source: draft-ietf-httpbis/latest/p2-semantics.xml @ 201

Last change on this file since 201 was 201, checked in by julian.reschke@…, 12 years ago

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