Network Working Group R. Fielding Request for Comments: 2616 ...

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21 Full Copyright Statement ....................................1761 Introduction1.1 PurposeThe Hypertext Transfer Protocol (HTTP) is an application-levelprotocol for distributed, collaborative, hypermedia informationsystems. HTTP has been in use by the World-Wide Web globalinformation initiative since 1990. The first version of HTTP,referred to as HTTP/0.9, was a simple protocol for raw data transferacross the Internet. HTTP/1.0, as defined by RFC 1945 [6], improvedthe protocol by allowing messages to be in the format of MIME-likemessages, containing metainformation about the data transferred andmodifiers on the request/response semantics. However, HTTP/1.0 doesnot sufficiently take into consideration the effects of hierarchicalproxies, caching, the need for persistent connections, or virtualhosts. In addition, the proliferation of incompletely-implementedapplications calling themselves "HTTP/1.0" has necessitated aprotocol version change in order for two communicating applicationsto 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 inorder to ensure reliable implementation of its features.Practical information systems require more functionality than simpleretrieval, including search, front-end update, and annotation. HTTPallows an open-ended set of methods and headers that indicate thepurpose of a request [47]. It builds on the discipline of referenceprovided by the Uniform Resource Identifier (URI) [3], as a location(URL) [4] or name (URN) [20], for indicating the resource to which aFielding, et al. Standards Track [Page 7]RFC 2616 HTTP/1.1 June 1999method is to be applied. Messages are passed in a format similar tothat used by Internet mail [9] as defined by the MultipurposeInternet Mail Extensions (MIME) [7].HTTP is also used as a generic protocol for communication betweenuser agents and proxies/gateways to other Internet systems, includingthose supported by the SMTP [16], NNTP [13], FTP [18], Gopher [2],and WAIS [10] protocols. In this way, HTTP allows basic hypermediaaccess to resources available from diverse applications.
1.2 RequirementsThe key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT","SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in thisdocument are to be interpreted as described in RFC 2119 [34].An implementation is not compliant if it fails to satisfy one or moreof the MUST or REQUIRED level requirements for the protocols itimplements. An implementation that satisfies all the MUST or REQUIREDlevel and all the SHOULD level requirements for its protocols is saidto be "unconditionally compliant"; one that satisfies all the MUSTlevel requirements but not all the SHOULD level requirements for itsprotocols is said to be "conditionally compliant."1.3 TerminologyThis specification uses a number of terms to refer to the rolesplayed by participants in, and objects of, the HTTP communication.connectionA transport layer virtual circuit established between two programsfor the purpose of communication.messageThe basic unit of HTTP communication, consisting of a structuredsequence of octets matching the syntax defined in section 4 andtransmitted via the connection.requestAn HTTP request message, as defined in section 5.responseAn HTTP response message, as defined in section 6.Fielding, et al. Standards Track [Page 8]RFC 2616 HTTP/1.1 June 1999resourceA network data object or service that can be identified by a URI,as defined in section 3.2. Resources may be available in multiplerepresentations (e.g. multiple languages, data formats, size, and
Page 2: eferred to as "HTTP/1.1", and is an
Page 5 and 6: 12.1 Server-driven Negotiation ....
Page 7: 14.40 Trailer .....................
Page 12 and 13: Fielding, et al. Standards Track [P
Page 14 and 15: equest chain ----------------------
Page 16 and 17: Elements separated by a bar ("|") a
Page 18 and 19: HTTP/1.1 header field values can be
Page 20 and 21: An application that sends a request
Page 22 and 23: 3.2.3 URI ComparisonWhen comparing
Page 26 and 27: is not desirable and is discouraged
Page 28 and 29: CRLFchunk = chunk-size [ chunk-exte
Page 30 and 31: When in canonical form, media subty
Page 32 and 33: 3.9 Quality ValuesHTTP content nego
Page 34 and 35: RFC 2616 HTTP/1.1 June 1999HTTP/1.1
Page 36 and 37: message-body = entity-body| Transfe
Page 38 and 39: in advance.Messages MUST NOT includ
Page 40 and 41: equested resource, and 501 (Not Imp
Page 42 and 43: names) MUST use the following rules
Page 44 and 45: values for the first digit:- 1xx: I
Page 48 and 49: how the transfer-length of a messag
Page 50 and 51: connection-token close.If either th
Page 52 and 53: idempotent (see section 9.1.2). Non
Page 54 and 55: compatibility with RFC 2068, a serv
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optional features implemented by th
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- Extending a database through an a
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intervention (or other means) on th
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10.1.2 101 Switching ProtocolsThe s
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esponse MAY include new or updated
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Fielding, et al. Standards Track [P
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The response MUST include the follo
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If the client is sending data, a se
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If the response could be unacceptab
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10.4.15 414 Request-URI Too LongThe
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10.5.5 504 Gateway TimeoutThe serve
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Caching would be useless if it did
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Warning (but without removing any e
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If the user has overridden the basi
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in the past. This means that the re
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RFC 2616 HTTP/1.1 June 1999the time
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simple:response_is_fresh = (freshne
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match.In HTTP/1.1, a conditional re
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validators or strong validators. Cl
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- MAY send a weak entity tag instea
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Unless specifically constrained by
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warn-code 1xx, which are deleted ev
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for the associated entity, its enti
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- DELETE- POSTIn order to prevent d
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The Accept request-header field can
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image/jpeg = 0.5text/html;level=2 =
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Note: If the request does not inclu
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Accept-Ranges: bytesbut are not req
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containing an Authorization field,
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- Restrictions on what may be store
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improve privacy in some cases, we c
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must-revalidateBecause a cache MAY
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understand.For example, consider a
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new coding is known to be acceptabl
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14.14 Content-LocationThe Content-L
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Note: while the definition of Conte
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server SHOULD return them in the or
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Some origin server implementations
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Expires = "Expires" ":" HTTP-dateAn
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A client MUST include a Host header
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een modified since the date given b
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RFC 2616 HTTP/1.1 June 1999If none
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14.29 Last-ModifiedThe Last-Modifie
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MAY require that behavior be consis
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yte-ranges-specifier = bytes-unit "
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Content) instead of 200 (OK).- The
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The TE request-header field indicat
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a cache cannot determine from the r
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SHOULD NOT, by default, forward the
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this user agent behavior in mind.Re
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designers and implementors be parti
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strongly correlated to the membersh
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serious security considerations. Co
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The HTTP protocol has evolved consi
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Protocol -- HTTP/1.0", RFC 1945, Ma
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Implementation and Analysis", RFC 1
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University of California, IrvineIrv
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Notes:1) Additional CRLFs may prece
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full compliance with the MIME proto
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ead chunk-size and CRLF}read entity
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- understand any valid response in
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CREATE had a race that required an
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also needed to be a general header,
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