source: draft-ietf-httpbis/latest/p2-semantics.xml @ 243

Last change on this file since 243 was 243, checked in by julian.reschke@…, 12 years ago

Fix typo (relates to #70).

  • Property svn:eol-style set to native
File size: 128.8 KB
Line 
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 "April">
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 notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY general-syntax             "<xref target='Part1' x:rel='#general.syntax' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY full-date                  "<xref target='Part1' x:rel='#full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-upgrade             "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
61  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
62  <!ENTITY product-tokens             "<xref target='Part1' x:rel='#product.tokens' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
63]>
64<?rfc toc="yes" ?>
65<?rfc symrefs="yes" ?>
66<?rfc sortrefs="yes" ?>
67<?rfc compact="yes"?>
68<?rfc subcompact="no" ?>
69<?rfc linkmailto="no" ?>
70<?rfc editing="no" ?>
71<?rfc comments="yes"?>
72<?rfc inline="yes"?>
73<?rfc-ext allow-markup-in-artwork="yes" ?>
74<?rfc-ext include-references-in-index="yes" ?>
75<rfc obsoletes="2616" category="std"
76     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
77     xmlns:x='http://purl.org/net/xml2rfc/ext'>
78<front>
79
80  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
81
82  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
83    <organization abbrev="Day Software">Day Software</organization>
84    <address>
85      <postal>
86        <street>23 Corporate Plaza DR, Suite 280</street>
87        <city>Newport Beach</city>
88        <region>CA</region>
89        <code>92660</code>
90        <country>USA</country>
91      </postal>
92      <phone>+1-949-706-5300</phone>
93      <facsimile>+1-949-706-5305</facsimile>
94      <email>fielding@gbiv.com</email>
95      <uri>http://roy.gbiv.com/</uri>
96    </address>
97  </author>
98
99  <author initials="J." surname="Gettys" fullname="Jim Gettys">
100    <organization>One Laptop per Child</organization>
101    <address>
102      <postal>
103        <street>21 Oak Knoll Road</street>
104        <city>Carlisle</city>
105        <region>MA</region>
106        <code>01741</code>
107        <country>USA</country>
108      </postal>
109      <email>jg@laptop.org</email>
110      <uri>http://www.laptop.org/</uri>
111    </address>
112  </author>
113 
114  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
115    <organization abbrev="HP">Hewlett-Packard Company</organization>
116    <address>
117      <postal>
118        <street>HP Labs, Large Scale Systems Group</street>
119        <street>1501 Page Mill Road, MS 1177</street>
120        <city>Palo Alto</city>
121        <region>CA</region>
122        <code>94304</code>
123        <country>USA</country>
124      </postal>
125      <email>JeffMogul@acm.org</email>
126    </address>
127  </author>
128
129  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
130    <organization abbrev="Microsoft">Microsoft Corporation</organization>
131    <address>
132      <postal>
133        <street>1 Microsoft Way</street>
134        <city>Redmond</city>
135        <region>WA</region>
136        <code>98052</code>
137        <country>USA</country>
138      </postal>
139      <email>henrikn@microsoft.com</email>
140    </address>
141  </author>
142
143  <author initials="L." surname="Masinter" fullname="Larry Masinter">
144    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
145    <address>
146      <postal>
147        <street>345 Park Ave</street>
148        <city>San Jose</city>
149        <region>CA</region>
150        <code>95110</code>
151        <country>USA</country>
152      </postal>
153      <email>LMM@acm.org</email>
154      <uri>http://larry.masinter.net/</uri>
155    </address>
156  </author>
157 
158  <author initials="P." surname="Leach" fullname="Paul J. Leach">
159    <organization abbrev="Microsoft">Microsoft Corporation</organization>
160    <address>
161      <postal>
162        <street>1 Microsoft Way</street>
163        <city>Redmond</city>
164        <region>WA</region>
165        <code>98052</code>
166      </postal>
167      <email>paulle@microsoft.com</email>
168    </address>
169  </author>
170   
171  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
172    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
173    <address>
174      <postal>
175        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
176        <street>The Stata Center, Building 32</street>
177        <street>32 Vassar Street</street>
178        <city>Cambridge</city>
179        <region>MA</region>
180        <code>02139</code>
181        <country>USA</country>
182      </postal>
183      <email>timbl@w3.org</email>
184      <uri>http://www.w3.org/People/Berners-Lee/</uri>
185    </address>
186  </author>
187
188  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
189    <organization abbrev="W3C">World Wide Web Consortium</organization>
190    <address>
191      <postal>
192        <street>W3C / ERCIM</street>
193        <street>2004, rte des Lucioles</street>
194        <city>Sophia-Antipolis</city>
195        <region>AM</region>
196        <code>06902</code>
197        <country>France</country>
198      </postal>
199      <email>ylafon@w3.org</email>
200      <uri>http://www.raubacapeu.net/people/yves/</uri>
201    </address>
202  </author>
203
204  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
205    <organization abbrev="greenbytes">greenbytes GmbH</organization>
206    <address>
207      <postal>
208        <street>Hafenweg 16</street>
209        <city>Muenster</city><region>NW</region><code>48155</code>
210        <country>Germany</country>
211      </postal>
212      <phone>+49 251 2807760</phone>   
213      <facsimile>+49 251 2807761</facsimile>   
214      <email>julian.reschke@greenbytes.de</email>       
215      <uri>http://greenbytes.de/tech/webdav/</uri>     
216    </address>
217  </author>
218
219  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
220
221<abstract>
222<t>
223   The Hypertext Transfer Protocol (HTTP) is an application-level
224   protocol for distributed, collaborative, hypermedia information
225   systems. HTTP has been in use by the World Wide Web global information
226   initiative since 1990. This document is Part 2 of the seven-part specification
227   that defines the protocol referred to as "HTTP/1.1" and, taken together,
228   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
229   as expressed by request methods, request-header fields, response status codes,
230   and response-header fields.
231</t>
232</abstract>
233
234<note title="Editorial Note (To be removed by RFC Editor)">
235  <t>
236    Discussion of this draft should take place on the HTTPBIS working group
237    mailing list (ietf-http-wg@w3.org). The current issues list is
238    at <eref target="http://www.tools.ietf.org/wg/httpbis/trac/report/11"/>
239    and related documents (including fancy diffs) can be found at
240    <eref target="http://www.tools.ietf.org/wg/httpbis/"/>.
241  </t>
242  <t>
243    This draft incorporates those issue resolutions that were either
244    collected in the original RFC2616 errata list (<eref target="http://purl.org/NET/http-errata"/>),
245    or which were agreed upon on the mailing list between October 2006 and
246    November 2007 (as published in "draft-lafon-rfc2616bis-03").
247  </t>
248</note>
249</front>
250<middle>
251<section title="Introduction" anchor="introduction">
252<t>
253   This document defines HTTP/1.1 request and response semantics.  Each HTTP
254   message, as defined in &messaging;, is in the form of either a request or
255   a response.  An HTTP server listens on a connection for HTTP requests and
256   responds to each request, in the order received on that connection, with
257   one or more HTTP response messages.  This document defines the commonly
258   agreed upon semantics of the HTTP uniform interface, the intentions defined
259   by each request method, and the various response messages that might be
260   expected as a result of applying that method for the requested resource.
261</t>
262<t>
263   This document is currently disorganized in order to minimize the changes
264   between drafts and enable reviewers to see the smaller errata changes.
265   The next draft will reorganize the sections to better reflect the content.
266   In particular, the sections will be ordered according to the typical
267   processing of an HTTP request message (after message parsing): resource
268   mapping, general header fields, methods, request modifiers, response
269   status, and resource metadata.  The current mess reflects how widely
270   dispersed these topics and associated requirements had become in
271   <xref target="RFC2616"/>.
272</t>
273
274<section title="Requirements" anchor="intro.requirements">
275<t>
276   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
277   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
278   document are to be interpreted as described in <xref target="RFC2119"/>.
279</t>
280<t>
281   An implementation is not compliant if it fails to satisfy one or more
282   of the &MUST; or &REQUIRED; level requirements for the protocols it
283   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
284   level and all the &SHOULD; level requirements for its protocols is said
285   to be "unconditionally compliant"; one that satisfies all the &MUST;
286   level requirements but not all the &SHOULD; level requirements for its
287   protocols is said to be "conditionally compliant."
288</t>
289</section>
290</section>
291
292<section title="Notational Conventions and Generic Grammar" anchor="notation">
293  <x:anchor-alias value="comment"/>
294  <x:anchor-alias value="DIGIT"/>
295  <x:anchor-alias value="quoted-string"/>
296  <x:anchor-alias value="token"/>
297<t>
298  This specification uses the ABNF syntax defined in &notation-abnf; and
299  the core rules defined in &basic-rules;:
300  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
301  <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>.</cref>
302</t>
303<figure><artwork type="abnf2616">
304  <x:ref>DIGIT</x:ref>         = &lt;DIGIT, defined in &basic-rules;&gt;
305</artwork></figure>
306<figure><artwork type="abnf2616">
307  <x:anchor-alias value="Accept"/>
308  <x:ref>comment</x:ref>       = &lt;comment, defined in &basic-rules;&gt;
309  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &basic-rules;&gt;
310  <x:ref>token</x:ref>         = &lt;token, defined in &basic-rules;&gt;
311</artwork></figure>
312<t anchor="abnf.dependencies">
313  <x:anchor-alias value="absoluteURI"/>
314  <x:anchor-alias value="Accept"/>
315  <x:anchor-alias value="Accept-Charset"/>
316  <x:anchor-alias value="Accept-Encoding"/>
317  <x:anchor-alias value="Accept-Language"/>
318  <x:anchor-alias value="Accept-Ranges"/>
319  <x:anchor-alias value="Age"/>
320  <x:anchor-alias value="Authorization"/>
321  <x:anchor-alias value="ETag"/>
322  <x:anchor-alias value="fragment"/>
323  <x:anchor-alias value="Host"/>
324  <x:anchor-alias value="HTTP-date"/>
325  <x:anchor-alias value="If-Match"/>
326  <x:anchor-alias value="If-Modified-Since"/>
327  <x:anchor-alias value="If-None-Match"/>
328  <x:anchor-alias value="If-Range"/>
329  <x:anchor-alias value="If-Unmodified-Since"/>
330  <x:anchor-alias value="product"/>
331  <x:anchor-alias value="Proxy-Authenticate"/>
332  <x:anchor-alias value="Proxy-Authorization"/>
333  <x:anchor-alias value="Range"/>
334  <x:anchor-alias value="relativeURI"/>
335  <x:anchor-alias value="TE"/>
336  <x:anchor-alias value="Vary"/>
337  <x:anchor-alias value="WWW-Authenticate"/>
338  The ABNF rules below are defined in other parts:
339</t>
340<figure><!--Part1--><artwork type="abnf2616">
341  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in &general-syntax;&gt;
342  <x:ref>fragment</x:ref>      = &lt;fragment, defined in &general-syntax;&gt;
343  <x:ref>Host</x:ref>          = &lt;Host, defined in &header-host;&gt;
344  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
345  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
346  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in &general-syntax;&gt;
347  <x:ref>TE</x:ref>            = &lt;TE, defined in &header-te;&gt;
348</artwork></figure>
349<figure><!--Part3--><artwork type="abnf2616">
350  <x:ref>Accept</x:ref>        = &lt;Accept, defined in &header-accept;&gt;
351  <x:ref>Accept-Charset</x:ref> =
352             &lt;Accept-Charset, defined in &header-accept-charset;&gt;
353  <x:ref>Accept-Encoding</x:ref> =
354             &lt;Accept-Encoding, defined in &header-accept-encoding;&gt;
355  <x:ref>Accept-Language</x:ref> =
356             &lt;Accept-Language, defined in &header-accept-language;&gt;
357</artwork></figure>
358<figure><!--Part4--><artwork type="abnf2616">
359  <x:ref>ETag</x:ref>          = &lt;ETag, defined in &header-etag;&gt;
360  <x:ref>If-Match</x:ref>      = &lt;If-Match, defined in &header-if-match;&gt;
361  <x:ref>If-Modified-Since</x:ref> =
362             &lt;If-Modified-Since, defined in &header-if-modified-since;&gt;
363  <x:ref>If-None-Match</x:ref> = &lt;If-None-Match, defined in &header-if-none-match;&gt;
364  <x:ref>If-Unmodified-Since</x:ref> =
365             &lt;If-Unmodified-Since, defined in &header-if-unmodified-since;&gt;
366</artwork></figure>
367<figure><!--Part5--><artwork type="abnf2616">
368  <x:ref>Accept-Ranges</x:ref> = &lt;Accept-Ranges, defined in &header-accept-ranges;&gt;
369  <x:ref>If-Range</x:ref>      = &lt;If-Range, defined in &header-if-range;&gt;
370  <x:ref>Range</x:ref>         = &lt;Range, defined in &header-range;&gt;
371</artwork></figure>
372<figure><!--Part6--><artwork type="abnf2616">
373  <x:ref>Age</x:ref>           = &lt;Age, defined in &header-age;&gt;
374  <x:ref>Vary</x:ref>          = &lt;Vary, defined in &header-vary;&gt;
375</artwork><!--Part7--></figure>
376<figure><artwork type="abnf2616">
377  <x:ref>Authorization</x:ref> = &lt;Authorization, defined in &header-authorization;&gt;
378  <x:ref>Proxy-Authenticate</x:ref> =
379             &lt;Proxy-Authenticate, defined in &header-proxy-authenticate;&gt;
380  <x:ref>Proxy-Authorization</x:ref> =
381             &lt;Proxy-Authorization, defined in &header-proxy-authorization;&gt;
382  <x:ref>WWW-Authenticate</x:ref> =
383             &lt;WWW-Authenticate, defined in &header-www-authenticate;&gt;
384</artwork></figure>
385</section>
386
387<section title="Method" anchor="method">
388  <x:anchor-alias value="Method"/>
389  <x:anchor-alias value="extension-method"/>
390<t>
391   The Method  token indicates the method to be performed on the
392   resource identified by the Request-URI. The method is case-sensitive.
393</t>
394<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
395  <x:ref>Method</x:ref>         = "OPTIONS"                ; <xref target="OPTIONS"/>
396                 | "GET"                    ; <xref target="GET"/>
397                 | "HEAD"                   ; <xref target="HEAD"/>
398                 | "POST"                   ; <xref target="POST"/>
399                 | "PUT"                    ; <xref target="PUT"/>
400                 | "DELETE"                 ; <xref target="DELETE"/>
401                 | "TRACE"                  ; <xref target="TRACE"/>
402                 | "CONNECT"                ; <xref target="CONNECT"/>
403                 | <x:ref>extension-method</x:ref>
404  <x:ref>extension-method</x:ref> = <x:ref>token</x:ref>
405</artwork></figure>
406<t>
407   The list of methods allowed by a resource can be specified in an
408   Allow header field (<xref target="header.allow"/>). The return code of the response
409   always notifies the client whether a method is currently allowed on a
410   resource, since the set of allowed methods can change dynamically. An
411   origin server &SHOULD; return the status code 405 (Method Not Allowed)
412   if the method is known by the origin server but not allowed for the
413   requested resource, and 501 (Not Implemented) if the method is
414   unrecognized or not implemented by the origin server. The methods GET
415   and HEAD &MUST; be supported by all general-purpose servers. All other
416   methods are &OPTIONAL;; however, if the above methods are implemented,
417   they &MUST; be implemented with the same semantics as those specified
418   in <xref target="method.definitions"/>.
419</t>
420</section>
421
422<section title="Request Header Fields" anchor="request.header.fields">
423  <x:anchor-alias value="extension-code"/>
424  <x:anchor-alias value="request-header"/>
425<t>
426   The request-header fields allow the client to pass additional
427   information about the request, and about the client itself, to the
428   server. These fields act as request modifiers, with semantics
429   equivalent to the parameters on a programming language method
430   invocation.
431</t>
432<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
433  <x:ref>request-header</x:ref> = <x:ref>Accept</x:ref>                   ; &header-accept;
434                 | <x:ref>Accept-Charset</x:ref>           ; &header-accept-charset;
435                 | <x:ref>Accept-Encoding</x:ref>          ; &header-accept-encoding;
436                 | <x:ref>Accept-Language</x:ref>          ; &header-accept-language;
437                 | <x:ref>Authorization</x:ref>            ; &header-authorization;
438                 | <x:ref>Expect</x:ref>                   ; <xref target="header.expect"/>
439                 | <x:ref>From</x:ref>                     ; <xref target="header.from"/>
440                 | <x:ref>Host</x:ref>                     ; &header-host;
441                 | <x:ref>If-Match</x:ref>                 ; &header-if-match;
442                 | <x:ref>If-Modified-Since</x:ref>        ; &header-if-modified-since;
443                 | <x:ref>If-None-Match</x:ref>            ; &header-if-none-match;
444                 | <x:ref>If-Range</x:ref>                 ; &header-if-range;
445                 | <x:ref>If-Unmodified-Since</x:ref>      ; &header-if-unmodified-since;
446                 | <x:ref>Max-Forwards</x:ref>             ; <xref target="header.max-forwards"/>
447                 | <x:ref>Proxy-Authorization</x:ref>      ; &header-proxy-authorization;
448                 | <x:ref>Range</x:ref>                    ; &header-range;
449                 | <x:ref>Referer</x:ref>                  ; <xref target="header.referer"/>
450                 | <x:ref>TE</x:ref>                       ; &header-te;
451                 | <x:ref>User-Agent</x:ref>               ; <xref target="header.user-agent"/>
452</artwork></figure>
453<t>
454   Request-header field names can be extended reliably only in
455   combination with a change in the protocol version. However, new or
456   experimental header fields &MAY; be given the semantics of request-header
457   fields if all parties in the communication recognize them to
458   be request-header fields. Unrecognized header fields are treated as
459   entity-header fields.
460</t>
461</section>
462
463<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
464  <x:anchor-alias value="Reason-Phrase"/>
465  <x:anchor-alias value="Status-Code"/>
466<t>
467   The Status-Code element is a 3-digit integer result code of the
468   attempt to understand and satisfy the request. The status codes listed
469   below are defined in <xref target="status.codes"/>.
470   The Reason-Phrase is intended to give a short
471   textual description of the Status-Code. The Status-Code is intended
472   for use by automata and the Reason-Phrase is intended for the human
473   user. The client is not required to examine or display the Reason-Phrase.
474</t>
475<t> 
476   The individual values of the numeric status codes defined for
477   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
478   presented below. The reason phrases listed here are only
479   recommendations -- they &MAY; be replaced by local equivalents without
480   affecting the protocol.
481</t>
482<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"/>
483  <x:ref>Status-Code</x:ref>    =
484         "100"  ; <xref target="status.100"/>: Continue
485       | "101"  ; <xref target="status.101"/>: Switching Protocols
486       | "200"  ; <xref target="status.200"/>: OK
487       | "201"  ; <xref target="status.201"/>: Created
488       | "202"  ; <xref target="status.202"/>: Accepted
489       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
490       | "204"  ; <xref target="status.204"/>: No Content
491       | "205"  ; <xref target="status.205"/>: Reset Content
492       | "206"  ; <xref target="status.206"/>: Partial Content
493       | "300"  ; <xref target="status.300"/>: Multiple Choices
494       | "301"  ; <xref target="status.301"/>: Moved Permanently
495       | "302"  ; <xref target="status.302"/>: Found
496       | "303"  ; <xref target="status.303"/>: See Other
497       | "304"  ; <xref target="status.304"/>: Not Modified
498       | "305"  ; <xref target="status.305"/>: Use Proxy
499       | "307"  ; <xref target="status.307"/>: Temporary Redirect
500       | "400"  ; <xref target="status.400"/>: Bad Request
501       | "401"  ; <xref target="status.401"/>: Unauthorized
502       | "402"  ; <xref target="status.402"/>: Payment Required
503       | "403"  ; <xref target="status.403"/>: Forbidden
504       | "404"  ; <xref target="status.404"/>: Not Found
505       | "405"  ; <xref target="status.405"/>: Method Not Allowed
506       | "406"  ; <xref target="status.406"/>: Not Acceptable
507       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
508       | "408"  ; <xref target="status.408"/>: Request Time-out
509       | "409"  ; <xref target="status.409"/>: Conflict
510       | "410"  ; <xref target="status.410"/>: Gone
511       | "411"  ; <xref target="status.411"/>: Length Required
512       | "412"  ; <xref target="status.412"/>: Precondition Failed
513       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
514       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
515       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
516       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
517       | "417"  ; <xref target="status.417"/>: Expectation Failed
518       | "500"  ; <xref target="status.500"/>: Internal Server Error
519       | "501"  ; <xref target="status.501"/>: Not Implemented
520       | "502"  ; <xref target="status.502"/>: Bad Gateway
521       | "503"  ; <xref target="status.503"/>: Service Unavailable
522       | "504"  ; <xref target="status.504"/>: Gateway Time-out
523       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
524       | <x:ref>extension-code</x:ref>
525
526  <x:ref>extension-code</x:ref> = 3<x:ref>DIGIT</x:ref>
527  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
528</artwork></figure>
529<t>
530   HTTP status codes are extensible. HTTP applications are not required
531   to understand the meaning of all registered status codes, though such
532   understanding is obviously desirable. However, applications &MUST;
533   understand the class of any status code, as indicated by the first
534   digit, and treat any unrecognized response as being equivalent to the
535   x00 status code of that class, with the exception that an
536   unrecognized response &MUST-NOT; be cached. For example, if an
537   unrecognized status code of 431 is received by the client, it can
538   safely assume that there was something wrong with its request and
539   treat the response as if it had received a 400 status code. In such
540   cases, user agents &SHOULD; present to the user the entity returned
541   with the response, since that entity is likely to include human-readable
542   information which will explain the unusual status.
543</t>
544</section>
545
546<section title="Response Header Fields" anchor="response.header.fields">
547  <x:anchor-alias value="response-header"/>
548<t>
549   The response-header fields allow the server to pass additional
550   information about the response which cannot be placed in the Status-Line.
551   These header fields give information about the server and about
552   further access to the resource identified by the Request-URI.
553</t>
554<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
555  <x:ref>response-header</x:ref> = <x:ref>Accept-Ranges</x:ref>           ; &header-accept-ranges;
556                  | <x:ref>Age</x:ref>                     ; &header-age;
557                  | <x:ref>Allow</x:ref>                   ; <xref target="header.allow"/>
558                  | <x:ref>ETag</x:ref>                    ; &header-etag;
559                  | <x:ref>Location</x:ref>                ; <xref target="header.location"/>
560                  | <x:ref>Proxy-Authenticate</x:ref>      ; &header-proxy-authenticate;
561                  | <x:ref>Retry-After</x:ref>             ; <xref target="header.retry-after"/>
562                  | <x:ref>Server</x:ref>                  ; <xref target="header.server"/>
563                  | <x:ref>Vary</x:ref>                    ; &header-vary;
564                  | <x:ref>WWW-Authenticate</x:ref>        ; &header-www-authenticate;
565</artwork></figure>
566<t>
567   Response-header field names can be extended reliably only in
568   combination with a change in the protocol version. However, new or
569   experimental header fields &MAY; be given the semantics of response-header
570   fields if all parties in the communication recognize them to
571   be response-header fields. Unrecognized header fields are treated as
572   entity-header fields.
573</t>
574</section>
575
576<section title="Entity" anchor="entity">
577<t>
578   Request and Response messages &MAY; transfer an entity if not otherwise
579   restricted by the request method or response status code. An entity
580   consists of entity-header fields and an entity-body, although some
581   responses will only include the entity-headers. HTTP entity-body and
582   entity-header fields are defined in &payload;.
583</t>
584<t>
585   An entity-body is only present in a message when a message-body is
586   present, as described in &message-body;. The entity-body is obtained
587   from the message-body by decoding any Transfer-Encoding that might
588   have been applied to ensure safe and proper transfer of the message.
589</t>
590</section>
591
592
593<section title="Method Definitions" anchor="method.definitions">
594<t>
595   The set of common methods for HTTP/1.1 is defined below. Although
596   this set can be expanded, additional methods cannot be assumed to
597   share the same semantics for separately extended clients and servers.
598</t>
599
600<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
601
602<section title="Safe Methods" anchor="safe.methods">
603<t>
604   Implementors should be aware that the software represents the user in
605   their interactions over the Internet, and should be careful to allow
606   the user to be aware of any actions they might take which may have an
607   unexpected significance to themselves or others.
608</t>
609<t>
610   In particular, the convention has been established that the GET and
611   HEAD methods &SHOULD-NOT;  have the significance of taking an action
612   other than retrieval. These methods ought to be considered "safe".
613   This allows user agents to represent other methods, such as POST, PUT
614   and DELETE, in a special way, so that the user is made aware of the
615   fact that a possibly unsafe action is being requested.
616</t>
617<t>
618   Naturally, it is not possible to ensure that the server does not
619   generate side-effects as a result of performing a GET request; in
620   fact, some dynamic resources consider that a feature. The important
621   distinction here is that the user did not request the side-effects,
622   so therefore cannot be held accountable for them.
623</t>
624</section>
625
626<section title="Idempotent Methods" anchor="idempotent.methods">
627<t>
628   Methods can also have the property of "idempotence" in that (aside
629   from error or expiration issues) the side-effects of N &gt; 0 identical
630   requests is the same as for a single request. The methods GET, HEAD,
631   PUT and DELETE share this property. Also, the methods OPTIONS and
632   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
633</t>
634<t>
635   However, it is possible that a sequence of several requests is non-idempotent,
636   even if all of the methods executed in that sequence are
637   idempotent. (A sequence is idempotent if a single execution of the
638   entire sequence always yields a result that is not changed by a
639   reexecution of all, or part, of that sequence.) For example, a
640   sequence is non-idempotent if its result depends on a value that is
641   later modified in the same sequence.
642</t>
643<t>
644   A sequence that never has side effects is idempotent, by definition
645   (provided that no concurrent operations are being executed on the
646   same set of resources).
647</t>
648</section>
649</section>
650
651<section title="OPTIONS" anchor="OPTIONS">
652  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
653  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
654<t>
655   The OPTIONS method represents a request for information about the
656   communication options available on the request/response chain
657   identified by the Request-URI. This method allows the client to
658   determine the options and/or requirements associated with a resource,
659   or the capabilities of a server, without implying a resource action
660   or initiating a resource retrieval.
661</t>
662<t>
663   Responses to this method are not cacheable.
664</t>
665<t>
666   If the OPTIONS request includes an entity-body (as indicated by the
667   presence of Content-Length or Transfer-Encoding), then the media type
668   &MUST; be indicated by a Content-Type field. Although this
669   specification does not define any use for such a body, future
670   extensions to HTTP might use the OPTIONS body to make more detailed
671   queries on the server. A server that does not support such an
672   extension &MAY; discard the request body.
673</t>
674<t>
675   If the Request-URI is an asterisk ("*"), the OPTIONS request is
676   intended to apply to the server in general rather than to a specific
677   resource. Since a server's communication options typically depend on
678   the resource, the "*" request is only useful as a "ping" or "no-op"
679   type of method; it does nothing beyond allowing the client to test
680   the capabilities of the server. For example, this can be used to test
681   a proxy for HTTP/1.1 compliance (or lack thereof).
682</t>
683<t>
684   If the Request-URI is not an asterisk, the OPTIONS request applies
685   only to the options that are available when communicating with that
686   resource.
687</t>
688<t>
689   A 200 response &SHOULD; include any header fields that indicate
690   optional features implemented by the server and applicable to that
691   resource (e.g., Allow), possibly including extensions not defined by
692   this specification. The response body, if any, &SHOULD; also include
693   information about the communication options. The format for such a
694   body is not defined by this specification, but might be defined by
695   future extensions to HTTP. Content negotiation &MAY; be used to select
696   the appropriate response format. If no response body is included, the
697   response &MUST; include a Content-Length field with a field-value of
698   "0".
699</t>
700<t>
701   The Max-Forwards request-header field &MAY; be used to target a
702   specific proxy in the request chain. When a proxy receives an OPTIONS
703   request on an absoluteURI for which request forwarding is permitted,
704   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
705   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
706   instead, the proxy &SHOULD; respond with its own communication options.
707   If the Max-Forwards field-value is an integer greater than zero, the
708   proxy &MUST; decrement the field-value when it forwards the request. If
709   no Max-Forwards field is present in the request, then the forwarded
710   request &MUST-NOT; include a Max-Forwards field.
711</t>
712</section>
713
714<section title="GET" anchor="GET">
715  <iref primary="true" item="GET method" x:for-anchor=""/>
716  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
717<t>
718   The GET method means retrieve whatever information (in the form of an
719   entity) is identified by the Request-URI. If the Request-URI refers
720   to a data-producing process, it is the produced data which shall be
721   returned as the entity in the response and not the source text of the
722   process, unless that text happens to be the output of the process.
723</t>
724<t>
725   The semantics of the GET method change to a "conditional GET" if the
726   request message includes an If-Modified-Since, If-Unmodified-Since,
727   If-Match, If-None-Match, or If-Range header field. A conditional GET
728   method requests that the entity be transferred only under the
729   circumstances described by the conditional header field(s). The
730   conditional GET method is intended to reduce unnecessary network
731   usage by allowing cached entities to be refreshed without requiring
732   multiple requests or transferring data already held by the client.
733</t>
734<t>
735   The semantics of the GET method change to a "partial GET" if the
736   request message includes a Range header field. A partial GET requests
737   that only part of the entity be transferred, as described in &header-range;.
738   The partial GET method is intended to reduce unnecessary
739   network usage by allowing partially-retrieved entities to be
740   completed without transferring data already held by the client.
741</t>
742<t>
743   The response to a GET request is cacheable if and only if it meets
744   the requirements for HTTP caching described in &caching;.
745</t>
746<t>
747   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
748</t>
749</section>
750
751<section title="HEAD" anchor="HEAD">
752  <iref primary="true" item="HEAD method" x:for-anchor=""/>
753  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
754<t>
755   The HEAD method is identical to GET except that the server &MUST-NOT;
756   return a message-body in the response. The metainformation contained
757   in the HTTP headers in response to a HEAD request &SHOULD; be identical
758   to the information sent in response to a GET request. This method can
759   be used for obtaining metainformation about the entity implied by the
760   request without transferring the entity-body itself. This method is
761   often used for testing hypertext links for validity, accessibility,
762   and recent modification.
763</t>
764<t>
765   The response to a HEAD request &MAY; be cacheable in the sense that the
766   information contained in the response &MAY; be used to update a
767   previously cached entity from that resource. If the new field values
768   indicate that the cached entity differs from the current entity (as
769   would be indicated by a change in Content-Length, Content-MD5, ETag
770   or Last-Modified), then the cache &MUST; treat the cache entry as
771   stale.
772</t>
773</section>
774
775<section title="POST" anchor="POST">
776  <iref primary="true" item="POST method" x:for-anchor=""/>
777  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
778<t>
779   The POST method is used to request that the origin server accept the
780   entity enclosed in the request as data to be processed by the resource
781   identified by the Request-URI in the Request-Line. POST is designed
782   to allow a uniform method to cover the following functions:
783  <list style="symbols">
784    <t>
785      Annotation of existing resources;
786    </t>
787    <t>
788        Posting a message to a bulletin board, newsgroup, mailing list,
789        or similar group of articles;
790    </t>
791    <t>
792        Providing a block of data, such as the result of submitting a
793        form, to a data-handling process;
794    </t>
795    <t>
796        Extending a database through an append operation.
797    </t>
798  </list>
799</t>
800<t>
801   The actual function performed by the POST method is determined by the
802   server and is usually dependent on the Request-URI.
803</t>
804<t>
805   The action performed by the POST method might not result in a
806   resource that can be identified by a URI. In this case, either 200
807   (OK) or 204 (No Content) is the appropriate response status,
808   depending on whether or not the response includes an entity that
809   describes the result.
810</t>
811<t>
812   If a resource has been created on the origin server, the response
813   &SHOULD; be 201 (Created) and contain an entity which describes the
814   status of the request and refers to the new resource, and a Location
815   header (see <xref target="header.location"/>).
816</t>
817<t>
818   Responses to this method are not cacheable, unless the response
819   includes appropriate Cache-Control or Expires header fields. However,
820   the 303 (See Other) response can be used to direct the user agent to
821   retrieve a cacheable resource.
822</t>
823</section>
824
825<section title="PUT" anchor="PUT">
826  <iref primary="true" item="PUT method" x:for-anchor=""/>
827  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
828<t>
829   The PUT method requests that the enclosed entity be stored at the
830   supplied Request-URI. If the Request-URI refers to an already
831   existing resource, the enclosed entity &SHOULD; be considered as a
832   modified version of the one residing on the origin server. If the
833   Request-URI does not point to an existing resource, and that URI is
834   capable of being defined as a new resource by the requesting user
835   agent, the origin server can create the resource with that URI. If a
836   new resource is created at the Request-URI, the origin server &MUST;
837         inform the user agent
838   via the 201 (Created) response. If an existing resource is modified,
839   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
840   to indicate successful completion of the request. If the resource
841   could not be created or modified with the Request-URI, an appropriate
842   error response &SHOULD; be given that reflects the nature of the
843   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
844   (e.g. Content-Range) headers that it does not understand or implement
845   and &MUST; return a 501 (Not Implemented) response in such cases.
846</t>
847<t>
848   If the request passes through a cache and the Request-URI identifies
849   one or more currently cached entities, those entries &SHOULD; be
850   treated as stale. Responses to this method are not cacheable.
851</t>
852<t>
853   The fundamental difference between the POST and PUT requests is
854   reflected in the different meaning of the Request-URI. The URI in a
855   POST request identifies the resource that will handle the enclosed
856   entity. That resource might be a data-accepting process, a gateway to
857   some other protocol, or a separate entity that accepts annotations.
858   In contrast, the URI in a PUT request identifies the entity enclosed
859   with the request -- the user agent knows what URI is intended and the
860   server &MUST-NOT; attempt to apply the request to some other resource.
861   If the server desires that the request be applied to a different URI,
862   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
863   then make its own decision regarding whether or not to redirect the
864   request.
865</t>
866<t>
867   A single resource &MAY; be identified by many different URIs. For
868   example, an article might have a URI for identifying "the current
869   version" which is separate from the URI identifying each particular
870   version. In this case, a PUT request on a general URI might result in
871   several other URIs being defined by the origin server.
872</t>
873<t>
874   HTTP/1.1 does not define how a PUT method affects the state of an
875   origin server.
876</t>
877<t>
878   Unless otherwise specified for a particular entity-header, the
879   entity-headers in the PUT request &SHOULD; be applied to the resource
880   created or modified by the PUT.
881</t>
882</section>
883
884<section title="DELETE" anchor="DELETE">
885  <iref primary="true" item="DELETE method" x:for-anchor=""/>
886  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
887<t>
888   The DELETE method requests that the origin server delete the resource
889   identified by the Request-URI. This method &MAY; be overridden by human
890   intervention (or other means) on the origin server. The client cannot
891   be guaranteed that the operation has been carried out, even if the
892   status code returned from the origin server indicates that the action
893   has been completed successfully. However, the server &SHOULD-NOT; 
894   indicate success unless, at the time the response is given, it
895   intends to delete the resource or move it to an inaccessible
896   location.
897</t>
898<t>
899   A successful response &SHOULD; be 200 (OK) if the response includes an
900   entity describing the status, 202 (Accepted) if the action has not
901   yet been enacted, or 204 (No Content) if the action has been enacted
902   but the response does not include an entity.
903</t>
904<t>
905   If the request passes through a cache and the Request-URI identifies
906   one or more currently cached entities, those entries &SHOULD; be
907   treated as stale. Responses to this method are not cacheable.
908</t>
909</section>
910
911<section title="TRACE" anchor="TRACE">
912  <iref primary="true" item="TRACE method" x:for-anchor=""/>
913  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
914<t>
915   The TRACE method is used to invoke a remote, application-layer loop-back
916   of the request message. The final recipient of the request
917   &SHOULD; reflect the message received back to the client as the
918   entity-body of a 200 (OK) response. The final recipient is either the
919   origin server or the first proxy or gateway to receive a Max-Forwards
920   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
921   &MUST-NOT; include an entity.
922</t>
923<t>
924   TRACE allows the client to see what is being received at the other
925   end of the request chain and use that data for testing or diagnostic
926   information. The value of the Via header field (&header-via;) is of
927   particular interest, since it acts as a trace of the request chain.
928   Use of the Max-Forwards header field allows the client to limit the
929   length of the request chain, which is useful for testing a chain of
930   proxies forwarding messages in an infinite loop.
931</t>
932<t>
933   If the request is valid, the response &SHOULD; contain the entire
934   request message in the entity-body, with a Content-Type of
935   "message/http". Responses to this method &MUST-NOT; be cached.
936</t>
937</section>
938
939<section title="CONNECT" anchor="CONNECT">
940  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
941  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
942<t>
943   This specification reserves the method name CONNECT for use with a
944   proxy that can dynamically switch to being a tunnel (e.g. SSL
945   tunneling <xref target="Luo1998"/>).
946</t>
947</section>
948</section>
949
950
951<section title="Status Code Definitions" anchor="status.codes">
952<t>
953   Each Status-Code is described below, including a description of which
954   method(s) it can follow and any metainformation required in the
955   response.
956</t>
957
958<section title="Informational 1xx" anchor="status.1xx">
959<t>
960   This class of status code indicates a provisional response,
961   consisting only of the Status-Line and optional headers, and is
962   terminated by an empty line. There are no required headers for this
963   class of status code. Since HTTP/1.0 did not define any 1xx status
964   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
965   except under experimental conditions.
966</t>
967<t>
968   A client &MUST; be prepared to accept one or more 1xx status responses
969   prior to a regular response, even if the client does not expect a 100
970   (Continue) status message. Unexpected 1xx status responses &MAY; be
971   ignored by a user agent.
972</t>
973<t>
974   Proxies &MUST; forward 1xx responses, unless the connection between the
975   proxy and its client has been closed, or unless the proxy itself
976   requested the generation of the 1xx response. (For example, if a
977   proxy adds a "Expect: 100-continue" field when it forwards a request,
978   then it need not forward the corresponding 100 (Continue)
979   response(s).)
980</t>
981
982<section title="100 Continue" anchor="status.100">
983  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
984  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
985<t>
986   The client &SHOULD; continue with its request. This interim response is
987   used to inform the client that the initial part of the request has
988   been received and has not yet been rejected by the server. The client
989   &SHOULD; continue by sending the remainder of the request or, if the
990   request has already been completed, ignore this response. The server
991   &MUST; send a final response after the request has been completed. See
992   &use100; for detailed discussion of the use and handling of this
993   status code.
994</t>
995</section>
996
997<section title="101 Switching Protocols" anchor="status.101">
998  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
999  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1000<t>
1001   The server understands and is willing to comply with the client's
1002   request, via the Upgrade message header field (&header-upgrade;), for a
1003   change in the application protocol being used on this connection. The
1004   server will switch protocols to those defined by the response's
1005   Upgrade header field immediately after the empty line which
1006   terminates the 101 response.
1007</t>
1008<t>
1009   The protocol &SHOULD; be switched only when it is advantageous to do
1010   so. For example, switching to a newer version of HTTP is advantageous
1011   over older versions, and switching to a real-time, synchronous
1012   protocol might be advantageous when delivering resources that use
1013   such features.
1014</t>
1015</section>
1016</section>
1017
1018<section title="Successful 2xx" anchor="status.2xx">
1019<t>
1020   This class of status code indicates that the client's request was
1021   successfully received, understood, and accepted.
1022</t>
1023
1024<section title="200 OK" anchor="status.200">
1025  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1026  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1027<t>
1028   The request has succeeded. The information returned with the response
1029   is dependent on the method used in the request, for example:
1030  <list style="hanging">
1031    <t hangText="GET">
1032          an entity corresponding to the requested resource is sent in
1033          the response;
1034    </t>
1035    <t hangText="HEAD">
1036          the entity-header fields corresponding to the requested
1037          resource are sent in the response without any message-body;
1038    </t>
1039    <t hangText="POST">
1040      an entity describing or containing the result of the action;
1041    </t>
1042    <t hangText="TRACE">
1043      an entity containing the request message as received by the
1044      end server.
1045    </t>
1046  </list>
1047</t>
1048</section>
1049
1050<section title="201 Created" anchor="status.201">
1051  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1052  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1053<t>
1054   The request has been fulfilled and resulted in a new resource being
1055   created. The newly created resource can be referenced by the URI(s)
1056   returned in the entity of the response, with the most specific URI
1057   for the resource given by a Location header field. The response
1058   &SHOULD; include an entity containing a list of resource
1059   characteristics and location(s) from which the user or user agent can
1060   choose the one most appropriate. The entity format is specified by
1061   the media type given in the Content-Type header field. The origin
1062   server &MUST; create the resource before returning the 201 status code.
1063   If the action cannot be carried out immediately, the server &SHOULD;
1064   respond with 202 (Accepted) response instead.
1065</t>
1066<t>
1067   A 201 response &MAY; contain an ETag response header field indicating
1068   the current value of the entity tag for the requested variant just
1069   created, see &header-etag;.
1070</t>
1071</section>
1072
1073<section title="202 Accepted" anchor="status.202">
1074  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1075  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1076<t>
1077   The request has been accepted for processing, but the processing has
1078   not been completed.  The request might or might not eventually be
1079   acted upon, as it might be disallowed when processing actually takes
1080   place. There is no facility for re-sending a status code from an
1081   asynchronous operation such as this.
1082</t>
1083<t>
1084   The 202 response is intentionally non-committal. Its purpose is to
1085   allow a server to accept a request for some other process (perhaps a
1086   batch-oriented process that is only run once per day) without
1087   requiring that the user agent's connection to the server persist
1088   until the process is completed. The entity returned with this
1089   response &SHOULD; include an indication of the request's current status
1090   and either a pointer to a status monitor or some estimate of when the
1091   user can expect the request to be fulfilled.
1092</t>
1093</section>
1094
1095<section title="203 Non-Authoritative Information" anchor="status.203">
1096  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1097  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1098<t>
1099   The returned metainformation in the entity-header is not the
1100   definitive set as available from the origin server, but is gathered
1101   from a local or a third-party copy. The set presented &MAY; be a subset
1102   or superset of the original version. For example, including local
1103   annotation information about the resource might result in a superset
1104   of the metainformation known by the origin server. Use of this
1105   response code is not required and is only appropriate when the
1106   response would otherwise be 200 (OK).
1107</t>
1108</section>
1109
1110<section title="204 No Content" anchor="status.204">
1111  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1112  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1113<t>
1114   The server has fulfilled the request but does not need to return an
1115   entity-body, and might want to return updated metainformation. The
1116   response &MAY; include new or updated metainformation in the form of
1117   entity-headers, which if present &SHOULD; be associated with the
1118   requested variant.
1119</t>
1120<t>
1121   If the client is a user agent, it &SHOULD-NOT;  change its document view
1122   from that which caused the request to be sent. This response is
1123   primarily intended to allow input for actions to take place without
1124   causing a change to the user agent's active document view, although
1125   any new or updated metainformation &SHOULD; be applied to the document
1126   currently in the user agent's active view.
1127</t>
1128<t>
1129   The 204 response &MUST-NOT; include a message-body, and thus is always
1130   terminated by the first empty line after the header fields.
1131</t>
1132</section>
1133
1134<section title="205 Reset Content" anchor="status.205">
1135  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1136  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1137<t>
1138   The server has fulfilled the request and the user agent &SHOULD; reset
1139   the document view which caused the request to be sent. This response
1140   is primarily intended to allow input for actions to take place via
1141   user input, followed by a clearing of the form in which the input is
1142   given so that the user can easily initiate another input action. The
1143   response &MUST-NOT; include an entity.
1144</t>
1145</section>
1146
1147<section title="206 Partial Content" anchor="status.206">
1148  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1149  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1150<t>
1151   The server has fulfilled the partial GET request for the resource
1152   and the enclosed entity is a partial representation as defined in &range;.
1153</t>
1154</section>
1155</section>
1156
1157<section title="Redirection 3xx" anchor="status.3xx">
1158<t>
1159   This class of status code indicates that further action needs to be
1160   taken by the user agent in order to fulfill the request.  The action
1161   required &MAY; be carried out by the user agent without interaction
1162   with the user if and only if the method used in the second request is
1163   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1164   such loops generate network traffic for each redirection.
1165  <list><t>
1166      <x:h>Note:</x:h> previous versions of this specification recommended a
1167      maximum of five redirections. Content developers should be aware
1168      that there might be clients that implement such a fixed
1169      limitation.
1170  </t></list>
1171</t>
1172
1173<section title="300 Multiple Choices" anchor="status.300">
1174  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1175  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1176<t>
1177   The requested resource corresponds to any one of a set of
1178   representations, each with its own specific location, and agent-driven
1179   negotiation information (&content-negotiation;) is being provided so that
1180   the user (or user agent) can select a preferred representation and
1181   redirect its request to that location.
1182</t>
1183<t>
1184   Unless it was a HEAD request, the response &SHOULD; include an entity
1185   containing a list of resource characteristics and location(s) from
1186   which the user or user agent can choose the one most appropriate. The
1187   entity format is specified by the media type given in the Content-Type
1188   header field. Depending upon the format and the capabilities of
1189   the user agent, selection of the most appropriate choice &MAY; be
1190   performed automatically. However, this specification does not define
1191   any standard for such automatic selection.
1192</t>
1193<t>
1194   If the server has a preferred choice of representation, it &SHOULD;
1195   include the specific URI for that representation in the Location
1196   field; user agents &MAY; use the Location field value for automatic
1197   redirection. This response is cacheable unless indicated otherwise.
1198</t>
1199</section>
1200
1201<section title="301 Moved Permanently" anchor="status.301">
1202  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1203  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1204<t>
1205   The requested resource has been assigned a new permanent URI and any
1206   future references to this resource &SHOULD; use one of the returned
1207   URIs.  Clients with link editing capabilities ought to automatically
1208   re-link references to the Request-URI to one or more of the new
1209   references returned by the server, where possible. This response is
1210   cacheable unless indicated otherwise.
1211</t>
1212<t>
1213   The new permanent URI &SHOULD; be given by the Location field in the
1214   response. Unless the request method was HEAD, the entity of the
1215   response &SHOULD; contain a short hypertext note with a hyperlink to
1216   the new URI(s).
1217</t>
1218<t>
1219   If the 301 status code is received in response to a request method
1220   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1221   then the request &MAY; be automatically redirected by the user agent without
1222   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1223   request unless it can be confirmed by the user, since this might
1224   change the conditions under which the request was issued.
1225  <list><t>
1226      <x:h>Note:</x:h> When automatically redirecting a POST request after
1227      receiving a 301 status code, some existing HTTP/1.0 user agents
1228      will erroneously change it into a GET request.
1229  </t></list>
1230</t>
1231</section>
1232
1233<section title="302 Found" anchor="status.302">
1234  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1235  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1236<t>
1237   The requested resource resides temporarily under a different URI.
1238   Since the redirection might be altered on occasion, the client &SHOULD;
1239   continue to use the Request-URI for future requests.  This response
1240   is only cacheable if indicated by a Cache-Control or Expires header
1241   field.
1242</t>
1243<t>
1244   The temporary URI &SHOULD; be given by the Location field in the
1245   response. Unless the request method was HEAD, the entity of the
1246   response &SHOULD; contain a short hypertext note with a hyperlink to
1247   the new URI(s).
1248</t>
1249<t>
1250   If the 302 status code is received in response to a request method
1251   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1252   then the request &MAY; be automatically redirected by the user agent without
1253   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1254   request unless it can be confirmed by the user, since this might
1255   change the conditions under which the request was issued.
1256  <list><t>
1257      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1258      to change the method on the redirected request.  However, most
1259      existing user agent implementations treat 302 as if it were a 303
1260      response, performing a GET on the Location field-value regardless
1261      of the original request method. The status codes 303 and 307 have
1262      been added for servers that wish to make unambiguously clear which
1263      kind of reaction is expected of the client.
1264  </t></list>
1265</t>
1266</section>
1267
1268<section title="303 See Other" anchor="status.303">
1269  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1270  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1271<t>
1272   The server directs the user agent to a different resource, indicated
1273   by a URI in the Location header field, that provides an indirect
1274   response to the original request.  The user agent &MAY; perform a GET
1275   request on the URI in the Location field in order to obtain a
1276   representation corresponding to the response, be redirected again,
1277   or end with an error status.  The Location URI is not a substitute
1278   reference for the originally requested resource.
1279</t>
1280<t>
1281   The 303 status is generally applicable to any HTTP method.  It is
1282   primarily used to allow the output of a POST action to redirect
1283   the user agent to a selected resource, since doing so provides the
1284   information corresponding to the POST response in a form that
1285   can be separately identified, bookmarked, and cached independent
1286   of the original request.
1287</t>
1288<t>
1289   A 303 response to a GET request indicates that the requested
1290   resource does not have a representation of its own that can be
1291   transferred by the server over HTTP.  The Location URI indicates a
1292   resource that is descriptive of the requested resource such that
1293   the follow-on representation may be useful without implying that
1294   it adequately represents the previously requested resource.
1295   Note that answers to the questions of what can be represented, what
1296   representations are adequate, and what might be a useful description
1297   are outside the scope of HTTP and thus entirely determined by the
1298   resource owner(s).
1299</t>
1300<t>
1301   A 303 response &SHOULD-NOT; be cached unless it is indicated as
1302   cacheable by Cache-Control or Expires header fields.  Except for
1303   responses to a HEAD request, the entity of a 303 response &SHOULD;
1304   contain a short hypertext note with a hyperlink to the Location URI.
1305</t>
1306</section>
1307
1308<section title="304 Not Modified" anchor="status.304">
1309  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1310  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1311<t>
1312   The response to the request has not been modified since the conditions
1313   indicated by the client's conditional GET request, as defined in &conditional;.
1314</t>
1315</section>
1316
1317<section title="305 Use Proxy" anchor="status.305">
1318  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1319  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1320<t>
1321   The 305 status was defined in a previous version of this specification
1322   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1323</t>
1324</section>
1325
1326<section title="306 (Unused)" anchor="status.306">
1327  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1328  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1329<t>
1330   The 306 status code was used in a previous version of the
1331   specification, is no longer used, and the code is reserved.
1332</t>
1333</section>
1334
1335<section title="307 Temporary Redirect" anchor="status.307">
1336  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1337  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1338<t>
1339   The requested resource resides temporarily under a different URI.
1340   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1341   continue to use the Request-URI for future requests.  This response
1342   is only cacheable if indicated by a Cache-Control or Expires header
1343   field.
1344</t>
1345<t>
1346   The temporary URI &SHOULD; be given by the Location field in the
1347   response. Unless the request method was HEAD, the entity of the
1348   response &SHOULD; contain a short hypertext note with a hyperlink to
1349   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1350   understand the 307 status. Therefore, the note &SHOULD; contain the
1351   information necessary for a user to repeat the original request on
1352   the new URI.
1353</t>
1354<t>
1355   If the 307 status code is received in response to a request method
1356   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1357   then the request &MAY; be automatically redirected by the user agent without
1358   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1359   request unless it can be confirmed by the user, since this might
1360   change the conditions under which the request was issued.
1361</t>
1362</section>
1363</section>
1364
1365<section title="Client Error 4xx" anchor="status.4xx">
1366<t>
1367   The 4xx class of status code is intended for cases in which the
1368   client seems to have erred. Except when responding to a HEAD request,
1369   the server &SHOULD; include an entity containing an explanation of the
1370   error situation, and whether it is a temporary or permanent
1371   condition. These status codes are applicable to any request method.
1372   User agents &SHOULD; display any included entity to the user.
1373</t>
1374<t>
1375   If the client is sending data, a server implementation using TCP
1376   &SHOULD; be careful to ensure that the client acknowledges receipt of
1377   the packet(s) containing the response, before the server closes the
1378   input connection. If the client continues sending data to the server
1379   after the close, the server's TCP stack will send a reset packet to
1380   the client, which may erase the client's unacknowledged input buffers
1381   before they can be read and interpreted by the HTTP application.
1382</t>
1383
1384<section title="400 Bad Request" anchor="status.400">
1385  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1386  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1387<t>
1388   The request could not be understood by the server due to malformed
1389   syntax. The client &SHOULD-NOT;  repeat the request without
1390   modifications.
1391</t>
1392</section>
1393
1394<section title="401 Unauthorized" anchor="status.401">
1395  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1396  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1397<t>
1398   The request requires user authentication (see &auth;).
1399</t>
1400</section>
1401
1402<section title="402 Payment Required" anchor="status.402">
1403  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1404  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1405<t>
1406   This code is reserved for future use.
1407</t>
1408</section>
1409
1410<section title="403 Forbidden" anchor="status.403">
1411  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1412  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1413<t>
1414   The server understood the request, but is refusing to fulfill it.
1415   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1416   If the request method was not HEAD and the server wishes to make
1417   public why the request has not been fulfilled, it &SHOULD; describe the
1418   reason for the refusal in the entity.  If the server does not wish to
1419   make this information available to the client, the status code 404
1420   (Not Found) can be used instead.
1421</t>
1422</section>
1423
1424<section title="404 Not Found" anchor="status.404">
1425  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1426  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1427<t>
1428   The server has not found anything matching the Request-URI. No
1429   indication is given of whether the condition is temporary or
1430   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1431   knows, through some internally configurable mechanism, that an old
1432   resource is permanently unavailable and has no forwarding address.
1433   This status code is commonly used when the server does not wish to
1434   reveal exactly why the request has been refused, or when no other
1435   response is applicable.
1436</t>
1437</section>
1438
1439<section title="405 Method Not Allowed" anchor="status.405">
1440  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1441  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1442<t>
1443   The method specified in the Request-Line is not allowed for the
1444   resource identified by the Request-URI. The response &MUST; include an
1445   Allow header containing a list of valid methods for the requested
1446   resource.
1447</t>
1448</section>
1449
1450<section title="406 Not Acceptable" anchor="status.406">
1451  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1452  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1453<t>
1454   The resource identified by the request is only capable of generating
1455   response entities which have content characteristics not acceptable
1456   according to the accept headers sent in the request.
1457</t>
1458<t>
1459   Unless it was a HEAD request, the response &SHOULD; include an entity
1460   containing a list of available entity characteristics and location(s)
1461   from which the user or user agent can choose the one most
1462   appropriate. The entity format is specified by the media type given
1463   in the Content-Type header field. Depending upon the format and the
1464   capabilities of the user agent, selection of the most appropriate
1465   choice &MAY; be performed automatically. However, this specification
1466   does not define any standard for such automatic selection.
1467  <list><t>
1468      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1469      not acceptable according to the accept headers sent in the
1470      request. In some cases, this may even be preferable to sending a
1471      406 response. User agents are encouraged to inspect the headers of
1472      an incoming response to determine if it is acceptable.
1473  </t></list>
1474</t>
1475<t>
1476   If the response could be unacceptable, a user agent &SHOULD;
1477   temporarily stop receipt of more data and query the user for a
1478   decision on further actions.
1479</t>
1480</section>
1481
1482<section title="407 Proxy Authentication Required" anchor="status.407">
1483  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1484  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1485<t>
1486   This code is similar to 401 (Unauthorized), but indicates that the
1487   client must first authenticate itself with the proxy (see &auth;).
1488</t>
1489</section>
1490
1491<section title="408 Request Timeout" anchor="status.408">
1492  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1493  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1494<t>
1495   The client did not produce a request within the time that the server
1496   was prepared to wait. The client &MAY; repeat the request without
1497   modifications at any later time.
1498</t>
1499</section>
1500
1501<section title="409 Conflict" anchor="status.409">
1502  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1503  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1504<t>
1505   The request could not be completed due to a conflict with the current
1506   state of the resource. This code is only allowed in situations where
1507   it is expected that the user might be able to resolve the conflict
1508   and resubmit the request. The response body &SHOULD; include enough
1509   information for the user to recognize the source of the conflict.
1510   Ideally, the response entity would include enough information for the
1511   user or user agent to fix the problem; however, that might not be
1512   possible and is not required.
1513</t>
1514<t>
1515   Conflicts are most likely to occur in response to a PUT request. For
1516   example, if versioning were being used and the entity being PUT
1517   included changes to a resource which conflict with those made by an
1518   earlier (third-party) request, the server might use the 409 response
1519   to indicate that it can't complete the request. In this case, the
1520   response entity would likely contain a list of the differences
1521   between the two versions in a format defined by the response
1522   Content-Type.
1523</t>
1524</section>
1525
1526<section title="410 Gone" anchor="status.410">
1527  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1528  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1529<t>
1530   The requested resource is no longer available at the server and no
1531   forwarding address is known. This condition is expected to be
1532   considered permanent. Clients with link editing capabilities &SHOULD;
1533   delete references to the Request-URI after user approval. If the
1534   server does not know, or has no facility to determine, whether or not
1535   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1536   used instead. This response is cacheable unless indicated otherwise.
1537</t>
1538<t>
1539   The 410 response is primarily intended to assist the task of web
1540   maintenance by notifying the recipient that the resource is
1541   intentionally unavailable and that the server owners desire that
1542   remote links to that resource be removed. Such an event is common for
1543   limited-time, promotional services and for resources belonging to
1544   individuals no longer working at the server's site. It is not
1545   necessary to mark all permanently unavailable resources as "gone" or
1546   to keep the mark for any length of time -- that is left to the
1547   discretion of the server owner.
1548</t>
1549</section>
1550
1551<section title="411 Length Required" anchor="status.411">
1552  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1553  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1554<t>
1555   The server refuses to accept the request without a defined Content-Length.
1556   The client &MAY; repeat the request if it adds a valid
1557   Content-Length header field containing the length of the message-body
1558   in the request message.
1559</t>
1560</section>
1561
1562<section title="412 Precondition Failed" anchor="status.412">
1563  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1564  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1565<t>
1566   The precondition given in one or more of the request-header fields
1567   evaluated to false when it was tested on the server, as defined in
1568   &conditional;.
1569</t>
1570</section>
1571
1572<section title="413 Request Entity Too Large" anchor="status.413">
1573  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1574  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1575<t>
1576   The server is refusing to process a request because the request
1577   entity is larger than the server is willing or able to process. The
1578   server &MAY; close the connection to prevent the client from continuing
1579   the request.
1580</t>
1581<t>
1582   If the condition is temporary, the server &SHOULD; include a Retry-After
1583   header field to indicate that it is temporary and after what
1584   time the client &MAY; try again.
1585</t>
1586</section>
1587
1588<section title="414 Request-URI Too Long" anchor="status.414">
1589  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1590  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1591<t>
1592   The server is refusing to service the request because the Request-URI
1593   is longer than the server is willing to interpret. This rare
1594   condition is only likely to occur when a client has improperly
1595   converted a POST request to a GET request with long query
1596   information, when the client has descended into a URI "black hole" of
1597   redirection (e.g., a redirected URI prefix that points to a suffix of
1598   itself), or when the server is under attack by a client attempting to
1599   exploit security holes present in some servers using fixed-length
1600   buffers for reading or manipulating the Request-URI.
1601</t>
1602</section>
1603
1604<section title="415 Unsupported Media Type" anchor="status.415">
1605  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1606  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1607<t>
1608   The server is refusing to service the request because the entity of
1609   the request is in a format not supported by the requested resource
1610   for the requested method.
1611</t>
1612</section>
1613
1614<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1615  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1616  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1617<t>
1618   The request included a Range request-header field (&header-range;) and none of
1619   the range-specifier values in this field overlap the current extent
1620   of the selected resource.
1621</t>
1622</section>
1623
1624<section title="417 Expectation Failed" anchor="status.417">
1625  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1626  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1627<t>
1628   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1629   could not be met by this server, or, if the server is a proxy,
1630   the server has unambiguous evidence that the request could not be met
1631   by the next-hop server.
1632</t>
1633</section>
1634</section>
1635
1636<section title="Server Error 5xx" anchor="status.5xx">
1637<t>
1638   Response status codes beginning with the digit "5" indicate cases in
1639   which the server is aware that it has erred or is incapable of
1640   performing the request. Except when responding to a HEAD request, the
1641   server &SHOULD; include an entity containing an explanation of the
1642   error situation, and whether it is a temporary or permanent
1643   condition. User agents &SHOULD; display any included entity to the
1644   user. These response codes are applicable to any request method.
1645</t>
1646
1647<section title="500 Internal Server Error" anchor="status.500">
1648  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1649  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1650<t>
1651   The server encountered an unexpected condition which prevented it
1652   from fulfilling the request.
1653</t>
1654</section>
1655
1656<section title="501 Not Implemented" anchor="status.501">
1657  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1658  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1659<t>
1660   The server does not support the functionality required to fulfill the
1661   request. This is the appropriate response when the server does not
1662   recognize the request method and is not capable of supporting it for
1663   any resource.
1664</t>
1665</section>
1666
1667<section title="502 Bad Gateway" anchor="status.502">
1668  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1669  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1670<t>
1671   The server, while acting as a gateway or proxy, received an invalid
1672   response from the upstream server it accessed in attempting to
1673   fulfill the request.
1674</t>
1675</section>
1676
1677<section title="503 Service Unavailable" anchor="status.503">
1678  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1679  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1680<t>
1681   The server is currently unable to handle the request due to a
1682   temporary overloading or maintenance of the server. The implication
1683   is that this is a temporary condition which will be alleviated after
1684   some delay. If known, the length of the delay &MAY; be indicated in a
1685   Retry-After header. If no Retry-After is given, the client &SHOULD;
1686   handle the response as it would for a 500 response.
1687  <list><t>
1688      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1689      server must use it when becoming overloaded. Some servers may wish
1690      to simply refuse the connection.
1691  </t></list>
1692</t>
1693</section>
1694
1695<section title="504 Gateway Timeout" anchor="status.504">
1696  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1697  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1698<t>
1699   The server, while acting as a gateway or proxy, did not receive a
1700   timely response from the upstream server specified by the URI (e.g.
1701   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1702   to access in attempting to complete the request.
1703  <list><t>
1704      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1705      return 400 or 500 when DNS lookups time out.
1706  </t></list>
1707</t>
1708</section>
1709
1710<section title="505 HTTP Version Not Supported" anchor="status.505">
1711  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1712  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1713<t>
1714   The server does not support, or refuses to support, the protocol
1715   version that was used in the request message. The server is
1716   indicating that it is unable or unwilling to complete the request
1717   using the same major version as the client, as described in &http-version;,
1718   other than with this error message. The response &SHOULD; contain
1719   an entity describing why that version is not supported and what other
1720   protocols are supported by that server.
1721</t>
1722
1723</section>
1724</section>
1725</section>
1726
1727
1728<section title="Header Field Definitions" anchor="header.fields">
1729<t>
1730   This section defines the syntax and semantics of HTTP/1.1 header fields
1731   related to request and response semantics.
1732</t>
1733<t>
1734   For entity-header fields, both sender and recipient refer to either the
1735   client or the server, depending on who sends and who receives the entity.
1736</t>
1737
1738<section title="Allow" anchor="header.allow">
1739  <iref primary="true" item="Allow header" x:for-anchor=""/>
1740  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1741  <x:anchor-alias value="Allow"/>
1742<t>
1743      The Allow response-header field lists the set of methods advertised as
1744      supported by the resource identified by the Request-URI. The purpose of
1745      this field is strictly to inform the recipient of valid methods
1746      associated with the resource. An Allow header field &MUST; be
1747      present in a 405 (Method Not Allowed) response.
1748</t>
1749<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1750  <x:ref>Allow</x:ref>   = "Allow" ":" #<x:ref>Method</x:ref>
1751</artwork></figure>
1752<t>
1753      Example of use:
1754</t>
1755<figure><artwork type="example">
1756       Allow: GET, HEAD, PUT
1757</artwork></figure>
1758<t>
1759      The actual set of allowed methods is defined
1760      by the origin server at the time of each request.
1761</t>
1762<t>
1763      A proxy &MUST-NOT; modify the Allow header field even if it does not
1764      understand all the methods specified, since the user agent might
1765      have other means of communicating with the origin server.
1766</t>
1767</section>
1768
1769<section title="Expect" anchor="header.expect">
1770  <iref primary="true" item="Expect header" x:for-anchor=""/>
1771  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1772  <x:anchor-alias value="Expect"/>
1773  <x:anchor-alias value="expectation"/>
1774  <x:anchor-alias value="expectation-extension"/>
1775  <x:anchor-alias value="expect-params"/>
1776<t>
1777   The Expect request-header field is used to indicate that particular
1778   server behaviors are required by the client.
1779</t>
1780<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"/>
1781  <x:ref>Expect</x:ref>       =  "Expect" ":" 1#<x:ref>expectation</x:ref>
1782 
1783  <x:ref>expectation</x:ref>  =  "100-continue" | <x:ref>expectation-extension</x:ref>
1784  <x:ref>expectation-extension</x:ref> =  <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> )
1785                           *<x:ref>expect-params</x:ref> ]
1786  <x:ref>expect-params</x:ref> =  ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> ) ]
1787</artwork></figure>
1788<t>
1789   A server that does not understand or is unable to comply with any of
1790   the expectation values in the Expect field of a request &MUST; respond
1791   with appropriate error status. The server &MUST; respond with a 417
1792   (Expectation Failed) status if any of the expectations cannot be met
1793   or, if there are other problems with the request, some other 4xx
1794   status.
1795</t>
1796<t>
1797   This header field is defined with extensible syntax to allow for
1798   future extensions. If a server receives a request containing an
1799   Expect field that includes an expectation-extension that it does not
1800   support, it &MUST; respond with a 417 (Expectation Failed) status.
1801</t>
1802<t>
1803   Comparison of expectation values is case-insensitive for unquoted
1804   tokens (including the 100-continue token), and is case-sensitive for
1805   quoted-string expectation-extensions.
1806</t>
1807<t>
1808   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1809   return a 417 (Expectation Failed) status if it receives a request
1810   with an expectation that it cannot meet. However, the Expect
1811   request-header itself is end-to-end; it &MUST; be forwarded if the
1812   request is forwarded.
1813</t>
1814<t>
1815   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1816   Expect header.
1817</t>
1818<t>
1819   See &use100; for the use of the 100 (Continue) status.
1820</t>
1821</section>
1822
1823<section title="From" anchor="header.from">
1824  <iref primary="true" item="From header" x:for-anchor=""/>
1825  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1826  <x:anchor-alias value="From"/>
1827  <x:anchor-alias value="mailbox"/>
1828<t>
1829   The From request-header field, if given, &SHOULD; contain an Internet
1830   e-mail address for the human user who controls the requesting user
1831   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1832   in <xref x:sec="3.4" x:fmt="of" target="RFC2822"/>:
1833</t>
1834<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1835  <x:ref>From</x:ref>    = "From" ":" <x:ref>mailbox</x:ref>
1836 
1837  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC2822"/>&gt;
1838</artwork></figure>
1839<t>
1840   An example is:
1841</t>
1842<figure><artwork type="example">
1843    From: webmaster@example.org
1844</artwork></figure>
1845<t>
1846   This header field &MAY; be used for logging purposes and as a means for
1847   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1848   be used as an insecure form of access protection. The interpretation
1849   of this field is that the request is being performed on behalf of the
1850   person given, who accepts responsibility for the method performed. In
1851   particular, robot agents &SHOULD; include this header so that the
1852   person responsible for running the robot can be contacted if problems
1853   occur on the receiving end.
1854</t>
1855<t>
1856   The Internet e-mail address in this field &MAY; be separate from the
1857   Internet host which issued the request. For example, when a request
1858   is passed through a proxy the original issuer's address &SHOULD; be
1859   used.
1860</t>
1861<t>
1862   The client &SHOULD-NOT;  send the From header field without the user's
1863   approval, as it might conflict with the user's privacy interests or
1864   their site's security policy. It is strongly recommended that the
1865   user be able to disable, enable, and modify the value of this field
1866   at any time prior to a request.
1867</t>
1868</section>
1869
1870<section title="Location" anchor="header.location">
1871  <iref primary="true" item="Location header" x:for-anchor=""/>
1872  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1873  <x:anchor-alias value="Location"/>
1874<t>
1875   The Location response-header field is used for the identification of a
1876   new resource or to redirect the recipient to a location other than the
1877   Request-URI for completion of the request.  For 201 (Created)
1878   responses, the Location is that of the new resource which was created
1879   by the request. For 3xx responses, the location &SHOULD; indicate the
1880   server's preferred URI for automatic redirection to the resource. The
1881   field value consists of a single absolute URI.
1882</t>
1883<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1884  <x:ref>Location</x:ref>       = "Location" ":" <x:ref>absoluteURI</x:ref> [ "#" <x:ref>fragment</x:ref> ]
1885</artwork></figure>
1886<t>
1887   An example is:
1888</t>
1889<figure><artwork type="example">
1890    Location: http://www.example.org/pub/WWW/People.html
1891</artwork></figure>
1892<t>
1893  <list><t>
1894      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1895      from Location in that the Content-Location identifies the original
1896      location of the entity enclosed in the request. It is therefore
1897      possible for a response to contain header fields for both Location
1898      and Content-Location.
1899  </t></list>
1900</t>
1901<t>
1902   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1903   <list style="symbols">
1904      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1905      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1906      <t>With 305 Use Proxy.</t>
1907   </list>
1908</t>
1909</section>
1910
1911<section title="Max-Forwards" anchor="header.max-forwards">
1912  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1913  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1914  <x:anchor-alias value="Max-Forwards"/>
1915<t>
1916   The Max-Forwards request-header field provides a mechanism with the
1917   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1918   number of proxies or gateways that can forward the request to the
1919   next inbound server. This can be useful when the client is attempting
1920   to trace a request chain which appears to be failing or looping in
1921   mid-chain.
1922</t>
1923<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1924  <x:ref>Max-Forwards</x:ref>   = "Max-Forwards" ":" 1*<x:ref>DIGIT</x:ref>
1925</artwork></figure>
1926<t>
1927   The Max-Forwards value is a decimal integer indicating the remaining
1928   number of times this request message may be forwarded.
1929</t>
1930<t>
1931   Each proxy or gateway recipient of a TRACE or OPTIONS request
1932   containing a Max-Forwards header field &MUST; check and update its
1933   value prior to forwarding the request. If the received value is zero
1934   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1935   respond as the final recipient. If the received Max-Forwards value is
1936   greater than zero, then the forwarded message &MUST; contain an updated
1937   Max-Forwards field with a value decremented by one (1).
1938</t>
1939<t>
1940   The Max-Forwards header field &MAY; be ignored for all other methods
1941   defined by this specification and for any extension methods for which
1942   it is not explicitly referred to as part of that method definition.
1943</t>
1944</section>
1945
1946<section title="Referer" anchor="header.referer">
1947  <iref primary="true" item="Referer header" x:for-anchor=""/>
1948  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1949  <x:anchor-alias value="Referer"/>
1950<t>
1951   The Referer[sic] request-header field allows the client to specify,
1952   for the server's benefit, the address (URI) of the resource from
1953   which the Request-URI was obtained (the "referrer", although the
1954   header field is misspelled.) The Referer request-header allows a
1955   server to generate lists of back-links to resources for interest,
1956   logging, optimized caching, etc. It also allows obsolete or mistyped
1957   links to be traced for maintenance. The Referer field &MUST-NOT; be
1958   sent if the Request-URI was obtained from a source that does not have
1959   its own URI, such as input from the user keyboard.
1960</t>
1961<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1962  <x:ref>Referer</x:ref>        = "Referer" ":" ( <x:ref>absoluteURI</x:ref> | <x:ref>relativeURI</x:ref> )
1963</artwork></figure>
1964<t>
1965   Example:
1966</t>
1967<figure><artwork type="example">
1968    Referer: http://www.example.org/hypertext/Overview.html
1969</artwork></figure>
1970<t>
1971   If the field value is a relative URI, it &SHOULD; be interpreted
1972   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1973   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1974</t>
1975</section>
1976
1977<section title="Retry-After" anchor="header.retry-after">
1978  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1979  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1980  <x:anchor-alias value="Retry-After"/>
1981<t>
1982   The Retry-After response-header field can be used with a 503 (Service
1983   Unavailable) response to indicate how long the service is expected to
1984   be unavailable to the requesting client. This field &MAY; also be used
1985   with any 3xx (Redirection) response to indicate the minimum time the
1986   user-agent is asked wait before issuing the redirected request. The
1987   value of this field can be either an HTTP-date or an integer number
1988   of seconds (in decimal) after the time of the response.
1989</t>
1990<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1991  <x:ref>Retry-After</x:ref>   = "Retry-After" ":" ( <x:ref>HTTP-date</x:ref> | <x:ref>delta-seconds</x:ref> )
1992</artwork></figure>
1993<t anchor="rule.delta-seconds">
1994  <x:anchor-alias value="delta-seconds"/>
1995   Time spans are non-negative decimal integers, representing time in
1996   seconds.
1997</t>
1998<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
1999  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2000</artwork></figure>
2001<t>
2002   Two examples of its use are
2003</t>
2004<figure><artwork type="example">
2005    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2006    Retry-After: 120
2007</artwork></figure>
2008<t>
2009   In the latter example, the delay is 2 minutes.
2010</t>
2011</section>
2012
2013<section title="Server" anchor="header.server">
2014  <iref primary="true" item="Server header" x:for-anchor=""/>
2015  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
2016  <x:anchor-alias value="Server"/>
2017<t>
2018   The Server response-header field contains information about the
2019   software used by the origin server to handle the request. The field
2020   can contain multiple product tokens (&product-tokens;) and comments
2021   identifying the server and any significant subproducts. The product
2022   tokens are listed in order of their significance for identifying the
2023   application.
2024</t>
2025<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2026  <x:ref>Server</x:ref>         = "Server" ":" 1*( <x:ref>product</x:ref> | <x:ref>comment</x:ref> )
2027</artwork></figure>
2028<t>
2029   Example:
2030</t>
2031<figure><artwork type="example">
2032    Server: CERN/3.0 libwww/2.17
2033</artwork></figure>
2034<t>
2035   If the response is being forwarded through a proxy, the proxy
2036   application &MUST-NOT; modify the Server response-header. Instead, it
2037   &MUST; include a Via field (as described in &header-via;).
2038  <list><t>
2039      <x:h>Note:</x:h> Revealing the specific software version of the server might
2040      allow the server machine to become more vulnerable to attacks
2041      against software that is known to contain security holes. Server
2042      implementors are encouraged to make this field a configurable
2043      option.
2044  </t></list>
2045</t>
2046</section>
2047
2048<section title="User-Agent" anchor="header.user-agent">
2049  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
2050  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
2051  <x:anchor-alias value="User-Agent"/>
2052<t>
2053   The User-Agent request-header field contains information about the
2054   user agent originating the request. This is for statistical purposes,
2055   the tracing of protocol violations, and automated recognition of user
2056   agents for the sake of tailoring responses to avoid particular user
2057   agent limitations. User agents &SHOULD; include this field with
2058   requests. The field can contain multiple product tokens (&product-tokens;)
2059   and comments identifying the agent and any subproducts which form a
2060   significant part of the user agent. By convention, the product tokens
2061   are listed in order of their significance for identifying the
2062   application.
2063</t>
2064<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2065  <x:ref>User-Agent</x:ref>     = "User-Agent" ":" 1*( <x:ref>product</x:ref> | <x:ref>comment</x:ref> )
2066</artwork></figure>
2067<t>
2068   Example:
2069</t>
2070<figure><artwork type="example">
2071    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2072</artwork></figure>
2073</section>
2074
2075</section>
2076
2077<section title="IANA Considerations" anchor="IANA.considerations">
2078<t>
2079   <cref>TBD.</cref>
2080</t>
2081</section>
2082
2083<section title="Security Considerations" anchor="security.considerations">
2084<t>
2085   This section is meant to inform application developers, information
2086   providers, and users of the security limitations in HTTP/1.1 as
2087   described by this document. The discussion does not include
2088   definitive solutions to the problems revealed, though it does make
2089   some suggestions for reducing security risks.
2090</t>
2091
2092<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2093<t>
2094   Like any generic data transfer protocol, HTTP cannot regulate the
2095   content of the data that is transferred, nor is there any a priori
2096   method of determining the sensitivity of any particular piece of
2097   information within the context of any given request. Therefore,
2098   applications &SHOULD; supply as much control over this information as
2099   possible to the provider of that information. Four header fields are
2100   worth special mention in this context: Server, Via, Referer and From.
2101</t>
2102<t>
2103   Revealing the specific software version of the server might allow the
2104   server machine to become more vulnerable to attacks against software
2105   that is known to contain security holes. Implementors &SHOULD; make the
2106   Server header field a configurable option.
2107</t>
2108<t>
2109   Proxies which serve as a portal through a network firewall &SHOULD;
2110   take special precautions regarding the transfer of header information
2111   that identifies the hosts behind the firewall. In particular, they
2112   &SHOULD; remove, or replace with sanitized versions, any Via fields
2113   generated behind the firewall.
2114</t>
2115<t>
2116   The Referer header allows reading patterns to be studied and reverse
2117   links drawn. Although it can be very useful, its power can be abused
2118   if user details are not separated from the information contained in
2119   the Referer. Even when the personal information has been removed, the
2120   Referer header might indicate a private document's URI whose
2121   publication would be inappropriate.
2122</t>
2123<t>
2124   The information sent in the From field might conflict with the user's
2125   privacy interests or their site's security policy, and hence it
2126   &SHOULD-NOT;  be transmitted without the user being able to disable,
2127   enable, and modify the contents of the field. The user &MUST; be able
2128   to set the contents of this field within a user preference or
2129   application defaults configuration.
2130</t>
2131<t>
2132   We suggest, though do not require, that a convenient toggle interface
2133   be provided for the user to enable or disable the sending of From and
2134   Referer information.
2135</t>
2136<t>
2137   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2138   fields can sometimes be used to determine that a specific client or
2139   server have a particular security hole which might be exploited.
2140   Unfortunately, this same information is often used for other valuable
2141   purposes for which HTTP currently has no better mechanism.
2142</t>
2143</section>
2144
2145<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2146<t>
2147   Because the source of a link might be private information or might
2148   reveal an otherwise private information source, it is strongly
2149   recommended that the user be able to select whether or not the
2150   Referer field is sent. For example, a browser client could have a
2151   toggle switch for browsing openly/anonymously, which would
2152   respectively enable/disable the sending of Referer and From
2153   information.
2154</t>
2155<t>
2156   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
2157   HTTP request if the referring page was transferred with a secure
2158   protocol.
2159</t>
2160<t>
2161   Authors of services should not use
2162   GET-based forms for the submission of sensitive data because that
2163   data will be encoded in the Request-URI. Many existing
2164   servers, proxies, and user agents log or display the Request-URI in
2165   places where it might be visible to third parties. Such services can
2166   use POST-based form submission instead.
2167</t>
2168</section>
2169
2170<section title="Location Headers and Spoofing" anchor="location.spoofing">
2171<t>
2172   If a single server supports multiple organizations that do not trust
2173   one another, then it &MUST; check the values of Location and Content-Location
2174   headers in responses that are generated under control of
2175   said organizations to make sure that they do not attempt to
2176   invalidate resources over which they have no authority.
2177</t>
2178</section>
2179
2180</section>
2181
2182<section title="Acknowledgments" anchor="ack">
2183</section>
2184</middle>
2185<back>
2186
2187<references title="Normative References">
2188
2189<reference anchor="Part1">
2190  <front>
2191    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2192    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2193      <organization abbrev="Day Software">Day Software</organization>
2194      <address><email>fielding@gbiv.com</email></address>
2195    </author>
2196    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2197      <organization>One Laptop per Child</organization>
2198      <address><email>jg@laptop.org</email></address>
2199    </author>
2200    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2201      <organization abbrev="HP">Hewlett-Packard Company</organization>
2202      <address><email>JeffMogul@acm.org</email></address>
2203    </author>
2204    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2205      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2206      <address><email>henrikn@microsoft.com</email></address>
2207    </author>
2208    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2209      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2210      <address><email>LMM@acm.org</email></address>
2211    </author>
2212    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2213      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2214      <address><email>paulle@microsoft.com</email></address>
2215    </author>
2216    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2217      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2218      <address><email>timbl@w3.org</email></address>
2219    </author>
2220    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2221      <organization abbrev="W3C">World Wide Web Consortium</organization>
2222      <address><email>ylafon@w3.org</email></address>
2223    </author>
2224    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2225      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2226      <address><email>julian.reschke@greenbytes.de</email></address>
2227    </author>
2228    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2229  </front>
2230  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2231  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2232</reference>
2233
2234<reference anchor="Part3">
2235  <front>
2236    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2237    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2238      <organization abbrev="Day Software">Day Software</organization>
2239      <address><email>fielding@gbiv.com</email></address>
2240    </author>
2241    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2242      <organization>One Laptop per Child</organization>
2243      <address><email>jg@laptop.org</email></address>
2244    </author>
2245    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2246      <organization abbrev="HP">Hewlett-Packard Company</organization>
2247      <address><email>JeffMogul@acm.org</email></address>
2248    </author>
2249    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2250      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2251      <address><email>henrikn@microsoft.com</email></address>
2252    </author>
2253    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2254      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2255      <address><email>LMM@acm.org</email></address>
2256    </author>
2257    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2258      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2259      <address><email>paulle@microsoft.com</email></address>
2260    </author>
2261    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2262      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2263      <address><email>timbl@w3.org</email></address>
2264    </author>
2265    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2266      <organization abbrev="W3C">World Wide Web Consortium</organization>
2267      <address><email>ylafon@w3.org</email></address>
2268    </author>
2269    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2270      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2271      <address><email>julian.reschke@greenbytes.de</email></address>
2272    </author>
2273    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2274  </front>
2275  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2276  <x:source href="p3-payload.xml" basename="p3-payload"/>
2277</reference>
2278
2279<reference anchor="Part4">
2280  <front>
2281    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2282    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2283      <organization abbrev="Day Software">Day Software</organization>
2284      <address><email>fielding@gbiv.com</email></address>
2285    </author>
2286    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2287      <organization>One Laptop per Child</organization>
2288      <address><email>jg@laptop.org</email></address>
2289    </author>
2290    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2291      <organization abbrev="HP">Hewlett-Packard Company</organization>
2292      <address><email>JeffMogul@acm.org</email></address>
2293    </author>
2294    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2295      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2296      <address><email>henrikn@microsoft.com</email></address>
2297    </author>
2298    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2299      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2300      <address><email>LMM@acm.org</email></address>
2301    </author>
2302    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2303      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2304      <address><email>paulle@microsoft.com</email></address>
2305    </author>
2306    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2307      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2308      <address><email>timbl@w3.org</email></address>
2309    </author>
2310    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2311      <organization abbrev="W3C">World Wide Web Consortium</organization>
2312      <address><email>ylafon@w3.org</email></address>
2313    </author>
2314    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2315      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2316      <address><email>julian.reschke@greenbytes.de</email></address>
2317    </author>
2318    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2319  </front>
2320  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2321  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2322</reference>
2323
2324<reference anchor="Part5">
2325  <front>
2326    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2327    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2328      <organization abbrev="Day Software">Day Software</organization>
2329      <address><email>fielding@gbiv.com</email></address>
2330    </author>
2331    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2332      <organization>One Laptop per Child</organization>
2333      <address><email>jg@laptop.org</email></address>
2334    </author>
2335    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2336      <organization abbrev="HP">Hewlett-Packard Company</organization>
2337      <address><email>JeffMogul@acm.org</email></address>
2338    </author>
2339    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2340      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2341      <address><email>henrikn@microsoft.com</email></address>
2342    </author>
2343    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2344      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2345      <address><email>LMM@acm.org</email></address>
2346    </author>
2347    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2348      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2349      <address><email>paulle@microsoft.com</email></address>
2350    </author>
2351    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2352      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2353      <address><email>timbl@w3.org</email></address>
2354    </author>
2355    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2356      <organization abbrev="W3C">World Wide Web Consortium</organization>
2357      <address><email>ylafon@w3.org</email></address>
2358    </author>
2359    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2360      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2361      <address><email>julian.reschke@greenbytes.de</email></address>
2362    </author>
2363    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2364  </front>
2365  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2366  <x:source href="p5-range.xml" basename="p5-range"/>
2367</reference>
2368
2369<reference anchor="Part6">
2370  <front>
2371    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2372    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2373      <organization abbrev="Day Software">Day Software</organization>
2374      <address><email>fielding@gbiv.com</email></address>
2375    </author>
2376    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2377      <organization>One Laptop per Child</organization>
2378      <address><email>jg@laptop.org</email></address>
2379    </author>
2380    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2381      <organization abbrev="HP">Hewlett-Packard Company</organization>
2382      <address><email>JeffMogul@acm.org</email></address>
2383    </author>
2384    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2385      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2386      <address><email>henrikn@microsoft.com</email></address>
2387    </author>
2388    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2389      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2390      <address><email>LMM@acm.org</email></address>
2391    </author>
2392    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2393      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2394      <address><email>paulle@microsoft.com</email></address>
2395    </author>
2396    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2397      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2398      <address><email>timbl@w3.org</email></address>
2399    </author>
2400    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2401      <organization abbrev="W3C">World Wide Web Consortium</organization>
2402      <address><email>ylafon@w3.org</email></address>
2403    </author>
2404    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2405      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2406      <address><email>julian.reschke@greenbytes.de</email></address>
2407    </author>
2408    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2409  </front>
2410  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2411  <x:source href="p6-cache.xml" basename="p6-cache"/>
2412</reference>
2413
2414<reference anchor="Part7">
2415  <front>
2416    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2417    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2418      <organization abbrev="Day Software">Day Software</organization>
2419      <address><email>fielding@gbiv.com</email></address>
2420    </author>
2421    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2422      <organization>One Laptop per Child</organization>
2423      <address><email>jg@laptop.org</email></address>
2424    </author>
2425    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2426      <organization abbrev="HP">Hewlett-Packard Company</organization>
2427      <address><email>JeffMogul@acm.org</email></address>
2428    </author>
2429    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2430      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2431      <address><email>henrikn@microsoft.com</email></address>
2432    </author>
2433    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2434      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2435      <address><email>LMM@acm.org</email></address>
2436    </author>
2437    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2438      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2439      <address><email>paulle@microsoft.com</email></address>
2440    </author>
2441    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2442      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2443      <address><email>timbl@w3.org</email></address>
2444    </author>
2445    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2446      <organization abbrev="W3C">World Wide Web Consortium</organization>
2447      <address><email>ylafon@w3.org</email></address>
2448    </author>
2449    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2450      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2451      <address><email>julian.reschke@greenbytes.de</email></address>
2452    </author>
2453    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2454  </front>
2455  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2456  <x:source href="p7-auth.xml" basename="p7-auth"/>
2457</reference>
2458
2459<reference anchor="RFC2119">
2460  <front>
2461    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2462    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2463      <organization>Harvard University</organization>
2464      <address><email>sob@harvard.edu</email></address>
2465    </author>
2466    <date month="March" year="1997"/>
2467  </front>
2468  <seriesInfo name="BCP" value="14"/>
2469  <seriesInfo name="RFC" value="2119"/>
2470</reference>
2471
2472</references>
2473
2474<references title="Informative References">
2475
2476<reference anchor="Luo1998">
2477  <front>
2478    <title>Tunneling TCP based protocols through Web proxy servers</title>
2479    <author initials="A." surname="Luotonen" fullname="A. Luotonen">
2480      <organization/>
2481    </author>
2482    <date year="1998" month="August"/>
2483  </front>
2484  <seriesInfo name="Internet-Draft" value="draft-luotonen-web-proxy-tunneling-01"/>
2485</reference>
2486
2487<reference anchor="RFC1945">
2488  <front>
2489    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2490    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2491      <organization>MIT, Laboratory for Computer Science</organization>
2492      <address><email>timbl@w3.org</email></address>
2493    </author>
2494    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2495      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2496      <address><email>fielding@ics.uci.edu</email></address>
2497    </author>
2498    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2499      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2500      <address><email>frystyk@w3.org</email></address>
2501    </author>
2502    <date month="May" year="1996"/>
2503  </front>
2504  <seriesInfo name="RFC" value="1945"/>
2505</reference>
2506
2507<reference anchor="RFC2068">
2508  <front>
2509    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2510    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2511      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2512      <address><email>fielding@ics.uci.edu</email></address>
2513    </author>
2514    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2515      <organization>MIT Laboratory for Computer Science</organization>
2516      <address><email>jg@w3.org</email></address>
2517    </author>
2518    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2519      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2520      <address><email>mogul@wrl.dec.com</email></address>
2521    </author>
2522    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2523      <organization>MIT Laboratory for Computer Science</organization>
2524      <address><email>frystyk@w3.org</email></address>
2525    </author>
2526    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2527      <organization>MIT Laboratory for Computer Science</organization>
2528      <address><email>timbl@w3.org</email></address>
2529    </author>
2530    <date month="January" year="1997"/>
2531  </front>
2532  <seriesInfo name="RFC" value="2068"/>
2533</reference>
2534
2535<reference anchor="RFC2616">
2536  <front>
2537    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2538    <author initials="R." surname="Fielding" fullname="R. Fielding">
2539      <organization>University of California, Irvine</organization>
2540      <address><email>fielding@ics.uci.edu</email></address>
2541    </author>
2542    <author initials="J." surname="Gettys" fullname="J. Gettys">
2543      <organization>W3C</organization>
2544      <address><email>jg@w3.org</email></address>
2545    </author>
2546    <author initials="J." surname="Mogul" fullname="J. Mogul">
2547      <organization>Compaq Computer Corporation</organization>
2548      <address><email>mogul@wrl.dec.com</email></address>
2549    </author>
2550    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2551      <organization>MIT Laboratory for Computer Science</organization>
2552      <address><email>frystyk@w3.org</email></address>
2553    </author>
2554    <author initials="L." surname="Masinter" fullname="L. Masinter">
2555      <organization>Xerox Corporation</organization>
2556      <address><email>masinter@parc.xerox.com</email></address>
2557    </author>
2558    <author initials="P." surname="Leach" fullname="P. Leach">
2559      <organization>Microsoft Corporation</organization>
2560      <address><email>paulle@microsoft.com</email></address>
2561    </author>
2562    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2563      <organization>W3C</organization>
2564      <address><email>timbl@w3.org</email></address>
2565    </author>
2566    <date month="June" year="1999"/>
2567  </front>
2568  <seriesInfo name="RFC" value="2616"/>
2569</reference>
2570
2571<reference anchor="RFC2822">
2572  <front>
2573    <title>Internet Message Format</title>
2574    <author initials="P." surname="Resnick" fullname="P. Resnick">
2575      <organization>QUALCOMM Incorporated</organization>
2576    </author>
2577    <date year="2001" month="April"/>
2578  </front> 
2579  <seriesInfo name="RFC" value="2822"/>
2580</reference>
2581
2582</references>
2583
2584<section title="Compatibility with Previous Versions" anchor="compatibility">
2585<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2586<t>
2587   Clarified which error code should be used for inbound server failures
2588   (e.g. DNS failures). (<xref target="status.504"/>).
2589</t>
2590<t>
2591   201 (Created) had a race that required an Etag be sent when a resource is
2592   first created. (<xref target="status.201"/>).
2593</t>
2594<t>
2595   Rewrite of message transmission requirements to make it much harder
2596   for implementors to get it wrong, as the consequences of errors here
2597   can have significant impact on the Internet, and to deal with the
2598   following problems:
2599  <list style="numbers">
2600      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2601         this was incorrectly placing a requirement on the behavior of
2602         an implementation of a future version of HTTP/1.x</t>
2603
2604      <t>Made it clear that user-agents should retry requests, not
2605         "clients" in general.</t>
2606
2607      <t>Converted requirements for clients to ignore unexpected 100
2608         (Continue) responses, and for proxies to forward 100 responses,
2609         into a general requirement for 1xx responses.</t>
2610
2611      <t>Modified some TCP-specific language, to make it clearer that
2612         non-TCP transports are possible for HTTP.</t>
2613
2614      <t>Require that the origin server &MUST-NOT; wait for the request
2615         body before it sends a required 100 (Continue) response.</t>
2616
2617      <t>Allow, rather than require, a server to omit 100 (Continue) if
2618         it has already seen some of the request body.</t>
2619
2620      <t>Allow servers to defend against denial-of-service attacks and
2621         broken clients.</t>
2622  </list>
2623</t>
2624<t>
2625   This change adds the Expect header and 417 status code.
2626</t>
2627<t>
2628   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2629   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2630</t>
2631<t>
2632   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
2633   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2634</t>
2635</section>
2636
2637<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2638<t>
2639  Clarify definition of POST.
2640  (<xref target="POST"/>)
2641</t>
2642<t>
2643  Failed to consider that there are
2644  many other request methods that are safe to automatically redirect,
2645  and further that the user agent is able to make that determination
2646  based on the request method semantics.
2647  (Sections <xref format="counter" target="status.301"/>,
2648  <xref format="counter" target="status.302"/> and
2649  <xref format="counter" target="status.307"/>)
2650</t>
2651<t>
2652  Deprecate 305 Use Proxy status code, because user agents did not implement it.
2653  It used to indicate that the requested resource must be accessed through the
2654  proxy given by the Location field. The Location field gave the URI of the
2655  proxy. The recipient was expected to repeat this single request via the proxy.
2656  (<xref target="status.305"/>)
2657</t>
2658<t>
2659  Reclassify Allow header as response header, removing the option to
2660  specify it in a PUT request.
2661  Relax the server requirement on the contents of the Allow header and
2662  remove requirement on clients to always trust the header value.
2663  (<xref target="header.allow"/>)
2664</t>
2665<t>
2666  Correct syntax of Location header to allow fragment,
2667  as referred symbol wasn't what was expected, and add some
2668  clarifications as to when it would not be appropriate.
2669  (<xref target="header.location"/>)
2670</t>
2671<t>
2672  In the description of the Server header, the Via field
2673  was described as a SHOULD. The requirement was and is stated
2674  correctly in the description of the Via header in &header-via;.
2675  (<xref target="header.server"/>)
2676</t>
2677</section>
2678
2679</section>
2680
2681<section title="Change Log (to be removed by RFC Editor before publication)">
2682
2683<section title="Since RFC2616">
2684<t>
2685  Extracted relevant partitions from <xref target="RFC2616"/>.
2686</t>
2687</section>
2688
2689<section title="Since draft-ietf-httpbis-p2-semantics-00">
2690<t>
2691  Closed issues:
2692  <list style="symbols"> 
2693    <t>
2694      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
2695      "Via is a MUST"
2696      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
2697    </t>
2698    <t>
2699      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
2700      "Fragments allowed in Location"
2701      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
2702    </t>
2703    <t>
2704      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
2705      "Safe Methods vs Redirection"
2706      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
2707    </t>
2708    <t>
2709      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
2710      "Revise description of the POST method"
2711      (<eref target="http://purl.org/NET/http-errata#post"/>)
2712    </t>
2713    <t>
2714      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2715      "Normative and Informative references"
2716    </t>
2717    <t>
2718      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
2719      "RFC2606 Compliance"
2720    </t>
2721    <t>
2722      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2723      "Informative references"
2724    </t>
2725    <t>
2726      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
2727      "Redundant cross-references"
2728    </t>
2729  </list>
2730</t>
2731<t>
2732  Other changes:
2733  <list style="symbols"> 
2734    <t>
2735      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
2736    </t>
2737  </list>
2738</t>
2739</section>
2740
2741<section title="Since draft-ietf-httpbis-p2-semantics-01">
2742<t>
2743  Closed issues:
2744  <list style="symbols"> 
2745    <t>
2746      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
2747      "PUT side effects"
2748    </t>
2749    <t>
2750      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
2751      "Duplicate Host header requirements"
2752    </t>
2753  </list>
2754</t>
2755<t>
2756  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2757  <list style="symbols"> 
2758    <t>
2759      Move "Product Tokens" section (back) into Part 1, as "token" is used
2760      in the definition of the Upgrade header.
2761    </t>
2762    <t>
2763      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2764    </t>
2765    <t>
2766      Copy definition of delta-seconds from Part6 instead of referencing it.
2767    </t>
2768  </list>
2769</t>
2770</section>
2771
2772<section title="Since draft-ietf-httpbis-p2-semantics-02">
2773<t>
2774  Closed issues:
2775  <list style="symbols"> 
2776    <t>
2777      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
2778      "Requiring Allow in 405 responses"
2779    </t>
2780    <t>
2781      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
2782      "Redirection vs. Location"
2783    </t>
2784    <t>
2785      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
2786      "Cacheability of 303 response"
2787    </t>
2788    <t>
2789      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
2790      "305 Use Proxy"
2791    </t>
2792    <t>
2793      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2794      "Classification for Allow header"
2795    </t>
2796    <t>
2797      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
2798      "PUT - 'store under' vs 'store at'"
2799    </t>
2800  </list>
2801</t>
2802</section>
2803
2804</section>
2805
2806</back>
2807</rfc>
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