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

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containing an Authorization field, it MUST NOT return thecorresponding response as a reply to any other request, unless oneof the following specific exceptions holds:1. If the response includes the "s-maxage" cache-controldirective, the cache MAY use that response in replying to asubsequent request. But (if the specified maximum age haspassed) a proxy cache MUST first revalidate it with the originserver, using the request-headers from the new request to allowthe origin server to authenticate the new request. (This is thedefined behavior for s-maxage.) If the response includes "smaxage=0",the proxy MUST always revalidate it before re-usingit.2. If the response includes the "must-revalidate" cache-controldirective, the cache MAY use that response in replying to asubsequent request. But if the response is stale, all cachesMUST first revalidate it with the origin server, using therequest-headers from the new request to allow the origin serverto authenticate the new request.3. If the response includes the "public" cache-control directive,it MAY be returned in reply to any subsequent request.Fielding, et al. Standards Track [Page 107]RFC 2616 HTTP/1.1 June 199914.9 Cache-ControlThe Cache-Control general-header field is used to specify directivesthat MUST be obeyed by all caching mechanisms along therequest/response chain. The directives specify behavior intended toprevent caches from adversely interfering with the request orresponse. These directives typically override the default cachingalgorithms. Cache directives are unidirectional in that the presenceof a directive in a request does not imply that the same directive isto be given in the response.Note that HTTP/1.0 caches might not implement Cache-Control andmight only implement Pragma: no-cache (see section 14.32).Cache directives MUST be passed through by a proxy or gatewayapplication, regardless of their significance to that application,since the directives might be applicable to all recipients along therequest/response chain. It is not possible to specify a cachedirectivefor a specific cache.
Cache-Control = "Cache-Control" ":" 1#cache-directivecache-directive = cache-request-directive| cache-response-directivecache-request-directive ="no-cache" ; Section 14.9.1| "no-store" ; Section 14.9.2| "max-age" "=" delta-seconds ; Section 14.9.3, 14.9.4| "max-stale" [ "=" delta-seconds ] ; Section 14.9.3| "min-fresh" "=" delta-seconds ; Section 14.9.3| "no-transform" ; Section 14.9.5| "only-if-cached" ; Section 14.9.4| cache-extension ; Section 14.9.6cache-response-directive ="public" ; Section 14.9.1| "private" [ "=" ] ; Section 14.9.1| "no-cache" [ "=" ]; Section 14.9.1| "no-store" ; Section 14.9.2| "no-transform" ; Section 14.9.5| "must-revalidate" ; Section 14.9.4| "proxy-revalidate" ; Section 14.9.4| "max-age" "=" delta-seconds ; Section 14.9.3| "s-maxage" "=" delta-seconds ; Section 14.9.3| cache-extension ; Section 14.9.6cache-extension = token [ "=" ( token | quoted-string ) ]Fielding, et al. Standards Track [Page 108]RFC 2616 HTTP/1.1 June 1999When a directive appears without any 1#field-name parameter, thedirective applies to the entire request or response. When such adirective appears with a 1#field-name parameter, it applies only tothe named field or fields, and not to the rest of the request orresponse. This mechanism supports extensibility; implementations offuture versions of the HTTP protocol might apply these directives toheader fields not defined in HTTP/1.1.The cache-control directives can be broken down into these generalcategories:- Restrictions on what are cacheable; these may only be imposed bythe origin server.
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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
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compatibility with RFC 2068, a serv
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If at any point an error status is
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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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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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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 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
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Page 132 and 133: 14.14 Content-LocationThe Content-L
Page 134 and 135: Note: while the definition of Conte
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Page 140 and 141: Expires = "Expires" ":" HTTP-dateAn
Page 142 and 143: A client MUST include a Host header
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Page 146 and 147: RFC 2616 HTTP/1.1 June 1999If none
Page 148 and 149: 14.29 Last-ModifiedThe Last-Modifie
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Page 154 and 155: Content) instead of 200 (OK).- The
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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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