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

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An application that sends a request or response message that includesHTTP-Version of "HTTP/1.1" MUST be at least conditionally compliantwith this specification. Applications that are at least conditionallycompliant with this specification SHOULD use an HTTP-Version of"HTTP/1.1" in their messages, and MUST do so for any message that isnot compatible with HTTP/1.0. For more details on when to sendspecific HTTP-Version values, see RFC 2145 [36].The HTTP version of an application is the highest HTTP version forwhich the application is at least conditionally compliant.Proxy and gateway applications need to be careful when forwardingmessages in protocol versions different from that of the application.Since the protocol version indicates the protocol capability of thesender, a proxy/gateway MUST NOT send a message with a versionindicator which is greater than its actual version. If a higherversion request is received, the proxy/gateway MUST either downgradethe request version, or respond with an error, or switch to tunnelbehavior.Due to interoperability problems with HTTP/1.0 proxies discoveredsince the publication of RFC 2068[33], caching proxies MUST, gatewaysMAY, and tunnels MUST NOT upgrade the request to the highest versionthey support. The proxy/gateway's response to that request MUST be inthe same major version as the request.Note: Converting between versions of HTTP may involve modificationof header fields required or forbidden by the versions involved.3.2 Uniform Resource IdentifiersURIs have been known by many names: WWW addresses, Universal DocumentIdentifiers, Universal Resource Identifiers [3], and finally thecombination of Uniform Resource Locators (URL) [4] and Names (URN)[20]. As far as HTTP is concerned, Uniform Resource Identifiers aresimply formatted strings which identify--via name, location, or anyother characteristic--a resource.Fielding, et al. Standards Track [Page 18]RFC 2616 HTTP/1.1 June 19993.2.1 General SyntaxURIs in HTTP can be represented in absolute form or relative to someknown base URI [11], depending upon the context of their use. The twoforms are differentiated by the fact that absolute URIs always begin
with a scheme name followed by a colon. For definitive information onURL syntax and semantics, see "Uniform Resource Identifiers (URI):Generic Syntax and Semantics," RFC 2396 [42] (which replaces RFCs1738 [4] and RFC 1808 [11]). This specification adopts thedefinitions of "URI-reference", "absoluteURI", "relativeURI", "port","host","abs_path", "rel_path", and "authority" from thatspecification.The HTTP protocol does not place any a priori limit on the length ofa URI. Servers MUST be able to handle the URI of any resource theyserve, and SHOULD be able to handle URIs of unbounded length if theyprovide GET-based forms that could generate such URIs. A serverSHOULD return 414 (Request-URI Too Long) status if a URI is longerthan the server can handle (see section 10.4.15).Note: Servers ought to be cautious about depending on URI lengthsabove 255 bytes, because some older client or proxyimplementations might not properly support these lengths.3.2.2 http URLThe "http" scheme is used to locate network resources via the HTTPprotocol. This section defines the scheme-specific syntax andsemantics for http URLs.http_URL = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]]If the port is empty or not given, port 80 is assumed. The semanticsare that the identified resource is located at the server listeningfor TCP connections on that port of that host, and the Request-URIfor the resource is abs_path (section 5.1.2). The use of IP addressesin URLs SHOULD be avoided whenever possible (see RFC 1900 [24]). Ifthe abs_path is not present in the URL, it MUST be given as "/" whenused as a Request-URI for a resource (section 5.1.2). If a proxyreceives a host name which is not a fully qualified domain name, itMAY add its domain to the host name it received. If a proxy receivesa fully qualified domain name, the proxy MUST NOT change the hostname.Fielding, et al. Standards Track [Page 19]RFC 2616 HTTP/1.1 June 1999
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 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 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
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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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Fielding, et al. Standards Track [P
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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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Network Working Group R. Fielding Request for Comments: 2616 ...

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