source: draft-ietf-httpbis/latest/p2-semantics.xml @ 154

Last change on this file since 154 was 153, checked in by julian.reschke@…, 12 years ago

Update "Editorial Note" stating that we now have incorporated everything that was in draft-lafon-rfc2616bis-03.

  • Property svn:eol-style set to native
File size: 120.0 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "January">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY diff2045entity             "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-upgrade             "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59]>
60<?rfc toc="yes" ?>
61<?rfc symrefs="yes" ?>
62<?rfc sortrefs="yes" ?>
63<?rfc compact="yes"?>
64<?rfc subcompact="no" ?>
65<?rfc linkmailto="no" ?>
66<?rfc editing="no" ?>
67<?rfc-ext allow-markup-in-artwork="yes" ?>
68<?rfc-ext include-references-in-index="yes" ?>
69<rfc obsoletes="2616" category="std"
70     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
71     xmlns:x='http://purl.org/net/xml2rfc/ext'>
72<front>
73
74  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
75
76  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
77    <organization abbrev="Day Software">Day Software</organization>
78    <address>
79      <postal>
80        <street>23 Corporate Plaza DR, Suite 280</street>
81        <city>Newport Beach</city>
82        <region>CA</region>
83        <code>92660</code>
84        <country>USA</country>
85      </postal>
86      <phone>+1-949-706-5300</phone>
87      <facsimile>+1-949-706-5305</facsimile>
88      <email>fielding@gbiv.com</email>
89      <uri>http://roy.gbiv.com/</uri>
90    </address>
91  </author>
92
93  <author initials="J." surname="Gettys" fullname="Jim Gettys">
94    <organization>One Laptop per Child</organization>
95    <address>
96      <postal>
97        <street>21 Oak Knoll Road</street>
98        <city>Carlisle</city>
99        <region>MA</region>
100        <code>01741</code>
101        <country>USA</country>
102      </postal>
103      <email>jg@laptop.org</email>
104      <uri>http://www.laptop.org/</uri>
105    </address>
106  </author>
107 
108  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
109    <organization abbrev="HP">Hewlett-Packard Company</organization>
110    <address>
111      <postal>
112        <street>HP Labs, Large Scale Systems Group</street>
113        <street>1501 Page Mill Road, MS 1177</street>
114        <city>Palo Alto</city>
115        <region>CA</region>
116        <code>94304</code>
117        <country>USA</country>
118      </postal>
119      <email>JeffMogul@acm.org</email>
120    </address>
121  </author>
122
123  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
124    <organization abbrev="Microsoft">Microsoft Corporation</organization>
125    <address>
126      <postal>
127        <street>1 Microsoft Way</street>
128        <city>Redmond</city>
129        <region>WA</region>
130        <code>98052</code>
131        <country>USA</country>
132      </postal>
133      <email>henrikn@microsoft.com</email>
134    </address>
135  </author>
136
137  <author initials="L." surname="Masinter" fullname="Larry Masinter">
138    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
139    <address>
140      <postal>
141        <street>345 Park Ave</street>
142        <city>San Jose</city>
143        <region>CA</region>
144        <code>95110</code>
145        <country>USA</country>
146      </postal>
147      <email>LMM@acm.org</email>
148      <uri>http://larry.masinter.net/</uri>
149    </address>
150  </author>
151 
152  <author initials="P." surname="Leach" fullname="Paul J. Leach">
153    <organization abbrev="Microsoft">Microsoft Corporation</organization>
154    <address>
155      <postal>
156        <street>1 Microsoft Way</street>
157        <city>Redmond</city>
158        <region>WA</region>
159        <code>98052</code>
160      </postal>
161      <email>paulle@microsoft.com</email>
162    </address>
163  </author>
164   
165  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
166    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
167    <address>
168      <postal>
169        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
170        <street>The Stata Center, Building 32</street>
171        <street>32 Vassar Street</street>
172        <city>Cambridge</city>
173        <region>MA</region>
174        <code>02139</code>
175        <country>USA</country>
176      </postal>
177      <email>timbl@w3.org</email>
178      <uri>http://www.w3.org/People/Berners-Lee/</uri>
179    </address>
180  </author>
181
182  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
183    <organization abbrev="W3C">World Wide Web Consortium</organization>
184    <address>
185      <postal>
186        <street>W3C / ERCIM</street>
187        <street>2004, rte des Lucioles</street>
188        <city>Sophia-Antipolis</city>
189        <region>AM</region>
190        <code>06902</code>
191        <country>France</country>
192      </postal>
193      <email>ylafon@w3.org</email>
194      <uri>http://www.raubacapeu.net/people/yves/</uri>
195    </address>
196  </author>
197
198  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
199    <organization abbrev="greenbytes">greenbytes GmbH</organization>
200    <address>
201      <postal>
202        <street>Hafenweg 16</street>
203        <city>Muenster</city><region>NW</region><code>48155</code>
204        <country>Germany</country>
205      </postal>
206      <phone>+49 251 2807760</phone>   
207      <facsimile>+49 251 2807761</facsimile>   
208      <email>julian.reschke@greenbytes.de</email>       
209      <uri>http://greenbytes.de/tech/webdav/</uri>     
210    </address>
211  </author>
212
213  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
214
215<abstract>
216<t>
217   The Hypertext Transfer Protocol (HTTP) is an application-level
218   protocol for distributed, collaborative, hypermedia information
219   systems. HTTP has been in use by the World Wide Web global information
220   initiative since 1990. This document is Part 2 of the seven-part specification
221   that defines the protocol referred to as "HTTP/1.1" and, taken together,
222   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
223   as expressed by request methods, request-header fields, response status codes,
224   and response-header fields.
225</t>
226</abstract>
227
228<note title="Editorial Note (To be removed by RFC Editor)">
229  <t>
230    Discussion of this draft should take place on the HTTPBIS working group
231    mailing list (ietf-http-wg@w3.org). The current issues list is
232    at <eref target="http://www.tools.ietf.org/wg/httpbis/trac/report/11"/>
233    and related documents (including fancy diffs) can be found at
234    <eref target="http://www.tools.ietf.org/wg/httpbis/"/>.
235  </t>
236  <t>
237    This draft incorporates those issue resolutions that were either
238    collected in the original RFC2616 errata list (<eref target="http://purl.org/NET/http-errata"/>),
239    or which were agreed upon on the mailing list between October 2006 and
240    November 2007 (as published in "draft-lafon-rfc2616bis-03").
241  </t>
242</note>
243</front>
244<middle>
245<section title="Introduction" anchor="introduction">
246<t>
247   This document will define aspects of HTTP related to request and response
248   semantics. Right now it only includes the extracted relevant sections of
249   RFC 2616 with only minor edits.
250</t>
251<t>
252   The HTTP protocol is a request/response protocol. A client sends a
253   request to the server in the form of a request method, URI, and
254   protocol version, followed by a MIME-like message containing request
255   modifiers, client information, and possible body content over a
256   connection with a server. The server responds with a status line,
257   including the message's protocol version and a success or error code,
258   followed by a MIME-like message containing server information, entity
259   metainformation, and possible entity-body content. The relationship
260   between HTTP and MIME is described in &diff2045entity;.
261</t>
262
263<section title="Requirements" anchor="intro.requirements">
264<t>
265   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
266   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
267   document are to be interpreted as described in <xref target="RFC2119"/>.
268</t>
269<t>
270   An implementation is not compliant if it fails to satisfy one or more
271   of the &MUST; or &REQUIRED; level requirements for the protocols it
272   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
273   level and all the &SHOULD; level requirements for its protocols is said
274   to be "unconditionally compliant"; one that satisfies all the &MUST;
275   level requirements but not all the &SHOULD; level requirements for its
276   protocols is said to be "conditionally compliant."
277</t>
278</section>
279</section>
280
281<section title="Product Tokens" anchor="product.tokens">
282<t>
283   Product tokens are used to allow communicating applications to
284   identify themselves by software name and version. Most fields using
285   product tokens also allow sub-products which form a significant part
286   of the application to be listed, separated by white space. By
287   convention, the products are listed in order of their significance
288   for identifying the application.
289</t>
290<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
291  product         = token ["/" product-version]
292  product-version = token
293</artwork></figure>
294<t>
295   Examples:
296</t>
297<figure><artwork type="example">
298    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
299    Server: Apache/0.8.4
300</artwork></figure>
301<t>
302   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
303   used for advertising or other non-essential information. Although any
304   token character &MAY; appear in a product-version, this token &SHOULD;
305   only be used for a version identifier (i.e., successive versions of
306   the same product &SHOULD; only differ in the product-version portion of
307   the product value).
308</t>
309</section>
310
311<section title="Method" anchor="method">
312<t>
313   The Method  token indicates the method to be performed on the
314   resource identified by the Request-URI. The method is case-sensitive.
315</t>
316<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
317  Method         = "OPTIONS"                ; <xref target="OPTIONS"/>
318                 | "GET"                    ; <xref target="GET"/>
319                 | "HEAD"                   ; <xref target="HEAD"/>
320                 | "POST"                   ; <xref target="POST"/>
321                 | "PUT"                    ; <xref target="PUT"/>
322                 | "DELETE"                 ; <xref target="DELETE"/>
323                 | "TRACE"                  ; <xref target="TRACE"/>
324                 | "CONNECT"                ; <xref target="CONNECT"/>
325                 | extension-method
326  extension-method = token
327</artwork></figure>
328<t>
329   The list of methods allowed by a resource can be specified in an
330   Allow header field (<xref target="header.allow"/>). The return code of the response
331   always notifies the client whether a method is currently allowed on a
332   resource, since the set of allowed methods can change dynamically. An
333   origin server &SHOULD; return the status code 405 (Method Not Allowed)
334   if the method is known by the origin server but not allowed for the
335   requested resource, and 501 (Not Implemented) if the method is
336   unrecognized or not implemented by the origin server. The methods GET
337   and HEAD &MUST; be supported by all general-purpose servers. All other
338   methods are &OPTIONAL;; however, if the above methods are implemented,
339   they &MUST; be implemented with the same semantics as those specified
340   in <xref target="method.definitions"/>.
341</t>
342</section>
343
344<section title="Request Header Fields" anchor="request.header.fields">
345<t>
346   The request-header fields allow the client to pass additional
347   information about the request, and about the client itself, to the
348   server. These fields act as request modifiers, with semantics
349   equivalent to the parameters on a programming language method
350   invocation.
351</t>
352<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
353  request-header = Accept                   ; &header-accept;
354                 | Accept-Charset           ; &header-accept-charset;
355                 | Accept-Encoding          ; &header-accept-encoding;
356                 | Accept-Language          ; &header-accept-language;
357                 | Authorization            ; &header-authorization;
358                 | Expect                   ; <xref target="header.expect"/>
359                 | From                     ; <xref target="header.from"/>
360                 | Host                     ; &header-host;
361                 | If-Match                 ; &header-if-match;
362                 | If-Modified-Since        ; &header-if-modified-since;
363                 | If-None-Match            ; &header-if-none-match;
364                 | If-Range                 ; &header-if-range;
365                 | If-Unmodified-Since      ; &header-if-unmodified-since;
366                 | Max-Forwards             ; <xref target="header.max-forwards"/>
367                 | Proxy-Authorization      ; &header-proxy-authorization;
368                 | Range                    ; &header-range;
369                 | Referer                  ; <xref target="header.referer"/>
370                 | TE                       ; &header-te;
371                 | User-Agent               ; <xref target="header.user-agent"/>
372</artwork></figure>
373<t>
374   Request-header field names can be extended reliably only in
375   combination with a change in the protocol version. However, new or
376   experimental header fields &MAY; be given the semantics of request-header
377   fields if all parties in the communication recognize them to
378   be request-header fields. Unrecognized header fields are treated as
379   entity-header fields.
380</t>
381</section>
382
383<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
384<t>
385   The Status-Code element is a 3-digit integer result code of the
386   attempt to understand and satisfy the request. The status codes listed
387   below are defined in <xref target="status.codes"/>.
388   The Reason-Phrase is intended to give a short
389   textual description of the Status-Code. The Status-Code is intended
390   for use by automata and the Reason-Phrase is intended for the human
391   user. The client is not required to examine or display the Reason-Phrase.
392</t>
393<t> 
394   The individual values of the numeric status codes defined for
395   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
396   presented below. The reason phrases listed here are only
397   recommendations -- they &MAY; be replaced by local equivalents without
398   affecting the protocol.
399</t>
400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
401  Status-Code    =
402         "100"  ; <xref target="status.100"/>: Continue
403       | "101"  ; <xref target="status.101"/>: Switching Protocols
404       | "200"  ; <xref target="status.200"/>: OK
405       | "201"  ; <xref target="status.201"/>: Created
406       | "202"  ; <xref target="status.202"/>: Accepted
407       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
408       | "204"  ; <xref target="status.204"/>: No Content
409       | "205"  ; <xref target="status.205"/>: Reset Content
410       | "206"  ; <xref target="status.206"/>: Partial Content
411       | "300"  ; <xref target="status.300"/>: Multiple Choices
412       | "301"  ; <xref target="status.301"/>: Moved Permanently
413       | "302"  ; <xref target="status.302"/>: Found
414       | "303"  ; <xref target="status.303"/>: See Other
415       | "304"  ; <xref target="status.304"/>: Not Modified
416       | "305"  ; <xref target="status.305"/>: Use Proxy
417       | "307"  ; <xref target="status.307"/>: Temporary Redirect
418       | "400"  ; <xref target="status.400"/>: Bad Request
419       | "401"  ; <xref target="status.401"/>: Unauthorized
420       | "402"  ; <xref target="status.402"/>: Payment Required
421       | "403"  ; <xref target="status.403"/>: Forbidden
422       | "404"  ; <xref target="status.404"/>: Not Found
423       | "405"  ; <xref target="status.405"/>: Method Not Allowed
424       | "406"  ; <xref target="status.406"/>: Not Acceptable
425       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
426       | "408"  ; <xref target="status.408"/>: Request Time-out
427       | "409"  ; <xref target="status.409"/>: Conflict
428       | "410"  ; <xref target="status.410"/>: Gone
429       | "411"  ; <xref target="status.411"/>: Length Required
430       | "412"  ; <xref target="status.412"/>: Precondition Failed
431       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
432       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
433       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
434       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
435       | "417"  ; <xref target="status.417"/>: Expectation Failed
436       | "500"  ; <xref target="status.500"/>: Internal Server Error
437       | "501"  ; <xref target="status.501"/>: Not Implemented
438       | "502"  ; <xref target="status.502"/>: Bad Gateway
439       | "503"  ; <xref target="status.503"/>: Service Unavailable
440       | "504"  ; <xref target="status.504"/>: Gateway Time-out
441       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
442       | extension-code
443
444  extension-code = 3DIGIT
445  Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
446</artwork></figure>
447<t>
448   HTTP status codes are extensible. HTTP applications are not required
449   to understand the meaning of all registered status codes, though such
450   understanding is obviously desirable. However, applications &MUST;
451   understand the class of any status code, as indicated by the first
452   digit, and treat any unrecognized response as being equivalent to the
453   x00 status code of that class, with the exception that an
454   unrecognized response &MUST-NOT; be cached. For example, if an
455   unrecognized status code of 431 is received by the client, it can
456   safely assume that there was something wrong with its request and
457   treat the response as if it had received a 400 status code. In such
458   cases, user agents &SHOULD; present to the user the entity returned
459   with the response, since that entity is likely to include human-readable
460   information which will explain the unusual status.
461</t>
462</section>
463
464<section title="Response Header Fields" anchor="response.header.fields">
465<t>
466   The response-header fields allow the server to pass additional
467   information about the response which cannot be placed in the Status-Line.
468   These header fields give information about the server and about
469   further access to the resource identified by the Request-URI.
470</t>
471<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
472  response-header = Accept-Ranges           ; &header-accept-ranges;
473                  | Age                     ; &header-age;
474                  | ETag                    ; &header-etag;
475                  | Location                ; <xref target="header.location"/>
476                  | Proxy-Authenticate      ; &header-proxy-authenticate;
477                  | Retry-After             ; <xref target="header.retry-after"/>
478                  | Server                  ; <xref target="header.server"/>
479                  | Vary                    ; &header-vary;
480                  | WWW-Authenticate        ; &header-www-authenticate;
481</artwork></figure>
482<t>
483   Response-header field names can be extended reliably only in
484   combination with a change in the protocol version. However, new or
485   experimental header fields &MAY; be given the semantics of response-header
486   fields if all parties in the communication recognize them to
487   be response-header fields. Unrecognized header fields are treated as
488   entity-header fields.
489</t>
490</section>
491
492<section title="Entity" anchor="entity">
493<t>
494   Request and Response messages &MAY; transfer an entity if not otherwise
495   restricted by the request method or response status code. An entity
496   consists of entity-header fields and an entity-body, although some
497   responses will only include the entity-headers. HTTP entity-body and
498   entity-header fields are defined in &payload;.
499</t>
500<t>
501   An entity-body is only present in a message when a message-body is
502   present, as described in &message-body;. The entity-body is obtained
503   from the message-body by decoding any Transfer-Encoding that might
504   have been applied to ensure safe and proper transfer of the message.
505</t>
506</section>
507
508
509<section title="Method Definitions" anchor="method.definitions">
510<t>
511   The set of common methods for HTTP/1.1 is defined below. Although
512   this set can be expanded, additional methods cannot be assumed to
513   share the same semantics for separately extended clients and servers.
514
515   The Host request-header field (&header-host;) &MUST; accompany all
516   HTTP/1.1 requests.
517</t>
518
519<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
520
521<section title="Safe Methods" anchor="safe.methods">
522<t>
523   Implementors should be aware that the software represents the user in
524   their interactions over the Internet, and should be careful to allow
525   the user to be aware of any actions they might take which may have an
526   unexpected significance to themselves or others.
527</t>
528<t>
529   In particular, the convention has been established that the GET and
530   HEAD methods &SHOULD-NOT;  have the significance of taking an action
531   other than retrieval. These methods ought to be considered "safe".
532   This allows user agents to represent other methods, such as POST, PUT
533   and DELETE, in a special way, so that the user is made aware of the
534   fact that a possibly unsafe action is being requested.
535</t>
536<t>
537   Naturally, it is not possible to ensure that the server does not
538   generate side-effects as a result of performing a GET request; in
539   fact, some dynamic resources consider that a feature. The important
540   distinction here is that the user did not request the side-effects,
541   so therefore cannot be held accountable for them.
542</t>
543</section>
544
545<section title="Idempotent Methods" anchor="idempotent.methods">
546<t>
547   Methods can also have the property of "idempotence" in that (aside
548   from error or expiration issues) the side-effects of N &gt; 0 identical
549   requests is the same as for a single request. The methods GET, HEAD,
550   PUT and DELETE share this property. Also, the methods OPTIONS and
551   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
552</t>
553<t>
554   However, it is possible that a sequence of several requests is non-idempotent,
555   even if all of the methods executed in that sequence are
556   idempotent. (A sequence is idempotent if a single execution of the
557   entire sequence always yields a result that is not changed by a
558   reexecution of all, or part, of that sequence.) For example, a
559   sequence is non-idempotent if its result depends on a value that is
560   later modified in the same sequence.
561</t>
562<t>
563   A sequence that never has side effects is idempotent, by definition
564   (provided that no concurrent operations are being executed on the
565   same set of resources).
566</t>
567</section>
568</section>
569
570<section title="OPTIONS" anchor="OPTIONS">
571  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
572  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
573<t>
574   The OPTIONS method represents a request for information about the
575   communication options available on the request/response chain
576   identified by the Request-URI. This method allows the client to
577   determine the options and/or requirements associated with a resource,
578   or the capabilities of a server, without implying a resource action
579   or initiating a resource retrieval.
580</t>
581<t>
582   Responses to this method are not cacheable.
583</t>
584<t>
585   If the OPTIONS request includes an entity-body (as indicated by the
586   presence of Content-Length or Transfer-Encoding), then the media type
587   &MUST; be indicated by a Content-Type field. Although this
588   specification does not define any use for such a body, future
589   extensions to HTTP might use the OPTIONS body to make more detailed
590   queries on the server. A server that does not support such an
591   extension &MAY; discard the request body.
592</t>
593<t>
594   If the Request-URI is an asterisk ("*"), the OPTIONS request is
595   intended to apply to the server in general rather than to a specific
596   resource. Since a server's communication options typically depend on
597   the resource, the "*" request is only useful as a "ping" or "no-op"
598   type of method; it does nothing beyond allowing the client to test
599   the capabilities of the server. For example, this can be used to test
600   a proxy for HTTP/1.1 compliance (or lack thereof).
601</t>
602<t>
603   If the Request-URI is not an asterisk, the OPTIONS request applies
604   only to the options that are available when communicating with that
605   resource.
606</t>
607<t>
608   A 200 response &SHOULD; include any header fields that indicate
609   optional features implemented by the server and applicable to that
610   resource (e.g., Allow), possibly including extensions not defined by
611   this specification. The response body, if any, &SHOULD; also include
612   information about the communication options. The format for such a
613   body is not defined by this specification, but might be defined by
614   future extensions to HTTP. Content negotiation &MAY; be used to select
615   the appropriate response format. If no response body is included, the
616   response &MUST; include a Content-Length field with a field-value of
617   "0".
618</t>
619<t>
620   The Max-Forwards request-header field &MAY; be used to target a
621   specific proxy in the request chain. When a proxy receives an OPTIONS
622   request on an absoluteURI for which request forwarding is permitted,
623   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
624   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
625   instead, the proxy &SHOULD; respond with its own communication options.
626   If the Max-Forwards field-value is an integer greater than zero, the
627   proxy &MUST; decrement the field-value when it forwards the request. If
628   no Max-Forwards field is present in the request, then the forwarded
629   request &MUST-NOT; include a Max-Forwards field.
630</t>
631</section>
632
633<section title="GET" anchor="GET">
634  <iref primary="true" item="GET method" x:for-anchor=""/>
635  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
636<t>
637   The GET method means retrieve whatever information (in the form of an
638   entity) is identified by the Request-URI. If the Request-URI refers
639   to a data-producing process, it is the produced data which shall be
640   returned as the entity in the response and not the source text of the
641   process, unless that text happens to be the output of the process.
642</t>
643<t>
644   The semantics of the GET method change to a "conditional GET" if the
645   request message includes an If-Modified-Since, If-Unmodified-Since,
646   If-Match, If-None-Match, or If-Range header field. A conditional GET
647   method requests that the entity be transferred only under the
648   circumstances described by the conditional header field(s). The
649   conditional GET method is intended to reduce unnecessary network
650   usage by allowing cached entities to be refreshed without requiring
651   multiple requests or transferring data already held by the client.
652</t>
653<t>
654   The semantics of the GET method change to a "partial GET" if the
655   request message includes a Range header field. A partial GET requests
656   that only part of the entity be transferred, as described in &header-range;.
657   The partial GET method is intended to reduce unnecessary
658   network usage by allowing partially-retrieved entities to be
659   completed without transferring data already held by the client.
660</t>
661<t>
662   The response to a GET request is cacheable if and only if it meets
663   the requirements for HTTP caching described in &caching;.
664</t>
665<t>
666   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
667</t>
668</section>
669
670<section title="HEAD" anchor="HEAD">
671  <iref primary="true" item="HEAD method" x:for-anchor=""/>
672  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
673<t>
674   The HEAD method is identical to GET except that the server &MUST-NOT;
675   return a message-body in the response. The metainformation contained
676   in the HTTP headers in response to a HEAD request &SHOULD; be identical
677   to the information sent in response to a GET request. This method can
678   be used for obtaining metainformation about the entity implied by the
679   request without transferring the entity-body itself. This method is
680   often used for testing hypertext links for validity, accessibility,
681   and recent modification.
682</t>
683<t>
684   The response to a HEAD request &MAY; be cacheable in the sense that the
685   information contained in the response &MAY; be used to update a
686   previously cached entity from that resource. If the new field values
687   indicate that the cached entity differs from the current entity (as
688   would be indicated by a change in Content-Length, Content-MD5, ETag
689   or Last-Modified), then the cache &MUST; treat the cache entry as
690   stale.
691</t>
692</section>
693
694<section title="POST" anchor="POST">
695  <iref primary="true" item="POST method" x:for-anchor=""/>
696  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
697<t>
698   The POST method is used to request that the origin server accept the
699   entity enclosed in the request as data to be processed by the resource
700   identified by the Request-URI in the Request-Line. POST is designed
701   to allow a uniform method to cover the following functions:
702  <list style="symbols">
703    <t>
704      Annotation of existing resources;
705    </t>
706    <t>
707        Posting a message to a bulletin board, newsgroup, mailing list,
708        or similar group of articles;
709    </t>
710    <t>
711        Providing a block of data, such as the result of submitting a
712        form, to a data-handling process;
713    </t>
714    <t>
715        Extending a database through an append operation.
716    </t>
717  </list>
718</t>
719<t>
720   The actual function performed by the POST method is determined by the
721   server and is usually dependent on the Request-URI.
722</t>
723<t>
724   The action performed by the POST method might not result in a
725   resource that can be identified by a URI. In this case, either 200
726   (OK) or 204 (No Content) is the appropriate response status,
727   depending on whether or not the response includes an entity that
728   describes the result.
729</t>
730<t>
731   If a resource has been created on the origin server, the response
732   &SHOULD; be 201 (Created) and contain an entity which describes the
733   status of the request and refers to the new resource, and a Location
734   header (see <xref target="header.location"/>).
735</t>
736<t>
737   Responses to this method are not cacheable, unless the response
738   includes appropriate Cache-Control or Expires header fields. However,
739   the 303 (See Other) response can be used to direct the user agent to
740   retrieve a cacheable resource.
741</t>
742</section>
743
744<section title="PUT" anchor="PUT">
745  <iref primary="true" item="PUT method" x:for-anchor=""/>
746  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
747<t>
748   The PUT method requests that the enclosed entity be stored under the
749   supplied Request-URI. If the Request-URI refers to an already
750   existing resource, the enclosed entity &SHOULD; be considered as a
751   modified version of the one residing on the origin server. If the
752   Request-URI does not point to an existing resource, and that URI is
753   capable of being defined as a new resource by the requesting user
754   agent, the origin server can create the resource with that URI. If a
755   new resource is created, the origin server &MUST; inform the user agent
756   via the 201 (Created) response. If an existing resource is modified,
757   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
758   to indicate successful completion of the request. If the resource
759   could not be created or modified with the Request-URI, an appropriate
760   error response &SHOULD; be given that reflects the nature of the
761   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
762   (e.g. Content-Range) headers that it does not understand or implement
763   and &MUST; return a 501 (Not Implemented) response in such cases.
764</t>
765<t>
766   If the request passes through a cache and the Request-URI identifies
767   one or more currently cached entities, those entries &SHOULD; be
768   treated as stale. Responses to this method are not cacheable.
769</t>
770<t>
771   The fundamental difference between the POST and PUT requests is
772   reflected in the different meaning of the Request-URI. The URI in a
773   POST request identifies the resource that will handle the enclosed
774   entity. That resource might be a data-accepting process, a gateway to
775   some other protocol, or a separate entity that accepts annotations.
776   In contrast, the URI in a PUT request identifies the entity enclosed
777   with the request -- the user agent knows what URI is intended and the
778   server &MUST-NOT; attempt to apply the request to some other resource.
779   If the server desires that the request be applied to a different URI,
780   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
781   then make its own decision regarding whether or not to redirect the
782   request.
783</t>
784<t>
785   A single resource &MAY; be identified by many different URIs. For
786   example, an article might have a URI for identifying "the current
787   version" which is separate from the URI identifying each particular
788   version. In this case, a PUT request on a general URI might result in
789   several other URIs being defined by the origin server.
790</t>
791<t>
792   HTTP/1.1 does not define how a PUT method affects the state of an
793   origin server.
794</t>
795<t>
796   Unless otherwise specified for a particular entity-header, the
797   entity-headers in the PUT request &SHOULD; be applied to the resource
798   created or modified by the PUT.
799</t>
800</section>
801
802<section title="DELETE" anchor="DELETE">
803  <iref primary="true" item="DELETE method" x:for-anchor=""/>
804  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
805<t>
806   The DELETE method requests that the origin server delete the resource
807   identified by the Request-URI. This method &MAY; be overridden by human
808   intervention (or other means) on the origin server. The client cannot
809   be guaranteed that the operation has been carried out, even if the
810   status code returned from the origin server indicates that the action
811   has been completed successfully. However, the server &SHOULD-NOT; 
812   indicate success unless, at the time the response is given, it
813   intends to delete the resource or move it to an inaccessible
814   location.
815</t>
816<t>
817   A successful response &SHOULD; be 200 (OK) if the response includes an
818   entity describing the status, 202 (Accepted) if the action has not
819   yet been enacted, or 204 (No Content) if the action has been enacted
820   but the response does not include an entity.
821</t>
822<t>
823   If the request passes through a cache and the Request-URI identifies
824   one or more currently cached entities, those entries &SHOULD; be
825   treated as stale. Responses to this method are not cacheable.
826</t>
827</section>
828
829<section title="TRACE" anchor="TRACE">
830  <iref primary="true" item="TRACE method" x:for-anchor=""/>
831  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
832<t>
833   The TRACE method is used to invoke a remote, application-layer loop-back
834   of the request message. The final recipient of the request
835   &SHOULD; reflect the message received back to the client as the
836   entity-body of a 200 (OK) response. The final recipient is either the
837   origin server or the first proxy or gateway to receive a Max-Forwards
838   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
839   &MUST-NOT; include an entity.
840</t>
841<t>
842   TRACE allows the client to see what is being received at the other
843   end of the request chain and use that data for testing or diagnostic
844   information. The value of the Via header field (&header-via;) is of
845   particular interest, since it acts as a trace of the request chain.
846   Use of the Max-Forwards header field allows the client to limit the
847   length of the request chain, which is useful for testing a chain of
848   proxies forwarding messages in an infinite loop.
849</t>
850<t>
851   If the request is valid, the response &SHOULD; contain the entire
852   request message in the entity-body, with a Content-Type of
853   "message/http". Responses to this method &MUST-NOT; be cached.
854</t>
855</section>
856
857<section title="CONNECT" anchor="CONNECT">
858  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
859  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
860<t>
861   This specification reserves the method name CONNECT for use with a
862   proxy that can dynamically switch to being a tunnel (e.g. SSL
863   tunneling <xref target="Luo1998"/>).
864</t>
865</section>
866</section>
867
868
869<section title="Status Code Definitions" anchor="status.codes">
870<t>
871   Each Status-Code is described below, including a description of which
872   method(s) it can follow and any metainformation required in the
873   response.
874</t>
875
876<section title="Informational 1xx" anchor="status.1xx">
877<t>
878   This class of status code indicates a provisional response,
879   consisting only of the Status-Line and optional headers, and is
880   terminated by an empty line. There are no required headers for this
881   class of status code. Since HTTP/1.0 did not define any 1xx status
882   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
883   except under experimental conditions.
884</t>
885<t>
886   A client &MUST; be prepared to accept one or more 1xx status responses
887   prior to a regular response, even if the client does not expect a 100
888   (Continue) status message. Unexpected 1xx status responses &MAY; be
889   ignored by a user agent.
890</t>
891<t>
892   Proxies &MUST; forward 1xx responses, unless the connection between the
893   proxy and its client has been closed, or unless the proxy itself
894   requested the generation of the 1xx response. (For example, if a
895   proxy adds a "Expect: 100-continue" field when it forwards a request,
896   then it need not forward the corresponding 100 (Continue)
897   response(s).)
898</t>
899
900<section title="100 Continue" anchor="status.100">
901  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
902  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
903<t>
904   The client &SHOULD; continue with its request. This interim response is
905   used to inform the client that the initial part of the request has
906   been received and has not yet been rejected by the server. The client
907   &SHOULD; continue by sending the remainder of the request or, if the
908   request has already been completed, ignore this response. The server
909   &MUST; send a final response after the request has been completed. See
910   &use100; for detailed discussion of the use and handling of this
911   status code.
912</t>
913</section>
914
915<section title="101 Switching Protocols" anchor="status.101">
916  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
917  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
918<t>
919   The server understands and is willing to comply with the client's
920   request, via the Upgrade message header field (&header-upgrade;), for a
921   change in the application protocol being used on this connection. The
922   server will switch protocols to those defined by the response's
923   Upgrade header field immediately after the empty line which
924   terminates the 101 response.
925</t>
926<t>
927   The protocol &SHOULD; be switched only when it is advantageous to do
928   so. For example, switching to a newer version of HTTP is advantageous
929   over older versions, and switching to a real-time, synchronous
930   protocol might be advantageous when delivering resources that use
931   such features.
932</t>
933</section>
934</section>
935
936<section title="Successful 2xx" anchor="status.2xx">
937<t>
938   This class of status code indicates that the client's request was
939   successfully received, understood, and accepted.
940</t>
941
942<section title="200 OK" anchor="status.200">
943  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
944  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
945<t>
946   The request has succeeded. The information returned with the response
947   is dependent on the method used in the request, for example:
948  <list style="hanging">
949    <t hangText="GET">
950          an entity corresponding to the requested resource is sent in
951          the response;
952    </t>
953    <t hangText="HEAD">
954          the entity-header fields corresponding to the requested
955          resource are sent in the response without any message-body;
956    </t>
957    <t hangText="POST">
958      an entity describing or containing the result of the action;
959    </t>
960    <t hangText="TRACE">
961      an entity containing the request message as received by the
962      end server.
963    </t>
964  </list>
965</t>
966</section>
967
968<section title="201 Created" anchor="status.201">
969  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
970  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
971<t>
972   The request has been fulfilled and resulted in a new resource being
973   created. The newly created resource can be referenced by the URI(s)
974   returned in the entity of the response, with the most specific URI
975   for the resource given by a Location header field. The response
976   &SHOULD; include an entity containing a list of resource
977   characteristics and location(s) from which the user or user agent can
978   choose the one most appropriate. The entity format is specified by
979   the media type given in the Content-Type header field. The origin
980   server &MUST; create the resource before returning the 201 status code.
981   If the action cannot be carried out immediately, the server &SHOULD;
982   respond with 202 (Accepted) response instead.
983</t>
984<t>
985   A 201 response &MAY; contain an ETag response header field indicating
986   the current value of the entity tag for the requested variant just
987   created, see &header-etag;.
988</t>
989</section>
990
991<section title="202 Accepted" anchor="status.202">
992  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
993  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
994<t>
995   The request has been accepted for processing, but the processing has
996   not been completed.  The request might or might not eventually be
997   acted upon, as it might be disallowed when processing actually takes
998   place. There is no facility for re-sending a status code from an
999   asynchronous operation such as this.
1000</t>
1001<t>
1002   The 202 response is intentionally non-committal. Its purpose is to
1003   allow a server to accept a request for some other process (perhaps a
1004   batch-oriented process that is only run once per day) without
1005   requiring that the user agent's connection to the server persist
1006   until the process is completed. The entity returned with this
1007   response &SHOULD; include an indication of the request's current status
1008   and either a pointer to a status monitor or some estimate of when the
1009   user can expect the request to be fulfilled.
1010</t>
1011</section>
1012
1013<section title="203 Non-Authoritative Information" anchor="status.203">
1014  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1015  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1016<t>
1017   The returned metainformation in the entity-header is not the
1018   definitive set as available from the origin server, but is gathered
1019   from a local or a third-party copy. The set presented &MAY; be a subset
1020   or superset of the original version. For example, including local
1021   annotation information about the resource might result in a superset
1022   of the metainformation known by the origin server. Use of this
1023   response code is not required and is only appropriate when the
1024   response would otherwise be 200 (OK).
1025</t>
1026</section>
1027
1028<section title="204 No Content" anchor="status.204">
1029  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1030  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1031<t>
1032   The server has fulfilled the request but does not need to return an
1033   entity-body, and might want to return updated metainformation. The
1034   response &MAY; include new or updated metainformation in the form of
1035   entity-headers, which if present &SHOULD; be associated with the
1036   requested variant.
1037</t>
1038<t>
1039   If the client is a user agent, it &SHOULD-NOT;  change its document view
1040   from that which caused the request to be sent. This response is
1041   primarily intended to allow input for actions to take place without
1042   causing a change to the user agent's active document view, although
1043   any new or updated metainformation &SHOULD; be applied to the document
1044   currently in the user agent's active view.
1045</t>
1046<t>
1047   The 204 response &MUST-NOT; include a message-body, and thus is always
1048   terminated by the first empty line after the header fields.
1049</t>
1050</section>
1051
1052<section title="205 Reset Content" anchor="status.205">
1053  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1054  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1055<t>
1056   The server has fulfilled the request and the user agent &SHOULD; reset
1057   the document view which caused the request to be sent. This response
1058   is primarily intended to allow input for actions to take place via
1059   user input, followed by a clearing of the form in which the input is
1060   given so that the user can easily initiate another input action. The
1061   response &MUST-NOT; include an entity.
1062</t>
1063</section>
1064
1065<section title="206 Partial Content" anchor="status.206">
1066  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1067  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1068<t>
1069   The server has fulfilled the partial GET request for the resource
1070   and the enclosed entity is a partial representation as defined in &range;.
1071</t>
1072</section>
1073</section>
1074
1075<section title="Redirection 3xx" anchor="status.3xx">
1076<t>
1077   This class of status code indicates that further action needs to be
1078   taken by the user agent in order to fulfill the request.  The action
1079   required &MAY; be carried out by the user agent without interaction
1080   with the user if and only if the method used in the second request is
1081   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1082   such loops generate network traffic for each redirection.
1083  <list><t>
1084      <x:h>Note:</x:h> previous versions of this specification recommended a
1085      maximum of five redirections. Content developers should be aware
1086      that there might be clients that implement such a fixed
1087      limitation.
1088  </t></list>
1089</t>
1090
1091<section title="300 Multiple Choices" anchor="status.300">
1092  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1093  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1094<t>
1095   The requested resource corresponds to any one of a set of
1096   representations, each with its own specific location, and agent-driven
1097   negotiation information (&content-negotiation;) is being provided so that
1098   the user (or user agent) can select a preferred representation and
1099   redirect its request to that location.
1100</t>
1101<t>
1102   Unless it was a HEAD request, the response &SHOULD; include an entity
1103   containing a list of resource characteristics and location(s) from
1104   which the user or user agent can choose the one most appropriate. The
1105   entity format is specified by the media type given in the Content-Type
1106   header field. Depending upon the format and the capabilities of
1107   the user agent, selection of the most appropriate choice &MAY; be
1108   performed automatically. However, this specification does not define
1109   any standard for such automatic selection.
1110</t>
1111<t>
1112   If the server has a preferred choice of representation, it &SHOULD;
1113   include the specific URI for that representation in the Location
1114   field; user agents &MAY; use the Location field value for automatic
1115   redirection. This response is cacheable unless indicated otherwise.
1116</t>
1117</section>
1118
1119<section title="301 Moved Permanently" anchor="status.301">
1120  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1121  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1122<t>
1123   The requested resource has been assigned a new permanent URI and any
1124   future references to this resource &SHOULD; use one of the returned
1125   URIs.  Clients with link editing capabilities ought to automatically
1126   re-link references to the Request-URI to one or more of the new
1127   references returned by the server, where possible. This response is
1128   cacheable unless indicated otherwise.
1129</t>
1130<t>
1131   The new permanent URI &SHOULD; be given by the Location field in the
1132   response. Unless the request method was HEAD, the entity of the
1133   response &SHOULD; contain a short hypertext note with a hyperlink to
1134   the new URI(s).
1135</t>
1136<t>
1137   If the 301 status code is received in response to a request method
1138   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1139   then the request &MAY; be automatically redirected by the user agent without
1140   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1141   request unless it can be confirmed by the user, since this might
1142   change the conditions under which the request was issued.
1143  <list><t>
1144      <x:h>Note:</x:h> When automatically redirecting a POST request after
1145      receiving a 301 status code, some existing HTTP/1.0 user agents
1146      will erroneously change it into a GET request.
1147  </t></list>
1148</t>
1149</section>
1150
1151<section title="302 Found" anchor="status.302">
1152  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1153  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1154<t>
1155   The requested resource resides temporarily under a different URI.
1156   Since the redirection might be altered on occasion, the client &SHOULD;
1157   continue to use the Request-URI for future requests.  This response
1158   is only cacheable if indicated by a Cache-Control or Expires header
1159   field.
1160</t>
1161<t>
1162   The temporary URI &SHOULD; be given by the Location field in the
1163   response. Unless the request method was HEAD, the entity of the
1164   response &SHOULD; contain a short hypertext note with a hyperlink to
1165   the new URI(s).
1166</t>
1167<t>
1168   If the 302 status code is received in response to a request method
1169   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1170   then the request &MAY; be automatically redirected by the user agent without
1171   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1172   request unless it can be confirmed by the user, since this might
1173   change the conditions under which the request was issued.
1174  <list><t>
1175      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1176      to change the method on the redirected request.  However, most
1177      existing user agent implementations treat 302 as if it were a 303
1178      response, performing a GET on the Location field-value regardless
1179      of the original request method. The status codes 303 and 307 have
1180      been added for servers that wish to make unambiguously clear which
1181      kind of reaction is expected of the client.
1182  </t></list>
1183</t>
1184</section>
1185
1186<section title="303 See Other" anchor="status.303">
1187  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1188  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1189<t>
1190   The response to the request can be found under a different URI and
1191   &SHOULD; be retrieved using a GET method on that resource. This method
1192   exists primarily to allow the output of a POST-activated script to
1193   redirect the user agent to a selected resource. The new URI is not a
1194   substitute reference for the originally requested resource. The 303
1195   response &MUST-NOT; be cached, but the response to the second
1196   (redirected) request might be cacheable.
1197</t>
1198<t>
1199   The different URI &SHOULD; be given by the Location field in the
1200   response. Unless the request method was HEAD, the entity of the
1201   response &SHOULD; contain a short hypertext note with a hyperlink to
1202   the new URI(s).
1203  <list><t>
1204      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1205      status. When interoperability with such clients is a concern, the
1206      302 status code may be used instead, since most user agents react
1207      to a 302 response as described here for 303.
1208  </t></list>
1209</t>
1210</section>
1211
1212<section title="304 Not Modified" anchor="status.304">
1213  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1214  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1215<t>
1216   The response to the request has not been modified since the conditions
1217   indicated by the client's conditional GET request, as defined in &conditional;.
1218</t>
1219</section>
1220
1221<section title="305 Use Proxy" anchor="status.305">
1222  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1223  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1224<t>
1225   The requested resource &MUST; be accessed through the proxy given by
1226   the Location field. The Location field gives the URI of the proxy.
1227   The recipient is expected to repeat this single request via the
1228   proxy. 305 responses &MUST; only be generated by origin servers.
1229  <list><t>
1230      <x:h>Note:</x:h> <xref target="RFC2068"/> was not clear that 305 was intended to redirect a
1231      single request, and to be generated by origin servers only.  Not
1232      observing these limitations has significant security consequences.
1233  </t></list>
1234</t>
1235</section>
1236
1237<section title="306 (Unused)" anchor="status.306">
1238  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1239  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1240<t>
1241   The 306 status code was used in a previous version of the
1242   specification, is no longer used, and the code is reserved.
1243</t>
1244</section>
1245
1246<section title="307 Temporary Redirect" anchor="status.307">
1247  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1248  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1249<t>
1250   The requested resource resides temporarily under a different URI.
1251   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1252   continue to use the Request-URI for future requests.  This response
1253   is only cacheable if indicated by a Cache-Control or Expires header
1254   field.
1255</t>
1256<t>
1257   The temporary URI &SHOULD; be given by the Location field in the
1258   response. Unless the request method was HEAD, the entity of the
1259   response &SHOULD; contain a short hypertext note with a hyperlink to
1260   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1261   understand the 307 status. Therefore, the note &SHOULD; contain the
1262   information necessary for a user to repeat the original request on
1263   the new URI.
1264</t>
1265<t>
1266   If the 307 status code is received in response to a request method
1267   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1268   then the request &MAY; be automatically redirected by the user agent without
1269   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1270   request unless it can be confirmed by the user, since this might
1271   change the conditions under which the request was issued.
1272</t>
1273</section>
1274</section>
1275
1276<section title="Client Error 4xx" anchor="status.4xx">
1277<t>
1278   The 4xx class of status code is intended for cases in which the
1279   client seems to have erred. Except when responding to a HEAD request,
1280   the server &SHOULD; include an entity containing an explanation of the
1281   error situation, and whether it is a temporary or permanent
1282   condition. These status codes are applicable to any request method.
1283   User agents &SHOULD; display any included entity to the user.
1284</t>
1285<t>
1286   If the client is sending data, a server implementation using TCP
1287   &SHOULD; be careful to ensure that the client acknowledges receipt of
1288   the packet(s) containing the response, before the server closes the
1289   input connection. If the client continues sending data to the server
1290   after the close, the server's TCP stack will send a reset packet to
1291   the client, which may erase the client's unacknowledged input buffers
1292   before they can be read and interpreted by the HTTP application.
1293</t>
1294
1295<section title="400 Bad Request" anchor="status.400">
1296  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1297  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1298<t>
1299   The request could not be understood by the server due to malformed
1300   syntax. The client &SHOULD-NOT;  repeat the request without
1301   modifications.
1302</t>
1303</section>
1304
1305<section title="401 Unauthorized" anchor="status.401">
1306  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1307  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1308<t>
1309   The request requires user authentication (see &auth;).
1310</t>
1311</section>
1312
1313<section title="402 Payment Required" anchor="status.402">
1314  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1315  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1316<t>
1317   This code is reserved for future use.
1318</t>
1319</section>
1320
1321<section title="403 Forbidden" anchor="status.403">
1322  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1323  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1324<t>
1325   The server understood the request, but is refusing to fulfill it.
1326   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1327   If the request method was not HEAD and the server wishes to make
1328   public why the request has not been fulfilled, it &SHOULD; describe the
1329   reason for the refusal in the entity.  If the server does not wish to
1330   make this information available to the client, the status code 404
1331   (Not Found) can be used instead.
1332</t>
1333</section>
1334
1335<section title="404 Not Found" anchor="status.404">
1336  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1337  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1338<t>
1339   The server has not found anything matching the Request-URI. No
1340   indication is given of whether the condition is temporary or
1341   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1342   knows, through some internally configurable mechanism, that an old
1343   resource is permanently unavailable and has no forwarding address.
1344   This status code is commonly used when the server does not wish to
1345   reveal exactly why the request has been refused, or when no other
1346   response is applicable.
1347</t>
1348</section>
1349
1350<section title="405 Method Not Allowed" anchor="status.405">
1351  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1352  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1353<t>
1354   The method specified in the Request-Line is not allowed for the
1355   resource identified by the Request-URI. The response &MUST; include an
1356   Allow header containing a list of valid methods for the requested
1357   resource.
1358</t>
1359</section>
1360
1361<section title="406 Not Acceptable" anchor="status.406">
1362  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1363  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1364<t>
1365   The resource identified by the request is only capable of generating
1366   response entities which have content characteristics not acceptable
1367   according to the accept headers sent in the request.
1368</t>
1369<t>
1370   Unless it was a HEAD request, the response &SHOULD; include an entity
1371   containing a list of available entity characteristics and location(s)
1372   from which the user or user agent can choose the one most
1373   appropriate. The entity format is specified by the media type given
1374   in the Content-Type header field. Depending upon the format and the
1375   capabilities of the user agent, selection of the most appropriate
1376   choice &MAY; be performed automatically. However, this specification
1377   does not define any standard for such automatic selection.
1378  <list><t>
1379      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1380      not acceptable according to the accept headers sent in the
1381      request. In some cases, this may even be preferable to sending a
1382      406 response. User agents are encouraged to inspect the headers of
1383      an incoming response to determine if it is acceptable.
1384  </t></list>
1385</t>
1386<t>
1387   If the response could be unacceptable, a user agent &SHOULD;
1388   temporarily stop receipt of more data and query the user for a
1389   decision on further actions.
1390</t>
1391</section>
1392
1393<section title="407 Proxy Authentication Required" anchor="status.407">
1394  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1395  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1396<t>
1397   This code is similar to 401 (Unauthorized), but indicates that the
1398   client must first authenticate itself with the proxy (see &auth;).
1399</t>
1400</section>
1401
1402<section title="408 Request Timeout" anchor="status.408">
1403  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1404  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1405<t>
1406   The client did not produce a request within the time that the server
1407   was prepared to wait. The client &MAY; repeat the request without
1408   modifications at any later time.
1409</t>
1410</section>
1411
1412<section title="409 Conflict" anchor="status.409">
1413  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1414  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1415<t>
1416   The request could not be completed due to a conflict with the current
1417   state of the resource. This code is only allowed in situations where
1418   it is expected that the user might be able to resolve the conflict
1419   and resubmit the request. The response body &SHOULD; include enough
1420   information for the user to recognize the source of the conflict.
1421   Ideally, the response entity would include enough information for the
1422   user or user agent to fix the problem; however, that might not be
1423   possible and is not required.
1424</t>
1425<t>
1426   Conflicts are most likely to occur in response to a PUT request. For
1427   example, if versioning were being used and the entity being PUT
1428   included changes to a resource which conflict with those made by an
1429   earlier (third-party) request, the server might use the 409 response
1430   to indicate that it can't complete the request. In this case, the
1431   response entity would likely contain a list of the differences
1432   between the two versions in a format defined by the response
1433   Content-Type.
1434</t>
1435</section>
1436
1437<section title="410 Gone" anchor="status.410">
1438  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1439  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1440<t>
1441   The requested resource is no longer available at the server and no
1442   forwarding address is known. This condition is expected to be
1443   considered permanent. Clients with link editing capabilities &SHOULD;
1444   delete references to the Request-URI after user approval. If the
1445   server does not know, or has no facility to determine, whether or not
1446   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1447   used instead. This response is cacheable unless indicated otherwise.
1448</t>
1449<t>
1450   The 410 response is primarily intended to assist the task of web
1451   maintenance by notifying the recipient that the resource is
1452   intentionally unavailable and that the server owners desire that
1453   remote links to that resource be removed. Such an event is common for
1454   limited-time, promotional services and for resources belonging to
1455   individuals no longer working at the server's site. It is not
1456   necessary to mark all permanently unavailable resources as "gone" or
1457   to keep the mark for any length of time -- that is left to the
1458   discretion of the server owner.
1459</t>
1460</section>
1461
1462<section title="411 Length Required" anchor="status.411">
1463  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1464  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1465<t>
1466   The server refuses to accept the request without a defined Content-Length.
1467   The client &MAY; repeat the request if it adds a valid
1468   Content-Length header field containing the length of the message-body
1469   in the request message.
1470</t>
1471</section>
1472
1473<section title="412 Precondition Failed" anchor="status.412">
1474  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1475  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1476<t>
1477   The precondition given in one or more of the request-header fields
1478   evaluated to false when it was tested on the server, as defined in
1479   &conditional;.
1480</t>
1481</section>
1482
1483<section title="413 Request Entity Too Large" anchor="status.413">
1484  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1485  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1486<t>
1487   The server is refusing to process a request because the request
1488   entity is larger than the server is willing or able to process. The
1489   server &MAY; close the connection to prevent the client from continuing
1490   the request.
1491</t>
1492<t>
1493   If the condition is temporary, the server &SHOULD; include a Retry-After
1494   header field to indicate that it is temporary and after what
1495   time the client &MAY; try again.
1496</t>
1497</section>
1498
1499<section title="414 Request-URI Too Long" anchor="status.414">
1500  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1501  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1502<t>
1503   The server is refusing to service the request because the Request-URI
1504   is longer than the server is willing to interpret. This rare
1505   condition is only likely to occur when a client has improperly
1506   converted a POST request to a GET request with long query
1507   information, when the client has descended into a URI "black hole" of
1508   redirection (e.g., a redirected URI prefix that points to a suffix of
1509   itself), or when the server is under attack by a client attempting to
1510   exploit security holes present in some servers using fixed-length
1511   buffers for reading or manipulating the Request-URI.
1512</t>
1513</section>
1514
1515<section title="415 Unsupported Media Type" anchor="status.415">
1516  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1517  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1518<t>
1519   The server is refusing to service the request because the entity of
1520   the request is in a format not supported by the requested resource
1521   for the requested method.
1522</t>
1523</section>
1524
1525<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1526  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1527  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1528<t>
1529   The request included a Range request-header field (&header-range;) and none of
1530   the range-specifier values in this field overlap the current extent
1531   of the selected resource.
1532</t>
1533</section>
1534
1535<section title="417 Expectation Failed" anchor="status.417">
1536  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1537  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1538<t>
1539   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1540   could not be met by this server, or, if the server is a proxy,
1541   the server has unambiguous evidence that the request could not be met
1542   by the next-hop server.
1543</t>
1544</section>
1545</section>
1546
1547<section title="Server Error 5xx" anchor="status.5xx">
1548<t>
1549   Response status codes beginning with the digit "5" indicate cases in
1550   which the server is aware that it has erred or is incapable of
1551   performing the request. Except when responding to a HEAD request, the
1552   server &SHOULD; include an entity containing an explanation of the
1553   error situation, and whether it is a temporary or permanent
1554   condition. User agents &SHOULD; display any included entity to the
1555   user. These response codes are applicable to any request method.
1556</t>
1557
1558<section title="500 Internal Server Error" anchor="status.500">
1559  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1560  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1561<t>
1562   The server encountered an unexpected condition which prevented it
1563   from fulfilling the request.
1564</t>
1565</section>
1566
1567<section title="501 Not Implemented" anchor="status.501">
1568  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1569  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1570<t>
1571   The server does not support the functionality required to fulfill the
1572   request. This is the appropriate response when the server does not
1573   recognize the request method and is not capable of supporting it for
1574   any resource.
1575</t>
1576</section>
1577
1578<section title="502 Bad Gateway" anchor="status.502">
1579  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1580  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1581<t>
1582   The server, while acting as a gateway or proxy, received an invalid
1583   response from the upstream server it accessed in attempting to
1584   fulfill the request.
1585</t>
1586</section>
1587
1588<section title="503 Service Unavailable" anchor="status.503">
1589  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1590  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1591<t>
1592   The server is currently unable to handle the request due to a
1593   temporary overloading or maintenance of the server. The implication
1594   is that this is a temporary condition which will be alleviated after
1595   some delay. If known, the length of the delay &MAY; be indicated in a
1596   Retry-After header. If no Retry-After is given, the client &SHOULD;
1597   handle the response as it would for a 500 response.
1598  <list><t>
1599      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1600      server must use it when becoming overloaded. Some servers may wish
1601      to simply refuse the connection.
1602  </t></list>
1603</t>
1604</section>
1605
1606<section title="504 Gateway Timeout" anchor="status.504">
1607  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1608  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1609<t>
1610   The server, while acting as a gateway or proxy, did not receive a
1611   timely response from the upstream server specified by the URI (e.g.
1612   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1613   to access in attempting to complete the request.
1614  <list><t>
1615      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1616      return 400 or 500 when DNS lookups time out.
1617  </t></list>
1618</t>
1619</section>
1620
1621<section title="505 HTTP Version Not Supported" anchor="status.505">
1622  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1623  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1624<t>
1625   The server does not support, or refuses to support, the HTTP protocol
1626   version that was used in the request message. The server is
1627   indicating that it is unable or unwilling to complete the request
1628   using the same major version as the client, as described in &http-version;,
1629   other than with this error message. The response &SHOULD; contain
1630   an entity describing why that version is not supported and what other
1631   protocols are supported by that server.
1632</t>
1633
1634</section>
1635</section>
1636</section>
1637
1638
1639<section title="Header Field Definitions" anchor="header.fields">
1640<t>
1641   This section defines the syntax and semantics of HTTP/1.1 header fields
1642   related to request and response semantics.
1643</t>
1644<t>
1645   For entity-header fields, both sender and recipient refer to either the
1646   client or the server, depending on who sends and who receives the entity.
1647</t>
1648
1649<section title="Allow" anchor="header.allow">
1650  <iref primary="true" item="Allow header" x:for-anchor=""/>
1651  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1652<t>
1653      The Allow entity-header field lists the set of methods supported
1654      by the resource identified by the Request-URI. The purpose of this
1655      field is strictly to inform the recipient of valid methods
1656      associated with the resource. An Allow header field &MUST; be
1657      present in a 405 (Method Not Allowed) response.
1658</t>
1659<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1660  Allow   = "Allow" ":" #Method
1661</artwork></figure>
1662<t>
1663      Example of use:
1664</t>
1665<figure><artwork type="example">
1666       Allow: GET, HEAD, PUT
1667</artwork></figure>
1668<t>
1669      This field cannot prevent a client from trying other methods.
1670      However, the indications given by the Allow header field value
1671      &SHOULD; be followed. The actual set of allowed methods is defined
1672      by the origin server at the time of each request.
1673</t>
1674<t>
1675      The Allow header field &MAY; be provided with a PUT request to
1676      recommend the methods to be supported by the new or modified
1677      resource. The server is not required to support these methods and
1678      &SHOULD; include an Allow header in the response giving the actual
1679      supported methods.
1680</t>
1681<t>
1682      A proxy &MUST-NOT; modify the Allow header field even if it does not
1683      understand all the methods specified, since the user agent might
1684      have other means of communicating with the origin server.
1685</t>
1686</section>
1687
1688<section title="Expect" anchor="header.expect">
1689  <iref primary="true" item="Expect header" x:for-anchor=""/>
1690  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1691<t>
1692   The Expect request-header field is used to indicate that particular
1693   server behaviors are required by the client.
1694</t>
1695<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/>
1696  Expect       =  "Expect" ":" 1#expectation
1697 
1698  expectation  =  "100-continue" | expectation-extension
1699  expectation-extension =  token [ "=" ( token | quoted-string )
1700                           *expect-params ]
1701  expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1702</artwork></figure>
1703<t>
1704   A server that does not understand or is unable to comply with any of
1705   the expectation values in the Expect field of a request &MUST; respond
1706   with appropriate error status. The server &MUST; respond with a 417
1707   (Expectation Failed) status if any of the expectations cannot be met
1708   or, if there are other problems with the request, some other 4xx
1709   status.
1710</t>
1711<t>
1712   This header field is defined with extensible syntax to allow for
1713   future extensions. If a server receives a request containing an
1714   Expect field that includes an expectation-extension that it does not
1715   support, it &MUST; respond with a 417 (Expectation Failed) status.
1716</t>
1717<t>
1718   Comparison of expectation values is case-insensitive for unquoted
1719   tokens (including the 100-continue token), and is case-sensitive for
1720   quoted-string expectation-extensions.
1721</t>
1722<t>
1723   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1724   return a 417 (Expectation Failed) status if it receives a request
1725   with an expectation that it cannot meet. However, the Expect
1726   request-header itself is end-to-end; it &MUST; be forwarded if the
1727   request is forwarded.
1728</t>
1729<t>
1730   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1731   Expect header.
1732</t>
1733<t>
1734   See &use100; for the use of the 100 (Continue) status.
1735</t>
1736</section>
1737
1738<section title="From" anchor="header.from">
1739  <iref primary="true" item="From header" x:for-anchor=""/>
1740  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1741<t>
1742   The From request-header field, if given, &SHOULD; contain an Internet
1743   e-mail address for the human user who controls the requesting user
1744   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1745   in <xref x:sec="3.4" x:fmt="of" target="RFC2822"/>:
1746</t>
1747<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1748  From   = "From" ":" mailbox
1749</artwork></figure>
1750<t>
1751   An example is:
1752</t>
1753<figure><artwork type="example">
1754    From: webmaster@example.org
1755</artwork></figure>
1756<t>
1757   This header field &MAY; be used for logging purposes and as a means for
1758   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1759   be used as an insecure form of access protection. The interpretation
1760   of this field is that the request is being performed on behalf of the
1761   person given, who accepts responsibility for the method performed. In
1762   particular, robot agents &SHOULD; include this header so that the
1763   person responsible for running the robot can be contacted if problems
1764   occur on the receiving end.
1765</t>
1766<t>
1767   The Internet e-mail address in this field &MAY; be separate from the
1768   Internet host which issued the request. For example, when a request
1769   is passed through a proxy the original issuer's address &SHOULD; be
1770   used.
1771</t>
1772<t>
1773   The client &SHOULD-NOT;  send the From header field without the user's
1774   approval, as it might conflict with the user's privacy interests or
1775   their site's security policy. It is strongly recommended that the
1776   user be able to disable, enable, and modify the value of this field
1777   at any time prior to a request.
1778</t>
1779</section>
1780
1781<section title="Location" anchor="header.location">
1782  <iref primary="true" item="Location header" x:for-anchor=""/>
1783  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1784<t>
1785   The Location response-header field is used to redirect the recipient
1786   to a location other than the Request-URI for completion of the
1787   request or identification of a new resource. For 201 (Created)
1788   responses, the Location is that of the new resource which was created
1789   by the request. For 3xx responses, the location &SHOULD; indicate the
1790   server's preferred URI for automatic redirection to the resource. The
1791   field value consists of a single absolute URI.
1792</t>
1793<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1794  Location       = "Location" ":" absoluteURI [ "#" fragment ]
1795</artwork></figure>
1796<t>
1797   An example is:
1798</t>
1799<figure><artwork type="example">
1800    Location: http://www.example.org/pub/WWW/People.html
1801</artwork></figure>
1802<t>
1803  <list><t>
1804      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1805      from Location in that the Content-Location identifies the original
1806      location of the entity enclosed in the request. It is therefore
1807      possible for a response to contain header fields for both Location
1808      and Content-Location.
1809  </t></list>
1810</t>
1811<t>
1812   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1813   <list style="symbols">
1814      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1815      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1816      <t>With 305 Use Proxy.</t>
1817   </list>
1818</t>
1819</section>
1820
1821<section title="Max-Forwards" anchor="header.max-forwards">
1822  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1823  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1824<t>
1825   The Max-Forwards request-header field provides a mechanism with the
1826   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1827   number of proxies or gateways that can forward the request to the
1828   next inbound server. This can be useful when the client is attempting
1829   to trace a request chain which appears to be failing or looping in
1830   mid-chain.
1831</t>
1832<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1833  Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1834</artwork></figure>
1835<t>
1836   The Max-Forwards value is a decimal integer indicating the remaining
1837   number of times this request message may be forwarded.
1838</t>
1839<t>
1840   Each proxy or gateway recipient of a TRACE or OPTIONS request
1841   containing a Max-Forwards header field &MUST; check and update its
1842   value prior to forwarding the request. If the received value is zero
1843   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1844   respond as the final recipient. If the received Max-Forwards value is
1845   greater than zero, then the forwarded message &MUST; contain an updated
1846   Max-Forwards field with a value decremented by one (1).
1847</t>
1848<t>
1849   The Max-Forwards header field &MAY; be ignored for all other methods
1850   defined by this specification and for any extension methods for which
1851   it is not explicitly referred to as part of that method definition.
1852</t>
1853</section>
1854
1855<section title="Referer" anchor="header.referer">
1856  <iref primary="true" item="Referer header" x:for-anchor=""/>
1857  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1858<t>
1859   The Referer[sic] request-header field allows the client to specify,
1860   for the server's benefit, the address (URI) of the resource from
1861   which the Request-URI was obtained (the "referrer", although the
1862   header field is misspelled.) The Referer request-header allows a
1863   server to generate lists of back-links to resources for interest,
1864   logging, optimized caching, etc. It also allows obsolete or mistyped
1865   links to be traced for maintenance. The Referer field &MUST-NOT; be
1866   sent if the Request-URI was obtained from a source that does not have
1867   its own URI, such as input from the user keyboard.
1868</t>
1869<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1870  Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1871</artwork></figure>
1872<t>
1873   Example:
1874</t>
1875<figure><artwork type="example">
1876    Referer: http://www.example.org/hypertext/Overview.html
1877</artwork></figure>
1878<t>
1879   If the field value is a relative URI, it &SHOULD; be interpreted
1880   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1881   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1882</t>
1883</section>
1884
1885<section title="Retry-After" anchor="header.retry-after">
1886  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1887  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1888<t>
1889   The Retry-After response-header field can be used with a 503 (Service
1890   Unavailable) response to indicate how long the service is expected to
1891   be unavailable to the requesting client. This field &MAY; also be used
1892   with any 3xx (Redirection) response to indicate the minimum time the
1893   user-agent is asked wait before issuing the redirected request. The
1894   value of this field can be either an HTTP-date or an integer number
1895   of seconds (in decimal) after the time of the response.
1896</t>
1897<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1898  Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1899</artwork></figure>
1900<t>
1901   Two examples of its use are
1902</t>
1903<figure><artwork type="example">
1904    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1905    Retry-After: 120
1906</artwork></figure>
1907<t>
1908   In the latter example, the delay is 2 minutes.
1909</t>
1910</section>
1911
1912<section title="Server" anchor="header.server">
1913  <iref primary="true" item="Server header" x:for-anchor=""/>
1914  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
1915<t>
1916   The Server response-header field contains information about the
1917   software used by the origin server to handle the request. The field
1918   can contain multiple product tokens (<xref target="product.tokens"/>) and comments
1919   identifying the server and any significant subproducts. The product
1920   tokens are listed in order of their significance for identifying the
1921   application.
1922</t>
1923<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
1924  Server         = "Server" ":" 1*( product | comment )
1925</artwork></figure>
1926<t>
1927   Example:
1928</t>
1929<figure><artwork type="example">
1930    Server: CERN/3.0 libwww/2.17
1931</artwork></figure>
1932<t>
1933   If the response is being forwarded through a proxy, the proxy
1934   application &MUST-NOT; modify the Server response-header. Instead, it
1935   &MUST; include a Via field (as described in &header-via;).
1936  <list><t>
1937      <x:h>Note:</x:h> Revealing the specific software version of the server might
1938      allow the server machine to become more vulnerable to attacks
1939      against software that is known to contain security holes. Server
1940      implementors are encouraged to make this field a configurable
1941      option.
1942  </t></list>
1943</t>
1944</section>
1945
1946<section title="User-Agent" anchor="header.user-agent">
1947  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
1948  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
1949<t>
1950   The User-Agent request-header field contains information about the
1951   user agent originating the request. This is for statistical purposes,
1952   the tracing of protocol violations, and automated recognition of user
1953   agents for the sake of tailoring responses to avoid particular user
1954   agent limitations. User agents &SHOULD; include this field with
1955   requests. The field can contain multiple product tokens (<xref target="product.tokens"/>)
1956   and comments identifying the agent and any subproducts which form a
1957   significant part of the user agent. By convention, the product tokens
1958   are listed in order of their significance for identifying the
1959   application.
1960</t>
1961<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
1962  User-Agent     = "User-Agent" ":" 1*( product | comment )
1963</artwork></figure>
1964<t>
1965   Example:
1966</t>
1967<figure><artwork type="example">
1968    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1969</artwork></figure>
1970</section>
1971
1972</section>
1973
1974<section title="IANA Considerations" anchor="IANA.considerations">
1975<t>
1976   TBD.
1977</t>
1978</section>
1979
1980<section title="Security Considerations" anchor="security.considerations">
1981<t>
1982   This section is meant to inform application developers, information
1983   providers, and users of the security limitations in HTTP/1.1 as
1984   described by this document. The discussion does not include
1985   definitive solutions to the problems revealed, though it does make
1986   some suggestions for reducing security risks.
1987</t>
1988
1989<section title="Transfer of Sensitive Information" anchor="security.sensitive">
1990<t>
1991   Like any generic data transfer protocol, HTTP cannot regulate the
1992   content of the data that is transferred, nor is there any a priori
1993   method of determining the sensitivity of any particular piece of
1994   information within the context of any given request. Therefore,
1995   applications &SHOULD; supply as much control over this information as
1996   possible to the provider of that information. Four header fields are
1997   worth special mention in this context: Server, Via, Referer and From.
1998</t>
1999<t>
2000   Revealing the specific software version of the server might allow the
2001   server machine to become more vulnerable to attacks against software
2002   that is known to contain security holes. Implementors &SHOULD; make the
2003   Server header field a configurable option.
2004</t>
2005<t>
2006   Proxies which serve as a portal through a network firewall &SHOULD;
2007   take special precautions regarding the transfer of header information
2008   that identifies the hosts behind the firewall. In particular, they
2009   &SHOULD; remove, or replace with sanitized versions, any Via fields
2010   generated behind the firewall.
2011</t>
2012<t>
2013   The Referer header allows reading patterns to be studied and reverse
2014   links drawn. Although it can be very useful, its power can be abused
2015   if user details are not separated from the information contained in
2016   the Referer. Even when the personal information has been removed, the
2017   Referer header might indicate a private document's URI whose
2018   publication would be inappropriate.
2019</t>
2020<t>
2021   The information sent in the From field might conflict with the user's
2022   privacy interests or their site's security policy, and hence it
2023   &SHOULD-NOT;  be transmitted without the user being able to disable,
2024   enable, and modify the contents of the field. The user &MUST; be able
2025   to set the contents of this field within a user preference or
2026   application defaults configuration.
2027</t>
2028<t>
2029   We suggest, though do not require, that a convenient toggle interface
2030   be provided for the user to enable or disable the sending of From and
2031   Referer information.
2032</t>
2033<t>
2034   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2035   fields can sometimes be used to determine that a specific client or
2036   server have a particular security hole which might be exploited.
2037   Unfortunately, this same information is often used for other valuable
2038   purposes for which HTTP currently has no better mechanism.
2039</t>
2040</section>
2041
2042<section title="Encoding Sensitive Information in URI's" anchor="encoding.sensitive.information.in.uris">
2043<t>
2044   Because the source of a link might be private information or might
2045   reveal an otherwise private information source, it is strongly
2046   recommended that the user be able to select whether or not the
2047   Referer field is sent. For example, a browser client could have a
2048   toggle switch for browsing openly/anonymously, which would
2049   respectively enable/disable the sending of Referer and From
2050   information.
2051</t>
2052<t>
2053   Clients &SHOULD-NOT;  include a Referer header field in a (non-secure)
2054   HTTP request if the referring page was transferred with a secure
2055   protocol.
2056</t>
2057<t>
2058   Authors of services which use the HTTP protocol &SHOULD-NOT;  use GET
2059   based forms for the submission of sensitive data, because this will
2060   cause this data to be encoded in the Request-URI. Many existing
2061   servers, proxies, and user agents will log the request URI in some
2062   place where it might be visible to third parties. Servers can use
2063   POST-based form submission instead
2064</t>
2065</section>
2066
2067<section title="Location Headers and Spoofing" anchor="location.spoofing">
2068<t>
2069   If a single server supports multiple organizations that do not trust
2070   one another, then it &MUST; check the values of Location and Content-Location
2071   headers in responses that are generated under control of
2072   said organizations to make sure that they do not attempt to
2073   invalidate resources over which they have no authority.
2074</t>
2075</section>
2076
2077</section>
2078
2079<section title="Acknowledgments" anchor="ack">
2080</section>
2081</middle>
2082<back>
2083
2084<references title="Normative References">
2085
2086<reference anchor="Part1">
2087  <front>
2088    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2089    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2090      <organization abbrev="Day Software">Day Software</organization>
2091      <address><email>fielding@gbiv.com</email></address>
2092    </author>
2093    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2094      <organization>One Laptop per Child</organization>
2095      <address><email>jg@laptop.org</email></address>
2096    </author>
2097    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2098      <organization abbrev="HP">Hewlett-Packard Company</organization>
2099      <address><email>JeffMogul@acm.org</email></address>
2100    </author>
2101    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2102      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2103      <address><email>henrikn@microsoft.com</email></address>
2104    </author>
2105    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2106      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2107      <address><email>LMM@acm.org</email></address>
2108    </author>
2109    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2110      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2111      <address><email>paulle@microsoft.com</email></address>
2112    </author>
2113    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2114      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2115      <address><email>timbl@w3.org</email></address>
2116    </author>
2117    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2118      <organization abbrev="W3C">World Wide Web Consortium</organization>
2119      <address><email>ylafon@w3.org</email></address>
2120    </author>
2121    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2122      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2123      <address><email>julian.reschke@greenbytes.de</email></address>
2124    </author>
2125    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2126  </front>
2127  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2128  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2129</reference>
2130
2131<reference anchor="Part3">
2132  <front>
2133    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2134    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2135      <organization abbrev="Day Software">Day Software</organization>
2136      <address><email>fielding@gbiv.com</email></address>
2137    </author>
2138    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2139      <organization>One Laptop per Child</organization>
2140      <address><email>jg@laptop.org</email></address>
2141    </author>
2142    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2143      <organization abbrev="HP">Hewlett-Packard Company</organization>
2144      <address><email>JeffMogul@acm.org</email></address>
2145    </author>
2146    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2147      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2148      <address><email>henrikn@microsoft.com</email></address>
2149    </author>
2150    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2151      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2152      <address><email>LMM@acm.org</email></address>
2153    </author>
2154    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2155      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2156      <address><email>paulle@microsoft.com</email></address>
2157    </author>
2158    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2159      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2160      <address><email>timbl@w3.org</email></address>
2161    </author>
2162    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2163      <organization abbrev="W3C">World Wide Web Consortium</organization>
2164      <address><email>ylafon@w3.org</email></address>
2165    </author>
2166    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2167      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2168      <address><email>julian.reschke@greenbytes.de</email></address>
2169    </author>
2170    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2171  </front>
2172  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2173  <x:source href="p3-payload.xml" basename="p3-payload"/>
2174</reference>
2175
2176<reference anchor="Part4">
2177  <front>
2178    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2179    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2180      <organization abbrev="Day Software">Day Software</organization>
2181      <address><email>fielding@gbiv.com</email></address>
2182    </author>
2183    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2184      <organization>One Laptop per Child</organization>
2185      <address><email>jg@laptop.org</email></address>
2186    </author>
2187    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2188      <organization abbrev="HP">Hewlett-Packard Company</organization>
2189      <address><email>JeffMogul@acm.org</email></address>
2190    </author>
2191    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2192      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2193      <address><email>henrikn@microsoft.com</email></address>
2194    </author>
2195    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2196      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2197      <address><email>LMM@acm.org</email></address>
2198    </author>
2199    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2200      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2201      <address><email>paulle@microsoft.com</email></address>
2202    </author>
2203    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2204      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2205      <address><email>timbl@w3.org</email></address>
2206    </author>
2207    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2208      <organization abbrev="W3C">World Wide Web Consortium</organization>
2209      <address><email>ylafon@w3.org</email></address>
2210    </author>
2211    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2212      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2213      <address><email>julian.reschke@greenbytes.de</email></address>
2214    </author>
2215    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2216  </front>
2217  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2218  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2219</reference>
2220
2221<reference anchor="Part5">
2222  <front>
2223    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2224    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2225      <organization abbrev="Day Software">Day Software</organization>
2226      <address><email>fielding@gbiv.com</email></address>
2227    </author>
2228    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2229      <organization>One Laptop per Child</organization>
2230      <address><email>jg@laptop.org</email></address>
2231    </author>
2232    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2233      <organization abbrev="HP">Hewlett-Packard Company</organization>
2234      <address><email>JeffMogul@acm.org</email></address>
2235    </author>
2236    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2237      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2238      <address><email>henrikn@microsoft.com</email></address>
2239    </author>
2240    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2241      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2242      <address><email>LMM@acm.org</email></address>
2243    </author>
2244    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2245      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2246      <address><email>paulle@microsoft.com</email></address>
2247    </author>
2248    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2249      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2250      <address><email>timbl@w3.org</email></address>
2251    </author>
2252    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2253      <organization abbrev="W3C">World Wide Web Consortium</organization>
2254      <address><email>ylafon@w3.org</email></address>
2255    </author>
2256    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2257      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2258      <address><email>julian.reschke@greenbytes.de</email></address>
2259    </author>
2260    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2261  </front>
2262  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2263  <x:source href="p5-range.xml" basename="p5-range"/>
2264</reference>
2265
2266<reference anchor="Part6">
2267  <front>
2268    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2269    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2270      <organization abbrev="Day Software">Day Software</organization>
2271      <address><email>fielding@gbiv.com</email></address>
2272    </author>
2273    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2274      <organization>One Laptop per Child</organization>
2275      <address><email>jg@laptop.org</email></address>
2276    </author>
2277    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2278      <organization abbrev="HP">Hewlett-Packard Company</organization>
2279      <address><email>JeffMogul@acm.org</email></address>
2280    </author>
2281    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2282      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2283      <address><email>henrikn@microsoft.com</email></address>
2284    </author>
2285    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2286      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2287      <address><email>LMM@acm.org</email></address>
2288    </author>
2289    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2290      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2291      <address><email>paulle@microsoft.com</email></address>
2292    </author>
2293    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2294      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2295      <address><email>timbl@w3.org</email></address>
2296    </author>
2297    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2298      <organization abbrev="W3C">World Wide Web Consortium</organization>
2299      <address><email>ylafon@w3.org</email></address>
2300    </author>
2301    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2302      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2303      <address><email>julian.reschke@greenbytes.de</email></address>
2304    </author>
2305    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2306  </front>
2307  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2308  <x:source href="p6-cache.xml" basename="p6-cache"/>
2309</reference>
2310
2311<reference anchor="Part7">
2312  <front>
2313    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2314    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2315      <organization abbrev="Day Software">Day Software</organization>
2316      <address><email>fielding@gbiv.com</email></address>
2317    </author>
2318    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2319      <organization>One Laptop per Child</organization>
2320      <address><email>jg@laptop.org</email></address>
2321    </author>
2322    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2323      <organization abbrev="HP">Hewlett-Packard Company</organization>
2324      <address><email>JeffMogul@acm.org</email></address>
2325    </author>
2326    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2327      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2328      <address><email>henrikn@microsoft.com</email></address>
2329    </author>
2330    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2331      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2332      <address><email>LMM@acm.org</email></address>
2333    </author>
2334    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2335      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2336      <address><email>paulle@microsoft.com</email></address>
2337    </author>
2338    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2339      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2340      <address><email>timbl@w3.org</email></address>
2341    </author>
2342    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2343      <organization abbrev="W3C">World Wide Web Consortium</organization>
2344      <address><email>ylafon@w3.org</email></address>
2345    </author>
2346    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2347      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2348      <address><email>julian.reschke@greenbytes.de</email></address>
2349    </author>
2350    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2351  </front>
2352  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2353  <x:source href="p7-auth.xml" basename="p7-auth"/>
2354</reference>
2355
2356<reference anchor="RFC2119">
2357  <front>
2358    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2359    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2360      <organization>Harvard University</organization>
2361      <address><email>sob@harvard.edu</email></address>
2362    </author>
2363    <date month="March" year="1997"/>
2364  </front>
2365  <seriesInfo name="BCP" value="14"/>
2366  <seriesInfo name="RFC" value="2119"/>
2367</reference>
2368
2369</references>
2370
2371<references title="Informative References">
2372
2373<reference anchor="Luo1998">
2374  <front>
2375    <title>Tunneling TCP based protocols through Web proxy servers</title>
2376    <author initials="A." surname="Luotonen" fullname="A. Luotonen">
2377      <organization/>
2378    </author>
2379    <date year="1998" month="August"/>
2380  </front>
2381  <seriesInfo name="Internet-Draft" value="draft-luotonen-web-proxy-tunneling-01"/>
2382</reference>
2383
2384<reference anchor="RFC1945">
2385  <front>
2386    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2387    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2388      <organization>MIT, Laboratory for Computer Science</organization>
2389      <address><email>timbl@w3.org</email></address>
2390    </author>
2391    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2392      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2393      <address><email>fielding@ics.uci.edu</email></address>
2394    </author>
2395    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2396      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2397      <address><email>frystyk@w3.org</email></address>
2398    </author>
2399    <date month="May" year="1996"/>
2400  </front>
2401  <seriesInfo name="RFC" value="1945"/>
2402</reference>
2403
2404<reference anchor="RFC2068">
2405  <front>
2406    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2407    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2408      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2409      <address><email>fielding@ics.uci.edu</email></address>
2410    </author>
2411    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2412      <organization>MIT Laboratory for Computer Science</organization>
2413      <address><email>jg@w3.org</email></address>
2414    </author>
2415    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2416      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2417      <address><email>mogul@wrl.dec.com</email></address>
2418    </author>
2419    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2420      <organization>MIT Laboratory for Computer Science</organization>
2421      <address><email>frystyk@w3.org</email></address>
2422    </author>
2423    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2424      <organization>MIT Laboratory for Computer Science</organization>
2425      <address><email>timbl@w3.org</email></address>
2426    </author>
2427    <date month="January" year="1997"/>
2428  </front>
2429  <seriesInfo name="RFC" value="2068"/>
2430</reference>
2431
2432<reference anchor="RFC2616">
2433  <front>
2434    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2435    <author initials="R." surname="Fielding" fullname="R. Fielding">
2436      <organization>University of California, Irvine</organization>
2437      <address><email>fielding@ics.uci.edu</email></address>
2438    </author>
2439    <author initials="J." surname="Gettys" fullname="J. Gettys">
2440      <organization>W3C</organization>
2441      <address><email>jg@w3.org</email></address>
2442    </author>
2443    <author initials="J." surname="Mogul" fullname="J. Mogul">
2444      <organization>Compaq Computer Corporation</organization>
2445      <address><email>mogul@wrl.dec.com</email></address>
2446    </author>
2447    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2448      <organization>MIT Laboratory for Computer Science</organization>
2449      <address><email>frystyk@w3.org</email></address>
2450    </author>
2451    <author initials="L." surname="Masinter" fullname="L. Masinter">
2452      <organization>Xerox Corporation</organization>
2453      <address><email>masinter@parc.xerox.com</email></address>
2454    </author>
2455    <author initials="P." surname="Leach" fullname="P. Leach">
2456      <organization>Microsoft Corporation</organization>
2457      <address><email>paulle@microsoft.com</email></address>
2458    </author>
2459    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2460      <organization>W3C</organization>
2461      <address><email>timbl@w3.org</email></address>
2462    </author>
2463    <date month="June" year="1999"/>
2464  </front>
2465  <seriesInfo name="RFC" value="2616"/>
2466</reference>
2467
2468<reference anchor="RFC2822">
2469  <front>
2470    <title>Internet Message Format</title>
2471    <author initials="P." surname="Resnick" fullname="P. Resnick">
2472      <organization>QUALCOMM Incorporated</organization>
2473    </author>
2474    <date year="2001" month="April"/>
2475  </front> 
2476  <seriesInfo name="RFC" value="2822"/>
2477</reference>
2478
2479</references>
2480
2481<section title="Compatibility with Previous Versions" anchor="compatibility">
2482<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2483<t>
2484   Clarified which error code should be used for inbound server failures
2485   (e.g. DNS failures). (<xref target="status.504"/>).
2486</t>
2487<t>
2488   201 (Created) had a race that required an Etag be sent when a resource is
2489   first created. (<xref target="status.201"/>).
2490</t>
2491<t>
2492   Rewrite of message transmission requirements to make it much harder
2493   for implementors to get it wrong, as the consequences of errors here
2494   can have significant impact on the Internet, and to deal with the
2495   following problems:
2496  <list style="numbers">
2497      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2498         this was incorrectly placing a requirement on the behavior of
2499         an implementation of a future version of HTTP/1.x</t>
2500
2501      <t>Made it clear that user-agents should retry requests, not
2502         "clients" in general.</t>
2503
2504      <t>Converted requirements for clients to ignore unexpected 100
2505         (Continue) responses, and for proxies to forward 100 responses,
2506         into a general requirement for 1xx responses.</t>
2507
2508      <t>Modified some TCP-specific language, to make it clearer that
2509         non-TCP transports are possible for HTTP.</t>
2510
2511      <t>Require that the origin server &MUST-NOT; wait for the request
2512         body before it sends a required 100 (Continue) response.</t>
2513
2514      <t>Allow, rather than require, a server to omit 100 (Continue) if
2515         it has already seen some of the request body.</t>
2516
2517      <t>Allow servers to defend against denial-of-service attacks and
2518         broken clients.</t>
2519  </list>
2520</t>
2521<t>
2522   This change adds the Expect header and 417 status code.
2523</t>
2524<t>
2525   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2526   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2527</t>
2528<t>
2529   The PATCH<iref item="PATCH method" primary="true"/><iref item="Methods" subitem="PATCH" primary="true"/>, LINK<iref item="LINK method" primary="true"/><iref item="Methods" subitem="LINK" primary="true"/>, UNLINK<iref item="UNLINK method" primary="true"/><iref item="Methods" subitem="UNLINK" primary="true"/> methods were defined but not commonly
2530   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2531</t>
2532</section>
2533
2534<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2535<t>
2536  Clarify definition of POST.
2537  (<xref target="POST"/>)
2538</t>
2539<t>
2540  Failed to consider that there are
2541  many other request methods that are safe to automatically redirect,
2542  and further that the user agent is able to make that determination
2543  based on the request method semantics.
2544  (Sections <xref format="counter" target="status.301"/>,
2545  <xref format="counter" target="status.302"/> and
2546  <xref format="counter" target="status.307"/> )
2547</t>
2548<t>
2549  Correct syntax of Location header to allow fragment,
2550  as referred symbol wasn't what was expected, and add some
2551  clarifications as to when it would not be appropriate.
2552  (<xref target="header.location"/>)
2553</t>
2554<t>
2555  In the description of the Server header, the Via field
2556  was described as a SHOULD. The requirement was and is stated
2557  correctly in the description of the Via header in &header-via;.
2558  (<xref target="header.server"/>)
2559</t>
2560</section>
2561
2562</section>
2563
2564<section title="Change Log (to be removed by RFC Editor before publication)">
2565
2566<section title="Since RFC2616">
2567<t>
2568  Extracted relevant partitions from <xref target="RFC2616"/>.
2569</t>
2570</section>
2571
2572<section title="Since draft-ietf-httpbis-p2-semantics-00">
2573<t>
2574  Closed issues:
2575  <list style="symbols"> 
2576    <t>
2577      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
2578      "Via is a MUST"
2579      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
2580    </t>
2581    <t>
2582      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
2583      "Fragments allowed in Location"
2584      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
2585    </t>
2586    <t>
2587      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
2588      "Safe Methods vs Redirection"
2589      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
2590    </t>
2591    <t>
2592      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
2593      "Revise description of the POST method"
2594      (<eref target="http://purl.org/NET/http-errata#post"/>)
2595    </t>
2596    <t>
2597      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2598      "Normative and Informative references"
2599    </t>
2600    <t>
2601      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
2602      "RFC2606 Compliance"
2603    </t>
2604    <t>
2605      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2606      "Informative references"
2607    </t>
2608    <t>
2609      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
2610      "Redundant cross-references"
2611    </t>
2612  </list>
2613</t>
2614<t>
2615  Other changes:
2616  <list style="symbols"> 
2617    <t>
2618      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
2619    </t>
2620  </list>
2621</t>
2622</section>
2623
2624</section>
2625
2626</back>
2627</rfc>
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