its value refers to where the user agent originally
agent originally obtained the content of the enclosed representation obtained the content of the enclosed representation (prior to any
(prior to any subsequent modification of the content by that user modifications made by that user agent). In other words, the user
agent). In other words, the user agent is providing the same agent is providing a back link to the source of the original
representation metadata that it received with the original representation.
representation. However, such interpretation MUST NOT be used to
alter the semantics of the method requested by the client. For
example, if a client makes a PUT request on a negotiated resource and
the origin server accepts that PUT (without redirection), then the
new set of values for that resource is expected to be consistent with
the one representation supplied in that PUT; the Content-Location
cannot be used as a form of reverse content selection that identifies
only one of the negotiated representations to be updated. If the
user agent had wanted the latter semantics, it would have applied the
PUT directly to the Content-Location URI.
A Content-Location field received in a request message is transitory An origin server that receives a Content-Location field in a request
information that SHOULD NOT be saved with other representation message MUST treat the information as transitory request context
metadata for use in later responses. The Content-Location's value rather than as metadata to be saved verbatim as part of the
might be saved for use in other contexts, such as within source links representation. An origin server MAY use that context to guide in
or other metadata. processing the request or to save it for other uses, such as within
source links or versioning metadata. However, an origin server MUST
NOT use such context information to alter the request semantics.
A cache cannot assume that a representation with a Content-Location For example, if a client makes a PUT request on a negotiated resource
different from the URI used to retrieve it can be used to respond to and the origin server accepts that PUT (without redirection), then
later requests on that Content-Location URI. the new state of that resource is expected to be consistent with the
one representation supplied in that PUT; the Content-Location cannot
be used as a form of reverse content selection identifier to update
only one of the negotiated representations. If the user agent had
wanted the latter semantics, it would have applied the PUT directly
to the Content-Location URI.
3.2. Representation Data 3.2. Representation Data
The representation data associated with an HTTP message is either The representation data associated with an HTTP message is either
provided as the payload body of the message or referred to by the provided as the payload body of the message or referred to by the
message semantics and the effective request URI. The representation message semantics and the effective request URI. The representation
data is in a format and encoding defined by the representation data is in a format and encoding defined by the representation
metadata header fields. metadata header fields.
The data type of the representation data is determined via the header The data type of the representation data is determined via the header
fields Content-Type and Content-Encoding. These define a two-layer, fields Content-Type and Content-Encoding. These define a two-layer,
ordered encoding model: ordered encoding model:
representation-data := Content-Encoding( Content-Type( bits ) ) representation-data := Content-Encoding( Content-Type( bits ) )
3.3. Payload Semantics 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 only contain 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).
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. In a response, the payload's purpose is defined by both semantics. For example, a representation in the payload of a PUT
the request method and the response status code. request (Section 4.3.4) represents the desired state of the target
resource if the request is successfully applied, whereas a
For example, a representation in the payload of a PUT request representation in the payload of a POST request (Section 4.3.3)
(Section 5.3.4) represents the desired state of the target resource represents an anonymous resource for providing data to be processed,
if the request is successfully applied, whereas a representation in such as the information that a user entered within an HTML form.
the payload of a POST request (Section 5.3.3) represents an anonymous
resource for providing data to be processed, such as the information
that a user entered within an HTML form.
Likewise, the payload of a 200 (OK) response to GET (Section 5.3.1) In a response, the payload's purpose is defined by both the request
contains a representation of the target resource, as observed at the method and the response status code. For example, the payload of a
time of the message origination date (Section 8.1.1.2), whereas the 200 (OK) response to GET (Section 4.3.1) represents the current state
same status code in a response to POST might contain either a of the target resource, as observed at the time of the message
representation of the processing result or a current representation origination date (Section 7.1.1.2), whereas the payload of the same
of the target resource after applying the processing. Response status code in a response to POST might represent either the
messages with an error status code usually contain a representation processing result or the new state of the target resource after
that describes the error and what next steps are suggested for applying the processing. Response messages with an error status code
resolving it. usually contain a payload that represents the error condition, such
that it describes the error state and what next steps are suggested
for resolving it.
Header fields that specifically describe the payload, rather than the Header fields that specifically describe the payload, rather than the
associated representation, are referred to as "payload header associated representation, are referred to as "payload header
fields". Payload header fields are defined in other parts of this fields". Payload header fields are defined in other parts of this
specification, due to their impact on message parsing. specification, due to their impact on message parsing.
+-------------------+--------------------------+ +-------------------+--------------------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+--------------------------+ +-------------------+--------------------------+
| Content-Length | Section 3.3.2 of [Part1] | | Content-Length | Section 3.3.2 of [Part1] |
| Content-Range | Section 5.2 of [Part5] | | Content-Range | Section 4.2 of [Part5] |
| Transfer-Encoding | Section 3.3.1 of [Part1] | | Transfer-Encoding | Section 3.3.1 of [Part1] |
+-------------------+--------------------------+ +-------------------+--------------------------+
3.4. Content Negotiation 3.4. Content Negotiation
HTTP responses include a representation which contains information When responses convey payload information, whether indicating a
for interpretation, whether by a human user or for further success or an error, the origin server often has different ways of
processing. Often, the server has different ways of representing the representing that information; for example, in different formats,
same information; for example, in different formats, languages, or languages, or encodings. Likewise, different users or user agents
using different character encodings. might have differing capabilities, characteristics, or preferences
that could influence which representation, among those available,
HTTP clients and their users might have different or variable would be best to deliver. For this reason, HTTP provides mechanisms
capabilities, characteristics or preferences which would influence for content negotiation.
which representation, among those available from the server, would be
best for the server to deliver. For this reason, HTTP provides
mechanisms for "content negotiation" -- a process of allowing
selection of a representation of a given resource, when more than one
is available.
This specification defines two patterns of content negotiation;
"proactive", where the server selects the representation based upon
the client's stated preferences, and "reactive" negotiation, where
the server provides a list of representations for the client to
choose from, based upon their metadata. In addition, there are other
patterns: some applications use an "active content" pattern, where
the server returns active content which runs on the client and, based
on client available parameters, selects additional resources to
invoke. "Transparent Content Negotiation" ([RFC2295]) has also been
proposed.
These patterns are all widely used, and have trade-offs in This specification defines two patterns of content negotiation that
applicability and practicality. In particular, when the number of can be made visible within the protocol: "proactive", where the
preferences or capabilities to be expressed by a client are large server selects the representation based upon the user agent's stated
(such as when many different formats are supported by a user-agent), preferences, and "reactive" negotiation, where the server provides a
proactive negotiation becomes unwieldy, and might not be appropriate. list of representations for the user agent to choose from. Other
Conversely, when the number of representations to choose from is very patterns of content negotiation include "conditional content", where
large, reactive negotiation might not be appropriate. the representation consists of multiple parts that are selectively
rendered based on user agent parameters, "active content", where the
representation contains a script that makes additional (more
specific) requests based on the user agent characteristics, and
"Transparent Content Negotiation" ([RFC2295]), where content
selection is performed by an intermediary. These patterns are not
mutually exclusive, and each has trade-offs in applicability and
practicality.
Note that, in all cases, the supplier of representations has the Note that, in all cases, the supplier of representations to the
responsibility for determining which representations might be origin server determines which representations might be considered to
considered to be the "same information". be the "same information".
3.4.1. Proactive Negotiation 3.4.1. Proactive Negotiation
If the selection of the best representation for a response is made by When content negotiation preferences are sent by the user agent in a
an algorithm located at the server, it is called proactive request in order to encourage an algorithm located at the server to
negotiation. Selection is based on the available representations of select the preferred representation, it is called proactive
the response (the dimensions over which it can vary; e.g., language, negotiation (a.k.a., server-driven negotiation). Selection is based
content-coding, etc.) and the contents of particular header fields in on the available representations for a response (the dimensions over
the request message or on other information pertaining to the request which it might vary, such as language, content-coding, etc.) compared
(such as the network address of the client). to various information supplied in the request, including both the
explicit negotiation fields of Section 5.3 and implicit
characteristics, such 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 the 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 client along with the first response (hoping to "best guess" to the user agent along with the first response (hoping
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, the user agent MAY include request header fields server's guess, a user agent MAY send request header fields that
(Accept, Accept-Language, Accept-Encoding, etc.) which describe its describe its preferences.
preferences for such a response.
Proactive negotiation has disadvantages: Proactive negotiation has serious disadvantages:
1. It is impossible for the server to accurately determine what o It is impossible for the server to accurately determine what might
might be "best" for any given user, since that would require be "best" for any given user, since that would require complete
complete knowledge of both the capabilities of the user agent and knowledge of both the capabilities of the user agent and the
the intended use for the response (e.g., does the user want to intended use for the response (e.g., does the user want to view it
view it on screen or print it on paper?). on screen or print it on paper?);
2. Having the user agent describe its capabilities in every request o Having the user agent describe its capabilities in every request
can be both very inefficient (given that only a small percentage can be both very inefficient (given that only a small percentage
of responses have multiple representations) and a potential of responses have multiple representations) and a potential risk
violation of the user's privacy. to the user's privacy;
3. It complicates the implementation of an origin server and the
algorithms for generating responses to a request.
4. It might limit a public cache's ability to use the same response
for multiple user's requests.
Proactive negotiation allows the user agent to specify its o It complicates the implementation of an origin server and the
preferences, but it cannot expect responses to always honor them. algorithms for generating responses to a request; and,
For example, the origin server might not implement proactive
negotiation, or it might decide that sending a response that doesn't
conform to them is better than sending a 406 (Not Acceptable)
response.
HTTP/1.1 includes the following header fields for enabling proactive o It limits the reusability of responses for shared caching.
negotiation through description of user agent capabilities and user
preferences: Accept (Section 6.3.2), Accept-Charset (Section 6.3.3),
Accept-Encoding (Section 6.3.4), Accept-Language (Section 6.3.5), and
User-Agent (Section 6.5.3). However, an origin server is not limited
to these dimensions and MAY vary the response based on any aspect of
the request, including aspects of the connection (e.g., IP address)
or information within extension header fields not defined by this
specification.
Note: In practice, User-Agent based negotiation is fragile, A user agent cannot rely on proactive negotiation preferences being
because new clients might not be recognized. consistently honored, since the origin server might not implement
proactive negotiation for the requested resource or might decide that
sending a response that doesn't conform to the user agent's
preferences is better than sending a 406 (Not Acceptable) response.
The Vary header field (Section 8.2.1) can be used to express the An origin server MAY generate a Vary header field (Section 7.1.4) in
parameters the server uses to select a representation that is subject responses that are subject to proactive negotiation to indicate what
to proactive negotiation. parameters of request information might be used in its selection
algorithm, thereby providing a means for recipients to determine the
reusability of that same response for user agents with differing
request information.
3.4.2. Reactive Negotiation 3.4.2. Reactive Negotiation
With reactive negotiation, selection of the best representation for a With reactive negotiation (a.k.a., agent-driven negotiation),
response is performed by the user agent after receiving an initial selection of the best representation for a response is performed by
response from the origin server. Selection is based on a list of the the user agent after receiving an initial response from the origin
available representations of the response included within the header server with a list of alternative resources. If the user agent is
fields or body of the initial response, with each representation not satisfied by the initial response, it can perform a GET request
identified by its own URI. Selection from among the representations on one or more of the alternative resources, selected based on
can be performed automatically (if the user agent is capable of doing metadata included in the list, to obtain a different form of
so) or manually by the user selecting from a generated (possibly representation. Selection of alternatives might be performed
hypertext) menu. automatically by the user agent or manually by the user selecting
from a generated (possibly hypertext) menu.
A server can send a 300 (Multiple Choices) response to indicate that
reactive negotiation by the user agent is desired, or a 406 (Not
Acceptable) status code to indicate that proactive negotiation has
failed. In both cases, the response ought to include information
about the available representations so that the user or user agent
can react by making a selection.
Reactive negotiation is advantageous when the response would vary Reactive negotiation is advantageous when the response would vary
over commonly-used dimensions (such as type, language, or encoding), over commonly-used dimensions (such as type, language, or encoding),
when the origin server is unable to determine a user agent's when the origin server is unable to determine a user agent's
capabilities from examining the request, and generally when public capabilities from examining the request, and generally when public
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 disadvantage of needing a Reactive negotiation suffers from the disadvantages of transmitting a
second request to obtain the best alternate representation. This list of alternatives to the user agent, which degrades user-perceived
second request is only efficient when caching is used. In addition, latency if transmitted in the header section, and needing a second
this specification does not define any mechanism for supporting request to obtain an alternate representation. Furthermore, this
automatic selection, though it also does not prevent any such specification does not define a mechanism for supporting automatic
mechanism from being developed as an extension and used within selection, though it does not prevent such a mechanism from being
HTTP/1.1. developed as an extension.
This specification defines the 300 (Multiple Choices) and 406 (Not
Acceptable) status codes for enabling reactive negotiation when the
server is unwilling or unable to provide a varying response using
proactive negotiation.
4. Product Tokens
Product tokens are used to allow communicating applications to
identify themselves by software name and version. Most fields using
product tokens also allow sub-products which form a significant part
of the application to be listed, separated by whitespace. By
convention, the products are listed in order of their significance
for identifying the application.
product = token ["/" product-version]
product-version = token
Examples:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Server: Apache/0.8.4
Product tokens SHOULD be short and to the point. They MUST NOT be
used for advertising or other non-essential information. Although
any token octet MAY appear in a product-version, this token SHOULD
only be used for a version identifier (i.e., successive versions of
the same product SHOULD only differ in the product-version portion of
the product value).
5. Request Methods 4. Request Methods
5.1. Overview 4.1. 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. The and what is expected by the client as a successful result. The
request semantics MAY be further specialized by the semantics of some request semantics might be further specialized by the semantics of
header fields when present in a request (Section 6) if those some header fields when present in a request (Section 5) if those
additional semantics do not conflict with the method. additional semantics do not conflict with the method.
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.
Unlike distributed objects, the standardized request methods in HTTP Unlike distributed objects, the standardized request methods in HTTP
are not resource-specific, since uniform interfaces provide for are not resource-specific, since uniform interfaces provide for
better visibility and reuse in network-based systems [REST]. Once better visibility and reuse in network-based systems [REST]. Once
defined, a standardized method MUST have the same semantics when defined, a standardized method ought to have the same semantics when
applied to any resource, though each resource determines for itself applied to any resource, though each resource determines for itself
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 ASCII convention, standardized methods are defined in all-uppercase ASCII
letters. letters.
+---------+-------------------------------------------------+-------+ +---------+-------------------------------------------------+-------+
| Method | Description | Sec. | | Method | Description | Sec. |
+---------+-------------------------------------------------+-------+ +---------+-------------------------------------------------+-------+
| GET | Transfer a current representation of the target | 5.3.1 | | GET | Transfer a current representation of the target | 4.3.1 |
| | resource. | | | | resource. | |
| HEAD | Same as GET, but do not include a message body | 5.3.2 | | HEAD | Same as GET, but only transfer the status line | 4.3.2 |
| | in the response. | | | | and header block. | |
| POST | Perform resource-specific processing on the | 5.3.3 | | POST | Perform resource-specific processing on the | 4.3.3 |
| | request payload. | | | | request payload. | |
| PUT | Replace all current representations of the | 5.3.4 | | PUT | Replace all current representations of the | 4.3.4 |
| | target resource with the request payload. | | | | target resource with the request payload. | |
| DELETE | Remove all current representations of the | 5.3.5 | | DELETE | Remove all current representations of the | 4.3.5 |
| | target resource. | | | | target resource. | |
| CONNECT | Establish a tunnel to the server identified by | 5.3.6 | | CONNECT | Establish a tunnel to the server identified by | 4.3.6 |
| | the target resource. | | | | the target resource. | |
| OPTIONS | Describe the communication options for the | 5.3.7 | | OPTIONS | Describe the communication options for the | 4.3.7 |
| | target resource. | | | | target resource. | |
| TRACE | Perform a message loop-back test along the path | 5.3.8 | | TRACE | Perform a message loop-back test along the path | 4.3.8 |
| | to the target resource. | | | | to the target resource. | |
+---------+-------------------------------------------------+-------+ +---------+-------------------------------------------------+-------+
The methods GET and HEAD MUST be supported by all general-purpose All general-purpose servers MUST support the methods GET and HEAD.
servers. All other methods are OPTIONAL. When implemented, a server All other methods are OPTIONAL; when implemented, a server MUST
MUST implement the above methods according to the semantics defined implement the above methods according to the semantics defined for
for them in Section 5.3. them in Section 4.3.
Additional methods MAY be used in HTTP; many have already been Additional methods, outside the scope of this specification, have
standardized outside the scope of this specification and registered been standardized for use in HTTP. All such methods ought to be
within the HTTP Method Registry maintained by IANA, as defined in registered within the HTTP Method Registry maintained by IANA, as
Section 9.1. 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 8.4.1). However, the set of allowed Allow header field (Section 7.4.1). However, the set of allowed
methods can change dynamically. When a request message 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 message 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.
5.2. Common Method Properties A client can send conditional request header fields (Section 5.2) to
make the requested action conditional on the current state of the
target resource ([Part4]).
5.2.1. Safe Methods 4.2. Common Method Properties
4.2.1. 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, not entirely from including behavior that is potentially harmful, not entirely
read-only, or which causes side-effects while invoking a safe method. read-only, or which causes side-effects while invoking a safe method.
What is important, however, is that the client did not request that What is important, however, is that the client did not request that
additional behavior and cannot be held accountable for it. For additional behavior and cannot be held accountable for it. For
example, most servers append request information to access log files example, most servers append request information to access log files
at the completion of every response, regardless of the method, and at the completion of every response, regardless of the method, and
that is considered safe even though the log storage might become full that is considered safe even though the log storage might become full
and crash the server. Likewise, a safe request initiated by and crash the server. Likewise, a safe request initiated by
selecting an advertisement on the Web will often have the side-effect selecting an advertisement on the Web will often have the side-effect
of charging an advertising account. of charging an advertising account.
The GET, HEAD, OPTIONS, and TRACE request methods are defined to be Of the request methods defined by this specification, the GET, HEAD,
safe. OPTIONS, and TRACE methods are defined to be safe.
The purpose of distinguishing between safe and unsafe methods is to The purpose of distinguishing between safe and unsafe methods is to
allow automated retrieval processes (spiders) and cache performance allow automated retrieval processes (spiders) and cache performance
optimization (pre-fetching) to work without fear of causing harm. In optimization (pre-fetching) to work without fear of causing harm. In
addition, it allows a user agent to apply appropriate constraints on addition, it allows a user agent to apply appropriate constraints on
the automated use of unsafe methods when processing potentially the automated use of unsafe methods when processing potentially
untrusted content. untrusted content.
A user agent SHOULD distinguish between safe and unsafe methods when A user agent SHOULD distinguish between safe and unsafe methods when
presenting potential actions to a user, such that the user can be presenting potential actions to a user, such that the user can be
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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 MUST resource is to perform an unsafe action, then the resource 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.
5.2.2. Idempotent Methods 4.2.2. Idempotent Methods
Request methods are considered "idempotent" if the intended effect of Request methods are considered "idempotent" if the intended effect of
multiple identical requests is the same as for a single request. multiple identical requests is the same as for a single request. Of
PUT, DELETE, and all safe request methods are idempotent. the request methods defined by this specification, the PUT, DELETE,
and safe request methods 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
other non-idempotent side-effects for each idempotent request. other non-idempotent side-effects for each idempotent request.
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 it can establish a new before any response is received, then it can establish a new
connection and retry the idempotent request because it knows that connection and retry the idempotent request because it knows that
repeating the request will have the same effect even if the original repeating the request will have the same effect even if the original
request succeeded. Note, however, that repeated failures would request succeeded. Note, however, that repeated failures would
indicate a problem within the server. indicate a problem within the server.
5.2.3. Cacheable Methods 4.2.3. Cacheable Methods
Request methods are considered "cacheable" if it is possible and Request methods are considered "cacheable" if it is possible and
useful to answer a current client request with a stored response from useful to answer a current client request with a stored response from
a prior request. GET and HEAD are defined to be cacheable. In a prior request. GET and HEAD are defined to be cacheable. In
general, safe methods that do not depend on a current or general, safe methods that do not depend on a current or
authoritative response are cacheable, though the overwhelming authoritative response are cacheable, though the overwhelming
majority of caches only support GET and HEAD. HTTP requirements for majority of caches only support GET and HEAD. HTTP requirements for
cache behavior and cacheable responses are defined in [Part6]. cache behavior and cacheable responses are defined in [Part6].
5.3. Method Definitions 4.3. Method Definitions
4.3.1. GET
5.3.1. GET
The GET method requests transfer of a current representation of the
target resource.
If the target resource is a data-producing process, it is the The GET method requests transfer of a current selected representation
produced data which shall be returned as the representation in the for the target resource. GET is the primary mechanism of information
response and not the source text of the process, unless that text retrieval and the focus of almost all performance optimizations.
happens to be the output of the process. Hence, when people speak of retrieving some identifiable information
via HTTP, they are generally referring to making a GET request.
The semantics of the GET method change to a "conditional GET" if the It is tempting to think of resource identifiers as remote filesystem
request message includes an If-Modified-Since, If-Unmodified-Since, pathnames, and of representations as being a copy of the contents of
If-Match, If-None-Match, or If-Range header field ([Part4]). A such files. In fact, that is how many resources are implemented (see
conditional GET requests that the representation be transferred only Section 9.1 for related security considerations). However, there are
under the circumstances described by the conditional header field(s). no such limitations in practice. The HTTP interface for a resource
The conditional GET request is intended to reduce unnecessary network is just as likely to be implemented as a tree of content objects, a
usage by allowing cached representations to be refreshed without programmatic view on various database records, or a gateway to other
requiring multiple requests or transferring data already held by the information systems. Even when the URI mapping mechanism is tied to
client. a filesystem, an origin server might be configured to execute the
files with the request as input and send the output as the
representation, rather then transfer the files directly. Regardless,
only the origin server needs to know how each of its resource
identifiers correspond to an implementation, and how each
implementation manages to select and send a current representation of
the target resource in a response to GET.
The semantics of the GET method change to a "partial GET" if the A client can alter the semantics of GET to be a "range request",
request message includes a Range header field ([Part5]). A partial requesting transfer of only some part(s) of the selected
GET requests that only part of the representation be transferred, as representation, by sending a Range header field in the request
described in Section 5.4 of [Part5]. The partial GET request is ([Part5]).
intended to reduce unnecessary network usage by allowing partially-
retrieved representations to be completed without transferring data
already held by the client.
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 and MAY be used to satisfy The response to a GET request is cacheable; a cache MAY use it to
subsequent GET and HEAD requests (see [Part6]). satisfy subsequent GET and HEAD requests unless otherwise indicated
by the Cache-Control header field (Section 7.2 of [Part6]).
See Section 10.2 for security considerations when used for forms.
5.3.2. HEAD 4.3.2. 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
return a message body in the response. The metadata contained in the send a message body in the response (i.e., the response terminates at
HTTP header fields in response to a HEAD request SHOULD be identical the end of the header block). Aside from the payload header fields
to the information sent in response to a GET request. This method (Section 3.3), the server SHOULD send the same header fields in
can be used for obtaining metadata about the representation implied response to a HEAD request as it would have sent if the request had
by the request without transferring the representation data. This been a GET. This method can be used for obtaining metadata about the
method is often used for testing hypertext links for validity, selected representation without transferring the representation data.
This method is often used for testing hypertext links for validity,
accessibility, and recent modification. accessibility, and recent modification.
The response to a HEAD request is cacheable and MAY be used to
satisfy a subsequent HEAD request. It also has potential side
effects on previously stored responses to GET; see Section 5 of
[Part6].
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.
5.3.3. POST The response to a HEAD request is cacheable; a cache MAY use it to
satisfy subsequent HEAD requests unless otherwise indicated by the
The POST method requests that the origin server accept the Cache-Control header field (Section 7.2 of [Part6]). A HEAD response
representation enclosed in the request as data to be processed by the might also have an effect on previously cached responses to GET; see
target resource. POST is designed to allow a uniform method to cover Section 5 of [Part6].
the following functions:
o Annotation of existing resources; 4.3.3. POST
o Posting a message to a bulletin board, newsgroup, mailing list, or The POST method requests that the target resource process the
similar group of articles; representation enclosed in the request according to the resource's
own specific semantics. For example, POST is used for the following
functions (among others):
o Providing a block of data, such as the result of submitting a 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 Extending a database through an append operation. o Posting a message to a bulletin board, newsgroup, mailing list,
blog, or similar group of articles;
The actual function performed by the POST method is determined by the o Creating a new resource that has yet to be identified by the
server and is usually dependent on the effective request URI. origin server; and
The action performed by the POST method might not result in a o Appending data to a resource's existing representation(s).
resource that can be identified by a URI. In this case, either 200
(OK) or 204 (No Content) is the appropriate response status code,
depending on whether or not the response includes a representation
that describes the result.
If a resource has been created on the origin server, the response An origin server indicates response semantics by choosing an
SHOULD be 201 (Created) and contain a representation which describes appropriate status code depending on the result of processing the
the status of the request and refers to the new resource, and a POST request; almost all of the status codes defined by this
Location header field (see Section 8.1.2). specification might be received in a response to POST (the exceptions
being 206, 304, and 416).
If one or more resources has been created on the origin server as a
result of successfully processing a POST request, the origin server
SHOULD send a 201 (Created) response containing a Location header
field that provides an identifier for the primary resource created
(Section 7.1.2) and a representation that describes the status of 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 4.1.1 of [Part6]). A explicit freshness information (see Section 4.1.1 of [Part6]).
cached POST response with a Content-Location header field (see However, POST caching is not widely implemented. For cases where an
Section 3.1.4.2) whose value is the effective Request URI MAY be used origin server wishes the client to be able to cache the result of a
to satisfy subsequent GET and HEAD (not POST) requests. 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-
Location header field that has the same value as the POST's effective
request URI (Section 3.1.4.2).
Note that POST caching is not widely implemented. However, the 303 If the result of processing a POST would be equivalent to a
(See Other) response can be used to direct the user agent to retrieve representation of an existing resource, an origin server MAY redirect
a cacheable representation of the resource. the user agent to that resource by sending a 303 (See Other) response
with the existing resource's identifier in the Location field. This
has the benefits of providing the user agent a resource identifier
and transferring the representation via a method more amenable to
shared caching, though at the cost of an extra request if the user
agent does not already have the representation cached.
5.3.4. PUT 4.3.4. 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
returned 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
subsequent GET is received. A successful response only implies that subsequent GET is received. A successful response only implies that
the user agent's intent was achieved at the time of its processing by the user agent's intent was achieved at the time of its processing by
the origin server. the origin server.
If the target resource does not have a current representation and the If the target resource does not have a current representation and the
PUT successfully creates one, then the origin server MUST inform the PUT successfully creates one, then the origin server MUST inform the
user agent by sending a 201 (Created) response. If the target user agent by sending a 201 (Created) response. If the target
resource does have a current representation and that representation resource does have a current representation and that representation
is successfully modified in accordance with the state of the enclosed is successfully modified in accordance with the state of the enclosed
representation, then either a 200 (OK) or 204 (No Content) response representation, then either a 200 (OK) or 204 (No Content) response
SHOULD be sent to indicate successful completion of the request. SHOULD be sent to indicate successful completion of the request.
Unrecognized header fields SHOULD be ignored (i.e., not saved as part An origin server SHOULD ignore unrecognized header fields received in
of the resource state). a PUT request (i.e., do not save them as part of the resource state).
An origin server SHOULD verify that the PUT representation is An origin server SHOULD verify that the PUT representation is
consistent with any constraints which the server has for the target consistent with any constraints the server has for the target
resource that cannot or will not be changed by the PUT. This is resource that cannot or will not be changed by the PUT. This is
particularly important when the origin server uses internal particularly important when the origin server uses internal
configuration information related to the URI in order to set the configuration information related to the URI in order to set the
values for representation metadata on GET responses. When a PUT values for representation metadata on GET responses. When a PUT
representation is inconsistent with the target resource, the origin representation is inconsistent with the target resource, the origin
server SHOULD either make them consistent, by transforming the server SHOULD either make them consistent, by transforming the
representation or changing the resource configuration, or respond representation or changing the resource configuration, or respond
with an appropriate error message containing sufficient information with an appropriate error message containing sufficient information
to explain why the representation is unsuitable. The 409 (Conflict) to explain why the representation is unsuitable. The 409 (Conflict)
or 415 (Unsupported Media Type) status codes are suggested, with the or 415 (Unsupported Media Type) status codes are suggested, with the
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origin server beyond what can be expressed by the intent of the user origin server beyond what can be expressed by the intent of the user
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
(Section 7.2), such as an ETag or Last-Modified field, in a
successful response to PUT unless the request's representation data
was saved without any transformation applied to the body (i.e., the
resource's new representation data is identical to the representation
data received in the PUT request) and the validator field value
reflects the new representation. This requirement allows a user
agent to know when the representation body it has in memory remains
current as a result of the PUT, thus not in need of retrieving again
from the origin server, and that the new validator(s) received in the
response can be used for future conditional requests in order to
prevent accidental overwrites (Section 5.2).
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 target resource. The highlighted by the different intent for the enclosed representation.
target resource in a POST request is intended to handle the enclosed The target resource in a POST request is intended to handle the
representation as a data-accepting process, such as for a gateway to enclosed representation according to the resource's own semantics,
some other protocol or a document that accepts annotations. In whereas the enclosed representation in a PUT request is defined as
contrast, the target resource in a PUT request is intended to take replacing the state of the target resource. Hence, the intent of PUT
the enclosed representation as a new or replacement value. Hence, is idempotent and visible to intermediaries, even though the exact
the intent of PUT is idempotent and visible to intermediaries, even effect is only known by the origin server.
though the exact 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 what target resource is desired. A service that is intended to knows which target resource is desired. A service that selects a
select a proper URI on behalf of the client, after receiving a state- proper URI on behalf of the client, after receiving a state-changing
changing request, SHOULD be implemented using the POST method rather request, SHOULD be implemented using the POST method rather than PUT.
than PUT. If the origin server will not make the requested PUT state If the origin server will not make the requested PUT state change to
change to the target resource and instead wishes to have it applied the target resource and instead wishes to have it applied to a
to a different resource, such as when the resource has been moved to different resource, such as when the resource has been moved to a
a different URI, then the origin server MUST send a 301 (Moved different URI, then the origin server MUST send an appropriate 3xx
Permanently) response; the user agent MAY then make its own decision (Redirection) response; the user agent MAY then make its own decision
regarding whether or not to redirect the request. regarding whether or not to redirect the request.
A PUT request applied to the target resource MAY have side-effects on A PUT request applied to the target resource MAY have side-effects on
other resources. For example, an article might have a URI for other resources. For example, an article might have a URI for
identifying "the current version" (a resource) which 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 SHOULD reject any PUT request that contains a An origin server SHOULD reject any PUT request that contains a
Content-Range header field (Section 5.2 of [Part5]), since it might Content-Range header field (Section 4.2 of [Part5]), since it might
be misinterpreted as partial content (or might be partial content be misinterpreted as partial content (or might be partial content
that is being mistakenly PUT as a full representation). Partial that is being mistakenly PUT as a full representation). Partial
content updates are possible by targeting a separately identified content updates are possible by targeting a separately identified
resource with state that overlaps a portion of the larger resource, resource with state that overlaps a portion of the larger resource,
or by using a different method that has been specifically defined for or by using a different method that has been specifically defined for
partial updates (for example, the PATCH method defined in [RFC5789]). partial updates (for example, the PATCH method defined in [RFC5789]).
Responses to the PUT method are not cacheable. If a PUT request Responses to the PUT method are not cacheable. If a PUT request
passes through a cache that has one or more stored responses for the passes through a cache that has one or more stored responses for the
effective request URI, those stored responses will be invalidated effective request URI, those stored responses will be invalidated
(see Section 6 of [Part6]). (see Section 6 of [Part6]).
5.3.5. DELETE 4.3.5. DELETE
The DELETE method requests that the origin server delete the target The DELETE method requests that the origin server remove the
resource. This method MAY be overridden by human intervention (or association between the target resource and its current
other means) on the origin server. The client cannot be guaranteed functionality. In effect, this method is similar to the rm command
that the operation has been carried out, even if the status code in UNIX: it expresses a deletion operation on the URI mapping of the
returned from the origin server indicates that the action has been origin server, rather than an expectation that the previously
completed successfully. However, the server SHOULD NOT indicate associated information be deleted.
success unless, at the time the response is given, it intends to
delete the resource or move it to an inaccessible location.
A successful response SHOULD be 200 (OK) if the response includes a If the target resource has one or more current representations, they
representation describing the status, 202 (Accepted) if the action might or might not be destroyed by the origin server, and the
has not yet been enacted, or 204 (No Content) if the action has been associated storage might or might not be reclaimed, depending
enacted but the response does not include a representation. entirely on the nature of the resource and its implementation by the
origin server (which are beyond the scope of this specification).
Likewise, other implementation aspects of a resource might need to be
deactivated or archived as a result of a DELETE, such as database or
gateway connections. In general, it is assumed that the origin
server will only allow DELETE on resources for which it has a
prescribed mechanism for accomplishing the deletion.
Relatively few resources allow the DELETE method -- its primary use
is for remote authoring environments, where the user has some
direction regarding its effect. For example, a resource that was
previously created using a PUT request, or identified via the
Location header field after a 201 (Created) response to a POST
request, might allow a corresponding DELETE request to undo those
actions. Similarly, custom user agent implementations that implement
an authoring function, such as revision control clients using HTTP
for remote operations, might use DELETE based on an assumption that
the server's URI space has been crafted to correspond to a version
repository.
If a DELETE method is successfully applied, the origin server SHOULD
send a 202 (Accepted) status code if the action seems okay but has
not yet been enacted, a 204 (No Content) status code if the action
has been enacted and no further information is to be supplied, or a
200 (OK) status code if the action has been enacted and the 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 6 of [Part6]). invalidated (see Section 6 of [Part6]).
5.3.6. CONNECT 4.3.6. CONNECT
The CONNECT method requests that the proxy establish a tunnel to the The CONNECT method requests that the recipient establish a tunnel to
request-target and, if successful, thereafter restrict its behavior the destination origin server identified by the request-target and,
to blind forwarding of packets until the connection is closed. if successful, thereafter restrict its behavior to blind forwarding
of packets, in both directions, until the connection is closed.
When using CONNECT, the request-target MUST use the authority form CONNECT is intended only for use in requests to a proxy. An origin
(Section 5.3 of [Part1]); i.e., the request-target consists of only server that receives a CONNECT request for itself MAY respond with a
the host name and port number of the tunnel destination, separated by 2xx status code to indicate that a connection is established.
a colon. For example,
However, most origin servers do not implement CONNECT.
A client sending a CONNECT request MUST send the authority form of
request-target (Section 5.3 of [Part1]); i.e., the request-target
consists of only the host name and port number of the tunnel
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
Any 2xx (Successful) response to a CONNECT request indicates that the The recipient proxy can establish a tunnel either by directly
proxy has established a connection to the requested host and port, connecting to the request-target or, if configured to use another
and has switched to tunneling the current connection to that server proxy, by forwarding the CONNECT request to the next inbound proxy.
connection. The tunneled data from the server begins immediately Any 2xx (Successful) response indicates that the sender (and all
after the blank line that concludes the successful response's header inbound proxies) will switch to tunnel mode immediately after the
block. blank line that concludes the successful response's header block;
data received after that blank line is from the server identified by
the request-target. Any response other than a successful response
indicates that the tunnel has not yet been formed and that the
connection remains governed by HTTP.
A server SHOULD NOT send any Transfer-Encoding or Content-Length A server SHOULD NOT send any Transfer-Encoding or Content-Length
header fields in a successful response. A client MUST ignore any header fields in a successful response. A client MUST ignore any
Content-Length or Transfer-Encoding header fields received in a Content-Length or Transfer-Encoding header fields received in a
successful response. successful response.
Any response other than a successful response indicates that the There are significant risks in establishing a tunnel to arbitrary
tunnel has not yet been formed and that the connection remains servers, particularly when the destination is a well-known or
governed by HTTP. reserved TCP port that is not intended for Web traffic. For example,
a CONNECT to a request-target of "example.com:25" would suggest that
the proxy connect to the reserved port for SMTP traffic; if allowed,
that could trick the proxy into relaying spam email. Proxies that
support CONNECT SHOULD restrict its use to a limited set of known
ports or a configurable whitelist of safe request targets.
Proxy authentication might be used to establish the authority to Proxy authentication might be used to establish the authority to
create a tunnel: create a tunnel. 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
Proxy-Authorization: basic aGVsbG86d29ybGQ= Proxy-Authorization: basic aGVsbG86d29ybGQ=
When a tunnel intermediary detects that either side has closed its
connection, any outstanding data that came from that side will first
be sent to the other side and then the intermediary will close both
connections. If there is outstanding data left undelivered, that
data will be discarded.
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.
Similar to a pipelined HTTP/1.1 request, data to be tunneled from Responses to the CONNECT method are not cacheable.
client to server MAY be sent immediately after the request (before a
response is received). The usual caveats also apply: data can be
discarded if the eventual response is negative, and the connection
can be reset with no response if more than one TCP segment is
outstanding.
It might be the case that the proxy itself can only reach the
requested origin server through another proxy. In this case, the
first proxy SHOULD make a CONNECT request of that next proxy,
requesting a tunnel to the authority. A proxy MUST NOT respond with
any 2xx status code unless it has either a direct or tunnel
connection established to the authority.
If at any point either one of the peers gets disconnected, any
outstanding data that came from that peer will be passed to the other
one, and after that also the other connection will be terminated by
the proxy. If there is outstanding data to that peer undelivered,
that data will be discarded.
An origin server which receives a CONNECT request for itself MAY
respond with a 2xx status code to indicate that a connection is
established. However, most origin servers do not implement CONNECT.
5.3.7. OPTIONS 4.3.7. OPTIONS
The OPTIONS method requests information about the communication The OPTIONS method requests information about the communication
options available on the request/response chain identified by the options available on the request/response chain identified by the
effective request URI. This method allows a client to determine the effective request URI. This method allows a client to determine the
options and/or requirements associated with a resource, or the options and/or requirements associated with a resource, or the
capabilities of a server, without implying a resource action or capabilities of a server, without implying a resource action.
initiating a resource retrieval.
Responses to the OPTIONS method are not cacheable.
If the OPTIONS request includes a payload, then the media type MUST
be indicated by a Content-Type field. Although this specification
does not define any use for such a body, future extensions to HTTP
might use the OPTIONS body to make more detailed queries on the
server.
If the request-target (Section 5.3 of [Part1]) is an asterisk ("*"), An OPTIONS request with an asterisk ("*") as the request-target
the OPTIONS request is intended to apply to the server in general (Section 5.3 of [Part1]) applies to the server in general rather than
rather than to a specific resource. Since a server's communication to a specific resource. Since a server's communication options
options typically depend on the resource, the "*" request is only typically depend on the resource, the "*" request is only useful as a
useful as a "ping" or "no-op" type of method; it does nothing beyond "ping" or "no-op" type of method; it does nothing beyond allowing the
allowing the client to test the capabilities of the server. For client to test the capabilities of the server. For example, this can
example, this can be used to test a proxy for HTTP/1.1 conformance be used to test a proxy for HTTP/1.1 conformance (or lack thereof).
(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
only to the options that are available when communicating with that to the options that are available when communicating with the target
resource. resource.
A 200 (OK) response SHOULD include any header fields that indicate A server generating a successful response to OPTIONS SHOULD send any
optional features implemented by the server and applicable to that header fields that might indicate optional features implemented by
resource (e.g., Allow), possibly including extensions not defined by the server and applicable to the target resource (e.g., Allow),
this specification. The response payload, if any, SHOULD also including potential extensions not defined by this specification.
include information about the communication options. The format for The response payload, if any, might also describe the communication
such a payload is not defined by this specification, but might be options in a machine or human-readable representation. A standard
defined by future extensions to HTTP. Content negotiation MAY be format for such a representation is not defined by this
used to select the appropriate representation. If no payload body is specification, but might be defined by future extensions to HTTP. A
included, the response MUST include a Content-Length field with a server MUST generate a Content-Length field with a value of "0" if no
field-value of "0". payload body is to be sent in the response.
The Max-Forwards header field MAY be used to target a specific proxy A client MAY send a Max-Forwards header field in an OPTIONS request
in the request chain (see Section 6.1.1). If no Max-Forwards field to target a specific recipient in the request chain (see
is present in the request, then the forwarded request MUST NOT Section 5.1.2). A proxy MUST NOT generate a Max-Forwards header
include a Max-Forwards field. field while forwarding a request unless that request was received
with a Max-Forwards field.
5.3.8. TRACE A client that generates an OPTIONS request containing a payload body
MUST send a valid Content-Type header field describing the
representation media type. Although this specification does not
define any use for such a payload, future extensions to HTTP might
use the OPTIONS body to make more detailed queries about the target
resource.
Responses to the OPTIONS method are not cacheable.
4.3.8. 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 back to the client as the message body reflect the message received, excluding some fields described below,
of a 200 (OK) response. The final recipient is either the origin back to the client as the message body of a 200 (OK) response with a
server or the first proxy to receive a Max-Forwards value of zero (0) Content-Type of "message/http" (Section 7.3.1 of [Part1]). The final
in the request (see Section 6.1.1). A TRACE request MUST NOT include recipient is either the origin server or the first server to receive
a message body. a Max-Forwards value of zero (0) in the request (Section 5.1.2).
A client MUST NOT send header fields in a TRACE request containing
sensitive data that might be disclosed by the response. For example,
it would be foolish for a user agent to send stored user credentials
[Part7] or cookies [RFC6265] in a TRACE request. The final recipient
SHOULD exclude any request header fields from the response body that
are likely to contain sensitive data.
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 of information. The value of the Via header field (Section 5.7.1 of
[Part1]) is of particular interest, since it acts as a trace of the [Part1]) is of particular interest, since it acts as a trace of the
request chain. Use of the Max-Forwards header field allows the request chain. Use of the Max-Forwards header field allows the
client to limit the length of the request chain, which is useful for client to limit the length of the request chain, which is useful for
testing a chain of proxies forwarding messages in an infinite loop. testing a chain of proxies forwarding messages in an infinite loop.
If the request is valid, the response SHOULD have a Content-Type of A client MUST NOT send a message body in a TRACE request.
"message/http" (see Section 7.3.1 of [Part1]) and contain a message
body that encloses a copy of the entire request message. Responses
to the TRACE method are not cacheable.
6. Request Header Fields Responses to the TRACE method are not cacheable.
5. 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.
6.1. Controls 5.1. 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 7.2 of [Part6] |
| Expect | Section 5.1.1 |
| Host | Section 5.4 of [Part1] | | Host | Section 5.4 of [Part1] |
| Max-Forwards | Section 6.1.1 | | Max-Forwards | Section 5.1.2 |
| Expect | Section 6.1.2 | | Pragma | Section 7.4 of [Part6] |
| Range | Section 5.4 of [Part5] | | Range | Section 3.1 of [Part5] |
| TE | Section 4.3 of [Part1] |
+-------------------+------------------------+ +-------------------+------------------------+
6.1.1. Max-Forwards 5.1.1. Expect
The "Max-Forwards" header field provides a mechanism with the TRACE
(Section 5.3.8) and OPTIONS (Section 5.3.7) methods to limit the
number of times that the request is forwarded by proxies. This can
be useful when the client is attempting to trace a request which
appears to be failing or looping mid-chain.
Max-Forwards = 1*DIGIT
The Max-Forwards value is a decimal integer indicating the remaining
number of times this request message can be forwarded.
Each recipient of a TRACE or OPTIONS request containing a Max-
Forwards header field MUST check and update its value prior to
forwarding the request. If the received value is zero (0), the
recipient MUST NOT forward the request; instead, it MUST respond as
the final recipient. If the received Max-Forwards value is greater
than zero, then the forwarded message MUST contain an updated Max-
Forwards field with a value decremented by one (1).
The Max-Forwards header field MAY be ignored for all other request
methods.
6.1.2. Expect
The "Expect" header field is used to indicate that particular server The "Expect" header field is used to indicate that particular server
behaviors are required by the client. behaviors are required by the client.
Expect = 1#expectation Expect = 1#expectation
expectation = expect-name [ BWS "=" BWS expect-value ] expectation = expect-name [ BWS "=" BWS expect-value ]
*( OWS ";" [ OWS expect-param ] ) *( OWS ";" [ OWS expect-param ] )
expect-param = expect-name [ BWS "=" BWS expect-value ] expect-param = expect-name [ BWS "=" BWS expect-value ]
expect-name = token expect-name = token
expect-value = token / quoted-string expect-value = token / quoted-string
If all received Expect header field(s) are syntactically valid but If all received Expect header field(s) are syntactically valid but
contain an expectation that the recipient does not understand or contain an expectation that the recipient does not understand or
cannot comply with, the recipient MUST respond with a 417 cannot comply with, the recipient MUST respond with a 417
(Expectation Failed) status code. A recipient of a syntactically (Expectation Failed) status code. A recipient of a syntactically
invalid Expectation header field MUST respond with a 4xx status code invalid Expectation header field MUST respond with a 4xx status code
other than 417. other than 417.
The only expectation defined by this specification is:
100-continue
The "100-continue" expectation is defined below. It does not
support any expect-params.
Comparison is case-insensitive for names (expect-name), and case- Comparison is case-insensitive for names (expect-name), and case-
sensitive for values (expect-value). sensitive for values (expect-value).
The Expect mechanism is hop-by-hop: the above requirements apply to The Expect header field MUST be forwarded if the request is
any server, including proxies. However, the Expect header field
itself is end-to-end; it MUST be forwarded if the request is
forwarded. forwarded.
Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Many older HTTP/1.0 and HTTP/1.1 servers do not understand the Expect
Expect header field. header field.
6.1.2.1. Use of the 100 (Continue) Status 5.1.1.1. Use of the 100 (Continue) Status
The purpose of the 100 (Continue) status code (Section 7.2.1) is to The only expectation defined by this specification is:
allow a client that is sending a request message with a payload to
determine if the origin server is willing to accept the request 100-continue
The request includes a payload body and the client will wait for a
100 (Continue) response after sending the request header section
but before sending the payload body. The 100-continue expectation
does not use any expect-params.
The primary purpose of the 100 (Continue) status code (Section 6.2.1)
is to allow a client that is sending a request message with a payload
to determine if the origin server is willing to accept the request
(based on the request header fields) before the client sends the (based on the request header fields) before the client sends the
payload body. In some cases, it might either be inappropriate or payload body. In some cases, it might either be inappropriate or
highly inefficient for the client to send the payload body if the highly inefficient for the client to send the payload body if the
server will reject the message without looking at the body. server will reject the message without looking at the body.
Requirements for HTTP/1.1 clients: Requirements for HTTP/1.1 clients:
o If a client will wait for a 100 (Continue) response before sending o If a client will wait for a 100 (Continue) response before sending
the payload body, it MUST send an Expect header field with the the payload body, it MUST send an Expect header field with the
"100-continue" expectation. "100-continue" expectation.
skipping to change at page 36, line 10 skipping to change at page 34, line 40
Because of the presence of older implementations, the protocol allows Because of the presence of older implementations, the protocol allows
ambiguous situations in which a client might send "Expect: 100- ambiguous situations in which a client might send "Expect: 100-
continue" without receiving either a 417 (Expectation Failed) or a continue" without receiving either a 417 (Expectation Failed) or a
100 (Continue) status code. Therefore, when a client sends this 100 (Continue) status code. Therefore, when a client sends this
header field to an origin server (possibly via a proxy) from which it header field to an origin server (possibly via a proxy) from which it
has never seen a 100 (Continue) status code, the client SHOULD NOT has never seen a 100 (Continue) status code, the client SHOULD NOT
wait for an indefinite period before sending the payload body. wait for an indefinite period before sending the payload body.
Requirements for HTTP/1.1 origin servers: Requirements for HTTP/1.1 origin servers:
o Upon receiving a request which includes an Expect header field o Upon receiving a request that includes an Expect header field with
with the "100-continue" expectation, an origin server MUST either the "100-continue" expectation, an origin server MUST either
respond with 100 (Continue) status code and continue to read from respond with 100 (Continue) status code and continue to read from
the input stream, or respond with a final status code. The origin the input stream, or respond with a final status code. The origin
server MUST NOT wait for the payload body before sending the 100 server MUST NOT wait for the payload body before sending the 100
(Continue) response. If it responds with a final status code, it (Continue) response. If the origin server responds with a final
MAY close the transport connection or it MAY continue to read and status code, it MUST NOT have performed the request method and MAY
discard the rest of the request. It MUST NOT perform the request either close the connection or continue to read and discard the
method if it returns a final status code. rest of the request.
o An origin server SHOULD NOT send a 100 (Continue) response if the o An origin server SHOULD NOT send a 100 (Continue) response if the
request message does not include an Expect header field with the request message does not include an Expect header field with the
"100-continue" expectation, and MUST NOT send a 100 (Continue) "100-continue" expectation, and MUST NOT send a 100 (Continue)
response if such a request comes from an HTTP/1.0 (or earlier) response if such a request comes from an HTTP/1.0 (or earlier)
client. There is an exception to this rule: for compatibility client. There is an exception to this rule: for compatibility
with [RFC2068], a server MAY send a 100 (Continue) status code in with [RFC2068], a server MAY send a 100 (Continue) status code in
response to an HTTP/1.1 PUT or POST request that does not include response to an HTTP/1.1 PUT or POST request that does not include
an Expect header field with the "100-continue" expectation. This an Expect header field with the "100-continue" expectation. This
exception, the purpose of which is to minimize any client exception, the purpose of which is to minimize any client
skipping to change at page 37, line 25 skipping to change at page 36, line 6
HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
respond with a 417 (Expectation Failed) status code. respond with a 417 (Expectation Failed) status code.
o Proxies SHOULD maintain a record of the HTTP version numbers o Proxies SHOULD maintain a record of the HTTP version numbers
received from recently-referenced next-hop servers. received from recently-referenced next-hop servers.
o A proxy MUST NOT forward a 100 (Continue) response if the request o A proxy MUST NOT forward a 100 (Continue) response if the request
message was received from an HTTP/1.0 (or earlier) client and did message was received from an HTTP/1.0 (or earlier) client and did
not include an Expect header field with the "100-continue" not include an Expect header field with the "100-continue"
expectation. This requirement overrides the general rule for expectation. This requirement overrides the general rule for
forwarding of 1xx responses (see Section 7.2.1). forwarding of 1xx responses (see Section 6.2.1).
6.2. Conditionals 5.1.2. Max-Forwards
Conditionals are request header fields that indicate a precondition The "Max-Forwards" header field provides a mechanism with the TRACE
to be tested before applying the method semantics to the target (Section 4.3.8) and OPTIONS (Section 4.3.7) methods to limit the
resource. Each precondition is based on metadata that is expected to number of times that the request is forwarded by proxies. This can
change if the selected representation of the target resource is be useful when the client is attempting to trace a request that
changed. The HTTP/1.1 conditional request mechanisms are defined in appears to be failing or looping mid-chain.
Max-Forwards = 1*DIGIT
The Max-Forwards value is a decimal integer indicating the remaining
number of times this request message can be forwarded.
Each recipient of a TRACE or OPTIONS request containing a Max-
Forwards header field MUST check and update its value prior to
forwarding the request. If the received value is zero (0), the
recipient MUST NOT forward the request; instead, it MUST respond as
the final recipient. If the received Max-Forwards value is greater
than zero, then the forwarded message MUST contain an updated Max-
Forwards field with a value decremented by one (1).
The Max-Forwards header field MAY be ignored for all other request
methods.
5.2. Conditionals
The HTTP conditional request header fields [Part4] 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 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
[Part4]. [Part4].
+---------------------+------------------------+ +---------------------+------------------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+---------------------+------------------------+ +---------------------+------------------------+
| If-Match | Section 3.1 of [Part4] | | If-Match | Section 3.1 of [Part4] |
| If-None-Match | Section 3.2 of [Part4] | | If-None-Match | Section 3.2 of [Part4] |
| If-Modified-Since | Section 3.3 of [Part4] | | If-Modified-Since | Section 3.3 of [Part4] |
| If-Unmodified-Since | Section 3.4 of [Part4] | | If-Unmodified-Since | Section 3.4 of [Part4] |
| If-Range | Section 5.3 of [Part5] | | If-Range | Section 3.2 of [Part5] |
+---------------------+------------------------+ +---------------------+------------------------+
6.3. Content Negotiation 5.3. Content Negotiation
The following request header fields are sent by a user agent to
engage in proactive negotiation of the response content, as defined
in Section 3.4.1. The preferences sent in these fields apply to any
content in the response, including representations of the target
resource, representations of error or processing status, and
potentially even the miscellaneous text strings that might appear
within the protocol.
+-------------------+---------------+ +-------------------+---------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+---------------+ +-------------------+---------------+
| Accept | Section 6.3.2 | | Accept | Section 5.3.2 |
| Accept-Charset | Section 6.3.3 | | Accept-Charset | Section 5.3.3 |
| Accept-Encoding | Section 6.3.4 | | Accept-Encoding | Section 5.3.4 |
| Accept-Language | Section 6.3.5 | | Accept-Language | Section 5.3.5 |
+-------------------+---------------+ +-------------------+---------------+
6.3.1. Quality Values 5.3.1. Quality Values
Many of the request header fields for proactive content negotiation Many of the request header fields for proactive negotiation use a
use a common parameter, named "q" (case-insensitive), to assign a common parameter, named "q" (case-insensitive), to assign a relative
relative "weight" to the preference for that associated kind of "weight" to the preference for that associated kind of content. This
content. This weight is referred to as a "quality value" (or weight is referred to as a "quality value" (or "qvalue") because the
"qvalue") because the same parameter name is often used within server same parameter name is often used within server configurations to
configurations to assign a weight to the relative quality of the assign a weight to the relative quality of the various
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,
where 0.001 is the least preferred and 1 is the most preferred; a where 0.001 is the least preferred and 1 is the most preferred; a
value of 0 means "not acceptable". If no "q" parameter is present, value of 0 means "not acceptable". If no "q" parameter is present,
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.
6.3.2. Accept 5.3.2. 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 = ( "*/*"
/ ( type "/" "*" ) / ( type "/" "*" )
/ ( type "/" subtype ) / ( type "/" subtype )
) *( OWS ";" OWS parameter ) ) *( OWS ";" OWS parameter )
accept-params = weight *( accept-ext ) accept-params = weight *( accept-ext )
accept-ext = OWS ";" OWS token [ "=" word ] accept-ext = OWS ";" OWS token [ "=" word ]
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 MAY 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 MAY be followed by one or more accept-params, Each media-range might be followed by zero or more applicable media
beginning with the "q" parameter for indicating a relative weight, as type parameters (e.g., charset), an optional "q" parameter for
defined in Section 6.3.1. The first "q" parameter (if any) separates indicating a relative weight (Section 5.3.1), and then zero or more
the media-range parameter(s) from the accept-params. extension parameters. The "q" parameter is necessary if any accept-
ext are present, since it acts as a separator 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
parameters in Accept. Future media types are discouraged from parameters in Accept. Future media types are discouraged from
registering any parameter named "q". registering any parameter named "q".
skipping to change at page 40, line 6 skipping to change at page 39, line 19
origin server MAY either honor the Accept header field by sending a origin server MAY either honor the Accept header field by sending a
406 (Not Acceptable) response or disregard the Accept header field by 406 (Not Acceptable) response or disregard the Accept header field by
treating the response as if it is not subject to content negotiation. treating the response as if it is not subject to content negotiation.
A more elaborate example is A more elaborate example is
Accept: text/plain; q=0.5, text/html, Accept: text/plain; q=0.5, text/html,
text/x-dvi; q=0.8, text/x-c text/x-dvi; q=0.8, text/x-c
Verbally, this would be interpreted as "text/html and text/x-c are Verbally, this would be interpreted as "text/html and text/x-c are
the preferred media types, but if they do not exist, then send the the equally preferred media types, but if they do not exist, then
text/x-dvi representation, and if that does not exist, send the text/ send the text/x-dvi representation, and if that does not exist, send
plain representation". the text/plain representation".
Media ranges can be overridden by more specific media ranges or Media ranges can be overridden by more specific media ranges or
specific media types. If more than one media range applies to a specific media types. If more than one media range applies to a
given type, the most specific reference has precedence. For example, given type, the most specific reference has precedence. For example,
Accept: text/*, text/plain, text/plain;format=flowed, */* Accept: text/*, text/plain, text/plain;format=flowed, */*
have the following precedence: have the following precedence:
1. text/plain;format=flowed 1. text/plain;format=flowed
2. text/plain 2. text/plain
3. text/* 3. text/*
4. */* 4. */*
The media type quality factor associated with a given type is The media type quality factor associated with a given type is
determined by finding the media range with the highest precedence determined by finding the media range with the highest precedence
which matches that type. For example, that matches the type. For example,
Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1, Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
text/html;level=2;q=0.4, */*;q=0.5 text/html;level=2;q=0.4, */*;q=0.5
would cause the following values to be associated: would cause the following values to be associated:
+-------------------+---------------+ +-------------------+---------------+
| Media Type | Quality Value | | Media Type | Quality Value |
+-------------------+---------------+ +-------------------+---------------+
| text/html;level=1 | 1 | | text/html;level=1 | 1 |
| text/html | 0.7 | | text/html | 0.7 |
| text/plain | 0.3 | | text/plain | 0.3 |
| 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 which 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.
6.3.3. Accept-Charset 5.3.3. Accept-Charset
The "Accept-Charset" header field can be used by user agents to The "Accept-Charset" header field can be sent by a user agent to
indicate what character encodings are acceptable in a response indicate what charsets are acceptable in textual response content.
payload. This field allows clients capable of understanding more This field allows user agents capable of understanding more
comprehensive or special-purpose character encodings to signal that comprehensive or special-purpose charsets to signal that capability
capability to a server which is capable of representing documents in to an origin server that is capable of representing information in
those character encodings. those charsets.
Accept-Charset = 1#( ( charset / "*" ) [ weight ] ) Accept-Charset = 1#( ( charset / "*" ) [ weight ] )
Character encoding values (a.k.a., charsets) are described in Charset names are defined in Section 3.1.1.2. A user agent MAY
Section 3.1.1.2. Each charset MAY be given an associated quality associate a quality value with each charset to indicate the user's
value which represents the user's preference for that charset, as relative preference for that charset, as defined in Section 5.3.1.
defined in Section 6.3.1. 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 character encoding which is not mentioned elsewhere in matches every charset that is not mentioned elsewhere in the Accept-
the Accept-Charset field. If no "*" is present in an Accept-Charset Charset field. If no "*" is present in an Accept-Charset field, then
field, then any character encodings not explicitly mentioned in the any charsets not explicitly mentioned in the field are considered
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 character encoding in response. user agent will accept any charset in response. Most general-purpose
user agents do not send Accept-Charset, unless specifically
configured to do so, because a detailed list of supported charsets
makes it easier for a server to identify an individual by virtue of
the user agent's request characteristics (Section 9.6).
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 have a character the available representations for the response has a charset that is
encoding that is listed as acceptable, the origin server MAY either listed as acceptable, the origin server MAY either honor the Accept-
honor the Accept-Charset header field by sending a 406 (Not Charset header field, by sending a 406 (Not Acceptable) response, or
Acceptable) response or disregard the Accept-Charset header field by disregard the Accept-Charset header field by treating the resource as
treating the response as if it is not subject to content negotiation. if it is not subject to content negotiation.
6.3.4. Accept-Encoding 5.3.4. 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 3.1.2.1) are
acceptable in the response. An "identity" token is used as a synonym acceptable in the response. An "identity" token is used as a synonym
for "no encoding" in order to communicate when no encoding is for "no 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 which Each codings value MAY be given an associated quality value
represents the preference for that encoding, as defined in representing the preference for that encoding, as defined in
Section 6.3.1. Section 5.3.1. The asterisk "*" symbol in an Accept-Encoding field
matches any available content-coding not explicitly listed in the
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
A request without an Accept-Encoding header field implies that the
user agent has no preferences regarding content-codings. Although
this allows the server to use any content-coding in a response, it
does not imply that the user agent will be able to correctly process
all encodings.
A server tests whether a content-coding for a given representation is A server tests whether a content-coding for a given representation is
acceptable, according to an Accept-Encoding field, using these rules: acceptable using these rules:
1. The special "*" symbol in an Accept-Encoding field matches any 1. If no Accept-Encoding field is in the request, any content-coding
available content-coding not explicitly listed in the header is considered acceptable by the user agent.
field.
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 6.3.1, a qvalue of 0 means "not acceptable".) defined in Section 5.3.1, 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.
A request without an Accept-Encoding header field implies that the
user agent will accept any content-coding in response.
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 will not associated with content-codings. This means that qvalues might
work and are not permitted with x-gzip or x-compress. not work and are not permitted with x-gzip or x-compress.
6.3.5. Accept-Language 5.3.5. 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 3.1.3.1.
Accept-Language = 1#( language-range [ weight ] ) Accept-Language = 1#( language-range [ weight ] )
language-range = language-range =
<language-range, defined in [RFC4647], Section 2.1> <language-range, defined in [RFC4647], Section 2.1>
Each language-range can be given an associated quality value which Each language-range can be given an associated quality value
represents 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 6.3.1. For example, specified by that range, as defined in Section 5.3.1. 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". (see also Section 2.3 of [RFC4647]) other types of English".
Note that some recipients treat the order in which language tags are
listed as an indication of descending priority, particularly for tags
that are assigned equal quality values (no value is the same as q=1).
However, this behavior cannot be relied upon. For consistency and to
maximize interoperability, many user agents assign each language tag
a unique quality value while also listing them in order of decreasing
quality. Additional discussion of language priority lists can be
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. scheme for their requirements. The "Basic Filtering" scheme
([RFC4647], Section 3.3.1) is identical to the matching scheme that
Note: The "Basic Filtering" scheme ([RFC4647], Section 3.3.1) is was previously defined for HTTP in Section 14.4 of [RFC2616].
identical to the matching scheme that was previously defined 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. For a discussion of this preferences of the user in every request (Section 9.6).
issue, see Section 10.5.
As intelligibility is highly dependent on the individual user, it is Since intelligibility is highly dependent on the individual user,
recommended that client applications make the choice of linguistic user agents need to allow user control over the linguistic
preference available to the user. If the choice is not made preference. A user agent that does not provide such control to the
available, then the Accept-Language header field MUST NOT be given in user MUST NOT send an Accept-Language header field.
the request.
Note: When making the choice of linguistic preference available to Note: User agents ought to provide guidance to users when setting
the user, we remind implementers of the fact that users are not a preference, since users are rarely familiar with the details of
familiar with the details of language matching as described above, language matching as described above. For example, users might
and ought to be provided appropriate guidance. As an example, assume that on selecting "en-gb", they will be served any kind of
users might assume that on selecting "en-gb", they will be served English document if British English is not available. A user
any kind of English document if British English is not available. agent might suggest, in such a case, to add "en" to the list for
A user agent might suggest in such a case to add "en" to get the better matching behavior.
best matching behavior.
6.4. Authentication Credentials 5.4. Authentication Credentials
Two header fields are used for carrying authentication credentials,
as defined in [Part7]. Note that various custom mechanisms for user
authentication use the Cookie header field for this purpose, as
defined in [RFC6265].
+---------------------+------------------------+ +---------------------+------------------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+---------------------+------------------------+ +---------------------+------------------------+
| Authorization | Section 4.1 of [Part7] | | Authorization | Section 4.1 of [Part7] |
| Proxy-Authorization | Section 4.3 of [Part7] | | Proxy-Authorization | Section 4.3 of [Part7] |
+---------------------+------------------------+ +---------------------+------------------------+
6.5. Context 5.5. Request Context
+-------------------+------------------------+ The following request header fields provide additional information
about the request context, including information about the user, user
agent, and resource behind the request.
+-------------------+---------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+------------------------+ +-------------------+---------------+
| From | Section 6.5.1 | | From | Section 5.5.1 |
| Referer | Section 6.5.2 | | Referer | Section 5.5.2 |
| TE | Section 4.3 of [Part1] | | User-Agent | Section 5.5.3 |
| User-Agent | Section 6.5.3 | +-------------------+---------------+
+-------------------+------------------------+
6.5.1. From 5.5.1. From
The "From" header field, if given, SHOULD contain an Internet e-mail The "From" header field contains an Internet email address for a
address for the human user who controls the requesting user agent. human user who controls the requesting user agent. The address ought
The address SHOULD be machine-usable, as defined by "mailbox" in to be machine-usable, as defined by "mailbox" in Section 3.4 of
Section 3.4 of [RFC5322]: [RFC5322]:
From = mailbox From = mailbox
mailbox = <mailbox, defined in [RFC5322], Section 3.4> mailbox = <mailbox, defined in [RFC5322], Section 3.4>
An example is: An example is:
From: webmaster@example.org From: webmaster@example.org
This header field MAY be used for logging purposes and as a means for The From header field is rarely sent by non-robotic user agents. A
identifying the source of invalid or unwanted requests. It SHOULD user agent SHOULD NOT send a From header field without explicit
NOT be used as an insecure form of access protection. The configuration by the user, since that might conflict with the user's
interpretation of this field is that the request is being performed privacy interests or their site's security policy.
on behalf of the person given, who accepts responsibility for the
method performed. In particular, robot agents SHOULD include this
header field so that the person responsible for running the robot can
be contacted if problems occur on the receiving end.
The Internet e-mail address in this field MAY be separate from the
Internet host which issued the request. For example, when a request
is passed through a proxy the original issuer's address SHOULD be
used.
The client SHOULD NOT send the From header field without the user's
approval, as it might conflict with the user's privacy interests or
their site's security policy. It is strongly recommended that the
user be able to disable, enable, and modify the value of this field
at any time prior to a request.
6.5.2. Referer Robotic user agents SHOULD send a valid From header field so that the
person responsible for running the robot can be contacted if problems
occur on servers, such as if the robot is sending excessive,
unwanted, or invalid requests.
The "Referer" [sic] header field allows the client to specify the URI Servers SHOULD NOT use the From header field for access control or
of the resource from which the target URI was obtained (the authentication, since most recipients will assume that the field
"referrer", although the header field is misspelled.). value is public information.
The Referer header field allows servers to generate lists of back- 5.5.2. Referer
links to resources for interest, logging, optimized caching, etc. It
also allows obsolete or mistyped links to be traced for maintenance.
Some servers use Referer as a means of controlling where they allow
links from (so-called "deep linking"), but legitimate requests do not
always contain a Referer header field.
If the target URI was obtained from a source that does not have its The "Referer" [sic] header field allows the user agent to specify a
own URI (e.g., input from the user keyboard), the Referer field MUST URI reference for the resource from which the target URI was obtained
either be sent with the value "about:blank", or not be sent at all. (i.e., the "referrer", though the field name is misspelled). A user
Note that this requirement does not apply to sources with non-HTTP agent MUST exclude any fragment or userinfo components [RFC3986] when
URIs (e.g., FTP). generating the Referer field value.
Referer = absolute-URI / partial-URI Referer = absolute-URI / partial-URI
Referer allows servers to generate back-links to other resources for
simple analytics, logging, optimized caching, etc. It also allows
obsolete or mistyped links to be found for maintenance. Some servers
use Referer as a means of denying links from other sites (so-called
"deep linking") or restricting cross-site request forgery (CSRF), but
not all requests contain a Referer header field.
Example: Example:
Referer: http://www.example.org/hypertext/Overview.html Referer: http://www.example.org/hypertext/Overview.html
If the field value is a relative URI, it SHOULD be interpreted If the target URI was obtained from a source that does not have its
relative to the effective request URI. The URI MUST NOT include a own URI (e.g., input from the user keyboard, or an entry within the
fragment. See Section 10.2 for security considerations. user's bookmarks/favorites), the user agent MUST either exclude
Referer or send it with a value of "about:blank".
6.5.3. User-Agent The Referer field has the potential to reveal information about the
request context or browsing history of the user, which is a privacy
concern if the referring resource's identifier reveals personal
information (such as an account name) or a resource that is supposed
to be confidential (such as behind a firewall or internal to a
secured service). Most general-purpose user agents do not send the
Referer header field when the referring resource is a local "file" or
"data" URI. A user agent SHOULD NOT send a Referer header field in
an unsecured HTTP request if the referring page was received with a
secure protocol. See Section 9.3 for additional security
considerations.
The "User-Agent" header field contains information about the user Some intermediaries have been known to indiscriminately remove
agent originating the request. User agents SHOULD include this field Referer header fields from outgoing requests. This has the
with requests. unfortunate side-effect of interfering with protection against CSRF
attacks, which can be far more harmful to their users.
Intermediaries and user agent extensions that wish to limit
information disclosure in Referer ought to restrict their changes to
specific edits, such as replacing internal domain names with
pseudonyms or truncating the query and/or path components.
Intermediaries SHOULD NOT modify or delete the Referer field when the
field value shares the same scheme and host as the request target.
Typically, it is used for statistical purposes, the tracing of 5.5.3. User-Agent
protocol violations, and tailoring responses to avoid particular user
agent limitations.
The field can contain multiple product tokens (Section 4) and The "User-Agent" header field contains information about the user
comments (Section 3.2 of [Part1]) identifying the agent and its agent originating the request, which is often used by servers to help
significant subproducts. By convention, the product tokens are identify the scope of reported interoperability problems, to work
listed in order of their significance for identifying the around or tailor responses to avoid particular user agent
application. limitations, and for analytics regarding browser or operating system
use. A user agent SHOULD send a User-Agent field in each request
unless specifically configured not to do so.
Because this field is usually sent on every request a user agent User-Agent = product *( RWS ( product / comment ) )
makes, implementations are encouraged not to include needlessly fine-
grained detail, and to limit (or even prohibit) the addition of
subproducts by third parties. Overly long and detailed User-Agent
field values make requests larger and can also be used to identify
("fingerprint") the user against their wishes.
Likewise, implementations are encouraged not to use the product The User-Agent field-value consists of one or more product
tokens of other implementations in order to declare compatibility identifiers, each followed by zero or more comments (Section 3.2 of
with them, as this circumvents the purpose of the field. Finally, [Part1]), which together identify the user agent software and its
they are encouraged not to use comments to identify products; doing significant subproducts. By convention, the product identifiers are
so makes the field value more difficult to parse. listed in decreasing order of their significance for identifying the
user agent software. Each product identifier consists of a name and
optional version.
User-Agent = product *( RWS ( product / comment ) ) product = token ["/" product-version]
product-version = token
Senders SHOULD limit generated product identifiers to what is
necessary to identify the product; senders MUST NOT generate
advertising or other non-essential information within the product
identifier. Senders SHOULD NOT generate information in product-
version that is not a version identifier (i.e., successive versions
of the same product name ought to only differ in the product-version
portion of the product identifier).
Example: Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3 User-Agent: CERN-LineMode/2.15 libwww/2.17b3
7. Response Status Codes A user agent SHOULD NOT generate a User-Agent field containing
needlessly fine-grained detail and SHOULD limit the addition of
subproducts by third parties. Overly long and detailed User-Agent
field values increase request latency and the risk of a user being
identified against their wishes ("fingerprinting").
The status-code element is a 3-digit integer result code of the Likewise, implementations are encouraged not to use the product
attempt to understand and satisfy the request. tokens of other implementations in order to declare compatibility
with them, as this circumvents the purpose of the field. If a user
agent masquerades as a different user agent, recipients can assume
that the user intentionally desires to see responses tailored for
that identified user agent, even if they might not work as well for
the actual user agent being used.
HTTP status codes are extensible. HTTP applications are not required 6. Response Status Codes
to understand the meaning of all registered status codes, though such
understanding is obviously desirable. However, applications MUST The status-code element is a 3-digit integer code giving the result
of the attempt to understand and satisfy the request.
HTTP status codes are extensible. HTTP clients are not required to
understand the meaning of all registered status codes, though such
understanding is obviously desirable. However, clients 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 any unrecognized response as being equivalent to the digit, and treat an unrecognized status code as being equivalent to
x00 status code of that class, with the exception that an the x00 status code of that class, with the exception that a response
unrecognized response MUST NOT be cached. For example, if an with an unrecognized status code MUST NOT be cached.
unrecognized status code of 431 is received by the client, it can
safely assume that there was something wrong with its request and For example, if an unrecognized status code of 471 is received by a
treat the response as if it had received a 400 status code. In such client, the client can assume that there was something wrong with its
cases, user agents SHOULD present to the user the representation request and treat the response as if it had received a 400 status
enclosed with the response, since that representation is likely to code. The response message will usually contain a representation
include human-readable information which will explain the unusual that explains the status.
status.
The first digit of the status-code defines the class of response. The first digit of the status-code defines the class of response.
The last two digits do not have any categorization role. There are 5 The last two digits do not have any categorization role. There are 5
values for the first digit: values for the first digit:
o 1xx (Informational): Request received, continuing process o 1xx (Informational): The request was received, continuing process
o 2xx (Successful): The action was successfully received,
o 2xx (Successful): The request was successfully received,
understood, and accepted understood, and accepted
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
For most status codes the response can carry a payload, in which case 6.1. Overview of Status Codes
a Content-Type header field indicates the payload's media type
(Section 3.1.1.5).
7.1. Overview of Status Codes
The status codes listed below are defined in this specification, The status codes listed below are defined in this specification,
Section 4 of [Part4], Section 3 of [Part5], and Section 3 of [Part7]. Section 4 of [Part4], Section 4 of [Part5], and Section 3 of [Part7].
The reason phrases listed here are only recommendations -- they can The reason phrases listed here are only recommendations -- they can
be replaced by local equivalents without affecting the protocol. be replaced by local equivalents without affecting the protocol.
+-------------+------------------------------+----------------------+ +------+-------------------------------+------------------------+
| status-code | reason-phrase | Defined in... | | code | reason-phrase | Defined in... |
+-------------+------------------------------+----------------------+ +------+-------------------------------+------------------------+
| 100 | Continue | Section 7.2.1 | | 100 | Continue | Section 6.2.1 |
| 101 | Switching Protocols | Section 7.2.2 | | 101 | Switching Protocols | Section 6.2.2 |
| 200 | OK | Section 7.3.1 | | 200 | OK | Section 6.3.1 |
| 201 | Created | Section 7.3.2 | | 201 | Created | Section 6.3.2 |
| 202 | Accepted | Section 7.3.3 | | 202 | Accepted | Section 6.3.3 |
| 203 | Non-Authoritative | Section 7.3.4 | | 203 | Non-Authoritative Information | Section 6.3.4 |
| | Information | | | 204 | No Content | Section 6.3.5 |
| 204 | No Content | Section 7.3.5 | | 205 | Reset Content | Section 6.3.6 |
| 205 | Reset Content | Section 7.3.6 | | 206 | Partial Content | Section 4.1 of [Part5] |
| 206 | Partial Content | Section 3.1 of | | 300 | Multiple Choices | Section 6.4.1 |
| | | [Part5] | | 301 | Moved Permanently | Section 6.4.2 |
| 300 | Multiple Choices | Section 7.4.1 | | 302 | Found | Section 6.4.3 |
| 301 | Moved Permanently | Section 7.4.2 | | 303 | See Other | Section 6.4.4 |
| 302 | Found | Section 7.4.3 | | 304 | Not Modified | Section 4.1 of [Part4] |
| 303 | See Other | Section 7.4.4 | | 305 | Use Proxy | Section 6.4.5 |
| 304 | Not Modified | Section 4.1 of | | 307 | Temporary Redirect | Section 6.4.7 |
| | | [Part4] | | 400 | Bad Request | Section 6.5.1 |
| 305 | Use Proxy | Section 7.4.5 | | 401 | Unauthorized | Section 3.1 of [Part7] |
| 307 | Temporary Redirect | Section 7.4.7 | | 402 | Payment Required | Section 6.5.2 |
| 400 | Bad Request | Section 7.5.1 | | 403 | Forbidden | Section 6.5.3 |
| 401 | Unauthorized | Section 3.1 of | | 404 | Not Found | Section 6.5.4 |
| | | [Part7] | | 405 | Method Not Allowed | Section 6.5.5 |
| 402 | Payment Required | Section 7.5.2 | | 406 | Not Acceptable | Section 6.5.6 |
| 403 | Forbidden | Section 7.5.3 | | 407 | Proxy Authentication Required | Section 3.2 of [Part7] |
| 404 | Not Found | Section 7.5.4 | | 408 | Request Time-out | Section 6.5.7 |
| 405 | Method Not Allowed | Section 7.5.5 | | 409 | Conflict | Section 6.5.8 |
| 406 | Not Acceptable | Section 7.5.6 | | 410 | Gone | Section 6.5.9 |
| 407 | Proxy Authentication | Section 3.2 of | | 411 | Length Required | Section 6.5.10 |
| | Required | [Part7] | | 412 | Precondition Failed | Section 4.2 of [Part4] |
| 408 | Request Time-out | Section 7.5.7 | | 413 | Payload Too Large | Section 6.5.11 |
| 409 | Conflict | Section 7.5.8 | | 414 | URI Too Long | Section 6.5.12 |
| 410 | Gone | Section 7.5.9 | | 415 | Unsupported Media Type | Section 6.5.13 |
| 411 | Length Required | Section 7.5.10 | | 416 | Range Not Satisfiable | Section 4.4 of [Part5] |
| 412 | Precondition Failed | Section 4.2 of | | 417 | Expectation Failed | Section 6.5.14 |
| | | [Part4] | | 426 | Upgrade Required | Section 6.5.15 |
| 413 | Request Representation Too | Section 7.5.11 | | 500 | Internal Server Error | Section 6.6.1 |
| | Large | | | 501 | Not Implemented | Section 6.6.2 |
| 414 | URI Too Long | Section 7.5.12 | | 502 | Bad Gateway | Section 6.6.3 |
| 415 | Unsupported Media Type | Section 7.5.13 | | 503 | Service Unavailable | Section 6.6.4 |
| 416 | Requested range not | Section 3.2 of | | 504 | Gateway Time-out | Section 6.6.5 |
| | satisfiable | [Part5] | | 505 | HTTP Version Not Supported | Section 6.6.6 |
| 417 | Expectation Failed | Section 7.5.14 | +------+-------------------------------+------------------------+
| 426 | Upgrade Required | Section 7.5.15 |
| 500 | Internal Server Error | Section 7.6.1 |
| 501 | Not Implemented | Section 7.6.2 |
| 502 | Bad Gateway | Section 7.6.3 |
| 503 | Service Unavailable | Section 7.6.4 |
| 504 | Gateway Time-out | Section 7.6.5 |
| 505 | HTTP Version not supported | Section 7.6.6 |
+-------------+------------------------------+----------------------+
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. extension status codes defined in other specifications.
7.2. Informational 1xx Responses with status codes that are defined as cacheable by default
(e.g., 200, 203, 206, 300, 301, and 410 in this specification) can be
reused by a cache with heuristic expiration unless otherwise
indicated by the method definition or explicit cache controls
[Part6]; all other status codes are not cacheable by default.
This class of status code indicates a provisional response, 6.2. Informational 1xx
consisting only of the status-line and optional header fields, and is
terminated by an empty line. There are no required header fields for The 1xx (Informational) class of status code indicates an interim
this class of status code. Since HTTP/1.0 did not define any 1xx response for communicating connection status or request progress
prior to completing the requested action and sending a final
response. All 1xx responses consist of only the status-line and
optional header fields, and thus are terminated by the empty line at
the end of the header block. Since HTTP/1.0 did not define any 1xx
status codes, servers MUST NOT send a 1xx response to an HTTP/1.0 status codes, servers MUST NOT send a 1xx response to an HTTP/1.0
client except under experimental conditions. client except under experimental conditions.
A client MUST be prepared to accept one or more 1xx status responses A client MUST be prepared to accept one or more 1xx status responses
prior to a regular response, even if the client does not expect a 100 prior to a final response, even if the client does not expect one. A
(Continue) status message. Unexpected 1xx status responses MAY be user agent MAY ignore unexpected 1xx status responses.
ignored by a user agent.
Proxies MUST forward 1xx responses, unless the connection between the Proxies MUST forward 1xx responses, unless the connection between the
proxy and its client has been closed, or unless the proxy itself proxy and its client has been closed, or unless the proxy itself
requested the generation of the 1xx response. (For example, if a requested the generation of the 1xx response. For example, if a
proxy adds an "Expect: 100-continue" field when it forwards a proxy adds an "Expect: 100-continue" field when it forwards a
request, then it need not forward the corresponding 100 (Continue) request, then it need not forward the corresponding 100 (Continue)
response(s).) response(s).
7.2.1. 100 Continue 6.2.1. 100 Continue
The client SHOULD continue with its request. This interim response The 100 (Continue) status code indicates that the initial part of a
is used to inform the client that the initial part of the request has request has been received and has not yet been rejected by the
been received and has not yet been rejected by the server. The server. The server intends to send a final response after the
client SHOULD continue by sending the remainder of the request or, if request has been fully received and acted upon.
the request has already been completed, ignore this response. The
server MUST send a final response after the request has been
completed. See Section 6.1.2.1 for detailed discussion of the use
and handling of this status code.
7.2.2. 101 Switching Protocols When the request contains an Expect header field that includes a 100-
continue expectation, the 100 response indicates that the server
wishes to receive the request payload body, as described in
Section 5.1.1.1. The client ought to continue sending the request
and discard the 100 response.
The server understands and is willing to comply with the client's If the request did not contain an Expect header field containing the
request, via the Upgrade message header field (Section 6.3 of 100-continue expectation, the client can simply discard this interim
[Part1]), for a change in the application protocol being used on this response.
connection. The server will switch protocols to those defined by the
response's Upgrade header field immediately after the empty line
which terminates the 101 response.
The protocol SHOULD be switched only when it is advantageous to do 6.2.2. 101 Switching Protocols
so. For example, switching to a newer version of HTTP is
advantageous over older versions, and switching to a real-time,
synchronous protocol might be advantageous when delivering resources
that use such features.
7.3. Successful 2xx The 101 (Switching Protocols) status code indicates that the server
understands and is willing to comply with the client's request, via
the Upgrade header field (Section 6.7 of [Part1]), for a change in
the application protocol being used on this connection. The server
MUST generate an Upgrade header field in the response that indicates
which protocol(s) will be switched to immediately after the empty
line that terminates the 101 response.
This class of status code indicates that the client's request was It is assumed that the server will only agree to switch protocols
successfully received, understood, and accepted. when it is advantageous to do so. For example, switching to a newer
version of HTTP might be advantageous over older versions, and
switching to a real-time, synchronous protocol might be advantageous
when delivering resources that use such features.
7.3.1. 200 OK 6.3. Successful 2xx
The request has succeeded. The payload returned with the response is The 2xx (Successful) class of status code indicates that the client's
dependent on the method used in the request, for example: request was successfully received, understood, and accepted.
GET a representation of the target resource is sent in the response; 6.3.1. 200 OK
HEAD the same representation as GET, except without the message The
body; 200 (OK) status code indicates that the request has succeeded. The
payload sent in a 200 response depends on the request method. For
the methods defined by this specification, the intended meaning of
the payload can be summarized as:
POST a representation describing or containing the result of the GET a representation of the target resource;
action;
TRACE a representation containing the request message as received by HEAD the same representation as GET, but without the representation
the end server. data;
Caches MAY use a heuristic (see Section 4.1.2 of [Part6]) to POST a representation of the status of, or results obtained from,
determine freshness for 200 responses. the action;
7.3.2. 201 Created PUT, DELETE a representation of the status of the action;
The request has been fulfilled and has resulted in one or more new OPTIONS a representation of the communications options;
resources being created.
Newly created resources are typically linked to from the response TRACE a representation of the request message as received by the end
payload, with the most relevant URI also being carried in the server.
Location header field. If the newly created resource's URI is the
same as the Effective Request URI, this information can be omitted
(e.g., in the case of a response to a PUT request).
The origin server MUST create the resource(s) before returning the Aside from responses to CONNECT, a 200 response always has a payload,
201 status code. If the action cannot be carried out immediately, though an origin server MAY generate a payload body of zero length.
the server SHOULD respond with 202 (Accepted) response instead. If no payload is desired, an origin server ought to send 204 (No
Content) instead. For CONNECT, no payload is allowed because the
successful result is a tunnel, which begins immediately after the 200
response header block.
A 201 response MAY contain an ETag response header field indicating A 200 response is cacheable unless otherwise indicated by the method
the current value of the entity-tag for the representation of the definition or explicit cache controls (see Section 4.1.2 of [Part6]).
resource identified by the Location header field or, in case the
Location header field was omitted, by the Effective Request URI (see
Section 2.3 of [Part4]).
7.3.3. 202 Accepted 6.3.2. 201 Created
The request has been accepted for processing, but the processing has The 201 (Created) status code indicates that the request has been
not been completed. The request might or might not eventually be fulfilled and has resulted in one or more new resources being
acted upon, as it might be disallowed when processing actually takes created. The primary resource created by the request is identified
place. There is no facility for re-sending a status code from an by either a Location header field in the response or, if no Location
asynchronous operation such as this. field is received, by the effective request URI.
The 201 response payload typically describes and links to the
resource(s) created. See Section 7.2 for a discussion of the meaning
and purpose of validator header fields, such as ETag and Last-
Modified, in a 201 response.
6.3.3. 202 Accepted
The 202 (Accepted) status code indicates that the request has been
accepted for processing, but the processing has not been completed.
The request might or might not eventually be acted upon, as it might
be disallowed when processing actually takes place. There is no
facility in HTTP for re-sending a status code from an asynchronous
operation.
The 202 response is intentionally non-committal. Its purpose is to The 202 response is intentionally non-committal. 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 returned with until the process is completed. The representation sent with this
this response SHOULD include an indication of the request's current response ought to describe the request's current status and point to
status and either a pointer to a status monitor or some estimate of (or embed) a status monitor that can provide the user with an
when the user can expect the request to be fulfilled. estimate of when the request will be fulfilled.
7.3.4. 203 Non-Authoritative Information 6.3.4. 203 Non-Authoritative Information
The representation in the response has been transformed or otherwise The 203 (Non-Authoritative Information) status code indicates that
modified by a transforming proxy (Section 2.3 of [Part1]). Note that the request was successful but the enclosed payload has been modified
the behavior of transforming intermediaries is controlled by the no- from that of the origin server's 200 (OK) response by a transforming
transform Cache-Control directive (Section 7.2 of [Part6]). proxy (Section 5.7.2 of [Part1]). This status code allows the proxy
to notify recipients when a transformation has been applied, since
that knowledge might impact later decisions regarding the content.
For example, future cache validation requests for the content might
only be applicable along the same request path (through the same
proxies).
This status code is only appropriate when the response status code The 203 response is similar to the Warning code of 214 Transformation
would have been 200 (OK) otherwise. When the status code before Applied (Section 7.5 of [Part6]), which has the advantage of being
transformation would have been different, the 214 Transformation applicable to responses with any status code.
Applied warn-code (Section 7.5 of [Part6]) is appropriate.
Caches MAY use a heuristic (see Section 4.1.2 of [Part6]) to A 203 response is cacheable unless otherwise indicated by the method
determine freshness for 203 responses. definition or explicit cache controls (see Section 4.1.2 of [Part6]).
7.3.5. 204 No Content 6.3.5. 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 return 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 current response header fields refer to the target resource and its selected
representation after the requested action. 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
the new representation of that target resource. the new representation of that target resource.
The 204 response allows a server to indicate that the action has been The 204 response allows a server to indicate that the action has been
successfully applied to the target resource while implying that the successfully applied to the target resource, while implying that the
user agent SHOULD NOT traverse away from its current "document view" user agent does not need to traverse away from its current "document
(if any). The server assumes that the user agent will provide some view" (if any). The server assumes that the user agent will provide
indication of the success to its user, in accord with its own some indication of the success to its user, in accord with its own
interface, and apply any new or updated metadata in the response to interface, and apply any new or updated metadata in the response to
the active representation. its active representation.
For example, a 204 status code is commonly used with document editing For example, a 204 status code is commonly used with document editing
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.
The 204 response MUST NOT include a message body, and thus is always A 204 response is terminated by the first empty line after the header
terminated by the first empty line after the header fields. fields because it cannot contain a message body.
7.3.6. 205 Reset Content A 204 response is cacheable unless otherwise indicated by the method
definition or explicit cache controls (see Section 4.1.2 of [Part6]).
The server has fulfilled the request and the user agent SHOULD reset 6.3.6. 205 Reset Content
the document view which caused the request to be sent. This response
is primarily intended to allow input for actions to take place via
user input, followed by a clearing of the form in which the input is
given so that the user can easily initiate another input action.
The message body included with the response MUST be empty. Note that The 205 (Reset Content) status code indicates that the server has
receivers still need to parse the response according to the algorithm fulfilled the request and desires that the user agent reset the
defined in Section 3.3 of [Part1]. "document view", which caused the request to be sent, to its original
state as received from the origin server.
7.4. Redirection 3xx This response is intended to support a common data entry use case
where the user receives content that supports data entry (a form,
notepad, canvas, etc.), enters or manipulates data in that space,
causes the entered data to be submitted in a request, and then the
data entry mechanism is reset for the next entry so that the user can
easily initiate another input action.
This class of status code indicates that further action needs to be Since the 205 status code implies that no additional content will be
taken by the user agent in order to fulfill the request. If the provided in the payload, the server MUST send a message body of zero
required action involves a subsequent HTTP request, it MAY be carried length. In other words, the server MUST send a "Content-Length: 0"
out by the user agent without interaction with the user if and only field in a 205 response or close the connection immediately after
if the method used in the second request is known to be "safe", as sending the blank line terminating the header section.
defined in Section 5.2.1.
There are several types of redirects: 6.4. Redirection 3xx
1. Redirects of the request to another URI, either temporarily or The 3xx (Redirection) class of status code indicates that further
permanently. The new URI is specified in the Location header action needs to be taken by the user agent in order to fulfill the
field. In this specification, the status codes 301 (Moved request. If a Location header field (Section 7.1.2) is provided, the
Permanently), 302 (Found), and 307 (Temporary Redirect) fall user agent MAY automatically redirect its request to the URI
under this category. referenced by the Location field value, even if the specific status
code is not understood. Automatic redirection needs to done with
care for methods not known to be safe, as defined in Section 4.2.1,
since the user might not wish to redirect an unsafe request.
2. Redirection to a new location that represents an indirect There are several types of redirects:
response to the request, such as the result of a POST operation
to be retrieved with a subsequent GET request. This is status
code 303 (See Other).
3. Redirection offering a choice of matching resources for use by 1. Redirects that indicate the resource might be available at a
reactive content negotiation (Section 3.4.2). This is status different URI, as provided by the Location field, as in the
code 300 (Multiple Choices). status codes 301 (Moved Permanently), 302 (Found), and 307
(Temporary Redirect).
4. Other kinds of redirection, such as to a cached result (status 2. Redirection that offers a choice of matching resources, each
code 304 (Not Modified), see Section 4.1 of [Part4]). capable of representing the original request target, as in the
300 (Multiple Choices) status code.
Note: In HTTP/1.0, only the status codes 301 (Moved Permanently) 3. Redirection to a different resource, identified by the Location
and 302 (Found) were defined for the first type of redirect, and field, that can represent an indirect response to the request, as
the second type did not exist at all ([RFC1945], Section 9.3). in the 303 (See Other) status code.
However it turned out that web forms using POST expected redirects
to change the operation for the subsequent request to retrieval
(GET). To address this use case, HTTP/1.1 introduced the second
type of redirect with the status code 303 (See Other) ([RFC2068],
Section 10.3.4). As user agents did not change their behavior to
maintain backwards compatibility, the first revision of HTTP/1.1
added yet another status code, 307 (Temporary Redirect), for which
the backwards compatibility problems did not apply ([RFC2616],
Section 10.3.8). Over 10 years later, most user agents still do
method rewriting for status codes 301 and 302, therefore this
specification makes that behavior conformant in case the original
request was POST.
A Location header field on a 3xx response indicates that a client MAY 4. Redirection to a previously cached result, as in the 304 (Not
automatically redirect to the URI provided; see Section 8.1.2. Modified) status code.
Note that for methods not known to be "safe", as defined in Note: In HTTP/1.0, the status codes 301 (Moved Permanently) and
Section 5.2.1, automatic redirection needs to done with care, since 302 (Found) were defined for the first type of redirect
the redirect might change the conditions under which the request was ([RFC1945], Section 9.3). Early user agents split on whether the
issued. method applied to the redirect target would be the same as the
original request or would be rewritten as GET. Although HTTP
originally defined the former semantics for 301 and 302 (to match
its original implementation at CERN), and defined 303 (See Other)
to match the latter semantics, prevailing practice gradually
converged on the latter semantics for 301 and 302 as well. The
first revision of HTTP/1.1 added 307 (Temporary Redirect) to
indicate the former semantics without being impacted by divergent
practice. Over 10 years later, most user agents still do method
rewriting for 301 and 302; therefore, this specification makes
that behavior conformant when the original request is POST.
Clients SHOULD detect and intervene in cyclical redirections (i.e., Clients SHOULD detect and intervene in cyclical redirections (i.e.,
"infinite" redirection loops). "infinite" redirection loops).
Note: An earlier version of this specification recommended a Note: An earlier version of this specification recommended a
maximum of five redirections ([RFC2068], Section 10.3). Content maximum of five redirections ([RFC2068], Section 10.3). Content
developers need to be aware that some clients might implement such developers need to be aware that some clients might implement such
a fixed limitation. a fixed limitation.
7.4.1. 300 Multiple Choices 6.4.1. 300 Multiple Choices
The target resource has more than one representation, each with its
own specific location, and reactive negotiation information
(Section 3.4) is being provided so that the user (or user agent) can
select a preferred representation by redirecting its request to that
location.
Unless it was a HEAD request, the response SHOULD include a The 300 (Multiple Choices) status code indicates that the target
representation containing a list of representation metadata and resource has more than one representation, each with its own more
location(s) from which the user or user agent can choose the one most specific identifier, and information about the alternatives is being
appropriate. Depending upon the format and the capabilities of the provided so that the user (or user agent) can select a preferred
user agent, selection of the most appropriate choice MAY be performed representation by redirecting its request to one or more of those
automatically. However, this specification does not define any identifiers. In other words, the server desires that the user agent
standard for such automatic selection. engage in reactive negotiation to select the most appropriate
representation(s) for its needs (Section 3.4).
If the server has a preferred choice of representation, it SHOULD If the server has a preferred choice, the server SHOULD generate a
include the specific URI for that representation in the Location Location header field containing a preferred choice's URI reference.
field; user agents MAY use the Location field value for automatic The user agent MAY use the Location field value for automatic
redirection. redirection.
Caches MAY use a heuristic (see Section 4.1.2 of [Part6]) to For request methods other than HEAD, the server SHOULD generate a
determine freshness for 300 responses. payload in the 300 response containing a list of representation
metadata and URI reference(s) from which the user or user agent can
choose the one most preferred. The user agent MAY make a selection
from that list automatically, depending upon the list format, but
this specification does not define a standard for such automatic
selection.
7.4.2. 301 Moved Permanently A 300 response is cacheable unless otherwise indicated by the method
definition or explicit cache controls (see Section 4.1.2 of [Part6]).
The target resource has been assigned a new permanent URI and any Note: The original proposal for 300 defined the URI header field
future references to this resource SHOULD use one of the returned as providing a list of alternative representations, such that it
URIs. Clients with link editing capabilities ought to automatically would be usable for 200, 300, and 406 responses and be transferred
re-link references to the effective request URI to one or more of the in responses to the HEAD method. However, lack of deployment and
new references returned by the server, where possible. disagreement over syntax led to both URI and Alternates (a
subsequent proposal) being dropped from this specification. It is
possible to communicate the list using a set of Link header fields
[RFC5988], each with a relationship of "alternate", though
deployment is a chicken-and-egg problem.
Caches MAY use a heuristic (see Section 4.1.2 of [Part6]) to 6.4.2. 301 Moved Permanently
determine freshness for 301 responses.
The new permanent URI SHOULD be given by the Location field in the The 301 (Moved Permanently) status code indicates that the target
response. A response payload can contain a short hypertext note with resource has been assigned a new permanent URI and any future
a hyperlink to the new URI(s). references to this resource ought to use one of the enclosed URIs.
Clients with link editing capabilities ought to automatically re-link
references to the effective request URI to one or more of the new
references sent by the server, where possible.
The server SHOULD generate a Location header field in the response
containing a preferred URI reference for the new permanent URI. The
user agent MAY use the Location field value for automatic
redirection. The server's response payload usually contains a short
hypertext note with a hyperlink to the new URI(s).
Note: For historic reasons, user agents MAY change the request Note: For historic reasons, user agents MAY change the request
method from POST to GET for the subsequent request. If this method from POST to GET for the subsequent request. If this
behavior is undesired, status code 307 (Temporary Redirect) can be behavior is undesired, status code 307 (Temporary Redirect) can be
used instead. used instead.
7.4.3. 302 Found A 301 response is cacheable unless otherwise indicated by the method
definition or explicit cache controls (see Section 4.1.2 of [Part6]).
The target resource resides temporarily under a different URI. Since 6.4.3. 302 Found
the redirection might be altered on occasion, the client SHOULD
continue to use the effective request URI for future requests.
The temporary URI SHOULD be given by the Location field in the The 302 (Found) status code indicates that the target resource
response. A response payload can contain a short hypertext note with resides temporarily under a different URI. Since the redirection
a hyperlink to the new URI(s). might be altered on occasion, the client ought to continue to use the
effective request URI for future requests.
The server SHOULD generate a Location header field in the response
containing a URI reference for the different URI. The user agent MAY
use the Location field value for automatic redirection. The server's
response payload usually contains a short hypertext note with a
hyperlink to the different URI(s).
Note: For historic reasons, user agents MAY change the request Note: For historic reasons, user agents MAY change the request
method from POST to GET for the subsequent request. If this method from POST to GET for the subsequent request. If this
behavior is undesired, status code 307 (Temporary Redirect) can be behavior is undesired, status code 307 (Temporary Redirect) can be
used instead. used instead.
7.4.4. 303 See Other 6.4.4. 303 See Other
The 303 status code indicates that the server is redirecting the user The 303 (See Other) status code indicates that the server is
agent to a different resource, as indicated by a URI in the Location redirecting the user agent to a different resource, as indicated by a
header field, that is intended to provide an indirect response to the URI in the Location header field, that is intended to provide an
original request. In order to satisfy the original request, a user indirect response to the original request. In order to satisfy the
agent SHOULD perform a retrieval request using the Location URI (a original request, a user agent ought to perform a retrieval request
GET or HEAD request if using HTTP), which can itself be redirected using the Location URI (a GET or HEAD request if using HTTP), which
further, and present the eventual result as an answer to the original can itself be redirected further, and present the eventual result as
request. Note that the new URI in the Location header field is not an answer to the original request. Note that the new URI in the
considered equivalent to the effective request URI. Location header field is not considered equivalent to the effective
request URI.
This status code is generally applicable to any HTTP method. It is This status code is applicable to any HTTP method. It is primarily
primarily used to allow the output of a POST action to redirect the used to allow the output of a POST action to redirect the user agent
user agent to a selected resource, since doing so provides the to a selected resource, since doing so provides the information
information corresponding to the POST response in a form that can be corresponding to the POST response in a form that can be separately
separately identified, bookmarked, and cached independent of the identified, bookmarked, and cached independent of the original
original request. request.
A 303 response to a GET request indicates that the requested resource A 303 response to a GET request indicates that the origin server does
does not have a representation of its own that can be transferred by not have a representation of the target resource that can be
the server over HTTP. The Location URI indicates a resource that is transferred by the server over HTTP. However, the Location field
descriptive of the target resource, such that the follow-on value refers to a resource that is descriptive of the target
representation might be useful to recipients without implying that it resource, such that making a retrieval request on that other resource
adequately represents the target resource. Note that answers to the might result in a representation that is useful to recipients without
questions of what can be represented, what representations are implying that it represents the original target resource. Note that
adequate, and what might be a useful description are outside the answers to the questions of what can be represented, what
scope of HTTP and thus entirely determined by the URI owner(s). representations are adequate, and what might be a useful description
are outside the scope of HTTP.
Except for responses to a HEAD request, the representation of a 303 Except for responses to a HEAD request, the representation of a 303
response SHOULD contain a short hypertext note with a hyperlink to response ought to contain a short hypertext note with a hyperlink to
the Location URI. the same URI reference provided in the Location header field.
7.4.5. 305 Use Proxy 6.4.5. 305 Use Proxy
The 305 status code was defined in a previous version of this The 305 (Use Proxy) status code was defined in a previous version of
specification (see Appendix C), and is now deprecated. this specification and is now deprecated (Appendix B).
7.4.6. 306 (Unused) 6.4.6. 306 (Unused)
The 306 status code was used in a previous version of the The 306 status code was defined in a previous version of this
specification, is no longer used, and the code is reserved. specification, is no longer used, and the code is reserved.
7.4.7. 307 Temporary Redirect 6.4.7. 307 Temporary Redirect
The target resource resides temporarily under a different URI. Since The 307 (Temporary Redirect) status code indicates that the target
the redirection can change over time, the client SHOULD continue to resource resides temporarily under a different URI and the user agent
use the effective request URI for future requests. MUST NOT change the request method if it performs an automatic
redirection to that URI. Since the redirection can change over time,
the client ought to continue using the original effective request URI
for future requests.
The temporary URI SHOULD be given by the Location field in the The server SHOULD generate a Location header field in the response
response. A response payload can contain a short hypertext note with containing a URI reference for the different URI. The user agent MAY
a hyperlink to the new URI(s). use the Location field value for automatic redirection. The server's
response payload usually contains a short hypertext note with a
hyperlink to the different URI(s).
Note: This status code is similar to 302 (Found), except that it Note: This status code is similar to 302 (Found), except that it
does not allow rewriting the request method from POST to GET. does not allow changing the request method from POST to GET. This
This specification defines no equivalent counterpart for 301 specification defines no equivalent counterpart for 301 (Moved
(Moved Permanently) ([status-308], however, defines the status Permanently) ([status-308], however, defines the status code 308
code 308 (Permanent Redirect) for this purpose). (Permanent Redirect) for this purpose).
7.5. Client Error 4xx 6.5. Client Error 4xx
The 4xx class of status code is intended for cases in which the The 4xx (Client Error) class of status code indicates that the client
client seems to have erred. Except when responding to a HEAD seems to have erred. Except when responding to a HEAD request, the
request, the server SHOULD include a representation containing an server SHOULD send a representation containing an explanation of the
explanation of the error situation, and whether it is a temporary or error situation, and whether it is a temporary or permanent
permanent condition. These status codes are applicable to any condition. These status codes are applicable to any request method.
request method. User agents SHOULD display any included User agents SHOULD display any included representation to the user.
representation to the user.
7.5.1. 400 Bad Request 6.5.1. 400 Bad Request
The server cannot or will not process the request, due to a client The 400 (Bad Request) status code indicates that the server cannot or
error (e.g., malformed syntax). will not process the request because the received syntax is invalid,
nonsensical, or exceeds some limitation on what the server is willing
to process.
7.5.2. 402 Payment Required 6.5.2. 402 Payment Required
This code is reserved for future use. The 402 (Payment Required) status code is reserved for future use.
7.5.3. 403 Forbidden 6.5.3. 403 Forbidden
The server understood the request, but refuses to authorize it. The 403 (Forbidden) status code indicates that the server understood
Providing different user authentication credentials might be the request but refuses to authorize it. A server that wishes to
successful, but any credentials that were provided in the request are make public why the request has been forbidden can describe that
insufficient. The request SHOULD NOT be repeated with the same reason in the response payload (if any).
credentials.
If the request method was not HEAD and the server wishes to make If authentication credentials were provided in the request, the
public why the request has not been fulfilled, it SHOULD describe the server considers them insufficient to grant access. The client
reason for the refusal in the representation. If the server does not SHOULD NOT repeat the request with the same credentials. The client
wish to make this information available to the client, the status MAY repeat the request with new or different credentials. However, a
code 404 (Not Found) MAY be used instead. request might be forbidden for reasons unrelated to the credentials.
7.5.4. 404 Not Found An origin server that wishes to "hide" the current existence of a
forbidden target resource MAY instead respond with a status code of
404 (Not Found).
The server has not found anything matching the effective request URI. 6.5.4. 404 Not Found
No indication is given of whether the condition is temporary or
permanent. The 410 (Gone) status code SHOULD be used if the server
knows, through some internally configurable mechanism, that an old
resource is permanently unavailable and has no forwarding address.
This status code is commonly used when the server does not wish to
reveal exactly why the request has been refused, or when no other
response is applicable.
7.5.5. 405 Method Not Allowed The 404 (Not Found) status code indicates that the origin server did
not find a current representation for the target resource or is not
willing to disclose that one exists. A 404 status does not indicate
whether this lack of representation is temporary or permanent; the
410 (Gone) status code is preferred over 404 if the origin server
knows, presumably through some configurable means, that the condition
is likely to be permanent.
The method specified in the request-line is not allowed for the A 404 response is cacheable unless otherwise indicated by the method
target resource. The response MUST include an Allow header field definition or explicit cache controls (see Section 4.1.2 of [Part6]).
containing a list of valid methods for the requested resource.
7.5.6. 406 Not Acceptable 6.5.5. 405 Method Not Allowed
The resource identified by the request is only capable of generating The 405 (Method Not Allowed) status code indicates that the method
response representations which have content characteristics not specified in the request-line is known by the origin server but not
acceptable according to the Accept and Accept-* header fields sent in supported by the target resource. The origin server MUST generate an
the request. Allow header field in a 405 response containing a list of the target
resource's currently supported methods.
Unless it was a HEAD request, the response SHOULD include a A 405 response is cacheable unless otherwise indicated by the method
representation containing a list of available representation definition or explicit cache controls (see Section 4.1.2 of [Part6]).
characteristics and location(s) from which the user or user agent can
choose the one most appropriate. Depending upon the format and the
capabilities of the user agent, selection of the most appropriate
choice MAY be performed automatically. However, this specification
does not define any standard for such automatic selection.
Note: HTTP/1.1 servers are allowed to return responses which are 6.5.6. 406 Not Acceptable
not acceptable according to the accept header fields sent in the
request. In some cases, this might even be preferable to sending
a 406 response. User agents are encouraged to inspect the header
fields of an incoming response to determine if it is acceptable.
If the response could be unacceptable, a user agent SHOULD The 406 (Not Acceptable) status code indicates that the target
temporarily stop receipt of more data and query the user for a resource does not have a current representation that would be
decision on further actions. acceptable to the user agent, according to the proactive negotiation
header fields received in the request (Section 5.3), and the server
is unwilling to supply a default representation.
7.5.7. 408 Request Timeout The server SHOULD generate a payload containing a list of available
representation characteristics and corresponding resource identifiers
from which the user or user agent can choose the one most
appropriate. A user agent MAY automatically select the most
appropriate choice from that list. However, this specification does
not define any standard for such automatic selection, as described in
Section 6.4.1.
The client did not produce a request within the time that the server 6.5.7. 408 Request Timeout
was prepared to wait. The client MAY repeat the request without
modifications at any later time.
7.5.8. 409 Conflict The 408 (Request Timeout) status code indicates that the server did
not receive a complete request message within the time that it was
prepared to wait. A server SHOULD send the close connection option
(Section 6.1 of [Part1]) in the response, since 408 implies that the
server has decided to close the connection rather than continue
waiting. If the client has an outstanding request in transit, the
client MAY repeat that request on a new connection.
The request could not be completed due to a conflict with the current 6.5.8. 409 Conflict
state of the resource. This code is only allowed in situations where
it is expected that the user might be able to resolve the conflict The 409 (Conflict) status code indicates that the request could not
and resubmit the request. The payload SHOULD include enough be completed due to a conflict with the current state of the
information for the user to recognize the source of the conflict. resource. This code is used in situations where the user might be
Ideally, the response representation would include enough information able to resolve the conflict and resubmit the request. The server
for the user or user agent to fix the problem; however, that might SHOULD generate a payload that includes enough information for a user
not be possible and is not required. to recognize the source of the conflict.
Conflicts are most likely to occur in response to a PUT request. For Conflicts are most likely to occur in response to a PUT request. For
example, if versioning were being used and the representation being example, if versioning were being used and the representation being
PUT included changes to a resource which conflict with those made by PUT included changes to a resource that conflict with those made by
an earlier (third-party) request, the server might use the 409 an earlier (third-party) request, the origin server might use a 409
response to indicate that it can't complete the request. In this response to indicate that it can't complete the request. In this
case, the response representation would likely contain a list of the case, the response representation would likely contain information
differences between the two versions. useful for merging the differences based on the revision history.
7.5.9. 410 Gone 6.5.9. 410 Gone
The target resource is no longer available at the server and no The 410 (Gone) status code indicates that access to the target
forwarding address is known. This condition is expected to be resource is no longer available at the origin server and that this
considered permanent. Clients with link editing capabilities SHOULD condition is likely to be permanent. If the origin server does not
delete references to the effective request URI after user approval. know, or has no facility to determine, whether or not the condition
If the server does not know, or has no facility to determine, whether is permanent, the status code 404 (Not Found) ought to be used
or not the condition is permanent, the status code 404 (Not Found) instead.
SHOULD be used instead.
The 410 response is primarily intended to assist the task of web The 410 response is primarily intended to assist the task of web
maintenance by notifying the recipient that the resource is maintenance by notifying the recipient that the resource is
intentionally unavailable and that the server owners desire that intentionally unavailable and that the server owners desire that
remote links to that resource be removed. Such an event is common remote links to that resource be removed. Such an event is common
for limited-time, promotional services and for resources belonging to for limited-time, promotional services and for resources belonging to
individuals no longer working at the server's site. It is not individuals no longer associated with the origin server's site. It
necessary to mark all permanently unavailable resources as "gone" or is not necessary to mark all permanently unavailable resources as
to keep the mark for any length of time -- that is left to the "gone" or to keep the mark for any length of time -- that is left to
discretion of the server owner. the discretion of the server owner.
Caches MAY use a heuristic (see Section 4.1.2 of [Part6]) to A 410 response is cacheable unless otherwise indicated by the method
determine freshness for 410 responses. definition or explicit cache controls (see Section 4.1.2 of [Part6]).
7.5.10. 411 Length Required 6.5.10. 411 Length Required
The server refuses to accept the request without a defined Content- The 411 (Length Required) status code indicates that the server
Length. The client MAY repeat the request if it adds a valid refuses to accept the request without a defined Content-Length
Content-Length header field containing the length of the message body (Section 3.3.2 of [Part1]). The client MAY repeat the request if it
in the request message. adds a valid Content-Length header field containing the length of the
message body in the request message.
7.5.11. 413 Request Representation Too Large 6.5.11. 413 Payload Too Large
The server is refusing to process a request because the request The 413 (Payload Too Large) status code indicates that the server is
representation is larger than the server is willing or able to refusing to process a request because the request payload is larger
process. The server MAY close the connection to prevent the client than the server is willing or able to process. The server MAY close
from continuing the request. the connection to prevent the client from continuing the request.
If the condition is temporary, the server SHOULD include a Retry- If the condition is temporary, the server SHOULD generate a Retry-
After header field to indicate that it is temporary and after what After header field to indicate that it is temporary and after what
time the client MAY try again. time the client MAY try again.
7.5.12. 414 URI Too Long 6.5.12. 414 URI Too Long
The server is refusing to service the request because the effective The 414 (URI Too Long) status code indicates that the server is
request URI is longer than the server is willing to interpret. This refusing to service the request because the request-target (Section
rare condition is only likely to occur when a client has improperly 5.3 of [Part1]) is longer than the server is willing to interpret.
converted a POST request to a GET request with long query This rare condition is only likely to occur when a client has
information, when the client has descended into a URI "black hole" of improperly converted a POST request to a GET request with long query
information, when the client has descended into a "black hole" of
redirection (e.g., a redirected URI prefix that points to a suffix of redirection (e.g., a redirected URI prefix that points to a suffix of
itself), or when the server is under attack by a client attempting to itself), or when the server is under attack by a client attempting to
exploit security holes present in some servers using fixed-length exploit potential security holes.
buffers for reading or manipulating the request-target.
7.5.13. 415 Unsupported Media Type A 414 response is cacheable unless otherwise indicated by the method
definition or explicit cache controls (see Section 4.1.2 of [Part6]).
The server is refusing to service the request because the request 6.5.13. 415 Unsupported Media Type
payload is in a format not supported by this request method on the
target resource.
7.5.14. 417 Expectation Failed The 415 (Unsupported Media Type) status code indicates that the
origin server is refusing to service the request because the payload
is in a format not supported by the target resource for this method.
The format problem might be due to the request's indicated Content-
Type or Content-Encoding, or as a result of inspecting the data
directly.
The expectation given in an Expect header field (see Section 6.1.2) 6.5.14. 417 Expectation Failed
could not be met by this server, or, if the server is a proxy, the
server has unambiguous evidence that the request could not be met by
the next-hop server.
7.5.15. 426 Upgrade Required The 417 (Expectation Failed) status code indicates that the
expectation given in the request's Expect header field
(Section 5.1.1) could not be met by at least one of the inbound
servers.
The request can not be completed without a prior protocol upgrade. 6.5.15. 426 Upgrade Required
This response MUST include an Upgrade header field (Section 6.3 of
[Part1]) specifying the required protocols. The 426 (Upgrade Required) status code indicates that the server
refuses to perform the request using the current protocol but might
be willing to do so after the client upgrades to a different
protocol. The server MUST send an Upgrade header field in a 426
response to indicate the required protocol(s) (Section 6.7 of
[Part1]).
Example: Example:
HTTP/1.1 426 Upgrade Required HTTP/1.1 426 Upgrade Required
Upgrade: HTTP/3.0 Upgrade: HTTP/3.0
Connection: Upgrade Connection: Upgrade
Content-Length: 53 Content-Length: 53
Content-Type: text/plain Content-Type: text/plain
This service requires use of the HTTP/3.0 protocol. This service requires use of the HTTP/3.0 protocol.
The server SHOULD include a message body in the 426 response which 6.6. Server Error 5xx
indicates in human readable form the reason for the error and
describes any alternative courses which might be available to the
user.
7.6. Server Error 5xx
Response status codes beginning with the digit "5" indicate cases in The 5xx (Server Error) class of status code indicates that the server
which the server is aware that it has erred or is incapable of is aware that it has erred or is incapable of performing the
performing the request. Except when responding to a HEAD request, requested method. Except when responding to a HEAD request, the
the server SHOULD include a representation containing an explanation server SHOULD send a representation containing an explanation of the
of the error situation, and whether it is a temporary or permanent error situation, and whether it is a temporary or permanent
condition. User agents SHOULD display any included representation to condition. User agents SHOULD display any included representation to
the user. These response codes are applicable to any request method. the user. These response codes are applicable to any request method.
7.6.1. 500 Internal Server Error 6.6.1. 500 Internal Server Error
The server encountered an unexpected condition which prevented it The 500 (Internal Server Error) status code indicates that the server
from fulfilling the request. encountered an unexpected condition that prevented it from fulfilling
the request.
7.6.2. 501 Not Implemented 6.6.2. 501 Not Implemented
The server does not support the functionality required to fulfill the The 501 (Not Implemented) status code indicates that the server does
request. This is the appropriate response when the server does not not support the functionality required to fulfill the request. This
recognize the request method and is not capable of supporting it for is the appropriate response when the server does not recognize the
any resource. request method and is not capable of supporting it for any resource.
7.6.3. 502 Bad Gateway A 501 response is cacheable unless otherwise indicated by the method
definition or explicit cache controls (see Section 4.1.2 of [Part6]).
The server, while acting as a gateway or proxy, received an invalid 6.6.3. 502 Bad Gateway
response from the upstream server it accessed in attempting to
fulfill the request.
7.6.4. 503 Service Unavailable The 502 (Bad Gateway) status code indicates that the server, while
acting as a gateway or proxy, received an invalid response from an
inbound server it accessed while attempting to fulfill the request.
The server is currently unable to handle the request due to a 6.6.4. 503 Service Unavailable
temporary overloading or maintenance of the server.
The implication is that this is a temporary condition which will be The 503 (Service Unavailable) status code indicates that the server
alleviated after some delay. If known, the length of the delay MAY is currently unable to handle the request due to a temporary overload
be indicated in a Retry-After header field (Section 8.1.3). If no or scheduled maintenance, which will likely be alleviated after some
Retry-After is given, the client SHOULD handle the response as it delay. The server MAY send a Retry-After header field
would for a 500 (Internal Server Error) response. (Section 7.1.3) to suggest an appropriate amount of time for the
client to wait before retrying the request.
Note: The existence of the 503 status code does not imply that a Note: The existence of the 503 status code does not imply that a
server has to use it when becoming overloaded. Some servers might server has to use it when becoming overloaded. Some servers might
wish to simply refuse the connection. simply refuse the connection.
7.6.5. 504 Gateway Timeout
The server, while acting as a gateway or proxy, did not receive a 6.6.5. 504 Gateway Timeout
timely response from the upstream server specified by the URI (e.g.,
HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
to access in attempting to complete the request.
Note to implementers: some deployed proxies are known to return The 504 (Gateway Timeout) status code indicates that the server,
400 (Bad Request) or 500 (Internal Server Error) when DNS lookups while acting as a gateway or proxy, did not receive a timely response
time out. from an upstream server it needed to access in order to complete the
request.
7.6.6. 505 HTTP Version Not Supported 6.6.6. 505 HTTP Version Not Supported
The server does not support, or refuses to support, the protocol The 505 (HTTP Version Not Supported) status code indicates that the
version that was used in the request message. The server is server does not support, or refuses to support, the protocol version
indicating that it is unable or unwilling to complete the request that was used in the request message. The server is indicating that
using the same major version as the client, as described in Section it is unable or unwilling to complete the request using the same
2.6 of [Part1], other than with this error message. The response major version as the client, as described in Section 2.6 of [Part1],
SHOULD contain a representation describing why that version is not other than with this error message. The server SHOULD generate a
supported and what other protocols are supported by that server. representation for the 505 response that describes why that version
is not supported and what other protocols are supported by that
server.
8. Response Header Fields 7. Response Header Fields
The response header fields allow the server to pass additional The response header fields allow the server to pass additional
information about the response which cannot be placed in the status- information about the response beyond what is placed in the status-
line. These header fields give information about the server and line. These header fields give information about the server, about
about further access to the target resource (Section 5.5 of [Part1]). further access to the target resource, or about related resources.
8.1. Control Data Although each response header field has a defined meaning, in
general, the precise semantics might be further refined by the
semantics of the request method and/or response status code.
7.1. Control Data
Response header fields can supply control data that supplements the Response header fields can supply control data that supplements the
status code or instructs the client where to go next. status code, directs caching, or instructs the client where to go
next.
+-------------------+------------------------+ +-------------------+------------------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+------------------------+ +-------------------+------------------------+
| Age | Section 7.1 of [Part6] | | Age | Section 7.1 of [Part6] |
| Date | Section 8.1.1.2 | | Cache-Control | Section 7.2 of [Part6] |
| Location | Section 8.1.2 | | Expires | Section 7.3 of [Part6] |
| Retry-After | Section 8.1.3 | | Date | Section 7.1.1.2 |
| Location | Section 7.1.2 |
| Retry-After | Section 7.1.3 |
| Vary | Section 7.1.4 |
| Warning | Section 7.5 of [Part6] |
+-------------------+------------------------+ +-------------------+------------------------+
8.1.1. Origination Date 7.1.1. Origination Date
8.1.1.1. Date/Time Formats 7.1.1.1. Date/Time Formats
HTTP applications have historically allowed three different formats Prior to 1995, there were three different formats commonly used by
for date/time stamps. However, the preferred format is a fixed- servers to communicate timestamps. For compatibility with old
length subset of that defined by [RFC1123]: implementations, all three are defined here. The preferred format is
a fixed-length and single-zone subset of the date and time
specification used by the Internet Message Format [RFC5322].
Sun, 06 Nov 1994 08:49:37 GMT ; RFC 1123 HTTP-date = IMF-fixdate / obs-date
The other formats are described here only for compatibility with An example of the preferred format is
obsolete implementations.
Sun, 06 Nov 1994 08:49:37 GMT ; IMF-fixdate
Examples of the two obsolete formats are
Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
HTTP/1.1 clients and servers that parse a date value MUST accept all A recipient that parses a timestamp value in an HTTP header field
three formats (for compatibility with HTTP/1.0), though they MUST MUST accept all three formats. A sender MUST generate the IMF-
only generate the RFC 1123 format for representing HTTP-date values fixdate format when sending an HTTP-date value in a header field.
in header fields.
All HTTP date/time stamps MUST be represented in Greenwich Mean Time
(GMT), without exception. For the purposes of HTTP, GMT is exactly
equal to UTC (Coordinated Universal Time). This is indicated in the
first two formats by the inclusion of "GMT" as the three-letter
abbreviation for time zone, and MUST be assumed when reading the
asctime format. HTTP-date is case sensitive and MUST NOT include
additional whitespace beyond that specifically included as SP in the
grammar.
HTTP-date = rfc1123-date / obs-date An HTTP-date value represents time as an instance of Coordinated
Universal Time (UTC). The first two formats indicate UTC by the
three-letter abbreviation for Greenwich Mean Time, "GMT", a
predecessor of the UTC name; values in the asctime format are assumed
to be in UTC. A sender that generates HTTP-date values from a local
clock ought to use NTP ([RFC1305]) or some similar protocol to
synchronize its clock to UTC.
Preferred format: Preferred format:
rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT IMF-fixdate = day-name "," SP date1 SP time-of-day SP GMT
; fixed length subset of the format defined in ; fixed length/zone subset of the format defined in
; Section 5.2.14 of [RFC1123] ; Section 3.3 of [RFC5322]
day-name = %x4D.6F.6E ; "Mon", case-sensitive day-name = %x4D.6F.6E ; "Mon", case-sensitive
/ %x54.75.65 ; "Tue", case-sensitive / %x54.75.65 ; "Tue", case-sensitive
/ %x57.65.64 ; "Wed", case-sensitive / %x57.65.64 ; "Wed", case-sensitive
/ %x54.68.75 ; "Thu", case-sensitive / %x54.68.75 ; "Thu", case-sensitive
/ %x46.72.69 ; "Fri", case-sensitive / %x46.72.69 ; "Fri", case-sensitive
/ %x53.61.74 ; "Sat", case-sensitive / %x53.61.74 ; "Sat", case-sensitive
/ %x53.75.6E ; "Sun", case-sensitive / %x53.75.6E ; "Sun", case-sensitive
date1 = day SP month SP year date1 = day SP month SP year
skipping to change at page 63, line 40 skipping to change at page 64, line 48
/ %x41.75.67 ; "Aug", case-sensitive / %x41.75.67 ; "Aug", case-sensitive
/ %x53.65.70 ; "Sep", case-sensitive / %x53.65.70 ; "Sep", case-sensitive
/ %x4F.63.74 ; "Oct", case-sensitive / %x4F.63.74 ; "Oct", case-sensitive
/ %x4E.6F.76 ; "Nov", case-sensitive / %x4E.6F.76 ; "Nov", case-sensitive
/ %x44.65.63 ; "Dec", case-sensitive / %x44.65.63 ; "Dec", case-sensitive
year = 4DIGIT year = 4DIGIT
GMT = %x47.4D.54 ; "GMT", case-sensitive GMT = %x47.4D.54 ; "GMT", case-sensitive
time-of-day = hour ":" minute ":" second time-of-day = hour ":" minute ":" second
; 00:00:00 - 23:59:59 ; 00:00:00 - 23:59:60 (leap second)
hour = 2DIGIT hour = 2DIGIT
minute = 2DIGIT minute = 2DIGIT
second = 2DIGIT second = 2DIGIT
The semantics of day-name, day, month, year, and time-of-day are the
same as those defined for the RFC 5322 constructs with the
corresponding name ([RFC5322], Section 3.3).
Obsolete formats: Obsolete formats:
obs-date = rfc850-date / asctime-date obs-date = rfc850-date / asctime-date
rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
date2 = day "-" month "-" 2DIGIT date2 = day "-" month "-" 2DIGIT
; day-month-year (e.g., 02-Jun-82) ; e.g., 02-Jun-82
day-name-l = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive day-name-l = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
/ %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
/ %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
/ %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
/ %x46.72.69.64.61.79 ; "Friday", case-sensitive / %x46.72.69.64.61.79 ; "Friday", case-sensitive
/ %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
/ %x53.75.6E.64.61.79 ; "Sunday", case-sensitive / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
asctime-date = day-name SP date3 SP time-of-day SP year asctime-date = day-name SP date3 SP time-of-day SP year
date3 = month SP ( 2DIGIT / ( SP 1DIGIT )) date3 = month SP ( 2DIGIT / ( SP 1DIGIT ))
; month day (e.g., Jun 2) ; e.g., Jun 2
Note: Recipients of date values are encouraged to be robust in HTTP-date is case sensitive. A sender MUST NOT generate additional
accepting date values that might have been sent by non-HTTP whitespace in an HTTP-date beyond that specifically included as SP in
applications, as is sometimes the case when retrieving or posting the grammar. The semantics of day-name, day, month, year, and time-
messages via proxies/gateways to SMTP or NNTP. of-day are the same as those defined for the Internet Message Format
constructs with the corresponding name ([RFC5322], Section 3.3).
Recipients of a timestamp value in rfc850-date format, which uses a
two-digit year, SHOULD interpret a timestamp that appears to be more
than 50 years in the future as representing the most recent year in
the past that had the same last two digits.
Recipients of timestamp values are encouraged to be robust in parsing
timestamps unless otherwise restricted by the field definition. For
example, messages are occasionally forwarded over HTTP from a non-
HTTP source that might generate any of the date and time
specifications defined by the Internet Message Format.
Note: HTTP requirements for the date/time stamp format apply only Note: HTTP requirements for the date/time stamp format apply only
to their usage within the protocol stream. Clients and servers to their usage within the protocol stream. Implementations are
are not required to use these formats for user presentation, not required to use these formats for user presentation, request
request logging, etc. logging, etc.
8.1.1.2. Date 7.1.1.2. Date
The "Date" header field represents the date and time at which the The "Date" header field represents the date and time at which the
message was originated, having the same semantics as the Origination message was originated, having the same semantics as the Origination
Date Field (orig-date) defined in Section 3.6.1 of [RFC5322]. The Date Field (orig-date) defined in Section 3.6.1 of [RFC5322]. The
field value is an HTTP-date, as defined in Section 8.1.1.1; it MUST field value is an HTTP-date, as defined in Section 7.1.1.1.
be sent in rfc1123-date format.
Date = HTTP-date Date = HTTP-date
An example is An example is
Date: Tue, 15 Nov 1994 08:12:31 GMT Date: Tue, 15 Nov 1994 08:12:31 GMT
Origin servers MUST include a Date header field in all responses, When a Date header field is generated, the sender SHOULD generate its
except in these cases: field value as the best available approximation of the date and time
of message generation. In theory, the date ought to represent the
1. If the response status code is 100 (Continue) or 101 (Switching moment just before the payload is generated. In practice, the date
Protocols), the response MAY include a Date header field, at the can be generated at any time during message origination.
server's option.
2. If the response status code conveys a server error, e.g., 500
(Internal Server Error) or 503 (Service Unavailable), and it is
inconvenient or impossible to generate a valid Date.
3. If the server does not have a clock that can provide a reasonable
approximation of the current time, its responses MUST NOT include
a Date header field.
A received message that does not have a Date header field MUST be An origin server MUST NOT send a Date header field if it does not
assigned one by the recipient if the message will be cached by that have a clock capable of providing a reasonable approximation of the
recipient. current instance in Coordinated Universal Time. An origin server MAY
send a Date header field if the response is in the 1xx
(Informational) or 5xx (Server Error) class of status codes. An
origin server MUST send a Date header field in all other cases.
Clients can use the Date header field as well; in order to keep A recipient with a clock that receives a response message without a
request messages small, they are advised not to include it when it Date header field MUST record the time it was received and append a
doesn't convey any useful information (as is usually the case for corresponding Date header field to the message's header block if it
requests that do not contain a payload). is cached or forwarded downstream.
The HTTP-date sent in a Date header field SHOULD NOT represent a date A user agent MAY send a Date header field in a request, though
and time subsequent to the generation of the message. It SHOULD generally will not do so unless it is believed to convey useful
represent the best available approximation of the date and time of information to the server. For example, custom applications of HTTP
message generation, unless the implementation has no means of might convey a Date if the server is expected to adjust its
generating a reasonably accurate date and time. In theory, the date interpretation of the user's request based on differences between the
ought to represent the moment just before the payload is generated. user agent and server clocks.
In practice, the date can be generated at any time during the message
origination without affecting its semantic value.
8.1.2. Location 7.1.2. Location
The "Location" header field MAY be sent in responses to refer to a The "Location" header field is used in some responses to refer to a
specific resource in accordance with the semantics of the status specific resource in relation to the response. The type of
code. relationship is defined by the combination of request method and
status code semantics.
Location = URI-reference Location = URI-reference
For 201 (Created) responses, the Location is the URI of the new
resource which was created by the request. For 3xx (Redirection)
responses, the location SHOULD indicate the server's preferred URI
for automatic redirection to the resource.
The field value consists of a single URI-reference. When it has the The field value consists of a single URI-reference. When it has the
form of a relative reference ([RFC3986], Section 4.2), the final form of a relative reference ([RFC3986], Section 4.2), the final
value is computed by resolving it against the effective request URI value is computed by resolving it against the effective request URI
([RFC3986], Section 5). If the original URI, as navigated to by the ([RFC3986], Section 5).
user agent, did contain a fragment identifier, and the final value
does not, then the original URI's fragment identifier is added to the
final value.
For example, the original URI "http://www.example.org/~tim", combined For 201 (Created) responses, the Location value refers to the primary
with a field value given as: resource created by the request. For 3xx (Redirection) responses,
the Location value refers to the preferred target resource for
automatically redirecting the request.
Location: /pub/WWW/People.html#tim When Location is provided in a 3xx (Redirection) response and the URI
reference that the user agent used to generate the request target
contains a fragment identifier, the user agent SHOULD process the
redirection as if the Location field value inherits the original
fragment. In other words, if the Location does not have a fragment
component, the user agent SHOULD interpret the Location reference as
if it had the original reference's fragment.
would result in a final value of For example, a GET request generated for the URI reference
"http://www.example.org/pub/WWW/People.html#tim" "http://www.example.org/~tim" might result in a 303 (See Other)
response containing the header field:
An original URI "http://www.example.org/index.html#larry", combined Location: /People.html#tim
with a field value given as:
which suggests that the user agent redirect to
"http://www.example.org/People.html#tim"
Likewise, a GET request generated for the URI reference
"http://www.example.org/index.html#larry" might result in a 301
(Moved Permanently) response containing the header field:
Location: http://www.example.net/index.html Location: http://www.example.net/index.html
would result in a final value of which suggests that the user agent redirect to
"http://www.example.net/index.html#larry", preserving the original "http://www.example.net/index.html#larry", preserving the original
fragment identifier. fragment identifier.
There are circumstances in which a fragment identifier in a Location
value would not be appropriate. For example, the Location header
field in a 201 (Created) response is supposed to provide a URI that
is specific to the created resource.
Note: Some recipients attempt to recover from Location fields that Note: Some recipients attempt to recover from Location fields that
are not valid URI references. This specification does not mandate are not valid URI references. This specification does not mandate
or define such processing, but does allow it. or define such processing, but does allow it for the sake of
robustness.
There are circumstances in which a fragment identifier in a Location
URI would not be appropriate. For instance, when it appears in a 201
(Created) response, where the Location header field specifies the URI
for the entire created resource.
Note: The Content-Location header field (Section 3.1.4.2) differs Note: The Content-Location header field (Section 3.1.4.2) differs
from Location in that the Content-Location identifies the most from Location in that the Content-Location refers to the most
specific resource corresponding to the enclosed representation. specific resource corresponding to the enclosed representation.
It is therefore possible for a response to contain header fields It is therefore possible for a response to contain both the
for both Location and Content-Location. Location and Content-Location header fields.
8.1.3. Retry-After 7.1.3. Retry-After
The header "Retry-After" field can be used with a 503 (Service Servers send the "Retry-After" header field to indicate how long the
Unavailable) response to indicate how long the service is expected to user agent ought to wait before making a follow-up request. When
be unavailable to the requesting client. This field MAY also be used sent with a 503 (Service Unavailable) response, Retry-After indicates
with any 3xx (Redirection) response to indicate the minimum time the how long the service is expected to be unavailable to the client.
user-agent is asked to wait before issuing the redirected request. When sent with any 3xx (Redirection) response, Retry-After indicates
the minimum time that the user agent is asked to wait before issuing
the redirected request.
The value of this field can be either an HTTP-date or an integer The value of this field can be either an HTTP-date or an integer
number of seconds (in decimal) after the time of the response. number of seconds (in decimal) after the time of the response.
Retry-After = HTTP-date / delta-seconds Retry-After = HTTP-date / delta-seconds
Time spans are non-negative decimal integers, representing time in Time spans are non-negative decimal integers, representing time in
seconds. seconds.
delta-seconds = 1*DIGIT delta-seconds = 1*DIGIT
Two examples of its use are Two examples of its use are
Retry-After: Fri, 31 Dec 1999 23:59:59 GMT Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
Retry-After: 120 Retry-After: 120
In the latter example, the delay is 2 minutes. In the latter example, the delay is 2 minutes.
8.2. Selected Representation Header Fields 7.1.4. Vary
We use the term "selected representation" to refer to the the current The "Vary" header field describes what parts of a request message,
representation of a target resource that would have been selected in aside from the method and request target, might influence the origin
a successful response if the same request had used the method GET and server's process for selecting and representing the response. The
excluded any conditional request header fields. value consists of either a single asterisk ("*") or a list of header
field names (case-insensitive).
Additional header fields define metadata about the selected Vary = "*" / 1#field-name
representation, which might differ from the representation included
in the message for responses to some state-changing methods. The
following header fields are defined as selected representation
metadata:
+-------------------+------------------------+ A Vary field value of "*" signals that anything about the request
| Header Field Name | Defined in... | might play a role in selecting the response representation, possibly
+-------------------+------------------------+ including elements outside the message syntax (e.g., the client's
| ETag | Section 2.3 of [Part4] | network address), and thus a recipient will not be able to determine
| Last-Modified | Section 2.2 of [Part4] | whether this response is appropriate for a later request without
| Vary | Section 8.2.1 | forwarding the request to the origin server. A proxy MUST NOT
+-------------------+------------------------+ generate a Vary field with a "*" value.
8.2.1. Vary A Vary field value consisting of a comma-separated list of names
indicates that the named request header fields, known as the
selecting header fields, might have a role in selecting the
representation. The potential selecting header fields are not
limited to those defined by this specification.
The "Vary" header field conveys the set of header fields that were For example, a response that contains
used to select the representation.
Caches use this information as part of determining whether a stored Vary: accept-encoding, accept-language
response can be used to satisfy a given request (Section 4.3 of
[Part6]).
In uncacheable or stale responses, the Vary field value advises the indicates that the origin server might have used the request's
user agent about the criteria that were used to select the Accept-Encoding and Accept-Language fields (or lack thereof) as
representation. determining factors while choosing the content for this response.
Vary = "*" / 1#field-name An origin server might send Vary with a list of fields for two
purposes:
The set of header fields named by the Vary field value is known as 1. To inform cache recipients that they MUST NOT use this response
the selecting header fields. to satisfy a later request unless the later request has the same
values for the listed fields as the original request (Section 4.3
of [Part6]). In other words, Vary expands the cache key required
to match a new request to the stored cache entry.
A server SHOULD include a Vary header field with any cacheable 2. To inform user agent recipients that this response is subject to
response that is subject to proactive negotiation. Doing so allows a content negotiation (Section 5.3) and that a different
cache to properly interpret future requests on that resource and representation might be sent in a subsequent request if
informs the user agent about the presence of negotiation on that additional parameters are provided in the listed header fields
resource. A server MAY include a Vary header field with a non- (proactive negotiation).
cacheable response that is subject to proactive negotiation, since
this might provide the user agent with useful information about the
dimensions over which the response varies at the time of the
response.
A Vary field value of "*" signals that unspecified parameters not An origin server SHOULD send a Vary header field when its algorithm
limited to the header fields (e.g., the network address of the for selecting a representation varies based on aspects of the request
client), play a role in the selection of the response representation; message other than the method and request target, unless the variance
therefore, a cache cannot determine whether this response is cannot be crossed or the origin server has been deliberately
appropriate. A proxy MUST NOT generate the "*" value. configured to prevent cache transparency. For example, there is no
need to send the Authorization field name in Vary because reuse
across users is constrained by the field definition (Section 4.1 of
[Part7]). Likewise, an origin server might use Cache-Control
directives (Section 7.2 of [Part6]) to supplant Vary if it considers
the variance less significant than the performance cost of Vary's
impact on caching.
The field-names given are not limited to the set of standard header 7.2. Validator Header Fields
fields defined by this specification. Field names are case-
insensitive.
8.3. Authentication Challenges Validator header fields convey metadata about the selected
representation (Section 3). In responses to safe requests, validator
fields describe the selected representation chosen by the origin
server while handling the response. Note that, depending on the
status code semantics, the selected representation for a given
response is not necessarily the same as the representation enclosed
as response payload.
In a successful response to a state-changing request, validator
fields describe the new representation that has replaced the prior
selected representation as a result of processing the request.
For example, an ETag header field in a 201 response communicates the
entity-tag of the newly created resource's representation, so that it
can be used in later conditional requests to prevent the "lost
update" problem [Part4].
+-------------------+------------------------+
| Header Field Name | Defined in... |
+-------------------+------------------------+
| ETag | Section 2.3 of [Part4] |
| Last-Modified | Section 2.2 of [Part4] |
+-------------------+------------------------+
7.3. Authentication Challenges
Authentication challenges indicate what mechanisms are available for Authentication challenges indicate what mechanisms are available for
the client to provide authentication credentials in future requests. the client to provide authentication credentials in future requests.
+--------------------+------------------------+ +--------------------+------------------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+--------------------+------------------------+ +--------------------+------------------------+
| WWW-Authenticate | Section 4.4 of [Part7] | | WWW-Authenticate | Section 4.4 of [Part7] |
| Proxy-Authenticate | Section 4.2 of [Part7] | | Proxy-Authenticate | Section 4.2 of [Part7] |
+--------------------+------------------------+ +--------------------+------------------------+
8.4. Informative 7.4. Response Context
The remaining response header fields provide more information about The remaining response header fields provide more information about
the target resource for potential use in later requests. the target resource for potential use in later requests.
+-------------------+------------------------+ +-------------------+------------------------+
| Header Field Name | Defined in... | | Header Field Name | Defined in... |
+-------------------+------------------------+ +-------------------+------------------------+
| Accept-Ranges | Section 5.1 of [Part5] | | Accept-Ranges | Section 2.3 of [Part5] |
| Allow | Section 8.4.1 | | Allow | Section 7.4.1 |
| Server | Section 8.4.2 | | Server | Section 7.4.2 |
+-------------------+------------------------+ +-------------------+------------------------+
8.4.1. Allow 7.4.1. Allow
The "Allow" header field lists the set of methods advertised as The "Allow" header field lists the set of methods advertised as
supported by the target resource. The purpose of this field is supported by the target resource. The purpose of this field is
strictly to inform the recipient of valid request methods associated strictly to inform the recipient of valid request methods associated
with the resource. with the resource.
Allow = #method Allow = #method
Example of use: Example of use:
Allow: GET, HEAD, PUT Allow: GET, HEAD, PUT
The actual set of allowed methods is defined by the origin server at The actual set of allowed methods is defined by the origin server at
the time of each request. the time of each request. An origin server MUST generate an Allow
field in a 405 (Method Not Allowed) response and MAY do so in any
other response. An empty Allow field value indicates that the
resource allows no methods, which might occur in a 405 response if
the resource has been temporarily disabled by configuration.
A proxy MUST NOT modify the Allow header field -- it does not need to A proxy MUST NOT modify the Allow header field -- it does not need to
understand all the methods specified in order to handle them understand all of the indicated methods in order to handle them
according to the generic message handling rules. according to the generic message handling rules.
8.4.2. Server 7.4.2. Server
The "Server" header field contains information about the software The "Server" header field contains information about the software
used by the origin server to handle the request. used by the origin server to handle the request, which is often used
by clients to help identify the scope of reported interoperability
The field can contain multiple product tokens (Section 4) and problems, to work around or tailor requests to avoid particular
comments (Section 3.2 of [Part1]) identifying the server and any server limitations, and for analytics regarding server or operating
significant subproducts. The product tokens are listed in order of system use. An origin server MAY generate a Server field in its
their significance for identifying the application. responses.
Server = product *( RWS ( product / comment ) ) Server = product *( RWS ( product / comment ) )
The Server field-value consists of one or more product identifiers,
each followed by zero or more comments (Section 3.2 of [Part1]),
which together identify the origin server software and its
significant subproducts. By convention, the product identifiers are
listed in decreasing order of their significance for identifying the
origin server software. Each product identifier consists of a name
and optional version, as defined in Section 5.5.3.
Example: Example:
Server: CERN/3.0 libwww/2.17 Server: CERN/3.0 libwww/2.17
If the response is being forwarded through a proxy, the proxy An origin server SHOULD NOT generate a Server field containing
application MUST NOT modify the Server header field. Instead, it needlessly fine-grained detail and SHOULD limit the addition of
MUST include a Via field (as described in Section 5.7 of [Part1]). subproducts by third parties. Overly long and detailed Server field
values increase response latency and potentially reveal internal
Note: Revealing the specific software version of the server might implementation details that might make it (slightly) easier for
allow the server machine to become more vulnerable to attacks attackers to find and exploit known security holes.
against software that is known to contain security holes. Server
implementers are encouraged to make this field a configurable
option.
9. IANA Considerations 8. IANA Considerations
9.1. Method Registry 8.1. Method Registry
The HTTP Method Registry defines the name space for the request The HTTP Method Registry defines the name space for the request
method token (Section 5). The method registry is maintained at method token (Section 4). The method registry is maintained at
<http://www.iana.org/assignments/http-methods>. <http://www.iana.org/assignments/http-methods>.
9.1.1. Procedure 8.1.1. Procedure
HTTP method registrations MUST include the following fields: HTTP method registrations MUST include the following fields:
o Method Name (see Section 5) o Method Name (see Section 4)
o Safe ("yes" or "no", see Section 5.2.1) o Safe ("yes" or "no", see Section 4.2.1)
o Idempotent ("yes" or "no", see Section 5.2.2) o Idempotent ("yes" or "no", see Section 4.2.2)
o Pointer to specification text o Pointer to specification text
Values to be added to this name space require IETF Review (see Values to be added to this name space require IETF Review (see
[RFC5226], Section 4.1). [RFC5226], Section 4.1).
9.1.2. Considerations for New Methods 8.1.2. Considerations for New Methods
Standardized methods are generic; that is, they are potentially Standardized methods are generic; that is, they are potentially
applicable to any resource, not just one particular media type, kind applicable to any resource, not just one particular media type, kind
of resource, or application. As such, it is preferred that new of resource, or application. As such, it is preferred that new
methods be registered in a document that isn't specific to a single methods be registered in a document that isn't specific to a single
application or data format, since orthogonal technologies deserve application or data format, since orthogonal technologies deserve
orthogonal specification. orthogonal specification.
Since message parsing (Section 3.3 of [Part1]) needs to be Since message parsing (Section 3.3 of [Part1]) needs to be
independent of method semantics (aside from responses to HEAD), independent of method semantics (aside from responses to HEAD),
definitions of new methods cannot change the parsing algorithm or definitions of new methods cannot change the parsing algorithm or
prohibit the presence of a message body on either the request or the prohibit the presence of a message body on either the request or the
response message. Definitions of new methods can specify that only a response message. Definitions of new methods can specify that only a
zero-length message body is allowed by requiring a Content-Length zero-length message body is allowed by requiring a Content-Length
header field with a value of "0". header field with a value of "0".
New method definitions need to indicate whether they are safe A new method definition needs to indicate whether it is safe
(Section 5.2.1), idempotent (Section 5.2.2), cacheable (Section 4.2.1), idempotent (Section 4.2.2), cacheable
(Section 5.2.3), and what semantics are to be associated with the (Section 4.2.3), what semantics are to be associated with the payload
payload body if any is present in the request. If a method is body if any is present in the request, and what refinements the
cacheable, the method definition ought to describe how, and under 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 what conditions, a cache can store a response and use it to satisfy a
subsequent request. subsequent request. The new method ought to describe whether it can
be made conditional (Section 5.2) 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 ([Part5]), it ought to
document this too.
9.1.3. Registrations 8.1.3. Registrations
The HTTP Method Registry shall be populated with the registrations The HTTP Method Registry shall be populated with the registrations
below: below:
+---------+------+------------+---------------+ +---------+------+------------+---------------+
| Method | Safe | Idempotent | Reference | | Method | Safe | Idempotent | Reference |
+---------+------+------------+---------------+ +---------+------+------------+---------------+
| CONNECT | no | no | Section 5.3.6 | | CONNECT | no | no | Section 4.3.6 |
| DELETE | no | yes | Section 5.3.5 | | DELETE | no | yes | Section 4.3.5 |
| GET | yes | yes | Section 5.3.1 | | GET | yes | yes | Section 4.3.1 |
| HEAD | yes | yes | Section 5.3.2 | | HEAD | yes | yes | Section 4.3.2 |
| OPTIONS | yes | yes | Section 5.3.7 | | OPTIONS | yes | yes | Section 4.3.7 |
| POST | no | no | Section 5.3.3 | | POST | no | no | Section 4.3.3 |
| PUT | no | yes | Section 5.3.4 | | PUT | no | yes | Section 4.3.4 |
| TRACE | yes | yes | Section 5.3.8 | | TRACE | yes | yes | Section 4.3.8 |
+---------+------+------------+---------------+ +---------+------+------------+---------------+
9.2. Status Code Registry 8.2. Status Code Registry
The HTTP Status Code Registry defines the name space for the response The HTTP Status Code Registry defines the name space for the response
status-code token (Section 7). The status code registry is status-code token (Section 6). The status code registry is
maintained at <http://www.iana.org/assignments/http-status-codes>. maintained at <http://www.iana.org/assignments/http-status-codes>.
This section replaces the registration procedure for HTTP Status This section replaces the registration procedure for HTTP Status
Codes previously defined in Section 7.1 of [RFC2817]. Codes previously defined in Section 7.1 of [RFC2817].
9.2.1. Procedure 8.2.1. Procedure
Values to be added to the HTTP status code name space require IETF Values to be added to the HTTP status code name space require IETF
Review (see [RFC5226], Section 4.1). Review (see [RFC5226], Section 4.1).
9.2.2. Considerations for New Status Codes 8.2.2. Considerations for New Status Codes
When it is necessary to express semantics for a response that are not When it is necessary to express semantics for a response that are not
defined by current status codes, a new status code can be registered. defined by current status codes, a new status code can be registered.
HTTP status codes are generic; they are potentially applicable to any
resource, not just one particular media type, "type" of resource, or Status codes are generic; they are potentially applicable to any
application. As such, it is preferred that new status codes be resource, not just one particular media type, kind of resource, or
registered in a document that isn't specific to a single application. application of HTTP. As such, it is preferred that new status codes
be registered in a document that isn't specific to a single
application.
New status codes are required to fall under one of the categories New status codes are required to fall under one of the categories
defined in Section 7. To allow existing parsers to properly handle defined in Section 6. To allow existing parsers to process the
them, new status codes cannot disallow a payload, although they can response message, new status codes cannot disallow a payload,
mandate a zero-length payload body. although they can mandate a zero-length payload body.
A definition for a new status code ought to explain the request Proposals for new status codes that are not yet widely deployed ought
conditions that produce a response containing that status code (e.g., to avoid allocating a specific number for the code until there is
combinations of request header fields and/or method(s)) along with clear consensus that it will be registered; instead, early drafts can
any dependencies on response header fields (e.g., what fields are use a notation such as "4NN", or "3N0" .. "3N9", to indicate the
required and what fields can modify the semantics). A response that class of the proposed status code(s) without consuming a number
can transfer a payload ought to specify expected cache behavior prematurely.
(e.g., cacheability and freshness criteria, as described in [Part6])
and whether the payload has any implied association with an
identified resource (Section 3.1.4.1).
9.2.3. Registrations The definition of a new status code ought to explain the request
conditions that would cause a response containing that status code
(e.g., combinations of request header fields and/or method(s)) along
with any dependencies on response header fields (e.g., what fields
are required, what fields can modify the semantics, and what header
field semantics are further refined when used with the new status
code).
The definition of a new status code ought to specify whether or not
it is cacheable. Note that all status codes can be cached if the
response they occur in has explicit freshness information; however,
status codes that are defined as being cacheable are allowed to be
cached without explicit freshness information. Likewise, the
definition of a status code can place constraints upon cache
behaviour. See [Part6] for more information.
Finally, the definition of a new status code ought to indicate
whether the payload has any implied association with an identified
resource (Section 3.1.4.1).
8.2.3. Registrations
The HTTP Status Code Registry shall be updated with the registrations The HTTP Status Code Registry shall be updated with the registrations
below: below:
+-------+----------------------------------+----------------+ +-------+-------------------------------+----------------+
| Value | Description | Reference | | Value | Description | Reference |
+-------+----------------------------------+----------------+ +-------+-------------------------------+----------------+
| 100 | Continue | Section 7.2.1 | | 100 | Continue | Section 6.2.1 |
| 101 | Switching Protocols | Section 7.2.2 | | 101 | Switching Protocols | Section 6.2.2 |
| 200 | OK | Section 7.3.1 | | 200 | OK | Section 6.3.1 |
| 201 | Created | Section 7.3.2 | | 201 | Created | Section 6.3.2 |
| 202 | Accepted | Section 7.3.3 | | 202 | Accepted | Section 6.3.3 |
| 203 | Non-Authoritative Information | Section 7.3.4 | | 203 | Non-Authoritative Information | Section 6.3.4 |
| 204 | No Content | Section 7.3.5 | | 204 | No Content | Section 6.3.5 |
| 205 | Reset Content | Section 7.3.6 | | 205 | Reset Content | Section 6.3.6 |
| 300 | Multiple Choices | Section 7.4.1 | | 300 | Multiple Choices | Section 6.4.1 |
| 301 | Moved Permanently | Section 7.4.2 | | 301 | Moved Permanently | Section 6.4.2 |
| 302 | Found | Section 7.4.3 | | 302 | Found | Section 6.4.3 |
| 303 | See Other | Section 7.4.4 | | 303 | See Other | Section 6.4.4 |
| 305 | Use Proxy | Section 7.4.5 | | 305 | Use Proxy | Section 6.4.5 |
| 306 | (Unused) | Section 7.4.6 | | 306 | (Unused) | Section 6.4.6 |
| 307 | Temporary Redirect | Section 7.4.7 | | 307 | Temporary Redirect | Section 6.4.7 |
| 400 | Bad Request | Section 7.5.1 | | 400 | Bad Request | Section 6.5.1 |
| 402 | Payment Required | Section 7.5.2 | | 402 | Payment Required | Section 6.5.2 |
| 403 | Forbidden | Section 7.5.3 | | 403 | Forbidden | Section 6.5.3 |
| 404 | Not Found | Section 7.5.4 | | 404 | Not Found | Section 6.5.4 |
| 405 | Method Not Allowed | Section 7.5.5 | | 405 | Method Not Allowed | Section 6.5.5 |
| 406 | Not Acceptable | Section 7.5.6 | | 406 | Not Acceptable | Section 6.5.6 |
| 408 | Request Timeout | Section 7.5.7 | | 408 | Request Timeout | Section 6.5.7 |
| 409 | Conflict | Section 7.5.8 | | 409 | Conflict | Section 6.5.8 |
| 410 | Gone | Section 7.5.9 | | 410 | Gone | Section 6.5.9 |
| 411 | Length Required | Section 7.5.10 | | 411 | Length Required | Section 6.5.10 |
| 413 | Request Representation Too Large | Section 7.5.11 | | 413 | Payload Too Large | Section 6.5.11 |
| 414 | URI Too Long | Section 7.5.12 | | 414 | URI Too Long | Section 6.5.12 |
| 415 | Unsupported Media Type | Section 7.5.13 | | 415 | Unsupported Media Type | Section 6.5.13 |
| 417 | Expectation Failed | Section 7.5.14 | | 417 | Expectation Failed | Section 6.5.14 |
| 426 | Upgrade Required | Section 7.5.15 | | 426 | Upgrade Required | Section 6.5.15 |
| 500 | Internal Server Error | Section 7.6.1 | | 500 | Internal Server Error | Section 6.6.1 |
| 501 | Not Implemented | Section 7.6.2 | | 501 | Not Implemented | Section 6.6.2 |
| 502 | Bad Gateway | Section 7.6.3 | | 502 | Bad Gateway | Section 6.6.3 |
| 503 | Service Unavailable | Section 7.6.4 | | 503 | Service Unavailable | Section 6.6.4 |
| 504 | Gateway Timeout | Section 7.6.5 | | 504 | Gateway Timeout | Section 6.6.5 |
| 505 | HTTP Version Not Supported | Section 7.6.6 | | 505 | HTTP Version Not Supported | Section 6.6.6 |
+-------+----------------------------------+----------------+ +-------+-------------------------------+----------------+
9.3. Header Field Registry 8.3. Header Field Registry
HTTP header fields are registered within the Message Header Field HTTP header fields are registered within the Message Header Field
Registry located at <http://www.iana.org/assignments/message-headers/ Registry located at <http://www.iana.org/assignments/message-headers/
message-header-index.html>, as defined by [RFC3864]. message-header-index.html>, as defined by [BCP90].
9.3.1. Considerations for New Header Fields 8.3.1. Considerations for New Header Fields
Header fields are key:value pairs that can be used to communicate Header fields are key:value pairs that can be used to communicate
data about the message, its payload, the target resource, or the data about the message, its payload, the target resource, or the
connection (i.e., control data). See Section 3.2 of [Part1] for a connection (i.e., control data). See Section 3.2 of [Part1] for a
general definition of header field syntax in HTTP messages. general definition of header field syntax in HTTP messages.
The requirements for header field names are defined in Section 4.1 of The requirements for header field names are defined in [BCP90].
[RFC3864]. Authors of specifications defining new fields are advised Authors of specifications defining new fields are advised to keep the
to keep the name as short as practical, and not to prefix them with name as short as practical and to not prefix the name with "X-"
"X-" if they are to be registered (either immediately or in the unless the header field will never be used on the Internet. (The
future). "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.)
New header field values typically have their syntax defined using New header field values typically have their syntax defined using
ABNF ([RFC5234]), using the extension defined in Appendix B of ABNF ([RFC5234]), using the extension defined in Appendix B of
[Part1] as necessary, and are usually constrained to the range of [Part1] as necessary, and are usually constrained to the range of
ASCII characters. Header fields needing a greater range of ASCII characters. Header fields needing a greater range of
characters can use an encoding such as the one defined in [RFC5987]. 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 3.2.4 of [Part1]). Field definitions where
leading or trailing whitespace in values is significant will have to
use a container syntax such as quoted-string.
Because commas (",") are used as a generic delimiter between field- Because commas (",") are used as a generic delimiter between field-
values, they need to be treated with care if they are allowed in the values, they need to be treated with care if they are allowed in the
field-value's payload. Typically, components that might contain a field-value. Typically, components that might contain a comma are
comma are protected with double-quotes using the quoted-string ABNF protected with double-quotes using the quoted-string ABNF production
production (Section 3.2.4 of [Part1]). (Section 3.2.6 of [Part1]).
For example, a textual date and a URI (either of which might contain For example, a textual date and a URI (either of which might contain
a comma) could be safely carried in field-values like these: a comma) could be safely carried in field-values like these:
Example-URI-Field: "http://example.com/a.html,foo", Example-URI-Field: "http://example.com/a.html,foo",
"http://without-a-comma.example.com/" "http://without-a-comma.example.com/"
Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005" Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
Note that double-quote delimiters almost always are used with the Note that double-quote delimiters almost always are used with the
quoted-string production; using a different syntax inside double- quoted-string production; using a different syntax inside double-
skipping to change at page 75, line 9 skipping to change at page 77, line 17
example, see the notes on parameter handling for media types in example, see the notes on parameter handling for media types in
Section 3.1.1.1). Section 3.1.1.1).
Authors of specifications defining new header fields are advised to Authors of specifications defining new header fields are advised to
consider documenting: consider documenting:
o Whether the field is a single value, or whether it can be a list o Whether the field is a single value, or whether it can be a list
(delimited by commas; see Section 3.2 of [Part1]). (delimited by commas; see Section 3.2 of [Part1]).
If it does not use the list syntax, document how to treat messages If it does not use the list syntax, document how to treat messages
where the header field occurs multiple times (a sensible default where the field occurs multiple times (a sensible default would be
would be to ignore the