source: draft-ietf-httpbis/latest/p2-semantics.xml @ 252

Last change on this file since 252 was 252, checked in by julian.reschke@…, 12 years ago

Tweak "Editorial Note", now pointing to Changes section in appendix.

  • Property svn:eol-style set to native
File size: 128.7 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "May">
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    The changes in this draft are summarized in <xref target="changes.since.02"/>.
244  </t>
245</note>
246</front>
247<middle>
248<section title="Introduction" anchor="introduction">
249<t>
250   This document defines HTTP/1.1 request and response semantics.  Each HTTP
251   message, as defined in &messaging;, is in the form of either a request or
252   a response.  An HTTP server listens on a connection for HTTP requests and
253   responds to each request, in the order received on that connection, with
254   one or more HTTP response messages.  This document defines the commonly
255   agreed upon semantics of the HTTP uniform interface, the intentions defined
256   by each request method, and the various response messages that might be
257   expected as a result of applying that method for the requested resource.
258</t>
259<t>
260   This document is currently disorganized in order to minimize the changes
261   between drafts and enable reviewers to see the smaller errata changes.
262   The next draft will reorganize the sections to better reflect the content.
263   In particular, the sections will be ordered according to the typical
264   processing of an HTTP request message (after message parsing): resource
265   mapping, general header fields, methods, request modifiers, response
266   status, and resource metadata.  The current mess reflects how widely
267   dispersed these topics and associated requirements had become in
268   <xref target="RFC2616"/>.
269</t>
270
271<section title="Requirements" anchor="intro.requirements">
272<t>
273   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
274   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
275   document are to be interpreted as described in <xref target="RFC2119"/>.
276</t>
277<t>
278   An implementation is not compliant if it fails to satisfy one or more
279   of the &MUST; or &REQUIRED; level requirements for the protocols it
280   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
281   level and all the &SHOULD; level requirements for its protocols is said
282   to be "unconditionally compliant"; one that satisfies all the &MUST;
283   level requirements but not all the &SHOULD; level requirements for its
284   protocols is said to be "conditionally compliant."
285</t>
286</section>
287</section>
288
289<section title="Notational Conventions and Generic Grammar" anchor="notation">
290  <x:anchor-alias value="comment"/>
291  <x:anchor-alias value="DIGIT"/>
292  <x:anchor-alias value="quoted-string"/>
293  <x:anchor-alias value="token"/>
294<t>
295  This specification uses the ABNF syntax defined in &notation-abnf; and
296  the core rules defined in &basic-rules;:
297  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
298  <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>.</cref>
299</t>
300<figure><artwork type="abnf2616">
301  <x:ref>DIGIT</x:ref>         = &lt;DIGIT, defined in &basic-rules;&gt;
302</artwork></figure>
303<figure><artwork type="abnf2616">
304  <x:anchor-alias value="Accept"/>
305  <x:ref>comment</x:ref>       = &lt;comment, defined in &basic-rules;&gt;
306  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &basic-rules;&gt;
307  <x:ref>token</x:ref>         = &lt;token, defined in &basic-rules;&gt;
308</artwork></figure>
309<t anchor="abnf.dependencies">
310  <x:anchor-alias value="absoluteURI"/>
311  <x:anchor-alias value="Accept"/>
312  <x:anchor-alias value="Accept-Charset"/>
313  <x:anchor-alias value="Accept-Encoding"/>
314  <x:anchor-alias value="Accept-Language"/>
315  <x:anchor-alias value="Accept-Ranges"/>
316  <x:anchor-alias value="Age"/>
317  <x:anchor-alias value="Authorization"/>
318  <x:anchor-alias value="ETag"/>
319  <x:anchor-alias value="fragment"/>
320  <x:anchor-alias value="Host"/>
321  <x:anchor-alias value="HTTP-date"/>
322  <x:anchor-alias value="If-Match"/>
323  <x:anchor-alias value="If-Modified-Since"/>
324  <x:anchor-alias value="If-None-Match"/>
325  <x:anchor-alias value="If-Range"/>
326  <x:anchor-alias value="If-Unmodified-Since"/>
327  <x:anchor-alias value="product"/>
328  <x:anchor-alias value="Proxy-Authenticate"/>
329  <x:anchor-alias value="Proxy-Authorization"/>
330  <x:anchor-alias value="Range"/>
331  <x:anchor-alias value="relativeURI"/>
332  <x:anchor-alias value="TE"/>
333  <x:anchor-alias value="Vary"/>
334  <x:anchor-alias value="WWW-Authenticate"/>
335  The ABNF rules below are defined in other parts:
336</t>
337<figure><!--Part1--><artwork type="abnf2616">
338  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in &general-syntax;&gt;
339  <x:ref>fragment</x:ref>      = &lt;fragment, defined in &general-syntax;&gt;
340  <x:ref>Host</x:ref>          = &lt;Host, defined in &header-host;&gt;
341  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
342  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
343  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in &general-syntax;&gt;
344  <x:ref>TE</x:ref>            = &lt;TE, defined in &header-te;&gt;
345</artwork></figure>
346<figure><!--Part3--><artwork type="abnf2616">
347  <x:ref>Accept</x:ref>        = &lt;Accept, defined in &header-accept;&gt;
348  <x:ref>Accept-Charset</x:ref> =
349             &lt;Accept-Charset, defined in &header-accept-charset;&gt;
350  <x:ref>Accept-Encoding</x:ref> =
351             &lt;Accept-Encoding, defined in &header-accept-encoding;&gt;
352  <x:ref>Accept-Language</x:ref> =
353             &lt;Accept-Language, defined in &header-accept-language;&gt;
354</artwork></figure>
355<figure><!--Part4--><artwork type="abnf2616">
356  <x:ref>ETag</x:ref>          = &lt;ETag, defined in &header-etag;&gt;
357  <x:ref>If-Match</x:ref>      = &lt;If-Match, defined in &header-if-match;&gt;
358  <x:ref>If-Modified-Since</x:ref> =
359             &lt;If-Modified-Since, defined in &header-if-modified-since;&gt;
360  <x:ref>If-None-Match</x:ref> = &lt;If-None-Match, defined in &header-if-none-match;&gt;
361  <x:ref>If-Unmodified-Since</x:ref> =
362             &lt;If-Unmodified-Since, defined in &header-if-unmodified-since;&gt;
363</artwork></figure>
364<figure><!--Part5--><artwork type="abnf2616">
365  <x:ref>Accept-Ranges</x:ref> = &lt;Accept-Ranges, defined in &header-accept-ranges;&gt;
366  <x:ref>If-Range</x:ref>      = &lt;If-Range, defined in &header-if-range;&gt;
367  <x:ref>Range</x:ref>         = &lt;Range, defined in &header-range;&gt;
368</artwork></figure>
369<figure><!--Part6--><artwork type="abnf2616">
370  <x:ref>Age</x:ref>           = &lt;Age, defined in &header-age;&gt;
371  <x:ref>Vary</x:ref>          = &lt;Vary, defined in &header-vary;&gt;
372</artwork><!--Part7--></figure>
373<figure><artwork type="abnf2616">
374  <x:ref>Authorization</x:ref> = &lt;Authorization, defined in &header-authorization;&gt;
375  <x:ref>Proxy-Authenticate</x:ref> =
376             &lt;Proxy-Authenticate, defined in &header-proxy-authenticate;&gt;
377  <x:ref>Proxy-Authorization</x:ref> =
378             &lt;Proxy-Authorization, defined in &header-proxy-authorization;&gt;
379  <x:ref>WWW-Authenticate</x:ref> =
380             &lt;WWW-Authenticate, defined in &header-www-authenticate;&gt;
381</artwork></figure>
382</section>
383
384<section title="Method" anchor="method">
385  <x:anchor-alias value="Method"/>
386  <x:anchor-alias value="extension-method"/>
387<t>
388   The Method  token indicates the method to be performed on the
389   resource identified by the Request-URI. The method is case-sensitive.
390</t>
391<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
392  <x:ref>Method</x:ref>         = "OPTIONS"                ; <xref target="OPTIONS"/>
393                 | "GET"                    ; <xref target="GET"/>
394                 | "HEAD"                   ; <xref target="HEAD"/>
395                 | "POST"                   ; <xref target="POST"/>
396                 | "PUT"                    ; <xref target="PUT"/>
397                 | "DELETE"                 ; <xref target="DELETE"/>
398                 | "TRACE"                  ; <xref target="TRACE"/>
399                 | "CONNECT"                ; <xref target="CONNECT"/>
400                 | <x:ref>extension-method</x:ref>
401  <x:ref>extension-method</x:ref> = <x:ref>token</x:ref>
402</artwork></figure>
403<t>
404   The list of methods allowed by a resource can be specified in an
405   Allow header field (<xref target="header.allow"/>). The return code of the response
406   always notifies the client whether a method is currently allowed on a
407   resource, since the set of allowed methods can change dynamically. An
408   origin server &SHOULD; return the status code 405 (Method Not Allowed)
409   if the method is known by the origin server but not allowed for the
410   requested resource, and 501 (Not Implemented) if the method is
411   unrecognized or not implemented by the origin server. The methods GET
412   and HEAD &MUST; be supported by all general-purpose servers. All other
413   methods are &OPTIONAL;; however, if the above methods are implemented,
414   they &MUST; be implemented with the same semantics as those specified
415   in <xref target="method.definitions"/>.
416</t>
417</section>
418
419<section title="Request Header Fields" anchor="request.header.fields">
420  <x:anchor-alias value="extension-code"/>
421  <x:anchor-alias value="request-header"/>
422<t>
423   The request-header fields allow the client to pass additional
424   information about the request, and about the client itself, to the
425   server. These fields act as request modifiers, with semantics
426   equivalent to the parameters on a programming language method
427   invocation.
428</t>
429<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
430  <x:ref>request-header</x:ref> = <x:ref>Accept</x:ref>                   ; &header-accept;
431                 | <x:ref>Accept-Charset</x:ref>           ; &header-accept-charset;
432                 | <x:ref>Accept-Encoding</x:ref>          ; &header-accept-encoding;
433                 | <x:ref>Accept-Language</x:ref>          ; &header-accept-language;
434                 | <x:ref>Authorization</x:ref>            ; &header-authorization;
435                 | <x:ref>Expect</x:ref>                   ; <xref target="header.expect"/>
436                 | <x:ref>From</x:ref>                     ; <xref target="header.from"/>
437                 | <x:ref>Host</x:ref>                     ; &header-host;
438                 | <x:ref>If-Match</x:ref>                 ; &header-if-match;
439                 | <x:ref>If-Modified-Since</x:ref>        ; &header-if-modified-since;
440                 | <x:ref>If-None-Match</x:ref>            ; &header-if-none-match;
441                 | <x:ref>If-Range</x:ref>                 ; &header-if-range;
442                 | <x:ref>If-Unmodified-Since</x:ref>      ; &header-if-unmodified-since;
443                 | <x:ref>Max-Forwards</x:ref>             ; <xref target="header.max-forwards"/>
444                 | <x:ref>Proxy-Authorization</x:ref>      ; &header-proxy-authorization;
445                 | <x:ref>Range</x:ref>                    ; &header-range;
446                 | <x:ref>Referer</x:ref>                  ; <xref target="header.referer"/>
447                 | <x:ref>TE</x:ref>                       ; &header-te;
448                 | <x:ref>User-Agent</x:ref>               ; <xref target="header.user-agent"/>
449</artwork></figure>
450<t>
451   Request-header field names can be extended reliably only in
452   combination with a change in the protocol version. However, new or
453   experimental header fields &MAY; be given the semantics of request-header
454   fields if all parties in the communication recognize them to
455   be request-header fields. Unrecognized header fields are treated as
456   entity-header fields.
457</t>
458</section>
459
460<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
461  <x:anchor-alias value="Reason-Phrase"/>
462  <x:anchor-alias value="Status-Code"/>
463<t>
464   The Status-Code element is a 3-digit integer result code of the
465   attempt to understand and satisfy the request. The status codes listed
466   below are defined in <xref target="status.codes"/>.
467   The Reason-Phrase is intended to give a short
468   textual description of the Status-Code. The Status-Code is intended
469   for use by automata and the Reason-Phrase is intended for the human
470   user. The client is not required to examine or display the Reason-Phrase.
471</t>
472<t> 
473   The individual values of the numeric status codes defined for
474   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
475   presented below. The reason phrases listed here are only
476   recommendations -- they &MAY; be replaced by local equivalents without
477   affecting the protocol.
478</t>
479<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"/>
480  <x:ref>Status-Code</x:ref>    =
481         "100"  ; <xref target="status.100"/>: Continue
482       | "101"  ; <xref target="status.101"/>: Switching Protocols
483       | "200"  ; <xref target="status.200"/>: OK
484       | "201"  ; <xref target="status.201"/>: Created
485       | "202"  ; <xref target="status.202"/>: Accepted
486       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
487       | "204"  ; <xref target="status.204"/>: No Content
488       | "205"  ; <xref target="status.205"/>: Reset Content
489       | "206"  ; <xref target="status.206"/>: Partial Content
490       | "300"  ; <xref target="status.300"/>: Multiple Choices
491       | "301"  ; <xref target="status.301"/>: Moved Permanently
492       | "302"  ; <xref target="status.302"/>: Found
493       | "303"  ; <xref target="status.303"/>: See Other
494       | "304"  ; <xref target="status.304"/>: Not Modified
495       | "305"  ; <xref target="status.305"/>: Use Proxy
496       | "307"  ; <xref target="status.307"/>: Temporary Redirect
497       | "400"  ; <xref target="status.400"/>: Bad Request
498       | "401"  ; <xref target="status.401"/>: Unauthorized
499       | "402"  ; <xref target="status.402"/>: Payment Required
500       | "403"  ; <xref target="status.403"/>: Forbidden
501       | "404"  ; <xref target="status.404"/>: Not Found
502       | "405"  ; <xref target="status.405"/>: Method Not Allowed
503       | "406"  ; <xref target="status.406"/>: Not Acceptable
504       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
505       | "408"  ; <xref target="status.408"/>: Request Time-out
506       | "409"  ; <xref target="status.409"/>: Conflict
507       | "410"  ; <xref target="status.410"/>: Gone
508       | "411"  ; <xref target="status.411"/>: Length Required
509       | "412"  ; <xref target="status.412"/>: Precondition Failed
510       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
511       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
512       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
513       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
514       | "417"  ; <xref target="status.417"/>: Expectation Failed
515       | "500"  ; <xref target="status.500"/>: Internal Server Error
516       | "501"  ; <xref target="status.501"/>: Not Implemented
517       | "502"  ; <xref target="status.502"/>: Bad Gateway
518       | "503"  ; <xref target="status.503"/>: Service Unavailable
519       | "504"  ; <xref target="status.504"/>: Gateway Time-out
520       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
521       | <x:ref>extension-code</x:ref>
522
523  <x:ref>extension-code</x:ref> = 3<x:ref>DIGIT</x:ref>
524  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
525</artwork></figure>
526<t>
527   HTTP status codes are extensible. HTTP applications are not required
528   to understand the meaning of all registered status codes, though such
529   understanding is obviously desirable. However, applications &MUST;
530   understand the class of any status code, as indicated by the first
531   digit, and treat any unrecognized response as being equivalent to the
532   x00 status code of that class, with the exception that an
533   unrecognized response &MUST-NOT; be cached. For example, if an
534   unrecognized status code of 431 is received by the client, it can
535   safely assume that there was something wrong with its request and
536   treat the response as if it had received a 400 status code. In such
537   cases, user agents &SHOULD; present to the user the entity returned
538   with the response, since that entity is likely to include human-readable
539   information which will explain the unusual status.
540</t>
541</section>
542
543<section title="Response Header Fields" anchor="response.header.fields">
544  <x:anchor-alias value="response-header"/>
545<t>
546   The response-header fields allow the server to pass additional
547   information about the response which cannot be placed in the Status-Line.
548   These header fields give information about the server and about
549   further access to the resource identified by the Request-URI.
550</t>
551<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
552  <x:ref>response-header</x:ref> = <x:ref>Accept-Ranges</x:ref>           ; &header-accept-ranges;
553                  | <x:ref>Age</x:ref>                     ; &header-age;
554                  | <x:ref>Allow</x:ref>                   ; <xref target="header.allow"/>
555                  | <x:ref>ETag</x:ref>                    ; &header-etag;
556                  | <x:ref>Location</x:ref>                ; <xref target="header.location"/>
557                  | <x:ref>Proxy-Authenticate</x:ref>      ; &header-proxy-authenticate;
558                  | <x:ref>Retry-After</x:ref>             ; <xref target="header.retry-after"/>
559                  | <x:ref>Server</x:ref>                  ; <xref target="header.server"/>
560                  | <x:ref>Vary</x:ref>                    ; &header-vary;
561                  | <x:ref>WWW-Authenticate</x:ref>        ; &header-www-authenticate;
562</artwork></figure>
563<t>
564   Response-header field names can be extended reliably only in
565   combination with a change in the protocol version. However, new or
566   experimental header fields &MAY; be given the semantics of response-header
567   fields if all parties in the communication recognize them to
568   be response-header fields. Unrecognized header fields are treated as
569   entity-header fields.
570</t>
571</section>
572
573<section title="Entity" anchor="entity">
574<t>
575   Request and Response messages &MAY; transfer an entity if not otherwise
576   restricted by the request method or response status code. An entity
577   consists of entity-header fields and an entity-body, although some
578   responses will only include the entity-headers. HTTP entity-body and
579   entity-header fields are defined in &payload;.
580</t>
581<t>
582   An entity-body is only present in a message when a message-body is
583   present, as described in &message-body;. The entity-body is obtained
584   from the message-body by decoding any Transfer-Encoding that might
585   have been applied to ensure safe and proper transfer of the message.
586</t>
587</section>
588
589
590<section title="Method Definitions" anchor="method.definitions">
591<t>
592   The set of common methods for HTTP/1.1 is defined below. Although
593   this set can be expanded, additional methods cannot be assumed to
594   share the same semantics for separately extended clients and servers.
595</t>
596
597<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
598
599<section title="Safe Methods" anchor="safe.methods">
600<t>
601   Implementors should be aware that the software represents the user in
602   their interactions over the Internet, and should be careful to allow
603   the user to be aware of any actions they might take which may have an
604   unexpected significance to themselves or others.
605</t>
606<t>
607   In particular, the convention has been established that the GET and
608   HEAD methods &SHOULD-NOT;  have the significance of taking an action
609   other than retrieval. These methods ought to be considered "safe".
610   This allows user agents to represent other methods, such as POST, PUT
611   and DELETE, in a special way, so that the user is made aware of the
612   fact that a possibly unsafe action is being requested.
613</t>
614<t>
615   Naturally, it is not possible to ensure that the server does not
616   generate side-effects as a result of performing a GET request; in
617   fact, some dynamic resources consider that a feature. The important
618   distinction here is that the user did not request the side-effects,
619   so therefore cannot be held accountable for them.
620</t>
621</section>
622
623<section title="Idempotent Methods" anchor="idempotent.methods">
624<t>
625   Methods can also have the property of "idempotence" in that (aside
626   from error or expiration issues) the side-effects of N &gt; 0 identical
627   requests is the same as for a single request. The methods GET, HEAD,
628   PUT and DELETE share this property. Also, the methods OPTIONS and
629   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
630</t>
631<t>
632   However, it is possible that a sequence of several requests is non-idempotent,
633   even if all of the methods executed in that sequence are
634   idempotent. (A sequence is idempotent if a single execution of the
635   entire sequence always yields a result that is not changed by a
636   reexecution of all, or part, of that sequence.) For example, a
637   sequence is non-idempotent if its result depends on a value that is
638   later modified in the same sequence.
639</t>
640<t>
641   A sequence that never has side effects is idempotent, by definition
642   (provided that no concurrent operations are being executed on the
643   same set of resources).
644</t>
645</section>
646</section>
647
648<section title="OPTIONS" anchor="OPTIONS">
649  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
650  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
651<t>
652   The OPTIONS method represents a request for information about the
653   communication options available on the request/response chain
654   identified by the Request-URI. This method allows the client to
655   determine the options and/or requirements associated with a resource,
656   or the capabilities of a server, without implying a resource action
657   or initiating a resource retrieval.
658</t>
659<t>
660   Responses to this method are not cacheable.
661</t>
662<t>
663   If the OPTIONS request includes an entity-body (as indicated by the
664   presence of Content-Length or Transfer-Encoding), then the media type
665   &MUST; be indicated by a Content-Type field. Although this
666   specification does not define any use for such a body, future
667   extensions to HTTP might use the OPTIONS body to make more detailed
668   queries on the server. A server that does not support such an
669   extension &MAY; discard the request body.
670</t>
671<t>
672   If the Request-URI is an asterisk ("*"), the OPTIONS request is
673   intended to apply to the server in general rather than to a specific
674   resource. Since a server's communication options typically depend on
675   the resource, the "*" request is only useful as a "ping" or "no-op"
676   type of method; it does nothing beyond allowing the client to test
677   the capabilities of the server. For example, this can be used to test
678   a proxy for HTTP/1.1 compliance (or lack thereof).
679</t>
680<t>
681   If the Request-URI is not an asterisk, the OPTIONS request applies
682   only to the options that are available when communicating with that
683   resource.
684</t>
685<t>
686   A 200 response &SHOULD; include any header fields that indicate
687   optional features implemented by the server and applicable to that
688   resource (e.g., Allow), possibly including extensions not defined by
689   this specification. The response body, if any, &SHOULD; also include
690   information about the communication options. The format for such a
691   body is not defined by this specification, but might be defined by
692   future extensions to HTTP. Content negotiation &MAY; be used to select
693   the appropriate response format. If no response body is included, the
694   response &MUST; include a Content-Length field with a field-value of
695   "0".
696</t>
697<t>
698   The Max-Forwards request-header field &MAY; be used to target a
699   specific proxy in the request chain. When a proxy receives an OPTIONS
700   request on an absoluteURI for which request forwarding is permitted,
701   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
702   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
703   instead, the proxy &SHOULD; respond with its own communication options.
704   If the Max-Forwards field-value is an integer greater than zero, the
705   proxy &MUST; decrement the field-value when it forwards the request. If
706   no Max-Forwards field is present in the request, then the forwarded
707   request &MUST-NOT; include a Max-Forwards field.
708</t>
709</section>
710
711<section title="GET" anchor="GET">
712  <iref primary="true" item="GET method" x:for-anchor=""/>
713  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
714<t>
715   The GET method means retrieve whatever information (in the form of an
716   entity) is identified by the Request-URI. If the Request-URI refers
717   to a data-producing process, it is the produced data which shall be
718   returned as the entity in the response and not the source text of the
719   process, unless that text happens to be the output of the process.
720</t>
721<t>
722   The semantics of the GET method change to a "conditional GET" if the
723   request message includes an If-Modified-Since, If-Unmodified-Since,
724   If-Match, If-None-Match, or If-Range header field. A conditional GET
725   method requests that the entity be transferred only under the
726   circumstances described by the conditional header field(s). The
727   conditional GET method is intended to reduce unnecessary network
728   usage by allowing cached entities to be refreshed without requiring
729   multiple requests or transferring data already held by the client.
730</t>
731<t>
732   The semantics of the GET method change to a "partial GET" if the
733   request message includes a Range header field. A partial GET requests
734   that only part of the entity be transferred, as described in &header-range;.
735   The partial GET method is intended to reduce unnecessary
736   network usage by allowing partially-retrieved entities to be
737   completed without transferring data already held by the client.
738</t>
739<t>
740   The response to a GET request is cacheable if and only if it meets
741   the requirements for HTTP caching described in &caching;.
742</t>
743<t>
744   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
745</t>
746</section>
747
748<section title="HEAD" anchor="HEAD">
749  <iref primary="true" item="HEAD method" x:for-anchor=""/>
750  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
751<t>
752   The HEAD method is identical to GET except that the server &MUST-NOT;
753   return a message-body in the response. The metainformation contained
754   in the HTTP headers in response to a HEAD request &SHOULD; be identical
755   to the information sent in response to a GET request. This method can
756   be used for obtaining metainformation about the entity implied by the
757   request without transferring the entity-body itself. This method is
758   often used for testing hypertext links for validity, accessibility,
759   and recent modification.
760</t>
761<t>
762   The response to a HEAD request &MAY; be cacheable in the sense that the
763   information contained in the response &MAY; be used to update a
764   previously cached entity from that resource. If the new field values
765   indicate that the cached entity differs from the current entity (as
766   would be indicated by a change in Content-Length, Content-MD5, ETag
767   or Last-Modified), then the cache &MUST; treat the cache entry as
768   stale.
769</t>
770</section>
771
772<section title="POST" anchor="POST">
773  <iref primary="true" item="POST method" x:for-anchor=""/>
774  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
775<t>
776   The POST method is used to request that the origin server accept the
777   entity enclosed in the request as data to be processed by the resource
778   identified by the Request-URI in the Request-Line. POST is designed
779   to allow a uniform method to cover the following functions:
780  <list style="symbols">
781    <t>
782      Annotation of existing resources;
783    </t>
784    <t>
785        Posting a message to a bulletin board, newsgroup, mailing list,
786        or similar group of articles;
787    </t>
788    <t>
789        Providing a block of data, such as the result of submitting a
790        form, to a data-handling process;
791    </t>
792    <t>
793        Extending a database through an append operation.
794    </t>
795  </list>
796</t>
797<t>
798   The actual function performed by the POST method is determined by the
799   server and is usually dependent on the Request-URI.
800</t>
801<t>
802   The action performed by the POST method might not result in a
803   resource that can be identified by a URI. In this case, either 200
804   (OK) or 204 (No Content) is the appropriate response status,
805   depending on whether or not the response includes an entity that
806   describes the result.
807</t>
808<t>
809   If a resource has been created on the origin server, the response
810   &SHOULD; be 201 (Created) and contain an entity which describes the
811   status of the request and refers to the new resource, and a Location
812   header (see <xref target="header.location"/>).
813</t>
814<t>
815   Responses to this method are not cacheable, unless the response
816   includes appropriate Cache-Control or Expires header fields. However,
817   the 303 (See Other) response can be used to direct the user agent to
818   retrieve a cacheable resource.
819</t>
820</section>
821
822<section title="PUT" anchor="PUT">
823  <iref primary="true" item="PUT method" x:for-anchor=""/>
824  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
825<t>
826   The PUT method requests that the enclosed entity be stored at the
827   supplied Request-URI. If the Request-URI refers to an already
828   existing resource, the enclosed entity &SHOULD; be considered as a
829   modified version of the one residing on the origin server. If the
830   Request-URI does not point to an existing resource, and that URI is
831   capable of being defined as a new resource by the requesting user
832   agent, the origin server can create the resource with that URI. If a
833   new resource is created at the Request-URI, the origin server &MUST;
834         inform the user agent
835   via the 201 (Created) response. If an existing resource is modified,
836   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
837   to indicate successful completion of the request. If the resource
838   could not be created or modified with the Request-URI, an appropriate
839   error response &SHOULD; be given that reflects the nature of the
840   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
841   (e.g. Content-Range) headers that it does not understand or implement
842   and &MUST; return a 501 (Not Implemented) response in such cases.
843</t>
844<t>
845   If the request passes through a cache and the Request-URI identifies
846   one or more currently cached entities, those entries &SHOULD; be
847   treated as stale. Responses to this method are not cacheable.
848</t>
849<t>
850   The fundamental difference between the POST and PUT requests is
851   reflected in the different meaning of the Request-URI. The URI in a
852   POST request identifies the resource that will handle the enclosed
853   entity. That resource might be a data-accepting process, a gateway to
854   some other protocol, or a separate entity that accepts annotations.
855   In contrast, the URI in a PUT request identifies the entity enclosed
856   with the request -- the user agent knows what URI is intended and the
857   server &MUST-NOT; attempt to apply the request to some other resource.
858   If the server desires that the request be applied to a different URI,
859   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
860   then make its own decision regarding whether or not to redirect the
861   request.
862</t>
863<t>
864   A single resource &MAY; be identified by many different URIs. For
865   example, an article might have a URI for identifying "the current
866   version" which is separate from the URI identifying each particular
867   version. In this case, a PUT request on a general URI might result in
868   several other URIs being defined by the origin server.
869</t>
870<t>
871   HTTP/1.1 does not define how a PUT method affects the state of an
872   origin server.
873</t>
874<t>
875   Unless otherwise specified for a particular entity-header, the
876   entity-headers in the PUT request &SHOULD; be applied to the resource
877   created or modified by the PUT.
878</t>
879</section>
880
881<section title="DELETE" anchor="DELETE">
882  <iref primary="true" item="DELETE method" x:for-anchor=""/>
883  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
884<t>
885   The DELETE method requests that the origin server delete the resource
886   identified by the Request-URI. This method &MAY; be overridden by human
887   intervention (or other means) on the origin server. The client cannot
888   be guaranteed that the operation has been carried out, even if the
889   status code returned from the origin server indicates that the action
890   has been completed successfully. However, the server &SHOULD-NOT; 
891   indicate success unless, at the time the response is given, it
892   intends to delete the resource or move it to an inaccessible
893   location.
894</t>
895<t>
896   A successful response &SHOULD; be 200 (OK) if the response includes an
897   entity describing the status, 202 (Accepted) if the action has not
898   yet been enacted, or 204 (No Content) if the action has been enacted
899   but the response does not include an entity.
900</t>
901<t>
902   If the request passes through a cache and the Request-URI identifies
903   one or more currently cached entities, those entries &SHOULD; be
904   treated as stale. Responses to this method are not cacheable.
905</t>
906</section>
907
908<section title="TRACE" anchor="TRACE">
909  <iref primary="true" item="TRACE method" x:for-anchor=""/>
910  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
911<t>
912   The TRACE method is used to invoke a remote, application-layer loop-back
913   of the request message. The final recipient of the request
914   &SHOULD; reflect the message received back to the client as the
915   entity-body of a 200 (OK) response. The final recipient is either the
916   origin server or the first proxy or gateway to receive a Max-Forwards
917   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
918   &MUST-NOT; include an entity.
919</t>
920<t>
921   TRACE allows the client to see what is being received at the other
922   end of the request chain and use that data for testing or diagnostic
923   information. The value of the Via header field (&header-via;) is of
924   particular interest, since it acts as a trace of the request chain.
925   Use of the Max-Forwards header field allows the client to limit the
926   length of the request chain, which is useful for testing a chain of
927   proxies forwarding messages in an infinite loop.
928</t>
929<t>
930   If the request is valid, the response &SHOULD; contain the entire
931   request message in the entity-body, with a Content-Type of
932   "message/http". Responses to this method &MUST-NOT; be cached.
933</t>
934</section>
935
936<section title="CONNECT" anchor="CONNECT">
937  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
938  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
939<t>
940   This specification reserves the method name CONNECT for use with a
941   proxy that can dynamically switch to being a tunnel (e.g. SSL
942   tunneling <xref target="Luo1998"/>).
943</t>
944</section>
945</section>
946
947
948<section title="Status Code Definitions" anchor="status.codes">
949<t>
950   Each Status-Code is described below, including a description of which
951   method(s) it can follow and any metainformation required in the
952   response.
953</t>
954
955<section title="Informational 1xx" anchor="status.1xx">
956<t>
957   This class of status code indicates a provisional response,
958   consisting only of the Status-Line and optional headers, and is
959   terminated by an empty line. There are no required headers for this
960   class of status code. Since HTTP/1.0 did not define any 1xx status
961   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
962   except under experimental conditions.
963</t>
964<t>
965   A client &MUST; be prepared to accept one or more 1xx status responses
966   prior to a regular response, even if the client does not expect a 100
967   (Continue) status message. Unexpected 1xx status responses &MAY; be
968   ignored by a user agent.
969</t>
970<t>
971   Proxies &MUST; forward 1xx responses, unless the connection between the
972   proxy and its client has been closed, or unless the proxy itself
973   requested the generation of the 1xx response. (For example, if a
974   proxy adds a "Expect: 100-continue" field when it forwards a request,
975   then it need not forward the corresponding 100 (Continue)
976   response(s).)
977</t>
978
979<section title="100 Continue" anchor="status.100">
980  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
981  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
982<t>
983   The client &SHOULD; continue with its request. This interim response is
984   used to inform the client that the initial part of the request has
985   been received and has not yet been rejected by the server. The client
986   &SHOULD; continue by sending the remainder of the request or, if the
987   request has already been completed, ignore this response. The server
988   &MUST; send a final response after the request has been completed. See
989   &use100; for detailed discussion of the use and handling of this
990   status code.
991</t>
992</section>
993
994<section title="101 Switching Protocols" anchor="status.101">
995  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
996  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
997<t>
998   The server understands and is willing to comply with the client's
999   request, via the Upgrade message header field (&header-upgrade;), for a
1000   change in the application protocol being used on this connection. The
1001   server will switch protocols to those defined by the response's
1002   Upgrade header field immediately after the empty line which
1003   terminates the 101 response.
1004</t>
1005<t>
1006   The protocol &SHOULD; be switched only when it is advantageous to do
1007   so. For example, switching to a newer version of HTTP is advantageous
1008   over older versions, and switching to a real-time, synchronous
1009   protocol might be advantageous when delivering resources that use
1010   such features.
1011</t>
1012</section>
1013</section>
1014
1015<section title="Successful 2xx" anchor="status.2xx">
1016<t>
1017   This class of status code indicates that the client's request was
1018   successfully received, understood, and accepted.
1019</t>
1020
1021<section title="200 OK" anchor="status.200">
1022  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1023  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1024<t>
1025   The request has succeeded. The information returned with the response
1026   is dependent on the method used in the request, for example:
1027  <list style="hanging">
1028    <t hangText="GET">
1029          an entity corresponding to the requested resource is sent in
1030          the response;
1031    </t>
1032    <t hangText="HEAD">
1033          the entity-header fields corresponding to the requested
1034          resource are sent in the response without any message-body;
1035    </t>
1036    <t hangText="POST">
1037      an entity describing or containing the result of the action;
1038    </t>
1039    <t hangText="TRACE">
1040      an entity containing the request message as received by the
1041      end server.
1042    </t>
1043  </list>
1044</t>
1045</section>
1046
1047<section title="201 Created" anchor="status.201">
1048  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1049  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1050<t>
1051   The request has been fulfilled and resulted in a new resource being
1052   created. The newly created resource can be referenced by the URI(s)
1053   returned in the entity of the response, with the most specific URI
1054   for the resource given by a Location header field. The response
1055   &SHOULD; include an entity containing a list of resource
1056   characteristics and location(s) from which the user or user agent can
1057   choose the one most appropriate. The entity format is specified by
1058   the media type given in the Content-Type header field. The origin
1059   server &MUST; create the resource before returning the 201 status code.
1060   If the action cannot be carried out immediately, the server &SHOULD;
1061   respond with 202 (Accepted) response instead.
1062</t>
1063<t>
1064   A 201 response &MAY; contain an ETag response header field indicating
1065   the current value of the entity tag for the requested variant just
1066   created, see &header-etag;.
1067</t>
1068</section>
1069
1070<section title="202 Accepted" anchor="status.202">
1071  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1072  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1073<t>
1074   The request has been accepted for processing, but the processing has
1075   not been completed.  The request might or might not eventually be
1076   acted upon, as it might be disallowed when processing actually takes
1077   place. There is no facility for re-sending a status code from an
1078   asynchronous operation such as this.
1079</t>
1080<t>
1081   The 202 response is intentionally non-committal. Its purpose is to
1082   allow a server to accept a request for some other process (perhaps a
1083   batch-oriented process that is only run once per day) without
1084   requiring that the user agent's connection to the server persist
1085   until the process is completed. The entity returned with this
1086   response &SHOULD; include an indication of the request's current status
1087   and either a pointer to a status monitor or some estimate of when the
1088   user can expect the request to be fulfilled.
1089</t>
1090</section>
1091
1092<section title="203 Non-Authoritative Information" anchor="status.203">
1093  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1094  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1095<t>
1096   The returned metainformation in the entity-header is not the
1097   definitive set as available from the origin server, but is gathered
1098   from a local or a third-party copy. The set presented &MAY; be a subset
1099   or superset of the original version. For example, including local
1100   annotation information about the resource might result in a superset
1101   of the metainformation known by the origin server. Use of this
1102   response code is not required and is only appropriate when the
1103   response would otherwise be 200 (OK).
1104</t>
1105</section>
1106
1107<section title="204 No Content" anchor="status.204">
1108  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1109  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1110<t>
1111   The server has fulfilled the request but does not need to return an
1112   entity-body, and might want to return updated metainformation. The
1113   response &MAY; include new or updated metainformation in the form of
1114   entity-headers, which if present &SHOULD; be associated with the
1115   requested variant.
1116</t>
1117<t>
1118   If the client is a user agent, it &SHOULD-NOT;  change its document view
1119   from that which caused the request to be sent. This response is
1120   primarily intended to allow input for actions to take place without
1121   causing a change to the user agent's active document view, although
1122   any new or updated metainformation &SHOULD; be applied to the document
1123   currently in the user agent's active view.
1124</t>
1125<t>
1126   The 204 response &MUST-NOT; include a message-body, and thus is always
1127   terminated by the first empty line after the header fields.
1128</t>
1129</section>
1130
1131<section title="205 Reset Content" anchor="status.205">
1132  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1133  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1134<t>
1135   The server has fulfilled the request and the user agent &SHOULD; reset
1136   the document view which caused the request to be sent. This response
1137   is primarily intended to allow input for actions to take place via
1138   user input, followed by a clearing of the form in which the input is
1139   given so that the user can easily initiate another input action. The
1140   response &MUST-NOT; include an entity.
1141</t>
1142</section>
1143
1144<section title="206 Partial Content" anchor="status.206">
1145  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1146  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1147<t>
1148   The server has fulfilled the partial GET request for the resource
1149   and the enclosed entity is a partial representation as defined in &range;.
1150</t>
1151</section>
1152</section>
1153
1154<section title="Redirection 3xx" anchor="status.3xx">
1155<t>
1156   This class of status code indicates that further action needs to be
1157   taken by the user agent in order to fulfill the request.  The action
1158   required &MAY; be carried out by the user agent without interaction
1159   with the user if and only if the method used in the second request is
1160   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1161   such loops generate network traffic for each redirection.
1162  <list><t>
1163      <x:h>Note:</x:h> previous versions of this specification recommended a
1164      maximum of five redirections. Content developers should be aware
1165      that there might be clients that implement such a fixed
1166      limitation.
1167  </t></list>
1168</t>
1169
1170<section title="300 Multiple Choices" anchor="status.300">
1171  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1172  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1173<t>
1174   The requested resource corresponds to any one of a set of
1175   representations, each with its own specific location, and agent-driven
1176   negotiation information (&content-negotiation;) is being provided so that
1177   the user (or user agent) can select a preferred representation and
1178   redirect its request to that location.
1179</t>
1180<t>
1181   Unless it was a HEAD request, the response &SHOULD; include an entity
1182   containing a list of resource characteristics and location(s) from
1183   which the user or user agent can choose the one most appropriate. The
1184   entity format is specified by the media type given in the Content-Type
1185   header field. Depending upon the format and the capabilities of
1186   the user agent, selection of the most appropriate choice &MAY; be
1187   performed automatically. However, this specification does not define
1188   any standard for such automatic selection.
1189</t>
1190<t>
1191   If the server has a preferred choice of representation, it &SHOULD;
1192   include the specific URI for that representation in the Location
1193   field; user agents &MAY; use the Location field value for automatic
1194   redirection. This response is cacheable unless indicated otherwise.
1195</t>
1196</section>
1197
1198<section title="301 Moved Permanently" anchor="status.301">
1199  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1200  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1201<t>
1202   The requested resource has been assigned a new permanent URI and any
1203   future references to this resource &SHOULD; use one of the returned
1204   URIs.  Clients with link editing capabilities ought to automatically
1205   re-link references to the Request-URI to one or more of the new
1206   references returned by the server, where possible. This response is
1207   cacheable unless indicated otherwise.
1208</t>
1209<t>
1210   The new permanent URI &SHOULD; be given by the Location field in the
1211   response. Unless the request method was HEAD, the entity of the
1212   response &SHOULD; contain a short hypertext note with a hyperlink to
1213   the new URI(s).
1214</t>
1215<t>
1216   If the 301 status code is received in response to a request method
1217   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1218   then the request &MAY; be automatically redirected by the user agent without
1219   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1220   request unless it can be confirmed by the user, since this might
1221   change the conditions under which the request was issued.
1222  <list><t>
1223      <x:h>Note:</x:h> When automatically redirecting a POST request after
1224      receiving a 301 status code, some existing HTTP/1.0 user agents
1225      will erroneously change it into a GET request.
1226  </t></list>
1227</t>
1228</section>
1229
1230<section title="302 Found" anchor="status.302">
1231  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1232  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1233<t>
1234   The requested resource resides temporarily under a different URI.
1235   Since the redirection might be altered on occasion, the client &SHOULD;
1236   continue to use the Request-URI for future requests.  This response
1237   is only cacheable if indicated by a Cache-Control or Expires header
1238   field.
1239</t>
1240<t>
1241   The temporary URI &SHOULD; be given by the Location field in the
1242   response. Unless the request method was HEAD, the entity of the
1243   response &SHOULD; contain a short hypertext note with a hyperlink to
1244   the new URI(s).
1245</t>
1246<t>
1247   If the 302 status code is received in response to a request method
1248   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1249   then the request &MAY; be automatically redirected by the user agent without
1250   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1251   request unless it can be confirmed by the user, since this might
1252   change the conditions under which the request was issued.
1253  <list><t>
1254      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1255      to change the method on the redirected request.  However, most
1256      existing user agent implementations treat 302 as if it were a 303
1257      response, performing a GET on the Location field-value regardless
1258      of the original request method. The status codes 303 and 307 have
1259      been added for servers that wish to make unambiguously clear which
1260      kind of reaction is expected of the client.
1261  </t></list>
1262</t>
1263</section>
1264
1265<section title="303 See Other" anchor="status.303">
1266  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1267  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1268<t>
1269   The server directs the user agent to a different resource, indicated
1270   by a URI in the Location header field, that provides an indirect
1271   response to the original request.  The user agent &MAY; perform a GET
1272   request on the URI in the Location field in order to obtain a
1273   representation corresponding to the response, be redirected again,
1274   or end with an error status.  The Location URI is not a substitute
1275   reference for the originally requested resource.
1276</t>
1277<t>
1278   The 303 status is generally applicable to any HTTP method.  It is
1279   primarily used to allow the output of a POST action to redirect
1280   the user agent to a selected resource, since doing so provides the
1281   information corresponding to the POST response in a form that
1282   can be separately identified, bookmarked, and cached independent
1283   of the original request.
1284</t>
1285<t>
1286   A 303 response to a GET request indicates that the requested
1287   resource does not have a representation of its own that can be
1288   transferred by the server over HTTP.  The Location URI indicates a
1289   resource that is descriptive of the requested resource such that
1290   the follow-on representation may be useful without implying that
1291   it adequately represents the previously requested resource.
1292   Note that answers to the questions of what can be represented, what
1293   representations are adequate, and what might be a useful description
1294   are outside the scope of HTTP and thus entirely determined by the
1295   resource owner(s).
1296</t>
1297<t>
1298   A 303 response &SHOULD-NOT; be cached unless it is indicated as
1299   cacheable by Cache-Control or Expires header fields.  Except for
1300   responses to a HEAD request, the entity of a 303 response &SHOULD;
1301   contain a short hypertext note with a hyperlink to the Location URI.
1302</t>
1303</section>
1304
1305<section title="304 Not Modified" anchor="status.304">
1306  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1307  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1308<t>
1309   The response to the request has not been modified since the conditions
1310   indicated by the client's conditional GET request, as defined in &conditional;.
1311</t>
1312</section>
1313
1314<section title="305 Use Proxy" anchor="status.305">
1315  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1316  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1317<t>
1318   The 305 status was defined in a previous version of this specification
1319   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1320</t>
1321</section>
1322
1323<section title="306 (Unused)" anchor="status.306">
1324  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1325  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1326<t>
1327   The 306 status code was used in a previous version of the
1328   specification, is no longer used, and the code is reserved.
1329</t>
1330</section>
1331
1332<section title="307 Temporary Redirect" anchor="status.307">
1333  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1334  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1335<t>
1336   The requested resource resides temporarily under a different URI.
1337   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1338   continue to use the Request-URI for future requests.  This response
1339   is only cacheable if indicated by a Cache-Control or Expires header
1340   field.
1341</t>
1342<t>
1343   The temporary URI &SHOULD; be given by the Location field in the
1344   response. Unless the request method was HEAD, the entity of the
1345   response &SHOULD; contain a short hypertext note with a hyperlink to
1346   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1347   understand the 307 status. Therefore, the note &SHOULD; contain the
1348   information necessary for a user to repeat the original request on
1349   the new URI.
1350</t>
1351<t>
1352   If the 307 status code is received in response to a request method
1353   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1354   then the request &MAY; be automatically redirected by the user agent without
1355   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1356   request unless it can be confirmed by the user, since this might
1357   change the conditions under which the request was issued.
1358</t>
1359</section>
1360</section>
1361
1362<section title="Client Error 4xx" anchor="status.4xx">
1363<t>
1364   The 4xx class of status code is intended for cases in which the
1365   client seems to have erred. Except when responding to a HEAD request,
1366   the server &SHOULD; include an entity containing an explanation of the
1367   error situation, and whether it is a temporary or permanent
1368   condition. These status codes are applicable to any request method.
1369   User agents &SHOULD; display any included entity to the user.
1370</t>
1371<t>
1372   If the client is sending data, a server implementation using TCP
1373   &SHOULD; be careful to ensure that the client acknowledges receipt of
1374   the packet(s) containing the response, before the server closes the
1375   input connection. If the client continues sending data to the server
1376   after the close, the server's TCP stack will send a reset packet to
1377   the client, which may erase the client's unacknowledged input buffers
1378   before they can be read and interpreted by the HTTP application.
1379</t>
1380
1381<section title="400 Bad Request" anchor="status.400">
1382  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1383  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1384<t>
1385   The request could not be understood by the server due to malformed
1386   syntax. The client &SHOULD-NOT;  repeat the request without
1387   modifications.
1388</t>
1389</section>
1390
1391<section title="401 Unauthorized" anchor="status.401">
1392  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1393  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1394<t>
1395   The request requires user authentication (see &auth;).
1396</t>
1397</section>
1398
1399<section title="402 Payment Required" anchor="status.402">
1400  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1401  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1402<t>
1403   This code is reserved for future use.
1404</t>
1405</section>
1406
1407<section title="403 Forbidden" anchor="status.403">
1408  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1409  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1410<t>
1411   The server understood the request, but is refusing to fulfill it.
1412   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1413   If the request method was not HEAD and the server wishes to make
1414   public why the request has not been fulfilled, it &SHOULD; describe the
1415   reason for the refusal in the entity.  If the server does not wish to
1416   make this information available to the client, the status code 404
1417   (Not Found) can be used instead.
1418</t>
1419</section>
1420
1421<section title="404 Not Found" anchor="status.404">
1422  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1423  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1424<t>
1425   The server has not found anything matching the Request-URI. No
1426   indication is given of whether the condition is temporary or
1427   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1428   knows, through some internally configurable mechanism, that an old
1429   resource is permanently unavailable and has no forwarding address.
1430   This status code is commonly used when the server does not wish to
1431   reveal exactly why the request has been refused, or when no other
1432   response is applicable.
1433</t>
1434</section>
1435
1436<section title="405 Method Not Allowed" anchor="status.405">
1437  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1438  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1439<t>
1440   The method specified in the Request-Line is not allowed for the
1441   resource identified by the Request-URI. The response &MUST; include an
1442   Allow header containing a list of valid methods for the requested
1443   resource.
1444</t>
1445</section>
1446
1447<section title="406 Not Acceptable" anchor="status.406">
1448  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1449  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1450<t>
1451   The resource identified by the request is only capable of generating
1452   response entities which have content characteristics not acceptable
1453   according to the accept headers sent in the request.
1454</t>
1455<t>
1456   Unless it was a HEAD request, the response &SHOULD; include an entity
1457   containing a list of available entity characteristics and location(s)
1458   from which the user or user agent can choose the one most
1459   appropriate. The entity format is specified by the media type given
1460   in the Content-Type header field. Depending upon the format and the
1461   capabilities of the user agent, selection of the most appropriate
1462   choice &MAY; be performed automatically. However, this specification
1463   does not define any standard for such automatic selection.
1464  <list><t>
1465      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1466      not acceptable according to the accept headers sent in the
1467      request. In some cases, this may even be preferable to sending a
1468      406 response. User agents are encouraged to inspect the headers of
1469      an incoming response to determine if it is acceptable.
1470  </t></list>
1471</t>
1472<t>
1473   If the response could be unacceptable, a user agent &SHOULD;
1474   temporarily stop receipt of more data and query the user for a
1475   decision on further actions.
1476</t>
1477</section>
1478
1479<section title="407 Proxy Authentication Required" anchor="status.407">
1480  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1481  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1482<t>
1483   This code is similar to 401 (Unauthorized), but indicates that the
1484   client must first authenticate itself with the proxy (see &auth;).
1485</t>
1486</section>
1487
1488<section title="408 Request Timeout" anchor="status.408">
1489  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1490  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1491<t>
1492   The client did not produce a request within the time that the server
1493   was prepared to wait. The client &MAY; repeat the request without
1494   modifications at any later time.
1495</t>
1496</section>
1497
1498<section title="409 Conflict" anchor="status.409">
1499  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1500  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1501<t>
1502   The request could not be completed due to a conflict with the current
1503   state of the resource. This code is only allowed in situations where
1504   it is expected that the user might be able to resolve the conflict
1505   and resubmit the request. The response body &SHOULD; include enough
1506   information for the user to recognize the source of the conflict.
1507   Ideally, the response entity would include enough information for the
1508   user or user agent to fix the problem; however, that might not be
1509   possible and is not required.
1510</t>
1511<t>
1512   Conflicts are most likely to occur in response to a PUT request. For
1513   example, if versioning were being used and the entity being PUT
1514   included changes to a resource which conflict with those made by an
1515   earlier (third-party) request, the server might use the 409 response
1516   to indicate that it can't complete the request. In this case, the
1517   response entity would likely contain a list of the differences
1518   between the two versions in a format defined by the response
1519   Content-Type.
1520</t>
1521</section>
1522
1523<section title="410 Gone" anchor="status.410">
1524  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1525  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1526<t>
1527   The requested resource is no longer available at the server and no
1528   forwarding address is known. This condition is expected to be
1529   considered permanent. Clients with link editing capabilities &SHOULD;
1530   delete references to the Request-URI after user approval. If the
1531   server does not know, or has no facility to determine, whether or not
1532   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1533   used instead. This response is cacheable unless indicated otherwise.
1534</t>
1535<t>
1536   The 410 response is primarily intended to assist the task of web
1537   maintenance by notifying the recipient that the resource is
1538   intentionally unavailable and that the server owners desire that
1539   remote links to that resource be removed. Such an event is common for
1540   limited-time, promotional services and for resources belonging to
1541   individuals no longer working at the server's site. It is not
1542   necessary to mark all permanently unavailable resources as "gone" or
1543   to keep the mark for any length of time -- that is left to the
1544   discretion of the server owner.
1545</t>
1546</section>
1547
1548<section title="411 Length Required" anchor="status.411">
1549  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1550  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1551<t>
1552   The server refuses to accept the request without a defined Content-Length.
1553   The client &MAY; repeat the request if it adds a valid
1554   Content-Length header field containing the length of the message-body
1555   in the request message.
1556</t>
1557</section>
1558
1559<section title="412 Precondition Failed" anchor="status.412">
1560  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1561  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1562<t>
1563   The precondition given in one or more of the request-header fields
1564   evaluated to false when it was tested on the server, as defined in
1565   &conditional;.
1566</t>
1567</section>
1568
1569<section title="413 Request Entity Too Large" anchor="status.413">
1570  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1571  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1572<t>
1573   The server is refusing to process a request because the request
1574   entity is larger than the server is willing or able to process. The
1575   server &MAY; close the connection to prevent the client from continuing
1576   the request.
1577</t>
1578<t>
1579   If the condition is temporary, the server &SHOULD; include a Retry-After
1580   header field to indicate that it is temporary and after what
1581   time the client &MAY; try again.
1582</t>
1583</section>
1584
1585<section title="414 Request-URI Too Long" anchor="status.414">
1586  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1587  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1588<t>
1589   The server is refusing to service the request because the Request-URI
1590   is longer than the server is willing to interpret. This rare
1591   condition is only likely to occur when a client has improperly
1592   converted a POST request to a GET request with long query
1593   information, when the client has descended into a URI "black hole" of
1594   redirection (e.g., a redirected URI prefix that points to a suffix of
1595   itself), or when the server is under attack by a client attempting to
1596   exploit security holes present in some servers using fixed-length
1597   buffers for reading or manipulating the Request-URI.
1598</t>
1599</section>
1600
1601<section title="415 Unsupported Media Type" anchor="status.415">
1602  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1603  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1604<t>
1605   The server is refusing to service the request because the entity of
1606   the request is in a format not supported by the requested resource
1607   for the requested method.
1608</t>
1609</section>
1610
1611<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1612  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1613  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1614<t>
1615   The request included a Range request-header field (&header-range;) and none of
1616   the range-specifier values in this field overlap the current extent
1617   of the selected resource.
1618</t>
1619</section>
1620
1621<section title="417 Expectation Failed" anchor="status.417">
1622  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1623  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1624<t>
1625   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1626   could not be met by this server, or, if the server is a proxy,
1627   the server has unambiguous evidence that the request could not be met
1628   by the next-hop server.
1629</t>
1630</section>
1631</section>
1632
1633<section title="Server Error 5xx" anchor="status.5xx">
1634<t>
1635   Response status codes beginning with the digit "5" indicate cases in
1636   which the server is aware that it has erred or is incapable of
1637   performing the request. Except when responding to a HEAD request, the
1638   server &SHOULD; include an entity containing an explanation of the
1639   error situation, and whether it is a temporary or permanent
1640   condition. User agents &SHOULD; display any included entity to the
1641   user. These response codes are applicable to any request method.
1642</t>
1643
1644<section title="500 Internal Server Error" anchor="status.500">
1645  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1646  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1647<t>
1648   The server encountered an unexpected condition which prevented it
1649   from fulfilling the request.
1650</t>
1651</section>
1652
1653<section title="501 Not Implemented" anchor="status.501">
1654  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1655  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1656<t>
1657   The server does not support the functionality required to fulfill the
1658   request. This is the appropriate response when the server does not
1659   recognize the request method and is not capable of supporting it for
1660   any resource.
1661</t>
1662</section>
1663
1664<section title="502 Bad Gateway" anchor="status.502">
1665  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1666  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1667<t>
1668   The server, while acting as a gateway or proxy, received an invalid
1669   response from the upstream server it accessed in attempting to
1670   fulfill the request.
1671</t>
1672</section>
1673
1674<section title="503 Service Unavailable" anchor="status.503">
1675  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1676  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1677<t>
1678   The server is currently unable to handle the request due to a
1679   temporary overloading or maintenance of the server. The implication
1680   is that this is a temporary condition which will be alleviated after
1681   some delay. If known, the length of the delay &MAY; be indicated in a
1682   Retry-After header. If no Retry-After is given, the client &SHOULD;
1683   handle the response as it would for a 500 response.
1684  <list><t>
1685      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1686      server must use it when becoming overloaded. Some servers may wish
1687      to simply refuse the connection.
1688  </t></list>
1689</t>
1690</section>
1691
1692<section title="504 Gateway Timeout" anchor="status.504">
1693  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1694  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1695<t>
1696   The server, while acting as a gateway or proxy, did not receive a
1697   timely response from the upstream server specified by the URI (e.g.
1698   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1699   to access in attempting to complete the request.
1700  <list><t>
1701      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1702      return 400 or 500 when DNS lookups time out.
1703  </t></list>
1704</t>
1705</section>
1706
1707<section title="505 HTTP Version Not Supported" anchor="status.505">
1708  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1709  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1710<t>
1711   The server does not support, or refuses to support, the protocol
1712   version that was used in the request message. The server is
1713   indicating that it is unable or unwilling to complete the request
1714   using the same major version as the client, as described in &http-version;,
1715   other than with this error message. The response &SHOULD; contain
1716   an entity describing why that version is not supported and what other
1717   protocols are supported by that server.
1718</t>
1719
1720</section>
1721</section>
1722</section>
1723
1724
1725<section title="Header Field Definitions" anchor="header.fields">
1726<t>
1727   This section defines the syntax and semantics of HTTP/1.1 header fields
1728   related to request and response semantics.
1729</t>
1730<t>
1731   For entity-header fields, both sender and recipient refer to either the
1732   client or the server, depending on who sends and who receives the entity.
1733</t>
1734
1735<section title="Allow" anchor="header.allow">
1736  <iref primary="true" item="Allow header" x:for-anchor=""/>
1737  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1738  <x:anchor-alias value="Allow"/>
1739<t>
1740      The Allow response-header field lists the set of methods advertised as
1741      supported by the resource identified by the Request-URI. The purpose of
1742      this field is strictly to inform the recipient of valid methods
1743      associated with the resource. An Allow header field &MUST; be
1744      present in a 405 (Method Not Allowed) response.
1745</t>
1746<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1747  <x:ref>Allow</x:ref>   = "Allow" ":" #<x:ref>Method</x:ref>
1748</artwork></figure>
1749<t>
1750      Example of use:
1751</t>
1752<figure><artwork type="example">
1753       Allow: GET, HEAD, PUT
1754</artwork></figure>
1755<t>
1756      The actual set of allowed methods is defined
1757      by the origin server at the time of each request.
1758</t>
1759<t>
1760      A proxy &MUST-NOT; modify the Allow header field even if it does not
1761      understand all the methods specified, since the user agent might
1762      have other means of communicating with the origin server.
1763</t>
1764</section>
1765
1766<section title="Expect" anchor="header.expect">
1767  <iref primary="true" item="Expect header" x:for-anchor=""/>
1768  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1769  <x:anchor-alias value="Expect"/>
1770  <x:anchor-alias value="expectation"/>
1771  <x:anchor-alias value="expectation-extension"/>
1772  <x:anchor-alias value="expect-params"/>
1773<t>
1774   The Expect request-header field is used to indicate that particular
1775   server behaviors are required by the client.
1776</t>
1777<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"/>
1778  <x:ref>Expect</x:ref>       =  "Expect" ":" 1#<x:ref>expectation</x:ref>
1779 
1780  <x:ref>expectation</x:ref>  =  "100-continue" | <x:ref>expectation-extension</x:ref>
1781  <x:ref>expectation-extension</x:ref> =  <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> )
1782                           *<x:ref>expect-params</x:ref> ]
1783  <x:ref>expect-params</x:ref> =  ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> ) ]
1784</artwork></figure>
1785<t>
1786   A server that does not understand or is unable to comply with any of
1787   the expectation values in the Expect field of a request &MUST; respond
1788   with appropriate error status. The server &MUST; respond with a 417
1789   (Expectation Failed) status if any of the expectations cannot be met
1790   or, if there are other problems with the request, some other 4xx
1791   status.
1792</t>
1793<t>
1794   This header field is defined with extensible syntax to allow for
1795   future extensions. If a server receives a request containing an
1796   Expect field that includes an expectation-extension that it does not
1797   support, it &MUST; respond with a 417 (Expectation Failed) status.
1798</t>
1799<t>
1800   Comparison of expectation values is case-insensitive for unquoted
1801   tokens (including the 100-continue token), and is case-sensitive for
1802   quoted-string expectation-extensions.
1803</t>
1804<t>
1805   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1806   return a 417 (Expectation Failed) status if it receives a request
1807   with an expectation that it cannot meet. However, the Expect
1808   request-header itself is end-to-end; it &MUST; be forwarded if the
1809   request is forwarded.
1810</t>
1811<t>
1812   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1813   Expect header.
1814</t>
1815<t>
1816   See &use100; for the use of the 100 (Continue) status.
1817</t>
1818</section>
1819
1820<section title="From" anchor="header.from">
1821  <iref primary="true" item="From header" x:for-anchor=""/>
1822  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1823  <x:anchor-alias value="From"/>
1824  <x:anchor-alias value="mailbox"/>
1825<t>
1826   The From request-header field, if given, &SHOULD; contain an Internet
1827   e-mail address for the human user who controls the requesting user
1828   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1829   in <xref x:sec="3.4" x:fmt="of" target="RFC2822"/>:
1830</t>
1831<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1832  <x:ref>From</x:ref>    = "From" ":" <x:ref>mailbox</x:ref>
1833 
1834  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC2822"/>&gt;
1835</artwork></figure>
1836<t>
1837   An example is:
1838</t>
1839<figure><artwork type="example">
1840    From: webmaster@example.org
1841</artwork></figure>
1842<t>
1843   This header field &MAY; be used for logging purposes and as a means for
1844   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1845   be used as an insecure form of access protection. The interpretation
1846   of this field is that the request is being performed on behalf of the
1847   person given, who accepts responsibility for the method performed. In
1848   particular, robot agents &SHOULD; include this header so that the
1849   person responsible for running the robot can be contacted if problems
1850   occur on the receiving end.
1851</t>
1852<t>
1853   The Internet e-mail address in this field &MAY; be separate from the
1854   Internet host which issued the request. For example, when a request
1855   is passed through a proxy the original issuer's address &SHOULD; be
1856   used.
1857</t>
1858<t>
1859   The client &SHOULD-NOT;  send the From header field without the user's
1860   approval, as it might conflict with the user's privacy interests or
1861   their site's security policy. It is strongly recommended that the
1862   user be able to disable, enable, and modify the value of this field
1863   at any time prior to a request.
1864</t>
1865</section>
1866
1867<section title="Location" anchor="header.location">
1868  <iref primary="true" item="Location header" x:for-anchor=""/>
1869  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1870  <x:anchor-alias value="Location"/>
1871<t>
1872   The Location response-header field is used for the identification of a
1873   new resource or to redirect the recipient to a location other than the
1874   Request-URI for completion of the request.  For 201 (Created)
1875   responses, the Location is that of the new resource which was created
1876   by the request. For 3xx responses, the location &SHOULD; indicate the
1877   server's preferred URI for automatic redirection to the resource. The
1878   field value consists of a single absolute URI.
1879</t>
1880<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1881  <x:ref>Location</x:ref>       = "Location" ":" <x:ref>absoluteURI</x:ref> [ "#" <x:ref>fragment</x:ref> ]
1882</artwork></figure>
1883<t>
1884   An example is:
1885</t>
1886<figure><artwork type="example">
1887    Location: http://www.example.org/pub/WWW/People.html
1888</artwork></figure>
1889<t>
1890  <list><t>
1891      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1892      from Location in that the Content-Location identifies the original
1893      location of the entity enclosed in the request. It is therefore
1894      possible for a response to contain header fields for both Location
1895      and Content-Location.
1896  </t></list>
1897</t>
1898<t>
1899   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1900   <list style="symbols">
1901      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1902      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1903      <t>With 305 Use Proxy.</t>
1904   </list>
1905</t>
1906</section>
1907
1908<section title="Max-Forwards" anchor="header.max-forwards">
1909  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1910  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1911  <x:anchor-alias value="Max-Forwards"/>
1912<t>
1913   The Max-Forwards request-header field provides a mechanism with the
1914   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1915   number of proxies or gateways that can forward the request to the
1916   next inbound server. This can be useful when the client is attempting
1917   to trace a request chain which appears to be failing or looping in
1918   mid-chain.
1919</t>
1920<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1921  <x:ref>Max-Forwards</x:ref>   = "Max-Forwards" ":" 1*<x:ref>DIGIT</x:ref>
1922</artwork></figure>
1923<t>
1924   The Max-Forwards value is a decimal integer indicating the remaining
1925   number of times this request message may be forwarded.
1926</t>
1927<t>
1928   Each proxy or gateway recipient of a TRACE or OPTIONS request
1929   containing a Max-Forwards header field &MUST; check and update its
1930   value prior to forwarding the request. If the received value is zero
1931   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1932   respond as the final recipient. If the received Max-Forwards value is
1933   greater than zero, then the forwarded message &MUST; contain an updated
1934   Max-Forwards field with a value decremented by one (1).
1935</t>
1936<t>
1937   The Max-Forwards header field &MAY; be ignored for all other methods
1938   defined by this specification and for any extension methods for which
1939   it is not explicitly referred to as part of that method definition.
1940</t>
1941</section>
1942
1943<section title="Referer" anchor="header.referer">
1944  <iref primary="true" item="Referer header" x:for-anchor=""/>
1945  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1946  <x:anchor-alias value="Referer"/>
1947<t>
1948   The Referer[sic] request-header field allows the client to specify,
1949   for the server's benefit, the address (URI) of the resource from
1950   which the Request-URI was obtained (the "referrer", although the
1951   header field is misspelled.) The Referer request-header allows a
1952   server to generate lists of back-links to resources for interest,
1953   logging, optimized caching, etc. It also allows obsolete or mistyped
1954   links to be traced for maintenance. The Referer field &MUST-NOT; be
1955   sent if the Request-URI was obtained from a source that does not have
1956   its own URI, such as input from the user keyboard.
1957</t>
1958<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1959  <x:ref>Referer</x:ref>        = "Referer" ":" ( <x:ref>absoluteURI</x:ref> | <x:ref>relativeURI</x:ref> )
1960</artwork></figure>
1961<t>
1962   Example:
1963</t>
1964<figure><artwork type="example">
1965    Referer: http://www.example.org/hypertext/Overview.html
1966</artwork></figure>
1967<t>
1968   If the field value is a relative URI, it &SHOULD; be interpreted
1969   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1970   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1971</t>
1972</section>
1973
1974<section title="Retry-After" anchor="header.retry-after">
1975  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1976  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1977  <x:anchor-alias value="Retry-After"/>
1978<t>
1979   The Retry-After response-header field can be used with a 503 (Service
1980   Unavailable) response to indicate how long the service is expected to
1981   be unavailable to the requesting client. This field &MAY; also be used
1982   with any 3xx (Redirection) response to indicate the minimum time the
1983   user-agent is asked wait before issuing the redirected request. The
1984   value of this field can be either an HTTP-date or an integer number
1985   of seconds (in decimal) after the time of the response.
1986</t>
1987<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1988  <x:ref>Retry-After</x:ref>   = "Retry-After" ":" ( <x:ref>HTTP-date</x:ref> | <x:ref>delta-seconds</x:ref> )
1989</artwork></figure>
1990<t anchor="rule.delta-seconds">
1991  <x:anchor-alias value="delta-seconds"/>
1992   Time spans are non-negative decimal integers, representing time in
1993   seconds.
1994</t>
1995<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
1996  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
1997</artwork></figure>
1998<t>
1999   Two examples of its use are
2000</t>
2001<figure><artwork type="example">
2002    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2003    Retry-After: 120
2004</artwork></figure>
2005<t>
2006   In the latter example, the delay is 2 minutes.
2007</t>
2008</section>
2009
2010<section title="Server" anchor="header.server">
2011  <iref primary="true" item="Server header" x:for-anchor=""/>
2012  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
2013  <x:anchor-alias value="Server"/>
2014<t>
2015   The Server response-header field contains information about the
2016   software used by the origin server to handle the request. The field
2017   can contain multiple product tokens (&product-tokens;) and comments
2018   identifying the server and any significant subproducts. The product
2019   tokens are listed in order of their significance for identifying the
2020   application.
2021</t>
2022<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2023  <x:ref>Server</x:ref>         = "Server" ":" 1*( <x:ref>product</x:ref> | <x:ref>comment</x:ref> )
2024</artwork></figure>
2025<t>
2026   Example:
2027</t>
2028<figure><artwork type="example">
2029    Server: CERN/3.0 libwww/2.17
2030</artwork></figure>
2031<t>
2032   If the response is being forwarded through a proxy, the proxy
2033   application &MUST-NOT; modify the Server response-header. Instead, it
2034   &MUST; include a Via field (as described in &header-via;).
2035  <list><t>
2036      <x:h>Note:</x:h> Revealing the specific software version of the server might
2037      allow the server machine to become more vulnerable to attacks
2038      against software that is known to contain security holes. Server
2039      implementors are encouraged to make this field a configurable
2040      option.
2041  </t></list>
2042</t>
2043</section>
2044
2045<section title="User-Agent" anchor="header.user-agent">
2046  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
2047  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
2048  <x:anchor-alias value="User-Agent"/>
2049<t>
2050   The User-Agent request-header field contains information about the
2051   user agent originating the request. This is for statistical purposes,
2052   the tracing of protocol violations, and automated recognition of user
2053   agents for the sake of tailoring responses to avoid particular user
2054   agent limitations. User agents &SHOULD; include this field with
2055   requests. The field can contain multiple product tokens (&product-tokens;)
2056   and comments identifying the agent and any subproducts which form a
2057   significant part of the user agent. By convention, the product tokens
2058   are listed in order of their significance for identifying the
2059   application.
2060</t>
2061<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2062  <x:ref>User-Agent</x:ref>     = "User-Agent" ":" 1*( <x:ref>product</x:ref> | <x:ref>comment</x:ref> )
2063</artwork></figure>
2064<t>
2065   Example:
2066</t>
2067<figure><artwork type="example">
2068    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2069</artwork></figure>
2070</section>
2071
2072</section>
2073
2074<section title="IANA Considerations" anchor="IANA.considerations">
2075<t>
2076   <cref>TBD.</cref>
2077</t>
2078</section>
2079
2080<section title="Security Considerations" anchor="security.considerations">
2081<t>
2082   This section is meant to inform application developers, information
2083   providers, and users of the security limitations in HTTP/1.1 as
2084   described by this document. The discussion does not include
2085   definitive solutions to the problems revealed, though it does make
2086   some suggestions for reducing security risks.
2087</t>
2088
2089<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2090<t>
2091   Like any generic data transfer protocol, HTTP cannot regulate the
2092   content of the data that is transferred, nor is there any a priori
2093   method of determining the sensitivity of any particular piece of
2094   information within the context of any given request. Therefore,
2095   applications &SHOULD; supply as much control over this information as
2096   possible to the provider of that information. Four header fields are
2097   worth special mention in this context: Server, Via, Referer and From.
2098</t>
2099<t>
2100   Revealing the specific software version of the server might allow the
2101   server machine to become more vulnerable to attacks against software
2102   that is known to contain security holes. Implementors &SHOULD; make the
2103   Server header field a configurable option.
2104</t>
2105<t>
2106   Proxies which serve as a portal through a network firewall &SHOULD;
2107   take special precautions regarding the transfer of header information
2108   that identifies the hosts behind the firewall. In particular, they
2109   &SHOULD; remove, or replace with sanitized versions, any Via fields
2110   generated behind the firewall.
2111</t>
2112<t>
2113   The Referer header allows reading patterns to be studied and reverse
2114   links drawn. Although it can be very useful, its power can be abused
2115   if user details are not separated from the information contained in
2116   the Referer. Even when the personal information has been removed, the
2117   Referer header might indicate a private document's URI whose
2118   publication would be inappropriate.
2119</t>
2120<t>
2121   The information sent in the From field might conflict with the user's
2122   privacy interests or their site's security policy, and hence it
2123   &SHOULD-NOT;  be transmitted without the user being able to disable,
2124   enable, and modify the contents of the field. The user &MUST; be able
2125   to set the contents of this field within a user preference or
2126   application defaults configuration.
2127</t>
2128<t>
2129   We suggest, though do not require, that a convenient toggle interface
2130   be provided for the user to enable or disable the sending of From and
2131   Referer information.
2132</t>
2133<t>
2134   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2135   fields can sometimes be used to determine that a specific client or
2136   server have a particular security hole which might be exploited.
2137   Unfortunately, this same information is often used for other valuable
2138   purposes for which HTTP currently has no better mechanism.
2139</t>
2140</section>
2141
2142<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2143<t>
2144   Because the source of a link might be private information or might
2145   reveal an otherwise private information source, it is strongly
2146   recommended that the user be able to select whether or not the
2147   Referer field is sent. For example, a browser client could have a
2148   toggle switch for browsing openly/anonymously, which would
2149   respectively enable/disable the sending of Referer and From
2150   information.
2151</t>
2152<t>
2153   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
2154   HTTP request if the referring page was transferred with a secure
2155   protocol.
2156</t>
2157<t>
2158   Authors of services should not use
2159   GET-based forms for the submission of sensitive data because that
2160   data will be encoded in the Request-URI. Many existing
2161   servers, proxies, and user agents log or display the Request-URI in
2162   places where it might be visible to third parties. Such services can
2163   use POST-based form submission instead.
2164</t>
2165</section>
2166
2167<section title="Location Headers and Spoofing" anchor="location.spoofing">
2168<t>
2169   If a single server supports multiple organizations that do not trust
2170   one another, then it &MUST; check the values of Location and Content-Location
2171   headers in responses that are generated under control of
2172   said organizations to make sure that they do not attempt to
2173   invalidate resources over which they have no authority.
2174</t>
2175</section>
2176
2177</section>
2178
2179<section title="Acknowledgments" anchor="ack">
2180</section>
2181</middle>
2182<back>
2183
2184<references title="Normative References">
2185
2186<reference anchor="Part1">
2187  <front>
2188    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2189    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2190      <organization abbrev="Day Software">Day Software</organization>
2191      <address><email>fielding@gbiv.com</email></address>
2192    </author>
2193    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2194      <organization>One Laptop per Child</organization>
2195      <address><email>jg@laptop.org</email></address>
2196    </author>
2197    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2198      <organization abbrev="HP">Hewlett-Packard Company</organization>
2199      <address><email>JeffMogul@acm.org</email></address>
2200    </author>
2201    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2202      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2203      <address><email>henrikn@microsoft.com</email></address>
2204    </author>
2205    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2206      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2207      <address><email>LMM@acm.org</email></address>
2208    </author>
2209    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2210      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2211      <address><email>paulle@microsoft.com</email></address>
2212    </author>
2213    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2214      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2215      <address><email>timbl@w3.org</email></address>
2216    </author>
2217    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2218      <organization abbrev="W3C">World Wide Web Consortium</organization>
2219      <address><email>ylafon@w3.org</email></address>
2220    </author>
2221    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2222      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2223      <address><email>julian.reschke@greenbytes.de</email></address>
2224    </author>
2225    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2226  </front>
2227  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2228  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2229</reference>
2230
2231<reference anchor="Part3">
2232  <front>
2233    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2234    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2235      <organization abbrev="Day Software">Day Software</organization>
2236      <address><email>fielding@gbiv.com</email></address>
2237    </author>
2238    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2239      <organization>One Laptop per Child</organization>
2240      <address><email>jg@laptop.org</email></address>
2241    </author>
2242    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2243      <organization abbrev="HP">Hewlett-Packard Company</organization>
2244      <address><email>JeffMogul@acm.org</email></address>
2245    </author>
2246    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2247      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2248      <address><email>henrikn@microsoft.com</email></address>
2249    </author>
2250    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2251      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2252      <address><email>LMM@acm.org</email></address>
2253    </author>
2254    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2255      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2256      <address><email>paulle@microsoft.com</email></address>
2257    </author>
2258    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2259      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2260      <address><email>timbl@w3.org</email></address>
2261    </author>
2262    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2263      <organization abbrev="W3C">World Wide Web Consortium</organization>
2264      <address><email>ylafon@w3.org</email></address>
2265    </author>
2266    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2267      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2268      <address><email>julian.reschke@greenbytes.de</email></address>
2269    </author>
2270    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2271  </front>
2272  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2273  <x:source href="p3-payload.xml" basename="p3-payload"/>
2274</reference>
2275
2276<reference anchor="Part4">
2277  <front>
2278    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2279    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2280      <organization abbrev="Day Software">Day Software</organization>
2281      <address><email>fielding@gbiv.com</email></address>
2282    </author>
2283    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2284      <organization>One Laptop per Child</organization>
2285      <address><email>jg@laptop.org</email></address>
2286    </author>
2287    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2288      <organization abbrev="HP">Hewlett-Packard Company</organization>
2289      <address><email>JeffMogul@acm.org</email></address>
2290    </author>
2291    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2292      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2293      <address><email>henrikn@microsoft.com</email></address>
2294    </author>
2295    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2296      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2297      <address><email>LMM@acm.org</email></address>
2298    </author>
2299    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2300      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2301      <address><email>paulle@microsoft.com</email></address>
2302    </author>
2303    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2304      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2305      <address><email>timbl@w3.org</email></address>
2306    </author>
2307    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2308      <organization abbrev="W3C">World Wide Web Consortium</organization>
2309      <address><email>ylafon@w3.org</email></address>
2310    </author>
2311    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2312      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2313      <address><email>julian.reschke@greenbytes.de</email></address>
2314    </author>
2315    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2316  </front>
2317  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2318  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2319</reference>
2320
2321<reference anchor="Part5">
2322  <front>
2323    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2324    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2325      <organization abbrev="Day Software">Day Software</organization>
2326      <address><email>fielding@gbiv.com</email></address>
2327    </author>
2328    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2329      <organization>One Laptop per Child</organization>
2330      <address><email>jg@laptop.org</email></address>
2331    </author>
2332    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2333      <organization abbrev="HP">Hewlett-Packard Company</organization>
2334      <address><email>JeffMogul@acm.org</email></address>
2335    </author>
2336    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2337      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2338      <address><email>henrikn@microsoft.com</email></address>
2339    </author>
2340    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2341      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2342      <address><email>LMM@acm.org</email></address>
2343    </author>
2344    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2345      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2346      <address><email>paulle@microsoft.com</email></address>
2347    </author>
2348    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2349      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2350      <address><email>timbl@w3.org</email></address>
2351    </author>
2352    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2353      <organization abbrev="W3C">World Wide Web Consortium</organization>
2354      <address><email>ylafon@w3.org</email></address>
2355    </author>
2356    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2357      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2358      <address><email>julian.reschke@greenbytes.de</email></address>
2359    </author>
2360    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2361  </front>
2362  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2363  <x:source href="p5-range.xml" basename="p5-range"/>
2364</reference>
2365
2366<reference anchor="Part6">
2367  <front>
2368    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2369    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2370      <organization abbrev="Day Software">Day Software</organization>
2371      <address><email>fielding@gbiv.com</email></address>
2372    </author>
2373    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2374      <organization>One Laptop per Child</organization>
2375      <address><email>jg@laptop.org</email></address>
2376    </author>
2377    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2378      <organization abbrev="HP">Hewlett-Packard Company</organization>
2379      <address><email>JeffMogul@acm.org</email></address>
2380    </author>
2381    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2382      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2383      <address><email>henrikn@microsoft.com</email></address>
2384    </author>
2385    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2386      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2387      <address><email>LMM@acm.org</email></address>
2388    </author>
2389    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2390      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2391      <address><email>paulle@microsoft.com</email></address>
2392    </author>
2393    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2394      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2395      <address><email>timbl@w3.org</email></address>
2396    </author>
2397    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2398      <organization abbrev="W3C">World Wide Web Consortium</organization>
2399      <address><email>ylafon@w3.org</email></address>
2400    </author>
2401    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2402      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2403      <address><email>julian.reschke@greenbytes.de</email></address>
2404    </author>
2405    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2406  </front>
2407  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2408  <x:source href="p6-cache.xml" basename="p6-cache"/>
2409</reference>
2410
2411<reference anchor="Part7">
2412  <front>
2413    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2414    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2415      <organization abbrev="Day Software">Day Software</organization>
2416      <address><email>fielding@gbiv.com</email></address>
2417    </author>
2418    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2419      <organization>One Laptop per Child</organization>
2420      <address><email>jg@laptop.org</email></address>
2421    </author>
2422    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2423      <organization abbrev="HP">Hewlett-Packard Company</organization>
2424      <address><email>JeffMogul@acm.org</email></address>
2425    </author>
2426    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2427      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2428      <address><email>henrikn@microsoft.com</email></address>
2429    </author>
2430    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2431      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2432      <address><email>LMM@acm.org</email></address>
2433    </author>
2434    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2435      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2436      <address><email>paulle@microsoft.com</email></address>
2437    </author>
2438    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2439      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2440      <address><email>timbl@w3.org</email></address>
2441    </author>
2442    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2443      <organization abbrev="W3C">World Wide Web Consortium</organization>
2444      <address><email>ylafon@w3.org</email></address>
2445    </author>
2446    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2447      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2448      <address><email>julian.reschke@greenbytes.de</email></address>
2449    </author>
2450    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2451  </front>
2452  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2453  <x:source href="p7-auth.xml" basename="p7-auth"/>
2454</reference>
2455
2456<reference anchor="RFC2119">
2457  <front>
2458    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2459    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2460      <organization>Harvard University</organization>
2461      <address><email>sob@harvard.edu</email></address>
2462    </author>
2463    <date month="March" year="1997"/>
2464  </front>
2465  <seriesInfo name="BCP" value="14"/>
2466  <seriesInfo name="RFC" value="2119"/>
2467</reference>
2468
2469</references>
2470
2471<references title="Informative References">
2472
2473<reference anchor="Luo1998">
2474  <front>
2475    <title>Tunneling TCP based protocols through Web proxy servers</title>
2476    <author initials="A." surname="Luotonen" fullname="A. Luotonen">
2477      <organization/>
2478    </author>
2479    <date year="1998" month="August"/>
2480  </front>
2481  <seriesInfo name="Internet-Draft" value="draft-luotonen-web-proxy-tunneling-01"/>
2482</reference>
2483
2484<reference anchor="RFC1945">
2485  <front>
2486    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2487    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2488      <organization>MIT, Laboratory for Computer Science</organization>
2489      <address><email>timbl@w3.org</email></address>
2490    </author>
2491    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2492      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2493      <address><email>fielding@ics.uci.edu</email></address>
2494    </author>
2495    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2496      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2497      <address><email>frystyk@w3.org</email></address>
2498    </author>
2499    <date month="May" year="1996"/>
2500  </front>
2501  <seriesInfo name="RFC" value="1945"/>
2502</reference>
2503
2504<reference anchor="RFC2068">
2505  <front>
2506    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2507    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2508      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2509      <address><email>fielding@ics.uci.edu</email></address>
2510    </author>
2511    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2512      <organization>MIT Laboratory for Computer Science</organization>
2513      <address><email>jg@w3.org</email></address>
2514    </author>
2515    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2516      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2517      <address><email>mogul@wrl.dec.com</email></address>
2518    </author>
2519    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2520      <organization>MIT Laboratory for Computer Science</organization>
2521      <address><email>frystyk@w3.org</email></address>
2522    </author>
2523    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2524      <organization>MIT Laboratory for Computer Science</organization>
2525      <address><email>timbl@w3.org</email></address>
2526    </author>
2527    <date month="January" year="1997"/>
2528  </front>
2529  <seriesInfo name="RFC" value="2068"/>
2530</reference>
2531
2532<reference anchor="RFC2616">
2533  <front>
2534    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2535    <author initials="R." surname="Fielding" fullname="R. Fielding">
2536      <organization>University of California, Irvine</organization>
2537      <address><email>fielding@ics.uci.edu</email></address>
2538    </author>
2539    <author initials="J." surname="Gettys" fullname="J. Gettys">
2540      <organization>W3C</organization>
2541      <address><email>jg@w3.org</email></address>
2542    </author>
2543    <author initials="J." surname="Mogul" fullname="J. Mogul">
2544      <organization>Compaq Computer Corporation</organization>
2545      <address><email>mogul@wrl.dec.com</email></address>
2546    </author>
2547    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2548      <organization>MIT Laboratory for Computer Science</organization>
2549      <address><email>frystyk@w3.org</email></address>
2550    </author>
2551    <author initials="L." surname="Masinter" fullname="L. Masinter">
2552      <organization>Xerox Corporation</organization>
2553      <address><email>masinter@parc.xerox.com</email></address>
2554    </author>
2555    <author initials="P." surname="Leach" fullname="P. Leach">
2556      <organization>Microsoft Corporation</organization>
2557      <address><email>paulle@microsoft.com</email></address>
2558    </author>
2559    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2560      <organization>W3C</organization>
2561      <address><email>timbl@w3.org</email></address>
2562    </author>
2563    <date month="June" year="1999"/>
2564  </front>
2565  <seriesInfo name="RFC" value="2616"/>
2566</reference>
2567
2568<reference anchor="RFC2822">
2569  <front>
2570    <title>Internet Message Format</title>
2571    <author initials="P." surname="Resnick" fullname="P. Resnick">
2572      <organization>QUALCOMM Incorporated</organization>
2573    </author>
2574    <date year="2001" month="April"/>
2575  </front> 
2576  <seriesInfo name="RFC" value="2822"/>
2577</reference>
2578
2579</references>
2580
2581<section title="Compatibility with Previous Versions" anchor="compatibility">
2582<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2583<t>
2584   Clarified which error code should be used for inbound server failures
2585   (e.g. DNS failures). (<xref target="status.504"/>).
2586</t>
2587<t>
2588   201 (Created) had a race that required an Etag be sent when a resource is
2589   first created. (<xref target="status.201"/>).
2590</t>
2591<t>
2592   Rewrite of message transmission requirements to make it much harder
2593   for implementors to get it wrong, as the consequences of errors here
2594   can have significant impact on the Internet, and to deal with the
2595   following problems:
2596  <list style="numbers">
2597      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2598         this was incorrectly placing a requirement on the behavior of
2599         an implementation of a future version of HTTP/1.x</t>
2600
2601      <t>Made it clear that user-agents should retry requests, not
2602         "clients" in general.</t>
2603
2604      <t>Converted requirements for clients to ignore unexpected 100
2605         (Continue) responses, and for proxies to forward 100 responses,
2606         into a general requirement for 1xx responses.</t>
2607
2608      <t>Modified some TCP-specific language, to make it clearer that
2609         non-TCP transports are possible for HTTP.</t>
2610
2611      <t>Require that the origin server &MUST-NOT; wait for the request
2612         body before it sends a required 100 (Continue) response.</t>
2613
2614      <t>Allow, rather than require, a server to omit 100 (Continue) if
2615         it has already seen some of the request body.</t>
2616
2617      <t>Allow servers to defend against denial-of-service attacks and
2618         broken clients.</t>
2619  </list>
2620</t>
2621<t>
2622   This change adds the Expect header and 417 status code.
2623</t>
2624<t>
2625   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2626   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2627</t>
2628<t>
2629   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
2630   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2631</t>
2632</section>
2633
2634<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2635<t>
2636  Clarify definition of POST.
2637  (<xref target="POST"/>)
2638</t>
2639<t>
2640  Failed to consider that there are
2641  many other request methods that are safe to automatically redirect,
2642  and further that the user agent is able to make that determination
2643  based on the request method semantics.
2644  (Sections <xref format="counter" target="status.301"/>,
2645  <xref format="counter" target="status.302"/> and
2646  <xref format="counter" target="status.307"/>)
2647</t>
2648<t>
2649  Deprecate 305 Use Proxy status code, because user agents did not implement it.
2650  It used to indicate that the requested resource must be accessed through the
2651  proxy given by the Location field. The Location field gave the URI of the
2652  proxy. The recipient was expected to repeat this single request via the proxy.
2653  (<xref target="status.305"/>)
2654</t>
2655<t>
2656  Reclassify Allow header as response header, removing the option to
2657  specify it in a PUT request.
2658  Relax the server requirement on the contents of the Allow header and
2659  remove requirement on clients to always trust the header value.
2660  (<xref target="header.allow"/>)
2661</t>
2662<t>
2663  Correct syntax of Location header to allow fragment,
2664  as referred symbol wasn't what was expected, and add some
2665  clarifications as to when it would not be appropriate.
2666  (<xref target="header.location"/>)
2667</t>
2668<t>
2669  In the description of the Server header, the Via field
2670  was described as a SHOULD. The requirement was and is stated
2671  correctly in the description of the Via header in &header-via;.
2672  (<xref target="header.server"/>)
2673</t>
2674</section>
2675
2676</section>
2677
2678<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
2679
2680<section title="Since RFC2616">
2681<t>
2682  Extracted relevant partitions from <xref target="RFC2616"/>.
2683</t>
2684</section>
2685
2686<section title="Since draft-ietf-httpbis-p2-semantics-00">
2687<t>
2688  Closed issues:
2689  <list style="symbols"> 
2690    <t>
2691      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
2692      "Via is a MUST"
2693      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
2694    </t>
2695    <t>
2696      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
2697      "Fragments allowed in Location"
2698      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
2699    </t>
2700    <t>
2701      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
2702      "Safe Methods vs Redirection"
2703      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
2704    </t>
2705    <t>
2706      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
2707      "Revise description of the POST method"
2708      (<eref target="http://purl.org/NET/http-errata#post"/>)
2709    </t>
2710    <t>
2711      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2712      "Normative and Informative references"
2713    </t>
2714    <t>
2715      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
2716      "RFC2606 Compliance"
2717    </t>
2718    <t>
2719      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2720      "Informative references"
2721    </t>
2722    <t>
2723      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
2724      "Redundant cross-references"
2725    </t>
2726  </list>
2727</t>
2728<t>
2729  Other changes:
2730  <list style="symbols"> 
2731    <t>
2732      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
2733    </t>
2734  </list>
2735</t>
2736</section>
2737
2738<section title="Since draft-ietf-httpbis-p2-semantics-01">
2739<t>
2740  Closed issues:
2741  <list style="symbols"> 
2742    <t>
2743      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
2744      "PUT side effects"
2745    </t>
2746    <t>
2747      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
2748      "Duplicate Host header requirements"
2749    </t>
2750  </list>
2751</t>
2752<t>
2753  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2754  <list style="symbols"> 
2755    <t>
2756      Move "Product Tokens" section (back) into Part 1, as "token" is used
2757      in the definition of the Upgrade header.
2758    </t>
2759    <t>
2760      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2761    </t>
2762    <t>
2763      Copy definition of delta-seconds from Part6 instead of referencing it.
2764    </t>
2765  </list>
2766</t>
2767</section>
2768
2769<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
2770<t>
2771  Closed issues:
2772  <list style="symbols"> 
2773    <t>
2774      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
2775      "Requiring Allow in 405 responses"
2776    </t>
2777    <t>
2778      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
2779      "Redirection vs. Location"
2780    </t>
2781    <t>
2782      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
2783      "Cacheability of 303 response"
2784    </t>
2785    <t>
2786      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
2787      "305 Use Proxy"
2788    </t>
2789    <t>
2790      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
2791      "Classification for Allow header"
2792    </t>
2793    <t>
2794      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
2795      "PUT - 'store under' vs 'store at'"
2796    </t>
2797  </list>
2798</t>
2799</section>
2800
2801</section>
2802
2803</back>
2804</rfc>
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