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

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The response MUST include the following header fields:- Date, unless its omission is required by section 14.18.1Fielding, et al. Standards Track [Page 63]RFC 2616 HTTP/1.1 June 1999If a clockless origin server obeys these rules, and proxies andclients add their own Date to any response received without one (asalready specified by [RFC 2068], section 14.19), caches will operatecorrectly.- ETag and/or Content-Location, if the header would have been sentin a 200 response to the same request- Expires, Cache-Control, and/or Vary, if the field-value mightdiffer from that sent in any previous response for the samevariantIf the conditional GET used a strong cache validator (see section13.3.3), the response SHOULD NOT include other entity-headers.Otherwise (i.e., the conditional GET used a weak validator), theresponse MUST NOT include other entity-headers; this preventsinconsistencies between cached entity-bodies and updated headers.If a 304 response indicates an entity not currently cached, then thecache MUST disregard the response and repeat the request without theconditional.If a cache uses a received 304 response to update a cache entry, thecache MUST update the entry to reflect any new field values given inthe response.10.3.6 305 Use ProxyThe requested resource MUST be accessed through the proxy given bythe Location field. The Location field gives the URI of the proxy.The recipient is expected to repeat this single request via theproxy. 305 responses MUST only be generated by origin servers.Note: RFC 2068 was not clear that 305 was intended to redirect asingle request, and to be generated by origin servers only. Not
observing these limitations has significant security consequences.10.3.7 306 (Unused)The 306 status code was used in a previous version of thespecification, is no longer used, and the code is reserved.Fielding, et al. Standards Track [Page 64]RFC 2616 HTTP/1.1 June 199910.3.8 307 Temporary RedirectThe requested resource resides temporarily under a different URI.Since the redirection MAY be altered on occasion, the client SHOULDcontinue to use the Request-URI for future requests. This responseis only cacheable if indicated by a Cache-Control or Expires headerfield.The temporary URI SHOULD be given by the Location field in theresponse. Unless the request method was HEAD, the entity of theresponse SHOULD contain a short hypertext note with a hyperlink tothe new URI(s) , since many pre-HTTP/1.1 user agents do notunderstand the 307 status. Therefore, the note SHOULD contain theinformation necessary for a user to repeat the original request onthe new URI.If the 307 status code is received in response to a request otherthan GET or HEAD, the user agent MUST NOT automatically redirect therequest unless it can be confirmed by the user, since this mightchange the conditions under which the request was issued.10.4 Client Error 4xxThe 4xx class of status code is intended for cases in which theclient seems to have erred. Except when responding to a HEAD request,the server SHOULD include an entity containing an explanation of theerror situation, and whether it is a temporary or permanentcondition. These status codes are applicable to any request method.User agents SHOULD display any included entity to the user.
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eferred to as "HTTP/1.1", and is an
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12.1 Server-driven Negotiation ....
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14.40 Trailer .....................
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1.2 RequirementsThe key words "MUST
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Fielding, et al. Standards Track [P
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equest chain ----------------------
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Elements separated by a bar ("|") a
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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 24 and 25: Fielding, et al. Standards Track [P
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 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
Page 96 and 97: validators or strong validators. Cl
Page 98 and 99: - MAY send a weak entity tag instea
Page 100 and 101: Unless specifically constrained by
Page 104 and 105: warn-code 1xx, which are deleted ev
Page 106 and 107: for the associated entity, its enti
Page 108 and 109: - DELETE- POSTIn order to prevent d
Page 110 and 111: The Accept request-header field can
Page 112 and 113: image/jpeg = 0.5text/html;level=2 =
Page 114 and 115: Note: If the request does not inclu
Page 116 and 117: Accept-Ranges: bytesbut are not req
Page 118 and 119: 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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Network Working Group R. Fielding Request for Comments: 2616 ...

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