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

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- understand any valid response in the format of HTTP/0.9, 1.0, or1.1.For most implementations of HTTP/1.0, each connection is establishedby the client prior to the request and closed by the server aftersending the response. Some implementations implement the Keep-Aliveversion of persistent connections described in section 19.7.1 of RFC2068 [33].19.6.1 Changes from HTTP/1.0This section summarizes major differences between versions HTTP/1.0and HTTP/1.1.19.6.1.1 Changes to Simplify Multi-homed Web Servers and Conserve IPAddressesThe requirements that clients and servers support the Host requestheader,report an error if the Host request-header (section 14.23) ismissing from an HTTP/1.1 request, and accept absolute URIs (section5.1.2) are among the most important changes defined by thisspecification.Older HTTP/1.0 clients assumed a one-to-one relationship of IPaddresses and servers; there was no other established mechanism fordistinguishing the intended server of a request than the IP addressto which that request was directed. The changes outlined above willallow the Internet, once older HTTP clients are no longer common, tosupport multiple Web sites from a single IP address, greatlysimplifying large operational Web servers, where allocation of manyIP addresses to a single host has created serious problems. TheInternet will also be able to recover the IP addresses that have beenallocated for the sole purpose of allowing special-purpose domainnames to be used in root-level HTTP URLs. Given the rate of growth ofthe Web, and the number of servers already deployed, it is extremelyFielding, et al. Standards Track [Page 171]RFC 2616 HTTP/1.1 June 1999important that all implementations of HTTP (including updates toexisting HTTP/1.0 applications) correctly implement theserequirements:- Both clients and servers MUST support the Host request-header.
- A client that sends an HTTP/1.1 request MUST send a Host header.- Servers MUST report a 400 (Bad Request) error if an HTTP/1.1request does not include a Host request-header.- Servers MUST accept absolute URIs.19.6.2 Compatibility with HTTP/1.0 Persistent ConnectionsSome clients and servers might wish to be compatible with someprevious implementations of persistent connections in HTTP/1.0clients and servers. Persistent connections in HTTP/1.0 areexplicitly negotiated as they are not the default behavior. HTTP/1.0experimental implementations of persistent connections are faulty,and the new facilities in HTTP/1.1 are designed to rectify theseproblems. The problem was that some existing 1.0 clients may besending Keep-Alive to a proxy server that doesn't understandConnection, which would then erroneously forward it to the nextinbound server, which would establish the Keep-Alive connection andresult in a hung HTTP/1.0 proxy waiting for the close on theresponse. The result is that HTTP/1.0 clients must be prevented fromusing Keep-Alive when talking to proxies.However, talking to proxies is the most important use of persistentconnections, so that prohibition is clearly unacceptable. Therefore,we need some other mechanism for indicating a persistent connectionis desired, which is safe to use even when talking to an old proxythat ignores Connection. Persistent connections are the default forHTTP/1.1 messages; we introduce a new keyword (Connection: close) fordeclaring non-persistence. See section 14.10.The original HTTP/1.0 form of persistent connections (the Connection:Keep-Alive and Keep-Alive header) is documented in RFC 2068. [33]19.6.3 Changes from RFC 2068This specification has been carefully audited to correct anddisambiguate key word usage; RFC 2068 had many problems in respect tothe conventions laid out in RFC 2119 [34].Clarified which error code should be used for inbound server failures(e.g. DNS failures). (Section 10.5.5).Fielding, et al. Standards Track [Page 172]RFC 2616 HTTP/1.1 June 1999
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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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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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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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Page 160 and 161: a cache cannot determine from the r
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Page 182 and 183: Notes:1) Additional CRLFs may prece
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Page 190 and 191: CREATE had a race that required an
Page 192 and 193: also needed to be a general header,
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