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

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warn-code 1xx, which are deleted even if not overridden).Note: this rule allows an origin server to use a 304 (NotModified) or a 206 (Partial Content) response to update any headerassociated with a previous response for the same entity or subrangesthereof, although it might not always be meaningful orcorrect to do so. This rule does not allow an origin server to usea 304 (Not Modified) or a 206 (Partial Content) response toentirely delete a header that it had provided with a previousresponse.Fielding, et al. Standards Track [Page 94]RFC 2616 HTTP/1.1 June 199913.5.4 Combining Byte RangesA response might transfer only a subrange of the bytes of an entitybody,either because the request included one or more Rangespecifications, or because a connection was broken prematurely. Afterseveral such transfers, a cache might have received several ranges ofthe same entity-body.If a cache has a stored non-empty set of subranges for an entity, andan incoming response transfers another subrange, the cache MAYcombine the new subrange with the existing set if both the followingconditions are met:- Both the incoming response and the cache entry have a cachevalidator.- The two cache validators match using the strong comparisonfunction (see section 13.3.3).If either requirement is not met, the cache MUST use only the mostrecent partial response (based on the Date values transmitted withevery response, and using the incoming response if these values areequal or missing), and MUST discard the other partial information.13.6 Caching Negotiated ResponsesUse of server-driven content negotiation (section 12.1), as indicatedby the presence of a Vary header field in a response, alters theconditions and procedure by which a cache can use the response forsubsequent requests. See section 14.44 for use of the Vary headerfield by servers.A server SHOULD use the Vary header field to inform a cache of what
equest-header fields were used to select among multiplerepresentations of a cacheable response subject to server-drivennegotiation. The set of header fields named by the Vary field valueis known as the "selecting" request-headers.When the cache receives a subsequent request whose Request-URIspecifies one or more cache entries including a Vary header field,the cache MUST NOT use such a cache entry to construct a response tothe new request unless all of the selecting request-headers presentin the new request match the corresponding stored request-headers inthe original request.The selecting request-headers from two requests are defined to matchif and only if the selecting request-headers in the first request canbe transformed to the selecting request-headers in the second requestFielding, et al. Standards Track [Page 95]RFC 2616 HTTP/1.1 June 1999by adding or removing linear white space (LWS) at places where thisis allowed by the corresponding BNF, and/or combining multiplemessage-header fields with the same field name following the rulesabout message headers in section 4.2.A Vary header field-value of "*" always fails to match and subsequentrequests on that resource can only be properly interpreted by theorigin server.If the selecting request header fields for the cached entry do notmatch the selecting request header fields of the new request, thenthe cache MUST NOT use a cached entry to satisfy the request unlessit first relays the new request to the origin server in a conditionalrequest and the server responds with 304 (Not Modified), including anentity tag or Content-Location that indicates the entity to be used.If an entity tag was assigned to a cached representation, theforwarded request SHOULD be conditional and include the entity tagsin an If-None-Match header field from all its cache entries for theresource. This conveys to the server the set of entities currentlyheld by the cache, so that if any one of these entities matches therequested entity, the server can use the ETag header field in its 304(Not Modified) response to tell the cache which entry is appropriate.If the entity-tag of the new response matches that of an existingentry, the new response SHOULD be used to update the header fields ofthe existing entry, and the result MUST be returned to the client.If any of the existing cache entries contains only partial content
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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
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An application that sends a request
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3.2.3 URI ComparisonWhen comparing
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is not desirable and is discouraged
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CRLFchunk = chunk-size [ chunk-exte
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When in canonical form, media subty
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3.9 Quality ValuesHTTP content nego
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RFC 2616 HTTP/1.1 June 1999HTTP/1.1
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message-body = entity-body| Transfe
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in advance.Messages MUST NOT includ
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equested resource, and 501 (Not Imp
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names) MUST use the following rules
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values for the first digit:- 1xx: I
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how the transfer-length of a messag
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connection-token close.If either th
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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 68 and 69: Fielding, et al. Standards Track [P
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
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 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,
Page 120 and 121: - Restrictions on what may be store
Page 122 and 123: improve privacy in some cases, we c
Page 126 and 127: must-revalidateBecause a cache MAY
Page 128 and 129: understand.For example, consider a
Page 130 and 131: new coding is known to be acceptabl
Page 132 and 133: 14.14 Content-LocationThe Content-L
Page 134 and 135: Note: while the definition of Conte
Page 136 and 137: server SHOULD return them in the or
Page 138 and 139: Some origin server implementations
Page 140 and 141: Expires = "Expires" ":" HTTP-dateAn
Page 142 and 143: A client MUST include a Host header
Page 144 and 145: een modified since the date given b
Page 146 and 147: RFC 2616 HTTP/1.1 June 1999If none
Page 148 and 149: 14.29 Last-ModifiedThe Last-Modifie
Page 150 and 151: MAY require that behavior be consis
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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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