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

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connection-token close.If either the client or the server sends the close token in theConnection header, that request becomes the last one for theconnection.Clients and servers SHOULD NOT assume that a persistent connection ismaintained for HTTP versions less than 1.1 unless it is explicitlysignaled. See section 19.6.2 for more information on backwardcompatibility with HTTP/1.0 clients.In order to remain persistent, all messages on the connection MUSThave a self-defined message length (i.e., one not defined by closureof the connection), as described in section 4.4.Fielding, et al. Standards Track [Page 45]RFC 2616 HTTP/1.1 June 19998.1.2.2 PipeliningA client that supports persistent connections MAY "pipeline" itsrequests (i.e., send multiple requests without waiting for eachresponse). A server MUST send its responses to those requests in thesame order that the requests were received.Clients which assume persistent connections and pipeline immediatelyafter connection establishment SHOULD be prepared to retry theirconnection if the first pipelined attempt fails. If a client doessuch a retry, it MUST NOT pipeline before it knows the connection ispersistent. Clients MUST also be prepared to resend their requests ifthe server closes the connection before sending all of thecorresponding responses.Clients SHOULD NOT pipeline requests using non-idempotent methods ornon-idempotent sequences of methods (see section 9.1.2). Otherwise, apremature termination of the transport connection could lead toindeterminate results. A client wishing to send a non-idempotentrequest SHOULD wait to send that request until it has received theresponse status for the previous request.8.1.3 Proxy Servers
It is especially important that proxies correctly implement theproperties of the Connection header field as specified in section14.10.The proxy server MUST signal persistent connections separately withits clients and the origin servers (or other proxy servers) that itconnects to. Each persistent connection applies to only one transportlink.A proxy server MUST NOT establish a HTTP/1.1 persistent connectionwith an HTTP/1.0 client (but see RFC 2068 [33] for information anddiscussion of the problems with the Keep-Alive header implemented bymany HTTP/1.0 clients).8.1.4 Practical ConsiderationsServers will usually have some time-out value beyond which they willno longer maintain an inactive connection. Proxy servers might makethis a higher value since it is likely that the client will be makingmore connections through the same server. The use of persistentconnections places no requirements on the length (or existence) ofthis time-out for either the client or the server.Fielding, et al. Standards Track [Page 46]RFC 2616 HTTP/1.1 June 1999When a client or server wishes to time-out it SHOULD issue a gracefulclose on the transport connection. Clients and servers SHOULD bothconstantly watch for the other side of the transport close, andrespond to it as appropriate. If a client or server does not detectthe other side's close promptly it could cause unnecessary resourcedrain on the network.A client, server, or proxy MAY close the transport connection at anytime. For example, a client might have started to send a new requestat the same time that the server has decided to close the "idle"connection. From the server's point of view, the connection is beingclosed while it was idle, but from the client's point of view, arequest is in progress.This means that clients, servers, and proxies MUST be able to recoverfrom asynchronous close events. Client software SHOULD reopen thetransport connection and retransmit the aborted sequence of requestswithout user interaction so long as the request sequence is
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 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
Page 96 and 97: validators or strong validators. Cl
Page 98 and 99: - 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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