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/labs/webarch/trunk/http/draft-fielding-http/orig/
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--- labs/webarch/trunk/http/draft-fielding-http/orig/rfc2616.txt (added)
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+
+
+
+
+
+
+Network Working Group R. Fielding
+Request for Comments: 2616 UC Irvine
+Obsoletes: 2068 J. Gettys
+Category: Standards Track Compaq/W3C
+ J. Mogul
+ Compaq
+ H. Frystyk
+ W3C/MIT
+ L. Masinter
+ Xerox
+ P. Leach
+ Microsoft
+ T. Berners-Lee
+ W3C/MIT
+ June 1999
+
+
+ Hypertext Transfer Protocol -- HTTP/1.1
+
+Status of this Memo
+
+ This document specifies an Internet standards track protocol for the
+ Internet community, and requests discussion and suggestions for
+ improvements. Please refer to the current edition of the "Internet
+ Official Protocol Standards" (STD 1) for the standardization state
+ and status of this protocol. Distribution of this memo is unlimited.
+
+Copyright Notice
+
+ Copyright (C) The Internet Society (1999). All Rights Reserved.
+
+Abstract
+
+ The Hypertext Transfer Protocol (HTTP) is an application-level
+ protocol for distributed, collaborative, hypermedia information
+ systems. It is a generic, stateless, protocol which can be used for
+ many tasks beyond its use for hypertext, such as name servers and
+ distributed object management systems, through extension of its
+ request methods, error codes and headers [47]. A feature of HTTP is
+ the typing and negotiation of data representation, allowing systems
+ to be built independently of the data being transferred.
+
+ HTTP has been in use by the World-Wide Web global information
+ initiative since 1990. This specification defines the protocol
+ referred to as "HTTP/1.1", and is an update to RFC 2068 [33].
+
+
+
+
+
+
+Fielding, et al. Standards Track [Page 1]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+Table of Contents
+
+ 1 Introduction ...................................................7
+ 1.1 Purpose......................................................7
+ 1.2 Requirements .................................................8
+ 1.3 Terminology ..................................................8
+ 1.4 Overall Operation ...........................................12
+ 2 Notational Conventions and Generic Grammar ....................14
+ 2.1 Augmented BNF ...............................................14
+ 2.2 Basic Rules .................................................15
+ 3 Protocol Parameters ...........................................17
+ 3.1 HTTP Version ................................................17
+ 3.2 Uniform Resource Identifiers ................................18
+ 3.2.1 General Syntax ...........................................19
+ 3.2.2 http URL .................................................19
+ 3.2.3 URI Comparison ...........................................20
+ 3.3 Date/Time Formats ...........................................20
+ 3.3.1 Full Date ................................................20
+ 3.3.2 Delta Seconds ............................................21
+ 3.4 Character Sets ..............................................21
+ 3.4.1 Missing Charset ..........................................22
+ 3.5 Content Codings .............................................23
+ 3.6 Transfer Codings ............................................24
+ 3.6.1 Chunked Transfer Coding ..................................25
+ 3.7 Media Types .................................................26
+ 3.7.1 Canonicalization and Text Defaults .......................27
+ 3.7.2 Multipart Types ..........................................27
+ 3.8 Product Tokens ..............................................28
+ 3.9 Quality Values ..............................................29
+ 3.10 Language Tags ...............................................29
+ 3.11 Entity Tags .................................................30
+ 3.12 Range Units .................................................30
+ 4 HTTP Message ..................................................31
+ 4.1 Message Types ...............................................31
+ 4.2 Message Headers .............................................31
+ 4.3 Message Body ................................................32
+ 4.4 Message Length ..............................................33
+ 4.5 General Header Fields .......................................34
+ 5 Request .......................................................35
+ 5.1 Request-Line ................................................35
+ 5.1.1 Method ...................................................36
+ 5.1.2 Request-URI ..............................................36
+ 5.2 The Resource Identified by a Request ........................38
+ 5.3 Request Header Fields .......................................38
+ 6 Response ......................................................39
+ 6.1 Status-Line .................................................39
+ 6.1.1 Status Code and Reason Phrase ............................39
+ 6.2 Response Header Fields ......................................41
+
+
+
+Fielding, et al. Standards Track [Page 2]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ 7 Entity ........................................................42
+ 7.1 Entity Header Fields ........................................42
+ 7.2 Entity Body .................................................43
+ 7.2.1 Type .....................................................43
+ 7.2.2 Entity Length ............................................43
+ 8 Connections ...................................................44
+ 8.1 Persistent Connections ......................................44
+ 8.1.1 Purpose ..................................................44
+ 8.1.2 Overall Operation ........................................45
+ 8.1.3 Proxy Servers ............................................46
+ 8.1.4 Practical Considerations .................................46
+ 8.2 Message Transmission Requirements ...........................47
+ 8.2.1 Persistent Connections and Flow Control ..................47
+ 8.2.2 Monitoring Connections for Error Status Messages .........48
+ 8.2.3 Use of the 100 (Continue) Status .........................48
+ 8.2.4 Client Behavior if Server Prematurely Closes Connection ..50
+ 9 Method Definitions ............................................51
+ 9.1 Safe and Idempotent Methods .................................51
+ 9.1.1 Safe Methods .............................................51
+ 9.1.2 Idempotent Methods .......................................51
+ 9.2 OPTIONS .....................................................52
+ 9.3 GET .........................................................53
+ 9.4 HEAD ........................................................54
+ 9.5 POST ........................................................54
+ 9.6 PUT .........................................................55
+ 9.7 DELETE ......................................................56
+ 9.8 TRACE .......................................................56
+ 9.9 CONNECT .....................................................57
+ 10 Status Code Definitions ......................................57
+ 10.1 Informational 1xx ...........................................57
+ 10.1.1 100 Continue .............................................58
+ 10.1.2 101 Switching Protocols ..................................58
+ 10.2 Successful 2xx ..............................................58
+ 10.2.1 200 OK ...................................................58
+ 10.2.2 201 Created ..............................................59
+ 10.2.3 202 Accepted .............................................59
+ 10.2.4 203 Non-Authoritative Information ........................59
+ 10.2.5 204 No Content ...........................................60
+ 10.2.6 205 Reset Content ........................................60
+ 10.2.7 206 Partial Content ......................................60
+ 10.3 Redirection 3xx .............................................61
+ 10.3.1 300 Multiple Choices .....................................61
+ 10.3.2 301 Moved Permanently ....................................62
+ 10.3.3 302 Found ................................................62
+ 10.3.4 303 See Other ............................................63
+ 10.3.5 304 Not Modified .........................................63
+ 10.3.6 305 Use Proxy ............................................64
+ 10.3.7 306 (Unused) .............................................64
+
+
+
+Fielding, et al. Standards Track [Page 3]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ 10.3.8 307 Temporary Redirect ...................................65
+ 10.4 Client Error 4xx ............................................65
+ 10.4.1 400 Bad Request .........................................65
+ 10.4.2 401 Unauthorized ........................................66
+ 10.4.3 402 Payment Required ....................................66
+ 10.4.4 403 Forbidden ...........................................66
+ 10.4.5 404 Not Found ...........................................66
+ 10.4.6 405 Method Not Allowed ..................................66
+ 10.4.7 406 Not Acceptable ......................................67
+ 10.4.8 407 Proxy Authentication Required .......................67
+ 10.4.9 408 Request Timeout .....................................67
+ 10.4.10 409 Conflict ............................................67
+ 10.4.11 410 Gone ................................................68
+ 10.4.12 411 Length Required .....................................68
+ 10.4.13 412 Precondition Failed .................................68
+ 10.4.14 413 Request Entity Too Large ............................69
+ 10.4.15 414 Request-URI Too Long ................................69
+ 10.4.16 415 Unsupported Media Type ..............................69
+ 10.4.17 416 Requested Range Not Satisfiable .....................69
+ 10.4.18 417 Expectation Failed ..................................70
+ 10.5 Server Error 5xx ............................................70
+ 10.5.1 500 Internal Server Error ................................70
+ 10.5.2 501 Not Implemented ......................................70
+ 10.5.3 502 Bad Gateway ..........................................70
+ 10.5.4 503 Service Unavailable ..................................70
+ 10.5.5 504 Gateway Timeout ......................................71
+ 10.5.6 505 HTTP Version Not Supported ...........................71
+ 11 Access Authentication ........................................71
+ 12 Content Negotiation ..........................................71
+ 12.1 Server-driven Negotiation ...................................72
+ 12.2 Agent-driven Negotiation ....................................73
+ 12.3 Transparent Negotiation .....................................74
+ 13 Caching in HTTP ..............................................74
+ 13.1.1 Cache Correctness ........................................75
+ 13.1.2 Warnings .................................................76
+ 13.1.3 Cache-control Mechanisms .................................77
+ 13.1.4 Explicit User Agent Warnings .............................78
+ 13.1.5 Exceptions to the Rules and Warnings .....................78
+ 13.1.6 Client-controlled Behavior ...............................79
+ 13.2 Expiration Model ............................................79
+ 13.2.1 Server-Specified Expiration ..............................79
+ 13.2.2 Heuristic Expiration .....................................80
+ 13.2.3 Age Calculations .........................................80
+ 13.2.4 Expiration Calculations ..................................83
+ 13.2.5 Disambiguating Expiration Values .........................84
+ 13.2.6 Disambiguating Multiple Responses ........................84
+ 13.3 Validation Model ............................................85
+ 13.3.1 Last-Modified Dates ......................................86
+
+
+
+Fielding, et al. Standards Track [Page 4]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ 13.3.2 Entity Tag Cache Validators ..............................86
+ 13.3.3 Weak and Strong Validators ...............................86
+ 13.3.4 Rules for When to Use Entity Tags and Last-Modified Dates.89
+ 13.3.5 Non-validating Conditionals ..............................90
+ 13.4 Response Cacheability .......................................91
+ 13.5 Constructing Responses From Caches ..........................92
+ 13.5.1 End-to-end and Hop-by-hop Headers ........................92
+ 13.5.2 Non-modifiable Headers ...................................92
+ 13.5.3 Combining Headers ........................................94
+ 13.5.4 Combining Byte Ranges ....................................95
+ 13.6 Caching Negotiated Responses ................................95
+ 13.7 Shared and Non-Shared Caches ................................96
+ 13.8 Errors or Incomplete Response Cache Behavior ................97
+ 13.9 Side Effects of GET and HEAD ................................97
+ 13.10 Invalidation After Updates or Deletions ...................97
+ 13.11 Write-Through Mandatory ...................................98
+ 13.12 Cache Replacement .........................................99
+ 13.13 History Lists .............................................99
+ 14 Header Field Definitions ....................................100
+ 14.1 Accept .....................................................100
+ 14.2 Accept-Charset .............................................102
+ 14.3 Accept-Encoding ............................................102
+ 14.4 Accept-Language ............................................104
+ 14.5 Accept-Ranges ..............................................105
+ 14.6 Age ........................................................106
+ 14.7 Allow ......................................................106
+ 14.8 Authorization ..............................................107
+ 14.9 Cache-Control ..............................................108
+ 14.9.1 What is Cacheable .......................................109
+ 14.9.2 What May be Stored by Caches ............................110
+ 14.9.3 Modifications of the Basic Expiration Mechanism .........111
+ 14.9.4 Cache Revalidation and Reload Controls ..................113
+ 14.9.5 No-Transform Directive ..................................115
+ 14.9.6 Cache Control Extensions ................................116
+ 14.10 Connection ...............................................117
+ 14.11 Content-Encoding .........................................118
+ 14.12 Content-Language .........................................118
+ 14.13 Content-Length ...........................................119
+ 14.14 Content-Location .........................................120
+ 14.15 Content-MD5 ..............................................121
+ 14.16 Content-Range ............................................122
+ 14.17 Content-Type .............................................124
+ 14.18 Date .....................................................124
+ 14.18.1 Clockless Origin Server Operation ......................125
+ 14.19 ETag .....................................................126
+ 14.20 Expect ...................................................126
+ 14.21 Expires ..................................................127
+ 14.22 From .....................................................128
+
+
+
+Fielding, et al. Standards Track [Page 5]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ 14.23 Host .....................................................128
+ 14.24 If-Match .................................................129
+ 14.25 If-Modified-Since ........................................130
+ 14.26 If-None-Match ............................................132
+ 14.27 If-Range .................................................133
+ 14.28 If-Unmodified-Since ......................................134
+ 14.29 Last-Modified ............................................134
+ 14.30 Location .................................................135
+ 14.31 Max-Forwards .............................................136
+ 14.32 Pragma ...................................................136
+ 14.33 Proxy-Authenticate .......................................137
+ 14.34 Proxy-Authorization ......................................137
+ 14.35 Range ....................................................138
+ 14.35.1 Byte Ranges ...........................................138
+ 14.35.2 Range Retrieval Requests ..............................139
+ 14.36 Referer ..................................................140
+ 14.37 Retry-After ..............................................141
+ 14.38 Server ...................................................141
+ 14.39 TE .......................................................142
+ 14.40 Trailer ..................................................143
+ 14.41 Transfer-Encoding..........................................143
+ 14.42 Upgrade ..................................................144
+ 14.43 User-Agent ...............................................145
+ 14.44 Vary .....................................................145
+ 14.45 Via ......................................................146
+ 14.46 Warning ..................................................148
+ 14.47 WWW-Authenticate .........................................150
+ 15 Security Considerations .......................................150
+ 15.1 Personal Information....................................151
+ 15.1.1 Abuse of Server Log Information .........................151
+ 15.1.2 Transfer of Sensitive Information .......................151
+ 15.1.3 Encoding Sensitive Information in URI's .................152
+ 15.1.4 Privacy Issues Connected to Accept Headers ..............152
+ 15.2 Attacks Based On File and Path Names .......................153
+ 15.3 DNS Spoofing ...............................................154
+ 15.4 Location Headers and Spoofing ..............................154
+ 15.5 Content-Disposition Issues .................................154
+ 15.6 Authentication Credentials and Idle Clients ................155
+ 15.7 Proxies and Caching ........................................155
+ 15.7.1 Denial of Service Attacks on Proxies....................156
+ 16 Acknowledgments .............................................156
+ 17 References ..................................................158
+ 18 Authors' Addresses ..........................................162
+ 19 Appendices ..................................................164
+ 19.1 Internet Media Type message/http and application/http ......164
+ 19.2 Internet Media Type multipart/byteranges ...................165
+ 19.3 Tolerant Applications ......................................166
+ 19.4 Differences Between HTTP Entities and RFC 2045 Entities ....167
+
+
+
+Fielding, et al. Standards Track [Page 6]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ 19.4.1 MIME-Version ............................................167
+ 19.4.2 Conversion to Canonical Form ............................167
+ 19.4.3 Conversion of Date Formats ..............................168
+ 19.4.4 Introduction of Content-Encoding ........................168
+ 19.4.5 No Content-Transfer-Encoding ............................168
+ 19.4.6 Introduction of Transfer-Encoding .......................169
+ 19.4.7 MHTML and Line Length Limitations .......................169
+ 19.5 Additional Features ........................................169
+ 19.5.1 Content-Disposition .....................................170
+ 19.6 Compatibility with Previous Versions .......................170
+ 19.6.1 Changes from HTTP/1.0 ...................................171
+ 19.6.2 Compatibility with HTTP/1.0 Persistent Connections ......172
+ 19.6.3 Changes from RFC 2068 ...................................172
+ 20 Index .......................................................175
+ 21 Full Copyright Statement ....................................176
+
+1 Introduction
+
+1.1 Purpose
+
+ The Hypertext Transfer Protocol (HTTP) is an application-level
+ protocol for distributed, collaborative, hypermedia information
+ systems. HTTP has been in use by the World-Wide Web global
+ information initiative since 1990. The first version of HTTP,
+ 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
+ the protocol by allowing messages to be in the format of MIME-like
+ messages, containing metainformation about the data transferred and
+ modifiers on the request/response semantics. However, HTTP/1.0 does
+ not sufficiently take into consideration the effects of hierarchical
+ proxies, caching, the need for persistent connections, or virtual
+ hosts. In addition, the proliferation of incompletely-implemented
+ applications calling themselves "HTTP/1.0" has necessitated a
+ protocol version change in order for two communicating applications
+ to determine each other's true capabilities.
+
+ This specification defines the protocol referred to as "HTTP/1.1".
+ This protocol includes more stringent requirements than HTTP/1.0 in
+ order to ensure reliable implementation of its features.
+
+ Practical information systems require more functionality than simple
+ retrieval, including search, front-end update, and annotation. HTTP
+ allows an open-ended set of methods and headers that indicate the
+ purpose of a request [47]. It builds on the discipline of reference
+ provided by the Uniform Resource Identifier (URI) [3], as a location
+ (URL) [4] or name (URN) [20], for indicating the resource to which a
+
+
+
+
+
+Fielding, et al. Standards Track [Page 7]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ method is to be applied. Messages are passed in a format similar to
+ that used by Internet mail [9] as defined by the Multipurpose
+ Internet Mail Extensions (MIME) [7].
+
+ HTTP is also used as a generic protocol for communication between
+ user agents and proxies/gateways to other Internet systems, including
+ those supported by the SMTP [16], NNTP [13], FTP [18], Gopher [2],
+ and WAIS [10] protocols. In this way, HTTP allows basic hypermedia
+ access to resources available from diverse applications.
+
+1.2 Requirements
+
+ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+ "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
+ document are to be interpreted as described in RFC 2119 [34].
+
+ An implementation is not compliant if it fails to satisfy one or more
+ of the MUST or REQUIRED level requirements for the protocols it
+ implements. An implementation that satisfies all the MUST or REQUIRED
+ level and all the SHOULD level requirements for its protocols is said
+ to be "unconditionally compliant"; one that satisfies all the MUST
+ level requirements but not all the SHOULD level requirements for its
+ protocols is said to be "conditionally compliant."
+
+1.3 Terminology
+
+ This specification uses a number of terms to refer to the roles
+ played by participants in, and objects of, the HTTP communication.
+
+ connection
+ A transport layer virtual circuit established between two programs
+ for the purpose of communication.
+
+ message
+ The basic unit of HTTP communication, consisting of a structured
+ sequence of octets matching the syntax defined in section 4 and
+ transmitted via the connection.
+
+ request
+ An HTTP request message, as defined in section 5.
+
+ response
+ An HTTP response message, as defined in section 6.
+
+
+
+
+
+
+
+
+Fielding, et al. Standards Track [Page 8]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ resource
+ A network data object or service that can be identified by a URI,
+ as defined in section 3.2. Resources may be available in multiple
+ representations (e.g. multiple languages, data formats, size, and
+ resolutions) or vary in other ways.
+
+ entity
+ The information transferred as the payload of a request or
+ response. An entity consists of metainformation in the form of
+ entity-header fields and content in the form of an entity-body, as
+ described in section 7.
+
+ representation
+ An entity included with a response that is subject to content
+ negotiation, as described in section 12. There may exist multiple
+ representations associated with a particular response status.
+
+ content negotiation
+ The mechanism for selecting the appropriate representation when
+ servicing a request, as described in section 12. The
+ representation of entities in any response can be negotiated
+ (including error responses).
+
+ variant
+ A resource may have one, or more than one, representation(s)
+ associated with it at any given instant. Each of these
+ representations is termed a `varriant'. Use of the term `variant'
+ does not necessarily imply that the resource is subject to content
+ negotiation.
+
+ client
+ A program that establishes connections for the purpose of sending
+ requests.
+
+ user agent
+ The client which initiates a request. These are often browsers,
+ editors, spiders (web-traversing robots), or other end user tools.
+
+ server
+ An application program that accepts connections in order to
+ service requests by sending back responses. Any given program may
+ be capable of being both a client and a server; our use of these
+ terms refers only to the role being performed by the program for a
+ particular connection, rather than to the program's capabilities
+ in general. Likewise, any server may act as an origin server,
+ proxy, gateway, or tunnel, switching behavior based on the nature
+ of each request.
+
+
+
+
+Fielding, et al. Standards Track [Page 9]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ origin server
+ The server on which a given resource resides or is to be created.
+
+ proxy
+ An intermediary program which acts as both a server and a client
+ for the purpose of making requests on behalf of other clients.
+ Requests are serviced internally or by passing them on, with
+ possible translation, to other servers. A proxy MUST implement
+ both the client and server requirements of this specification. A
+ "transparent proxy" is a proxy that does not modify the request or
+ response beyond what is required for proxy authentication and
+ identification. A "non-transparent proxy" is a proxy that modifies
+ the request or response in order to provide some added service to
+ the user agent, such as group annotation services, media type
+ transformation, protocol reduction, or anonymity filtering. Except
+ where either transparent or non-transparent behavior is explicitly
+ stated, the HTTP proxy requirements apply to both types of
+ proxies.
+
+ gateway
+ A server which acts as an intermediary for some other server.
+ Unlike a proxy, a gateway receives requests as if it were the
+ origin server for the requested resource; the requesting client
+ may not be aware that it is communicating with a gateway.
+
+ tunnel
+ An intermediary program which is acting as a blind relay between
+ two connections. Once active, a tunnel is not considered a party
+ to the HTTP communication, though the tunnel may have been
+ initiated by an HTTP request. The tunnel ceases to exist when both
+ ends of the relayed connections are closed.
+
+ cache
+ A program's local store of response messages and the subsystem
+ that controls its message storage, retrieval, and deletion. A
+ cache stores cacheable responses in order to reduce the response
+ time and network bandwidth consumption on future, equivalent
+ requests. Any client or server may include a cache, though a cache
+ cannot be used by a server that is acting as a tunnel.
+
+ cacheable
+ A response is cacheable if a cache is allowed to store a copy of
+ the response message for use in answering subsequent requests. The
+ rules for determining the cacheability of HTTP responses are
+ defined in section 13. Even if a resource is cacheable, there may
+ be additional constraints on whether a cache can use the cached
+ copy for a particular request.
+
+
+
+
+Fielding, et al. Standards Track [Page 10]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ first-hand
+ A response is first-hand if it comes directly and without
+ unnecessary delay from the origin server, perhaps via one or more
+ proxies. A response is also first-hand if its validity has just
+ been checked directly with the origin server.
+
+ explicit expiration time
+ The time at which the origin server intends that an entity should
+ no longer be returned by a cache without further validation.
+
+ heuristic expiration time
+ An expiration time assigned by a cache when no explicit expiration
+ time is available.
+
+ age
+ The age of a response is the time since it was sent by, or
+ successfully validated with, the origin server.
+
+ freshness lifetime
+ The length of time between the generation of a response and its
+ expiration time.
+
+ fresh
+ A response is fresh if its age has not yet exceeded its freshness
+ lifetime.
+
+ stale
+ A response is stale if its age has passed its freshness lifetime.
+
+ semantically transparent
+ A cache behaves in a "semantically transparent" manner, with
+ respect to a particular response, when its use affects neither the
+ requesting client nor the origin server, except to improve
+ performance. When a cache is semantically transparent, the client
+ receives exactly the same response (except for hop-by-hop headers)
+ that it would have received had its request been handled directly
+ by the origin server.
+
+ validator
+ A protocol element (e.g., an entity tag or a Last-Modified time)
+ that is used to find out whether a cache entry is an equivalent
+ copy of an entity.
+
+ upstream/downstream
+ Upstream and downstream describe the flow of a message: all
+ messages flow from upstream to downstream.
+
+
+
+
+
+Fielding, et al. Standards Track [Page 11]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ inbound/outbound
+ Inbound and outbound refer to the request and response paths for
+ messages: "inbound" means "traveling toward the origin server",
+ and "outbound" means "traveling toward the user agent"
+
+1.4 Overall Operation
+
+ 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
+ protocol version, followed by a MIME-like message containing request
+ modifiers, client information, and possible body content over a
+ connection with a server. The server responds with a status line,
+ including the message's protocol version and a success or error code,
+ followed by a MIME-like message containing server information, entity
+ metainformation, and possible entity-body content. The relationship
+ between HTTP and MIME is described in appendix 19.4.
+
+ 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
+ simplest case, this may be accomplished via a single connection (v)
+ between the user agent (UA) and the origin server (O).
+
+ request chain ------------------------>
+ UA -------------------v------------------- O
+ <----------------------- response chain
+
+ A more complicated situation occurs when one or more intermediaries
+ are present in the request/response chain. There are three common
+ forms of intermediary: proxy, gateway, and tunnel. A proxy is a
+ forwarding agent, receiving requests for a URI in its absolute form,
+ rewriting all or part of the message, and forwarding the reformatted
+ request toward the server identified by the URI. A gateway is a
+ receiving agent, acting as a layer above some other server(s) and, if
+ necessary, translating the requests to the underlying server's
+ protocol. A tunnel acts as a relay point between two connections
+ without changing the messages; tunnels are used when the
+ communication needs to pass through an intermediary (such as a
+ firewall) even when the intermediary cannot understand the contents
+ of the messages.
+
+ request chain -------------------------------------->
+ UA -----v----- A -----v----- B -----v----- C -----v----- O
+ <------------------------------------- response chain
+
+ The figure above shows three intermediaries (A, B, and C) between the
+ user agent and origin server. A request or response message that
+ travels the whole chain will pass through four separate connections.
+ This distinction is important because some HTTP communication options
+
+
+
+Fielding, et al. Standards Track [Page 12]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ may apply only to the connection with the nearest, non-tunnel
+ neighbor, only to the end-points of the chain, or to all connections
+ along the chain. Although the diagram is linear, each participant may
+ be engaged in multiple, simultaneous communications. For example, B
+ may be receiving requests from many clients other than A, and/or
+ forwarding requests to servers other than C, at the same time that it
+ is handling A's request.
+
+ Any party to the communication which is not acting as a tunnel may
+ employ an internal cache for handling requests. The effect of a cache
+ is that the request/response chain is shortened if one of the
+ participants along the chain has a cached response applicable to that
+ request. The following illustrates the resulting chain if B has a
+ cached copy of an earlier response from O (via C) for a request which
+ has not been cached by UA or A.
+
+ request chain ---------->
+ UA -----v----- A -----v----- B - - - - - - C - - - - - - O
+ <--------- response chain
+
+ Not all responses are usefully cacheable, and some requests may
+ contain modifiers which place special requirements on cache behavior.
+ HTTP requirements for cache behavior and cacheable responses are
+ defined in section 13.
+
+ In fact, there are a wide variety of architectures and configurations
+ of caches and proxies currently being experimented with or deployed
+ across the World Wide Web. These systems include national hierarchies
+ of proxy caches to save transoceanic bandwidth, systems that
+ broadcast or multicast cache entries, organizations that distribute
+ 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
+ PDAs with low-power radio links and intermittent connectivity. The
+ goal of HTTP/1.1 is to support the wide diversity of configurations
+ already deployed while introducing protocol constructs that meet the
+ needs of those who build web applications that require high
+ reliability and, failing that, at least reliable indications of
+ failure.
+
+ HTTP communication usually takes place over TCP/IP connections. The
+ default port is TCP 80 [19], but other ports can be used. This does
+ not preclude HTTP from being implemented on top of any other protocol
+ on the Internet, or on other networks. HTTP only presumes a reliable
+ transport; any protocol that provides such guarantees can be used;
+ the mapping of the HTTP/1.1 request and response structures onto the
+ transport data units of the protocol in question is outside the scope
+ of this specification.
+
+
+
+
+Fielding, et al. Standards Track [Page 13]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ 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
+ one or more request/response exchanges, although connections may be
+ closed for a variety of reasons (see section 8.1).
+
+2 Notational Conventions and Generic Grammar
+
+2.1 Augmented BNF
+
+ All of the mechanisms specified in this document are described in
+ 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
+ notation in order to understand this specification. The augmented BNF
+ includes the following constructs:
+
+ name = definition
+ The name of a rule is simply the name itself (without any
+ enclosing "<" and ">") and is separated from its definition by the
+ equal "=" character. White space is only significant in that
+ indentation of continuation lines is used to indicate a rule
+ definition that spans more than one line. Certain basic rules are
+ in uppercase, such as SP, LWS, HT, CRLF, DIGIT, ALPHA, etc. Angle
+ brackets are used within definitions whenever their presence will
+ facilitate discerning the use of rule names.
+
+ "literal"
+ Quotation marks surround literal text. Unless stated otherwise,
+ the text is case-insensitive.
+
+ rule1 | rule2
+ Elements separated by a bar ("|") are alternatives, e.g., "yes |
+ no" will accept yes or no.
+
+ (rule1 rule2)
+ Elements enclosed in parentheses are treated as a single element.
+ Thus, "(elem (foo | bar) elem)" allows the token sequences "elem
+ foo elem" and "elem bar elem".
+
+ *rule
+ The character "*" preceding an element indicates repetition. The
+ full form is "<n>*<m>element" indicating at least <n> and at most
+ <m> occurrences of element. Default values are 0 and infinity so
+ that "*(element)" allows any number, including zero; "1*element"
+ requires at least one; and "1*2element" allows one or two.
+
+ [rule]
+ Square brackets enclose optional elements; "[foo bar]" is
+ equivalent to "*1(foo bar)".
+
+
+
+Fielding, et al. Standards Track [Page 14]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ N rule
+ Specific repetition: "<n>(element)" is equivalent to
+ "<n>*<n>(element)"; that is, exactly <n> occurrences of (element).
+ Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of three
+ alphabetic characters.
+
+ #rule
+ A construct "#" is defined, similar to "*", for defining lists of
+ elements. The full form is "<n>#<m>element" indicating at least
+ <n> and at most <m> elements, each separated by one or more commas
+ (",") and OPTIONAL linear white space (LWS). This makes the usual
+ form of lists very easy; a rule such as
+ ( *LWS element *( *LWS "," *LWS element ))
+ can be shown as
+ 1#element
+ Wherever this construct is used, null elements are allowed, but do
+ not contribute to the count of elements present. That is,
+ "(element), , (element) " is permitted, but counts as only two
+ elements. Therefore, where at least one element is required, at
+ least one non-null element MUST be present. Default values are 0
+ and infinity so that "#element" allows any number, including zero;
+ "1#element" requires at least one; and "1#2element" allows one or
+ two.
+
+ ; comment
+ A semi-colon, set off some distance to the right of rule text,
+ starts a comment that continues to the end of line. This is a
+ simple way of including useful notes in parallel with the
+ specifications.
+
+ implied *LWS
+ The grammar described by this specification is word-based. Except
+ where noted otherwise, linear white space (LWS) can be included
+ between any two adjacent words (token or quoted-string), and
+ between adjacent words and separators, without changing the
+ interpretation of a field. At least one delimiter (LWS and/or
+
+ separators) MUST exist between any two tokens (for the definition
+ of "token" below), since they would otherwise be interpreted as a
+ single token.
+
+2.2 Basic Rules
+
+ The following rules are used throughout this specification to
+ describe basic parsing constructs. The US-ASCII coded character set
+ is defined by ANSI X3.4-1986 [21].
+
+
+
+
+
+Fielding, et al. Standards Track [Page 15]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ OCTET = <any 8-bit sequence of data>
+ CHAR = <any US-ASCII character (octets 0 - 127)>
+ UPALPHA = <any US-ASCII uppercase letter "A".."Z">
+ LOALPHA = <any US-ASCII lowercase letter "a".."z">
+ ALPHA = UPALPHA | LOALPHA
+ DIGIT = <any US-ASCII digit "0".."9">
+ CTL = <any US-ASCII control character
+ (octets 0 - 31) and DEL (127)>
+ CR = <US-ASCII CR, carriage return (13)>
+ LF = <US-ASCII LF, linefeed (10)>
+ SP = <US-ASCII SP, space (32)>
+ HT = <US-ASCII HT, horizontal-tab (9)>
+ <"> = <US-ASCII double-quote mark (34)>
+
+ HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
+ protocol elements except the entity-body (see appendix 19.3 for
+ tolerant applications). The end-of-line marker within an entity-body
+ is defined by its associated media type, as described in section 3.7.
+
+ CRLF = CR LF
+
+ 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
+ white space, including folding, has the same semantics as SP. A
+ recipient MAY replace any linear white space with a single SP before
+ interpreting the field value or forwarding the message downstream.
+
+ LWS = [CRLF] 1*( SP | HT )
+
+ The TEXT rule is only used for descriptive field contents and values
+ that are not intended to be interpreted by the message parser. Words
+ of *TEXT MAY contain characters from character sets other than ISO-
+ 8859-1 [22] only when encoded according to the rules of RFC 2047
+ [14].
+
+ TEXT = <any OCTET except CTLs,
+ but including LWS>
+
+ 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
+ replaced with a single SP before interpretation of the TEXT value.
+
+ Hexadecimal numeric characters are used in several protocol elements.
+
+ HEX = "A" | "B" | "C" | "D" | "E" | "F"
+ | "a" | "b" | "c" | "d" | "e" | "f" | DIGIT
+
+
+
+
+
+Fielding, et al. Standards Track [Page 16]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ Many HTTP/1.1 header field values consist of words separated by LWS
+ or special characters. These special characters MUST be in a quoted
+ string to be used within a parameter value (as defined in section
+ 3.6).
+
+ token = 1*<any CHAR except CTLs or separators>
+ separators = "(" | ")" | "<" | ">" | "@"
+ | "," | ";" | ":" | "\" | <">
+ | "/" | "[" | "]" | "?" | "="
+ | "{" | "}" | SP | HT
+
+ Comments can be included in some HTTP header fields by surrounding
+ the comment text with parentheses. Comments are only allowed in
+ fields containing "comment" as part of their field value definition.
+ In all other fields, parentheses are considered part of the field
+ value.
+
+ comment = "(" *( ctext | quoted-pair | comment ) ")"
+ ctext = <any TEXT excluding "(" and ")">
+
+ A string of text is parsed as a single word if it is quoted using
+ double-quote marks.
+
+ quoted-string = ( <"> *(qdtext | quoted-pair ) <"> )
+ qdtext = <any TEXT except <">>
+
+ The backslash character ("\") MAY be used as a single-character
+ quoting mechanism only within quoted-string and comment constructs.
+
+ quoted-pair = "\" CHAR
+
+3 Protocol Parameters
+
+3.1 HTTP Version
+
+ HTTP uses a "<major>.<minor>" numbering scheme to indicate versions
+ of the protocol. The protocol versioning policy is intended to allow
+ the sender to indicate the format of a message and its capacity for
+ understanding further HTTP communication, rather than the features
+ obtained via that communication. No change is made to the version
+ number for the addition of message components which do not affect
+ communication behavior or which only add to extensible field values.
+ The <minor> number is incremented when the changes made to the
+ protocol add features which do not change the general message parsing
+ algorithm, but which may add to the message semantics and imply
+ additional capabilities of the sender. The <major> number is
+ incremented when the format of a message within the protocol is
+ changed. See RFC 2145 [36] for a fuller explanation.
+
+
+
+Fielding, et al. Standards Track [Page 17]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ The version of an HTTP message is indicated by an HTTP-Version field
+ in the first line of the message.
+
+ HTTP-Version = "HTTP" "/" 1*DIGIT "." 1*DIGIT
+
+ Note that the major and minor numbers MUST be treated as separate
+ 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
+ lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and
+ MUST NOT be sent.
+
+ An application that sends a request or response message that includes
+ HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
+ with this specification. Applications that are at least conditionally
+ compliant with this specification SHOULD use an HTTP-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 when to send
+ specific HTTP-Version values, see RFC 2145 [36].
+
+ The HTTP version of an application is the highest HTTP version for
+ which the application is at least conditionally compliant.
+
+ Proxy and gateway applications need to be careful when forwarding
+ messages in protocol versions different from that of the application.
+ Since the protocol version indicates the protocol capability of the
+ sender, a proxy/gateway MUST NOT send a message with a version
+ indicator which is greater than its actual version. If a higher
+ version request is received, the proxy/gateway MUST either downgrade
+ the request version, or respond with an error, or switch to tunnel
+ behavior.
+
+ Due to interoperability problems with HTTP/1.0 proxies discovered
+ since the publication of RFC 2068[33], caching proxies MUST, gateways
+ MAY, and tunnels MUST NOT upgrade the request to the highest version
+ they support. The proxy/gateway's response to that request MUST be in
+ the same major version as the request.
+
+ Note: Converting between versions of HTTP may involve modification
+ of header fields required or forbidden by the versions involved.
+
+3.2 Uniform Resource Identifiers
+
+ URIs have been known by many names: WWW addresses, Universal Document
+ Identifiers, Universal Resource Identifiers [3], and finally the
+ combination of Uniform Resource Locators (URL) [4] and Names (URN)
+ [20]. As far as HTTP is concerned, Uniform Resource Identifiers are
+ simply formatted strings which identify--via name, location, or any
+ other characteristic--a resource.
+
+
+
+Fielding, et al. Standards Track [Page 18]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+3.2.1 General Syntax
+
+ 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 two
+ forms are differentiated by the fact that absolute URIs always begin
+ with a scheme name followed by a colon. For definitive information on
+ URL syntax and semantics, see "Uniform Resource Identifiers (URI):
+ Generic Syntax and Semantics," RFC 2396 [42] (which replaces RFCs
+ 1738 [4] and RFC 1808 [11]). This specification adopts the
+ definitions of "URI-reference", "absoluteURI", "relativeURI", "port",
+ "host","abs_path", "rel_path", and "authority" from that
+ specification.
+
+ 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
+ serve, and SHOULD be able to handle URIs of unbounded length if they
+ provide GET-based forms that could generate such URIs. A server
+ SHOULD return 414 (Request-URI Too Long) status if a URI is longer
+ than the server can handle (see section 10.4.15).
+
+ Note: Servers ought to be cautious about depending on URI lengths
+ above 255 bytes, because some older client or proxy
+ implementations might not properly support these lengths.
+
+3.2.2 http URL
+
+ The "http" scheme is used to locate network resources via the HTTP
+ protocol. This section defines the scheme-specific syntax and
+ semantics for http URLs.
+
+ http_URL = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]]
+
+ 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
+ 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 addresses
+ in URLs SHOULD be avoided whenever possible (see RFC 1900 [24]). If
+ the abs_path is not present in the URL, it MUST be given as "/" when
+ used as a Request-URI for a resource (section 5.1.2). If a proxy
+ receives a host name which is not a fully qualified domain name, it
+ MAY add its domain to the host name it received. If a proxy receives
+ a fully qualified domain name, the proxy MUST NOT change the host
+ name.
+
+
+
+
+
+
+
+
+Fielding, et al. Standards Track [Page 19]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+3.2.3 URI Comparison
+
+ 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
+ URIs, with these exceptions:
+
+ - A port that is empty or not given is equivalent to the default
+ port for that URI-reference;
+
+ - Comparisons of host names MUST be case-insensitive;
+
+ - Comparisons of scheme names MUST be case-insensitive;
+
+ - An empty abs_path is equivalent to an abs_path of "/".
+
+ Characters other than those in the "reserved" and "unsafe" sets (see
+ RFC 2396 [42]) are equivalent to their ""%" HEX HEX" encoding.
+
+ For example, the following three URIs are equivalent:
+
+ http://abc.com:80/~smith/home.html
+ http://ABC.com/%7Esmith/home.html
+ http://ABC.com:/%7esmith/home.html
+
+3.3 Date/Time Formats
+
+3.3.1 Full Date
+
+ HTTP applications have historically allowed three different formats
+ for the representation of date/time stamps:
+
+ Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123
+ Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
+ Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format
+
+ 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
+ RFC 822 [9]). The second format is in common use, but is based on the
+ obsolete RFC 850 [12] date format and lacks a four-digit year.
+ HTTP/1.1 clients and servers that parse the date value MUST accept
+ all three formats (for compatibility with HTTP/1.0), though they MUST
+ only generate the RFC 1123 format for representing HTTP-date values
+ in header fields. See section 19.3 for further information.
+
+ Note: Recipients of date values are encouraged to be robust in
+ accepting date values that may have been sent by non-HTTP
+ applications, as is sometimes the case when retrieving or posting
+ messages via proxies/gateways to SMTP or NNTP.
+
+
+
+Fielding, et al. Standards Track [Page 20]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ All HTTP date/time stamps MUST be represented in Greenwich Mean Time
+ (GMT), without exception. For the purposes of HTTP, GMT is exactly
+ equal to UTC (Coordinated Universal Time). This is indicated in the
+ first two formats by the inclusion of "GMT" as the three-letter
+ abbreviation for time zone, and MUST be assumed when reading the
+ asctime format. HTTP-date is case sensitive and MUST NOT include
+ additional LWS beyond that specifically included as SP in the
+ grammar.
+
+ HTTP-date = rfc1123-date | rfc850-date | asctime-date
+ rfc1123-date = wkday "," SP date1 SP time SP "GMT"
+ rfc850-date = weekday "," SP date2 SP time SP "GMT"
+ asctime-date = wkday SP date3 SP time SP 4DIGIT
+ date1 = 2DIGIT SP month SP 4DIGIT
+ ; day month year (e.g., 02 Jun 1982)
+ date2 = 2DIGIT "-" month "-" 2DIGIT
+ ; day-month-year (e.g., 02-Jun-82)
+ date3 = month SP ( 2DIGIT | ( SP 1DIGIT ))
+ ; month day (e.g., Jun 2)
+ time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
+ ; 00:00:00 - 23:59:59
+ wkday = "Mon" | "Tue" | "Wed"
+ | "Thu" | "Fri" | "Sat" | "Sun"
+ weekday = "Monday" | "Tuesday" | "Wednesday"
+ | "Thursday" | "Friday" | "Saturday" | "Sunday"
+ 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 their usage within the protocol stream. Clients and servers are
+ not required to use these formats for user presentation, request
+ logging, etc.
+
+3.3.2 Delta Seconds
+
+ Some HTTP header fields allow a time value to be specified as an
+ integer number of seconds, represented in decimal, after the time
+ that the message was received.
+
+ delta-seconds = 1*DIGIT
+
+3.4 Character Sets
+
+ HTTP uses the same definition of the term "character set" as that
+ described for MIME:
+
+
+
+
+
+Fielding, et al. Standards Track [Page 21]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ 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
+ into a sequence of characters. Note that unconditional conversion in
+ the other direction is not required, in that not all characters may
+ be available in a given character set and a character set may provide
+ more than one sequence of octets to represent a particular character.
+ This definition is intended to allow various kinds of character
+ encoding, from simple single-table mappings such as US-ASCII to
+ complex table switching methods such as those that use ISO-2022's
+ techniques. However, the definition associated with a MIME character
+ set name MUST fully specify the mapping to be performed from octets
+ to characters. In particular, use of external profiling information
+ to determine the exact mapping is not permitted.
+
+ Note: This use of the term "character set" is more commonly
+ referred to as a "character encoding." However, since HTTP and
+ MIME share the same registry, it is important that the terminology
+ also be shared.
+
+ HTTP character sets are identified by case-insensitive tokens. The
+ complete set of tokens is defined by the IANA Character Set registry
+ [19].
+
+ charset = token
+
+ Although HTTP allows an arbitrary token to be used as a charset
+ value, any token that has a predefined value within the IANA
+ Character Set registry [19] MUST represent the character set defined
+ by that registry. Applications SHOULD limit their use of character
+ sets to those defined by the IANA registry.
+
+ Implementors should be aware of IETF character set requirements [38]
+ [41].
+
+3.4.1 Missing Charset
+
+ Some HTTP/1.0 software has interpreted a Content-Type header without
+ charset parameter incorrectly to mean "recipient should guess."
+ Senders wishing to defeat this behavior MAY include a charset
+ parameter even when the charset is ISO-8859-1 and SHOULD do so when
+ it is known that it will not confuse the recipient.
+
+ Unfortunately, some older HTTP/1.0 clients did not deal properly with
+ an explicit charset parameter. HTTP/1.1 recipients MUST respect the
+ charset label provided by the sender; and those user agents that have
+ a provision to "guess" a charset MUST use the charset from the
+
+
+
+
+
+Fielding, et al. Standards Track [Page 22]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ content-type field if they support that charset, rather than the
+ recipient's preference, when initially displaying a document. See
+ section 3.7.1.
+
+3.5 Content Codings
+
+ Content coding values indicate an encoding transformation that has
+ been or can be applied to an entity. Content codings are primarily
+ used to allow a document to be compressed or otherwise usefully
+ transformed without losing the identity of its underlying media type
+ and without loss of information. Frequently, the entity is stored in
+ coded form, transmitted directly, and only decoded by the recipient.
+
+ content-coding = token
+
+ All content-coding values are case-insensitive. HTTP/1.1 uses
+ content-coding values in the Accept-Encoding (section 14.3) and
+ Content-Encoding (section 14.11) header fields. Although the value
+ describes the content-coding, what is more important is that it
+ indicates what decoding mechanism will be required to remove the
+ encoding.
+
+ The Internet Assigned Numbers Authority (IANA) acts as a registry for
+ content-coding value tokens. Initially, the registry contains the
+ following tokens:
+
+ gzip An encoding format produced by the file compression program
+ "gzip" (GNU zip) as described in RFC 1952 [25]. This format is a
+ Lempel-Ziv coding (LZ77) with a 32 bit CRC.
+
+ compress
+ The encoding format produced by the common UNIX file compression
+ program "compress". This format is an adaptive Lempel-Ziv-Welch
+ coding (LZW).
+
+ Use of program names for the identification of encoding formats
+ is not desirable and is discouraged for future encodings. Their
+ use here is representative of historical practice, not good
+ design. For compatibility with previous implementations of HTTP,
+ applications SHOULD consider "x-gzip" and "x-compress" to be
+ equivalent to "gzip" and "compress" respectively.
+
+ deflate
+ The "zlib" format defined in RFC 1950 [31] in combination with
+ the "deflate" compression mechanism described in RFC 1951 [29].
+
+
+
+
+
+
+Fielding, et al. Standards Track [Page 23]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ identity
+ The default (identity) encoding; the use of no transformation
+ whatsoever. This content-coding is used only in the Accept-
+ Encoding header, and SHOULD NOT be used in the Content-Encoding
+ header.
+
+ New content-coding value tokens SHOULD be registered; to allow
+ interoperability between clients and servers, specifications of the
+ content coding algorithms needed to implement a new value SHOULD be
+ publicly available and adequate for independent implementation, and
+ conform to the purpose of content coding defined in this section.
+
+3.6 Transfer Codings
+
+ Transfer-coding values are used to indicate an encoding
+ 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.
+ This differs from a content coding in that the transfer-coding is a
+ property of the message, not of the original entity.
+
+ transfer-coding = "chunked" | transfer-extension
+ transfer-extension = token *( ";" parameter )
+
+ Parameters are in the form of attribute/value pairs.
+
+ parameter = attribute "=" value
+ attribute = token
+ value = token | quoted-string
+
+ All transfer-coding values are case-insensitive. HTTP/1.1 uses
+ transfer-coding values in the TE header field (section 14.39) and in
+ the Transfer-Encoding header field (section 14.41).
+
+ Whenever a transfer-coding is applied to a message-body, the set of
+ transfer-codings MUST include "chunked", unless the message is
+ terminated by closing the connection. When the "chunked" transfer-
+ coding is used, it MUST be the last transfer-coding applied to the
+ message-body. The "chunked" transfer-coding MUST NOT be applied more
+ than once to a message-body. These rules allow the recipient to
+ determine the transfer-length of the message (section 4.4).
+
+ Transfer-codings are analogous to the Content-Transfer-Encoding
+ values of MIME [7], which were designed to enable safe transport of
+ binary data over a 7-bit transport service. However, safe transport
+ has a different focus for an 8bit-clean transfer protocol. In HTTP,
+ the only unsafe characteristic of message-bodies is the difficulty in
+ determining the exact body length (section 7.2.2), or the desire to
+ encrypt data over a shared transport.
+
+
+
+Fielding, et al. Standards Track [Page 24]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ The Internet Assigned Numbers Authority (IANA) acts as a registry for
+ transfer-coding value tokens. Initially, the registry contains the
+ following tokens: "chunked" (section 3.6.1), "identity" (section
+ 3.6.2), "gzip" (section 3.5), "compress" (section 3.5), and "deflate"
+ (section 3.5).
+
+ New transfer-coding value tokens SHOULD be registered in the same way
+ as new content-coding value tokens (section 3.5).
+
+ A server which receives an entity-body with a transfer-coding it does
+ not understand SHOULD return 501 (Unimplemented), and close the
+ connection. A server MUST NOT send transfer-codings to an HTTP/1.0
+ client.
+
+3.6.1 Chunked Transfer Coding
+
+ 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,
+ followed by an OPTIONAL trailer containing entity-header fields. This
+ allows dynamically produced content to be transferred along with the
+ information necessary for the recipient to verify that it has
+ received the full message.
+
+ Chunked-Body = *chunk
+ last-chunk
+ trailer
+ CRLF
+
+ chunk = chunk-size [ chunk-extension ] CRLF
+ chunk-data CRLF
+ chunk-size = 1*HEX
+ last-chunk = 1*("0") [ chunk-extension ] CRLF
+
+ chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
+ chunk-ext-name = token
+ chunk-ext-val = token | quoted-string
+ chunk-data = chunk-size(OCTET)
+ trailer = *(entity-header CRLF)
+
+ 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
+ zero, followed by the trailer, which is terminated by an empty line.
+
+ The trailer allows the sender to include additional HTTP header
+ 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
+ section 14.40).
+
+
+
+
+Fielding, et al. Standards Track [Page 25]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ 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
+ true:
+
+ a)the request included a TE header field that indicates "trailers" is
+ acceptable in the transfer-coding of the response, as described in
+ section 14.39; or,
+
+ b)the server is the origin server for the response, the trailer
+ fields consist entirely of optional metadata, and the recipient
+ could use the message (in a manner acceptable to the origin server)
+ without receiving this metadata. In other words, the origin server
+ is willing to accept the possibility that the trailer fields might
+ be silently discarded along the path to the client.
+
+ This requirement prevents an interoperability failure when the
+ 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
+ compliance with the protocol would have necessitated a possibly
+ infinite buffer on the proxy.
+
+ An example process for decoding a Chunked-Body is presented in
+ appendix 19.4.6.
+
+ All HTTP/1.1 applications MUST be able to receive and decode the
+ "chunked" transfer-coding, and MUST ignore chunk-extension extensions
+ they do not understand.
+
+3.7 Media Types
+
+ HTTP uses Internet Media Types [17] in the Content-Type (section
+ 14.17) and Accept (section 14.1) header fields in order to provide
+ open and extensible data typing and type negotiation.
+
+ media-type = type "/" subtype *( ";" parameter )
+ type = token
+ subtype = token
+
+ Parameters MAY follow the type/subtype in the form of attribute/value
+ pairs (as defined in section 3.6).
+
+ The type, subtype, and parameter attribute names are case-
+ insensitive. Parameter values might or might not be case-sensitive,
+ depending on the semantics of the parameter name. Linear white space
+ (LWS) MUST NOT be used between the type and subtype, nor between an
+ attribute and its value. The presence or absence of a parameter might
+ be significant to the processing of a media-type, depending on its
+ definition within the media type registry.
+
+
+
+Fielding, et al. Standards Track [Page 26]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ Note that some older HTTP applications do not recognize media type
+ parameters. When sending data to older HTTP applications,
+ implementations SHOULD only use media type parameters when they are
+ required by that type/subtype definition.
+
+ Media-type values are registered with the Internet Assigned Number
+ Authority (IANA [19]). The media type registration process is
+ outlined in RFC 1590 [17]. Use of non-registered media types is
+ discouraged.
+
+3.7.1 Canonicalization and Text Defaults
+
+ Internet media types are registered with a canonical form. An
+ entity-body transferred via HTTP messages MUST be represented in the
+ appropriate canonical form prior to its transmission except for
+ "text" types, as defined in the next paragraph.
+
+ When in canonical form, media subtypes of the "text" type use CRLF as
+ the text line break. HTTP relaxes this requirement and allows the
+ transport of text media with plain CR or LF alone representing a line
+ break when it is done consistently for an entire entity-body. HTTP
+ applications MUST accept CRLF, bare CR, and bare LF as being
+ representative of a line break in text media received via HTTP. In
+ addition, if the text is represented in a character set that does not
+ use octets 13 and 10 for CR and LF respectively, as is the case for
+ some multi-byte character sets, HTTP allows the use of whatever octet
+ sequences are defined by that character set to represent the
+ equivalent of CR and LF for line breaks. This flexibility regarding
+ line breaks applies only to text media in the entity-body; a bare CR
+ or LF MUST NOT be substituted for CRLF within any of the HTTP control
+ structures (such as header fields and multipart boundaries).
+
+ If an entity-body is encoded with a content-coding, the underlying
+ data MUST be in a form defined above prior to being encoded.
+
+ The "charset" parameter is used with some media types to define the
+ character set (section 3.4) of the data. When no explicit charset
+ 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
+ received via HTTP. Data in character sets other than "ISO-8859-1" or
+ its subsets MUST be labeled with an appropriate charset value. See
+ section 3.4.1 for compatibility problems.
+
+3.7.2 Multipart Types
+
+ MIME provides for a number of "multipart" types -- encapsulations of
+ 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
+
+
+
+Fielding, et al. Standards Track [Page 27]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ [40], and MUST include a boundary parameter as part of the media type
+ value. The message body is itself a protocol element and MUST
+ therefore use only CRLF to represent line breaks between body-parts.
+ Unlike in RFC 2046, the epilogue of any multipart message MUST be
+ empty; HTTP applications MUST NOT transmit the epilogue (even if the
+ original multipart contains an epilogue). These restrictions exist in
+ order to preserve the self-delimiting nature of a multipart message-
+ body, wherein the "end" of the message-body is indicated by the
+ ending multipart boundary.
+
+ In general, HTTP treats a multipart message-body no differently than
+ any other media type: strictly as payload. The one exception is the
+ "multipart/byteranges" type (appendix 19.2) when it appears in a 206
+ (Partial Content) response, which will be interpreted by some HTTP
+ 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
+ behavior as a MIME user agent would upon receipt of a multipart type.
+ The MIME header fields within each body-part of a multipart message-
+ body do not have any significance to HTTP beyond that defined by
+ their MIME semantics.
+
+ 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.
+ If an application receives an unrecognized multipart subtype, the
+ application MUST treat it as being equivalent to "multipart/mixed".
+
+ Note: The "multipart/form-data" type has been specifically defined
+ for carrying form data suitable for processing via the POST
+ request method, as described in RFC 1867 [15].
+
+3.8 Product Tokens
+
+ Product tokens are used to allow communicating applications to
+ identify themselves by software name and version. Most fields using
+ product tokens also allow sub-products which form a significant part
+ of the application to be listed, separated by white space. By
+ convention, the products are listed in order of their significance
+ for identifying the application.
+
+ product = token ["/" product-version]
+ product-version = token
+
+ Examples:
+
+ User-Agent: CERN-LineMode/2.15 libwww/2.17b3
+ Server: Apache/0.8.4
+
+
+
+
+
+Fielding, et al. Standards Track [Page 28]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ Product tokens SHOULD be short and to the point. They MUST NOT be
+ used for advertising or other non-essential information. Although any
+ token character MAY appear in a product-version, this token SHOULD
+ only be used for a version identifier (i.e., successive versions of
+ the same product SHOULD only differ in the product-version portion of
+ the product value).
+
+3.9 Quality Values
+
+ HTTP content negotiation (section 12) uses short "floating point"
+ numbers to indicate the relative importance ("weight") of various
+ 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
+ value. If a parameter has a quality value of 0, then content with
+ this parameter is `not acceptable' for the client. HTTP/1.1
+ applications MUST NOT generate more than three digits after the
+ decimal point. User configuration of these values SHOULD also be
+ limited in this fashion.
+
+ qvalue = ( "0" [ "." 0*3DIGIT ] )
+ | ( "1" [ "." 0*3("0") ] )
+
+ "Quality values" is a misnomer, since these values merely represent
+ relative degradation in desired quality.
+
+3.10 Language Tags
+
+ A language tag identifies a natural language spoken, written, or
+ otherwise conveyed by human beings for communication of information
+ to other human beings. Computer languages are explicitly excluded.
+ HTTP uses language tags within the Accept-Language and Content-
+ Language fields.
+
+ The syntax and registry of HTTP language tags is the same as that
+ defined by RFC 1766 [1]. In summary, a language tag is composed of 1
+ or more parts: A primary language tag and a possibly empty series of
+ subtags:
+
+ language-tag = primary-tag *( "-" subtag )
+ primary-tag = 1*8ALPHA
+ subtag = 1*8ALPHA
+
+ White space is not allowed within the tag and all tags are case-
+ insensitive. The name space of language tags is administered by the
+ IANA. Example tags include:
+
+ en, en-US, en-cockney, i-cherokee, x-pig-latin
+
+
+
+
+Fielding, et al. Standards Track [Page 29]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ 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
+ last three tags above are not registered tags; all but the last are
+ examples of tags which could be registered in future.)
+
+3.11 Entity Tags
+
+ Entity tags are used for comparing two or more entities from the same
+ requested resource. HTTP/1.1 uses entity tags in the ETag (section
+ 14.19), If-Match (section 14.24), If-None-Match (section 14.26), and
+ If-Range (section 14.27) header fields. The 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 string, possibly prefixed by
+ a weakness indicator.
+
+ entity-tag = [ weak ] opaque-tag
+ weak = "W/"
+ opaque-tag = quoted-string
+
+ A "strong entity tag" MAY be shared by two entities of a resource
+ only if they are equivalent by octet equality.
+
+ 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
+ could be substituted for each other with no significant change in
+ semantics. A weak entity tag can only be used for weak comparison.
+
+ An entity tag MUST be unique across all versions of all entities
+ associated with a particular resource. A given entity tag value MAY
+ be used for entities obtained by requests on different URIs. The use
+ of the same entity tag value in conjunction with entities obtained by
+ requests on different URIs does not imply the equivalence of those
+ entities.
+
+3.12 Range Units
+
+ 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
+ units in the Range (section 14.35) and Content-Range (section 14.16)
+ header fields. An entity can be broken down into subranges according
+ to various structural units.
+
+ range-unit = bytes-unit | other-range-unit
+ bytes-unit = "bytes"
+ other-range-unit = token
+
+ The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1
+ implementations MAY ignore ranges specified using other units.
+
+
+
+Fielding, et al. Standards Track [Page 30]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ HTTP/1.1 has been designed to allow implementations of applications
+ that do not depend on knowledge of ranges.
+
+4 HTTP Message
+
+4.1 Message Types
+
+ HTTP messages consist of requests from client to server and responses
+ from server to client.
+
+ HTTP-message = Request | Response ; HTTP/1.1 messages
+
+ Request (section 5) and Response (section 6) messages use the generic
+ message format of RFC 822 [9] for transferring entities (the payload
+ of the message). Both types of message consist of a start-line, zero
+ or more header fields (also known as "headers"), an empty line (i.e.,
+ a line with nothing preceding the CRLF) indicating the end of the
+ header fields, and possibly a message-body.
+
+ generic-message = start-line
+ *(message-header CRLF)
+ CRLF
+ [ message-body ]
+ start-line = Request-Line | Status-Line
+
+ In the interest of robustness, servers SHOULD ignore any empty
+ 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
+ message and receives a CRLF first, it should ignore the CRLF.
+
+ Certain buggy HTTP/1.0 client implementations generate extra CRLF's
+ 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
+ extra CRLF.
+
+4.2 Message Headers
+
+ HTTP header fields, which include general-header (section 4.5),
+ request-header (section 5.3), response-header (section 6.2), and
+ 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
+ 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
+ of LWS, though a single SP is preferred. Header fields can be
+ extended over multiple lines by preceding each extra line with at
+ least one SP or HT. Applications ought to follow "common form", where
+ one is known or indicated, when generating HTTP constructs, since
+ there might exist some implementations that fail to accept anything
+
+
+
+Fielding, et al. Standards Track [Page 31]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ beyond the common forms.
+
+ message-header = field-name ":" [ field-value ]
+ field-name = token
+ field-value = *( field-content | LWS )
+ field-content = <the OCTETs making up the field-value
+ and consisting of either *TEXT or combinations
+ of token, separators, and quoted-string>
+
+ The field-content does not include any leading or trailing LWS:
+ 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. Such leading or trailing LWS MAY be
+ removed without changing the semantics of the field value. Any LWS
+ that occurs between field-content MAY be replaced with a single SP
+ before interpreting the field value or forwarding the message
+ downstream.
+
+ The order in which header fields with differing field names are
+ received is not significant. However, it is "good practice" to send
+ general-header fields first, followed by request-header or response-
+ header fields, and ending with the entity-header fields.
+
+ Multiple message-header fields with the same field-name MAY be
+ present in a message if and only if the entire field-value for that
+ header field is defined as a comma-separated list [i.e., #(values)].
+ It MUST be possible to combine the multiple header fields into one
+ "field-name: field-value" pair, without changing the semantics of the
+ message, by appending each subsequent field-value to the first, each
+ separated by a comma. The order in which header fields with the same
+ field-name are received is therefore significant to the
+ interpretation of the combined field value, and thus a proxy MUST NOT
+ change the order of these field values when a message is forwarded.
+
+4.3 Message Body
+
+ The message-body (if any) of an HTTP message is used to carry the
+ entity-body associated with the request or response. The message-body
+ differs from the entity-body only when a transfer-coding has been
+ applied, as indicated by the Transfer-Encoding header field (section
+ 14.41).
+
+ message-body = entity-body
+ | <entity-body encoded as per Transfer-Encoding>
+
+ Transfer-Encoding MUST be used to indicate any transfer-codings
+ applied by an application to ensure safe and proper transfer of the
+ message. Transfer-Encoding is a property of the message, not of the
+
+
+
+Fielding, et al. Standards Track [Page 32]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ entity, and thus MAY be added or removed by any application along the
+ request/response chain. (However, section 3.6 places restrictions on
+ when certain transfer-codings may be used.)
+
+ The rules for when a message-body is allowed in a message differ for
+ requests and responses.
+
+ The presence of a message-body in a request is signaled by the
+ inclusion of a Content-Length or Transfer-Encoding header field in
+ the request's message-headers. A message-body MUST NOT be included in
+ a request if the specification of the request method (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 request method
+ does not include defined semantics for an entity-body, then the
+ message-body SHOULD be ignored when handling the request.
+
+ For response messages, whether or not a message-body is included with
+ a message is dependent on both the request method and the response
+ status code (section 6.1.1). All responses to the HEAD request method
+ MUST NOT include a message-body, even though the presence of entity-
+ header fields might lead one to believe they do. All 1xx
+ (informational), 204 (no content), and 304 (not modified) responses
+ MUST NOT include a message-body. All other responses do include a
+ message-body, although it MAY be of zero length.
+
+4.4 Message Length
+
+ 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
+ been applied. When a message-body is included with a message, the
+ transfer-length of that body is determined by one of the following
+ (in order of precedence):
+
+ 1.Any response message which "MUST NOT" include a message-body (such
+ as the 1xx, 204, and 304 responses and any response to a HEAD
+ request) is always terminated by the first empty line after the
+ header fields, regardless of the entity-header fields present in
+ the message.
+
+ 2.If a Transfer-Encoding header field (section 14.41) is present and
+ has any value other than "identity", then the transfer-length is
+ defined by use of the "chunked" transfer-coding (section 3.6),
+ unless the message is terminated by closing the connection.
+
+ 3.If a Content-Length header field (section 14.13) is present, its
+ decimal value in OCTETs represents both the entity-length and the
+ transfer-length. The Content-Length header field MUST NOT be sent
+ if these two lengths are different (i.e., if a Transfer-Encoding
+
+
+
+Fielding, et al. Standards Track [Page 33]
+
+RFC 2616 HTTP/1.1 June 1999
+
+
+ header field is present). If a message is received with both a
+ Transfer-Encoding header field and a Content-Length header field,
+ the latter MUST be ignored.
+
+ 4.If the message uses the media type "multipart/byteranges", and the
+ ransfer-length is not otherwise specified, then this self-
+ elimiting media type defines the transfer-length. This media type
+ UST NOT be used unless the sender knows that the recipient can arse
+ it; the presence in a request of a Range header with ultiple byte-
+ range specifiers from a 1.1 client implies that the lient can parse
+ multipart/byteranges responses.
+
+ A range header might be forwarded by a 1.0 proxy that does not
+ understand multipart/byteranges; in this case the server MUST
+ delimit the message using methods defined in items 1,3 or 5 of
+ this section.
+
+ 5.By the server closing the connection. (Closing the connection
+ cannot be used to indicate the end of a request body, since that
+ would leave no possibility for the server to send back a response.)
+
+ For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
+ 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
+ request contains a message-body and a Content-Length is not given,
+ the server SHOULD respond with 400 (bad request) if it cannot
+ determine the length of the message, or with 411 (length required) if
+ it wishes to insist on receiving a valid Content-Length.
+
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