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

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Fielding, et al. Standards Track [Page 41]RFC 2616 HTTP/1.1 June 1999| Retry-After ; Section 14.37| Server ; Section 14.38| Vary ; Section 14.44| WWW-Authenticate ; Section 14.47Response-header field names can be extended reliably only incombination with a change in the protocol version. However, new orexperimental header fields MAY be given the semantics of responseheaderfields if all parties in the communication recognize them tobe response-header fields. Unrecognized header fields are treated asentity-header fields.7 EntityRequest and Response messages MAY transfer an entity if not otherwiserestricted by the request method or response status code. An entityconsists of entity-header fields and an entity-body, although someresponses will only include the entity-headers.In this section, both sender and recipient refer to either the clientor the server, depending on who sends and who receives the entity.7.1 Entity Header FieldsEntity-header fields define metainformation about the entity-body or,if no body is present, about the resource identified by the request.Some of this metainformation is OPTIONAL; some might be REQUIRED byportions of this specification.entity-header = Allow ; Section 14.7| Content-Encoding ; Section 14.11| Content-Language ; Section 14.12| Content-Length ; Section 14.13| Content-Location ; Section 14.14| Content-MD5 ; Section 14.15| Content-Range ; Section 14.16| Content-Type ; Section 14.17| Expires ; Section 14.21| Last-Modified ; Section 14.29| extension-headerextension-header = message-header
The extension-header mechanism allows additional entity-header fieldsto be defined without changing the protocol, but these fields cannotbe assumed to be recognizable by the recipient. Unrecognized headerfields SHOULD be ignored by the recipient and MUST be forwarded bytransparent proxies.Fielding, et al. Standards Track [Page 42]RFC 2616 HTTP/1.1 June 19997.2 Entity BodyThe entity-body (if any) sent with an HTTP request or response is ina format and encoding defined by the entity-header fields.entity-body= *OCTETAn entity-body is only present in a message when a message-body ispresent, as described in section 4.3. The entity-body is obtainedfrom the message-body by decoding any Transfer-Encoding that mighthave been applied to ensure safe and proper transfer of the message.7.2.1 TypeWhen an entity-body is included with a message, the data type of thatbody is determined via the header fields Content-Type and Content-Encoding. These define a two-layer, ordered encoding model:entity-body := Content-Encoding( Content-Type( data ) )Content-Type specifies the media type of the underlying data.Content-Encoding may be used to indicate any additional contentcodings applied to the data, usually for the purpose of datacompression, that are a property of the requested resource. There isno default encoding.Any HTTP/1.1 message containing an entity-body SHOULD include aContent-Type header field defining the media type of that body. Ifand only if the media type is not given by a Content-Type field, therecipient MAY attempt to guess the media type via inspection of itscontent and/or the name extension(s) of the URI used to identify theresource. If the media type remains unknown, the recipient SHOULDtreat it as type "application/octet-stream".7.2.2 Entity LengthThe entity-length of a message is the length of the message-bodybefore any transfer-codings have been applied. Section 4.4 defines
Page 2: eferred to as "HTTP/1.1", and is an
Page 5 and 6: 12.1 Server-driven Negotiation ....
Page 7 and 8: 14.40 Trailer .....................
Page 9 and 10: 1.2 RequirementsThe key words "MUST
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
Page 56 and 57: If at any point an error status is
Page 58 and 59: optional features implemented by th
Page 60 and 61: - Extending a database through an a
Page 62 and 63: intervention (or other means) on th
Page 64 and 65: 10.1.2 101 Switching ProtocolsThe s
Page 66 and 67: esponse MAY include new or updated
Page 70 and 71: The response MUST include the follo
Page 72 and 73: If the client is sending data, a se
Page 74 and 75: If the response could be unacceptab
Page 76 and 77: 10.4.15 414 Request-URI Too LongThe
Page 78 and 79: 10.5.5 504 Gateway TimeoutThe serve
Page 82 and 83: Caching would be useless if it did
Page 84 and 85: Warning (but without removing any e
Page 86 and 87: If the user has overridden the basi
Page 88 and 89: in the past. This means that the re
Page 90 and 91: RFC 2616 HTTP/1.1 June 1999the time
Page 92 and 93: simple:response_is_fresh = (freshne
Page 94 and 95: 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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Fielding, et al. Standards Track [P
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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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