rfc2616.txt   draft-lafon-rfc2616bis-latest.txt 
Network Working Group R. Fielding Network Working Group R. Fielding
Request for Comments: 2616 UC Irvine Internet-Draft Day Software
Obsoletes: 2068 J. Gettys Obsoletes: 2616 (if approved) J. Gettys
Category: Standards Track Compaq/W3C Intended status: Standards Track One Laptop per Child
J. Mogul Expires: June 3, 2008 J. Mogul
Compaq HP
H. Frystyk H. Frystyk
W3C/MIT Microsoft
L. Masinter L. Masinter
Xerox Adobe Systems
P. Leach P. Leach
Microsoft Microsoft
T. Berners-Lee T. Berners-Lee
W3C/MIT W3C/MIT
June 1999 Y. Lafon, Ed.
W3C
J. Reschke, Ed.
greenbytes
December 2007
Hypertext Transfer Protocol -- HTTP/1.1 Hypertext Transfer Protocol -- HTTP/1.1
draft-lafon-rfc2616bis-latest
Status of this Memo Status of this Memo
This document specifies an Internet standards track protocol for the By submitting this Internet-Draft, each author represents that any
Internet community, and requests discussion and suggestions for applicable patent or other IPR claims of which he or she is aware
improvements. Please refer to the current edition of the "Internet have been or will be disclosed, and any of which he or she becomes
Official Protocol Standards" (STD 1) for the standardization state aware will be disclosed, in accordance with Section 6 of BCP 79.
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
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Drafts.
Copyright (C) The Internet Society (1999). All Rights Reserved. Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on June 3, 2008.
Abstract Abstract
The Hypertext Transfer Protocol (HTTP) is an application-level The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypermedia information protocol for distributed, collaborative, hypermedia information
systems. It is a generic, stateless, protocol which can be used for systems. It is a generic, stateless, protocol which can be used for
many tasks beyond its use for hypertext, such as name servers and many tasks beyond its use for hypertext, such as name servers and
distributed object management systems, through extension of its distributed object management systems, through extension of its
request methods, error codes and headers [47]. A feature of HTTP is request methods, error codes and headers [RFC2324]. A feature of
the typing and negotiation of data representation, allowing systems HTTP is the typing and negotiation of data representation, allowing
to be built independently of the data being transferred. systems to be built independently of the data being transferred.
HTTP has been in use by the World-Wide Web global information HTTP has been in use by the World-Wide Web global information
initiative since 1990. This specification defines the protocol initiative since 1990. This specification defines the protocol
referred to as "HTTP/1.1", and is an update to RFC 2068 [33]. referred to as "HTTP/1.1", and is an update to RFC2616.
Editorial Note (To be removed by RFC Editor before publication)
Distribution of this document is unlimited. Please send comments to
the Hypertext Transfer Protocol (HTTP) mailing list at
ietf-http-wg@w3.org [1], which may be joined by sending a message
with subject "subscribe" to ietf-http-wg-request@w3.org [2].
Discussions of the HTTP working group are archived at
<http://lists.w3.org/Archives/Public/ietf-http-wg/>. XML versions,
latest edits and the issues list for this document are available from
<http://www.w3.org/Protocols/HTTP/1.1/rfc2616bis/>.
The purpose of this document is to revise [RFC2616], doing only
minimal corrections. For now, it is not planned to advance the
standards level of HTTP, thus - if published - the specification will
still be a "Proposed Standard" (see [RFC2026]).
The current plan is to incorporate known errata, and to update the
specification text according to the current IETF publication
guidelines. In particular:
o Incorporate the corrections collected in the RFC2616 errata
document (<http://purl.org/NET/http-errata>) (most of the
suggested fixes have been applied to draft 01 [3]).
o Incorporate corrections for newly discovered and agreed-upon
problems, using the HTTP WG mailing list as forum and
<http://www.w3.org/Protocols/HTTP/1.1/rfc2616bis/issues/> as
issues list.
o Update references, and re-classify them into "Normative" and
"Informative", based on the prior work done by Jim Gettys in
<http://tools.ietf.org/html/draft-gettys-http-v11-spec-rev-00>.
This document is based on a variant of the original RFC2616
specification formatted using Marshall T. Rose's "xml2rfc" tool (see
<http://xml.resource.org>) and therefore deviates from the original
text in word wrapping, page breaks, list formatting, reference
formatting, whitespace usage and appendix numbering. Otherwise, it
is supposed to contain an accurate copy of the original specification
text. See <http://www.w3.org/Protocols/HTTP/1.1/
rfc2616bis-00-from-rfc2616.diff.html> for a comparison between both
documents, as generated by "rfcdiff"
(<http://tools.ietf.org/tools/rfcdiff/>).
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 12
1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . 8 1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . 12
1.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 8 1.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 12
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . 9 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . 13
1.4. Overall Operation . . . . . . . . . . . . . . . . . . . 13 1.4. Overall Operation . . . . . . . . . . . . . . . . . . . 17
2. Notational Conventions and Generic Grammar . . . . . . . . . 16 2. Notational Conventions and Generic Grammar . . . . . . . . . 20
2.1. Augmented BNF . . . . . . . . . . . . . . . . . . . . . 16 2.1. Augmented BNF . . . . . . . . . . . . . . . . . . . . . 20
2.2. Basic Rules . . . . . . . . . . . . . . . . . . . . . . 18 2.2. Basic Rules . . . . . . . . . . . . . . . . . . . . . . 22
3. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 20 3. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 24
3.1. HTTP Version . . . . . . . . . . . . . . . . . . . . . . 20 3.1. HTTP Version . . . . . . . . . . . . . . . . . . . . . . 24
3.2. Uniform Resource Identifiers . . . . . . . . . . . . . . 21 3.2. Uniform Resource Identifiers . . . . . . . . . . . . . . 25
3.2.1. General Syntax . . . . . . . . . . . . . . . . . . . 21 3.2.1. General Syntax . . . . . . . . . . . . . . . . . . . 25
3.2.2. http URL . . . . . . . . . . . . . . . . . . . . . . 21 3.2.2. http URL . . . . . . . . . . . . . . . . . . . . . . 26
3.2.3. URI Comparison . . . . . . . . . . . . . . . . . . . 22 3.2.3. URI Comparison . . . . . . . . . . . . . . . . . . . 26
3.3. Date/Time Formats . . . . . . . . . . . . . . . . . . . 22 3.3. Date/Time Formats . . . . . . . . . . . . . . . . . . . 27
3.3.1. Full Date . . . . . . . . . . . . . . . . . . . . . 22 3.3.1. Full Date . . . . . . . . . . . . . . . . . . . . . 27
3.3.2. Delta Seconds . . . . . . . . . . . . . . . . . . . 24 3.3.2. Delta Seconds . . . . . . . . . . . . . . . . . . . 28
3.4. Character Sets . . . . . . . . . . . . . . . . . . . . . 24 3.4. Character Sets . . . . . . . . . . . . . . . . . . . . . 28
3.4.1. Missing Charset . . . . . . . . . . . . . . . . . . 25 3.4.1. Missing Charset . . . . . . . . . . . . . . . . . . 29
3.5. Content Codings . . . . . . . . . . . . . . . . . . . . 25 3.5. Content Codings . . . . . . . . . . . . . . . . . . . . 30
3.6. Transfer Codings . . . . . . . . . . . . . . . . . . . . 26 3.6. Transfer Codings . . . . . . . . . . . . . . . . . . . . 31
3.6.1. Chunked Transfer Coding . . . . . . . . . . . . . . 27 3.6.1. Chunked Transfer Coding . . . . . . . . . . . . . . 32
3.7. Media Types . . . . . . . . . . . . . . . . . . . . . . 29 3.7. Media Types . . . . . . . . . . . . . . . . . . . . . . 33
3.7.1. Canonicalization and Text Defaults . . . . . . . . . 29 3.7.1. Canonicalization and Text Defaults . . . . . . . . . 34
3.7.2. Multipart Types . . . . . . . . . . . . . . . . . . 30 3.7.2. Multipart Types . . . . . . . . . . . . . . . . . . 35
3.8. Product Tokens . . . . . . . . . . . . . . . . . . . . . 31 3.8. Product Tokens . . . . . . . . . . . . . . . . . . . . . 35
3.9. Quality Values . . . . . . . . . . . . . . . . . . . . . 31 3.9. Quality Values . . . . . . . . . . . . . . . . . . . . . 36
3.10. Language Tags . . . . . . . . . . . . . . . . . . . . . 32 3.10. Language Tags . . . . . . . . . . . . . . . . . . . . . 36
3.11. Entity Tags . . . . . . . . . . . . . . . . . . . . . . 32 3.11. Entity Tags . . . . . . . . . . . . . . . . . . . . . . 37
3.12. Range Units . . . . . . . . . . . . . . . . . . . . . . 33 3.12. Range Units . . . . . . . . . . . . . . . . . . . . . . 37
4. HTTP Message . . . . . . . . . . . . . . . . . . . . . . . . 39
4.1. Message Types . . . . . . . . . . . . . . . . . . . . . 39
4.2. Message Headers . . . . . . . . . . . . . . . . . . . . 39
4.3. Message Body . . . . . . . . . . . . . . . . . . . . . . 40
4.4. Message Length . . . . . . . . . . . . . . . . . . . . . 41
4.5. General Header Fields . . . . . . . . . . . . . . . . . 42
5. Request . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.1. Request-Line . . . . . . . . . . . . . . . . . . . . . . 44
5.1.1. Method . . . . . . . . . . . . . . . . . . . . . . . 44
5.1.2. Request-URI . . . . . . . . . . . . . . . . . . . . 45
5.2. The Resource Identified by a Request . . . . . . . . . . 46
5.3. Request Header Fields . . . . . . . . . . . . . . . . . 47
6. Response . . . . . . . . . . . . . . . . . . . . . . . . . . 48
6.1. Status-Line . . . . . . . . . . . . . . . . . . . . . . 48
6.1.1. Status Code and Reason Phrase . . . . . . . . . . . 48
6.2. Response Header Fields . . . . . . . . . . . . . . . . . 51
4. HTTP Message . . . . . . . . . . . . . . . . . . . . . . . . 34 7. Entity . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.1. Message Types . . . . . . . . . . . . . . . . . . . . . 34 7.1. Entity Header Fields . . . . . . . . . . . . . . . . . . 52
4.2. Message Headers . . . . . . . . . . . . . . . . . . . . 34 7.2. Entity Body . . . . . . . . . . . . . . . . . . . . . . 52
4.3. Message Body . . . . . . . . . . . . . . . . . . . . . . 35 7.2.1. Type . . . . . . . . . . . . . . . . . . . . . . . . 53
4.4. Message Length . . . . . . . . . . . . . . . . . . . . . 36 7.2.2. Entity Length . . . . . . . . . . . . . . . . . . . 53
4.5. General Header Fields . . . . . . . . . . . . . . . . . 37 8. Connections . . . . . . . . . . . . . . . . . . . . . . . . . 54
5. Request . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 8.1. Persistent Connections . . . . . . . . . . . . . . . . . 54
5.1. Request-Line . . . . . . . . . . . . . . . . . . . . . . 39 8.1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . 54
5.1.1. Method . . . . . . . . . . . . . . . . . . . . . . . 39 8.1.2. Overall Operation . . . . . . . . . . . . . . . . . 54
5.1.2. Request-URI . . . . . . . . . . . . . . . . . . . . 40 8.1.3. Proxy Servers . . . . . . . . . . . . . . . . . . . 56
5.2. The Resource Identified by a Request . . . . . . . . . . 41 8.1.4. Practical Considerations . . . . . . . . . . . . . . 56
5.3. Request Header Fields . . . . . . . . . . . . . . . . . 42 8.2. Message Transmission Requirements . . . . . . . . . . . 57
6. Response . . . . . . . . . . . . . . . . . . . . . . . . . . 43 8.2.1. Persistent Connections and Flow Control . . . . . . 57
6.1. Status-Line . . . . . . . . . . . . . . . . . . . . . . 43 8.2.2. Monitoring Connections for Error Status Messages . . 57
6.1.1. Status Code and Reason Phrase . . . . . . . . . . . 43 8.2.3. Use of the 100 (Continue) Status . . . . . . . . . . 58
6.2. Response Header Fields . . . . . . . . . . . . . . . . . 46
7. Entity . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
7.1. Entity Header Fields . . . . . . . . . . . . . . . . . . 47
7.2. Entity Body . . . . . . . . . . . . . . . . . . . . . . 47
7.2.1. Type . . . . . . . . . . . . . . . . . . . . . . . . 48
7.2.2. Entity Length . . . . . . . . . . . . . . . . . . . 48
8. Connections . . . . . . . . . . . . . . . . . . . . . . . . . 49
8.1. Persistent Connections . . . . . . . . . . . . . . . . . 49
8.1.1. Purpose . . . . . . . . . . . . . . . . . . . . . . 49
8.1.2. Overall Operation . . . . . . . . . . . . . . . . . 49
8.1.3. Proxy Servers . . . . . . . . . . . . . . . . . . . 51
8.1.4. Practical Considerations . . . . . . . . . . . . . . 51
8.2. Message Transmission Requirements . . . . . . . . . . . 52
8.2.1. Persistent Connections and Flow Control . . . . . . 52
8.2.2. Monitoring Connections for Error Status Messages . . 52
8.2.3. Use of the 100 (Continue) Status . . . . . . . . . . 53
8.2.4. Client Behavior if Server Prematurely Closes 8.2.4. Client Behavior if Server Prematurely Closes
Connection . . . . . . . . . . . . . . . . . . . . . 55 Connection . . . . . . . . . . . . . . . . . . . . . 60
9. Method Definitions . . . . . . . . . . . . . . . . . . . . . 56 9. Method Definitions . . . . . . . . . . . . . . . . . . . . . 61
9.1. Safe and Idempotent Methods . . . . . . . . . . . . . . 56 9.1. Safe and Idempotent Methods . . . . . . . . . . . . . . 61
9.1.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 56 9.1.1. Safe Methods . . . . . . . . . . . . . . . . . . . . 61
9.1.2. Idempotent Methods . . . . . . . . . . . . . . . . . 56 9.1.2. Idempotent Methods . . . . . . . . . . . . . . . . . 61
9.2. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . 57 9.2. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . 62
9.3. GET . . . . . . . . . . . . . . . . . . . . . . . . . . 58 9.3. GET . . . . . . . . . . . . . . . . . . . . . . . . . . 63
9.4. HEAD . . . . . . . . . . . . . . . . . . . . . . . . . . 58 9.4. HEAD . . . . . . . . . . . . . . . . . . . . . . . . . . 63
9.5. POST . . . . . . . . . . . . . . . . . . . . . . . . . . 59 9.5. POST . . . . . . . . . . . . . . . . . . . . . . . . . . 64
9.6. PUT . . . . . . . . . . . . . . . . . . . . . . . . . . 60 9.6. PUT . . . . . . . . . . . . . . . . . . . . . . . . . . 64
9.7. DELETE . . . . . . . . . . . . . . . . . . . . . . . . . 61 9.7. DELETE . . . . . . . . . . . . . . . . . . . . . . . . . 66
9.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . . 61 9.8. TRACE . . . . . . . . . . . . . . . . . . . . . . . . . 66
9.9. CONNECT . . . . . . . . . . . . . . . . . . . . . . . . 62 9.9. CONNECT . . . . . . . . . . . . . . . . . . . . . . . . 66
10. Status Code Definitions . . . . . . . . . . . . . . . . . . . 63 10. Status Code Definitions . . . . . . . . . . . . . . . . . . . 67
10.1. Informational 1xx . . . . . . . . . . . . . . . . . . . 63 10.1. Informational 1xx . . . . . . . . . . . . . . . . . . . 67
10.1.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 63 10.1.1. 100 Continue . . . . . . . . . . . . . . . . . . . . 67
10.1.2. 101 Switching Protocols . . . . . . . . . . . . . . 63 10.1.2. 101 Switching Protocols . . . . . . . . . . . . . . 67
10.2. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 64 10.2. Successful 2xx . . . . . . . . . . . . . . . . . . . . . 68
10.2.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 64 10.2.1. 200 OK . . . . . . . . . . . . . . . . . . . . . . . 68
10.2.2. 201 Created . . . . . . . . . . . . . . . . . . . . 64 10.2.2. 201 Created . . . . . . . . . . . . . . . . . . . . 68
10.2.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 64 10.2.3. 202 Accepted . . . . . . . . . . . . . . . . . . . . 68
10.2.4. 203 Non-Authoritative Information . . . . . . . . . 65 10.2.4. 203 Non-Authoritative Information . . . . . . . . . 69
10.2.5. 204 No Content . . . . . . . . . . . . . . . . . . . 65 10.2.5. 204 No Content . . . . . . . . . . . . . . . . . . . 69
10.2.6. 205 Reset Content . . . . . . . . . . . . . . . . . 65 10.2.6. 205 Reset Content . . . . . . . . . . . . . . . . . 69
10.2.7. 206 Partial Content . . . . . . . . . . . . . . . . 66 10.2.7. 206 Partial Content . . . . . . . . . . . . . . . . 70
10.3. Redirection 3xx . . . . . . . . . . . . . . . . . . . . 66 10.3. Redirection 3xx . . . . . . . . . . . . . . . . . . . . 70
10.3.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 67 10.3.1. 300 Multiple Choices . . . . . . . . . . . . . . . . 71
10.3.2. 301 Moved Permanently . . . . . . . . . . . . . . . 67 10.3.2. 301 Moved Permanently . . . . . . . . . . . . . . . 71
10.3.3. 302 Found . . . . . . . . . . . . . . . . . . . . . 68 10.3.3. 302 Found . . . . . . . . . . . . . . . . . . . . . 72
10.3.4. 303 See Other . . . . . . . . . . . . . . . . . . . 68 10.3.4. 303 See Other . . . . . . . . . . . . . . . . . . . 72
10.3.5. 304 Not Modified . . . . . . . . . . . . . . . . . . 69 10.3.5. 304 Not Modified . . . . . . . . . . . . . . . . . . 73
10.3.6. 305 Use Proxy . . . . . . . . . . . . . . . . . . . 69 10.3.6. 305 Use Proxy . . . . . . . . . . . . . . . . . . . 74
10.3.7. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 70 10.3.7. 306 (Unused) . . . . . . . . . . . . . . . . . . . . 74
10.3.8. 307 Temporary Redirect . . . . . . . . . . . . . . . 70 10.3.8. 307 Temporary Redirect . . . . . . . . . . . . . . . 74
10.4. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 70 10.4. Client Error 4xx . . . . . . . . . . . . . . . . . . . . 74
10.4.1. 400 Bad Request . . . . . . . . . . . . . . . . . . 71 10.4.1. 400 Bad Request . . . . . . . . . . . . . . . . . . 75
10.4.2. 401 Unauthorized . . . . . . . . . . . . . . . . . . 71 10.4.2. 401 Unauthorized . . . . . . . . . . . . . . . . . . 75
10.4.3. 402 Payment Required . . . . . . . . . . . . . . . . 71 10.4.3. 402 Payment Required . . . . . . . . . . . . . . . . 75
10.4.4. 403 Forbidden . . . . . . . . . . . . . . . . . . . 71 10.4.4. 403 Forbidden . . . . . . . . . . . . . . . . . . . 75
10.4.5. 404 Not Found . . . . . . . . . . . . . . . . . . . 71 10.4.5. 404 Not Found . . . . . . . . . . . . . . . . . . . 76
10.4.6. 405 Method Not Allowed . . . . . . . . . . . . . . . 72 10.4.6. 405 Method Not Allowed . . . . . . . . . . . . . . . 76
10.4.7. 406 Not Acceptable . . . . . . . . . . . . . . . . . 72 10.4.7. 406 Not Acceptable . . . . . . . . . . . . . . . . . 76
10.4.8. 407 Proxy Authentication Required . . . . . . . . . 72 10.4.8. 407 Proxy Authentication Required . . . . . . . . . 77
10.4.9. 408 Request Timeout . . . . . . . . . . . . . . . . 73 10.4.9. 408 Request Timeout . . . . . . . . . . . . . . . . 77
10.4.10. 409 Conflict . . . . . . . . . . . . . . . . . . . . 73 10.4.10. 409 Conflict . . . . . . . . . . . . . . . . . . . . 77
10.4.11. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 73 10.4.11. 410 Gone . . . . . . . . . . . . . . . . . . . . . . 77
10.4.12. 411 Length Required . . . . . . . . . . . . . . . . 74 10.4.12. 411 Length Required . . . . . . . . . . . . . . . . 78
10.4.13. 412 Precondition Failed . . . . . . . . . . . . . . 74 10.4.13. 412 Precondition Failed . . . . . . . . . . . . . . 78
10.4.14. 413 Request Entity Too Large . . . . . . . . . . . . 74 10.4.14. 413 Request Entity Too Large . . . . . . . . . . . . 78
10.4.15. 414 Request-URI Too Long . . . . . . . . . . . . . . 74 10.4.15. 414 Request-URI Too Long . . . . . . . . . . . . . . 78
10.4.16. 415 Unsupported Media Type . . . . . . . . . . . . . 74 10.4.16. 415 Unsupported Media Type . . . . . . . . . . . . . 79
10.4.17. 416 Requested Range Not Satisfiable . . . . . . . . 74 10.4.17. 416 Requested Range Not Satisfiable . . . . . . . . 79
10.4.18. 417 Expectation Failed . . . . . . . . . . . . . . . 75 10.4.18. 417 Expectation Failed . . . . . . . . . . . . . . . 79
10.5. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 75 10.5. Server Error 5xx . . . . . . . . . . . . . . . . . . . . 79
10.5.1. 500 Internal Server Error . . . . . . . . . . . . . 75 10.5.1. 500 Internal Server Error . . . . . . . . . . . . . 79
10.5.2. 501 Not Implemented . . . . . . . . . . . . . . . . 75 10.5.2. 501 Not Implemented . . . . . . . . . . . . . . . . 79
10.5.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . 75 10.5.3. 502 Bad Gateway . . . . . . . . . . . . . . . . . . 80
10.5.4. 503 Service Unavailable . . . . . . . . . . . . . . 76 10.5.4. 503 Service Unavailable . . . . . . . . . . . . . . 80
10.5.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . 76 10.5.5. 504 Gateway Timeout . . . . . . . . . . . . . . . . 80
10.5.6. 505 HTTP Version Not Supported . . . . . . . . . . . 76 10.5.6. 505 HTTP Version Not Supported . . . . . . . . . . . 80
11. Access Authentication . . . . . . . . . . . . . . . . . . . . 77 11. Access Authentication . . . . . . . . . . . . . . . . . . . . 81
12. Content Negotiation . . . . . . . . . . . . . . . . . . . . . 78 12. Content Negotiation . . . . . . . . . . . . . . . . . . . . . 82
12.1. Server-driven Negotiation . . . . . . . . . . . . . . . 78 12.1. Server-driven Negotiation . . . . . . . . . . . . . . . 82
12.2. Agent-driven Negotiation . . . . . . . . . . . . . . . . 79 12.2. Agent-driven Negotiation . . . . . . . . . . . . . . . . 83
12.3. Transparent Negotiation . . . . . . . . . . . . . . . . 80 12.3. Transparent Negotiation . . . . . . . . . . . . . . . . 84
13. Caching in HTTP . . . . . . . . . . . . . . . . . . . . . . . 81 13. Caching in HTTP . . . . . . . . . . . . . . . . . . . . . . . 85
13.1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 13.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 85
13.1.1. Cache Correctness . . . . . . . . . . . . . . . . . 82 13.1.1. Cache Correctness . . . . . . . . . . . . . . . . . 86
13.1.2. Warnings . . . . . . . . . . . . . . . . . . . . . . 83 13.1.2. Warnings . . . . . . . . . . . . . . . . . . . . . . 87
13.1.3. Cache-control Mechanisms . . . . . . . . . . . . . . 84 13.1.3. Cache-control Mechanisms . . . . . . . . . . . . . . 88
13.1.4. Explicit User Agent Warnings . . . . . . . . . . . . 84 13.1.4. Explicit User Agent Warnings . . . . . . . . . . . . 88
13.1.5. Exceptions to the Rules and Warnings . . . . . . . . 85 13.1.5. Exceptions to the Rules and Warnings . . . . . . . . 89
13.1.6. Client-controlled Behavior . . . . . . . . . . . . . 85 13.1.6. Client-controlled Behavior . . . . . . . . . . . . . 89
13.2. Expiration Model . . . . . . . . . . . . . . . . . . . . 86 13.2. Expiration Model . . . . . . . . . . . . . . . . . . . . 90
13.2.1. Server-Specified Expiration . . . . . . . . . . . . 86 13.2.1. Server-Specified Expiration . . . . . . . . . . . . 90
13.2.2. Heuristic Expiration . . . . . . . . . . . . . . . . 86 13.2.2. Heuristic Expiration . . . . . . . . . . . . . . . . 90
13.2.3. Age Calculations . . . . . . . . . . . . . . . . . . 87 13.2.3. Age Calculations . . . . . . . . . . . . . . . . . . 91
13.2.4. Expiration Calculations . . . . . . . . . . . . . . 89 13.2.4. Expiration Calculations . . . . . . . . . . . . . . 93
13.2.5. Disambiguating Expiration Values . . . . . . . . . . 90 13.2.5. Disambiguating Expiration Values . . . . . . . . . . 94
13.2.6. Disambiguating Multiple Responses . . . . . . . . . 91 13.2.6. Disambiguating Multiple Responses . . . . . . . . . 95
13.3. Validation Model . . . . . . . . . . . . . . . . . . . . 91
13.3.1. Last-Modified Dates . . . . . . . . . . . . . . . . 92 13.3. Validation Model . . . . . . . . . . . . . . . . . . . . 95
13.3.2. Entity Tag Cache Validators . . . . . . . . . . . . 92 13.3.1. Last-Modified Dates . . . . . . . . . . . . . . . . 96
13.3.3. Weak and Strong Validators . . . . . . . . . . . . . 93 13.3.2. Entity Tag Cache Validators . . . . . . . . . . . . 96
13.3.3. Weak and Strong Validators . . . . . . . . . . . . . 97
13.3.4. Rules for When to Use Entity Tags and 13.3.4. Rules for When to Use Entity Tags and
Last-Modified Dates . . . . . . . . . . . . . . . . 95 Last-Modified Dates . . . . . . . . . . . . . . . . 100
13.3.5. Non-validating Conditionals . . . . . . . . . . . . 97 13.3.5. Non-validating Conditionals . . . . . . . . . . . . 101
13.4. Response Cacheability . . . . . . . . . . . . . . . . . 97 13.4. Response Cacheability . . . . . . . . . . . . . . . . . 102
13.5. Constructing Responses From Caches . . . . . . . . . . . 98 13.5. Constructing Responses From Caches . . . . . . . . . . . 102
13.5.1. End-to-end and Hop-by-hop Headers . . . . . . . . . 98 13.5.1. End-to-end and Hop-by-hop Headers . . . . . . . . . 103
13.5.2. Non-modifiable Headers . . . . . . . . . . . . . . . 99 13.5.2. Non-modifiable Headers . . . . . . . . . . . . . . . 103
13.5.3. Combining Headers . . . . . . . . . . . . . . . . . 100 13.5.3. Combining Headers . . . . . . . . . . . . . . . . . 105
13.5.4. Combining Byte Ranges . . . . . . . . . . . . . . . 101 13.5.4. Combining Byte Ranges . . . . . . . . . . . . . . . 106
13.6. Caching Negotiated Responses . . . . . . . . . . . . . . 102 13.6. Caching Negotiated Responses . . . . . . . . . . . . . . 106
13.7. Shared and Non-Shared Caches . . . . . . . . . . . . . . 103 13.7. Shared and Non-Shared Caches . . . . . . . . . . . . . . 107
13.8. Errors or Incomplete Response Cache Behavior . . . . . . 103 13.8. Errors or Incomplete Response Cache Behavior . . . . . . 108
13.9. Side Effects of GET and HEAD . . . . . . . . . . . . . . 104 13.9. Side Effects of GET and HEAD . . . . . . . . . . . . . . 108
13.10. Invalidation After Updates or Deletions . . . . . . . . 104 13.10. Invalidation After Updates or Deletions . . . . . . . . 108
13.11. Write-Through Mandatory . . . . . . . . . . . . . . . . 105 13.11. Write-Through Mandatory . . . . . . . . . . . . . . . . 109
13.12. Cache Replacement . . . . . . . . . . . . . . . . . . . 105 13.12. Cache Replacement . . . . . . . . . . . . . . . . . . . 110
13.13. History Lists . . . . . . . . . . . . . . . . . . . . . 106 13.13. History Lists . . . . . . . . . . . . . . . . . . . . . 110
14. Header Field Definitions . . . . . . . . . . . . . . . . . . 107 14. Header Field Definitions . . . . . . . . . . . . . . . . . . 111
14.1. Accept . . . . . . . . . . . . . . . . . . . . . . . . . 107 14.1. Accept . . . . . . . . . . . . . . . . . . . . . . . . . 111
14.2. Accept-Charset . . . . . . . . . . . . . . . . . . . . . 109 14.2. Accept-Charset . . . . . . . . . . . . . . . . . . . . . 113
14.3. Accept-Encoding . . . . . . . . . . . . . . . . . . . . 109 14.3. Accept-Encoding . . . . . . . . . . . . . . . . . . . . 113
14.4. Accept-Language . . . . . . . . . . . . . . . . . . . . 111 14.4. Accept-Language . . . . . . . . . . . . . . . . . . . . 115
14.5. Accept-Ranges . . . . . . . . . . . . . . . . . . . . . 112 14.5. Accept-Ranges . . . . . . . . . . . . . . . . . . . . . 116
14.6. Age . . . . . . . . . . . . . . . . . . . . . . . . . . 112 14.6. Age . . . . . . . . . . . . . . . . . . . . . . . . . . 116
14.7. Allow . . . . . . . . . . . . . . . . . . . . . . . . . 113 14.7. Allow . . . . . . . . . . . . . . . . . . . . . . . . . 117
14.8. Authorization . . . . . . . . . . . . . . . . . . . . . 113 14.8. Authorization . . . . . . . . . . . . . . . . . . . . . 117
14.9. Cache-Control . . . . . . . . . . . . . . . . . . . . . 114 14.9. Cache-Control . . . . . . . . . . . . . . . . . . . . . 118
14.9.1. What is Cacheable . . . . . . . . . . . . . . . . . 116 14.9.1. What is Cacheable . . . . . . . . . . . . . . . . . 120
14.9.2. What May be Stored by Caches . . . . . . . . . . . . 117 14.9.2. What May be Stored by Caches . . . . . . . . . . . . 121
14.9.3. Modifications of the Basic Expiration Mechanism . . 118 14.9.3. Modifications of the Basic Expiration Mechanism . . 122
14.9.4. Cache Revalidation and Reload Controls . . . . . . . 120 14.9.4. Cache Revalidation and Reload Controls . . . . . . . 124
14.9.5. No-Transform Directive . . . . . . . . . . . . . . . 122 14.9.5. No-Transform Directive . . . . . . . . . . . . . . . 126
14.9.6. Cache Control Extensions . . . . . . . . . . . . . . 123 14.9.6. Cache Control Extensions . . . . . . . . . . . . . . 127
14.10. Connection . . . . . . . . . . . . . . . . . . . . . . . 124 14.10. Connection . . . . . . . . . . . . . . . . . . . . . . . 128
14.11. Content-Encoding . . . . . . . . . . . . . . . . . . . . 125 14.11. Content-Encoding . . . . . . . . . . . . . . . . . . . . 129
14.12. Content-Language . . . . . . . . . . . . . . . . . . . . 125 14.12. Content-Language . . . . . . . . . . . . . . . . . . . . 130
14.13. Content-Length . . . . . . . . . . . . . . . . . . . . . 126 14.13. Content-Length . . . . . . . . . . . . . . . . . . . . . 130
14.14. Content-Location . . . . . . . . . . . . . . . . . . . . 127 14.14. Content-Location . . . . . . . . . . . . . . . . . . . . 131
14.15. Content-MD5 . . . . . . . . . . . . . . . . . . . . . . 128 14.15. Content-MD5 . . . . . . . . . . . . . . . . . . . . . . 132
14.16. Content-Range . . . . . . . . . . . . . . . . . . . . . 129 14.16. Content-Range . . . . . . . . . . . . . . . . . . . . . 133
14.17. Content-Type . . . . . . . . . . . . . . . . . . . . . . 131 14.17. Content-Type . . . . . . . . . . . . . . . . . . . . . . 135
14.18. Date . . . . . . . . . . . . . . . . . . . . . . . . . . 131 14.18. Date . . . . . . . . . . . . . . . . . . . . . . . . . . 136
14.18.1. Clockless Origin Server Operation . . . . . . . . . 132 14.18.1. Clockless Origin Server Operation . . . . . . . . . 137
14.19. ETag . . . . . . . . . . . . . . . . . . . . . . . . . . 133 14.19. ETag . . . . . . . . . . . . . . . . . . . . . . . . . . 137
14.20. Expect . . . . . . . . . . . . . . . . . . . . . . . . . 133 14.20. Expect . . . . . . . . . . . . . . . . . . . . . . . . . 137
14.21. Expires . . . . . . . . . . . . . . . . . . . . . . . . 134 14.21. Expires . . . . . . . . . . . . . . . . . . . . . . . . 138
14.22. From . . . . . . . . . . . . . . . . . . . . . . . . . . 135 14.22. From . . . . . . . . . . . . . . . . . . . . . . . . . . 139
14.23. Host . . . . . . . . . . . . . . . . . . . . . . . . . . 135 14.23. Host . . . . . . . . . . . . . . . . . . . . . . . . . . 140
14.24. If-Match . . . . . . . . . . . . . . . . . . . . . . . . 136 14.24. If-Match . . . . . . . . . . . . . . . . . . . . . . . . 140
14.25. If-Modified-Since . . . . . . . . . . . . . . . . . . . 137 14.25. If-Modified-Since . . . . . . . . . . . . . . . . . . . 141
14.26. If-None-Match . . . . . . . . . . . . . . . . . . . . . 139 14.26. If-None-Match . . . . . . . . . . . . . . . . . . . . . 143
14.27. If-Range . . . . . . . . . . . . . . . . . . . . . . . . 140 14.27. If-Range . . . . . . . . . . . . . . . . . . . . . . . . 144
14.28. If-Unmodified-Since . . . . . . . . . . . . . . . . . . 141 14.28. If-Unmodified-Since . . . . . . . . . . . . . . . . . . 145
14.29. Last-Modified . . . . . . . . . . . . . . . . . . . . . 141 14.29. Last-Modified . . . . . . . . . . . . . . . . . . . . . 145
14.30. Location . . . . . . . . . . . . . . . . . . . . . . . . 142 14.30. Location . . . . . . . . . . . . . . . . . . . . . . . . 146
14.31. Max-Forwards . . . . . . . . . . . . . . . . . . . . . . 142 14.31. Max-Forwards . . . . . . . . . . . . . . . . . . . . . . 147
14.32. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . 143 14.32. Pragma . . . . . . . . . . . . . . . . . . . . . . . . . 147
14.33. Proxy-Authenticate . . . . . . . . . . . . . . . . . . . 144 14.33. Proxy-Authenticate . . . . . . . . . . . . . . . . . . . 148
14.34. Proxy-Authorization . . . . . . . . . . . . . . . . . . 144 14.34. Proxy-Authorization . . . . . . . . . . . . . . . . . . 149
14.35. Range . . . . . . . . . . . . . . . . . . . . . . . . . 144 14.35. Range . . . . . . . . . . . . . . . . . . . . . . . . . 149
14.35.1. Byte Ranges . . . . . . . . . . . . . . . . . . . . 144 14.35.1. Byte Ranges . . . . . . . . . . . . . . . . . . . . 149
14.35.2. Range Retrieval Requests . . . . . . . . . . . . . . 146 14.35.2. Range Retrieval Requests . . . . . . . . . . . . . . 151
14.36. Referer . . . . . . . . . . . . . . . . . . . . . . . . 147 14.36. Referer . . . . . . . . . . . . . . . . . . . . . . . . 152
14.37. Retry-After . . . . . . . . . . . . . . . . . . . . . . 147 14.37. Retry-After . . . . . . . . . . . . . . . . . . . . . . 152
14.38. Server . . . . . . . . . . . . . . . . . . . . . . . . . 148 14.38. Server . . . . . . . . . . . . . . . . . . . . . . . . . 152
14.39. TE . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 14.39. TE . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
14.40. Trailer . . . . . . . . . . . . . . . . . . . . . . . . 149 14.40. Trailer . . . . . . . . . . . . . . . . . . . . . . . . 154
14.41. Transfer-Encoding . . . . . . . . . . . . . . . . . . . 150 14.41. Transfer-Encoding . . . . . . . . . . . . . . . . . . . 155
14.42. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . 150 14.42. Upgrade . . . . . . . . . . . . . . . . . . . . . . . . 155
14.43. User-Agent . . . . . . . . . . . . . . . . . . . . . . . 152 14.43. User-Agent . . . . . . . . . . . . . . . . . . . . . . . 156
14.44. Vary . . . . . . . . . . . . . . . . . . . . . . . . . . 152 14.44. Vary . . . . . . . . . . . . . . . . . . . . . . . . . . 157
14.45. Via . . . . . . . . . . . . . . . . . . . . . . . . . . 153 14.45. Via . . . . . . . . . . . . . . . . . . . . . . . . . . 157
14.46. Warning . . . . . . . . . . . . . . . . . . . . . . . . 154 14.46. Warning . . . . . . . . . . . . . . . . . . . . . . . . 159
14.47. WWW-Authenticate . . . . . . . . . . . . . . . . . . . . 157 14.47. WWW-Authenticate . . . . . . . . . . . . . . . . . . . . 162
15. Security Considerations . . . . . . . . . . . . . . . . . . . 158 15. Security Considerations . . . . . . . . . . . . . . . . . . . 163
15.1. Personal Information . . . . . . . . . . . . . . . . . . 158 15.1. Personal Information . . . . . . . . . . . . . . . . . . 163
15.1.1. Abuse of Server Log Information . . . . . . . . . . 158 15.1.1. Abuse of Server Log Information . . . . . . . . . . 163
15.1.2. Transfer of Sensitive Information . . . . . . . . . 158 15.1.2. Transfer of Sensitive Information . . . . . . . . . 163
15.1.3. Encoding Sensitive Information in URI's . . . . . . 159 15.1.3. Encoding Sensitive Information in URI's . . . . . . 164
15.1.4. Privacy Issues Connected to Accept Headers . . . . . 160 15.1.4. Privacy Issues Connected to Accept Headers . . . . . 165
15.2. Attacks Based On File and Path Names . . . . . . . . . . 160 15.2. Attacks Based On File and Path Names . . . . . . . . . . 165
15.3. DNS Spoofing . . . . . . . . . . . . . . . . . . . . . . 161 15.3. DNS Spoofing . . . . . . . . . . . . . . . . . . . . . . 166
15.4. Location Headers and Spoofing . . . . . . . . . . . . . 161 15.4. Location Headers and Spoofing . . . . . . . . . . . . . 166
15.5. Content-Disposition Issues . . . . . . . . . . . . . . . 162 15.5. Content-Disposition Issues . . . . . . . . . . . . . . . 167
15.6. Authentication Credentials and Idle Clients . . . . . . 162 15.6. Authentication Credentials and Idle Clients . . . . . . 167
15.7. Proxies and Caching . . . . . . . . . . . . . . . . . . 162 15.7. Proxies and Caching . . . . . . . . . . . . . . . . . . 167
15.7.1. Denial of Service Attacks on Proxies . . . . . . . . 163 15.7.1. Denial of Service Attacks on Proxies . . . . . . . . 168
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 164 16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 169
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 166 16.1. (RFC2616) . . . . . . . . . . . . . . . . . . . . . . . 169
Appendix A. Appendices . . . . . . . . . . . . . . . . . . . . . 170 16.2. (This Document) . . . . . . . . . . . . . . . . . . . . 170
A.1. Internet Media Type message/http and application/http . 170 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 171
A.2. Internet Media Type multipart/byteranges . . . . . . . . 171 17.1. Normative References . . . . . . . . . . . . . . . . . . 171
A.3. Tolerant Applications . . . . . . . . . . . . . . . . . 172 17.2. Informative References . . . . . . . . . . . . . . . . . 172
A.4. Differences Between HTTP Entities and RFC 2045 Appendix A. Internet Media Type message/http and
Entities . . . . . . . . . . . . . . . . . . . . . . . . 173 application/http . . . . . . . . . . . . . . . . . . 177
A.4.1. MIME-Version . . . . . . . . . . . . . . . . . . . . 174 Appendix B. Internet Media Type multipart/byteranges . . . . . . 180
A.4.2. Conversion to Canonical Form . . . . . . . . . . . . 174 Appendix C. Tolerant Applications . . . . . . . . . . . . . . . 182
A.4.3. Conversion of Date Formats . . . . . . . . . . . . . 174 Appendix D. Differences Between HTTP Entities and RFC 2045
A.4.4. Introduction of Content-Encoding . . . . . . . . . . 175 Entities . . . . . . . . . . . . . . . . . . . . . . 183
A.4.5. No Content-Transfer-Encoding . . . . . . . . . . . . 175 D.1. MIME-Version . . . . . . . . . . . . . . . . . . . . . . 183
A.4.6. Introduction of Transfer-Encoding . . . . . . . . . 175 D.2. Conversion to Canonical Form . . . . . . . . . . . . . . 183
A.4.7. MHTML and Line Length Limitations . . . . . . . . . 176 D.3. Conversion of Date Formats . . . . . . . . . . . . . . . 184
A.5. Additional Features . . . . . . . . . . . . . . . . . . 176 D.4. Introduction of Content-Encoding . . . . . . . . . . . . 184
A.5.1. Content-Disposition . . . . . . . . . . . . . . . . 176 D.5. No Content-Transfer-Encoding . . . . . . . . . . . . . . 184
A.6. Compatibility with Previous Versions . . . . . . . . . . 177 D.6. Introduction of Transfer-Encoding . . . . . . . . . . . 185
A.6.1. Changes from HTTP/1.0 . . . . . . . . . . . . . . . 178 D.7. MHTML and Line Length Limitations . . . . . . . . . . . 185
A.6.2. Compatibility with HTTP/1.0 Persistent Connections . 179 Appendix E. Additional Features . . . . . . . . . . . . . . . . 186
A.6.3. Changes from RFC 2068 . . . . . . . . . . . . . . . 179 E.1. Content-Disposition . . . . . . . . . . . . . . . . . . 186
Appendix B. Index . . . . . . . . . . . . . . . . . . . . . . . 183 Appendix F. Compatibility with Previous Versions . . . . . . . . 187
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 F.1. Changes from HTTP/1.0 . . . . . . . . . . . . . . . . . 187
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 196 F.1.1. Changes to Simplify Multi-homed Web Servers and
Intellectual Property and Copyright Statements . . . . . . . . . 198 Conserve IP Addresses . . . . . . . . . . . . . . . 187
F.2. Compatibility with HTTP/1.0 Persistent Connections . . . 188
F.3. Changes from RFC 2068 . . . . . . . . . . . . . . . . . 189
F.4. Changes from RFC 2616 . . . . . . . . . . . . . . . . . 191
Appendix G. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 193
G.1. Since RFC2616 . . . . . . . . . . . . . . . . . . . . . 193
G.2. Since draft-lafon-rfc2616bis-00 . . . . . . . . . . . . 193
G.3. Since draft-lafon-rfc2616bis-01 . . . . . . . . . . . . 193
G.4. Since draft-lafon-rfc2616bis-02 . . . . . . . . . . . . 193
G.5. Since draft-lafon-rfc2616bis-03 . . . . . . . . . . . . 194
G.6. Since draft-lafon-rfc2616bis-04 . . . . . . . . . . . . 195
Appendix H. Resolved issues (to be removed by RFC Editor
before publication) . . . . . . . . . . . . . . . . 196
H.1. abnf-dquote . . . . . . . . . . . . . . . . . . . . . . 196
H.2. abnf-rule-names . . . . . . . . . . . . . . . . . . . . 196
H.3. abnf-prose-cr . . . . . . . . . . . . . . . . . . . . . 196
H.4. abnf-case-insensitive . . . . . . . . . . . . . . . . . 196
H.5. i82-rel_path-not-used . . . . . . . . . . . . . . . . . 197
H.6. abnf-chunk-data . . . . . . . . . . . . . . . . . . . . 198
H.7. i70-cacheability-of-303 . . . . . . . . . . . . . . . . 198
Appendix I. Open issues (to be removed by RFC Editor prior to
publication) . . . . . . . . . . . . . . . . . . . . 201
I.1. rfc2616bis . . . . . . . . . . . . . . . . . . . . . . . 201
I.2. i35-split-normative-and-informative-references . . . . . 201
I.3. i40-header-registration . . . . . . . . . . . . . . . . 201
I.4. need_iana_considerations . . . . . . . . . . . . . . . . 201
I.5. edit . . . . . . . . . . . . . . . . . . . . . . . . . . 202
I.6. abnf-avoid-prose . . . . . . . . . . . . . . . . . . . . 202
I.7. abnf . . . . . . . . . . . . . . . . . . . . . . . . . . 202
I.8. rfc2822_normative . . . . . . . . . . . . . . . . . . . 202
I.9. rfc1737_informative_and_obsolete . . . . . . . . . . . . 203
I.10. rfc2048_informative_and_obsolete . . . . . . . . . . . . 203
I.11. i34-updated-reference-for-uris . . . . . . . . . . . . . 203
I.12. i50-misc-typos . . . . . . . . . . . . . . . . . . . . . 203
I.13. i52-sort-1.3-terminology . . . . . . . . . . . . . . . . 204
I.14. i63-header-length-limit-with-encoded-words . . . . . . . 204
I.15. i74-character-encodings-for-headers . . . . . . . . . . 205
I.16. i64-ws-in-quoted-pair . . . . . . . . . . . . . . . . . 205
I.17. i75-rfc2145-normative . . . . . . . . . . . . . . . . . 206
I.18. i58-what-identifies-an-http-resource . . . . . . . . . . 206
I.19. i51-http-date-vs-rfc1123-date . . . . . . . . . . . . . 206
I.20. i73-clarification-of-the-term-deflate . . . . . . . . . 207
I.21. i67-quoting-charsets . . . . . . . . . . . . . . . . . . 207
I.22. i20-default-charsets-for-text-media-types . . . . . . . 208
I.23. i90-delimiting-messages-with-multipart-byteranges . . . 209
I.24. languagetag . . . . . . . . . . . . . . . . . . . . . . 210
I.25. i85-custom-ranges . . . . . . . . . . . . . . . . . . . 210
I.26. i30-header-lws . . . . . . . . . . . . . . . . . . . . . 211
I.27. i77-line-folding . . . . . . . . . . . . . . . . . . . . 211
I.28. i93-repeating-single-value-headers . . . . . . . . . . . 212
I.29. i19-bodies-on-GET . . . . . . . . . . . . . . . . . . . 212
I.30. i88-205-bodies . . . . . . . . . . . . . . . . . . . . . 213
I.31. i28-connection-closing . . . . . . . . . . . . . . . . . 213
I.32. uri_vs_request_uri . . . . . . . . . . . . . . . . . . . 213
I.33. i32-options-asterisk . . . . . . . . . . . . . . . . . . 213
I.34. i83-options-asterisk-and-proxies . . . . . . . . . . . . 214
I.35. i56-6.1.1-can-be-misread-as-a-complete-list . . . . . . 215
I.36. i57-status-code-and-reason-phrase . . . . . . . . . . . 215
I.37. i59-status-code-registry . . . . . . . . . . . . . . . . 216
I.38. i94-reason-phrase-bnf . . . . . . . . . . . . . . . . . 216
I.39. i91-duplicate-host-header-requirements . . . . . . . . . 216
I.40. i72-request-method-registry . . . . . . . . . . . . . . 217
I.41. i21-put-side-effects . . . . . . . . . . . . . . . . . . 217
I.42. i27-put-idempotency . . . . . . . . . . . . . . . . . . 218
I.43. i79-content-headers-vs-put . . . . . . . . . . . . . . . 219
I.44. i33-trace-security-considerations . . . . . . . . . . . 219
I.45. i69-clarify-requested-variant . . . . . . . . . . . . . 220
I.46. i76-deprecate-305-use-proxy . . . . . . . . . . . . . . 220
I.47. i78-relationship-between-401-authorization-and-www-authe 221
I.48. i24-requiring-allow-in-405-responses . . . . . . . . . . 221
I.49. i81-content-negotiation-for-media-types . . . . . . . . 222
I.50. i54-definition-of-1xx-warn-codes . . . . . . . . . . . . 223
I.51. i29-age-calculation . . . . . . . . . . . . . . . . . . 223
I.52. i71-examples-for-etag-matching . . . . . . . . . . . . . 225
I.53. i60-13.5.1-and-13.5.2 . . . . . . . . . . . . . . . . . 225
I.54. i53-allow-is-not-in-13.5.2 . . . . . . . . . . . . . . . 225
I.55. i37-vary-and-non-existant-headers . . . . . . . . . . . 226
I.56. i38-mismatched-vary . . . . . . . . . . . . . . . . . . 226
I.57. i39-etag-uniqueness . . . . . . . . . . . . . . . . . . 227
I.58. i23-no-store-invalidation . . . . . . . . . . . . . . . 227
I.59. 14.11-content-encoding_response_vs_message . . . . . . . 228
I.60. i80-content-location-is-not-special . . . . . . . . . . 229
I.61. i22-etag-and-other-metadata-in-status-messages . . . . . 229
I.62. i92-empty-host-headers . . . . . . . . . . . . . . . . . 229
I.63. i89-if-dash-and-entities . . . . . . . . . . . . . . . . 230
I.64. i61-redirection-vs-location . . . . . . . . . . . . . . 231
I.65. fragment-combination . . . . . . . . . . . . . . . . . . 231
I.66. i41-security-considerations . . . . . . . . . . . . . . 231
I.67. i55-updating-to-rfc4288 . . . . . . . . . . . . . . . . 232
I.68. link-header . . . . . . . . . . . . . . . . . . . . . . 232
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 245
Intellectual Property and Copyright Statements . . . . . . . . . 248
1. Introduction 1. Introduction
1.1. Purpose 1.1. Purpose
The Hypertext Transfer Protocol (HTTP) is an application-level The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypermedia information protocol for distributed, collaborative, hypermedia information
systems. HTTP has been in use by the World-Wide Web global systems. HTTP has been in use by the World-Wide Web global
information initiative since 1990. The first version of HTTP, information initiative since 1990. The first version of HTTP,
referred to as HTTP/0.9, was a simple protocol for raw data transfer referred to as HTTP/0.9, was a simple protocol for raw data transfer
across the Internet. HTTP/1.0, as defined by RFC 1945 [6], improved across the Internet. HTTP/1.0, as defined by [RFC1945], improved the
the protocol by allowing messages to be in the format of MIME-like protocol by allowing messages to be in the format of MIME-like
messages, containing metainformation about the data transferred and messages, containing metainformation about the data transferred and
modifiers on the request/response semantics. However, HTTP/1.0 does modifiers on the request/response semantics. However, HTTP/1.0 does
not sufficiently take into consideration the effects of hierarchical not sufficiently take into consideration the effects of hierarchical
proxies, caching, the need for persistent connections, or virtual proxies, caching, the need for persistent connections, or virtual
hosts. In addition, the proliferation of incompletely-implemented hosts. In addition, the proliferation of incompletely-implemented
applications calling themselves "HTTP/1.0" has necessitated a applications calling themselves "HTTP/1.0" has necessitated a
protocol version change in order for two communicating applications protocol version change in order for two communicating applications
to determine each other's true capabilities. to determine each other's true capabilities.
This specification defines the protocol referred to as "HTTP/1.1". This specification defines the protocol referred to as "HTTP/1.1".
This protocol includes more stringent requirements than HTTP/1.0 in This protocol includes more stringent requirements than HTTP/1.0 in
order to ensure reliable implementation of its features. order to ensure reliable implementation of its features.
Practical information systems require more functionality than simple Practical information systems require more functionality than simple
retrieval, including search, front-end update, and annotation. HTTP retrieval, including search, front-end update, and annotation. HTTP
allows an open-ended set of methods and headers that indicate the allows an open-ended set of methods and headers that indicate the
purpose of a request [47]. It builds on the discipline of reference purpose of a request [RFC2324]. It builds on the discipline of
provided by the Uniform Resource Identifier (URI) [3], as a location reference provided by the Uniform Resource Identifier (URI)
(URL) [4] or name (URN) [20], for indicating the resource to which a [RFC1630], as a location (URL) [RFC1738] or name (URN) [RFC1737], for
method is to be applied. Messages are passed in a format similar to indicating the resource to which a method is to be applied. Messages
that used by Internet mail [9] as defined by the Multipurpose are passed in a format similar to that used by Internet mail
Internet Mail Extensions (MIME) [7]. [RFC2822] as defined by the Multipurpose Internet Mail Extensions
(MIME) [RFC2045].
HTTP is also used as a generic protocol for communication between HTTP is also used as a generic protocol for communication between
user agents and proxies/gateways to other Internet systems, including user agents and proxies/gateways to other Internet systems, including
those supported by the SMTP [16], NNTP [13], FTP [18], Gopher [2], those supported by the SMTP [RFC2821], NNTP [RFC3977], FTP [RFC959],
and WAIS [10] protocols. In this way, HTTP allows basic hypermedia Gopher [RFC1436], and WAIS [WAIS] protocols. In this way, HTTP
access to resources available from diverse applications. allows basic hypermedia access to resources available from diverse
applications.
1.2. Requirements 1.2. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [34]. document are to be interpreted as described in [RFC2119].
An implementation is not compliant if it fails to satisfy one or more An implementation is not compliant if it fails to satisfy one or more
of the MUST or REQUIRED level requirements for the protocols it of the MUST or REQUIRED level requirements for the protocols it
implements. An implementation that satisfies all the MUST or implements. An implementation that satisfies all the MUST or
REQUIRED level and all the SHOULD level requirements for its REQUIRED level and all the SHOULD level requirements for its
protocols is said to be "unconditionally compliant"; one that protocols is said to be "unconditionally compliant"; one that
satisfies all the MUST level requirements but not all the SHOULD satisfies all the MUST level requirements but not all the SHOULD
level requirements for its protocols is said to be "conditionally level requirements for its protocols is said to be "conditionally
compliant." compliant."
skipping to change at page 10, line 19 skipping to change at page 14, line 19
The mechanism for selecting the appropriate representation when The mechanism for selecting the appropriate representation when
servicing a request, as described in Section 12. The servicing a request, as described in Section 12. The
representation of entities in any response can be negotiated representation of entities in any response can be negotiated
(including error responses). (including error responses).
variant variant
A resource may have one, or more than one, representation(s) A resource may have one, or more than one, representation(s)
associated with it at any given instant. Each of these associated with it at any given instant. Each of these
representations is termed a `varriant'. Use of the term `variant' representations is termed a `variant'. Use of the term `variant'
does not necessarily imply that the resource is subject to content does not necessarily imply that the resource is subject to content
negotiation. negotiation.
client client
A program that establishes connections for the purpose of sending A program that establishes connections for the purpose of sending
requests. requests.
user agent user agent
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1.4. Overall Operation 1.4. Overall Operation
The HTTP protocol is a request/response protocol. A client sends a The HTTP protocol is a request/response protocol. A client sends a
request to the server in the form of a request method, URI, and request to the server in the form of a request method, URI, and
protocol version, followed by a MIME-like message containing request protocol version, followed by a MIME-like message containing request
modifiers, client information, and possible body content over a modifiers, client information, and possible body content over a
connection with a server. The server responds with a status line, connection with a server. The server responds with a status line,
including the message's protocol version and a success or error code, including the message's protocol version and a success or error code,
followed by a MIME-like message containing server information, entity followed by a MIME-like message containing server information, entity
metainformation, and possible entity-body content. The relationship metainformation, and possible entity-body content. The relationship
between HTTP and MIME is described in Appendix A.4. between HTTP and MIME is described in Appendix D.
Most HTTP communication is initiated by a user agent and consists of Most HTTP communication is initiated by a user agent and consists of
a request to be applied to a resource on some origin server. In the a request to be applied to a resource on some origin server. In the
simplest case, this may be accomplished via a single connection (v) simplest case, this may be accomplished via a single connection (v)
between the user agent (UA) and the origin server (O). between the user agent (UA) and the origin server (O).
request chain ------------------------> request chain ------------------------>
UA -------------------v------------------- O UA -------------------v------------------- O
<----------------------- response chain <----------------------- response chain
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subsets of cached data via CD-ROM, and so on. HTTP systems are used subsets of cached data via CD-ROM, and so on. HTTP systems are used
in corporate intranets over high-bandwidth links, and for access via in corporate intranets over high-bandwidth links, and for access via
PDAs with low-power radio links and intermittent connectivity. The PDAs with low-power radio links and intermittent connectivity. The
goal of HTTP/1.1 is to support the wide diversity of configurations goal of HTTP/1.1 is to support the wide diversity of configurations
already deployed while introducing protocol constructs that meet the already deployed while introducing protocol constructs that meet the
needs of those who build web applications that require high needs of those who build web applications that require high
reliability and, failing that, at least reliable indications of reliability and, failing that, at least reliable indications of
failure. failure.
HTTP communication usually takes place over TCP/IP connections. The HTTP communication usually takes place over TCP/IP connections. The
default port is TCP 80 [19], but other ports can be used. This does default port is TCP 80
not preclude HTTP from being implemented on top of any other protocol (<http://www.iana.org/assignments/port-numbers>), but other ports can
on the Internet, or on other networks. HTTP only presumes a reliable be used. This does not preclude HTTP from being implemented on top
transport; any protocol that provides such guarantees can be used; of any other protocol on the Internet, or on other networks. HTTP
the mapping of the HTTP/1.1 request and response structures onto the only presumes a reliable transport; any protocol that provides such
transport data units of the protocol in question is outside the scope guarantees can be used; the mapping of the HTTP/1.1 request and
of this specification. response structures onto the transport data units of the protocol in
question is outside the scope of this specification.
In HTTP/1.0, most implementations used a new connection for each In HTTP/1.0, most implementations used a new connection for each
request/response exchange. In HTTP/1.1, a connection may be used for request/response exchange. In HTTP/1.1, a connection may be used for
one or more request/response exchanges, although connections may be one or more request/response exchanges, although connections may be
closed for a variety of reasons (see Section 8.1). closed for a variety of reasons (see Section 8.1).
2. Notational Conventions and Generic Grammar 2. Notational Conventions and Generic Grammar
2.1. Augmented BNF 2.1. Augmented BNF
All of the mechanisms specified in this document are described in All of the mechanisms specified in this document are described in
both prose and an augmented Backus-Naur Form (BNF) similar to that both prose and an augmented Backus-Naur Form (BNF) similar to that
used by RFC 822 [9]. Implementors will need to be familiar with the used by [RFC822ABNF]. Implementors will need to be familiar with the
notation in order to understand this specification. The augmented notation in order to understand this specification. The augmented
BNF includes the following constructs: BNF includes the following constructs:
name = definition name = definition
The name of a rule is simply the name itself (without any The name of a rule is simply the name itself (without any
enclosing "<" and ">") and is separated from its definition by the enclosing "<" and ">") and is separated from its definition by the
equal "=" character. White space is only significant in that equal "=" character. White space is only significant in that
indentation of continuation lines is used to indicate a rule indentation of continuation lines is used to indicate a rule
definition that spans more than one line. Certain basic rules are definition that spans more than one line. Certain basic rules are
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between adjacent words and separators, without changing the between adjacent words and separators, without changing the
interpretation of a field. At least one delimiter (LWS and/or interpretation of a field. At least one delimiter (LWS and/or
separators) MUST exist between any two tokens (for the definition separators) MUST exist between any two tokens (for the definition
of "token" below), since they would otherwise be interpreted as a of "token" below), since they would otherwise be interpreted as a
single token. single token.
2.2. Basic Rules 2.2. Basic Rules
The following rules are used throughout this specification to The following rules are used throughout this specification to
describe basic parsing constructs. The US-ASCII coded character set describe basic parsing constructs. The US-ASCII coded character set
is defined by ANSI X3.4-1986 [21]. is defined by ANSI X3.4-1986 [USASCII].
OCTET = <any 8-bit sequence of data> OCTET = <any 8-bit sequence of data>
CHAR = <any US-ASCII character (octets 0 - 127)> CHAR = <any US-ASCII character (octets 0 - 127)>
UPALPHA = <any US-ASCII uppercase letter "A".."Z"> UPALPHA = <any US-ASCII uppercase letter "A".."Z">
LOALPHA = <any US-ASCII lowercase letter "a".."z"> LOALPHA = <any US-ASCII lowercase letter "a".."z">
ALPHA = UPALPHA | LOALPHA ALPHA = UPALPHA | LOALPHA
DIGIT = <any US-ASCII digit "0".."9"> DIGIT = <any US-ASCII digit "0".."9">
CTL = <any US-ASCII control character CTL = %x00-1F | %x7F
(octets 0 - 31) and DEL (127)> ; (octets 0 - 31) and DEL (127)
CR = <US-ASCII CR, carriage return (13)> CR = <US-ASCII CR, carriage return (13)>
LF = <US-ASCII LF, linefeed (10)> LF = <US-ASCII LF, linefeed (10)>
SP = <US-ASCII SP, space (32)> SP = <US-ASCII SP, space (32)>
HT = <US-ASCII HT, horizontal-tab (9)> HT = <US-ASCII HT, horizontal-tab (9)>
<"> = <US-ASCII double-quote mark (34)> DQUOTE = <US-ASCII double-quote mark (34)>
HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
protocol elements except the entity-body (see Appendix A.3 for protocol elements except the entity-body (see Appendix C for tolerant
tolerant applications). The end-of-line marker within an entity-body applications). The end-of-line marker within an entity-body is
is defined by its associated media type, as described in Section 3.7. defined by its associated media type, as described in Section 3.7.
CRLF = CR LF CRLF = CR LF
HTTP/1.1 header field values can be folded onto multiple lines if the HTTP/1.1 header field values can be folded onto multiple lines if the
continuation line begins with a space or horizontal tab. All linear continuation line begins with a space or horizontal tab. All linear
white space, including folding, has the same semantics as SP. A white space, including folding, has the same semantics as SP. A
recipient MAY replace any linear white space with a single SP before recipient MAY replace any linear white space with a single SP before
interpreting the field value or forwarding the message downstream. interpreting the field value or forwarding the message downstream.
LWS = [CRLF] 1*( SP | HT ) LWS = [CRLF] 1*( SP | HT )
The TEXT rule is only used for descriptive field contents and values The TEXT rule is only used for descriptive field contents and values
that are not intended to be interpreted by the message parser. Words that are not intended to be interpreted by the message parser. Words
of *TEXT MAY contain characters from character sets other than ISO- of *TEXT MAY contain characters from character sets other than ISO-
8859-1 [22] only when encoded according to the rules of RFC 2047 8859-1 [ISO-8859-1] only when encoded according to the rules of
[14]. [RFC2047].
TEXT = <any OCTET except CTLs, TEXT = %x20-7E | %x80-FF | LWS
but including LWS> ; any OCTET except CTLs, but including LWS
A CRLF is allowed in the definition of TEXT only as part of a header A CRLF is allowed in the definition of TEXT only as part of a header
field continuation. It is expected that the folding LWS will be field continuation. It is expected that the folding LWS will be
replaced with a single SP before interpretation of the TEXT value. replaced with a single SP before interpretation of the TEXT value.
Hexadecimal numeric characters are used in several protocol elements. Hexadecimal numeric characters are used in several protocol elements.
HEX = "A" | "B" | "C" | "D" | "E" | "F" HEX = "A" | "B" | "C" | "D" | "E" | "F"
| "a" | "b" | "c" | "d" | "e" | "f" | DIGIT | "a" | "b" | "c" | "d" | "e" | "f" | DIGIT
Many HTTP/1.1 header field values consist of words separated by LWS Many HTTP/1.1 header field values consist of words separated by LWS
or special characters. These special characters MUST be in a quoted or special characters. These special characters MUST be in a quoted
string to be used within a parameter value (as defined in string to be used within a parameter value (as defined in
Section 3.6). Section 3.6).
token = 1*<any CHAR except CTLs or separators> separators = "(" | ")" | "<" | ">" | "@"
separators = "(" | ")" | "<" | ">" | "@" | "," | ";" | ":" | "\" | DQUOTE
| "," | ";" | ":" | "\" | <"> | "/" | "[" | "]" | "?" | "="
| "/" | "[" | "]" | "?" | "=" | "{" | "}" | SP | HT
| "{" | "}" | SP | HT
tchar = "!" | "#" | "$" | "%" | "&" | "'" | "*" | "+" | "-"
| "." | "^" | "_" | "`" | "|" | "~" | DIGIT | ALPHA
; any CHAR except CTLs or separators
token = 1*tchar
Comments can be included in some HTTP header fields by surrounding Comments can be included in some HTTP header fields by surrounding
the comment text with parentheses. Comments are only allowed in the comment text with parentheses. Comments are only allowed in
fields containing "comment" as part of their field value definition. fields containing "comment" as part of their field value definition.
In all other fields, parentheses are considered part of the field In all other fields, parentheses are considered part of the field
value. value.
comment = "(" *( ctext | quoted-pair | comment ) ")" comment = "(" *( ctext | quoted-pair | comment ) ")"
ctext = <any TEXT excluding "(" and ")"> ctext = %x20-27 | %x2A-7E | %x80-FF | LWS
; any TEXT excluding "(" and ")"
A string of text is parsed as a single word if it is quoted using A string of text is parsed as a single word if it is quoted using
double-quote marks. double-quote marks.
quoted-string = ( <"> *(qdtext | quoted-pair ) <"> ) quoted-string = ( DQUOTE *(qdtext | quoted-pair ) DQUOTE )
qdtext = <any TEXT except <">> qdtext = %x20-21 | %x23-5B | %x5D-7E | %x80-FF | LWS
; any TEXT excluding DQUOTE and "\"
The backslash character ("\") MAY be used as a single-character The backslash character ("\") MAY be used as a single-character
quoting mechanism only within quoted-string and comment constructs. quoting mechanism only within quoted-string and comment constructs.
quoted-pair = "\" CHAR quoted-pair = "\" CHAR
3. Protocol Parameters 3. Protocol Parameters
3.1. HTTP Version 3.1. HTTP Version
HTTP uses a "<major>.<minor>" numbering scheme to indicate versions HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
of the protocol. The protocol versioning policy is intended to allow of the protocol. The protocol versioning policy is intended to allow
the sender to indicate the format of a message and its capacity for the sender to indicate the format of a message and its capacity for
understanding further HTTP communication, rather than the features understanding further HTTP communication, rather than the features
obtained via that communication. No change is made to the version obtained via that communication. No change is made to the version
number for the addition of message components which do not affect number for the addition of message components which do not affect
communication behavior or which only add to extensible field values. communication behavior or which only add to extensible field values.
The <minor> number is incremented when the changes made to the The <minor> number is incremented when the changes made to the
protocol add features which do not change the general message parsing protocol add features which do not change the general message parsing
algorithm, but which may add to the message semantics and imply algorithm, but which may add to the message semantics and imply
additional capabilities of the sender. The <major> number is additional capabilities of the sender. The <major> number is
incremented when the format of a message within the protocol is incremented when the format of a message within the protocol is
changed. See RFC 2145 [36] for a fuller explanation. changed. See [RFC2145] for a fuller explanation.
The version of an HTTP message is indicated by an HTTP-Version field The version of an HTTP message is indicated by an HTTP-Version field
in the first line of the message. in the first line of the message. HTTP-Version is case-sensitive.
HTTP-Version = "HTTP" "/" 1*DIGIT "." 1*DIGIT HTTP-Version = "HTTP" "/" 1*DIGIT "." 1*DIGIT
Note that the major and minor numbers MUST be treated as separate Note that the major and minor numbers MUST be treated as separate
integers and that each MAY be incremented higher than a single digit. integers and that each MAY be incremented higher than a single digit.
Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
lower than HTTP/12.3. Leading zeros MUST be ignored by recipients lower than HTTP/12.3. Leading zeros MUST be ignored by recipients
and MUST NOT be sent. and MUST NOT be sent.
An application that sends a request or response message that includes An application that sends a request or response message that includes
HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
with this specification. Applications that are at least with this specification. Applications that are at least
conditionally compliant with this specification SHOULD use an HTTP- conditionally compliant with this specification SHOULD use an HTTP-
Version of "HTTP/1.1" in their messages, and MUST do so for any Version of "HTTP/1.1" in their messages, and MUST do so for any
message that is not compatible with HTTP/1.0. For more details on message that is not compatible with HTTP/1.0. For more details on
when to send specific HTTP-Version values, see RFC 2145 [36]. when to send specific HTTP-Version values, see [RFC2145].
The HTTP version of an application is the highest HTTP version for The HTTP version of an application is the highest HTTP version for
which the application is at least conditionally compliant. which the application is at least conditionally compliant.
Proxy and gateway applications need to be careful when forwarding Proxy and gateway applications need to be careful when forwarding
messages in protocol versions different from that of the application. messages in protocol versions different from that of the application.
Since the protocol version indicates the protocol capability of the Since the protocol version indicates the protocol capability of the
sender, a proxy/gateway MUST NOT send a message with a version sender, a proxy/gateway MUST NOT send a message with a version
indicator which is greater than its actual version. If a higher indicator which is greater than its actual version. If a higher
version request is received, the proxy/gateway MUST either downgrade version request is received, the proxy/gateway MUST either downgrade
the request version, or respond with an error, or switch to tunnel the request version, or respond with an error, or switch to tunnel
behavior. behavior.
Due to interoperability problems with HTTP/1.0 proxies discovered Due to interoperability problems with HTTP/1.0 proxies discovered
since the publication of RFC 2068 [33], caching proxies MUST, since the publication of [RFC2068], caching proxies MUST, gateways
gateways MAY, and tunnels MUST NOT upgrade the request to the highest MAY, and tunnels MUST NOT upgrade the request to the highest version
version they support. The proxy/gateway's response to that request they support. The proxy/gateway's response to that request MUST be
MUST be in the same major version as the request. in the same major version as the request.
Note: Converting between versions of HTTP may involve modification Note: Converting between versions of HTTP may involve modification
of header fields required or forbidden by the versions involved. of header fields required or forbidden by the versions involved.
3.2. Uniform Resource Identifiers 3.2. Uniform Resource Identifiers
URIs have been known by many names: WWW addresses, Universal Document URIs have been known by many names: WWW addresses, Universal Document
Identifiers, Universal Resource Identifiers [3], and finally the Identifiers, Universal Resource Identifiers [RFC1630], and finally
combination of Uniform Resource Locators (URL) [4] and Names (URN) the combination of Uniform Resource Locators (URL) [RFC1738] and
[20]. As far as HTTP is concerned, Uniform Resource Identifiers are Names (URN) [RFC1737]. As far as HTTP is concerned, Uniform Resource
simply formatted strings which identify--via name, location, or any Identifiers are simply formatted strings which identify--via name,
other characteristic--a resource. location, or any other characteristic--a resource.
3.2.1. General Syntax 3.2.1. General Syntax
URIs in HTTP can be represented in absolute form or relative to some URIs in HTTP can be represented in absolute form or relative to some
known base URI [11], depending upon the context of their use. The known base URI [RFC1808], depending upon the context of their use.
two forms are differentiated by the fact that absolute URIs always The two forms are differentiated by the fact that absolute URIs
begin with a scheme name followed by a colon. For definitive always begin with a scheme name followed by a colon. For definitive
information on URL syntax and semantics, see "Uniform Resource information on URL syntax and semantics, see "Uniform Resource
Identifiers (URI): Generic Syntax and Semantics," RFC 2396 [42] Identifiers (URI): Generic Syntax and Semantics," [RFC2396] (which
(which replaces RFCs 1738 [4] and RFC 1808 [11]). This specification replaces [RFC1738] and [RFC1808]). This specification adopts the
adopts the definitions of "URI-reference", "absoluteURI", definitions of "URI-reference", "absoluteURI", "relativeURI", "port",
"relativeURI", "port", "host","abs_path", "rel_path", and "authority" "host", "abs_path", "query", and "authority" from that specification.
from that specification.
absoluteURI = <absoluteURI, defined in [RFC2396], Section 3>
authority = <authority, defined in [RFC2396], Section 3.2>
path-absolute = <abs_path, defined in [RFC2396], Section 3>
port = <port, defined in [RFC2396], Section 3.2.2>
query = <query, defined in [RFC2396], Section 3.4>
relativeURI = <relativeURI, defined in [RFC2396], Section 5>
uri-host = <host, defined in [RFC2396], Section 3.2.2>
The HTTP protocol does not place any a priori limit on the length of The HTTP protocol does not place any a priori limit on the length of
a URI. Servers MUST be able to handle the URI of any resource they a URI. Servers MUST be able to handle the URI of any resource they
serve, and SHOULD be able to handle URIs of unbounded length if they serve, and SHOULD be able to handle URIs of unbounded length if they
provide GET-based forms that could generate such URIs. A server provide GET-based forms that could generate such URIs. A server
SHOULD return 414 (Request-URI Too Long) status if a URI is longer SHOULD return 414 (Request-URI Too Long) status if a URI is longer
than the server can handle (see Section 10.4.15). than the server can handle (see Section 10.4.15).
Note: Servers ought to be cautious about depending on URI lengths Note: Servers ought to be cautious about depending on URI lengths
above 255 bytes, because some older client or proxy above 255 bytes, because some older client or proxy
implementations might not properly support these lengths. implementations might not properly support these lengths.
3.2.2. http URL 3.2.2. http URL
The "http" scheme is used to locate network resources via the HTTP The "http" scheme is used to locate network resources via the HTTP
protocol. This section defines the scheme-specific syntax and protocol. This section defines the scheme-specific syntax and
semantics for http URLs. semantics for http URLs.
http_URL = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]] http-URL = "http:" "//" uri-host [ ":" port ] [ path-absolute [ "?" query ]]
If the port is empty or not given, port 80 is assumed. The semantics If the port is empty or not given, port 80 is assumed. The semantics
are that the identified resource is located at the server listening are that the identified resource is located at the server listening
for TCP connections on that port of that host, and the Request-URI for TCP connections on that port of that host, and the Request-URI
for the resource is abs_path (Section 5.1.2). The use of IP for the resource is path-absolute (Section 5.1.2). The use of IP
addresses in URLs SHOULD be avoided whenever possible (see RFC 1900 addresses in URLs SHOULD be avoided whenever possible (see
[24]). If the abs_path is not present in the URL, it MUST be given [RFC1900]). If the path-absolute is not present in the URL, it MUST
as "/" when used as a Request-URI for a resource (Section 5.1.2). If be given as "/" when used as a Request-URI for a resource
a proxy receives a host name which is not a fully qualified domain (Section 5.1.2). If a proxy receives a host name which is not a
name, it MAY add its domain to the host name it received. If a proxy fully qualified domain name, it MAY add its domain to the host name
receives a fully qualified domain name, the proxy MUST NOT change the it received. If a proxy receives a fully qualified domain name, the
host name. proxy MUST NOT change the host name.
3.2.3. URI Comparison 3.2.3. URI Comparison
When comparing two URIs to decide if they match or not, a client When comparing two URIs to decide if they match or not, a client
SHOULD use a case-sensitive octet-by-octet comparison of the entire SHOULD use a case-sensitive octet-by-octet comparison of the entire
URIs, with these exceptions: URIs, with these exceptions:
o A port that is empty or not given is equivalent to the default o A port that is empty or not given is equivalent to the default
port for that URI-reference; port for that URI-reference;
o Comparisons of host names MUST be case-insensitive; o Comparisons of host names MUST be case-insensitive;
o Comparisons of scheme names MUST be case-insensitive; o Comparisons of scheme names MUST be case-insensitive;
o An empty abs_path is equivalent to an abs_path of "/". o An empty path-absolute is equivalent to an path-absolute of "/".
Characters other than those in the "reserved" and "unsafe" sets (see Characters other than those in the "reserved" set (see [RFC2396]) are
RFC 2396 [42]) are equivalent to their ""%" HEX HEX" encoding. equivalent to their ""%" HEX HEX" encoding.
For example, the following three URIs are equivalent: For example, the following three URIs are equivalent:
http://abc.com:80/~smith/home.html http://example.com:80/~smith/home.html
http://ABC.com/%7Esmith/home.html http://EXAMPLE.com/%7Esmith/home.html
http://ABC.com:/%7esmith/home.html http://EXAMPLE.com:/%7esmith/home.html
3.3. Date/Time Formats 3.3. Date/Time Formats
3.3.1. Full Date 3.3.1. Full Date
HTTP applications have historically allowed three different formats HTTP applications have historically allowed three different formats
for the representation of date/time stamps: for the representation of date/time stamps:
Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123 Sun, 06 Nov 1994 08:49:37 GMT ; [RFC822], updated by [RFC1123]
Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036 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
The first format is preferred as an Internet standard and represents The first format is preferred as an Internet standard and represents
a fixed-length subset of that defined by RFC 1123 [8] (an update to a fixed-length subset of that defined by [RFC1123] (an update to
RFC 822 [9]). The second format is in common use, but is based on [RFC822]). The other formats are described here only for
the obsolete RFC 850 [12] date format and lacks a four-digit year. compatibility with obsolete implementations. HTTP/1.1 clients and
HTTP/1.1 clients and servers that parse the date value MUST accept servers that parse the date value MUST accept all three formats (for
all three formats (for compatibility with HTTP/1.0), though they MUST compatibility with HTTP/1.0), though they MUST only generate the RFC
only generate the RFC 1123 format for representing HTTP-date values 1123 format for representing HTTP-date values in header fields. See
in header fields. See Appendix A.3 for further information. Appendix C for further information.
Note: Recipients of date values are encouraged to be robust in Note: Recipients of date values are encouraged to be robust in
accepting date values that may have been sent by non-HTTP accepting date values that may have been sent by non-HTTP
applications, as is sometimes the case when retrieving or posting applications, as is sometimes the case when retrieving or posting
messages via proxies/gateways to SMTP or NNTP. messages via proxies/gateways to SMTP or NNTP.
All HTTP date/time stamps MUST be represented in Greenwich Mean Time All HTTP date/time stamps MUST be represented in Greenwich Mean Time
(GMT), without exception. For the purposes of HTTP, GMT is exactly (GMT), without exception. For the purposes of HTTP, GMT is exactly
equal to UTC (Coordinated Universal Time). This is indicated in the equal to UTC (Coordinated Universal Time). This is indicated in the
first two formats by the inclusion of "GMT" as the three-letter first two formats by the inclusion of "GMT" as the three-letter
abbreviation for time zone, and MUST be assumed when reading the abbreviation for time zone, and MUST be assumed when reading the
asctime format. HTTP-date is case sensitive and MUST NOT include asctime format. HTTP-date is case sensitive and MUST NOT include
additional LWS beyond that specifically included as SP in the additional LWS beyond that specifically included as SP in the
grammar. grammar.
HTTP-date = rfc1123-date | rfc850-date | asctime-date HTTP-date = rfc1123-date ; for use in message producers
rfc1123-date = wkday "," SP date1 SP time SP "GMT" | obsolete-date ; only allowed in message parsing
rfc850-date = weekday "," SP date2 SP time SP "GMT" obsolete-date = rfc850-date | asctime-date
asctime-date = wkday SP date3 SP time SP 4DIGIT rfc1123-date = wkday "," SP date1 SP time SP "GMT"
date1 = 2DIGIT SP month SP 4DIGIT rfc850-date = weekday "," SP date2 SP time SP "GMT"
; day month year (e.g., 02 Jun 1982) asctime-date = wkday SP date3 SP time SP 4DIGIT
date2 = 2DIGIT "-" month "-" 2DIGIT date1 = 2DIGIT SP month SP 4DIGIT
; day-month-year (e.g., 02-Jun-82) ; day month year (e.g., 02 Jun 1982)
date3 = month SP ( 2DIGIT | ( SP 1DIGIT )) date2 = 2DIGIT "-" month "-" 2DIGIT
; month day (e.g., Jun 2) ; day-month-year (e.g., 02-Jun-82)
time = 2DIGIT ":" 2DIGIT ":" 2DIGIT date3 = month SP ( 2DIGIT | ( SP 1DIGIT ))
; 00:00:00 - 23:59:59 ; month day (e.g., Jun 2)
wkday = "Mon" | "Tue" | "Wed" time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
| "Thu" | "Fri" | "Sat" | "Sun" ; 00:00:00 - 23:59:59
weekday = "Monday" | "Tuesday" | "Wednesday" wkday = "Mon" | "Tue" | "Wed"
| "Thursday" | "Friday" | "Saturday" | "Sunday" | "Thu" | "Fri" | "Sat" | "Sun"
month = "Jan" | "Feb" | "Mar" | "Apr" weekday = "Monday" | "Tuesday" | "Wednesday"
| "May" | "Jun" | "Jul" | "Aug" | "Thursday" | "Friday" | "Saturday" | "Sunday"
| "Sep" | "Oct" | "Nov" | "Dec" month = "Jan" | "Feb" | "Mar" | "Apr"
| "May" | "Jun" | "Jul" | "Aug"
| "Sep" | "Oct" | "Nov" | "Dec"
Note: HTTP requirements for the date/time stamp format apply only to Note: HTTP requirements for the date/time stamp format apply only to
their usage within the protocol stream. Clients and servers are not their usage within the protocol stream. Clients and servers are not
required to use these formats for user presentation, request logging, required to use these formats for user presentation, request logging,
etc. etc.
3.3.2. Delta Seconds 3.3.2. Delta Seconds
Some HTTP header fields allow a time value to be specified as an Some HTTP header fields allow a time value to be specified as an
integer number of seconds, represented in decimal, after the time integer number of seconds, represented in decimal, after the time
that the message was received. that the message was received.
delta-seconds = 1*DIGIT delta-seconds = 1*DIGIT
3.4. Character Sets 3.4. Character Sets
HTTP uses the same definition of the term "character set" as that HTTP uses the same definition of the term "character set" as that
described for MIME: described for MIME:
The term "character set" is used in this document to refer to a The term "character set" is used in this document to refer to a
method used with one or more tables to convert a sequence of octets method used with one or more tables to convert a sequence of octets
into a sequence of characters. Note that unconditional conversion in into a sequence of characters. Note that unconditional conversion in
the other direction is not required, in that not all characters may the other direction is not required, in that not all characters may
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to characters. In particular, use of external profiling information to characters. In particular, use of external profiling information
to determine the exact mapping is not permitted. to determine the exact mapping is not permitted.
Note: This use of the term "character set" is more commonly Note: This use of the term "character set" is more commonly
referred to as a "character encoding." However, since HTTP and referred to as a "character encoding." However, since HTTP and
MIME share the same registry, it is important that the terminology MIME share the same registry, it is important that the terminology
also be shared. also be shared.
HTTP character sets are identified by case-insensitive tokens. The HTTP character sets are identified by case-insensitive tokens. The
complete set of tokens is defined by the IANA Character Set registry complete set of tokens is defined by the IANA Character Set registry
[19]. (<http://www.iana.org/assignments/character-sets>).
charset = token charset = token
Although HTTP allows an arbitrary token to be used as a charset Although HTTP allows an arbitrary token to be used as a charset
value, any token that has a predefined value within the IANA value, any token that has a predefined value within the IANA
Character Set registry [19] MUST represent the character set defined Character Set registry MUST represent the character set defined by
by that registry. Applications SHOULD limit their use of character that registry. Applications SHOULD limit their use of character sets
sets to those defined by the IANA registry. to those defined by the IANA registry.
Implementors should be aware of IETF character set requirements [38] HTTP uses charset in two contexts: within an Accept-Charset request
[41]. header (in which the charset value is an unquoted token) and as the
value of a parameter in a Content-Type header (within a request or
response), in which case the parameter value of the charset parameter
may be quoted.
Implementors should be aware of IETF character set requirements
[RFC3629] [RFC2277].
3.4.1. Missing Charset 3.4.1. Missing Charset
Some HTTP/1.0 software has interpreted a Content-Type header without Some HTTP/1.0 software has interpreted a Content-Type header without
charset parameter incorrectly to mean "recipient should guess." charset parameter incorrectly to mean "recipient should guess."
Senders wishing to defeat this behavior MAY include a charset Senders wishing to defeat this behavior MAY include a charset
parameter even when the charset is ISO-8859-1 and SHOULD do so when parameter even when the charset is ISO-8859-1 and SHOULD do so when
it is known that it will not confuse the recipient. it is known that it will not confuse the recipient.
Unfortunately, some older HTTP/1.0 clients did not deal properly with Unfortunately, some older HTTP/1.0 clients did not deal properly with
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3.5. Content Codings 3.5. 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 an entity. Content codings are primarily been or can be applied to an entity. Content codings are primarily
used to allow a document to be compressed or otherwise usefully used to allow a document to be compressed or otherwise usefully
transformed without losing the identity of its underlying media type transformed without losing the identity of its underlying media type
and without loss of information. Frequently, the entity is stored in and without loss of information. Frequently, the entity is stored in
coded form, transmitted directly, and only decoded by the recipient. coded form, transmitted directly, and only decoded by the recipient.
content-coding = token content-coding = token
All content-coding values are case-insensitive. HTTP/1.1 uses All content-coding values are case-insensitive. HTTP/1.1 uses
content-coding values in the Accept-Encoding (Section 14.3) and content-coding values in the Accept-Encoding (Section 14.3) and
Content-Encoding (Section 14.11) header fields. Although the value Content-Encoding (Section 14.11) header fields. Although the value
describes the content-coding, what is more important is that it describes the content-coding, what is more important is that it
indicates what decoding mechanism will be required to remove the indicates what decoding mechanism will be required to remove the
encoding. encoding.
The Internet Assigned Numbers Authority (IANA) acts as a registry for The Internet Assigned Numbers Authority (IANA) acts as a registry for
content-coding value tokens. Initially, the registry contains the content-coding value tokens. Initially, the registry contains the
following tokens: following tokens:
gzip gzip
An encoding format produced by the file compression program "gzip" An encoding format produced by the file compression program "gzip"
(GNU zip) as described in RFC 1952 [25]. This format is a Lempel- (GNU zip) as described in [RFC1952]. This format is a Lempel-Ziv
Ziv coding (LZ77) with a 32 bit CRC. coding (LZ77) with a 32 bit CRC.
compress compress
The encoding format produced by the common UNIX file compression The encoding format produced by the common UNIX file compression
program "compress". This format is an adaptive Lempel-Ziv-Welch program "compress". This format is an adaptive Lempel-Ziv-Welch
coding (LZW). coding (LZW).
Use of program names for the identification of encoding formats is Use of program names for the identification of encoding formats is
not desirable and is discouraged for future encodings. Their use not desirable and is discouraged for future encodings. Their use
here is representative of historical practice, not good design. here is representative of historical practice, not good design.
For compatibility with previous implementations of HTTP, For compatibility with previous implementations of HTTP,
applications SHOULD consider "x-gzip" and "x-compress" to be applications SHOULD consider "x-gzip" and "x-compress" to be
equivalent to "gzip" and "compress" respectively. equivalent to "gzip" and "compress" respectively.
deflate deflate
The "zlib" format defined in RFC 1950 [31] in combination with the The "zlib" format defined in [RFC1950] in combination with the
"deflate" compression mechanism described in RFC 1951 [29]. "deflate" compression mechanism described in [RFC1951].
identity identity
The default (identity) encoding; the use of no transformation The default (identity) encoding; the use of no transformation
whatsoever. This content-coding is used only in the Accept- whatsoever. This content-coding is used only in the Accept-
Encoding header, and SHOULD NOT be used in the Content-Encoding Encoding header, and SHOULD NOT be used in the Content-Encoding
header. header.
New content-coding value tokens SHOULD be registered; to allow New content-coding value tokens SHOULD be registered; to allow
interoperability between clients and servers, specifications of the interoperability between clients and servers, specifications of the
content coding algorithms needed to implement a new value SHOULD be content coding algorithms needed to implement a new value SHOULD be
publicly available and adequate for independent implementation, and publicly available and adequate for independent implementation, and
conform to the purpose of content coding defined in this section. conform to the purpose of content coding defined in this section.
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conform to the purpose of content coding defined in this section. conform to the purpose of content coding defined in this section.
3.6. Transfer Codings 3.6. Transfer Codings
Transfer-coding values are used to indicate an encoding Transfer-coding values are used to indicate an encoding
transformation that has been, can be, or may need to be applied to an transformation that has been, can be, or may need to be applied to an
entity-body in order to ensure "safe transport" through the network. entity-body in order to ensure "safe transport" through the network.
This differs from a content coding in that the transfer-coding is a This differs from a content coding in that the transfer-coding is a
property of the message, not of the original entity. property of the message, not of the original entity.
transfer-coding = "chunked" | transfer-extension transfer-coding = "chunked" | transfer-extension
transfer-extension = token *( ";" parameter ) transfer-extension = token *( ";" parameter )
Parameters are in the form of attribute/value pairs. Parameters are in the form of attribute/value pairs.
parameter = attribute "=" value parameter = attribute "=" value
attribute = token attribute = token
value = token | quoted-string value = token | quoted-string
All transfer-coding values are case-insensitive. HTTP/1.1 uses All transfer-coding values are case-insensitive. HTTP/1.1 uses
transfer-coding values in the TE header field (Section 14.39) and in transfer-coding values in the TE header field (Section 14.39) and in
the Transfer-Encoding header field (Section 14.41). the Transfer-Encoding header field (Section 14.41).
Whenever a transfer-coding is applied to a message-body, the set of Whenever a transfer-coding is applied to a message-body, the set of
transfer-codings MUST include "chunked", unless the message is transfer-codings MUST include "chunked", unless the message is
terminated by closing the connection. When the "chunked" transfer- terminated by closing the connection. When the "chunked" transfer-
coding is used, it MUST be the last transfer-coding applied to the coding is used, it MUST be the last transfer-coding applied to the
message-body. The "chunked" transfer-coding MUST NOT be applied more message-body. The "chunked" transfer-coding MUST NOT be applied more
than once to a message-body. These rules allow the recipient to than once to a message-body. These rules allow the recipient to
determine the transfer-length of the message (Section 4.4). determine the transfer-length of the message (Section 4.4).
Transfer-codings are analogous to the Content-Transfer-Encoding Transfer-codings are analogous to the Content-Transfer-Encoding
values of MIME [7], which were designed to enable safe transport of values of MIME [RFC2045], which were designed to enable safe
binary data over a 7-bit transport service. However, safe transport transport of binary data over a 7-bit transport service. However,
has a different focus for an 8bit-clean transfer protocol. In HTTP, safe transport has a different focus for an 8bit-clean transfer
the only unsafe characteristic of message-bodies is the difficulty in protocol. In HTTP, the only unsafe characteristic of message-bodies
determining the exact body length (Section 7.2.2), or the desire to is the difficulty in determining the exact body length
encrypt data over a shared transport. (Section 7.2.2), or the desire to encrypt data over a shared
transport.
The Internet Assigned Numbers Authority (IANA) acts as a registry for The Internet Assigned Numbers Authority (IANA) acts as a registry for
transfer-coding value tokens. Initially, the registry contains the transfer-coding value tokens. Initially, the registry contains the
following tokens: "chunked" (Section 3.6.1), "identity" (section following tokens: "chunked" (Section 3.6.1), "gzip" (Section 3.5),
3.6.2), "gzip" (Section 3.5), "compress" (Section 3.5), and "deflate" "compress" (Section 3.5), and "deflate" (Section 3.5).
(Section 3.5).
New transfer-coding value tokens SHOULD be registered in the same way New transfer-coding value tokens SHOULD be registered in the same way
as new content-coding value tokens (Section 3.5). as new content-coding value tokens (Section 3.5).
A server which receives an entity-body with a transfer-coding it does A server which receives an entity-body with a transfer-coding it does
not understand SHOULD return 501 (Unimplemented), and close the not understand SHOULD return 501 (Not Implemented), and close the
connection. A server MUST NOT send transfer-codings to an HTTP/1.0 connection. A server MUST NOT send transfer-codings to an HTTP/1.0
client. client.
3.6.1. Chunked Transfer Coding 3.6.1. Chunked Transfer Coding
The chunked encoding modifies the body of a message in order to The chunked encoding modifies the body of a message in order to
transfer it as a series of chunks, each with its own size indicator, transfer it as a series of chunks, each with its own size indicator,
followed by an OPTIONAL trailer containing entity-header fields. followed by an OPTIONAL trailer containing entity-header fields.
This allows dynamically produced content to be transferred along with This allows dynamically produced content to be transferred along with
the information necessary for the recipient to verify that it has the information necessary for the recipient to verify that it has
received the full message. received the full message.
Chunked-Body = *chunk Chunked-Body = *chunk
last-chunk last-chunk
trailer trailer-part
CRLF CRLF
chunk = chunk-size [ chunk-extension ] CRLF chunk = chunk-size [ chunk-extension ] CRLF
chunk-data CRLF chunk-data CRLF
chunk-size = 1*HEX chunk-size = 1*HEX
last-chunk = 1*("0") [ chunk-extension ] CRLF last-chunk = 1*("0") [ chunk-extension ] CRLF
chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] ) chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
chunk-ext-name = token chunk-ext-name = token
chunk-ext-val = token | quoted-string chunk-ext-val = token | quoted-string
chunk-data = chunk-size(OCTET)
trailer = *(entity-header CRLF) chunk-data = 1*OCTET ; a sequence of chunk-size octets
trailer-part = *(entity-header CRLF)
The chunk-size field is a string of hex digits indicating the size of The chunk-size field is a string of hex digits indicating the size of
the chunk. The chunked encoding is ended by any chunk whose size is the chunk-data in octets. The chunked encoding is ended by any chunk
zero, followed by the trailer, which is terminated by an empty line. whose size is zero, followed by the trailer, which is terminated by
an empty line.
The trailer allows the sender to include additional HTTP header The trailer allows the sender to include additional HTTP header
fields at the end of the message. The Trailer header field can be fields at the end of the message. The Trailer header field can be
used to indicate which header fields are included in a trailer (see used to indicate which header fields are included in a trailer (see
Section 14.40). Section 14.40).
A server using chunked transfer-coding in a response MUST NOT use the A server using chunked transfer-coding in a response MUST NOT use the
trailer for any header fields unless at least one of the following is trailer for any header fields unless at least one of the following is
true: true:
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trailer fields might be silently discarded along the path to the trailer fields might be silently discarded along the path to the
client. client.
This requirement prevents an interoperability failure when the This requirement prevents an interoperability failure when the
message is being received by an HTTP/1.1 (or later) proxy and message is being received by an HTTP/1.1 (or later) proxy and
forwarded to an HTTP/1.0 recipient. It avoids a situation where forwarded to an HTTP/1.0 recipient. It avoids a situation where
compliance with the protocol would have necessitated a possibly compliance with the protocol would have necessitated a possibly
infinite buffer on the proxy. infinite buffer on the proxy.
An example process for decoding a Chunked-Body is presented in An example process for decoding a Chunked-Body is presented in
Appendix A.4.6. Appendix D.6.
All HTTP/1.1 applications MUST be able to receive and decode the All HTTP/1.1 applications MUST be able to receive and decode the
"chunked" transfer-coding, and MUST ignore chunk-extension extensions "chunked" transfer-coding, and MUST ignore chunk-extension extensions
they do not understand. they do not understand.
3.7. Media Types 3.7. Media Types
HTTP uses Internet Media Types [17] in the Content-Type HTTP uses Internet Media Types [RFC2046] in the Content-Type
(Section 14.17) and Accept (Section 14.1) header fields in order to (Section 14.17) and Accept (Section 14.1) header fields in order to
provide open and extensible data typing and type negotiation. provide open and extensible data typing and type negotiation.
media-type = type "/" subtype *( ";" parameter ) media-type = type "/" subtype *( ";" parameter )
type = token type = token
subtype = token subtype = token
Parameters MAY follow the type/subtype in the form of attribute/value Parameters MAY follow the type/subtype in the form of attribute/value
pairs (as defined in Section 3.6). pairs (as defined in Section 3.6).
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. Linear white space depending on the semantics of the parameter name. Linear white space
(LWS) MUST NOT be used between the type and subtype, nor between an (LWS) MUST NOT be used between the type and subtype, nor between an
attribute and its value. The presence or absence of a parameter attribute and its value. The presence or absence of a parameter
might be significant to the processing of a media-type, depending on might be significant to the processing of a media-type, depending on
its definition within the media type registry. its definition within the media type registry.
Note that some older HTTP applications do not recognize media type Note that some older HTTP applications do not recognize media type
parameters. When sending data to older HTTP applications, parameters. When sending data to older HTTP applications,
implementations SHOULD only use media type parameters when they are implementations SHOULD only use media type parameters when they are
required by that type/subtype definition. required by that type/subtype definition.
Media-type values are registered with the Internet Assigned Number Media-type values are registered with the Internet Assigned Number
Authority (IANA [19]). The media type registration process is Authority (IANA). The media type registration process is outlined in
outlined in RFC 1590 [17]. Use of non-registered media types is [RFC4288]. Use of non-registered media types is discouraged.
discouraged.
3.7.1. Canonicalization and Text Defaults 3.7.1. Canonicalization and Text Defaults
Internet media types are registered with a canonical form. An Internet media types are registered with a canonical form. An
entity-body transferred via HTTP messages MUST be represented in the entity-body transferred via HTTP messages MUST be represented in the
appropriate canonical form prior to its transmission except for appropriate canonical form prior to its transmission except for
"text" types, as defined in the next paragraph. "text" types, as defined in the next paragraph.
When in canonical form, media subtypes of the "text" type use CRLF as When in canonical form, media subtypes of the "text" type use CRLF as
the text line break. HTTP relaxes this requirement and allows the the text line break. HTTP relaxes this requirement and allows the
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parameter is provided by the sender, media subtypes of the "text" parameter is provided by the sender, media subtypes of the "text"
type are defined to have a default charset value of "ISO-8859-1" when type are defined to have a default charset value of "ISO-8859-1" when
received via HTTP. Data in character sets other than "ISO-8859-1" or received via HTTP. Data in character sets other than "ISO-8859-1" or
its subsets MUST be labeled with an appropriate charset value. See its subsets MUST be labeled with an appropriate charset value. See
Section 3.4.1 for compatibility problems. Section 3.4.1 for compatibility problems.
3.7.2. Multipart Types 3.7.2. 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 entities within a single message-body. All multipart one or more entities within a single message-body. All multipart
types share a common syntax, as defined in section 5.1.1 of RFC 2046 types share a common syntax, as defined in Section 5.1.1 of
[40], and MUST include a boundary parameter as part of the media type [RFC2046], and MUST include a boundary parameter as part of the media
value. The message body is itself a protocol element and MUST type value. The message body is itself a protocol element and MUST
therefore use only CRLF to represent line breaks between body-parts. therefore use only CRLF to represent line breaks between body-parts.
Unlike in RFC 2046, the epilogue of any multipart message MUST be Unlike in RFC 2046, the epilogue of any multipart message MUST be
empty; HTTP applications MUST NOT transmit the epilogue (even if the empty; HTTP applications MUST NOT transmit the epilogue (even if the
original multipart contains an epilogue). These restrictions exist original multipart contains an epilogue). These restrictions exist
in order to preserve the self-delimiting nature of a multipart in order to preserve the self-delimiting nature of a multipart
message-body, wherein the "end" of the message-body is indicated by message-body, wherein the "end" of the message-body is indicated by
the ending multipart boundary. the ending multipart boundary.
In general, HTTP treats a multipart message-body no differently than In general, HTTP treats a multipart message-body no differently than
any other media type: strictly as payload. The one exception is the any other media type: strictly as payload. The one exception is the
"multipart/byteranges" type (Appendix A.2) when it appears in a 206 "multipart/byteranges" type (Appendix B) when it appears in a 206
(Partial Content) response, which will be interpreted by some HTTP (Partial Content) response, which will be interpreted by some HTTP
caching mechanisms as described in sections 13.5.4 and 14.16. In all caching mechanisms as described in Sections 13.5.4 and 14.16. In all
other cases, an HTTP user agent SHOULD follow the same or similar other cases, an HTTP user agent SHOULD follow the same or similar
behavior as a MIME user agent would upon receipt of a multipart type. 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- The MIME header fields within each body-part of a multipart message-
body do not have any significance to HTTP beyond that defined by body do not have any significance to HTTP beyond that defined by
their MIME semantics. their MIME semantics.
In general, an HTTP user agent SHOULD follow the same or similar In general, an HTTP user agent SHOULD follow the same or similar
behavior as a MIME user agent would upon receipt of a multipart type. behavior as a MIME user agent would upon receipt of a multipart type.
If an application receives an unrecognized multipart subtype, the If an application receives an unrecognized multipart subtype, the
application MUST treat it as being equivalent to "multipart/mixed". application MUST treat it as being equivalent to "multipart/mixed".
Note: The "multipart/form-data" type has been specifically defined Note: The "multipart/form-data" type has been specifically defined
for carrying form data suitable for processing via the POST for carrying form data suitable for processing via the POST
request method, as described in RFC 1867 [15]. request method, as described in [RFC2388].
3.8. Product Tokens 3.8. Product Tokens
Product tokens are used to allow communicating applications to Product tokens are used to allow communicating applications to
identify themselves by software name and version. Most fields using identify themselves by software name and version. Most fields using
product tokens also allow sub-products which form a significant part product tokens also allow sub-products which form a significant part
of the application to be listed, separated by white space. By of the application to be listed, separated by white space. By
convention, the products are listed in order of their significance convention, the products are listed in order of their significance
for identifying the application. for identifying the application.
product = token ["/" product-version] product = token ["/" product-version]
product-version = token product-version = token
Examples: Examples:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3 User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Server: Apache/0.8.4 Server: Apache/0.8.4
Product tokens SHOULD be short and to the point. They MUST NOT be Product tokens SHOULD be short and to the point. They MUST NOT be
used for advertising or other non-essential information. Although used for advertising or other non-essential information. Although
any token character MAY appear in a product-version, this token any token character MAY appear in a product-version, this token
SHOULD only be used for a version identifier (i.e., successive SHOULD only be used for a version identifier (i.e., successive
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HTTP content negotiation (Section 12) uses short "floating point" HTTP content negotiation (Section 12) uses short "floating point"
numbers to indicate the relative importance ("weight") of various numbers to indicate the relative importance ("weight") of various
negotiable parameters. A weight is normalized to a real number in negotiable parameters. A weight is normalized to a real number in
the range 0 through 1, where 0 is the minimum and 1 the maximum the range 0 through 1, where 0 is the minimum and 1 the maximum
value. If a parameter has a quality value of 0, then content with value. If a parameter has a quality value of 0, then content with
this parameter is `not acceptable' for the client. HTTP/1.1 this parameter is `not acceptable' for the client. HTTP/1.1
applications MUST NOT generate more than three digits after the applications MUST NOT generate more than three digits after the
decimal point. User configuration of these values SHOULD also be decimal point. User configuration of these values SHOULD also be
limited in this fashion. limited in this fashion.
qvalue = ( "0" [ "." 0*3DIGIT ] ) qvalue = ( "0" [ "." 0*3DIGIT ] )
| ( "1" [ "." 0*3("0") ] ) | ( "1" [ "." 0*3("0") ] )
"Quality values" is a misnomer, since these values merely represent "Quality values" is a misnomer, since these values merely represent
relative degradation in desired quality. relative degradation in desired quality.
3.10. Language Tags 3.10. Language Tags
A language tag identifies a natural language spoken, written, or A language tag identifies a natural language spoken, written, or
otherwise conveyed by human beings for communication of information otherwise conveyed by human beings for communication of information
to other human beings. Computer languages are explicitly excluded. to other human beings. Computer languages are explicitly excluded.
HTTP uses language tags within the Accept-Language and Content- HTTP uses language tags within the Accept-Language and Content-
Language fields. Language fields.
The syntax and registry of HTTP language tags is the same as that The syntax and registry of HTTP language tags is defined by
defined by RFC 1766 [1]. In summary, a language tag is composed of 1 [RFC4646]:
or more parts: A primary language tag and a possibly empty series of
subtags:
language-tag = primary-tag *( "-" subtag ) Language-Tag = <defined in [RFC4646], Section 2.1>
primary-tag = 1*8ALPHA
subtag = 1*8ALPHA
White space is not allowed within the tag and all tags are case- White space is not allowed within the tag and all tags are case-
insensitive. The name space of language tags is administered by the insensitive. The name space of language tags is administered by the
IANA. Example tags include: IANA. Example tags include:
en, en-US, en-cockney, i-cherokee, x-pig-latin en, en-US, en-cockney, i-cherokee, x-pig-latin
where any two-letter primary-tag is an ISO-639 language abbreviation where any two-letter primary-tag is an ISO-639 language abbreviation
and any two-letter initial subtag is an ISO-3166 country code. (The and any two-letter initial subtag is an ISO-3166 country code. (The
last three tags above are not registered tags; all but the last are last three tags above are not registered tags; all but the last are
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3.11. Entity Tags 3.11. Entity Tags
Entity tags are used for comparing two or more entities from the same Entity tags are used for comparing two or more entities from the same
requested resource. HTTP/1.1 uses entity tags in the ETag requested resource. HTTP/1.1 uses entity tags in the ETag
(Section 14.19), If-Match (Section 14.24), If-None-Match (Section 14.19), If-Match (Section 14.24), If-None-Match
(Section 14.26), and If-Range (Section 14.27) header fields. The (Section 14.26), and If-Range (Section 14.27) header fields. The
definition of how they are used and compared as cache validators is definition of how they are used and compared as cache validators is
in Section 13.3.3. An entity tag consists of an opaque quoted in Section 13.3.3. An entity tag consists of an opaque quoted
string, possibly prefixed by a weakness indicator. string, possibly prefixed by a weakness indicator.
entity-tag = [ weak ] opaque-tag entity-tag = [ weak ] opaque-tag
weak = "W/" weak = "W/"
opaque-tag = quoted-string opaque-tag = quoted-string
A "strong entity tag" MAY be shared by two entities of a resource A "strong entity tag" MAY be shared by two entities of a resource
only if they are equivalent by octet equality. only if they are equivalent by octet equality.
A "weak entity tag," indicated by the "W/" prefix, MAY be shared by A "weak entity tag," indicated by the "W/" prefix, MAY be shared by
two entities of a resource only if the entities are equivalent and two entities of a resource only if the entities are equivalent and
could be substituted for each other with no significant change in could be substituted for each other with no significant change in
semantics. A weak entity tag can only be used for weak comparison. semantics. A weak entity tag can only be used for weak comparison.
An entity tag MUST be unique across all versions of all entities An entity tag MUST be unique across all versions of all entities
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entities. entities.
3.12. Range Units 3.12. Range Units
HTTP/1.1 allows a client to request that only part (a range of) the HTTP/1.1 allows a client to request that only part (a range of) the
response entity be included within the response. HTTP/1.1 uses range response entity be included within the response. HTTP/1.1 uses range
units in the Range (Section 14.35) and Content-Range (Section 14.16) units in the Range (Section 14.35) and Content-Range (Section 14.16)
header fields. An entity can be broken down into subranges according header fields. An entity can be broken down into subranges according
to various structural units. to various structural units.
range-unit = bytes-unit | other-range-unit range-unit = bytes-unit | other-range-unit
bytes-unit = "bytes" bytes-unit = "bytes"
other-range-unit = token other-range-unit = token
The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1 The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1
implementations MAY ignore ranges specified using other units. implementations MAY ignore ranges specified using other units.
HTTP/1.1 has been designed to allow implementations of applications HTTP/1.1 has been designed to allow implementations of applications
that do not depend on knowledge of ranges. that do not depend on knowledge of ranges.
4. HTTP Message 4. HTTP Message
4.1. Message Types 4.1. Message Types
HTTP messages consist of requests from client to server and responses HTTP messages consist of requests from client to server and responses
from server to client. from server to client.
HTTP-message = Request | Response ; HTTP/1.1 messages HTTP-message = Request | Response ; HTTP/1.1 messages
Request (Section 5) and Response (Section 6) messages use the generic Request (Section 5) and Response (Section 6) messages use the generic
message format of RFC 822 [9] for transferring entities (the payload message format of [RFC2822] for transferring entities (the payload of
of the message). Both types of message consist of a start-line, zero the message). Both types of message consist of a start-line, zero or
or more header fields (also known as "headers"), an empty line (i.e., more header fields (also known as "headers"), an empty line (i.e., a
a line with nothing preceding the CRLF) indicating the end of the line with nothing preceding the CRLF) indicating the end of the
header fields, and possibly a message-body. header fields, and possibly a message-body.
generic-message = start-line generic-message = start-line
*(message-header CRLF) *(message-header CRLF)
CRLF CRLF
[ message-body ] [ message-body ]
start-line = Request-Line | Status-Line start-line = Request-Line | Status-Line
In the interest of robustness, servers SHOULD ignore any empty In the interest of robustness, servers SHOULD ignore any empty
line(s) received where a Request-Line is expected. In other words, line(s) received where a Request-Line is expected. In other words,
if the server is reading the protocol stream at the beginning of a if the server is reading the protocol stream at the beginning of a
message and receives a CRLF first, it should ignore the CRLF. message and receives a CRLF first, it should ignore the CRLF.
Certain buggy HTTP/1.0 client implementations generate extra CRLF's Certain buggy HTTP/1.0 client implementations generate extra CRLF's
after a POST request. To restate what is explicitly forbidden by the after a POST request. To restate what is explicitly forbidden by the
BNF, an HTTP/1.1 client MUST NOT preface or follow a request with an BNF, an HTTP/1.1 client MUST NOT preface or follow a request with an
extra CRLF. extra CRLF.
4.2. Message Headers 4.2. Message Headers
HTTP header fields, which include general-header (Section 4.5), HTTP header fields, which include general-header (Section 4.5),
request-header (Section 5.3), response-header (Section 6.2), and request-header (Section 5.3), response-header (Section 6.2), and
entity-header (Section 7.1) fields, follow the same generic format as entity-header (Section 7.1) fields, follow the same generic format as
that given in Section 3.1 of RFC 822 [9]. Each header field consists that given in Section 2.1 of [RFC2822]. Each header field consists
of a name followed by a colon (":") and the field value. Field names of a name followed by a colon (":") and the field value. Field names
are case-insensitive. The field value MAY be preceded by any amount are case-insensitive. The field value MAY be preceded by any amount
of LWS, though a single SP is preferred. Header fields can be of LWS, though a single SP is preferred. Header fields can be
extended over multiple lines by preceding each extra line with at extended over multiple lines by preceding each extra line with at
least one SP or HT. Applications ought to follow "common form", least one SP or HT. Applications ought to follow "common form",
where one is known or indicated, when generating HTTP constructs, where one is known or indicated, when generating HTTP constructs,
since there might exist some implementations that fail to accept since there might exist some implementations that fail to accept
anything beyond the common forms. anything beyond the common forms.
message-header = field-name ":" [ field-value ] message-header = field-name ":" [ field-value ]
field-name = token field-name = token
field-value = *( field-content | LWS ) field-value = *( field-content | LWS )
field-content = <the OCTETs making up the field-value field-content = <field content>
and consisting of either *TEXT or combinations ; the OCTETs making up the field-value
of token, separators, and quoted-string> ; and consisting of either *TEXT or combinations
; of token, separators, and quoted-string
The field-content does not include any leading or trailing LWS: The field-content does not include any leading or trailing LWS:
linear white space occurring before the first non-whitespace linear white space occurring before the first non-whitespace
character of the field-value or after the last non-whitespace character of the field-value or after the last non-whitespace
character of the field-value. Such leading or trailing LWS MAY be character of the field-value. Such leading or trailing LWS MAY be
removed without changing the semantics of the field value. Any LWS removed without changing the semantics of the field value. Any LWS
that occurs between field-content MAY be replaced with a single SP that occurs between field-content MAY be replaced with a single SP
before interpreting the field value or forwarding the message before interpreting the field value or forwarding the message
downstream. downstream.
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change the order of these field values when a message is forwarded. change the order of these field values when a message is forwarded.
4.3. Message Body 4.3. Message Body
The message-body (if any) of an HTTP message is used to carry the The message-body (if any) of an HTTP message is used to carry the
entity-body associated with the request or response. The message- entity-body associated with the request or response. The message-
body differs from the entity-body only when a transfer-coding has body differs from the entity-body only when a transfer-coding has
been applied, as indicated by the Transfer-Encoding header field been applied, as indicated by the Transfer-Encoding header field
(Section 14.41). (Section 14.41).
message-body = entity-body message-body = entity-body
| <entity-body encoded as per Transfer-Encoding> | <entity-body encoded as per Transfer-Encoding>
Transfer-Encoding MUST be used to indicate any transfer-codings Transfer-Encoding MUST be used to indicate any transfer-codings
applied by an application to ensure safe and proper transfer of the applied by an application to ensure safe and proper transfer of the
message. Transfer-Encoding is a property of the message, not of the message. Transfer-Encoding is a property of the message, not of the
entity, and thus MAY be added or removed by any application along the entity, and thus MAY be added or removed by any application along the
request/response chain. (However, Section 3.6 places restrictions on request/response chain. (However, Section 3.6 places restrictions on
when certain transfer-codings may be used.) when certain transfer-codings may be used.)
The rules for when a message-body is allowed in a message differ for The rules for when a message-body is allowed in a message differ for
requests and responses. requests and responses.
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(Section 5.1.1) does not allow sending an entity-body in requests. A (Section 5.1.1) does not allow sending an entity-body in requests. A
server SHOULD read and forward a message-body on any request; if the server SHOULD read and forward a message-body on any request; if the
request method does not include defined semantics for an entity-body, request method does not include defined semantics for an entity-body,
then the message-body SHOULD be ignored when handling the request. then the message-body SHOULD be ignored when handling the request.
For response messages, whether or not a message-body is included with For response messages, whether or not a message-body is included with
a message is dependent on both the request method and the response a message is dependent on both the request method and the response
status code (Section 6.1.1). All responses to the HEAD request status code (Section 6.1.1). All responses to the HEAD request
method MUST NOT include a message-body, even though the presence of method MUST NOT include a message-body, even though the presence of
entity-header fields might lead one to believe they do. All 1xx entity-header fields might lead one to believe they do. All 1xx
(informational), 204 (no content), and 304 (not modified) responses (informational), 204 (No Content), and 304 (Not Modified) responses
MUST NOT include a message-body. All other responses do include a MUST NOT include a message-body. All other responses do include a
message-body, although it MAY be of zero length. message-body, although it MAY be of zero length.
4.4. Message Length 4.4. Message Length
The transfer-length of a message is the length of the message-body as The transfer-length of a message is the length of the message-body as
it appears in the message; that is, after any transfer-codings have it appears in the message; that is, after any transfer-codings have
been applied. When a message-body is included with a message, the been applied. When a message-body is included with a message, the
transfer-length of that body is determined by one of the following transfer-length of that body is determined by one of the following
(in order of precedence): (in order of precedence):
1. Any response message which "MUST NOT" include a message-body 1. Any response message which "MUST NOT" include a message-body
(such as the 1xx, 204, and 304 responses and any response to a (such as the 1xx, 204, and 304 responses and any response to a
HEAD request) is always terminated by the first empty line after HEAD request) is always terminated by the first empty line after
the header fields, regardless of the entity-header fields present the header fields, regardless of the entity-header fields present
in the message. in the message.
2. If a Transfer-Encoding header field (Section 14.41) is present 2. If a Transfer-Encoding header field (Section 14.41) is present,
and has any value other than "identity", then the transfer-length then the transfer-length is defined by use of the "chunked"
is defined by use of the "chunked" transfer-coding (Section 3.6), transfer-coding (Section 3.6), unless the message is terminated
unless the message is terminated by closing the connection. by closing the connection.
3. If a Content-Length header field (Section 14.13) is present, its 3. If a Content-Length header field (Section 14.13) is present, its
decimal value in OCTETs represents both the entity-length and the decimal value in OCTETs represents both the entity-length and the
transfer-length. The Content-Length header field MUST NOT be transfer-length. The Content-Length header field MUST NOT be
sent if these two lengths are different (i.e., if a Transfer- sent if these two lengths are different (i.e., if a Transfer-
Encoding header field is present). If a message is received with Encoding header field is present). If a message is received with
both a Transfer-Encoding header field and a Content-Length header both a Transfer-Encoding header field and a Content-Length header
field, the latter MUST be ignored. field, the latter MUST be ignored.
4. If the message uses the media type "multipart/byteranges", and 4. If the message uses the media type "multipart/byteranges", and
the ransfer-length is not otherwise specified, then this self- the transfer-length is not otherwise specified, then this self-
elimiting media type defines the transfer-length. This media delimiting media type defines the transfer-length. This media
type UST NOT be used unless the sender knows that the recipient type MUST NOT be used unless the sender knows that the recipient
can arse it; the presence in a request of a Range header with can parse it; the presence in a request of a Range header with
ultiple byte-range specifiers from a 1.1 client implies that the multiple byte-range specifiers from a 1.1 client implies that the
lient can parse multipart/byteranges responses. client can parse multipart/byteranges responses.
A range header might be forwarded by a 1.0 proxy that does not A range header might be forwarded by a 1.0 proxy that does not
understand multipart/byteranges; in this case the server MUST understand multipart/byteranges; in this case the server MUST
delimit the message using methods defined in items 1, 3 or 5 delimit the message using methods defined in items 1, 3 or 5
of this section. of this section.
5. By the server closing the connection. (Closing the connection 5. By the server closing the connection. (Closing the connection
cannot be used to indicate the end of a request body, since that cannot be used to indicate the end of a request body, since that
would leave no possibility for the server to send back a would leave no possibility for the server to send back a
response.) response.)
For compatibility with HTTP/1.0 applications, HTTP/1.1 requests For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
containing a message-body MUST include a valid Content-Length header containing a message-body MUST include a valid Content-Length header
field unless the server is known to be HTTP/1.1 compliant. If a field unless the server is known to be HTTP/1.1 compliant. If a
request contains a message-body and a Content-Length is not given, request contains a message-body and a Content-Length is not given,
the server SHOULD respond with 400 (bad request) if it cannot the server SHOULD respond with 400 (Bad Request) if it cannot
determine the length of the message, or with 411 (length required) if determine the length of the message, or with 411 (Length Required) if
it wishes to insist on receiving a valid Content-Length. it wishes to insist on receiving a valid Content-Length.
All HTTP/1.1 applications that receive entities MUST accept the All HTTP/1.1 applications that receive entities MUST accept the
"chunked" transfer-coding (Section 3.6), thus allowing this mechanism "chunked" transfer-coding (Section 3.6), thus allowing this mechanism
to be used for messages when the message length cannot be determined to be used for messages when the message length cannot be determined
in advance. in advance.
Messages MUST NOT include both a Content-Length header field and a Messages MUST NOT include both a Content-Length header field and a
non-identity transfer-coding. If the message does include a non- transfer-coding. If the message does include a transfer-coding, the
identity transfer-coding, the Content-Length MUST be ignored. Content-Length MUST be ignored.
When a Content-Length is given in a message where a message-body is When a Content-Length is given in a message where a message-body is
allowed, its field value MUST exactly match the number of OCTETs in allowed, its field value MUST exactly match the number of OCTETs in
the message-body. HTTP/1.1 user agents MUST notify the user when an the message-body. HTTP/1.1 user agents MUST notify the user when an
invalid length is received and detected. invalid length is received and detected.
4.5. General Header Fields 4.5. General Header Fields
There are a few header fields which have general applicability for There are a few header fields which have general applicability for
both request and response messages, but which do not apply to the both request and response messages, but which do not apply to the
entity being transferred. These header fields apply only to the entity being transferred. These header fields apply only to the
message being transmitted. message being transmitted.
general-header = Cache-Control ; Section 14.9 general-header = Cache-Control ; Section 14.9
| Connection ; Section 14.10 | Connection ; Section 14.10
| Date ; Section 14.18 | Date ; Section 14.18
| Pragma ; Section 14.32 | Pragma ; Section 14.32
| Trailer ; Section 14.40 | Trailer ; Section 14.40
| Transfer-Encoding ; Section 14.41 | Transfer-Encoding ; Section 14.41
| Upgrade ; Section 14.42 | Upgrade ; Section 14.42
| Via ; Section 14.45 | Via ; Section 14.45
| Warning ; Section 14.46 | Warning ; Section 14.46
General-header field names can be extended reliably only in General-header field names can be extended reliably only in
combination with a change in the protocol version. However, new or combination with a change in the protocol version. However, new or
experimental header fields may be given the semantics of general experimental header fields may be given the semantics of general
header fields if all parties in the communication recognize them to header fields if all parties in the communication recognize them to
be general-header fields. Unrecognized header fields are treated as be general-header fields. Unrecognized header fields are treated as
entity-header fields. entity-header fields.
5. Request 5. Request
A request message from a client to a server includes, within the A request message from a client to a server includes, within the
first line of that message, the method to be applied to the resource, first line of that message, the method to be applied to the resource,
the identifier of the resource, and the protocol version in use. the identifier of the resource, and the protocol version in use.
Request = Request-Line ; Section 5.1 Request = Request-Line ; Section 5.1
*(( general-header ; Section 4.5 *(( general-header ; Section 4.5
| request-header ; Section 5.3 | request-header ; Section 5.3
| entity-header ) CRLF) ; Section 7.1 | entity-header ) CRLF) ; Section 7.1
CRLF CRLF
[ message-body ] ; Section 4.3 [ message-body ] ; Section 4.3
5.1. Request-Line 5.1. Request-Line
The Request-Line begins with a method token, followed by the Request- The Request-Line begins with a method token, followed by the Request-
URI and the protocol version, and ending with CRLF. The elements are URI and the protocol version, and ending with CRLF. The elements are
separated by SP characters. No CR or LF is allowed except in the separated by SP characters. No CR or LF is allowed except in the
final CRLF sequence. final CRLF sequence.
Request-Line = Method SP Request-URI SP HTTP-Version CRLF Request-Line = Method SP Request-URI SP HTTP-Version CRLF
5.1.1. Method 5.1.1. Method
The Method token indicates the method to be performed on the resource The Method token indicates the method to be performed on the resource
identified by the Request-URI. The method is case-sensitive. identified by the Request-URI. The method is case-sensitive.
Method = "OPTIONS" ; Section 9.2 Method = "OPTIONS" ; Section 9.2
| "GET" ; Section 9.3 | "GET" ; Section 9.3
| "HEAD" ; Section 9.4 | "HEAD" ; Section 9.4
| "POST" ; Section 9.5 | "POST" ; Section 9.5
| "PUT" ; Section 9.6 | "PUT" ; Section 9.6
| "DELETE" ; Section 9.7 | "DELETE" ; Section 9.7
| "TRACE" ; Section 9.8 | "TRACE" ; Section 9.8
| "CONNECT" ; Section 9.9 | "CONNECT" ; Section 9.9
| extension-method | extension-method
extension-method = token extension-method = token
The list of methods allowed by a resource can be specified in an The list of methods allowed by a resource can be specified in an
Allow header field (Section 14.7). The return code of the response Allow header field (Section 14.7). The return code of the response
always notifies the client whether a method is currently allowed on a always notifies the client whether a method is currently allowed on a
resource, since the set of allowed methods can change dynamically. resource, since the set of allowed methods can change dynamically.
An origin server SHOULD return the status code 405 (Method Not An origin server SHOULD return the status code 405 (Method Not
Allowed) if the method is known by the origin server but not allowed Allowed) if the method is known by the origin server but not allowed
for the requested resource, and 501 (Not Implemented) if the method for the requested resource, and 501 (Not Implemented) if the method
is unrecognized or not implemented by the origin server. The methods is unrecognized or not implemented by the origin server. The methods
GET and HEAD MUST be supported by all general-purpose servers. All GET and HEAD MUST be supported by all general-purpose servers. All
other methods are OPTIONAL; however, if the above methods are other methods are OPTIONAL; however, if the above methods are
implemented, they MUST be implemented with the same semantics as implemented, they MUST be implemented with the same semantics as
those specified in Section 9. those specified in Section 9.
5.1.2. Request-URI 5.1.2. Request-URI
The Request-URI is a Uniform Resource Identifier (Section 3.2) and The Request-URI is a Uniform Resource Identifier (Section 3.2) and
identifies the resource upon which to apply the request. identifies the resource upon which to apply the request.
Request-URI = "*" | absoluteURI | abs_path | authority Request-URI = "*"
| absoluteURI
| path-absolute [ "?" query ]
| authority
The four options for Request-URI are dependent on the nature of the The four options for Request-URI are dependent on the nature of the
request. The asterisk "*" means that the request does not apply to a request. The asterisk "*" means that the request does not apply to a
particular resource, but to the server itself, and is only allowed particular resource, but to the server itself, and is only allowed
when the method used does not necessarily apply to a resource. One when the method used does not necessarily apply to a resource. One
example would be example would be
OPTIONS * HTTP/1.1 OPTIONS * HTTP/1.1
The absoluteURI form is REQUIRED when the request is being made to a The absoluteURI form is REQUIRED when the request is being made to a
proxy. The proxy is requested to forward the request or service it proxy. The proxy is requested to forward the request or service it
from a valid cache, and return the response. Note that the proxy MAY from a valid cache, and return the response. Note that the proxy MAY
forward the request on to another proxy or directly to the server forward the request on to another proxy or directly to the server
specified by the absoluteURI. In order to avoid request loops, a specified by the absoluteURI. In order to avoid request loops, a
proxy MUST be able to recognize all of its server names, including proxy MUST be able to recognize all of its server names, including
any aliases, local variations, and the numeric IP address. An any aliases, local variations, and the numeric IP address. An
example Request-Line would be: example Request-Line would be:
GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1 GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
To allow for transition to absoluteURIs in all requests in future To allow for transition to absoluteURIs in all requests in future
versions of HTTP, all HTTP/1.1 servers MUST accept the absoluteURI versions of HTTP, all HTTP/1.1 servers MUST accept the absoluteURI
form in requests, even though HTTP/1.1 clients will only generate form in requests, even though HTTP/1.1 clients will only generate
them in requests to proxies. them in requests to proxies.
The authority form is only used by the CONNECT method (Section 9.9). The authority form is only used by the CONNECT method (Section 9.9).
The most common form of Request-URI is that used to identify a The most common form of Request-URI is that used to identify a
resource on an origin server or gateway. In this case the absolute resource on an origin server or gateway. In this case the absolute
path of the URI MUST be transmitted (see Section 3.2.1, abs_path) as path of the URI MUST be transmitted (see Section 3.2.1, path-
the Request-URI, and the network location of the URI (authority) MUST absolute) as the Request-URI, and the network location of the URI
be transmitted in a Host header field. For example, a client wishing (authority) MUST be transmitted in a Host header field. For example,
to retrieve the resource above directly from the origin server would a client wishing to retrieve the resource above directly from the
create a TCP connection to port 80 of the host "www.w3.org" and send origin server would create a TCP connection to port 80 of the host
the lines: "www.example.org" and send the lines:
GET /pub/WWW/TheProject.html HTTP/1.1 GET /pub/WWW/TheProject.html HTTP/1.1
Host: www.w3.org Host: www.example.org
followed by the remainder of the Request. Note that the absolute followed by the remainder of the Request. Note that the absolute
path cannot be empty; if none is present in the original URI, it MUST path cannot be empty; if none is present in the original URI, it MUST
be given as "/" (the server root). be given as "/" (the server root).
The Request-URI is transmitted in the format specified in The Request-URI is transmitted in the format specified in
Section 3.2.1. If the Request-URI is encoded using the "% HEX HEX" Section 3.2.1. If the Request-URI is encoded using the "% HEX HEX"
encoding [42], the origin server MUST decode the Request-URI in order encoding [RFC2396], the origin server MUST decode the Request-URI in
to properly interpret the request. Servers SHOULD respond to invalid order to properly interpret the request. Servers SHOULD respond to
Request-URIs with an appropriate status code. invalid Request-URIs with an appropriate status code.
A transparent proxy MUST NOT rewrite the "abs_path" part of the A transparent proxy MUST NOT rewrite the "path-absolute" part of the
received Request-URI when forwarding it to the next inbound server, received Request-URI when forwarding it to the next inbound server,
except as noted above to replace a null abs_path with "/". except as noted above to replace a null path-absolute with "/".
Note: The "no rewrite" rule prevents the proxy from changing the Note: The "no rewrite" rule prevents the proxy from changing the
meaning of the request when the origin server is improperly using meaning of the request when the origin server is improperly using
a non-reserved URI character for a reserved purpose. Implementors a non-reserved URI character for a reserved purpose. Implementors
should be aware that some pre-HTTP/1.1 proxies have been known to should be aware that some pre-HTTP/1.1 proxies have been known to
rewrite the Request-URI. rewrite the Request-URI.
5.2. The Resource Identified by a Request 5.2. The Resource Identified by a Request
The exact resource identified by an Internet request is determined by The exact resource identified by an Internet request is determined by
examining both the Request-URI and the Host header field. examining both the Request-URI and the Host header field.
An origin server that does not allow resources to differ by the An origin server that does not allow resources to differ by the
requested host MAY ignore the Host header field value when requested host MAY ignore the Host header field value when
determining the resource identified by an HTTP/1.1 request. (But see determining the resource identified by an HTTP/1.1 request. (But see
Appendix A.6.1.1 for other requirements on Host support in HTTP/1.1.) Appendix F.1.1 for other requirements on Host support in HTTP/1.1.)
An origin server that does differentiate resources based on the host An origin server that does differentiate resources based on the host
requested (sometimes referred to as virtual hosts or vanity host requested (sometimes referred to as virtual hosts or vanity host
names) MUST use the following rules for determining the requested names) MUST use the following rules for determining the requested
resource on an HTTP/1.1 request: resource on an HTTP/1.1 request:
1. If Request-URI is an absoluteURI, the host is part of the 1. If Request-URI is an absoluteURI, the host is part of the
Request-URI. Any Host header field value in the request MUST be Request-URI. Any Host header field value in the request MUST be
ignored. ignored.
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exact resource is being requested. exact resource is being requested.
5.3. Request Header Fields 5.3. Request Header Fields
The request-header fields allow the client to pass additional The request-header fields allow the client to pass additional
information about the request, and about the client itself, to the information about the request, and about the client itself, to the
server. These fields act as request modifiers, with semantics server. These fields act as request modifiers, with semantics
equivalent to the parameters on a programming language method equivalent to the parameters on a programming language method
invocation. invocation.
request-header = Accept ; Section 14.1 request-header = Accept ; Section 14.1
| Accept-Charset ; Section 14.2 | Accept-Charset ; Section 14.2
| Accept-Encoding ; Section 14.3 | Accept-Encoding ; Section 14.3
| Accept-Language ; Section 14.4 | Accept-Language ; Section 14.4
| Authorization ; Section 14.8 | Authorization ; Section 14.8
| Expect ; Section 14.20 | Expect ; Section 14.20
| From ; Section 14.22 | From ; Section 14.22
| Host ; Section 14.23 | Host ; Section 14.23
| If-Match ; Section 14.24 | If-Match ; Section 14.24
| If-Modified-Since ; Section 14.25 | If-Modified-Since ; Section 14.25
| If-None-Match ; Section 14.26 | If-None-Match ; Section 14.26
| If-Range ; Section 14.27 | If-Range ; Section 14.27
| If-Unmodified-Since ; Section 14.28 | If-Unmodified-Since ; Section 14.28
| Max-Forwards ; Section 14.31 | Max-Forwards ; Section 14.31
| Proxy-Authorization ; Section 14.34 | Proxy-Authorization ; Section 14.34
| Range ; Section 14.35 | Range ; Section 14.35
| Referer ; Section 14.36 | Referer ; Section 14.36
| TE ; Section 14.39 | TE ; Section 14.39
| User-Agent ; Section 14.43 | User-Agent ; Section 14.43
Request-header field names can be extended reliably only in Request-header field names can be extended reliably only in
combination with a change in the protocol version. However, new or combination with a change in the protocol version. However, new or
experimental header fields MAY be given the semantics of request- experimental header fields MAY be given the semantics of request-
header fields if all parties in the communication recognize them to header fields if all parties in the communication recognize them to
be request-header fields. Unrecognized header fields are treated as be request-header fields. Unrecognized header fields are treated as
entity-header fields. entity-header fields.
6. Response 6. Response
After receiving and interpreting a request message, a server responds After receiving and interpreting a request message, a server responds
with an HTTP response message. with an HTTP response message.
Response = Status-Line ; Section 6.1 Response = Status-Line ; Section 6.1
*(( general-header ; Section 4.5 *(( general-header ; Section 4.5
| response-header ; Section 6.2 | response-header ; Section 6.2
| entity-header ) CRLF) ; Section 7.1 | entity-header ) CRLF) ; Section 7.1
CRLF CRLF
[ message-body ] ; Section 7.2 [ message-body ] ; Section 7.2
6.1. Status-Line 6.1. Status-Line
The first line of a Response message is the Status-Line, consisting The first line of a Response message is the Status-Line, consisting
of the protocol version followed by a numeric status code and its of the protocol version followed by a numeric status code and its
associated textual phrase, with each element separated by SP associated textual phrase, with each element separated by SP
characters. No CR or LF is allowed except in the final CRLF characters. No CR or LF is allowed except in the final CRLF
sequence. sequence.
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
6.1.1. Status Code and Reason Phrase 6.1.1. Status Code and Reason Phrase
The Status-Code element is a 3-digit integer result code of the The Status-Code element is a 3-digit integer result code of the
attempt to understand and satisfy the request. These codes are fully attempt to understand and satisfy the request. These codes are fully
defined in Section 10. The Reason-Phrase is intended to give a short defined in Section 10. The Reason-Phrase is intended to give a short
textual description of the Status-Code. The Status-Code is intended textual description of the Status-Code. The Status-Code is intended
for use by automata and the Reason-Phrase is intended for the human for use by automata and the Reason-Phrase is intended for the human
user. The client is not required to examine or display the Reason- user. The client is not required to examine or display the Reason-
Phrase. Phrase.
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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
The individual values of the numeric status codes defined for The individual values of the numeric status codes defined for
HTTP/1.1, and an example set of corresponding Reason-Phrase's, are HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
presented below. The reason phrases listed here are only presented below. The reason phrases listed here are only
recommendations -- they MAY be replaced by local equivalents without recommendations -- they MAY be replaced by local equivalents without
affecting the protocol. affecting the protocol.
Status-Code = Status-Code =
"100" ; Section 10.1.1: Continue "100" ; Section 10.1.1: Continue
| "101" ; Section 10.1.2: Switching Protocols | "101" ; Section 10.1.2: Switching Protocols
| "200" ; Section 10.2.1: OK | "200" ; Section 10.2.1: OK
| "201" ; Section 10.2.2: Created | "201" ; Section 10.2.2: Created
| "202" ; Section 10.2.3: Accepted | "202" ; Section 10.2.3: Accepted
| "203" ; Section 10.2.4: Non-Authoritative Information | "203" ; Section 10.2.4: Non-Authoritative Information
| "204" ; Section 10.2.5: No Content | "204" ; Section 10.2.5: No Content
| "205" ; Section 10.2.6: Reset Content | "205" ; Section 10.2.6: Reset Content
| "206" ; Section 10.2.7: Partial Content | "206" ; Section 10.2.7: Partial Content
| "300" ; Section 10.3.1: Multiple Choices | "300" ; Section 10.3.1: Multiple Choices
| "301" ; Section 10.3.2: Moved Permanently | "301" ; Section 10.3.2: Moved Permanently
| "302" ; Section 10.3.3: Found | "302" ; Section 10.3.3: Found
| "303" ; Section 10.3.4: See Other | "303" ; Section 10.3.4: See Other
| "304" ; Section 10.3.5: Not Modified | "304" ; Section 10.3.5: Not Modified
| "305" ; Section 10.3.6: Use Proxy | "305" ; Section 10.3.6: Use Proxy
| "307" ; Section 10.3.8: Temporary Redirect | "307" ; Section 10.3.8: Temporary Redirect
| "400" ; Section 10.4.1: Bad Request | "400" ; Section 10.4.1: Bad Request
| "401" ; Section 10.4.2: Unauthorized | "401" ; Section 10.4.2: Unauthorized
| "402" ; Section 10.4.3: Payment Required | "402" ; Section 10.4.3: Payment Required
| "403" ; Section 10.4.4: Forbidden | "403" ; Section 10.4.4: Forbidden
| "404" ; Section 10.4.5: Not Found | "404" ; Section 10.4.5: Not Found
| "405" ; Section 10.4.6: Method Not Allowed | "405" ; Section 10.4.6: Method Not Allowed
| "406" ; Section 10.4.7: Not Acceptable | "406" ; Section 10.4.7: Not Acceptable
| "407" ; Section 10.4.8: Proxy Authentication Required | "407" ; Section 10.4.8: Proxy Authentication Required
| "408" ; Section 10.4.9: Request Time-out | "408" ; Section 10.4.9: Request Time-out
| "409" ; Section 10.4.10: Conflict | "409" ; Section 10.4.10: Conflict
| "410" ; Section 10.4.11: Gone | "410" ; Section 10.4.11: Gone
| "411" ; Section 10.4.12: Length Required | "411" ; Section 10.4.12: Length Required
| "412" ; Section 10.4.13: Precondition Failed | "412" ; Section 10.4.13: Precondition Failed
| "413" ; Section 10.4.14: Request Entity Too Large | "413" ; Section 10.4.14: Request Entity Too Large
| "414" ; Section 10.4.15: Request-URI Too Large | "414" ; Section 10.4.15: Request-URI Too Large
| "415" ; Section 10.4.16: Unsupported Media Type | "415" ; Section 10.4.16: Unsupported Media Type
| "416" ; Section 10.4.17: Requested range not satisfiable | "416" ; Section 10.4.17: Requested range not satisfiable
| "417" ; Section 10.4.18: Expectation Failed | "417" ; Section 10.4.18: Expectation Failed
| "500" ; Section 10.5.1: Internal Server Error | "500" ; Section 10.5.1: Internal Server Error
| "501" ; Section 10.5.2: Not Implemented | "501" ; Section 10.5.2: Not Implemented
| "502" ; Section 10.5.3: Bad Gateway | "502" ; Section 10.5.3: Bad Gateway
| "503" ; Section 10.5.4: Service Unavailable | "503" ; Section 10.5.4: Service Unavailable
| "504" ; Section 10.5.5: Gateway Time-out | "504" ; Section 10.5.5: Gateway Time-out
| "505" ; Section 10.5.6: HTTP Version not supported | "505" ; Section 10.5.6: HTTP Version not supported
| extension-code | extension-code
extension-code = 3DIGIT extension-code = 3DIGIT
Reason-Phrase = *<TEXT, excluding CR, LF> Reason-Phrase = *( HT | %x20-7E | %x80-FF )
HTTP status codes are extensible. HTTP applications are not required HTTP status codes are extensible. HTTP applications are not required
to understand the meaning of all registered status codes, though such to understand the meaning of all registered status codes, though such
understanding is obviously desirable. However, applications MUST understanding is obviously desirable. However, applications 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 any unrecognized response as being equivalent to the
x00 status code of that class, with the exception that an x00 status code of that class, with the exception that an
unrecognized response MUST NOT be cached. For example, if an unrecognized response MUST NOT be cached. For example, if an
unrecognized status code of 431 is received by the client, it can unrecognized status code of 431 is received by the client, it can
safely assume that there was something wrong with its request and safely assume that there was something wrong with its request and
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with the response, since that entity is likely to include human- with the response, since that entity is likely to include human-
readable information which will explain the unusual status. readable information which will explain the unusual status.
6.2. Response Header Fields 6.2. 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 which cannot be placed in the Status-
Line. These header fields give information about the server and Line. These header fields give information about the server and
about further access to the resource identified by the Request-URI. about further access to the resource identified by the Request-URI.
response-header = Accept-Ranges ; Section 14.5 response-header = Accept-Ranges ; Section 14.5
| Age ; Section 14.6 | Age ; Section 14.6
| ETag ; Section 14.19 | ETag ; Section 14.19
| Location ; Section 14.30 | Location ; Section 14.30
| Proxy-Authenticate ; Section 14.33 | Proxy-Authenticate ; Section 14.33
| Retry-After ; Section 14.37 | Retry-After ; Section 14.37
| Server ; Section 14.38 | Server ; Section 14.38
| Vary ; Section 14.44 | Vary ; Section 14.44
| WWW-Authenticate ; Section 14.47 | WWW-Authenticate ; Section 14.47
Response-header field names can be extended reliably only in Response-header field names can be extended reliably only in
combination with a change in the protocol version. However, new or combination with a change in the protocol version. However, new or
experimental header fields MAY be given the semantics of response- experimental header fields MAY be given the semantics of response-
header fields if all parties in the communication recognize them to header fields if all parties in the communication recognize them to
be response-header fields. Unrecognized header fields are treated as be response-header fields. Unrecognized header fields are treated as
entity-header fields. entity-header fields.
7. Entity 7. Entity
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In this section, both sender and recipient refer to either the client In this section, both sender and recipient refer to either the client
or the server, depending on who sends and who receives the entity. or the server, depending on who sends and who receives the entity.
7.1. Entity Header Fields 7.1. Entity Header Fields
Entity-header fields define metainformation about the entity-body or, Entity-header fields define metainformation about the entity-body or,
if no body is present, about the resource identified by the request. if no body is present, about the resource identified by the request.
Some of this metainformation is OPTIONAL; some might be REQUIRED by Some of this metainformation is OPTIONAL; some might be REQUIRED by
portions of this specification. portions of this specification.
entity-header = Allow ; Section 14.7 entity-header = Allow ; Section 14.7
| Content-Encoding ; Section 14.11 | Content-Encoding ; Section 14.11
| Content-Language ; Section 14.12 | Content-Language ; Section 14.12
| Content-Length ; Section 14.13 | Content-Length ; Section 14.13
| Content-Location ; Section 14.14 | Content-Location ; Section 14.14
| Content-MD5 ; Section 14.15 | Content-MD5 ; Section 14.15
| Content-Range ; Section 14.16 | Content-Range ; Section 14.16
| Content-Type ; Section 14.17 | Content-Type ; Section 14.17
| Expires ; Section 14.21 | Expires ; Section 14.21
| Last-Modified ; Section 14.29 | Last-Modified ; Section 14.29
| extension-header | extension-header
extension-header = message-header extension-header = message-header
The extension-header mechanism allows additional entity-header fields The extension-header mechanism allows additional entity-header fields
to be defined without changing the protocol, but these fields cannot to be defined without changing the protocol, but these fields cannot
be assumed to be recognizable by the recipient. Unrecognized header be assumed to be recognizable by the recipient. Unrecognized header
fields SHOULD be ignored by the recipient and MUST be forwarded by fields SHOULD be ignored by the recipient and MUST be forwarded by
transparent proxies. transparent proxies.
7.2. Entity Body 7.2. Entity Body
The entity-body (if any) sent with an HTTP request or response is in The entity-body (if any) sent with an HTTP request or response is in
a format and encoding defined by the entity-header fields. a format and encoding defined by the entity-header fields.
entity-body = *OCTET entity-body = *OCTET
An entity-body is only present in a message when a message-body is An entity-body is only present in a message when a message-body is
present, as described in Section 4.3. The entity-body is obtained present, as described in Section 4.3. The entity-body is obtained
from the message-body by decoding any Transfer-Encoding that might from the message-body by decoding any Transfer-Encoding that might
have been applied to ensure safe and proper transfer of the message. have been applied to ensure safe and proper transfer of the message.
7.2.1. Type 7.2.1. Type
When an entity-body is included with a message, the data type of that When an entity-body is included with a message, the data type of that
body is determined via the header fields Content-Type and Content- body is determined via the header fields Content-Type and Content-
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8.1. Persistent Connections 8.1. Persistent Connections
8.1.1. Purpose 8.1.1. Purpose
Prior to persistent connections, a separate TCP connection was Prior to persistent connections, a separate TCP connection was
established to fetch each URL, increasing the load on HTTP servers established to fetch each URL, increasing the load on HTTP servers
and causing congestion on the Internet. The use of inline images and and causing congestion on the Internet. The use of inline images and
other associated data often require a client to make multiple other associated data often require a client to make multiple
requests of the same server in a short amount of time. Analysis of requests of the same server in a short amount of time. Analysis of
these performance problems and results from a prototype these performance problems and results from a prototype
implementation are available [26] [30]. Implementation experience implementation are available [Pad1995] [Spero]. Implementation
and measurements of actual HTTP/1.1 (RFC 2068) implementations show experience and measurements of actual HTTP/1.1 ([RFC2068])
good results [39]. Alternatives have also been explored, for implementations show good results [Nie1997]. Alternatives have also
example, T/TCP [27]. been explored, for example, T/TCP [Tou1998].
Persistent HTTP connections have a number of advantages: Persistent HTTP connections have a number of advantages:
o By opening and closing fewer TCP connections, CPU time is saved in o By opening and closing fewer TCP connections, CPU time is saved in
routers and hosts (clients, servers, proxies, gateways, tunnels, routers and hosts (clients, servers, proxies, gateways, tunnels,
or caches), and memory used for TCP protocol control blocks can be or caches), and memory used for TCP protocol control blocks can be
saved in hosts. saved in hosts.
o HTTP requests and responses can be pipelined on a connection. o HTTP requests and responses can be pipelined on a connection.
Pipelining allows a client to make multiple requests without Pipelining allows a client to make multiple requests without
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case the client does not want to maintain a connection for more than case the client does not want to maintain a connection for more than
that request, it SHOULD send a Connection header including the that request, it SHOULD send a Connection header including the
connection-token close. connection-token close.
If either the client or the server sends the close token in the If either the client or the server sends the close token in the
Connection header, that request becomes the last one for the Connection header, that request becomes the last one for the
connection. connection.
Clients and servers SHOULD NOT assume that a persistent connection is Clients and servers SHOULD NOT assume that a persistent connection is
maintained for HTTP versions less than 1.1 unless it is explicitly maintained for HTTP versions less than 1.1 unless it is explicitly
signaled. See Appendix A.6.2 for more information on backward signaled. See Appendix F.2 for more information on backward
compatibility with HTTP/1.0 clients. compatibility with HTTP/1.0 clients.
In order to remain persistent, all messages on the connection MUST In order to remain persistent, all messages on the connection MUST
have a self-defined message length (i.e., one not defined by closure have a self-defined message length (i.e., one not defined by closure
of the connection), as described in Section 4.4. of the connection), as described in Section 4.4.
8.1.2.2. Pipelining 8.1.2.2. Pipelining
A client that supports persistent connections MAY "pipeline" its A client that supports persistent connections MAY "pipeline" its
requests (i.e., send multiple requests without waiting for each requests (i.e., send multiple requests without waiting for each
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It is especially important that proxies correctly implement the It is especially important that proxies correctly implement the
properties of the Connection header field as specified in properties of the Connection header field as specified in
Section 14.10. Section 14.10.
The proxy server MUST signal persistent connections separately with The proxy server MUST signal persistent connections separately with
its clients and the origin servers (or other proxy servers) that it its clients and the origin servers (or other proxy servers) that it
connects to. Each persistent connection applies to only one connects to. Each persistent connection applies to only one
transport link. transport link.
A proxy server MUST NOT establish a HTTP/1.1 persistent connection A proxy server MUST NOT establish a HTTP/1.1 persistent connection
with an HTTP/1.0 client (but see RFC 2068 [33] for information and with an HTTP/1.0 client (but see [RFC2068] for information and
discussion of the problems with the Keep-Alive header implemented by discussion of the problems with the Keep-Alive header implemented by
many HTTP/1.0 clients). many HTTP/1.0 clients).
8.1.4. Practical Considerations 8.1.4. Practical Considerations
Servers will usually have some time-out value beyond which they will Servers will usually have some time-out value beyond which they will
no longer maintain an inactive connection. Proxy servers might make no longer maintain an inactive connection. Proxy servers might make
this a higher value since it is likely that the client will be making this a higher value since it is likely that the client will be making
more connections through the same server. The use of persistent more connections through the same server. The use of persistent
connections places no requirements on the length (or existence) of connections places no requirements on the length (or existence) of
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information contained in the response MAY be used to update a information contained in the response MAY be used to update a
previously cached entity from that resource. If the new field values previously cached entity from that resource. If the new field values
indicate that the cached entity differs from the current entity (as indicate that the cached entity differs from the current entity (as
would be indicated by a change in Content-Length, Content-MD5, ETag would be indicated by a change in Content-Length, Content-MD5, ETag
or Last-Modified), then the cache MUST treat the cache entry as or Last-Modified), then the cache MUST treat the cache entry as
stale. stale.
9.5. POST 9.5. POST
The POST method is used to request that the origin server accept the The POST method is used to request that the origin server accept the
entity enclosed in the request as a new subordinate of the resource entity enclosed in the request as data to be processed by the
identified by the Request-URI in the Request-Line. POST is designed resource identified by the Request-URI in the Request-Line. POST is
to allow a uniform method to cover the following functions: designed to allow a uniform method to cover the following functions:
o Annotation of existing resources; o Annotation of existing resources;
o Posting a message to a bulletin board, newsgroup, mailing list, or o Posting a message to a bulletin board, newsgroup, mailing list, or
similar group of articles; similar group of articles;
o Providing a block of data, such as the result of submitting a o Providing a block of data, such as the result of submitting a
form, to a data-handling process; form, to a data-handling process;
o Extending a database through an append operation. o Extending a database through an append operation.
The actual function performed by the POST method is determined by the The actual function performed by the POST method is determined by the
server and is usually dependent on the Request-URI. The posted server and is usually dependent on the Request-URI.
entity is subordinate to that URI in the same way that a file is
subordinate to a directory containing it, a news article is
subordinate to a newsgroup to which it is posted, or a record is
subordinate to a database.
The action performed by the POST method might not result in a The action performed by the POST method might not result in a
resource that can be identified by a URI. In this case, either 200 resource that can be identified by a URI. In this case, either 200
(OK) or 204 (No Content) is the appropriate response status, (OK) or 204 (No Content) is the appropriate response status,
depending on whether or not the response includes an entity that depending on whether or not the response includes an entity that
describes the result. describes the result.
If a resource has been created on the origin server, the response If a resource has been created on the origin server, the response
SHOULD be 201 (Created) and contain an entity which describes the SHOULD be 201 (Created) and contain an entity which describes the
status of the request and refers to the new resource, and a Location status of the request and refers to the new resource, and a Location
header (see Section 14.30). header (see Section 14.30).
Responses to this method are not cacheable, unless the response Responses to this method are not cacheable, unless the response
includes appropriate Cache-Control or Expires header fields. includes appropriate Cache-Control or Expires header fields.
However, the 303 (See Other) response can be used to direct the user However, the 303 (See Other) response can be used to direct the user
agent to retrieve a cacheable resource. agent to retrieve a cacheable resource.
POST requests MUST obey the message transmission requirements set out
in Section 8.2.
See Section 15.1.3 for security considerations.
9.6. PUT 9.6. PUT
The PUT method requests that the enclosed entity be stored under the The PUT method requests that the enclosed entity be stored under the
supplied Request-URI. If the Request-URI refers to an already supplied Request-URI. If the Request-URI refers to an already
existing resource, the enclosed entity SHOULD be considered as a existing resource, the enclosed entity SHOULD be considered as a
modified version of the one residing on the origin server. If the modified version of the one residing on the origin server. If the
Request-URI does not point to an existing resource, and that URI is Request-URI does not point to an existing resource, and that URI is
capable of being defined as a new resource by the requesting user capable of being defined as a new resource by the requesting user
agent, the origin server can create the resource with that URI. If a agent, the origin server can create the resource with that URI. If a
new resource is created, the origin server MUST inform the user agent new resource is created, the origin server MUST inform the user agent
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A single resource MAY be identified by many different URIs. For A single resource MAY be identified by many different URIs. For
example, an article might have a URI for identifying "the current example, an article might have a URI for identifying "the current
version" which is separate from the URI identifying each particular version" which is separate from the URI identifying each particular
version. In this case, a PUT request on a general URI might result version. In this case, a PUT request on a general URI might result
in several other URIs being defined by the origin server. in several other URIs being defined by the origin server.
HTTP/1.1 does not define how a PUT method affects the state of an HTTP/1.1 does not define how a PUT method affects the state of an
origin server. origin server.
PUT requests MUST obey the message transmission requirements set out
in Section 8.2.
Unless otherwise specified for a particular entity-header, the Unless otherwise specified for a particular entity-header, the
entity-headers in the PUT request SHOULD be applied to the resource entity-headers in the PUT request SHOULD be applied to the resource
created or modified by the PUT. created or modified by the PUT.
9.7. DELETE 9.7. DELETE
The DELETE method requests that the origin server delete the resource The DELETE method requests that the origin server delete the resource
identified by the Request-URI. This method MAY be overridden by identified by the Request-URI. This method MAY be overridden by
human intervention (or other means) on the origin server. The client human intervention (or other means) on the origin server. The client
cannot be guaranteed that the operation has been carried out, even if cannot be guaranteed that the operation has been carried out, even if
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proxies forwarding messages in an infinite loop. proxies forwarding messages in an infinite loop.
If the request is valid, the response SHOULD contain the entire If the request is valid, the response SHOULD contain the entire
request message in the entity-body, with a Content-Type of "message/ request message in the entity-body, with a Content-Type of "message/
http". Responses to this method MUST NOT be cached. http". Responses to this method MUST NOT be cached.
9.9. CONNECT 9.9. CONNECT
This specification reserves the method name CONNECT for use with a This specification reserves the method name CONNECT for use with a
proxy that can dynamically switch to being a tunnel (e.g. SSL proxy that can dynamically switch to being a tunnel (e.g. SSL
tunneling [44]). tunneling [Luo1998]).
10. Status Code Definitions 10. Status Code Definitions
Each Status-Code is described below, including a description of which Each Status-Code is described below, including a description of which
method(s) it can follow and any metainformation required in the method(s) it can follow and any metainformation required in the
response. response.
10.1. Informational 1xx 10.1. Informational 1xx
This class of status code indicates a provisional response, This class of status code indicates a provisional response,
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o Date o Date
o ETag and/or Content-Location, if the header would have been sent o ETag and/or Content-Location, if the header would have been sent
in a 200 response to the same request in a 200 response to the same request
o Expires, Cache-Control, and/or Vary, if the field-value might o Expires, Cache-Control, and/or Vary, if the field-value might
differ from that sent in any previous response for the same differ from that sent in any previous response for the same
variant variant
If the 206 response is the result of an If-Range request that used a If the 206 response is the result of an If-Range request, the
strong cache validator (see Section 13.3.3), the response SHOULD NOT response SHOULD NOT include other entity-headers. Otherwise, the
include other entity-headers. If the response is the result of an response MUST include all of the entity-headers that would have been
If-Range request that used a weak validator, the response MUST NOT returned with a 200 (OK) response to the same request.
include other entity-headers; this prevents inconsistencies between
cached entity-bodies and updated headers. Otherwise, the response
MUST include all of the entity-headers that would have been returned
with a 200 (OK) response to the same request.
A cache MUST NOT combine a 206 response with other previously cached A cache MUST NOT combine a 206 response with other previously cached
content if the ETag or Last-Modified headers do not match exactly, content if the ETag or Last-Modified headers do not match exactly,
see 13.5.4. see 13.5.4.
A cache that does not support the Range and Content-Range headers A cache that does not support the Range and Content-Range headers
MUST NOT cache 206 (Partial) responses. MUST NOT cache 206 (Partial Content) responses.
10.3. Redirection 3xx 10.3. Redirection 3xx
This class of status code indicates that further action needs to be This class of status code indicates that further action needs to be
taken by the user agent in order to fulfill the request. The action taken by the user agent in order to fulfill the request. The action
required MAY be carried out by the user agent without interaction required MAY be carried out by the user agent without interaction
with the user if and only if the method used in the second request is with the user if and only if the method used in the second request is
GET or HEAD. A client SHOULD detect infinite redirection loops, GET or HEAD. A client SHOULD detect infinite redirection loops,
since such loops generate network traffic for each redirection. since such loops generate network traffic for each redirection.
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URIs. Clients with link editing capabilities ought to automatically URIs. Clients with link editing capabilities ought to automatically
re-link references to the Request-URI to one or more of the new re-link references to the Request-URI to one or more of the new
references returned by the server, where possible. This response is references returned by the server, where possible. This response is
cacheable unless indicated otherwise. cacheable unless indicated otherwise.
The new permanent URI SHOULD be given by the Location field in the The new permanent URI SHOULD be given by the Location field in the
response. Unless the request method was HEAD, the entity of the response. Unless the request method was HEAD, the entity of the
response SHOULD contain a short hypertext note with a hyperlink to response SHOULD contain a short hypertext note with a hyperlink to
the new URI(s). the new URI(s).
If the 301 status code is received in response to a request other If the 301 status code is received in response to a request method
than GET or HEAD, the user agent MUST NOT automatically redirect the that is known to be "safe", as defined in Section 9.1.1, then the
request unless it can be confirmed by the user, since this might request MAY be automatically redirected by the user agent without
change the conditions under which the request was issued. confirmation. Otherwise, the user agent MUST NOT automatically
redirect the request unless it can be confirmed by the user, since
this might change the conditions under which the request was issued.
Note: When automatically redirecting a POST request after Note: When automatically redirecting a POST request after
receiving a 301 status code, some existing HTTP/1.0 user agents receiving a 301 status code, some existing HTTP/1.0 user agents
will erroneously change it into a GET request. will erroneously change it into a GET request.
10.3.3. 302 Found 10.3.3. 302 Found
The requested resource resides temporarily under a different URI. The requested resource resides temporarily under a different URI.
Since the redirection might be altered on occasion, the client SHOULD Since the redirection might be altered on occasion, the client SHOULD
continue to use the Request-URI for future requests. This response continue to use the Request-URI for future requests. This response
is only cacheable if indicated by a Cache-Control or Expires header is only cacheable if indicated by a Cache-Control or Expires header
field. field.
The temporary URI SHOULD be given by the Location field in the The temporary URI SHOULD be given by the Location field in the
response. Unless the request method was HEAD, the entity of the response. Unless the request method was HEAD, the entity of the
response SHOULD contain a short hypertext note with a hyperlink to response SHOULD contain a short hypertext note with a hyperlink to
the new URI(s). the new URI(s).
If the 302 status code is received in response to a request other If the 302 status code is received in response to a request method
than GET or HEAD, the user agent MUST NOT automatically redirect the that is known to be "safe", as defined in Section 9.1.1, then the
request unless it can be confirmed by the user, since this might request MAY be automatically redirected by the user agent without
change the conditions under which the request was issued. confirmation. Otherwise, the user agent MUST NOT automatically
redirect the request unless it can be confirmed by the user, since
this might change the conditions under which the request was issued.
Note: RFC 1945 and RFC 2068 specify that the client is not allowed Note: RFC 1945 and RFC 2068 specify that the client is not allowed
to change the method on the redirected request. However, most to change the method on the redirected request. However, most
existing user agent implementations treat 302 as if it were a 303 existing user agent implementations treat 302 as if it were a 303
response, performing a GET on the Location field-value regardless response, performing a GET on the Location field-value regardless
of the original request method. The status codes 303 and 307 have of the original request method. The status codes 303 and 307 have
been added for servers that wish to make unambiguously clear which been added for servers that wish to make unambiguously clear which
kind of reaction is expected of the client. kind of reaction is expected of the client.
10.3.4. 303 See Other 10.3.4. 303 See Other
The response to the request can be found under a different URI and The server directs the user agent to a different resource, indicated
SHOULD be retrieved using a GET method on that resource. This method by a URI in the Location header field, that provides an indirect
exists primarily to allow the output of a POST-activated script to response to the original request. The user agent MAY perform a GET
redirect the user agent to a selected resource. The new URI is not a request on the URI in the Location field in order to obtain a
substitute reference for the originally requested resource. The 303 representation corresponding to the response, be redirected again, or
response MUST NOT be cached, but the response to the second end with an error status. The Location URI is not a substitute
(redirected) request might be cacheable. reference for the originally requested resource.
The different URI SHOULD be given by the Location field in the The 303 status is generally applicable to any HTTP method. It is
response. Unless the request method was HEAD, the entity of the primarily used to allow the output of a POST action to redirect the
response SHOULD contain a short hypertext note with a hyperlink to user agent to a selected resource, since doing so provides the
the new URI(s). information corresponding to the POST response in a form that can be
separately identified, bookmarked, and cached independent of the
original request.
Note: Many pre-HTTP/1.1 user agents do not understand the 303 A 303 response to a GET request indicates that the requested resource
status. When interoperability with such clients is a concern, the does not have a representation of its own that can be transferred by
302 status code may be used instead, since most user agents react the server over HTTP. The Location URI indicates a resource that is
to a 302 response as described here for 303. descriptive of the requested resource such that the follow-on
representation may be useful without implying that it adequately
represents the previously requested resource. Note that answers to
the questions of what can be represented, what representations are
adequate, and what might be a useful description are outside the
scope of HTTP and thus entirely determined by the resource owner(s).
A 303 response SHOULD NOT be cached unless it is indicated as
cacheable by Cache-Control or Expires header fields. Except for
responses to a HEAD request, the entity of a 303 response SHOULD
contain a short hypertext note with a hyperlink to the Location URI.
10.3.5. 304 Not Modified 10.3.5. 304 Not Modified
If the client has performed a conditional GET request and access is If the client has performed a conditional GET request and access is
allowed, but the document has not been modified, the server SHOULD allowed, but the document has not been modified, the server SHOULD
respond with this status code. The 304 response MUST NOT contain a respond with this status code. The 304 response MUST NOT contain a
message-body, and thus is always terminated by the first empty line message-body, and thus is always terminated by the first empty line
after the header fields. after the header fields.
The response MUST include the following header fields: The response MUST include the following header fields:
o Date, unless its omission is required by Section 14.18.1 o Date, unless its omission is required by Section 14.18.1
If a clockless origin server obeys these rules, and proxies and If a clockless origin server obeys these rules, and proxies and
clients add their own Date to any response received without one (as clients add their own Date to any response received without one (as
already specified by [RFC 2068], section 14.19), caches will operate already specified by [RFC2068], Section 14.19), caches will operate
correctly. correctly.
o ETag and/or Content-Location, if the header would have been sent o ETag and/or Content-Location, if the header would have been sent
in a 200 response to the same request in a 200 response to the same request
o Expires, Cache-Control, and/or Vary, if the field-value might o Expires, Cache-Control, and/or Vary, if the field-value might
differ from that sent in any previous response for the same differ from that sent in any previous response for the same
variant variant
If the conditional GET used a strong cache validator (see If the conditional GET used a strong cache validator (see
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The requested resource resides temporarily under a different URI. The requested resource resides temporarily under a different URI.
Since the redirection MAY be altered on occasion, the client SHOULD Since the redirection MAY be altered on occasion, the client SHOULD
continue to use the Request-URI for future requests. This response continue to use the Request-URI for future requests. This response
is only cacheable if indicated by a Cache-Control or Expires header is only cacheable if indicated by a Cache-Control or Expires header
field. field.
The temporary URI SHOULD be given by the Location field in the The temporary URI SHOULD be given by the Location field in the
response. Unless the request method was HEAD, the entity of the response. Unless the request method was HEAD, the entity of the
response SHOULD contain a short hypertext note with a hyperlink to response SHOULD contain a short hypertext note with a hyperlink to
the new URI(s) , since many pre-HTTP/1.1 user agents do not the new URI(s), since many pre-HTTP/1.1 user agents do not understand
understand the 307 status. Therefore, the note SHOULD contain the the 307 status. Therefore, the note SHOULD contain the information
information necessary for a user to repeat the original request on necessary for a user to repeat the original request on the new URI.
the new URI.
If the 307 status code is received in response to a request other If the 307 status code is received in response to a request method
than GET or HEAD, the user agent MUST NOT automatically redirect the that is known to be "safe", as defined in Section 9.1.1, then the
request unless it can be confirmed by the user, since this might request MAY be automatically redirected by the user agent without
change the conditions under which the request was issued. confirmation. Otherwise, the user agent MUST NOT automatically
redirect the request unless it can be confirmed by the user, since
this might change the conditions under which the request was issued.
10.4. Client Error 4xx 10.4. Client Error 4xx
The 4xx class of status code is intended for cases in which the The 4xx class of status code is intended for cases in which the
client seems to have erred. Except when responding to a HEAD client seems to have erred. Except when responding to a HEAD
request, the server SHOULD include an entity containing an request, the server SHOULD include an entity containing an
explanation of the error situation, and whether it is a temporary or explanation of the error situation, and whether it is a temporary or
permanent condition. These status codes are applicable to any permanent condition. These status codes are applicable to any
request method. User agents SHOULD display any included entity to request method. User agents SHOULD display any included entity to
the user. the user.
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challenge applicable to the requested resource. The client MAY challenge applicable to the requested resource. The client MAY
repeat the request with a suitable Authorization header field repeat the request with a suitable Authorization header field
(Section 14.8). If the request already included Authorization (Section 14.8). If the request already included Authorization
credentials, then the 401 response indicates that authorization has credentials, then the 401 response indicates that authorization has
been refused for those credentials. If the 401 response contains the been refused for those credentials. If the 401 response contains the
same challenge as the prior response, and the user agent has already same challenge as the prior response, and the user agent has already
attempted authentication at least once, then the user SHOULD be attempted authentication at least once, then the user SHOULD be
presented the entity that was given in the response, since that presented the entity that was given in the response, since that
entity might include relevant diagnostic information. HTTP access entity might include relevant diagnostic information. HTTP access
authentication is explained in "HTTP Authentication: Basic and Digest authentication is explained in "HTTP Authentication: Basic and Digest
Access Authentication" [43]. Access Authentication" [RFC2617].
10.4.3. 402 Payment Required 10.4.3. 402 Payment Required
This code is reserved for future use. This code is reserved for future use.
10.4.4. 403 Forbidden 10.4.4. 403 Forbidden
The server understood the request, but is refusing to fulfill it. The server understood the request, but is refusing to fulfill it.
Authorization will not help and the request SHOULD NOT be repeated. Authorization will not help and the request SHOULD NOT be repeated.
If the request method was not HEAD and the server wishes to make If the request method was not HEAD and the server wishes to make
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10.4.8. 407 Proxy Authentication Required 10.4.8. 407 Proxy Authentication Required
This code is similar to 401 (Unauthorized), but indicates that the This code is similar to 401 (Unauthorized), but indicates that the
client must first authenticate itself with the proxy. The proxy MUST client must first authenticate itself with the proxy. The proxy MUST
return a Proxy-Authenticate header field (Section 14.33) containing a return a Proxy-Authenticate header field (Section 14.33) containing a
challenge applicable to the proxy for the requested resource. The challenge applicable to the proxy for the requested resource. The
client MAY repeat the request with a suitable Proxy-Authorization client MAY repeat the request with a suitable Proxy-Authorization
header field (Section 14.34). HTTP access authentication is header field (Section 14.34). HTTP access authentication is
explained in "HTTP Authentication: Basic and Digest Access explained in "HTTP Authentication: Basic and Digest Access
Authentication" [43]. Authentication" [RFC2617].
10.4.9. 408 Request Timeout 10.4.9. 408 Request Timeout
The client did not produce a request within the time that the server The client did not produce a request within the time that the server
was prepared to wait. The client MAY repeat the request without was prepared to wait. The client MAY repeat the request without
modifications at any later time. modifications at any later time.
10.4.10. 409 Conflict 10.4.10. 409 Conflict
The request could not be completed due to a conflict with the current The request could not be completed due to a conflict with the current
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contain an entity describing why that version is not supported and contain an entity describing why that version is not supported and
what other protocols are supported by that server. what other protocols are supported by that server.
11. Access Authentication 11. Access Authentication
HTTP provides several OPTIONAL challenge-response authentication HTTP provides several OPTIONAL challenge-response authentication
mechanisms which can be used by a server to challenge a client mechanisms which can be used by a server to challenge a client
request and by a client to provide authentication information. The request and by a client to provide authentication information. The
general framework for access authentication, and the specification of general framework for access authentication, and the specification of
"basic" and "digest" authentication, are specified in "HTTP "basic" and "digest" authentication, are specified in "HTTP
Authentication: Basic and Digest Access Authentication" [43]. This Authentication: Basic and Digest Access Authentication" [RFC2617].
specification adopts the definitions of "challenge" and "credentials" This specification adopts the definitions of "challenge" and
from that specification. "credentials" from that specification.
12. Content Negotiation 12. Content Negotiation
Most HTTP responses include an entity which contains information for Most HTTP responses include an entity which contains information for
interpretation by a human user. Naturally, it is desirable to supply interpretation by a human user. Naturally, it is desirable to supply
the user with the "best available" entity corresponding to the the user with the "best available" entity corresponding to the
request. Unfortunately for servers and caches, not all users have request. Unfortunately for servers and caches, not all users have
the same preferences for what is "best," and not all user agents are the same preferences for what is "best," and not all user agents are
equally capable of rendering all entity types. For that reason, HTTP equally capable of rendering all entity types. For that reason, HTTP
has provisions for several mechanisms for "content negotiation" -- has provisions for several mechanisms for "content negotiation" --
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server and also removing the second request delay of agent-driven server and also removing the second request delay of agent-driven
negotiation when the cache is able to correctly guess the right negotiation when the cache is able to correctly guess the right
response. response.
This specification does not define any mechanism for transparent This specification does not define any mechanism for transparent
negotiation, though it also does not prevent any such mechanism from negotiation, though it also does not prevent any such mechanism from
being developed as an extension that could be used within HTTP/1.1. being developed as an extension that could be used within HTTP/1.1.
13. Caching in HTTP 13. Caching in HTTP
13.1. Overview
HTTP is typically used for distributed information systems, where HTTP is typically used for distributed information systems, where
performance can be improved by the use of response caches. The performance can be improved by the use of response caches. The
HTTP/1.1 protocol includes a number of elements intended to make HTTP/1.1 protocol includes a number of elements intended to make
caching work as well as possible. Because these elements are caching work as well as possible. Because these elements are
inextricable from other aspects of the protocol, and because they inextricable from other aspects of the protocol, and because they
interact with each other, it is useful to describe the basic caching interact with each other, it is useful to describe the basic caching
design of HTTP separately from the detailed descriptions of methods, design of HTTP separately from the detailed descriptions of methods,
headers, response codes, etc. headers, response codes, etc.
Caching would be useless if it did not significantly improve Caching would be useless if it did not significantly improve
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A basic principle is that it must be possible for the clients to A basic principle is that it must be possible for the clients to
detect any potential relaxation of semantic transparency. detect any potential relaxation of semantic transparency.
Note: The server, cache, or client implementor might be faced with Note: The server, cache, or client implementor might be faced with
design decisions not explicitly discussed in this specification. design decisions not explicitly discussed in this specification.
If a decision might affect semantic transparency, the implementor If a decision might affect semantic transparency, the implementor
ought to err on the side of maintaining transparency unless a ought to err on the side of maintaining transparency unless a
careful and complete analysis shows significant benefits in careful and complete analysis shows significant benefits in
breaking transparency. breaking transparency.
13.1.
13.1.1. Cache Correctness 13.1.1. Cache Correctness
A correct cache MUST respond to a request with the most up-to-date A correct cache MUST respond to a request with the most up-to-date
response held by the cache that is appropriate to the request (see response held by the cache that is appropriate to the request (see
sections 13.2.5, 13.2.6, and 13.12) which meets one of the following Sections 13.2.5, 13.2.6, and 13.12) which meets one of the following
conditions: conditions:
1. It has been checked for equivalence with what the origin server 1. It has been checked for equivalence with what the origin server
would have returned by revalidating the response with the origin would have returned by revalidating the response with the origin
server (Section 13.3); server (Section 13.3);
2. It is "fresh enough" (see Section 13.2). In the default case, 2. It is "fresh enough" (see Section 13.2). In the default case,
this means it meets the least restrictive freshness requirement this means it meets the least restrictive freshness requirement
of the client, origin server, and cache (see Section 14.9); if of the client, origin server, and cache (see Section 14.9); if
the origin server so specifies, it is the freshness requirement the origin server so specifies, it is the freshness requirement
of the origin server alone. If a stored response is not "fresh of the origin server alone. If a stored response is not "fresh
enough" by the most restrictive freshness requirement of both the enough" by the most restrictive freshness requirement of both the
client and the origin server, in carefully considered client and the origin server, in carefully considered
circumstances the cache MAY still return the response with the circumstances the cache MAY still return the response with the
appropriate Warning header (see section 13.1.5 and 14.46), unless appropriate Warning header (see Section 13.1.5 and 14.46), unless
such a response is prohibited (e.g., by a "no-store" cache- such a response is prohibited (e.g., by a "no-store" cache-
directive, or by a "no-cache" cache-request-directive; see directive, or by a "no-cache" cache-request-directive; see
Section 14.9). Section 14.9).
3. It is an appropriate 304 (Not Modified), 305 (Proxy Redirect), or 3. It is an appropriate 304 (Not Modified), 305 (Use Proxy), or
error (4xx or 5xx) response message. error (4xx or 5xx) response message.
If the cache can not communicate with the origin server, then a If the cache can not communicate with the origin server, then a
correct cache SHOULD respond as above if the response can be correct cache SHOULD respond as above if the response can be
correctly served from the cache; if not it MUST return an error or correctly served from the cache; if not it MUST return an error or
warning indicating that there was a communication failure. warning indicating that there was a communication failure.
If a cache receives a response (either an entire response, or a 304 If a cache receives a response (either an entire response, or a 304
(Not Modified) response) that it would normally forward to the (Not Modified) response) that it would normally forward to the
requesting client, and the received response is no longer fresh, the requesting client, and the received response is no longer fresh, the
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Warnings MAY be used for other purposes, both cache-related and Warnings MAY be used for other purposes, both cache-related and
otherwise. The use of a warning, rather than an error status code, otherwise. The use of a warning, rather than an error status code,
distinguish these responses from true failures. distinguish these responses from true failures.
Warnings are assigned three digit warn-codes. The first digit Warnings are assigned three digit warn-codes. The first digit
indicates whether the Warning MUST or MUST NOT be deleted from a indicates whether the Warning MUST or MUST NOT be deleted from a
stored cache entry after a successful revalidation: stored cache entry after a successful revalidation:
1xx Warnings that describe the freshness or revalidation status of 1xx Warnings that describe the freshness or revalidation status of
the response, and so MUST be deleted after a successful the response, and so MUST be deleted after a successful
revalidation. 1XX warn-codes MAY be generated by a cache only when revalidation. 1xx warn-codes MAY be generated by a cache only when
validating a cached entry. It MUST NOT be generated by clients. validating a cached entry. It MUST NOT be generated by clients.
2xx Warnings that describe some aspect of the entity body or entity 2xx Warnings that describe some aspect of the entity body or entity
headers that is not rectified by a revalidation (for example, a headers that is not rectified by a revalidation (for example, a
lossy compression of the entity bodies) and which MUST NOT be lossy compression of the entity bodies) and which MUST NOT be
deleted after a successful revalidation. deleted after a successful revalidation.
See Section 14.46 for the definitions of the codes themselves. See Section 14.46 for the definitions of the codes themselves.
HTTP/1.0 caches will cache all Warnings in responses, without HTTP/1.0 caches will cache all Warnings in responses, without
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and history mechanisms. and history mechanisms.
13.2.2. Heuristic Expiration 13.2.2. Heuristic Expiration
Since origin servers do not always provide explicit expiration times, Since origin servers do not always provide explicit expiration times,
HTTP caches typically assign heuristic expiration times, employing HTTP caches typically assign heuristic expiration times, employing
algorithms that use other header values (such as the Last-Modified algorithms that use other header values (such as the Last-Modified
time) to estimate a plausible expiration time. The HTTP/1.1 time) to estimate a plausible expiration time. The HTTP/1.1
specification does not provide specific algorithms, but does impose specification does not provide specific algorithms, but does impose
worst-case constraints on their results. Since heuristic expiration worst-case constraints on their results. Since heuristic expiration
times might compromise semantic transparency, they ought to used times might compromise semantic transparency, they ought to be used
cautiously, and we encourage origin servers to provide explicit cautiously, and we encourage origin servers to provide explicit
expiration times as much as possible. expiration times as much as possible.
13.2.3. Age Calculations 13.2.3. Age Calculations
In order to know if a cached entry is fresh, a cache needs to know if In order to know if a cached entry is fresh, a cache needs to know if
its age exceeds its freshness lifetime. We discuss how to calculate its age exceeds its freshness lifetime. We discuss how to calculate
the latter in Section 13.2.4; this section describes how to calculate the latter in Section 13.2.4; this section describes how to calculate
the age of a response or cache entry. the age of a response or cache entry.
In this discussion, we use the term "now" to mean "the current value In this discussion, we use the term "now" to mean "the current value
of the clock at the host performing the calculation." Hosts that use of the clock at the host performing the calculation." Hosts that use
HTTP, but especially hosts running origin servers and caches, SHOULD HTTP, but especially hosts running origin servers and caches, SHOULD
use NTP [28] or some similar protocol to synchronize their clocks to use NTP [RFC1305] or some similar protocol to synchronize their
a globally accurate time standard. clocks to a globally accurate time standard.
HTTP/1.1 requires origin servers to send a Date header, if possible, HTTP/1.1 requires origin servers to send a Date header, if possible,
with every response, giving the time at which the response was with every response, giving the time at which the response was
generated (see Section 14.18). We use the term "date_value" to generated (see Section 14.18). We use the term "date_value" to
denote the value of the Date header, in a form appropriate for denote the value of the Date header, in a form appropriate for
arithmetic operations. arithmetic operations.
HTTP/1.1 uses the Age response-header to convey the estimated age of HTTP/1.1 uses the Age response-header to convey the estimated age of
the response message when obtained from a cache. The Age field value the response message when obtained from a cache. The Age field value
is the cache's estimate of the amount of time since the response was is the cache's estimate of the amount of time since the response was
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13.3.2. Entity Tag Cache Validators 13.3.2. Entity Tag Cache Validators
The ETag response-header field value, an entity tag, provides for an The ETag response-header field value, an entity tag, provides for an
"opaque" cache validator. This might allow more reliable validation "opaque" cache validator. This might allow more reliable validation
in situations where it is inconvenient to store modification dates, in situations where it is inconvenient to store modification dates,
where the one-second resolution of HTTP date values is not where the one-second resolution of HTTP date values is not
sufficient, or where the origin server wishes to avoid certain sufficient, or where the origin server wishes to avoid certain
paradoxes that might arise from the use of modification dates. paradoxes that might arise from the use of modification dates.
Entity Tags are described in Section 3.11. The headers used with Entity Tags are described in Section 3.11. The headers used with
entity tags are described in sections 14.19, 14.24, 14.26 and 14.44. entity tags are described in Sections 14.19, 14.24, 14.26 and 14.44.
13.3.3. Weak and Strong Validators 13.3.3. Weak and Strong Validators
Since both origin servers and caches will compare two validators to Since both origin servers and caches will compare two validators to
decide if they represent the same or different entities, one normally decide if they represent the same or different entities, one normally
would expect that if the entity (the entity-body or any entity- would expect that if the entity (the entity-body or any entity-
headers) changes in any way, then the associated validator would headers) changes in any way, then the associated validator would
change as well. If this is true, then we call this validator a change as well. If this is true, then we call this validator a
"strong validator." "strong validator."
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or not: or not:
o The strong comparison function: in order to be considered equal, o The strong comparison function: in order to be considered equal,
both validators MUST be identical in every way, and both MUST NOT both validators MUST be identical in every way, and both MUST NOT
be weak. be weak.
o The weak comparison function: in order to be considered equal, o The weak comparison function: in order to be considered equal,
both validators MUST be identical in every way, but either or both both validators MUST be identical in every way, but either or both
of them MAY be tagged as "weak" without affecting the result. of them MAY be tagged as "weak" without affecting the result.
The example below shows the results for a set of entity tag pairs,
and both the weak and strong comparison function results:
+--------+--------+-------------------+-----------------+
| ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |
+--------+--------+-------------------+-----------------+
| W/"1" | W/"1" | no match | match |
| | | | |
| W/"1" | W/"2" | no match | no match |
| | | | |
| W/"1" | "1" | no match | match |
| | | | |
| "1" | "1" | match | match |
+--------+--------+-------------------+-----------------+
An entity tag is strong unless it is explicitly tagged as weak. An entity tag is strong unless it is explicitly tagged as weak.
Section 3.11 gives the syntax for entity tags. Section 3.11 gives the syntax for entity tags.
A Last-Modified time, when used as a validator in a request, is A Last-Modified time, when used as a validator in a request, is
implicitly weak unless it is possible to deduce that it is strong, implicitly weak unless it is possible to deduce that it is strong,
using the following rules: using the following rules:
o The validator is being compared by an origin server to the actual o The validator is being compared by an origin server to the actual
current validator for the entity and, current validator for the entity and,
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o Connection o Connection
o Keep-Alive o Keep-Alive
o Proxy-Authenticate o Proxy-Authenticate
o Proxy-Authorization o Proxy-Authorization
o TE o TE
o Trailers o Trailer
o Transfer-Encoding o Transfer-Encoding
o Upgrade o Upgrade
All other headers defined by HTTP/1.1 are end-to-end headers. All other headers defined by HTTP/1.1 are end-to-end headers.
Other hop-by-hop headers MUST be listed in a Connection header, Other hop-by-hop headers, if they are introduced either in HTTP/1.1
(Section 14.10) to be introduced into HTTP/1.1 (or later). or later versions of HTTP/1.x, MUST be listed in a Connection header
(Section 14.10).
13.5.2. Non-modifiable Headers 13.5.2. Non-modifiable Headers
Some features of the HTTP/1.1 protocol, such as Digest Some features of the HTTP/1.1 protocol, such as Digest
Authentication, depend on the value of certain end-to-end headers. A Authentication, depend on the value of certain end-to-end headers. A
transparent proxy SHOULD NOT modify an end-to-end header unless the transparent proxy SHOULD NOT modify an end-to-end header unless the
definition of that header requires or specifically allows that. definition of that header requires or specifically allows that.
A transparent proxy MUST NOT modify any of the following fields in a A transparent proxy MUST NOT modify any of the following fields in a
request or response, and it MUST NOT add any of these fields if not request or response, and it MUST NOT add any of these fields if not
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Unless the origin server explicitly prohibits the caching of their Unless the origin server explicitly prohibits the caching of their
responses, the application of GET and HEAD methods to any resources responses, the application of GET and HEAD methods to any resources
SHOULD NOT have side effects that would lead to erroneous behavior if SHOULD NOT have side effects that would lead to erroneous behavior if
these responses are taken from a cache. They MAY still have side these responses are taken from a cache. They MAY still have side
effects, but a cache is not required to consider such side effects in effects, but a cache is not required to consider such side effects in
its caching decisions. Caches are always expected to observe an its caching decisions. Caches are always expected to observe an
origin server's explicit restrictions on caching. origin server's explicit restrictions on caching.
We note one exception to this rule: since some applications have We note one exception to this rule: since some applications have
traditionally used GETs and HEADs with query URLs (those containing a traditionally used GETs and HEADs with URLs containing a query part
"?" in the rel_path part) to perform operations with significant side to perform operations with significant side effects, caches MUST NOT
effects, caches MUST NOT treat responses to such URIs as fresh unless treat responses to such URIs as fresh unless the server provides an
the server provides an explicit expiration time. This specifically explicit expiration time. This specifically means that responses
means that responses from HTTP/1.0 servers for such URIs SHOULD NOT from HTTP/1.0 servers for such URIs SHOULD NOT be taken from a cache.
be taken from a cache. See Section 9.1.1 for related information. See Section 9.1.1 for related information.
13.10. Invalidation After Updates or Deletions 13.10. Invalidation After Updates or Deletions
The effect of certain methods performed on a resource at the origin The effect of certain methods performed on a resource at the origin
server might cause one or more existing cache entries to become non- server might cause one or more existing cache entries to become non-
transparently invalid. That is, although they might continue to be transparently invalid. That is, although they might continue to be
"fresh," they do not accurately reflect what the origin server would "fresh," they do not accurately reflect what the origin server would
return for a new request on that resource. return for a new request on that resource.
There is no way for the HTTP protocol to guarantee that all such There is no way for the HTTP protocol to guarantee that all such
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is either the entity referred to by the Request-URI, or by the is either the entity referred to by the Request-URI, or by the
Location or Content-Location headers (if present). These methods Location or Content-Location headers (if present). These methods
are: are:
o PUT o PUT
o DELETE o DELETE
o POST o POST
In order to prevent denial of service attacks, an invalidation based An invalidation based on the URI in a Location or Content-Location
on the URI in a Location or Content-Location header MUST only be header MUST NOT be performed if the host part of that URI differs
performed if the host part is the same as in the Request-URI. from the host part in the Request-URI. This helps prevent denial of
service attacks.
A cache that passes through requests for methods it does not A cache that passes through requests for methods it does not
understand SHOULD invalidate any entities referred to by the Request- understand SHOULD invalidate any entities referred to by the Request-
URI. URI.
13.11. Write-Through Mandatory 13.11. Write-Through Mandatory
All methods that might be expected to cause modifications to the All methods that might be expected to cause modifications to the
origin server's resources MUST be written through to the origin origin server's resources MUST be written through to the origin
server. This currently includes all methods except for GET and HEAD. server. This currently includes all methods except for GET and HEAD.
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prevent a proxy cache from sending a 100 (Continue) response before prevent a proxy cache from sending a 100 (Continue) response before
the inbound server has sent its final reply. the inbound server has sent its final reply.
The alternative (known as "write-back" or "copy-back" caching) is not The alternative (known as "write-back" or "copy-back" caching) is not
allowed in HTTP/1.1, due to the difficulty of providing consistent allowed in HTTP/1.1, due to the difficulty of providing consistent
updates and the problems arising from server, cache, or network updates and the problems arising from server, cache, or network
failure prior to write-back. failure prior to write-back.
13.12. Cache Replacement 13.12. Cache Replacement
If a new cacheable (see sections 14.9.2, 13.2.5, 13.2.6 and 13.8) If a new cacheable (see Sections 14.9.2, 13.2.5, 13.2.6 and 13.8)
response is received from a resource while any existing responses for response is received from a resource while any existing responses for
the same resource are cached, the cache SHOULD use the new response the same resource are cached, the cache SHOULD use the new response
to reply to the current request. It MAY insert it into cache storage to reply to the current request. It MAY insert it into cache storage
and MAY, if it meets all other requirements, use it to respond to any and MAY, if it meets all other requirements, use it to respond to any
future requests that would previously have caused the old response to future requests that would previously have caused the old response to
be returned. If it inserts the new response into cache storage the be returned. If it inserts the new response into cache storage the
rules in Section 13.5.3 apply. rules in Section 13.5.3 apply.
Note: a new response that has an older Date header value than Note: a new response that has an older Date header value than
existing cached responses is not cacheable. existing cached responses is not cacheable.
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This is not to be construed to prohibit the history mechanism from This is not to be construed to prohibit the history mechanism from
telling the user that a view might be stale. telling the user that a view might be stale.
Note: if history list mechanisms unnecessarily prevent users from Note: if history list mechanisms unnecessarily prevent users from
viewing stale resources, this will tend to force service authors viewing stale resources, this will tend to force service authors
to avoid using HTTP expiration controls and cache controls when to avoid using HTTP expiration controls and cache controls when
they would otherwise like to. Service authors may consider it they would otherwise like to. Service authors may consider it
important that users not be presented with error messages or important that users not be presented with error messages or
warning messages when they use navigation controls (such as BACK) warning messages when they use navigation controls (such as BACK)
to view previously fetched resources. Even though sometimes such to view previously fetched resources. Even though sometimes such
resources ought not to cached, or ought to expire quickly, user resources ought not be cached, or ought to expire quickly, user
interface considerations may force service authors to resort to interface considerations may force service authors to resort to
other means of preventing caching (e.g. "once-only" URLs) in order other means of preventing caching (e.g. "once-only" URLs) in order
not to suffer the effects of improperly functioning history not to suffer the effects of improperly functioning history
mechanisms. mechanisms.
14. Header Field Definitions 14. Header Field Definitions
This section defines the syntax and semantics of all standard This section defines the syntax and semantics of all standard
HTTP/1.1 header fields. For entity-header fields, both sender and HTTP/1.1 header fields. For entity-header fields, both sender and
recipient refer to either the client or the server, depending on who recipient refer to either the client or the server, depending on who
sends and who receives the entity. sends and who receives the entity.
14.1. Accept 14.1. Accept
The Accept request-header field can be used to specify certain media The Accept request-header field can be used to specify certain media
types which are acceptable for the response. Accept headers can be types which are acceptable for the response. Accept headers can be
used to indicate that the request is specifically limited to a small 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-line set of desired types, as in the case of a request for an in-line
image. image.
Accept = "Accept" ":" Accept = "Accept" ":"
#( media-range [ accept-params ] ) #( media-range [ accept-params ] )
media-range = ( "*/*" media-range = ( "*/*"
| ( type "/" "*" ) | ( type "/" "*" )
| ( type "/" subtype ) | ( type "/" subtype )
) *( ";" parameter ) ) *( ";" parameter )
accept-params = ";" "q" "=" qvalue *( accept-extension ) accept-params = ";" "q" "=" qvalue *( accept-extension )
accept-extension = ";" token [ "=" ( token | quoted-string ) ] accept-extension = ";" token [ "=" ( token | quoted-string ) ]
The asterisk "*" character is used to group media types into ranges, The asterisk "*" character is used to group media types into ranges,
with "*/*" indicating all media types and "type/*" indicating all with "*/*" indicating all media types and "type/*" indicating all
subtypes of that type. The media-range MAY include media type subtypes of that type. The media-range MAY 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 MAY be followed by one or more accept-params,
beginning with the "q" parameter for indicating a relative quality beginning with the "q" parameter for indicating a relative quality
factor. The first "q" parameter (if any) separates the media-range factor. The first "q" parameter (if any) separates the media-range
parameter(s) from the accept-params. Quality factors allow the user parameter(s) from the accept-params. Quality factors allow the user
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The example The example
Accept: audio/*; q=0.2, audio/basic Accept: audio/*; q=0.2, audio/basic
SHOULD be interpreted as "I prefer audio/basic, but send me any audio SHOULD be interpreted as "I prefer audio/basic, but send me any audio
type if it is the best available after an 80% mark-down in quality." type if it is the best available after an 80% mark-down in quality."
If no Accept header field is present, then it is assumed that the If no Accept header field is present, then it is assumed that the
client accepts all media types. If an Accept header field is client accepts all media types. If an Accept header field is
present, and if the server cannot send a response which is acceptable present, and if the server cannot send a response which is acceptable
according to the combined Accept field value, then the server SHOULD according to the combined Accept field value, then the server SHOULD
send a 406 (not acceptable) response. send a 406 (Not Acceptable) response.
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 preferred media types, but if they do not exist, then send the
text/x-dvi entity, and if that does not exist, send the text/plain text/x-dvi entity, and if that does not exist, send the text/plain
entity." entity."
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default set ought to be configurable by the user. default set ought to be configurable by the user.
14.2. Accept-Charset 14.2. Accept-Charset
The Accept-Charset request-header field can be used to indicate what The Accept-Charset request-header field can be used to indicate what
character sets are acceptable for the response. This field allows character sets are acceptable for the response. This field allows
clients capable of understanding more comprehensive or special- clients capable of understanding more comprehensive or special-
purpose character sets to signal that capability to a server which is purpose character sets to signal that capability to a server which is
capable of representing documents in those character sets. capable of representing documents in those character sets.
Accept-Charset = "Accept-Charset" ":" Accept-Charset = "Accept-Charset" ":"
1#( ( charset | "*" )[ ";" "q" "=" qvalue ] ) 1#( ( charset | "*" ) [ ";" "q" "=" qvalue ] )
Character set values are described in Section 3.4. Each charset MAY Character set values are described in Section 3.4. Each charset MAY
be given an associated quality value which represents the user's be given an associated quality value which represents the user's
preference for that charset. The default value is q=1. An example preference for that charset. The default value is q=1. An example
is 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 set (including ISO-8859-1) which is not matches every character set (including ISO-8859-1) which is not
mentioned elsewhere in the Accept-Charset field. If no "*" is mentioned elsewhere in the Accept-Charset field. If no "*" is
present in an Accept-Charset field, then all character sets not present in an Accept-Charset field, then all character sets not
explicitly mentioned get a quality value of 0, except for ISO-8859-1, explicitly mentioned get a quality value of 0, except for ISO-8859-1,
which gets a quality value of 1 if not explicitly mentioned. which gets a quality value of 1 if not explicitly mentioned.
If no Accept-Charset header is present, the default is that any If no Accept-Charset header is present, the default is that any
character set is acceptable. If an Accept-Charset header is present, character set is acceptable. If an Accept-Charset header is present,
and if the server cannot send a response which is acceptable and if the server cannot send a response which is acceptable
according to the Accept-Charset header, then the server SHOULD send according to the Accept-Charset header, then the server SHOULD send
an error response with the 406 (not acceptable) status code, though an error response with the 406 (Not Acceptable) status code, though
the sending of an unacceptable response is also allowed. the sending of an unacceptable response is also allowed.
14.3. Accept-Encoding 14.3. Accept-Encoding
The Accept-Encoding request-header field is similar to Accept, but The Accept-Encoding request-header field is similar to Accept, but
restricts the content-codings (Section 3.5) that are acceptable in restricts the content-codings (Section 3.5) that are acceptable in
the response. the response.
Accept-Encoding = "Accept-Encoding" ":" Accept-Encoding = "Accept-Encoding" ":"
1#( codings [ ";" "q" "=" qvalue ] ) #( codings [ ";" "q" "=" qvalue ] )
codings = ( content-coding | "*" ) codings = ( content-coding | "*" )
Examples of its use are: Examples of its use are:
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 server tests whether a content-coding is acceptable, according to A server tests whether a content-coding is acceptable, according to
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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 will not
work and are not permitted with x-gzip or x-compress. work and are not permitted with x-gzip or x-compress.
14.4. Accept-Language 14.4. Accept-Language
The Accept-Language request-header field is similar to Accept, but The Accept-Language request-header field is similar to Accept, but
restricts the set of natural languages that are preferred as a restricts the set of natural languages that are preferred as a
response to the request. Language tags are defined in Section 3.10. response to the request. Language tags are defined in Section 3.10.
Accept-Language = "Accept-Language" ":" Accept-Language = "Accept-Language" ":"
1#( language-range [ ";" "q" "=" qvalue ] ) 1#( language-range [ ";" "q" "=" qvalue ] )
language-range = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" ) language-range = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )
Each language-range MAY be given an associated quality value which Each language-range MAY be given an associated quality value which
represents an estimate of the user's preference for the languages represents an estimate of the user's preference for the languages
specified by that range. The quality value defaults to "q=1". For specified by that range. The quality value defaults to "q=1". For
example, 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." A language-range matches a language-tag if other types of English." A language-range matches a Language-Tag if
it exactly equals the tag, or if it exactly equals a prefix of the it exactly equals the tag, or if it exactly equals a prefix of the
tag such that the first tag character following the prefix is "-". tag such that the first tag character following the prefix is "-".
The special range "*", if present in the Accept-Language field, The special range "*", if present in the Accept-Language field,
matches every tag not matched by any other range present in the matches every tag not matched by any other range present in the
Accept-Language field. Accept-Language field.
Note: This use of a prefix matching rule does not imply that Note: This use of a prefix matching rule does not imply that
language tags are assigned to languages in such a way that it is language tags are assigned to languages in such a way that it is
always true that if a user understands a language with a certain always true that if a user understands a language with a certain
tag, then this user will also understand all languages with tags tag, then this user will also understand all languages with tags
for which this tag is a prefix. The prefix rule simply allows the for which this tag is a prefix. The prefix rule simply allows the
use of prefix tags if this is the case. use of prefix tags if this is the case.
The language quality factor assigned to a language-tag by the Accept- The language quality factor assigned to a Language-Tag by the Accept-
Language field is the quality value of the longest language-range in Language field is the quality value of the longest language-range in
the field that matches the language-tag. If no language-range in the the field that matches the Language-Tag. If no language-range in the
field matches the tag, the language quality factor assigned is 0. If field matches the tag, the language quality factor assigned is 0. If
no Accept-Language header is present in the request, the server no Accept-Language header is present in the request, the server
SHOULD assume that all languages are equally acceptable. If an SHOULD assume that all languages are equally acceptable. If an
Accept-Language header is present, then all languages which are Accept-Language header is present, then all languages which are
assigned a quality factor greater than 0 are acceptable. assigned a quality factor greater than 0 are acceptable.
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 with the complete linguistic preferences of an Accept-Language header with the complete linguistic preferences of
the user in every request. For a discussion of this issue, see the user in every request. For a discussion of this issue, see
Section 15.1.4. Section 15.1.4.
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might assume that on selecting "en-gb", they will be served any might assume that on selecting "en-gb", they will be served any
kind of English document if British English is not available. A kind of English document if British English is not available. A
user agent might suggest in such a case to add "en" to get the user agent might suggest in such a case to add "en" to get the
best matching behavior. best matching behavior.
14.5. Accept-Ranges 14.5. Accept-Ranges
The Accept-Ranges response-header field allows the server to indicate The Accept-Ranges response-header field allows the server to indicate
its acceptance of range requests for a resource: its acceptance of range requests for a resource:
Accept-Ranges = "Accept-Ranges" ":" acceptable-ranges Accept-Ranges = "Accept-Ranges" ":" acceptable-ranges
acceptable-ranges = 1#range-unit | "none" acceptable-ranges = 1#range-unit | "none"
Origin servers that accept byte-range requests MAY send Origin servers that accept byte-range requests MAY send
Accept-Ranges: bytes Accept-Ranges: bytes
but are not required to do so. Clients MAY generate byte-range but are not required to do so. Clients MAY generate byte-range
requests without having received this header for the resource requests without having received this header for the resource
involved. Range units are defined in Section 3.12. involved. Range units are defined in Section 3.12.
Servers that do not accept any kind of range request for a resource Servers that do not accept any kind of range request for a resource
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to advise the client not to attempt a range request. to advise the client not to attempt a range request.
14.6. Age 14.6. Age
The Age response-header field conveys the sender's estimate of the The Age response-header field conveys the sender's estimate of the
amount of time since the response (or its revalidation) was generated amount of time since the response (or its revalidation) was generated
at the origin server. A cached response is "fresh" if its age does at the origin server. A cached response is "fresh" if its age does
not exceed its freshness lifetime. Age values are calculated as not exceed its freshness lifetime. Age values are calculated as
specified in Section 13.2.3. specified in Section 13.2.3.
Age = "Age" ":" age-value Age = "Age" ":" age-value
age-value = delta-seconds age-value = delta-seconds
Age values are non-negative decimal integers, representing time in Age values are non-negative decimal integers, representing time in
seconds. seconds.
If a cache receives a value larger than the largest positive integer If a cache receives a value larger than the largest positive integer
it can represent, or if any of its age calculations overflows, it it can represent, or if any of its age calculations overflows, it
MUST transmit an Age header with a value of 2147483648 (2^31). An MUST transmit an Age header with a value of 2147483648 (2^31). An
HTTP/1.1 server that includes a cache MUST include an Age header HTTP/1.1 server that includes a cache MUST include an Age header
field in every response generated from its own cache. Caches SHOULD field in every response generated from its own cache. Caches SHOULD
use an arithmetic type of at least 31 bits of range. use an arithmetic type of at least 31 bits of range.
14.7. Allow 14.7. Allow
The Allow entity-header field lists the set of methods supported by The Allow entity-header field lists the set of methods supported by
the resource identified by the Request-URI. The purpose of this the resource identified by the Request-URI. The purpose of this
field is strictly to inform the recipient of valid methods associated field is strictly to inform the recipient of valid methods associated
with the resource. An Allow header field MUST be present in a 405 with the resource. An Allow header field MUST be present in a 405
(Method Not Allowed) response. (Method Not Allowed) response.
Allow = "Allow" ":" #Method Allow = "Allow" ":" #Method
Example of use: Example of use:
Allow: GET, HEAD, PUT Allow: GET, HEAD, PUT
This field cannot prevent a client from trying other methods. This field cannot prevent a client from trying other methods.
However, the indications given by the Allow header field value SHOULD However, the indications given by the Allow header field value SHOULD
be followed. The actual set of allowed methods is defined by the be followed. The actual set of allowed methods is defined by the
origin server at the time of each request. origin server at the time of each request.
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14.8. Authorization 14.8. Authorization
A user agent that wishes to authenticate itself with a server-- A user agent that wishes to authenticate itself with a server--
usually, but not necessarily, after receiving a 401 response--does so usually, but not necessarily, after receiving a 401 response--does so
by including an Authorization request-header field with the request. by including an Authorization request-header field with the request.
The Authorization field value consists of credentials containing the The Authorization field value consists of credentials containing the
authentication information of the user agent for the realm of the authentication information of the user agent for the realm of the
resource being requested. resource being requested.
Authorization = "Authorization" ":" credentials Authorization = "Authorization" ":" credentials
HTTP access authentication is described in "HTTP Authentication: HTTP access authentication is described in "HTTP Authentication:
Basic and Digest Access Authentication" [43]. If a request is Basic and Digest Access Authentication" [RFC2617]. If a request is
authenticated and a realm specified, the same credentials SHOULD be authenticated and a realm specified, the same credentials SHOULD be
valid for all other requests within this realm (assuming that the valid for all other requests within this realm (assuming that the
authentication scheme itself does not require otherwise, such as authentication scheme itself does not require otherwise, such as
credentials that vary according to a challenge value or using credentials that vary according to a challenge value or using
synchronized clocks). synchronized clocks).
When a shared cache (see Section 13.7) receives a request containing When a shared cache (see Section 13.7) receives a request containing
an Authorization field, it MUST NOT return the corresponding response an Authorization field, it MUST NOT return the corresponding response
as a reply to any other request, unless one of the following specific as a reply to any other request, unless one of the following specific
exceptions holds: exceptions holds:
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cache-request-directive = cache-request-directive =
"no-cache" ; Section 14.9.1 "no-cache" ; Section 14.9.1
| "no-store" ; Section 14.9.2 | "no-store" ; Section 14.9.2
| "max-age" "=" delta-seconds ; Section 14.9.3, 14.9.4 | "max-age" "=" delta-seconds ; Section 14.9.3, 14.9.4
| "max-stale" [ "=" delta-seconds ] ; Section 14.9.3 | "max-stale" [ "=" delta-seconds ] ; Section 14.9.3
| "min-fresh" "=" delta-seconds ; Section 14.9.3 | "min-fresh" "=" delta-seconds ; Section 14.9.3
| "no-transform" ; Section 14.9.5 | "no-transform" ; Section 14.9.5
| "only-if-cached" ; Section 14.9.4 | "only-if-cached" ; Section 14.9.4
| cache-extension ; Section 14.9.6 | cache-extension ; Section 14.9.6
cache-response-directive = cache-response-directive =
"public" ; Section 14.9.1 "public" ; Section 14.9.1
| "private" [ "=" <"> 1#field-name <"> ] ; Section 14.9.1 | "private" [ "=" DQUOTE 1#field-name DQUOTE ]
| "no-cache" [ "=" <"> 1#field-name <"> ]; Section 14.9.1 ; Section 14.9.1
| "no-store" ; Section 14.9.2 | "no-cache" [ "=" DQUOTE 1#field-name DQUOTE ]
| "no-transform" ; Section 14.9.5 ; Section 14.9.1
| "must-revalidate" ; Section 14.9.4 | "no-store" ; Section 14.9.2
| "proxy-revalidate" ; Section 14.9.4 | "no-transform" ; Section 14.9.5
| "max-age" "=" delta-seconds ; Section 14.9.3 | "must-revalidate" ; Section 14.9.4
| "s-maxage" "=" delta-seconds ; Section 14.9.3 | "proxy-revalidate" ; Section 14.9.4
| cache-extension ; Section 14.9.6 | "max-age" "=" delta-seconds ; Section 14.9.3
| "s-maxage" "=" delta-seconds ; Section 14.9.3
| cache-extension ; Section 14.9.6
cache-extension = token [ "=" ( token | quoted-string ) ] cache-extension = token [ "=" ( token | quoted-string ) ]
When a directive appears without any 1#field-name parameter, the When a directive appears without any 1#field-name parameter, the
directive applies to the entire request or response. When such a directive applies to the entire request or response. When such a
directive appears with a 1#field-name parameter, it applies only to directive appears with a 1#field-name parameter, it applies only to
the named field or fields, and not to the rest of the request or the named field or fields, and not to the rest of the request or
response. This mechanism supports extensibility; implementations of response. This mechanism supports extensibility; implementations of
future versions of the HTTP protocol might apply these directives to future versions of the HTTP protocol might apply these directives to
header fields not defined in HTTP/1.1. header fields not defined in HTTP/1.1.
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correct even if the cache does not understand the extension(s). correct even if the cache does not understand the extension(s).
14.10. Connection 14.10. Connection
The Connection general-header field allows the sender to specify The Connection general-header field allows the sender to specify
options that are desired for that particular connection and MUST NOT options that are desired for that particular connection and MUST NOT
be communicated by proxies over further connections. be communicated by proxies over further connections.
The Connection header has the following grammar: The Connection header has the following grammar:
Connection = "Connection" ":" 1#(connection-token) Connection = "Connection" ":" 1#(connection-token)
connection-token = token connection-token = token
HTTP/1.1 proxies MUST parse the Connection header field before a HTTP/1.1 proxies MUST parse the Connection header field before a
message is forwarded and, for each connection-token in this field, message is forwarded and, for each connection-token in this field,
remove any header field(s) from the message with the same name as the remove any header field(s) from the message with the same name as the
connection-token. Connection options are signaled by the presence of connection-token. Connection options are signaled by the presence of
a connection-token in the Connection header field, not by any a connection-token in the Connection header field, not by any
corresponding additional header field(s), since the additional header corresponding additional header field(s), since the additional header
field may not be sent if there are no parameters associated with that field may not be sent if there are no parameters associated with that
connection option. connection option.
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HTTP/1.1 defines the "close" connection option for the sender to HTTP/1.1 defines the "close" connection option for the sender to
signal that the connection will be closed after completion of the signal that the connection will be closed after completion of the
response. For example, response. For example,
Connection: close Connection: close
in either the request or the response header fields indicates that in either the request or the response header fields indicates that
the connection SHOULD NOT be considered `persistent' (Section 8.1) the connection SHOULD NOT be considered `persistent' (Section 8.1)
after the current request/response is complete. after the current request/response is complete.
HTTP/1.1 applications that do not support persistent connections MUST An HTTP/1.1 client that does not support persistent connections MUST
include the "close" connection option in every message. include the "close" connection option in every request message.
An HTTP/1.1 server that does not support persistent connections MUST
include the "close" connection option in every response message that
does not have a 1xx (informational) status code.
A system receiving an HTTP/1.0 (or lower-version) message that A system receiving an HTTP/1.0 (or lower-version) message that
includes a Connection header MUST, for each connection-token in this includes a Connection header MUST, for each connection-token in this
field, remove and ignore any header field(s) from the message with field, remove and ignore any header field(s) from the message with
the same name as the connection-token. This protects against the same name as the connection-token. This protects against
mistaken forwarding of such header fields by pre-HTTP/1.1 proxies. mistaken forwarding of such header fields by pre-HTTP/1.1 proxies.
See Appendix A.6.2. See Appendix F.2.
14.11. Content-Encoding 14.11. Content-Encoding
The Content-Encoding entity-header field is used as a modifier to the The Content-Encoding entity-header field is used as a modifier to the
media-type. When present, its value indicates what additional media-type. When present, its value indicates what additional
content codings have been applied to the entity-body, and thus what content codings have been applied to the entity-body, and thus what
decoding mechanisms must be applied in order to obtain the media-type decoding mechanisms must be applied in order to obtain the media-type
referenced by the Content-Type header field. Content-Encoding is referenced by the Content-Type header field. Content-Encoding is
primarily used to allow a document to be compressed without losing primarily used to allow a document to be compressed without losing
the identity of its underlying media type. the identity of its underlying media type.
Content-Encoding = "Content-Encoding" ":" 1#content-coding Content-Encoding = "Content-Encoding" ":" 1#content-coding
Content codings are defined in Section 3.5. An example of its use is Content codings are defined in Section 3.5. An example of its use is
Content-Encoding: gzip Content-Encoding: gzip
The content-coding is a characteristic of the entity identified by The content-coding is a characteristic of the entity identified by
the Request-URI. Typically, the entity-body is stored with this the Request-URI. Typically, the entity-body is stored with this
encoding and is only decoded before rendering or analogous usage. encoding and is only decoded before rendering or analogous usage.
However, a non-transparent proxy MAY modify the content-coding if the However, a non-transparent proxy MAY modify the content-coding if the
new coding is known to be acceptable to the recipient, unless the new coding is known to be acceptable to the recipient, unless the
"no-transform" cache-control directive is present in the message. "no-transform" cache-control directive is present in the message.
If the content-coding of an entity is not "identity", then the If the content-coding of an entity is not "identity", then the
response MUST include a Content-Encoding entity-header response MUST include a Content-Encoding entity-header that lists the
(Section 14.11) that lists the non-identity content-coding(s) used. non-identity content-coding(s) used.
If the content-coding of an entity in a request message is not If the content-coding of an entity in a request message is not
acceptable to the origin server, the server SHOULD respond with a acceptable to the origin server, the server SHOULD respond with a
status code of 415 (Unsupported Media Type). status code of 415 (Unsupported Media Type).
If multiple encodings have been applied to an entity, the content If multiple encodings have been applied to an entity, the content
codings MUST be listed in the order in which they were applied. codings MUST be listed in the order in which they were applied.
Additional information about the encoding parameters MAY be provided Additional information about the encoding parameters MAY be provided
by other entity-header fields not defined by this specification. by other entity-header fields not defined by this specification.
14.12. Content-Language 14.12. Content-Language
The Content-Language entity-header field describes the natural The Content-Language entity-header field describes the natural
language(s) of the intended audience for the enclosed entity. Note language(s) of the intended audience for the enclosed entity. Note
that this might not be equivalent to all the languages used within that this might not be equivalent to all the languages used within
the entity-body. the entity-body.
Content-Language = "Content-Language" ":" 1#language-tag Content-Language = "Content-Language" ":" 1#Language-Tag
Language tags are defined in Section 3.10. The primary purpose of Language tags are defined in Section 3.10. 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
entities according to the user's own preferred language. Thus, if entities according to the user's own preferred language. Thus, if
the body content is intended only for a Danish-literate audience, the the body content is intended only for a Danish-literate audience, the
appropriate field is 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
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Content-Language MAY be applied to any media type -- it is not Content-Language MAY be applied to any media type -- it is not
limited to textual documents. limited to textual documents.
14.13. Content-Length 14.13. Content-Length
The Content-Length entity-header field indicates the size of the The Content-Length entity-header field indicates the size of the
entity-body, in decimal number of OCTETs, sent to the recipient or, entity-body, in decimal number of OCTETs, sent to the recipient or,
in the case of the HEAD method, the size of the entity-body that in the case of the HEAD method, the size of the entity-body that
would have been sent had the request been a GET. would have been sent had the request been a GET.
Content-Length = "Content-Length" ":" 1*DIGIT Content-Length = "Content-Length" ":" 1*DIGIT
An example is An example is
Content-Length: 3495 Content-Length: 3495
Applications SHOULD use this field to indicate the transfer-length of Applications SHOULD use this field to indicate the transfer-length of
the message-body, unless this is prohibited by the rules in the message-body, unless this is prohibited by the rules in
Section 4.4. Section 4.4.
Any Content-Length greater than or equal to zero is a valid value. Any Content-Length greater than or equal to zero is a valid value.
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The Content-Location entity-header field MAY be used to supply the The Content-Location entity-header field MAY be used to supply the
resource location for the entity enclosed in the message when that resource location for the entity enclosed in the message when that
entity is accessible from a location separate from the requested entity is accessible from a location separate from the requested
resource's URI. A server SHOULD provide a Content-Location for the resource's URI. A server SHOULD provide a Content-Location for the
variant corresponding to the response entity; especially in the case variant corresponding to the response entity; especially in the case
where a resource has multiple entities associated with it, and those where a resource has multiple entities associated with it, and those
entities actually have separate locations by which they might be entities actually have separate locations by which they might be
individually accessed, the server SHOULD provide a Content-Location individually accessed, the server SHOULD provide a Content-Location
for the particular variant which is returned. for the particular variant which is returned.
Content-Location = "Content-Location" ":" Content-Location = "Content-Location" ":"
( absoluteURI | relativeURI ) ( absoluteURI | relativeURI )
The value of Content-Location also defines the base URI for the The value of Content-Location also defines the base URI for the
entity. entity.
The Content-Location value is not a replacement for the original The Content-Location value is not a replacement for the original
requested URI; it is only a statement of the location of the resource requested URI; it is only a statement of the location of the resource
corresponding to this particular entity at the time of the request. corresponding to this particular entity at the time of the request.
Future requests MAY specify the Content-Location URI as the request- Future requests MAY specify the Content-Location URI as the request-
URI if the desire is to identify the source of that particular URI if the desire is to identify the source of that particular
entity. entity.
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Section 13.6. Section 13.6.
If the Content-Location is a relative URI, the relative URI is If the Content-Location is a relative URI, the relative URI is
interpreted relative to the Request-URI. interpreted relative to the Request-URI.
The meaning of the Content-Location header in PUT or POST requests is The meaning of the Content-Location header in PUT or POST requests is
undefined; servers are free to ignore it in those cases. undefined; servers are free to ignore it in those cases.
14.15. Content-MD5 14.15. Content-MD5
The Content-MD5 entity-header field, as defined in RFC 1864 [23], is The Content-MD5 entity-header field, as defined in [RFC1864], is an
an MD5 digest of the entity-body for the purpose of providing an end- MD5 digest of the entity-body for the purpose of providing an end-to-
to-end message integrity check (MIC) of the entity-body. (Note: a end message integrity check (MIC) of the entity-body. (Note: a MIC
MIC is good for detecting accidental modification of the entity-body is good for detecting accidental modification of the entity-body in
in transit, but is not proof against malicious attacks.) transit, but is not proof against malicious attacks.)
Content-MD5 = "Content-MD5" ":" md5-digest Content-MD5 = "Content-MD5" ":" md5-digest
md5-digest = <base64 of 128 bit MD5 digest as per RFC 1864> md5-digest = <base64 of 128 bit MD5 digest as per [RFC1864]>
The Content-MD5 header field MAY be generated by an origin server or The Content-MD5 header field MAY be generated by an origin server or
client to function as an integrity check of the entity-body. Only client to function as an integrity check of the entity-body. Only
origin servers or clients MAY generate the Content-MD5 header field; origin servers or clients MAY generate the Content-MD5 header field;
proxies and gateways MUST NOT generate it, as this would defeat its proxies and gateways MUST NOT generate it, as this would defeat its
value as an end-to-end integrity check. Any recipient of the entity- value as an end-to-end integrity check. Any recipient of the entity-
body, including gateways and proxies, MAY check that the digest value body, including gateways and proxies, MAY check that the digest value
in this header field matches that of the entity-body as received. in this header field matches that of the entity-body as received.
The MD5 digest is computed based on the content of the entity-body, The MD5 digest is computed based on the content of the entity-body,
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the digest is the transmission byte order defined for the type. the digest is the transmission byte order defined for the type.
Lastly, HTTP allows transmission of text types with any of several Lastly, HTTP allows transmission of text types with any of several
line break conventions and not just the canonical form using CRLF. line break conventions and not just the canonical form using CRLF.
14.16. Content-Range 14.16. Content-Range
The Content-Range entity-header is sent with a partial entity-body to The Content-Range entity-header is sent with a partial entity-body to
specify where in the full entity-body the partial body should be specify where in the full entity-body the partial body should be
applied. Range units are defined in Section 3.12. applied. Range units are defined in Section 3.12.
Content-Range = "Content-Range" ":" content-range-spec Content-Range = "Content-Range" ":" content-range-spec
content-range-spec = byte-content-range-spec content-range-spec = byte-content-range-spec
byte-content-range-spec = bytes-unit SP byte-content-range-spec = bytes-unit SP
byte-range-resp-spec "/" byte-range-resp-spec "/"
( instance-length | "*" ) ( instance-length | "*" )
byte-range-resp-spec = (first-byte-pos "-" last-byte-pos) byte-range-resp-spec = (first-byte-pos "-" last-byte-pos)
| "*" | "*"
instance-length = 1*DIGIT instance-length = 1*DIGIT
The header SHOULD indicate the total length of the full entity-body, The header SHOULD indicate the total length of the full entity-body,
unless this length is unknown or difficult to determine. The unless this length is unknown or difficult to determine. The
asterisk "*" character means that the instance-length is unknown at asterisk "*" character means that the instance-length is unknown at
the time when the response was generated. the time when the response was generated.
Unlike byte-ranges-specifier values (see Section 14.35.1), a byte- Unlike byte-ranges-specifier values (see Section 14.35.1), a byte-
range-resp-spec MUST only specify one range, and MUST contain range-resp-spec MUST only specify one range, and MUST contain
absolute byte positions for both the first and last byte of the absolute byte positions for both the first and last byte of the
range. range.
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o The last 500 bytes: o The last 500 bytes:
bytes 734-1233/1234 bytes 734-1233/1234
When an HTTP message includes the content of a single range (for When an HTTP message includes the content of a single range (for
example, a response to a request for a single range, or to a request example, a response to a request for a single range, or to a request
for a set of ranges that overlap without any holes), this content is for a set of ranges that overlap without any holes), this content is
transmitted with a Content-Range header, and a Content-Length header transmitted with a Content-Range header, and a Content-Length header
showing the number of bytes actually transferred. For example, showing the number of bytes actually transferred. For example,
HTTP/1.1 206 Partial content HTTP/1.1 206 Partial Content
Date: Wed, 15 Nov 1995 06:25:24 GMT Date: Wed, 15 Nov 1995 06:25:24 GMT
Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
Content-Range: bytes 21010-47021/47022 Content-Range: bytes 21010-47021/47022
Content-Length: 26012 Content-Length: 26012
Content-Type: image/gif Content-Type: image/gif
When an HTTP message includes the content of multiple ranges (for When an HTTP message includes the content of multiple ranges (for
example, a response to a request for multiple non-overlapping example, a response to a request for multiple non-overlapping
ranges), these are transmitted as a multipart message. The multipart ranges), these are transmitted as a multipart message. The multipart
media type used for this purpose is "multipart/byteranges" as defined media type used for this purpose is "multipart/byteranges" as defined
in Appendix A.2. See Appendix A.6.3 for a compatibility issue. in Appendix B. See Appendix F.3 for a compatibility issue.
A response to a request for a single range MUST NOT be sent using the A response to a request for a single range MUST NOT be sent using the
multipart/byteranges media type. A response to a request for multipart/byteranges media type. A response to a request for
multiple ranges, whose result is a single range, MAY be sent as a multiple ranges, whose result is a single range, MAY be sent as a
multipart/byteranges media type with one part. A client that cannot multipart/byteranges media type with one part. A client that cannot
decode a multipart/byteranges message MUST NOT ask for multiple byte- decode a multipart/byteranges message MUST NOT ask for multiple byte-
ranges in a single request. ranges in a single request.
When a client requests multiple byte-ranges in one request, the When a client requests multiple byte-ranges in one request, the
server SHOULD return them in the order that they appeared in the server SHOULD return them in the order that they appeared in the
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range not satisfiable) response instead of a 200 (OK) response for range not satisfiable) response instead of a 200 (OK) response for
an unsatisfiable Range request-header, since not all servers an unsatisfiable Range request-header, since not all servers
implement this request-header. implement this request-header.
14.17. Content-Type 14.17. Content-Type
The Content-Type entity-header field indicates the media type of the The Content-Type entity-header field indicates the media type of the
entity-body sent to the recipient or, in the case of the HEAD method, entity-body sent to the recipient or, in the case of the HEAD method,
the media type that would have been sent had the request been a GET. the media type that would have been sent had the request been a GET.
Content-Type = "Content-Type" ":" media-type Content-Type = "Content-Type" ":" media-type
Media types are defined in Section 3.7. An example of the field is Media types are defined in Section 3.7. An example of the field is
Content-Type: text/html; charset=ISO-8859-4 Content-Type: text/html; charset=ISO-8859-4
Further discussion of methods for identifying the media type of an Further discussion of methods for identifying the media type of an
entity is provided in Section 7.2.1. entity is provided in Section 7.2.1.
14.18. Date 14.18. Date
The Date general-header field represents the date and time at which The Date general-header field represents the date and time at which
the message was originated, having the same semantics as orig-date in the message was originated, having the same semantics as orig-date in
RFC 822. The field value is an HTTP-date, as described in [RFC2822]. The field value is an HTTP-date, as described in
Section 3.3.1; it MUST be sent in RFC 1123 [8]-date format. Section 3.3.1; it MUST be sent in rfc1123-date format.
Date = "Date" ":" HTTP-date 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, Origin servers MUST include a Date header field in all responses,
except in these cases: except in these cases:
1. If the response status code is 100 (Continue) or 101 (Switching 1. If the response status code is 100 (Continue) or 101 (Switching
Protocols), the response MAY include a Date header field, at the Protocols), the response MAY include a Date header field, at the
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3. If the server does not have a clock that can provide a reasonable 3. If the server does not have a clock that can provide a reasonable
approximation of the current time, its responses MUST NOT include approximation of the current time, its responses MUST NOT include
a Date header field. In this case, the rules in Section 14.18.1 a Date header field. In this case, the rules in Section 14.18.1
MUST be followed. MUST be followed.
A received message that does not have a Date header field MUST be A received message that does not have a Date header field MUST be
assigned one by the recipient if the message will be cached by that assigned one by the recipient if the message will be cached by that
recipient or gatewayed via a protocol which requires a Date. An HTTP recipient or gatewayed via a protocol which requires a Date. An HTTP
implementation without a clock MUST NOT cache responses without implementation without a clock MUST NOT cache responses without
revalidating them on every use. An HTTP cache, especially a shared revalidating them on every use. An HTTP cache, especially a shared
cache, SHOULD use a mechanism, such as NTP [28], to synchronize its cache, SHOULD use a mechanism, such as NTP [RFC1305], to synchronize
clock with a reliable external standard. its clock with a reliable external standard.
Clients SHOULD only send a Date header field in messages that include Clients SHOULD only send a Date header field in messages that include
an entity-body, as in the case of the PUT and POST requests, and even an entity-body, as in the case of the PUT and POST requests, and even
then it is optional. A client without a clock MUST NOT send a Date then it is optional. A client without a clock MUST NOT send a Date
header field in a request. header field in a request.
The HTTP-date sent in a Date header SHOULD NOT represent a date and The HTTP-date sent in a Date header SHOULD NOT represent a date and
time subsequent to the generation of the message. It SHOULD time subsequent to the generation of the message. It SHOULD
represent the best available approximation of the date and time of represent the best available approximation of the date and time of
message generation, unless the implementation has no means of message generation, unless the implementation has no means of
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with the resource by a system or user with a reliable clock. It MAY with the resource by a system or user with a reliable clock. It MAY
assign an Expires value that is known, at or before server assign an Expires value that is known, at or before server
configuration time, to be in the past (this allows "pre-expiration" configuration time, to be in the past (this allows "pre-expiration"
of responses without storing separate Expires values for each of responses without storing separate Expires values for each
resource). resource).
14.19. ETag 14.19. ETag
The ETag response-header field provides the current value of the The ETag response-header field provides the current value of the
entity tag for the requested variant. The headers used with entity entity tag for the requested variant. The headers used with entity
tags are described in sections 14.24, 14.26 and 14.44. The entity tags are described in Sections 14.24, 14.26 and 14.44. The entity
tag MAY be used for comparison with other entities from the same tag MAY be used for comparison with other entities from the same
resource (see Section 13.3.3). resource (see Section 13.3.3).
ETag = "ETag" ":" entity-tag ETag = "ETag" ":" entity-tag
Examples: Examples:
ETag: "xyzzy" ETag: "xyzzy"
ETag: W/"xyzzy" ETag: W/"xyzzy"
ETag: "" ETag: ""
14.20. Expect 14.20. Expect
The Expect request-header field is used to indicate that particular The Expect request-header field is used to indicate that particular
server behaviors are required by the client. server behaviors are required by the client.
Expect = "Expect" ":" 1#expectation Expect = "Expect" ":" 1#expectation
expectation = "100-continue" | expectation-extension expectation = "100-continue" | expectation-extension
expectation-extension = token [ "=" ( token | quoted-string ) expectation-extension = token [ "=" ( token | quoted-string )
*expect-params ] *expect-params ]
expect-params = ";" token [ "=" ( token | quoted-string ) ] expect-params = ";" token [ "=" ( token | quoted-string ) ]
A server that does not understand or is unable to comply with any of A server that does not understand or is unable to comply with any of
the expectation values in the Expect field of a request MUST respond the expectation values in the Expect field of a request MUST respond
with appropriate error status. The server MUST respond with a 417 with appropriate error status. The server MUST respond with a 417
(Expectation Failed) status if any of the expectations cannot be met (Expectation Failed) status if any of the expectations cannot be met
or, if there are other problems with the request, some other 4xx or, if there are other problems with the request, some other 4xx
status. status.
This header field is defined with extensible syntax to allow for This header field is defined with extensible syntax to allow for
future extensions. If a server receives a request containing an future extensions. If a server receives a request containing an
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The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST
return a 417 (Expectation Failed) status if it receives a request return a 417 (Expectation Failed) status if it receives a request
with an expectation that it cannot meet. However, the Expect with an expectation that it cannot meet. However, the Expect
request-header itself is end-to-end; it MUST be forwarded if the request-header itself is end-to-end; it MUST be forwarded if the
request is forwarded. request is forwarded.
Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
Expect header. Expect header.
See Section 8.2.3 for the use of the 100 (continue) status. See Section 8.2.3 for the use of the 100 (Continue) status.
14.21. Expires 14.21. Expires
The Expires entity-header field gives the date/time after which the The Expires entity-header field gives the date/time after which the
response is considered stale. A stale cache entry may not normally response is considered stale. A stale cache entry may not normally
be returned by a cache (either a proxy cache or a user agent cache) be returned by a cache (either a proxy cache or a user agent cache)
unless it is first validated with the origin server (or with an unless it is first validated with the origin server (or with an
intermediate cache that has a fresh copy of the entity). See intermediate cache that has a fresh copy of the entity). See
Section 13.2 for further discussion of the expiration model. Section 13.2 for further discussion of the expiration model.
The presence of an Expires field does not imply that the original The presence of an Expires field does not imply that the original
resource will change or cease to exist at, before, or after that resource will change or cease to exist at, before, or after that
time. time.
The format is an absolute date and time as defined by HTTP-date in The format is an absolute date and time as defined by HTTP-date in
Section 3.3.1; it MUST be in RFC 1123 date format: Section 3.3.1; it MUST be in rfc1123-date format:
Expires = "Expires" ":" HTTP-date Expires = "Expires" ":" HTTP-date
An example of its use is An example of its use is
Expires: Thu, 01 Dec 1994 16:00:00 GMT Expires: Thu, 01 Dec 1994 16:00:00 GMT
Note: if a response includes a Cache-Control field with the max- Note: if a response includes a Cache-Control field with the max-
age directive (see Section 14.9.3), that directive overrides the age directive (see Section 14.9.3), that directive overrides the
Expires field. Expires field.
HTTP/1.1 clients and caches MUST treat other invalid date formats, HTTP/1.1 clients and caches MUST treat other invalid date formats,
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The presence of an Expires header field with a date value of some The presence of an Expires header field with a date value of some
time in the future on a response that otherwise would by default be time in the future on a response that otherwise would by default be
non-cacheable indicates that the response is cacheable, unless non-cacheable indicates that the response is cacheable, unless
indicated otherwise by a Cache-Control header field (Section 14.9). indicated otherwise by a Cache-Control header field (Section 14.9).
14.22. From 14.22. From
The From request-header field, if given, SHOULD contain an Internet The From request-header field, if given, SHOULD contain an Internet
e-mail address for the human user who controls the requesting user e-mail address for the human user who controls the requesting user
agent. The address SHOULD be machine-usable, as defined by "mailbox" agent. The address SHOULD be machine-usable, as defined by "mailbox"
in RFC 822 [9] as updated by RFC 1123 [8]: in Section 3.4 of [RFC2822]:
From = "From" ":" mailbox From = "From" ":" mailbox
An example is: An example is:
From: webmaster@w3.org From: webmaster@w3.org
This header field MAY be used for logging purposes and as a means for This header field MAY be used for logging purposes and as a means for
identifying the source of invalid or unwanted requests. It SHOULD identifying the source of invalid or unwanted requests. It SHOULD
NOT be used as an insecure form of access protection. The NOT be used as an insecure form of access protection. The
interpretation of this field is that the request is being performed interpretation of this field is that the request is being performed
on behalf of the person given, who accepts responsibility for the on behalf of the person given, who accepts responsibility for the
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The Host request-header field specifies the Internet host and port The Host request-header field specifies the Internet host and port
number of the resource being requested, as obtained from the original number of the resource being requested, as obtained from the original
URI given by the user or referring resource (generally an HTTP URL, URI given by the user or referring resource (generally an HTTP URL,
as described in Section 3.2.2). The Host field value MUST represent as described in Section 3.2.2). The Host field value MUST represent
the naming authority of the origin server or gateway given by the the naming authority of the origin server or gateway given by the
original URL. This allows the origin server or gateway to original URL. This allows the origin server or gateway to
differentiate between internally-ambiguous URLs, such as the root "/" differentiate between internally-ambiguous URLs, such as the root "/"
URL of a server for multiple host names on a single IP address. URL of a server for multiple host names on a single IP address.
Host = "Host" ":" host [ ":" port ] ; Section 3.2.2 Host = "Host" ":" uri-host [ ":" port ] ; Section 3.2.2
A "host" without any trailing port information implies the default A "host" without any trailing port information implies the default
port for the service requested (e.g., "80" for an HTTP URL). For port for the service requested (e.g., "80" for an HTTP URL). For
example, a request on the origin server for example, a request on the origin server for
<http://www.w3.org/pub/WWW/> would properly include: <http://www.example.org/pub/WWW/> would properly include:
GET /pub/WWW/ HTTP/1.1 GET /pub/WWW/ HTTP/1.1
Host: www.w3.org Host: www.example.org
A client MUST include a Host header field in all HTTP/1.1 request A client MUST include a Host header field in all HTTP/1.1 request
messages . If the requested URI does not include an Internet host messages. If the requested URI does not include an Internet host
name for the service being requested, then the Host header field MUST name for the service being requested, then the Host header field MUST
be given with an empty value. An HTTP/1.1 proxy MUST ensure that any be given with an empty value. An HTTP/1.1 proxy MUST ensure that any
request message it forwards does contain an appropriate Host header request message it forwards does contain an appropriate Host header
field that identifies the service being requested by the proxy. All field that identifies the service being requested by the proxy. All
Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request) Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request)
status code to any HTTP/1.1 request message which lacks a Host header status code to any HTTP/1.1 request message which lacks a Host header
field. field.
See sections 5.2 and A.6.1.1 for other requirements relating to Host. See Sections 5.2 and F.1.1 for other requirements relating to Host.
14.24. If-Match 14.24. If-Match
The If-Match request-header field is used with a method to make it The If-Match request-header field is used with a method to make it
conditional. A client that has one or more entities previously conditional. A client that has one or more entities previously
obtained from the resource can verify that one of those entities is obtained from the resource can verify that one of those entities is
current by including a list of their associated entity tags in the current by including a list of their associated entity tags in the
If-Match header field. Entity tags are defined in Section 3.11. The If-Match header field. Entity tags are defined in Section 3.11. The
purpose of this feature is to allow efficient updates of cached purpose of this feature is to allow efficient updates of cached
information with a minimum amount of transaction overhead. It is information with a minimum amount of transaction overhead. It is
also used, on updating requests, to prevent inadvertent modification also used, on updating requests, to prevent inadvertent modification
of the wrong version of a resource. As a special case, the value "*" of the wrong version of a resource. As a special case, the value "*"
matches any current entity of the resource. matches any current entity of the resource.
If-Match = "If-Match" ":" ( "*" | 1#entity-tag ) If-Match = "If-Match" ":" ( "*" | 1#entity-tag )
If any of the entity tags match the entity tag of the entity that If any of the entity tags match the entity tag of the entity that
would have been returned in the response to a similar GET request would have been returned in the response to a similar GET request
(without the If-Match header) on that resource, or if "*" is given (without the If-Match header) on that resource, or if "*" is given
and any current entity exists for that resource, then the server MAY and any current entity exists for that resource, then the server MAY
perform the requested method as if the If-Match header field did not perform the requested method as if the If-Match header field did not
exist. exist.
A server MUST use the strong comparison function (see Section 13.3.3) A server MUST use the strong comparison function (see Section 13.3.3)
to compare the entity tags in If-Match. to compare the entity tags in If-Match.
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The result of a request having both an If-Match header field and The result of a request having both an If-Match header field and
either an If-None-Match or an If-Modified-Since header fields is either an If-None-Match or an If-Modified-Since header fields is
undefined by this specification. undefined by this specification.
14.25. If-Modified-Since 14.25. If-Modified-Since
The If-Modified-Since request-header field is used with a method to The If-Modified-Since request-header field is used with a method to
make it conditional: if the requested variant has not been modified make it conditional: if the requested variant has not been modified
since the time specified in this field, an entity will not be since the time specified in this field, an entity will not be
returned from the server; instead, a 304 (not modified) response will returned from the server; instead, a 304 (Not Modified) response will
be returned without any message-body. be returned without any message-body.
If-Modified-Since = "If-Modified-Since" ":" HTTP-date If-Modified-Since = "If-Modified-Since" ":" HTTP-date
An example of the field is: An example of the field is:
If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
A GET method with an If-Modified-Since header and no Range header A GET method with an If-Modified-Since header and no Range header
requests that the identified entity be transferred only if it has requests that the identified entity be transferred only if it has
been modified since the date given by the If-Modified-Since header. been modified since the date given by the If-Modified-Since header.
The algorithm for determining this includes the following cases: The algorithm for determining this includes the following cases:
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current by including a list of their associated entity tags in the current by including a list of their associated entity tags in the
If-None-Match header field. The purpose of this feature is to allow If-None-Match header field. The purpose of this feature is to allow
efficient updates of cached information with a minimum amount of efficient updates of cached information with a minimum amount of
transaction overhead. It is also used to prevent a method (e.g. transaction overhead. It is also used to prevent a method (e.g.
PUT) from inadvertently modifying an existing resource when the PUT) from inadvertently modifying an existing resource when the
client believes that the resource does not exist. client believes that the resource does not exist.
As a special case, the value "*" matches any current entity of the As a special case, the value "*" matches any current entity of the
resource. resource.
If-None-Match = "If-None-Match" ":" ( "*" | 1#entity-tag ) If-None-Match = "If-None-Match" ":" ( "*" | 1#entity-tag )
If any of the entity tags match the entity tag of the entity that If any of the entity tags match the entity tag of the entity that
would have been returned in the response to a similar GET request would have been returned in the response to a similar GET request
(without the If-None-Match header) on that resource, or if "*" is (without the If-None-Match header) on that resource, or if "*" is
given and any current entity exists for that resource, then the given and any current entity exists for that resource, then the
server MUST NOT perform the requested method, unless required to do server MUST NOT perform the requested method, unless required to do
so because the resource's modification date fails to match that so because the resource's modification date fails to match that
supplied in an If-Modified-Since header field in the request. supplied in an If-Modified-Since header field in the request.
Instead, if the request method was GET or HEAD, the server SHOULD Instead, if the request method was GET or HEAD, the server SHOULD
respond with a 304 (Not Modified) response, including the cache- respond with a 304 (Not Modified) response, including the cache-
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either or both of If-Unmodified-Since and If-Match.) However, if the either or both of If-Unmodified-Since and If-Match.) However, if the
condition fails because the entity has been modified, the client condition fails because the entity has been modified, the client
would then have to make a second request to obtain the entire current would then have to make a second request to obtain the entire current
entity-body. entity-body.
The If-Range header allows a client to "short-circuit" the second The If-Range header allows a client to "short-circuit" the second
request. Informally, its meaning is `if the entity is unchanged, request. Informally, its meaning is `if the entity is unchanged,
send me the part(s) that I am missing; otherwise, send me the entire send me the part(s) that I am missing; otherwise, send me the entire
new entity'. new entity'.
If-Range = "If-Range" ":" ( entity-tag | HTTP-date ) If-Range = "If-Range" ":" ( entity-tag | HTTP-date )
If the client has no entity tag for an entity, but does have a Last- If the client has no entity tag for an entity, but does have a Last-
Modified date, it MAY use that date in an If-Range header. (The Modified date, it MAY use that date in an If-Range header. (The
server can distinguish between a valid HTTP-date and any form of server can distinguish between a valid HTTP-date and any form of
entity-tag by examining no more than two characters.) The If-Range entity-tag by examining no more than two characters.) The If-Range
header SHOULD only be used together with a Range header, and MUST be header SHOULD only be used together with a Range header, and MUST be
ignored if the request does not include a Range header, or if the ignored if the request does not include a Range header, or if the
server does not support the sub-range operation. server does not support the sub-range operation.
If the entity tag given in the If-Range header matches the current If the entity tag given in the If-Range header matches the current
entity tag for the entity, then the server SHOULD provide the entity tag for the entity, then the server SHOULD provide the
specified sub-range of the entity using a 206 (Partial content) specified sub-range of the entity using a 206 (Partial Content)
response. If the entity tag does not match, then the server SHOULD response. If the entity tag does not match, then the server SHOULD
return the entire entity using a 200 (OK) response. return the entire entity using a 200 (OK) response.
14.28. If-Unmodified-Since 14.28. If-Unmodified-Since
The If-Unmodified-Since request-header field is used with a method to The If-Unmodified-Since request-header field is used with a method to
make it conditional. If the requested resource has not been modified make it conditional. If the requested resource has not been modified
since the time specified in this field, the server SHOULD perform the since the time specified in this field, the server SHOULD perform the
requested operation as if the If-Unmodified-Since header were not requested operation as if the If-Unmodified-Since header were not
present. present.
If the requested variant has been modified since the specified time, If the requested variant has been modified since the specified time,
the server MUST NOT perform the requested operation, and MUST return the server MUST NOT perform the requested operation, and MUST return
a 412 (Precondition Failed). a 412 (Precondition Failed).
If-Unmodified-Since = "If-Unmodified-Since" ":" HTTP-date If-Unmodified-Since = "If-Unmodified-Since" ":" HTTP-date
An example of the field is: An example of the field is:
If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
If the request normally (i.e., without the If-Unmodified-Since If the request normally (i.e., without the If-Unmodified-Since
header) would result in anything other than a 2xx or 412 status, the header) would result in anything other than a 2xx or 412 status, the
If-Unmodified-Since header SHOULD be ignored. If-Unmodified-Since header SHOULD be ignored.
If the specified date is invalid, the header is ignored. If the specified date is invalid, the header is ignored.
The result of a request having both an If-Unmodified-Since header The result of a request having both an If-Unmodified-Since header
field and either an If-None-Match or an If-Modified-Since header field and either an If-None-Match or an If-Modified-Since header
fields is undefined by this specification. fields is undefined by this specification.
14.29. Last-Modified 14.29. Last-Modified
The Last-Modified entity-header field indicates the date and time at The Last-Modified entity-header field indicates the date and time at
which the origin server believes the variant was last modified. which the origin server believes the variant was last modified.
Last-Modified = "Last-Modified" ":" HTTP-date Last-Modified = "Last-Modified" ":" HTTP-date
An example of its use is An example of its use is
Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
The exact meaning of this header field depends on the implementation The exact meaning of this header field depends on the implementation
of the origin server and the nature of the original resource. For of the origin server and the nature of the original resource. For
files, it may be just the file system last-modified time. For files, it may be just the file system last-modified time. For
entities with dynamically included parts, it may be the most recent entities with dynamically included parts, it may be the most recent
of the set of last-modify times for its component parts. For of the set of last-modify times for its component parts. For
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14.30. Location 14.30. Location
The Location response-header field is used to redirect the recipient The Location response-header field is used to redirect the recipient
to a location other than the Request-URI for completion of the to a location other than the Request-URI for completion of the
request or identification of a new resource. For 201 (Created) request or identification of a new resource. For 201 (Created)
responses, the Location is that of the new resource which was created responses, the Location is that of the new resource which was created
by the request. For 3xx responses, the location SHOULD indicate the by the request. For 3xx responses, the location SHOULD indicate the
server's preferred URI for automatic redirection to the resource. server's preferred URI for automatic redirection to the resource.
The field value consists of a single absolute URI. The field value consists of a single absolute URI.
Location = "Location" ":" absoluteURI Location = "Location" ":" absoluteURI [ "#" fragment ]
An example is: An example is:
Location: http://www.w3.org/pub/WWW/People.html Location: http://www.example.org/pub/WWW/People.html
Note: The Content-Location header field (Section 14.14) differs Note: The Content-Location header field (Section 14.14) differs
from Location in that the Content-Location identifies the original from Location in that the Content-Location identifies the original
location of the entity enclosed in the request. It is therefore location of the entity enclosed in the request. It is therefore
possible for a response to contain header fields for both Location possible for a response to contain header fields for both Location
and Content-Location. Also see Section 13.10 for cache and Content-Location. Also see Section 13.10 for cache
requirements of some methods. requirements of some methods.
There are circumstances in which a fragment identifier in a Location
URL would not be appropriate:
o With a 201 Created response, because in this usage the Location
header specifies the URL for the entire created resource.
o With a 300 Multiple Choices, since the choice decision is intended
to be made on resource characteristics and not fragment
characteristics.
o With 305 Use Proxy.
14.31. Max-Forwards 14.31. Max-Forwards
The Max-Forwards request-header field provides a mechanism with the The Max-Forwards request-header field provides a mechanism with the
TRACE (Section 9.8) and OPTIONS (Section 9.2) methods to limit the TRACE (Section 9.8) and OPTIONS (Section 9.2) methods to limit the
number of proxies or gateways that can forward the request to the number of proxies or gateways that can forward the request to the
next inbound server. This can be useful when the client is next inbound server. This can be useful when the client is
attempting to trace a request chain which appears to be failing or attempting to trace a request chain which appears to be failing or
looping in mid-chain. looping in mid-chain.
Max-Forwards = "Max-Forwards" ":" 1*DIGIT Max-Forwards = "Max-Forwards" ":" 1*DIGIT
The Max-Forwards value is a decimal integer indicating the remaining The Max-Forwards value is a decimal integer indicating the remaining
number of times this request message may be forwarded. number of times this request message may be forwarded.
Each proxy or gateway recipient of a TRACE or OPTIONS request Each proxy or gateway recipient of a TRACE or OPTIONS request
containing a Max-Forwards header field MUST check and update its containing a Max-Forwards header field MUST check and update its
value prior to forwarding the request. If the received value is zero value prior to forwarding the request. If the received value is zero
(0), the recipient MUST NOT forward the request; instead, it MUST (0), the recipient MUST NOT forward the request; instead, it MUST
respond as the final recipient. If the received Max-Forwards value respond as the final recipient. If the received Max-Forwards value
is greater than zero, then the forwarded message MUST contain an is greater than zero, then the forwarded message MUST contain an
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it is not explicitly referred to as part of that method definition. it is not explicitly referred to as part of that method definition.
14.32. Pragma 14.32. Pragma
The Pragma general-header field is used to include implementation- The Pragma general-header field is used to include implementation-
specific directives that might apply to any recipient along the specific directives that might apply to any recipient along the
request/response chain. All pragma directives specify optional request/response chain. All pragma directives specify optional
behavior from the viewpoint of the protocol; however, some systems behavior from the viewpoint of the protocol; however, some systems
MAY require that behavior be consistent with the directives. MAY require that behavior be consistent with the directives.
Pragma = "Pragma" ":" 1#pragma-directive Pragma = "Pragma" ":" 1#pragma-directive
pragma-directive = "no-cache" | extension-pragma pragma-directive = "no-cache" | extension-pragma
extension-pragma = token [ "=" ( token | quoted-string ) ] extension-pragma = token [ "=" ( token | quoted-string ) ]
When the no-cache directive is present in a request message, an When the no-cache directive is present in a request message, an
application SHOULD forward the request toward the origin server even application SHOULD forward the request toward the origin server even
if it has a cached copy of what is being requested. This pragma if it has a cached copy of what is being requested. This pragma
directive has the same semantics as the no-cache cache-directive (see directive has the same semantics as the no-cache cache-directive (see
Section 14.9) and is defined here for backward compatibility with Section 14.9) and is defined here for backward compatibility with
HTTP/1.0. Clients SHOULD include both header fields when a no-cache HTTP/1.0. Clients SHOULD include both header fields when a no-cache
request is sent to a server not known to be HTTP/1.1 compliant. request is sent to a server not known to be HTTP/1.1 compliant.
Pragma directives MUST be passed through by a proxy or gateway Pragma directives MUST be passed through by a proxy or gateway
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header field is not actually specified, it does not provide a header field is not actually specified, it does not provide a
reliable replacement for "Cache-Control: no-cache" in a response reliable replacement for "Cache-Control: no-cache" in a response
14.33. Proxy-Authenticate 14.33. Proxy-Authenticate
The Proxy-Authenticate response-header field MUST be included as part The Proxy-Authenticate response-header field MUST be included as part
of a 407 (Proxy Authentication Required) response. The field value of a 407 (Proxy Authentication Required) response. The field value
consists of a challenge that indicates the authentication scheme and consists of a challenge that indicates the authentication scheme and
parameters applicable to the proxy for this Request-URI. parameters applicable to the proxy for this Request-URI.
Proxy-Authenticate = "Proxy-Authenticate" ":" 1#challenge Proxy-Authenticate = "Proxy-Authenticate" ":" 1#challenge
The HTTP access authentication process is described in "HTTP The HTTP access authentication process is described in "HTTP
Authentication: Basic and Digest Access Authentication" [43]. Unlike Authentication: Basic and Digest Access Authentication" [RFC2617].
WWW-Authenticate, the Proxy-Authenticate header field applies only to Unlike WWW-Authenticate, the Proxy-Authenticate header field applies
the current connection and SHOULD NOT be passed on to downstream only to the current connection and SHOULD NOT be passed on to
clients. However, an intermediate proxy might need to obtain its own downstream clients. However, an intermediate proxy might need to
credentials by requesting them from the downstream client, which in obtain its own credentials by requesting them from the downstream
some circumstances will appear as if the proxy is forwarding the client, which in some circumstances will appear as if the proxy is
Proxy-Authenticate header field. forwarding the Proxy-Authenticate header field.
14.34. Proxy-Authorization 14.34. Proxy-Authorization
The Proxy-Authorization request-header field allows the client to The Proxy-Authorization request-header field allows the client to
identify itself (or its user) to a proxy which requires identify itself (or its user) to a proxy which requires
authentication. The Proxy-Authorization field value consists of authentication. The Proxy-Authorization field value consists of
credentials containing the authentication information of the user credentials containing the authentication information of the user
agent for the proxy and/or realm of the resource being requested. agent for the proxy and/or realm of the resource being requested.
Proxy-Authorization = "Proxy-Authorization" ":" credentials Proxy-Authorization = "Proxy-Authorization" ":" credentials
The HTTP access authentication process is described in "HTTP The HTTP access authentication process is described in "HTTP
Authentication: Basic and Digest Access Authentication" [43]. Unlike Authentication: Basic and Digest Access Authentication" [RFC2617].
Authorization, the Proxy-Authorization header field applies only to Unlike Authorization, the Proxy-Authorization header field applies
the next outbound proxy that demanded authentication using the Proxy- only to the next outbound proxy that demanded authentication using
Authenticate field. When multiple proxies are used in a chain, the the Proxy-Authenticate field. When multiple proxies are used in a
Proxy-Authorization header field is consumed by the first outbound chain, the Proxy-Authorization header field is consumed by the first
proxy that was expecting to receive credentials. A proxy MAY relay outbound proxy that was expecting to receive credentials. A proxy
the credentials from the client request to the next proxy if that is MAY relay the credentials from the client request to the next proxy
the mechanism by which the proxies cooperatively authenticate a given if that is the mechanism by which the proxies cooperatively
request. authenticate a given request.
14.35. Range 14.35. Range
14.35.1. Byte Ranges 14.35.1. Byte Ranges
Since all HTTP entities are represented in HTTP messages as sequences Since all HTTP entities are represented in HTTP messages as sequences
of bytes, the concept of a byte range is meaningful for any HTTP of bytes, the concept of a byte range is meaningful for any HTTP
entity. (However, not all clients and servers need to support byte- entity. (However, not all clients and servers need to support byte-
range operations.) range operations.)
Byte range specifications in HTTP apply to the sequence of bytes in Byte range specifications in HTTP apply to the sequence of bytes in
the entity-body (not necessarily the same as the message-body). the entity-body (not necessarily the same as the message-body).
A byte range operation MAY specify a single range of bytes, or a set A byte range operation MAY specify a single range of bytes, or a set
of ranges within a single entity. of ranges within a single entity.
ranges-specifier = byte-ranges-specifier ranges-specifier = byte-ranges-specifier
byte-ranges-specifier = bytes-unit "=" byte-range-set byte-ranges-specifier = bytes-unit "=" byte-range-set
byte-range-set = 1#( byte-range-spec | suffix-byte-range-spec ) byte-range-set = 1#( byte-range-spec | suffix-byte-range-spec )
byte-range-spec = first-byte-pos "-" [last-byte-pos] byte-range-spec = first-byte-pos "-" [last-byte-pos]
first-byte-pos = 1*DIGIT first-byte-pos = 1*DIGIT
last-byte-pos = 1*DIGIT last-byte-pos = 1*DIGIT
The first-byte-pos value in a byte-range-spec gives the byte-offset The first-byte-pos value in a byte-range-spec gives the byte-offset
of the first byte in a range. The last-byte-pos value gives the of the first byte in a range. The last-byte-pos value gives the
byte-offset of the last byte in the range; that is, the byte byte-offset of the last byte in the range; that is, the byte
positions specified are inclusive. Byte offsets start at zero. positions specified are inclusive. Byte offsets start at zero.
If the last-byte-pos value is present, it MUST be greater than or If the last-byte-pos value is present, it MUST be greater than or
equal to the first-byte-pos in that byte-range-spec, or the byte- equal to the first-byte-pos in that byte-range-spec, or the byte-
range-spec is syntactically invalid. The recipient of a byte-range- range-spec is syntactically invalid. The recipient of a byte-range-
set that includes one or more syntactically invalid byte-range-spec set that includes one or more syntactically invalid byte-range-spec
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set. set.
If the last-byte-pos value is absent, or if the value is greater than If the last-byte-pos value is absent, or if the value is greater than
or equal to the current length of the entity-body, last-byte-pos is or equal to the current length of the entity-body, last-byte-pos is
taken to be equal to one less than the current length of the entity- taken to be equal to one less than the current length of the entity-
body in bytes. body in bytes.
By its choice of last-byte-pos, a client can limit the number of By its choice of last-byte-pos, a client can limit the number of
bytes retrieved without knowing the size of the entity. bytes retrieved without knowing the size of the entity.
suffix-byte-range-spec = "-" suffix-length suffix-byte-range-spec = "-" suffix-length
suffix-length = 1*DIGIT suffix-length = 1*DIGIT
A suffix-byte-range-spec is used to specify the suffix of the entity- A suffix-byte-range-spec is used to specify the suffix of the entity-
body, of a length given by the suffix-length value. (That is, this body, of a length given by the suffix-length value. (That is, this
form specifies the last N bytes of an entity-body.) If the entity is form specifies the last N bytes of an entity-body.) If the entity is
shorter than the specified suffix-length, the entire entity-body is shorter than the specified suffix-length, the entire entity-body is
used. used.
If a syntactically valid byte-range-set includes at least one byte- If a syntactically valid byte-range-set includes at least one byte-
range-spec whose first-byte-pos is less than the current length of range-spec whose first-byte-pos is less than the current length of
the entity-body, or at least one suffix-byte-range-spec with a non- the entity-body, or at least one suffix-byte-range-spec with a non-
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bytes=500-600,601-999 bytes=500-600,601-999
bytes=500-700,601-999 bytes=500-700,601-999
14.35.2. Range Retrieval Requests 14.35.2. Range Retrieval Requests
HTTP retrieval requests using conditional or unconditional GET HTTP retrieval requests using conditional or unconditional GET
methods MAY request one or more sub-ranges of the entity, instead of methods MAY request one or more sub-ranges of the entity, instead of
the entire entity, using the Range request header, which applies to the entire entity, using the Range request header, which applies to
the entity returned as the result of the request: the entity returned as the result of the request:
Range = "Range" ":" ranges-specifier Range = "Range" ":" ranges-specifier
A server MAY ignore the Range header. However, HTTP/1.1 origin A server MAY ignore the Range header. However, HTTP/1.1 origin
servers and intermediate caches ought to support byte ranges when servers and intermediate caches ought to support byte ranges when
possible, since Range supports efficient recovery from partially possible, since Range supports efficient recovery from partially
failed transfers, and supports efficient partial retrieval of large failed transfers, and supports efficient partial retrieval of large
entities. entities.
If the server supports the Range header and the specified range or If the server supports the Range header and the specified range or
ranges are appropriate for the entity: ranges are appropriate for the entity:
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The Referer[sic] request-header field allows the client to specify, The Referer[sic] request-header field allows the client to specify,
for the server's benefit, the address (URI) of the resource from for the server's benefit, the address (URI) of the resource from
which the Request-URI was obtained (the "referrer", although the which the Request-URI was obtained (the "referrer", although the
header field is misspelled.) The Referer request-header allows a header field is misspelled.) The Referer request-header allows a
server to generate lists of back-links to resources for interest, server to generate lists of back-links to resources for interest,
logging, optimized caching, etc. It also allows obsolete or mistyped logging, optimized caching, etc. It also allows obsolete or mistyped
links to be traced for maintenance. The Referer field MUST NOT be links to be traced for maintenance. The Referer field MUST NOT be
sent if the Request-URI was obtained from a source that does not have sent if the Request-URI was obtained from a source that does not have
its own URI, such as input from the user keyboard. its own URI, such as input from the user keyboard.
Referer = "Referer" ":" ( absoluteURI | relativeURI ) Referer = "Referer" ":" ( absoluteURI | relativeURI )
Example: Example:
Referer: http://www.w3.org/hypertext/DataSources/Overview.html Referer: http://www.example.org/hypertext/Overview.html
If the field value is a relative URI, it SHOULD be interpreted If the field value is a relative URI, it SHOULD be interpreted
relative to the Request-URI. The URI MUST NOT include a fragment. relative to the Request-URI. The URI MUST NOT include a fragment.
See Section 15.1.3 for security considerations. See Section 15.1.3 for security considerations.
14.37. Retry-After 14.37. Retry-After
The Retry-After response-header field can be used with a 503 (Service The Retry-After response-header field can be used with a 503 (Service
Unavailable) response to indicate how long the service is expected to Unavailable) response to indicate how long the service is expected to
be unavailable to the requesting client. This field MAY also be used be unavailable to the requesting client. This field MAY also be used
with any 3xx (Redirection) response to indicate the minimum time the with any 3xx (Redirection) response to indicate the minimum time the
user-agent is asked wait before issuing the redirected request. The user-agent is asked wait before issuing the redirected request. The
value of this field can be either an HTTP-date or an integer number value of this field can be either an HTTP-date or an integer number
of seconds (in decimal) after the time of the response. of seconds (in decimal) after the time of the response.
Retry-After = "Retry-After" ":" ( HTTP-date | delta-seconds ) Retry-After = "Retry-After" ":" ( HTTP-date | delta-seconds )
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.
14.38. Server 14.38. Server
The Server response-header field contains information about the The Server response-header field contains information about the
software used by the origin server to handle the request. The field software used by the origin server to handle the request. The field
can contain multiple product tokens (Section 3.8) and comments can contain multiple product tokens (Section 3.8) and comments
identifying the server and any significant subproducts. The product identifying the server and any significant subproducts. The product
tokens are listed in order of their significance for identifying the tokens are listed in order of their significance for identifying the
application. application.
Server = "Server" ":" 1*( product | comment ) Server = "Server" ":" 1*( product | comment )
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 If the response is being forwarded through a proxy, the proxy
application MUST NOT modify the Server response-header. Instead, it application MUST NOT modify the Server response-header. Instead, it
SHOULD include a Via field (as described in Section 14.45). MUST include a Via field (as described in Section 14.45).
Note: Revealing the specific software version of the server might Note: Revealing the specific software version of the server might
allow the server machine to become more vulnerable to attacks allow the server machine to become more vulnerable to attacks
against software that is known to contain security holes. Server against software that is known to contain security holes. Server
implementors are encouraged to make this field a configurable implementors are encouraged to make this field a configurable
option. option.
14.39. TE 14.39. TE
The TE request-header field indicates what extension transfer-codings The TE request-header field indicates what extension transfer-codings
it is willing to accept in the response and whether or not it is it is willing to accept in the response and whether or not it is
willing to accept trailer fields in a chunked transfer-coding. Its willing to accept trailer fields in a chunked transfer-coding. Its
value may consist of the keyword "trailers" and/or a comma-separated value may consist of the keyword "trailers" and/or a comma-separated
list of extension transfer-coding names with optional accept list of extension transfer-coding names with optional accept
parameters (as described in Section 3.6). parameters (as described in Section 3.6).
TE = "TE" ":" #( t-codings ) TE = "TE" ":" #( t-codings )
t-codings = "trailers" | ( transfer-extension [ accept-params ] ) t-codings = "trailers" | ( transfer-extension [ accept-params ] )
The presence of the keyword "trailers" indicates that the client is The presence of the keyword "trailers" indicates that the client is
willing to accept trailer fields in a chunked transfer-coding, as willing to accept trailer fields in a chunked transfer-coding, as
defined in Section 3.6.1. This keyword is reserved for use with defined in Section 3.6.1. This keyword is reserved for use with
transfer-coding values even though it does not itself represent a transfer-coding values even though it does not itself represent a
transfer-coding. transfer-coding.
Examples of its use are: Examples of its use are:
TE: deflate TE: deflate
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If the TE field-value is empty or if no TE field is present, the only If the TE field-value is empty or if no TE field is present, the only
transfer-coding is "chunked". A message with no transfer-coding is transfer-coding is "chunked". A message with no transfer-coding is
always acceptable. always acceptable.
14.40. Trailer 14.40. Trailer
The Trailer general field value indicates that the given set of The Trailer general field value indicates that the given set of
header fields is present in the trailer of a message encoded with header fields is present in the trailer of a message encoded with
chunked transfer-coding. chunked transfer-coding.
Trailer = "Trailer" ":" 1#field-name Trailer = "Trailer" ":" 1#field-name
An HTTP/1.1 message SHOULD include a Trailer header field in a An HTTP/1.1 message SHOULD include a Trailer header field in a
message using chunked transfer-coding with a non-empty trailer. message using chunked transfer-coding with a non-empty trailer.
Doing so allows the recipient to know which header fields to expect Doing so allows the recipient to know which header fields to expect
in the trailer. in the trailer.
If no Trailer header field is present, the trailer SHOULD NOT include If no Trailer header field is present, the trailer SHOULD NOT include
any header fields. See Section 3.6.1 for restrictions on the use of any header fields. See Section 3.6.1 for restrictions on the use of
trailer fields in a "chunked" transfer-coding. trailer fields in a "chunked" transfer-coding.
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Encoding header. Encoding header.
14.42. Upgrade 14.42. Upgrade
The Upgrade general-header allows the client to specify what The Upgrade general-header allows the client to specify what
additional communication protocols it supports and would like to use additional communication protocols it supports and would like to use
if the server finds it appropriate to switch protocols. The server if the server finds it appropriate to switch protocols. The server
MUST use the Upgrade header field within a 101 (Switching Protocols) MUST use the Upgrade header field within a 101 (Switching Protocols)
response to indicate which protocol(s) are being switched. response to indicate which protocol(s) are being switched.
Upgrade = "Upgrade" ":" 1#product Upgrade = "Upgrade" ":" 1#product
For example, For example,
Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11 Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
The Upgrade header field is intended to provide a simple mechanism The Upgrade header field is intended to provide a simple mechanism
for transition from HTTP/1.1 to some other, incompatible protocol. for transition from HTTP/1.1 to some other, incompatible protocol.
It does so by allowing the client to advertise its desire to use It does so by allowing the client to advertise its desire to use
another protocol, such as a later version of HTTP with a higher major another protocol, such as a later version of HTTP with a higher major
version number, even though the current request has been made using version number, even though the current request has been made using
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user agent originating the request. This is for statistical user agent originating the request. This is for statistical
purposes, the tracing of protocol violations, and automated purposes, the tracing of protocol violations, and automated
recognition of user agents for the sake of tailoring responses to recognition of user agents for the sake of tailoring responses to
avoid particular user agent limitations. User agents SHOULD include avoid particular user agent limitations. User agents SHOULD include
this field with requests. The field can contain multiple product this field with requests. The field can contain multiple product
tokens (Section 3.8) and comments identifying the agent and any tokens (Section 3.8) and comments identifying the agent and any
subproducts which form a significant part of the user agent. By subproducts which form a significant part of the user agent. By
convention, the product tokens are listed in order of their convention, the product tokens are listed in order of their
significance for identifying the application. significance for identifying the application.
User-Agent = "User-Agent" ":" 1*( product | comment ) User-Agent = "User-Agent" ":" 1*( product | comment )
Example: Example:
User-Agent: CERN-LineMode/2.15 libwww/2.17b3 User-Agent: CERN-LineMode/2.15 libwww/2.17b3
14.44. Vary 14.44. Vary
The Vary field value indicates the set of request-header fields that The Vary field value indicates the set of request-header fields that
fully determines, while the response is fresh, whether a cache is fully determines, while the response is fresh, whether a cache is
permitted to use the response to reply to a subsequent request permitted to use the response to reply to a subsequent request
without revalidation. For uncacheable or stale responses, the Vary without revalidation. For uncacheable or stale responses, the Vary
field value advises the user agent about the criteria that were used field value advises the user agent about the criteria that were used
to select the representation. A Vary field value of "*" implies that to select the representation. A Vary field value of "*" implies that
a cache cannot determine from the request headers of a subsequent a cache cannot determine from the request headers of a subsequent
request whether this response is the appropriate representation. See request whether this response is the appropriate representation. See
Section 13.6 for use of the Vary header field by caches. Section 13.6 for use of the Vary header field by caches.
Vary = "Vary" ":" ( "*" | 1#field-name ) Vary = "Vary" ":" ( "*" | 1#field-name )
An HTTP/1.1 server SHOULD include a Vary header field with any An HTTP/1.1 server SHOULD include a Vary header field with any
cacheable response that is subject to server-driven negotiation. cacheable response that is subject to server-driven negotiation.
Doing so allows a cache to properly interpret future requests on that Doing so allows a cache to properly interpret future requests on that
resource and informs the user agent about the presence of negotiation resource and informs the user agent about the presence of negotiation
on that resource. A server MAY include a Vary header field with a on that resource. A server MAY include a Vary header field with a
non-cacheable response that is subject to server-driven negotiation, non-cacheable response that is subject to server-driven negotiation,
since this might provide the user agent with useful information about since this might provide the user agent with useful information about
the dimensions over which the response varies at the time of the the dimensions over which the response varies at the time of the
response. response.
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client), play a role in the selection of the response representation. client), play a role in the selection of the response representation.
The "*" value MUST NOT be generated by a proxy server; it may only be The "*" value MUST NOT be generated by a proxy server; it may only be
generated by an origin server. generated by an origin server.
14.45. Via 14.45. Via
The Via general-header field MUST be used by gateways and proxies to The Via general-header field MUST be used by gateways and proxies to
indicate the intermediate protocols and recipients between the user indicate the intermediate protocols and recipients between the user
agent and the server on requests, and between the origin server and agent and the server on requests, and between the origin server and
the client on responses. It is analogous to the "Received" field of the client on responses. It is analogous to the "Received" field of
RFC 822 [9] and is intended to be used for tracking message forwards,
[RFC2822] and is intended to be used for tracking message forwards,
avoiding request loops, and identifying the protocol capabilities of avoiding request loops, and identifying the protocol capabilities of
all senders along the request/response chain. all senders along the request/response chain.
Via = "Via" ":" 1#( received-protocol received-by [ comment ] ) Via = "Via" ":" 1#( received-protocol received-by [ comment ] )
received-protocol = [ protocol-name "/" ] protocol-version received-protocol = [ protocol-name "/" ] protocol-version
protocol-name = token protocol-name = token
protocol-version = token protocol-version = token
received-by = ( host [ ":" port ] ) | pseudonym received-by = ( uri-host [ ":" port ] ) | pseudonym
pseudonym = token pseudonym = token
The received-protocol indicates the protocol version of the message The received-protocol indicates the protocol version of the message
received by the server or client along each segment of the request/ received by the server or client along each segment of the request/
response chain. The received-protocol version is appended to the Via response chain. The received-protocol version is appended to the Via
field value when the message is forwarded so that information about field value when the message is forwarded so that information about
the protocol capabilities of upstream applications remains visible to the protocol capabilities of upstream applications remains visible to
all recipients. all recipients.
The protocol-name is optional if and only if it would be "HTTP". The The protocol-name is optional if and only if it would be "HTTP". The
received-by field is normally the host and optional port number of a received-by field is normally the host and optional port number of a
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The Warning general-header field is used to carry additional The Warning general-header field is used to carry additional
information about the status or transformation of a message which information about the status or transformation of a message which
might not be reflected in the message. This information is typically might not be reflected in the message. This information is typically
used to warn about a possible lack of semantic transparency from used to warn about a possible lack of semantic transparency from
caching operations or transformations applied to the entity body of caching operations or transformations applied to the entity body of
the message. the message.
Warning headers are sent with responses using: Warning headers are sent with responses using:
Warning = "Warning" ":" 1#warning-value Warning = "Warning" ":" 1#warning-value
warning-value = warn-code SP warn-agent SP warn-text warning-value = warn-code SP warn-agent SP warn-text
[SP warn-date] [SP warn-date]
warn-code = 3DIGIT warn-code = 3DIGIT
warn-agent = ( host [ ":" port ] ) | pseudonym warn-agent = ( uri-host [ ":" port ] ) | pseudonym
; the name or pseudonym of the server adding ; the name or pseudonym of the server adding
; the Warning header, for use in debugging ; the Warning header, for use in debugging
warn-text = quoted-string warn-text = quoted-string
warn-date = <"> HTTP-date <"> warn-date = DQUOTE HTTP-date DQUOTE
A response MAY carry more than one Warning header. A response MAY carry more than one Warning header.
The warn-text SHOULD be in a natural language and character set that The warn-text SHOULD be in a natural language and character set that
is most likely to be intelligible to the human user receiving the is most likely to be intelligible to the human user receiving the
response. This decision MAY be based on any available knowledge, response. This decision MAY be based on any available knowledge,
such as the location of the cache or user, the Accept-Language field such as the location of the cache or user, the Accept-Language field
in a request, the Content-Language field in a response, etc. The in a request, the Content-Language field in a response, etc. The
default language is English and the default character set is ISO- default language is English and the default character set is ISO-
8859-1. 8859-1.
If a character set other than ISO-8859-1 is used, it MUST be encoded If a character set other than ISO-8859-1 is used, it MUST be encoded
in the warn-text using the method described in RFC 2047 [14]. in the warn-text using the method described in [RFC2047].
Warning headers can in general be applied to any message, however Warning headers can in general be applied to any message, however
some specific warn-codes are specific to caches and can only be some specific warn-codes are specific to caches and can only be
applied to response messages. New Warning headers SHOULD be added applied to response messages. New Warning headers SHOULD be added
after any existing Warning headers. A cache MUST NOT delete any after any existing Warning headers. A cache MUST NOT delete any
Warning header that it received with a message. However, if a cache Warning header that it received with a message. However, if a cache
successfully validates a cache entry, it SHOULD remove any Warning successfully validates a cache entry, it SHOULD remove any Warning
headers previously attached to that entry except as specified for headers previously attached to that entry except as specified for
specific Warning codes. It MUST then add any Warning headers specific Warning codes. It MUST then add any Warning headers
received in the validating response. In other words, Warning headers received in the validating response. In other words, Warning headers
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of the warning-values are deleted for this reason, the Warning header of the warning-values are deleted for this reason, the Warning header
MUST be deleted as well. MUST be deleted as well.
14.47. WWW-Authenticate 14.47. WWW-Authenticate
The WWW-Authenticate response-header field MUST be included in 401 The WWW-Authenticate response-header field MUST be included in 401
(Unauthorized) response messages. The field value consists of at (Unauthorized) response messages. The field value consists of at
least one challenge that indicates the authentication scheme(s) and least one challenge that indicates the authentication scheme(s) and
parameters applicable to the Request-URI. parameters applicable to the Request-URI.
WWW-Authenticate = "WWW-Authenticate" ":" 1#challenge WWW-Authenticate = "WWW-Authenticate" ":" 1#challenge
The HTTP access authentication process is described in "HTTP The HTTP access authentication process is described in "HTTP
Authentication: Basic and Digest Access Authentication" [43]. User Authentication: Basic and Digest Access Authentication" [RFC2617].
agents are advised to take special care in parsing the WWW- User agents are advised to take special care in parsing the WWW-
Authenticate field value as it might contain more than one challenge, Authenticate field value as it might contain more than one challenge,
or if more than one WWW-Authenticate header field is provided, the or if more than one WWW-Authenticate header field is provided, the
contents of a challenge itself can contain a comma-separated list of contents of a challenge itself can contain a comma-separated list of
authentication parameters. authentication parameters.
15. Security Considerations 15. Security Considerations
This section is meant to inform application developers, information This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include described by this document. The discussion does not include
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to be cached, however, only when the TTL (Time To Live) information to be cached, however, only when the TTL (Time To Live) information
reported by the name server makes it likely that the cached reported by the name server makes it likely that the cached
information will remain useful. information will remain useful.
If HTTP clients cache the results of host name lookups in order to If HTTP clients cache the results of host name lookups in order to
achieve a performance improvement, they MUST observe the TTL achieve a performance improvement, they MUST observe the TTL
information reported by DNS. information reported by DNS.
If HTTP clients do not observe this rule, they could be spoofed when If HTTP clients do not observe this rule, they could be spoofed when
a previously-accessed server's IP address changes. As network a previously-accessed server's IP address changes. As network
renumbering is expected to become increasingly common [24], the renumbering is expected to become increasingly common [RFC1900], the
possibility of this form of attack will grow. Observing this possibility of this form of attack will grow. Observing this
requirement thus reduces this potential security vulnerability. requirement thus reduces this potential security vulnerability.
This requirement also improves the load-balancing behavior of clients This requirement also improves the load-balancing behavior of clients
for replicated servers using the same DNS name and reduces the for replicated servers using the same DNS name and reduces the
likelihood of a user's experiencing failure in accessing sites which likelihood of a user's experiencing failure in accessing sites which
use that strategy. use that strategy.
15.4. Location Headers and Spoofing 15.4. Location Headers and Spoofing
If a single server supports multiple organizations that do not trust If a single server supports multiple organizations that do not trust
one another, then it MUST check the values of Location and Content- one another, then it MUST check the values of Location and Content-
Location headers in responses that are generated under control of Location headers in responses that are generated under control of
said organizations to make sure that they do not attempt to said organizations to make sure that they do not attempt to
invalidate resources over which they have no authority. invalidate resources over which they have no authority.
15.5. Content-Disposition Issues 15.5. Content-Disposition Issues
RFC 1806 [35], from which the often implemented Content-Disposition [RFC1806], from which the often implemented Content-Disposition (see
(see Appendix A.5.1) header in HTTP is derived, has a number of very Appendix E.1) header in HTTP is derived, has a number of very serious
serious security considerations. Content-Disposition is not part of security considerations. Content-Disposition is not part of the HTTP
the HTTP standard, but since it is widely implemented, we are standard, but since it is widely implemented, we are documenting its
documenting its use and risks for implementors. See RFC 2183 [49] use and risks for implementors. See [RFC2183] (which updates RFC
(which updates RFC 1806) for details. 1806) for details.
15.6. Authentication Credentials and Idle Clients 15.6. Authentication Credentials and Idle Clients
Existing HTTP clients and user agents typically retain authentication Existing HTTP clients and user agents typically retain authentication
information indefinitely. HTTP/1.1. does not provide a method for a information indefinitely. HTTP/1.1 does not provide a method for a
server to direct clients to discard these cached credentials. This server to direct clients to discard these cached credentials. This
is a significant defect that requires further extensions to HTTP. is a significant defect that requires further extensions to HTTP.
Circumstances under which credential caching can interfere with the Circumstances under which credential caching can interfere with the
application's security model include but are not limited to: application's security model include but are not limited to:
o Clients which have been idle for an extended period following o Clients which have been idle for an extended period following
which the server might wish to cause the client to reprompt the which the server might wish to cause the client to reprompt the
user for credentials. user for credentials.
o Applications which include a session termination indication (such o Applications which include a session termination indication (such
skipping to change at page 164, line 7 skipping to change at page 169, line 7
protect against a broad range of security and privacy attacks. Such protect against a broad range of security and privacy attacks. Such
cryptography is beyond the scope of the HTTP/1.1 specification. cryptography is beyond the scope of the HTTP/1.1 specification.
15.7.1. Denial of Service Attacks on Proxies 15.7.1. Denial of Service Attacks on Proxies
They exist. They are hard to defend against. Research continues. They exist. They are hard to defend against. Research continues.
Beware. Beware.
16. Acknowledgments 16. Acknowledgments
16.1. (RFC2616)
This specification makes heavy use of the augmented BNF and generic This specification makes heavy use of the augmented BNF and generic
constructs defined by David H. Crocker for RFC 822 [9]. Similarly, constructs defined by David H. Crocker for [RFC822ABNF]. Similarly,
it reuses many of the definitions provided by Nathaniel Borenstein it reuses many of the definitions provided by Nathaniel Borenstein
and Ned Freed for MIME [7]. We hope that their inclusion in this and Ned Freed for MIME [RFC2045]. We hope that their inclusion in
specification will help reduce past confusion over the relationship this specification will help reduce past confusion over the
between HTTP and Internet mail message formats. relationship between HTTP and Internet mail message formats.
The HTTP protocol has evolved considerably over the years. It has The HTTP protocol has evolved considerably over the years. It has
benefited from a large and active developer community--the many benefited from a large and active developer community--the many
people who have participated on the www-talk mailing list--and it is people who have participated on the www-talk mailing list--and it is
that community which has been most responsible for the success of that community which has been most responsible for the success of
HTTP and of the World-Wide Web in general. Marc Andreessen, Robert HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
VanHeyningen deserve special recognition for their efforts in VanHeyningen deserve special recognition for their efforts in
defining early aspects of the protocol. defining early aspects of the protocol.
This document has benefited greatly from the comments of all those This document has benefited greatly from the comments of all those
participating in the HTTP-WG. In addition to those already participating in the HTTP-WG. In addition to those already
mentioned, the following individuals have contributed to this mentioned, the following individuals have contributed to this
specification: specification:
Gary Adams Ross Patterson Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
Harald Tveit Alvestrand Albert Lunde Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
Keith Ball John C. Mallery Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc
Brian Behlendorf Jean-Philippe Martin-Flatin Hedlund, Greg Herlihy, Koen Holtman, Alex Hopmann, Bob Jernigan, Shel
Paul Burchard Mitra Kaphan, Rohit Khare, John Klensin, Martijn Koster, Alexei Kosut,
Maurizio Codogno David Morris David M. Kristol, Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert
Mike Cowlishaw Gavin Nicol Lunde, John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David
Roman Czyborra Bill Perry Morris, Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott
Michael A. Dolan Jeffrey Perry Powers, Owen Rees, Luigi Rizzo, David Robinson, Marc Salomon, Rich
David J. Fiander Scott Powers Salz, Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
Alan Freier Owen Rees Simon E. Spero, Richard N. Taylor, Robert S. Thau, Bill (BearHeart)
Marc Hedlund Luigi Rizzo Weinman, Francois Yergeau, Mary Ellen Zurko, Josh Cohen.
Greg Herlihy David Robinson
Koen Holtman Marc Salomon
Alex Hopmann Rich Salz
Bob Jernigan Allan M. Schiffman
Shel Kaphan Jim Seidman
Rohit Khare Chuck Shotton
John Klensin Eric W. Sink
Martijn Koster Simon E. Spero
Alexei Kosut Richard N. Taylor
David M. Kristol Robert S. Thau
Daniel LaLiberte Bill (BearHeart) Weinman
Ben Laurie Francois Yergeau
Paul J. Leach Mary Ellen Zurko
Daniel DuBois Josh Cohen
Much of the content and presentation of the caching design is due to Much of the content and presentation of the caching design is due to
suggestions and comments from individuals including: Shel Kaphan, suggestions and comments from individuals including: Shel Kaphan,
Paul Leach, Koen Holtman, David Morris, and Larry Masinter. Paul Leach, Koen Holtman, David Morris, and Larry Masinter.
Most of the specification of ranges is based on work originally done Most of the specification of ranges is based on work originally done
by Ari Luotonen and John Franks, with additional input from Steve by Ari Luotonen and John Franks, with additional input from Steve
Zilles. Zilles.
Thanks to the "cave men" of Palo Alto. You know who you are. Thanks to the "cave men" of Palo Alto. You know who you are.
Jim Gettys (the current editor of this document) wishes particularly Jim Gettys (the editor of [RFC2616]) wishes particularly to thank Roy
to thank Roy Fielding, the previous editor of this document, along Fielding, the editor of [RFC2068], along with John Klensin, Jeff
with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen Mogul, Paul Leach, Dave Kristol, Koen Holtman, John Franks, Josh
Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and Cohen, Alex Hopmann, Scott Lawrence, and Larry Masinter for their
Larry Masinter for their help. And thanks go particularly to Jeff help. And thanks go particularly to Jeff Mogul and Scott Lawrence
Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit. for performing the "MUST/MAY/SHOULD" audit.
The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
Frystyk implemented RFC 2068 early, and we wish to thank them for the Frystyk implemented RFC 2068 early, and we wish to thank them for the
discovery of many of the problems that this document attempts to discovery of many of the problems that this document attempts to
rectify. rectify.
16.2. (This Document)
This document has benefited greatly from the comments of all those
participating in the HTTP-WG. In particular, we thank Scott Lawrence
for maintaining the RFC2616 Errata list, and Mark Baker, David Booth,
Adrien de Croy, Martin Duerst, Roy Fielding, Hugo Haas, Bjoern
Hoehrmann, Brian Kell, Jamie Lokier, Paul Marquess, Larry Masinter,
Howard Melman, Alexey Melnikov, Jeff Mogul, Henrik Nordstrom, Joe
Orton, Alex Rousskov, Travis Snoozy and Dan Winship for further
contributions.
17. References 17. References
[1] Alvestrand, H., "Tags for the Identification of Languages", 17.1. Normative References
RFC 1766, March 1995.
[2] Anklesaria, F., McCahill, M., Lindner, P., Johnson, D., Torrey, [ISO-8859-1]
D., and B. Alberti, "The Internet Gopher Protocol (a International Organization for Standardization,
distributed document search and retrieval protocol)", RFC 1436, "Information technology -- 8-bit single-byte coded graphic
March 1993. character sets -- Part 1: Latin alphabet No. 1", ISO/
IEC 8859-1:1998, 1998.
[3] Berners-Lee, T., "Universal Resource Identifiers in WWW: A [RFC1864] Myers, J. and M. Rose, "The Content-MD5 Header Field",
Unifying Syntax for the Expression of Names and Addresses of RFC 1864, October 1995.
Objects on the Network as used in the World-Wide Web",
RFC 1630, June 1994.
[4] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform [RFC1950] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data Format
Resource Locators (URL)", RFC 1738, December 1994. Specification version 3.3", RFC 1950, May 1996.
[5] Berners-Lee, T. and D. Connolly, "Hypertext Markup Language - RFC1950 is an Informational RFC, thus it may be less
2.0", RFC 1866, November 1995. stable than this specification. On the other hand, this
downward reference was present since [RFC2068] (published
in 1997), therefore it is unlikely to cause problems in
practice.
[6] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext [RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification
Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996. version 1.3", RFC 1951, May 1996.
[7] Freed, N. and N. Borenstein, "Multipurpose Internet Mail RFC1951 is an Informational RFC, thus it may be less
Extensions (MIME) Part One: Format of Internet Message Bodies", stable than this specification. On the other hand, this
RFC 2045, November 1996. downward reference was present since [RFC2068] (published
in 1997), therefore it is unlikely to cause problems in
practice.
[8] Braden, R., "Requirements for Internet Hosts - Application and [RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G.
Support", STD 3, RFC 1123, October 1989. Randers-Pehrson, "GZIP file format specification version
4.3", RFC 1952, May 1996.
[9] Crocker, D., "Standard for the format of ARPA Internet text RFC1952 is an Informational RFC, thus it may be less
messages", STD 11, RFC 822, August 1982. stable than this specification. On the other hand, this
downward reference was present since [RFC2068] (published
in 1997), therefore it is unlikely to cause problems in
practice.
[10] Davis, F., Kahle, B., Morris, H., Salem, J., Shen, T., Wang, [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
R., Sui, J., and M. Grinbaum, "WAIS Interface Protocol Extensions (MIME) Part One: Format of Internet Message
Prototype Functional Specification (v1.5)", Thinking Machines Bodies", RFC 2045, November 1996.
Corporation , April 1990.
[11] Fielding, R., "Relative Uniform Resource Locators", RFC 1808, [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
June 1995. Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.
[12] Horton, M. and R. Adams, "Standard for interchange of USENET [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail Extensions)
messages", RFC 1036, December 1987. Part Three: Message Header Extensions for Non-ASCII Text",
RFC 2047, November 1996.
[13] Kantor, B. and P. Lapsley, "Network News Transfer Protocol", [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
RFC 977, February 1986. Requirement Levels", BCP 14, RFC 2119, March 1997.
[14] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part [RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Three: Message Header Extensions for Non-ASCII Text", RFC 2047, Resource Identifiers (URI): Generic Syntax", RFC 2396,
November 1996. August 1998.
[15] Masinter, L. and E. Nebel, "Form-based File Upload in HTML", [RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
RFC 1867, November 1995. Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[16] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821, [RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
August 1982. April 2001.
[17] Postel, J., "Media Type Registration Procedure", RFC 1590, [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
November 1996. Registration Procedures", BCP 13, RFC 4288, December 2005.
[18] Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9, [RFC4646] Phillips, A. and M. Davis, "Tags for Identifying
RFC 959, October 1985. Languages", BCP 47, RFC 4646, September 2006.
[19] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, [RFC822ABNF]
RFC 1700, October 1994. Crocker, D., "Standard for the format of ARPA Internet
text messages", STD 11, RFC 822, August 1982.
[20] Masinter, L. and K. Sollins, "Functional Requirements for [USASCII] American National Standards Institute, "Coded Character
Uniform Resource Names", RFC 1737, December 1994. Set -- 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
[21] American National Standards Institute, "Coded Character Set -- 17.2. Informative References
7-bit American Standard Code for Information Interchange",
ANSI X3.4, 1986.
[22] International Organization for Standardization, "Information [Luo1998] Luotonen, A., "Tunneling TCP based protocols through Web
technology - 8-bit single byte coded graphic - character sets", proxy servers", draft-luotonen-web-proxy-tunneling-01
1987-1990. (work in progress), August 1998.
Part 1: Latin alphabet No. 1, ISO-8859-1:1987. Part 2: Latin [Nie1997] Nielsen, H., Gettys, J., Prud'hommeaux, E., Lie, H., and
alphabet No. 2, ISO-8859-2, 1987. Part 3: Latin alphabet No. C. Lilley, "Network Performance Effects of HTTP/1.1, CSS1,
3, ISO-8859-3, 1988. Part 4: Latin alphabet No. 4, ISO-8859-4, and PNG", Proceedings of ACM SIGCOMM '97, Cannes France ,
1988. Part 5: Latin/Cyrillic alphabet, ISO-8859-5, 1988. Part Sep 1997.
6: Latin/Arabic alphabet, ISO-8859-6, 1987. Part 7: Latin/
Greek alphabet, ISO-8859-7, 1987. Part 8: Latin/Hebrew
alphabet, ISO-8859-8, 1988. Part 9: Latin alphabet No. 5, ISO-
8859-9, 1990.
[23] Myers, J. and M. Rose, "The Content-MD5 Header Field", [Pad1995] Padmanabhan, V. and J. Mogul, "Improving HTTP Latency",
RFC 1864, October 1995. Computer Networks and ISDN Systems v. 28, pp. 25-35,
Dec 1995.
[24] Carpenter, B. and Y. Rekhter, "Renumbering Needs Work", Slightly revised version of paper in Proc. 2nd
RFC 1900, February 1996. International WWW Conference '94: Mosaic and the Web, Oct.
1994, which is available at <http://www.ncsa.uiuc.edu/SDG/
IT94/Proceedings/DDay/mogul/HTTPLatency.html>.
[25] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G. [RFC1123] Braden, R., "Requirements for Internet Hosts - Application
Randers-Pehrson, "GZIP file format specification version 4.3", and Support", STD 3, RFC 1123, October 1989.
RFC 1952, May 1996.
[26] Padmanabhan, V. and J. Mogul, "Improving HTTP Latency", [RFC1305] Mills, D., "Network Time Protocol (Version 3)
Computer Networks and ISDN Systems v. 28, pp. 25-35, Dec 1995. Specification, Implementation", RFC 1305, March 1992.
Slightly revised version of paper in Proc. 2nd International [RFC1436] Anklesaria, F., McCahill, M., Lindner, P., Johnson, D.,
WWW Conference '94: Mosaic and the Web, Oct. 1994, which is Torrey, D., and B. Alberti, "The Internet Gopher Protocol
available at <http://www.ncsa.uiuc.edu/SDG/IT94/Proceedings/ (a distributed document search and retrieval protocol)",
DDay/mogul/HTTPLatency.html>. RFC 1436, March 1993.
[27] Touch, J., Heidemann, J., and K. Obraczka, "Analysis of HTTP [RFC1630] Berners-Lee, T., "Universal Resource Identifiers in WWW: A
Performance", ISI Research Report ISI/RR-98-463 (original Unifying Syntax for the Expression of Names and Addresses
report dated Aug.1996), Aug 1998, of Objects on the Network as used in the World-Wide Web",
<http://www.isi.edu/touch/pubs/http-perf96/>. RFC 1630, June 1994.
[28] Mills, D., "Network Time Protocol (Version 3) Specification, [RFC1737] Masinter, L. and K. Sollins, "Functional Requirements for
Implementation", RFC 1305, March 1992. Uniform Resource Names", RFC 1737, December 1994.
[29] Deutsch, P., "DEFLATE Compressed Data Format Specification [RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
version 1.3", RFC 1951, May 1996. Resource Locators (URL)", RFC 1738, December 1994.
[30] Spero, S., "Analysis of HTTP Performance Problems", [RFC1806] Troost, R. and S. Dorner, "Communicating Presentation
<http://sunsite.unc.edu/mdma-release/http-prob.html>. Information in Internet Messages: The Content-Disposition
Header", RFC 1806, June 1995.
[31] Deutsch, L. and J-L. Gailly, "ZLIB Compressed Data Format [RFC1808] Fielding, R., "Relative Uniform Resource Locators",
Specification version 3.3", RFC 1950, May 1996. RFC 1808, June 1995.
[32] Franks, J., Hallam-Baker, P., Hostetler, J., Leach, P., [RFC1900] Carpenter, B. and Y. Rekhter, "Renumbering Needs Work",
Luotonen, A., Sink, E., and L. Stewart, "An Extension to HTTP : RFC 1900, February 1996.
Digest Access Authentication", RFC 2069, January 1997.
[33] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T. [RFC1945] Berners-Lee, T., Fielding, R., and H. Nielsen, "Hypertext
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
RFC 2068, January 1997.
[34] Bradner, S., "Key words for use in RFCs to Indicate Requirement [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
Levels", BCP 14, RFC 2119, March 1997. 3", BCP 9, RFC 2026, October 1996.
[35] Troost, R. and S. Dorner, "Communicating Presentation [RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Information in Internet Messages: The Content-Disposition Extensions (MIME) Part Five: Conformance Criteria and
Header", RFC 1806, June 1995. Examples", RFC 2049, November 1996.
[36] Mogul, J., Fielding, R., Gettys, J., and H. Nielsen, "Use and [RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
Interpretation of HTTP Version Numbers", RFC 2145, May 1997.
[37] Palme, J., "Common Internet Message Headers", RFC 2076, Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
February 1997. RFC 2068, January 1997.
[38] Yergeau, F., "UTF-8, a transformation format of ISO 10646", [RFC2076] Palme, J., "Common Internet Message Headers", RFC 2076,
RFC 2279, January 1998. February 1997.
[39] Nielsen, H., Gettys, J., Prud'hommeaux, E., Lie, H., and C. [RFC2145] Mogul, J., Fielding, R., Gettys, J., and H. Nielsen, "Use
Lilley, "Network Performance Effects of HTTP/1.1, CSS1, and and Interpretation of HTTP Version Numbers", RFC 2145,
PNG", Proceedings of ACM SIGCOMM '97, Cannes France , Sep 1997. May 1997.
[40] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2183] Troost, R., Dorner, S., and K. Moore, "Communicating
Extensions (MIME) Part Two: Media Types", RFC 2046, Presentation Information in Internet Messages: The
November 1996. Content-Disposition Header Field", RFC 2183, August 1997.
[41] Alvestrand, H., "IETF Policy on Character Sets and Languages", [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
BCP 18, RFC 2277, January 1998. Languages", BCP 18, RFC 2277, January 1998.
[42] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC2324] Masinter, L., "Hyper Text Coffee Pot Control Protocol
Resource Identifiers (URI): Generic Syntax", RFC 2396, (HTCPCP/1.0)", RFC 2324, April 1998.
August 1998.
[43] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., [RFC2388] Masinter, L., "Returning Values from Forms: multipart/
Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication: form-data", RFC 2388, August 1998.
Basic and Digest Access Authentication", RFC 2617, June 1999.
[44] Luotonen, A., "Tunneling TCP based protocols through Web proxy [RFC2557] Palme, F., Hopmann, A., Shelness, N., and E. Stefferud,
servers", Work in Progress. "MIME Encapsulation of Aggregate Documents, such as HTML
(MHTML)", RFC 2557, March 1999.
[45] Palme, J. and A. Hopmann, "MIME E-mail Encapsulation of [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Aggregate Documents, such as HTML (MHTML)", RFC 2110, Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
March 1997. Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[46] Bradner, S., "The Internet Standards Process -- Revision 3", [RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
BCP 9, RFC 2026, October 1996. April 2001.
[47] Masinter, L., "Hyper Text Coffee Pot Control Protocol [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
(HTCPCP/1.0)", RFC 2324, April 1998. 10646", RFC 3629, STD 63, November 2003.
[48] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC3977] Feather, C., "Network News Transfer Protocol (NNTP)",
Extensions (MIME) Part Five: Conformance Criteria and RFC 3977, October 2006.
Examples", RFC 2049, November 1996.
[49] Troost, R., Dorner, S., and K. Moore, "Communicating [RFC822] Crocker, D., "Standard for the format of ARPA Internet
Presentation Information in Internet Messages: The Content- text messages", STD 11, RFC 822, August 1982.
Disposition Header Field", RFC 2183, August 1997.
Appendix A. Appendices [RFC959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
A.1. Internet Media Type message/http and application/http [Spero] Spero, S., "Analysis of HTTP Performance Problems",
<http://sunsite.unc.edu/mdma-release/http-prob.html>.
[Tou1998] Touch, J., Heidemann, J., and K. Obraczka, "Analysis of
HTTP Performance", USC/ISI ISI/RR-98-463, Dec 1998,
<http://www.isi.edu/touch/pubs/http-perf96/>.
(Original report dated Aug. 1996)
[WAIS] Davis, F., Kahle, B., Morris, H., Salem, J., Shen, T.,
Wang, R., Sui, J., and M. Grinbaum, "WAIS Interface
Protocol Prototype Functional Specification (v1.5)",
Thinking Machines Corporation , April 1990.
URIs
[1] <mailto:ietf-http-wg@w3.org>
[2] <mailto:ietf-http-wg-request@w3.org?subject=subscribe>
[3] <http://tools.ietf.org/html/draft-lafon-rfc2616bis-01>
Appendix A. Internet Media Type message/http and application/http
In addition to defining the HTTP/1.1 protocol, this document serves In addition to defining the HTTP/1.1 protocol, this document serves
as the specification for the Internet media type "message/http" and as the specification for the Internet media type "message/http" and
"application/http". The message/http type can be used to enclose a "application/http". The message/http type can be used to enclose a
single HTTP request or response message, provided that it obeys the single HTTP request or response message, provided that it obeys the
MIME restrictions for all "message" types regarding line length and MIME restrictions for all "message" types regarding line length and
encodings. The application/http type can be used to enclose a encodings. The application/http type can be used to enclose a
pipeline of one or more HTTP request or response messages (not pipeline of one or more HTTP request or response messages (not
intermixed). The following is to be registered with IANA [17]. intermixed). The following is to be registered with IANA [RFC4288].
Media Type name: message Type name: message
Media subtype name: http Subtype name: http
Required parameters: none Required parameters: none
Optional parameters: version, msgtype Optional parameters: version, msgtype
version: The HTTP-Version number of the enclosed message (e.g., version: The HTTP-Version number of the enclosed message (e.g.,
"1.1"). If not present, the version can be determined from the "1.1"). If not present, the version can be determined from the
first line of the body. first line of the body.
msgtype: The message type -- "request" or "response". If not msgtype: The message type -- "request" or "response". If not
present, the type can be determined from the first line of the present, the type can be determined from the first line of the
body. body.
Encoding considerations: only "7bit", "8bit", or "binary" are Encoding considerations: only "7bit", "8bit", or "binary" are
permitted permitted
Security considerations: none Security considerations: none
Media Type name: application Interoperability considerations: none
Media subtype name: http Published specification: This specification (see Appendix A).
Applications that use this media type:
Additional information:
Magic number(s): none
File extension(s): none
Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IESG
Type name: application
Subtype name: http
Required parameters: none Required parameters: none
Optional parameters: version, msgtype Optional parameters: version, msgtype
version: The HTTP-Version number of the enclosed messages (e.g., version: The HTTP-Version number of the enclosed messages (e.g.,
"1.1"). If not present, the version can be determined from the "1.1"). If not present, the version can be determined from the
first line of the body. first line of the body.
msgtype: The message type -- "request" or "response". If not msgtype: The message type -- "request" or "response". If not
present, the type can be determined from the first line of the present, the type can be determined from the first line of the
body. body.
Encoding considerations: HTTP messages enclosed by this type are in Encoding considerations: HTTP messages enclosed by this type are in
"binary" format; use of an appropriate Content-Transfer-Encoding "binary" format; use of an appropriate Content-Transfer-Encoding
is required when transmitted via E-mail. is required when transmitted via E-mail.
Security considerations: none Security considerations: none
A.2. Internet Media Type multipart/byteranges Interoperability considerations: none
Published specification: This specification (see Appendix A).
Applications that use this media type:
Additional information:
Magic number(s): none
File extension(s): none
Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IESG
Appendix B. Internet Media Type multipart/byteranges
When an HTTP 206 (Partial Content) response message includes the When an HTTP 206 (Partial Content) response message includes the
content of multiple ranges (a response to a request for multiple non- content of multiple ranges (a response to a request for multiple non-
overlapping ranges), these are transmitted as a multipart message- overlapping ranges), these are transmitted as a multipart message-
body. The media type for this purpose is called "multipart/ body. The media type for this purpose is called "multipart/
byteranges". byteranges".
The multipart/byteranges media type includes two or more parts, each The multipart/byteranges media type includes two or more parts, each
with its own Content-Type and Content-Range fields. The required with its own Content-Type and Content-Range fields. The required
boundary parameter specifies the boundary string used to separate boundary parameter specifies the boundary string used to separate
each body-part. each body-part.
Media Type name: multipart Type name: multipart
Media subtype name: byteranges Subtype name: byteranges
Required parameters: boundary Required parameters: boundary
Optional parameters: none Optional parameters: none
Encoding considerations: only "7bit", "8bit", or "binary" are Encoding considerations: only "7bit", "8bit", or "binary" are
permitted permitted
Security considerations: none Security considerations: none
Interoperability considerations: none
Published specification: This specification (see Appendix B).
Applications that use this media type:
Additional information:
Magic number(s): none
File extension(s): none
Macintosh file type code(s): none
Person and email address to contact for further information: See
Authors Section.
Intended usage: COMMON
Restrictions on usage: none
Author/Change controller: IESG
For example: For example:
HTTP/1.1 206 Partial Content HTTP/1.1 206 Partial Content
Date: Wed, 15 Nov 1995 06:25:24 GMT Date: Wed, 15 Nov 1995 06:25:24 GMT
Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
--THIS_STRING_SEPARATES --THIS_STRING_SEPARATES
Content-type: application/pdf Content-type: application/pdf
Content-range: bytes 500-999/8000 Content-range: bytes 500-999/8000
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Content-range: bytes 7000-7999/8000 Content-range: bytes 7000-7999/8000
...the second range ...the second range
--THIS_STRING_SEPARATES-- --THIS_STRING_SEPARATES--
Notes: Notes:
1. Additional CRLFs may precede the first boundary string in the 1. Additional CRLFs may precede the first boundary string in the
entity. entity.
2. Although RFC 2046 [40] permits the boundary string to be quoted, 2. Although [RFC2046] permits the boundary string to be quoted, some
some existing implementations handle a quoted boundary string existing implementations handle a quoted boundary string
incorrectly. incorrectly.
3. A number of browsers and servers were coded to an early draft of 3. A number of browsers and servers were coded to an early draft of
the byteranges specification to use a media type of multipart/ the byteranges specification to use a media type of multipart/
x-byteranges, which is almost, but not quite compatible with the x-byteranges, which is almost, but not quite compatible with the
version documented in HTTP/1.1. version documented in HTTP/1.1.
A.3. Tolerant Applications Appendix C. Tolerant Applications
Although this document specifies the requirements for the generation Although this document specifies the requirements for the generation
of HTTP/1.1 messages, not all applications will be correct in their of HTTP/1.1 messages, not all applications will be correct in their
implementation. We therefore recommend that operational applications implementation. We therefore recommend that operational applications
be tolerant of deviations whenever those deviations can be be tolerant of deviations whenever those deviations can be
interpreted unambiguously. interpreted unambiguously.
Clients SHOULD be tolerant in parsing the Status-Line and servers Clients SHOULD be tolerant in parsing the Status-Line and servers
tolerant when parsing the Request-Line. In particular, they SHOULD tolerant when parsing the Request-Line. In particular, they SHOULD
accept any amount of SP or HT characters between fields, even though accept any amount of SP or HT characters between fields, even though
only a single SP is required. only a single SP is required.
The line terminator for message-header fields is the sequence CRLF. The line terminator for message-header fields is the sequence CRLF.
However, we recommend that applications, when parsing such headers, However, we recommend that applications, when parsing such headers,
recognize a single LF as a line terminator and ignore the leading CR. recognize a single LF as a line terminator and ignore the leading CR.
The character set of an entity-body SHOULD be labeled as the lowest The character set of an entity-body SHOULD be labeled as the lowest
common denominator of the character codes used within that body, with common denominator of the character codes used within that body, with
the exception that not labeling the entity is preferred over labeling the exception that not labeling the entity is preferred over labeling
the entity with the labels US-ASCII or ISO-8859-1. See section 3.7.1 the entity with the labels US-ASCII or ISO-8859-1. See Section 3.7.1
and 3.4.1. and 3.4.1.
Additional rules for requirements on parsing and encoding of dates Additional rules for requirements on parsing and encoding of dates
and other potential problems with date encodings include: and other potential problems with date encodings include:
o HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date o HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
which appears to be more than 50 years in the future is in fact in which appears to be more than 50 years in the future is in fact in
the past (this helps solve the "year 2000" problem). the past (this helps solve the "year 2000" problem).
o An HTTP/1.1 implementation MAY internally represent a parsed o An HTTP/1.1 implementation MAY internally represent a parsed
skipping to change at page 173, line 32 skipping to change at page 183, line 5
proper value. proper value.
o All expiration-related calculations MUST be done in GMT. The o All expiration-related calculations MUST be done in GMT. The
local time zone MUST NOT influence the calculation or comparison local time zone MUST NOT influence the calculation or comparison
of an age or expiration time. of an age or expiration time.
o If an HTTP header incorrectly carries a date value with a time o If an HTTP header incorrectly carries a date value with a time
zone other than GMT, it MUST be converted into GMT using the most zone other than GMT, it MUST be converted into GMT using the most
conservative possible conversion. conservative possible conversion.
A.4. Differences Between HTTP Entities and RFC 2045 Entities Appendix D. Differences Between HTTP Entities and RFC 2045 Entities
HTTP/1.1 uses many of the constructs defined for Internet Mail (RFC HTTP/1.1 uses many of the constructs defined for Internet Mail
822 [9]) and the Multipurpose Internet Mail Extensions (MIME [7]) to ([RFC2822]) and the Multipurpose Internet Mail Extensions (MIME
allow entities to be transmitted in an open variety of [RFC2045]) to allow entities to be transmitted in an open variety of
representations and with extensible mechanisms. However, RFC 2045 representations and with extensible mechanisms. However, RFC 2045
discusses mail, and HTTP has a few features that are different from discusses mail, and HTTP has a few features that are different from
those described in RFC 2045. These differences were carefully chosen those described in RFC 2045. These differences were carefully chosen
to optimize performance over binary connections, to allow greater to optimize performance over binary connections, to allow greater
freedom in the use of new media types, to make date comparisons freedom in the use of new media types, to make date comparisons
easier, and to acknowledge the practice of some early HTTP servers easier, and to acknowledge the practice of some early HTTP servers
and clients. and clients.
This appendix describes specific areas where HTTP differs from RFC This appendix describes specific areas where HTTP differs from RFC
2045. Proxies and gateways to strict MIME environments SHOULD be 2045. Proxies and gateways to strict MIME environments SHOULD be
aware of these differences and provide the appropriate conversions aware of these differences and provide the appropriate conversions
where necessary. Proxies and gateways from MIME environments to HTTP where necessary. Proxies and gateways from MIME environments to HTTP
also need to be aware of the differences because some conversions also need to be aware of the differences because some conversions
might be required. might be required.
A.4.1. MIME-Version D.1. MIME-Version
HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages
MAY include a single MIME-Version general-header field to indicate MAY include a single MIME-Version general-header field to indicate
what version of the MIME protocol was used to construct the message. what version of the MIME protocol was used to construct the message.
Use of the MIME-Version header field indicates that the message is in Use of the MIME-Version header field indicates that the message is in
full compliance with the MIME protocol (as defined in RFC 2045[7]). full compliance with the MIME protocol (as defined in [RFC2045]).
Proxies/gateways are responsible for ensuring full compliance (where Proxies/gateways are responsible for ensuring full compliance (where
possible) when exporting HTTP messages to strict MIME environments. possible) when exporting HTTP messages to strict MIME environments.
MIME-Version = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT MIME-Version = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
MIME version "1.0" is the default for use in HTTP/1.1. However, MIME version "1.0" is the default for use in HTTP/1.1. However,
HTTP/1.1 message parsing and semantics are defined by this document HTTP/1.1 message parsing and semantics are defined by this document
and not the MIME specification. and not the MIME specification.
A.4.2. Conversion to Canonical Form D.2. Conversion to Canonical Form
RFC 2045 [7] requires that an Internet mail entity be converted to [RFC2045] requires that an Internet mail entity be converted to
canonical form prior to being transferred, as described in section 4 canonical form prior to being transferred, as described in Section 4
of