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

More documents

Recommendations

Info

Fielding, et al. Standards Track [Page 72]RFC 2616 HTTP/1.1 June 19994. It may limit a public cache's ability to use the same responsefor multiple user's requests.HTTP/1.1 includes the following request-header fields for enablingserver-driven negotiation through description of user agentcapabilities and user preferences: Accept (section 14.1), Accept-Charset (section 14.2), Accept-Encoding (section 14.3), Accept-Language (section 14.4), and User-Agent (section 14.43). However, anorigin server is not limited to these dimensions and MAY vary theresponse based on any aspect of the request, including informationoutside the request-header fields or within extension header fieldsnot defined by this specification.The Vary header field can be used to express the parameters theserver uses to select a representation that is subject to serverdrivennegotiation. See section 13.6 for use of the Vary header fieldby caches and section 14.44 for use of the Vary header field byservers.12.2 Agent-driven NegotiationWith agent-driven negotiation, selection of the best representationfor a response is performed by the user agent after receiving aninitial response from the origin server. Selection is based on a listof the available representations of the response included within theheader fields or entity-body of the initial response, with eachrepresentation identified by its own URI. Selection from among therepresentations may be performed automatically (if the user agent iscapable of doing so) or manually by the user selecting from agenerated (possibly hypertext) menu.Agent-driven negotiation is advantageous when the response would varyover commonly-used dimensions (such as type, language, or encoding),when the origin server is unable to determine a user agent'scapabilities from examining the request, and generally when publiccaches are used to distribute server load and reduce network usage.Agent-driven negotiation suffers from the disadvantage of needing asecond request to obtain the best alternate representation. Thissecond request is only efficient when caching is used. In addition,this specification does not define any mechanism for supporting
automatic selection, though it also does not prevent any suchmechanism from being developed as an extension and used withinHTTP/1.1.Fielding, et al. Standards Track [Page 73]RFC 2616 HTTP/1.1 June 1999HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)status codes for enabling agent-driven negotiation when the server isunwilling or unable to provide a varying response using server-drivennegotiation.12.3 Transparent NegotiationTransparent negotiation is a combination of both server-driven andagent-driven negotiation. When a cache is supplied with a form of thelist of available representations of the response (as in agent-drivennegotiation) and the dimensions of variance are completely understoodby the cache, then the cache becomes capable of performing serverdrivennegotiation on behalf of the origin server for subsequentrequests on that resource.Transparent negotiation has the advantage of distributing thenegotiation work that would otherwise be required of the originserver and also removing the second request delay of agent-drivennegotiation when the cache is able to correctly guess the rightresponse.This specification does not define any mechanism for transparentnegotiation, though it also does not prevent any such mechanism frombeing developed as an extension that could be used within HTTP/1.1.13 Caching in HTTPHTTP is typically used for distributed information systems, whereperformance can be improved by the use of response caches. TheHTTP/1.1 protocol includes a number of elements intended to makecaching work as well as possible. Because these elements areinextricable from other aspects of the protocol, and because theyinteract with each other, it is useful to describe the basic cachingdesign of HTTP separately from the detailed descriptions of methods,headers, response codes, etc.
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 24 and 25:
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
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
Page 100 and 101: Unless specifically constrained by
Page 104 and 105: warn-code 1xx, which are deleted ev
Page 106 and 107: for the associated entity, its enti
Page 108 and 109: - DELETE- POSTIn order to prevent d
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 118 and 119: containing an Authorization field,
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
Page 130 and 131:
new coding is known to be acceptabl
Page 132 and 133:
14.14 Content-LocationThe Content-L
Page 134 and 135:
Note: while the definition of Conte
Page 136 and 137:
server SHOULD return them in the or
Page 138 and 139:
Some origin server implementations
Page 140 and 141:
Expires = "Expires" ":" HTTP-dateAn
Page 142 and 143:
A client MUST include a Host header
Page 144 and 145:
een modified since the date given b
Page 146 and 147:
RFC 2616 HTTP/1.1 June 1999If none
Page 148 and 149:
14.29 Last-ModifiedThe Last-Modifie
Page 150 and 151:
MAY require that behavior be consis
Page 152 and 153:
yte-ranges-specifier = bytes-unit "
Page 154 and 155:
Content) instead of 200 (OK).- The
Page 156 and 157:
The TE request-header field indicat
Page 158 and 159:
Page 160 and 161:
a cache cannot determine from the r
Page 162 and 163:
SHOULD NOT, by default, forward the
Page 164 and 165:
this user agent behavior in mind.Re
Page 166 and 167:
designers and implementors be parti
Page 168 and 169:
strongly correlated to the membersh
Page 170 and 171:
serious security considerations. Co
Page 172 and 173:
The HTTP protocol has evolved consi
Page 174 and 175:
Protocol -- HTTP/1.0", RFC 1945, Ma
Page 176 and 177:
Implementation and Analysis", RFC 1
Page 178 and 179:
University of California, IrvineIrv
Page 180 and 181:
Page 182 and 183:
Notes:1) Additional CRLFs may prece
Page 184 and 185:
full compliance with the MIME proto
Page 186 and 187:
ead chunk-size and CRLF}read entity
Page 188 and 189:
- understand any valid response in
Page 190 and 191:
CREATE had a race that required an
Page 192 and 193:
also needed to be a general header,
Page 194:
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?