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

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Fielding, et al. Standards Track [Page 10]RFC 2616 HTTP/1.1 June 1999first-handA response is first-hand if it comes directly and withoutunnecessary delay from the origin server, perhaps via one or moreproxies. A response is also first-hand if its validity has justbeen checked directly with the origin server.explicit expiration timeThe time at which the origin server intends that an entity shouldno longer be returned by a cache without further validation.heuristic expiration timeAn expiration time assigned by a cache when no explicit expirationtime is available.ageThe age of a response is the time since it was sent by, orsuccessfully validated with, the origin server.freshness lifetimeThe length of time between the generation of a response and itsexpiration time.freshA response is fresh if its age has not yet exceeded its freshnesslifetime.staleA response is stale if its age has passed its freshness lifetime.semantically transparentA cache behaves in a "semantically transparent" manner, withrespect to a particular response, when its use affects neither therequesting client nor the origin server, except to improveperformance. When a cache is semantically transparent, the clientreceives exactly the same response (except for hop-by-hop headers)that it would have received had its request been handled directlyby the origin server.validatorA protocol element (e.g., an entity tag or a Last-Modified time)that is used to find out whether a cache entry is an equivalentcopy of an entity.upstream/downstreamUpstream and downstream describe the flow of a message: all
messages flow from upstream to downstream.Fielding, et al. Standards Track [Page 11]RFC 2616 HTTP/1.1 June 1999inbound/outboundInbound and outbound refer to the request and response paths formessages: "inbound" means "traveling toward the origin server",and "outbound" means "traveling toward the user agent"1.4 Overall OperationThe HTTP protocol is a request/response protocol. A client sends arequest to the server in the form of a request method, URI, andprotocol version, followed by a MIME-like message containing requestmodifiers, client information, and possible body content over aconnection with a server. The server responds with a status line,including the message's protocol version and a success or error code,followed by a MIME-like message containing server information, entitymetainformation, and possible entity-body content. The relationshipbetween HTTP and MIME is described in appendix 19.4.Most HTTP communication is initiated by a user agent and consists ofa request to be applied to a resource on some origin server. In thesimplest case, this may be accomplished via a single connection (v)between the user agent (UA) and the origin server (O).request chain ------------------------>UA -------------------v------------------- O
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 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 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 46 and 47: Fielding, et al. Standards Track [P
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
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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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