source: draft-ietf-httpbis/latest/p2-semantics.xml @ 229

Last change on this file since 229 was 229, checked in by julian.reschke@…, 12 years ago

add linking between ABNF rules (does not affect TXT version), relates to #36.

  • Property svn:eol-style set to native
File size: 127.4 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 "March">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY general-syntax             "<xref target='Part1' x:rel='#general.syntax' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY full-date                  "<xref target='Part1' x:rel='#full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-upgrade             "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
61  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
62  <!ENTITY product-tokens             "<xref target='Part1' x:rel='#product.tokens' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
63]>
64<?rfc toc="yes" ?>
65<?rfc symrefs="yes" ?>
66<?rfc sortrefs="yes" ?>
67<?rfc compact="yes"?>
68<?rfc subcompact="no" ?>
69<?rfc linkmailto="no" ?>
70<?rfc editing="no" ?>
71<?rfc comments="yes"?>
72<?rfc inline="yes"?>
73<?rfc-ext allow-markup-in-artwork="yes" ?>
74<?rfc-ext include-references-in-index="yes" ?>
75<rfc obsoletes="2616" category="std"
76     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
77     xmlns:x='http://purl.org/net/xml2rfc/ext'>
78<front>
79
80  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
81
82  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
83    <organization abbrev="Day Software">Day Software</organization>
84    <address>
85      <postal>
86        <street>23 Corporate Plaza DR, Suite 280</street>
87        <city>Newport Beach</city>
88        <region>CA</region>
89        <code>92660</code>
90        <country>USA</country>
91      </postal>
92      <phone>+1-949-706-5300</phone>
93      <facsimile>+1-949-706-5305</facsimile>
94      <email>fielding@gbiv.com</email>
95      <uri>http://roy.gbiv.com/</uri>
96    </address>
97  </author>
98
99  <author initials="J." surname="Gettys" fullname="Jim Gettys">
100    <organization>One Laptop per Child</organization>
101    <address>
102      <postal>
103        <street>21 Oak Knoll Road</street>
104        <city>Carlisle</city>
105        <region>MA</region>
106        <code>01741</code>
107        <country>USA</country>
108      </postal>
109      <email>jg@laptop.org</email>
110      <uri>http://www.laptop.org/</uri>
111    </address>
112  </author>
113 
114  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
115    <organization abbrev="HP">Hewlett-Packard Company</organization>
116    <address>
117      <postal>
118        <street>HP Labs, Large Scale Systems Group</street>
119        <street>1501 Page Mill Road, MS 1177</street>
120        <city>Palo Alto</city>
121        <region>CA</region>
122        <code>94304</code>
123        <country>USA</country>
124      </postal>
125      <email>JeffMogul@acm.org</email>
126    </address>
127  </author>
128
129  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
130    <organization abbrev="Microsoft">Microsoft Corporation</organization>
131    <address>
132      <postal>
133        <street>1 Microsoft Way</street>
134        <city>Redmond</city>
135        <region>WA</region>
136        <code>98052</code>
137        <country>USA</country>
138      </postal>
139      <email>henrikn@microsoft.com</email>
140    </address>
141  </author>
142
143  <author initials="L." surname="Masinter" fullname="Larry Masinter">
144    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
145    <address>
146      <postal>
147        <street>345 Park Ave</street>
148        <city>San Jose</city>
149        <region>CA</region>
150        <code>95110</code>
151        <country>USA</country>
152      </postal>
153      <email>LMM@acm.org</email>
154      <uri>http://larry.masinter.net/</uri>
155    </address>
156  </author>
157 
158  <author initials="P." surname="Leach" fullname="Paul J. Leach">
159    <organization abbrev="Microsoft">Microsoft Corporation</organization>
160    <address>
161      <postal>
162        <street>1 Microsoft Way</street>
163        <city>Redmond</city>
164        <region>WA</region>
165        <code>98052</code>
166      </postal>
167      <email>paulle@microsoft.com</email>
168    </address>
169  </author>
170   
171  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
172    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
173    <address>
174      <postal>
175        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
176        <street>The Stata Center, Building 32</street>
177        <street>32 Vassar Street</street>
178        <city>Cambridge</city>
179        <region>MA</region>
180        <code>02139</code>
181        <country>USA</country>
182      </postal>
183      <email>timbl@w3.org</email>
184      <uri>http://www.w3.org/People/Berners-Lee/</uri>
185    </address>
186  </author>
187
188  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
189    <organization abbrev="W3C">World Wide Web Consortium</organization>
190    <address>
191      <postal>
192        <street>W3C / ERCIM</street>
193        <street>2004, rte des Lucioles</street>
194        <city>Sophia-Antipolis</city>
195        <region>AM</region>
196        <code>06902</code>
197        <country>France</country>
198      </postal>
199      <email>ylafon@w3.org</email>
200      <uri>http://www.raubacapeu.net/people/yves/</uri>
201    </address>
202  </author>
203
204  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
205    <organization abbrev="greenbytes">greenbytes GmbH</organization>
206    <address>
207      <postal>
208        <street>Hafenweg 16</street>
209        <city>Muenster</city><region>NW</region><code>48155</code>
210        <country>Germany</country>
211      </postal>
212      <phone>+49 251 2807760</phone>   
213      <facsimile>+49 251 2807761</facsimile>   
214      <email>julian.reschke@greenbytes.de</email>       
215      <uri>http://greenbytes.de/tech/webdav/</uri>     
216    </address>
217  </author>
218
219  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
220
221<abstract>
222<t>
223   The Hypertext Transfer Protocol (HTTP) is an application-level
224   protocol for distributed, collaborative, hypermedia information
225   systems. HTTP has been in use by the World Wide Web global information
226   initiative since 1990. This document is Part 2 of the seven-part specification
227   that defines the protocol referred to as "HTTP/1.1" and, taken together,
228   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
229   as expressed by request methods, request-header fields, response status codes,
230   and response-header fields.
231</t>
232</abstract>
233
234<note title="Editorial Note (To be removed by RFC Editor)">
235  <t>
236    Discussion of this draft should take place on the HTTPBIS working group
237    mailing list (ietf-http-wg@w3.org). The current issues list is
238    at <eref target="http://www.tools.ietf.org/wg/httpbis/trac/report/11"/>
239    and related documents (including fancy diffs) can be found at
240    <eref target="http://www.tools.ietf.org/wg/httpbis/"/>.
241  </t>
242  <t>
243    This draft incorporates those issue resolutions that were either
244    collected in the original RFC2616 errata list (<eref target="http://purl.org/NET/http-errata"/>),
245    or which were agreed upon on the mailing list between October 2006 and
246    November 2007 (as published in "draft-lafon-rfc2616bis-03").
247  </t>
248</note>
249</front>
250<middle>
251<section title="Introduction" anchor="introduction">
252<t>
253   This document defines HTTP/1.1 request and response semantics.  Each HTTP
254   message, as defined in &messaging;, is in the form of either a request or
255   a response.  An HTTP server listens on a connection for HTTP requests and
256   responds to each request, in the order received on that connection, with
257   one or more HTTP response messages.  This document defines the commonly
258   agreed upon semantics of the HTTP uniform interface, the intentions defined
259   by each request method, and the various response messages that might be
260   expected as a result of applying that method for the requested resource.
261</t>
262<t>
263   This document is currently disorganized in order to minimize the changes
264   between drafts and enable reviewers to see the smaller errata changes.
265   The next draft will reorganize the sections to better reflect the content.
266   In particular, the sections will be ordered according to the typical
267   processing of an HTTP request message (after message parsing): resource
268   mapping, general header fields, methods, request modifiers, response
269   status, and resource metadata.  The current mess reflects how widely
270   dispersed these topics and associated requirements had become in
271   <xref target="RFC2616"/>.
272</t>
273
274<section title="Requirements" anchor="intro.requirements">
275<t>
276   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
277   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
278   document are to be interpreted as described in <xref target="RFC2119"/>.
279</t>
280<t>
281   An implementation is not compliant if it fails to satisfy one or more
282   of the &MUST; or &REQUIRED; level requirements for the protocols it
283   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
284   level and all the &SHOULD; level requirements for its protocols is said
285   to be "unconditionally compliant"; one that satisfies all the &MUST;
286   level requirements but not all the &SHOULD; level requirements for its
287   protocols is said to be "conditionally compliant."
288</t>
289</section>
290</section>
291
292<section title="Notational Conventions and Generic Grammar" anchor="notation">
293  <x:anchor-alias value="comment"/>
294  <x:anchor-alias value="DIGIT"/>
295  <x:anchor-alias value="quoted-string"/>
296  <x:anchor-alias value="token"/>
297<t>
298  This specification uses the ABNF syntax defined in &notation-abnf; and
299  the core rules defined in &basic-rules;:
300  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
301  <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>.</cref>
302</t>
303<figure><artwork type="abnf2616">
304  <x:ref>DIGIT</x:ref>         = &lt;DIGIT, defined in &basic-rules;&gt;
305</artwork></figure>
306<figure><artwork type="abnf2616">
307  <x:anchor-alias value="Accept"/>
308  <x:ref>comment</x:ref>       = &lt;comment, defined in &basic-rules;&gt;
309  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &basic-rules;&gt;
310  <x:ref>token</x:ref>         = &lt;token, defined in &basic-rules;&gt;
311</artwork></figure>
312<t anchor="abnf.dependencies">
313  <x:anchor-alias value="absoluteURI"/>
314  <x:anchor-alias value="Accept"/>
315  <x:anchor-alias value="Accept-Charset"/>
316  <x:anchor-alias value="Accept-Encoding"/>
317  <x:anchor-alias value="Accept-Language"/>
318  <x:anchor-alias value="Accept-Ranges"/>
319  <x:anchor-alias value="Age"/>
320  <x:anchor-alias value="Authorization"/>
321  <x:anchor-alias value="ETag"/>
322  <x:anchor-alias value="fragment"/>
323  <x:anchor-alias value="Host"/>
324  <x:anchor-alias value="HTTP-date"/>
325  <x:anchor-alias value="If-Match"/>
326  <x:anchor-alias value="If-Modified-Since"/>
327  <x:anchor-alias value="If-None-Match"/>
328  <x:anchor-alias value="If-Range"/>
329  <x:anchor-alias value="If-Unmodified-Since"/>
330  <x:anchor-alias value="product"/>
331  <x:anchor-alias value="Proxy-Authenticate"/>
332  <x:anchor-alias value="Proxy-Authorization"/>
333  <x:anchor-alias value="Range"/>
334  <x:anchor-alias value="relativeURI"/>
335  <x:anchor-alias value="TE"/>
336  <x:anchor-alias value="Vary"/>
337  <x:anchor-alias value="WWW-Authenticate"/>
338  The ABNF rules below are defined in other parts:
339</t>
340<figure><!--Part1--><artwork type="abnf2616">
341  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in &general-syntax;&gt;
342  <x:ref>fragment</x:ref>      = &lt;fragment, defined in &general-syntax;&gt;
343  <x:ref>Host</x:ref>          = &lt;Host, defined in &header-host;&gt;
344  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
345  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
346  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in &general-syntax;&gt;
347  <x:ref>TE</x:ref>            = &lt;TE, defined in &header-te;&gt;
348</artwork></figure>
349<figure><!--Part3--><artwork type="abnf2616">
350  <x:ref>Accept</x:ref>        = &lt;Accept, defined in &header-accept;&gt;
351  <x:ref>Accept-Charset</x:ref> =
352             &lt;Accept-Charset, defined in &header-accept-charset;&gt;
353  <x:ref>Accept-Encoding</x:ref> =
354             &lt;Accept-Encoding, defined in &header-accept-encoding;&gt;
355  <x:ref>Accept-Language</x:ref> =
356             &lt;Accept-Language, defined in &header-accept-language;&gt;
357</artwork></figure>
358<figure><!--Part4--><artwork type="abnf2616">
359  <x:ref>ETag</x:ref>          = &lt;ETag, defined in &header-etag;&gt;
360  <x:ref>If-Match</x:ref>      = &lt;If-Match, defined in &header-if-match;&gt;
361  <x:ref>If-Modified-Since</x:ref> =
362             &lt;If-Modified-Since, defined in &header-if-modified-since;&gt;
363  <x:ref>If-None-Match</x:ref> = &lt;If-None-Match, defined in &header-if-none-match;&gt;
364  <x:ref>If-Unmodified-Since</x:ref> =
365             &lt;If-Unmodified-Since, defined in &header-if-unmodified-since;&gt;
366</artwork></figure>
367<figure><!--Part5--><artwork type="abnf2616">
368  <x:ref>Accept-Ranges</x:ref> = &lt;Accept-Ranges, defined in &header-accept-ranges;&gt;
369  <x:ref>If-Range</x:ref>      = &lt;If-Range, defined in &header-if-range;&gt;
370  <x:ref>Range</x:ref>         = &lt;Range, defined in &header-range;&gt;
371</artwork></figure>
372<figure><!--Part6--><artwork type="abnf2616">
373  <x:ref>Age</x:ref>           = &lt;Age, defined in &header-age;&gt;
374  <x:ref>Vary</x:ref>          = &lt;Vary, defined in &header-vary;&gt;
375</artwork><!--Part7--></figure>
376<figure><artwork type="abnf2616">
377  <x:ref>Authorization</x:ref> = &lt;Authorization, defined in &header-authorization;&gt;
378  <x:ref>Proxy-Authenticate</x:ref> =
379             &lt;Proxy-Authenticate, defined in &header-proxy-authenticate;&gt;
380  <x:ref>Proxy-Authorization</x:ref> =
381             &lt;Proxy-Authorization, defined in &header-proxy-authorization;&gt;
382  <x:ref>WWW-Authenticate</x:ref> =
383             &lt;WWW-Authenticate, defined in &header-www-authenticate;&gt;
384</artwork></figure>
385</section>
386
387<section title="Method" anchor="method">
388  <x:anchor-alias value="Method"/>
389  <x:anchor-alias value="extension-method"/>
390<t>
391   The Method  token indicates the method to be performed on the
392   resource identified by the Request-URI. The method is case-sensitive.
393</t>
394<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
395  <x:ref>Method</x:ref>         = "OPTIONS"                ; <xref target="OPTIONS"/>
396                 | "GET"                    ; <xref target="GET"/>
397                 | "HEAD"                   ; <xref target="HEAD"/>
398                 | "POST"                   ; <xref target="POST"/>
399                 | "PUT"                    ; <xref target="PUT"/>
400                 | "DELETE"                 ; <xref target="DELETE"/>
401                 | "TRACE"                  ; <xref target="TRACE"/>
402                 | "CONNECT"                ; <xref target="CONNECT"/>
403                 | <x:ref>extension-method</x:ref>
404  <x:ref>extension-method</x:ref> = <x:ref>token</x:ref>
405</artwork></figure>
406<t>
407   The list of methods allowed by a resource can be specified in an
408   Allow header field (<xref target="header.allow"/>). The return code of the response
409   always notifies the client whether a method is currently allowed on a
410   resource, since the set of allowed methods can change dynamically. An
411   origin server &SHOULD; return the status code 405 (Method Not Allowed)
412   if the method is known by the origin server but not allowed for the
413   requested resource, and 501 (Not Implemented) if the method is
414   unrecognized or not implemented by the origin server. The methods GET
415   and HEAD &MUST; be supported by all general-purpose servers. All other
416   methods are &OPTIONAL;; however, if the above methods are implemented,
417   they &MUST; be implemented with the same semantics as those specified
418   in <xref target="method.definitions"/>.
419</t>
420</section>
421
422<section title="Request Header Fields" anchor="request.header.fields">
423  <x:anchor-alias value="extension-code"/>
424  <x:anchor-alias value="request-header"/>
425<t>
426   The request-header fields allow the client to pass additional
427   information about the request, and about the client itself, to the
428   server. These fields act as request modifiers, with semantics
429   equivalent to the parameters on a programming language method
430   invocation.
431</t>
432<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
433  <x:ref>request-header</x:ref> = <x:ref>Accept</x:ref>                   ; &header-accept;
434                 | <x:ref>Accept-Charset</x:ref>           ; &header-accept-charset;
435                 | <x:ref>Accept-Encoding</x:ref>          ; &header-accept-encoding;
436                 | <x:ref>Accept-Language</x:ref>          ; &header-accept-language;
437                 | <x:ref>Authorization</x:ref>            ; &header-authorization;
438                 | <x:ref>Expect</x:ref>                   ; <xref target="header.expect"/>
439                 | <x:ref>From</x:ref>                     ; <xref target="header.from"/>
440                 | <x:ref>Host</x:ref>                     ; &header-host;
441                 | <x:ref>If-Match</x:ref>                 ; &header-if-match;
442                 | <x:ref>If-Modified-Since</x:ref>        ; &header-if-modified-since;
443                 | <x:ref>If-None-Match</x:ref>            ; &header-if-none-match;
444                 | <x:ref>If-Range</x:ref>                 ; &header-if-range;
445                 | <x:ref>If-Unmodified-Since</x:ref>      ; &header-if-unmodified-since;
446                 | <x:ref>Max-Forwards</x:ref>             ; <xref target="header.max-forwards"/>
447                 | <x:ref>Proxy-Authorization</x:ref>      ; &header-proxy-authorization;
448                 | <x:ref>Range</x:ref>                    ; &header-range;
449                 | <x:ref>Referer</x:ref>                  ; <xref target="header.referer"/>
450                 | <x:ref>TE</x:ref>                       ; &header-te;
451                 | <x:ref>User-Agent</x:ref>               ; <xref target="header.user-agent"/>
452</artwork></figure>
453<t>
454   Request-header field names can be extended reliably only in
455   combination with a change in the protocol version. However, new or
456   experimental header fields &MAY; be given the semantics of request-header
457   fields if all parties in the communication recognize them to
458   be request-header fields. Unrecognized header fields are treated as
459   entity-header fields.
460</t>
461</section>
462
463<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
464  <x:anchor-alias value="Reason-Phrase"/>
465  <x:anchor-alias value="Status-Code"/>
466<t>
467   The Status-Code element is a 3-digit integer result code of the
468   attempt to understand and satisfy the request. The status codes listed
469   below are defined in <xref target="status.codes"/>.
470   The Reason-Phrase is intended to give a short
471   textual description of the Status-Code. The Status-Code is intended
472   for use by automata and the Reason-Phrase is intended for the human
473   user. The client is not required to examine or display the Reason-Phrase.
474</t>
475<t> 
476   The individual values of the numeric status codes defined for
477   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
478   presented below. The reason phrases listed here are only
479   recommendations -- they &MAY; be replaced by local equivalents without
480   affecting the protocol.
481</t>
482<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
483  <x:ref>Status-Code</x:ref>    =
484         "100"  ; <xref target="status.100"/>: Continue
485       | "101"  ; <xref target="status.101"/>: Switching Protocols
486       | "200"  ; <xref target="status.200"/>: OK
487       | "201"  ; <xref target="status.201"/>: Created
488       | "202"  ; <xref target="status.202"/>: Accepted
489       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
490       | "204"  ; <xref target="status.204"/>: No Content
491       | "205"  ; <xref target="status.205"/>: Reset Content
492       | "206"  ; <xref target="status.206"/>: Partial Content
493       | "300"  ; <xref target="status.300"/>: Multiple Choices
494       | "301"  ; <xref target="status.301"/>: Moved Permanently
495       | "302"  ; <xref target="status.302"/>: Found
496       | "303"  ; <xref target="status.303"/>: See Other
497       | "304"  ; <xref target="status.304"/>: Not Modified
498       | "305"  ; <xref target="status.305"/>: Use Proxy
499       | "307"  ; <xref target="status.307"/>: Temporary Redirect
500       | "400"  ; <xref target="status.400"/>: Bad Request
501       | "401"  ; <xref target="status.401"/>: Unauthorized
502       | "402"  ; <xref target="status.402"/>: Payment Required
503       | "403"  ; <xref target="status.403"/>: Forbidden
504       | "404"  ; <xref target="status.404"/>: Not Found
505       | "405"  ; <xref target="status.405"/>: Method Not Allowed
506       | "406"  ; <xref target="status.406"/>: Not Acceptable
507       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
508       | "408"  ; <xref target="status.408"/>: Request Time-out
509       | "409"  ; <xref target="status.409"/>: Conflict
510       | "410"  ; <xref target="status.410"/>: Gone
511       | "411"  ; <xref target="status.411"/>: Length Required
512       | "412"  ; <xref target="status.412"/>: Precondition Failed
513       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
514       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
515       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
516       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
517       | "417"  ; <xref target="status.417"/>: Expectation Failed
518       | "500"  ; <xref target="status.500"/>: Internal Server Error
519       | "501"  ; <xref target="status.501"/>: Not Implemented
520       | "502"  ; <xref target="status.502"/>: Bad Gateway
521       | "503"  ; <xref target="status.503"/>: Service Unavailable
522       | "504"  ; <xref target="status.504"/>: Gateway Time-out
523       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
524       | <x:ref>extension-code</x:ref>
525
526  <x:ref>extension-code</x:ref> = 3<x:ref>DIGIT</x:ref>
527  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
528</artwork></figure>
529<t>
530   HTTP status codes are extensible. HTTP applications are not required
531   to understand the meaning of all registered status codes, though such
532   understanding is obviously desirable. However, applications &MUST;
533   understand the class of any status code, as indicated by the first
534   digit, and treat any unrecognized response as being equivalent to the
535   x00 status code of that class, with the exception that an
536   unrecognized response &MUST-NOT; be cached. For example, if an
537   unrecognized status code of 431 is received by the client, it can
538   safely assume that there was something wrong with its request and
539   treat the response as if it had received a 400 status code. In such
540   cases, user agents &SHOULD; present to the user the entity returned
541   with the response, since that entity is likely to include human-readable
542   information which will explain the unusual status.
543</t>
544</section>
545
546<section title="Response Header Fields" anchor="response.header.fields">
547  <x:anchor-alias value="response-header"/>
548<t>
549   The response-header fields allow the server to pass additional
550   information about the response which cannot be placed in the Status-Line.
551   These header fields give information about the server and about
552   further access to the resource identified by the Request-URI.
553</t>
554<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
555  <x:ref>response-header</x:ref> = <x:ref>Accept-Ranges</x:ref>           ; &header-accept-ranges;
556                  | <x:ref>Age</x:ref>                     ; &header-age;
557                  | <x:ref>ETag</x:ref>                    ; &header-etag;
558                  | <x:ref>Location</x:ref>                ; <xref target="header.location"/>
559                  | <x:ref>Proxy-Authenticate</x:ref>      ; &header-proxy-authenticate;
560                  | <x:ref>Retry-After</x:ref>             ; <xref target="header.retry-after"/>
561                  | <x:ref>Server</x:ref>                  ; <xref target="header.server"/>
562                  | <x:ref>Vary</x:ref>                    ; &header-vary;
563                  | <x:ref>WWW-Authenticate</x:ref>        ; &header-www-authenticate;
564</artwork></figure>
565<t>
566   Response-header field names can be extended reliably only in
567   combination with a change in the protocol version. However, new or
568   experimental header fields &MAY; be given the semantics of response-header
569   fields if all parties in the communication recognize them to
570   be response-header fields. Unrecognized header fields are treated as
571   entity-header fields.
572</t>
573</section>
574
575<section title="Entity" anchor="entity">
576<t>
577   Request and Response messages &MAY; transfer an entity if not otherwise
578   restricted by the request method or response status code. An entity
579   consists of entity-header fields and an entity-body, although some
580   responses will only include the entity-headers. HTTP entity-body and
581   entity-header fields are defined in &payload;.
582</t>
583<t>
584   An entity-body is only present in a message when a message-body is
585   present, as described in &message-body;. The entity-body is obtained
586   from the message-body by decoding any Transfer-Encoding that might
587   have been applied to ensure safe and proper transfer of the message.
588</t>
589</section>
590
591
592<section title="Method Definitions" anchor="method.definitions">
593<t>
594   The set of common methods for HTTP/1.1 is defined below. Although
595   this set can be expanded, additional methods cannot be assumed to
596   share the same semantics for separately extended clients and servers.
597</t>
598
599<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
600
601<section title="Safe Methods" anchor="safe.methods">
602<t>
603   Implementors should be aware that the software represents the user in
604   their interactions over the Internet, and should be careful to allow
605   the user to be aware of any actions they might take which may have an
606   unexpected significance to themselves or others.
607</t>
608<t>
609   In particular, the convention has been established that the GET and
610   HEAD methods &SHOULD-NOT;  have the significance of taking an action
611   other than retrieval. These methods ought to be considered "safe".
612   This allows user agents to represent other methods, such as POST, PUT
613   and DELETE, in a special way, so that the user is made aware of the
614   fact that a possibly unsafe action is being requested.
615</t>
616<t>
617   Naturally, it is not possible to ensure that the server does not
618   generate side-effects as a result of performing a GET request; in
619   fact, some dynamic resources consider that a feature. The important
620   distinction here is that the user did not request the side-effects,
621   so therefore cannot be held accountable for them.
622</t>
623</section>
624
625<section title="Idempotent Methods" anchor="idempotent.methods">
626<t>
627   Methods can also have the property of "idempotence" in that (aside
628   from error or expiration issues) the side-effects of N &gt; 0 identical
629   requests is the same as for a single request. The methods GET, HEAD,
630   PUT and DELETE share this property. Also, the methods OPTIONS and
631   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
632</t>
633<t>
634   However, it is possible that a sequence of several requests is non-idempotent,
635   even if all of the methods executed in that sequence are
636   idempotent. (A sequence is idempotent if a single execution of the
637   entire sequence always yields a result that is not changed by a
638   reexecution of all, or part, of that sequence.) For example, a
639   sequence is non-idempotent if its result depends on a value that is
640   later modified in the same sequence.
641</t>
642<t>
643   A sequence that never has side effects is idempotent, by definition
644   (provided that no concurrent operations are being executed on the
645   same set of resources).
646</t>
647</section>
648</section>
649
650<section title="OPTIONS" anchor="OPTIONS">
651  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
652  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
653<t>
654   The OPTIONS method represents a request for information about the
655   communication options available on the request/response chain
656   identified by the Request-URI. This method allows the client to
657   determine the options and/or requirements associated with a resource,
658   or the capabilities of a server, without implying a resource action
659   or initiating a resource retrieval.
660</t>
661<t>
662   Responses to this method are not cacheable.
663</t>
664<t>
665   If the OPTIONS request includes an entity-body (as indicated by the
666   presence of Content-Length or Transfer-Encoding), then the media type
667   &MUST; be indicated by a Content-Type field. Although this
668   specification does not define any use for such a body, future
669   extensions to HTTP might use the OPTIONS body to make more detailed
670   queries on the server. A server that does not support such an
671   extension &MAY; discard the request body.
672</t>
673<t>
674   If the Request-URI is an asterisk ("*"), the OPTIONS request is
675   intended to apply to the server in general rather than to a specific
676   resource. Since a server's communication options typically depend on
677   the resource, the "*" request is only useful as a "ping" or "no-op"
678   type of method; it does nothing beyond allowing the client to test
679   the capabilities of the server. For example, this can be used to test
680   a proxy for HTTP/1.1 compliance (or lack thereof).
681</t>
682<t>
683   If the Request-URI is not an asterisk, the OPTIONS request applies
684   only to the options that are available when communicating with that
685   resource.
686</t>
687<t>
688   A 200 response &SHOULD; include any header fields that indicate
689   optional features implemented by the server and applicable to that
690   resource (e.g., Allow), possibly including extensions not defined by
691   this specification. The response body, if any, &SHOULD; also include
692   information about the communication options. The format for such a
693   body is not defined by this specification, but might be defined by
694   future extensions to HTTP. Content negotiation &MAY; be used to select
695   the appropriate response format. If no response body is included, the
696   response &MUST; include a Content-Length field with a field-value of
697   "0".
698</t>
699<t>
700   The Max-Forwards request-header field &MAY; be used to target a
701   specific proxy in the request chain. When a proxy receives an OPTIONS
702   request on an absoluteURI for which request forwarding is permitted,
703   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
704   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
705   instead, the proxy &SHOULD; respond with its own communication options.
706   If the Max-Forwards field-value is an integer greater than zero, the
707   proxy &MUST; decrement the field-value when it forwards the request. If
708   no Max-Forwards field is present in the request, then the forwarded
709   request &MUST-NOT; include a Max-Forwards field.
710</t>
711</section>
712
713<section title="GET" anchor="GET">
714  <iref primary="true" item="GET method" x:for-anchor=""/>
715  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
716<t>
717   The GET method means retrieve whatever information (in the form of an
718   entity) is identified by the Request-URI. If the Request-URI refers
719   to a data-producing process, it is the produced data which shall be
720   returned as the entity in the response and not the source text of the
721   process, unless that text happens to be the output of the process.
722</t>
723<t>
724   The semantics of the GET method change to a "conditional GET" if the
725   request message includes an If-Modified-Since, If-Unmodified-Since,
726   If-Match, If-None-Match, or If-Range header field. A conditional GET
727   method requests that the entity be transferred only under the
728   circumstances described by the conditional header field(s). The
729   conditional GET method is intended to reduce unnecessary network
730   usage by allowing cached entities to be refreshed without requiring
731   multiple requests or transferring data already held by the client.
732</t>
733<t>
734   The semantics of the GET method change to a "partial GET" if the
735   request message includes a Range header field. A partial GET requests
736   that only part of the entity be transferred, as described in &header-range;.
737   The partial GET method is intended to reduce unnecessary
738   network usage by allowing partially-retrieved entities to be
739   completed without transferring data already held by the client.
740</t>
741<t>
742   The response to a GET request is cacheable if and only if it meets
743   the requirements for HTTP caching described in &caching;.
744</t>
745<t>
746   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
747</t>
748</section>
749
750<section title="HEAD" anchor="HEAD">
751  <iref primary="true" item="HEAD method" x:for-anchor=""/>
752  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
753<t>
754   The HEAD method is identical to GET except that the server &MUST-NOT;
755   return a message-body in the response. The metainformation contained
756   in the HTTP headers in response to a HEAD request &SHOULD; be identical
757   to the information sent in response to a GET request. This method can
758   be used for obtaining metainformation about the entity implied by the
759   request without transferring the entity-body itself. This method is
760   often used for testing hypertext links for validity, accessibility,
761   and recent modification.
762</t>
763<t>
764   The response to a HEAD request &MAY; be cacheable in the sense that the
765   information contained in the response &MAY; be used to update a
766   previously cached entity from that resource. If the new field values
767   indicate that the cached entity differs from the current entity (as
768   would be indicated by a change in Content-Length, Content-MD5, ETag
769   or Last-Modified), then the cache &MUST; treat the cache entry as
770   stale.
771</t>
772</section>
773
774<section title="POST" anchor="POST">
775  <iref primary="true" item="POST method" x:for-anchor=""/>
776  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
777<t>
778   The POST method is used to request that the origin server accept the
779   entity enclosed in the request as data to be processed by the resource
780   identified by the Request-URI in the Request-Line. POST is designed
781   to allow a uniform method to cover the following functions:
782  <list style="symbols">
783    <t>
784      Annotation of existing resources;
785    </t>
786    <t>
787        Posting a message to a bulletin board, newsgroup, mailing list,
788        or similar group of articles;
789    </t>
790    <t>
791        Providing a block of data, such as the result of submitting a
792        form, to a data-handling process;
793    </t>
794    <t>
795        Extending a database through an append operation.
796    </t>
797  </list>
798</t>
799<t>
800   The actual function performed by the POST method is determined by the
801   server and is usually dependent on the Request-URI.
802</t>
803<t>
804   The action performed by the POST method might not result in a
805   resource that can be identified by a URI. In this case, either 200
806   (OK) or 204 (No Content) is the appropriate response status,
807   depending on whether or not the response includes an entity that
808   describes the result.
809</t>
810<t>
811   If a resource has been created on the origin server, the response
812   &SHOULD; be 201 (Created) and contain an entity which describes the
813   status of the request and refers to the new resource, and a Location
814   header (see <xref target="header.location"/>).
815</t>
816<t>
817   Responses to this method are not cacheable, unless the response
818   includes appropriate Cache-Control or Expires header fields. However,
819   the 303 (See Other) response can be used to direct the user agent to
820   retrieve a cacheable resource.
821</t>
822</section>
823
824<section title="PUT" anchor="PUT">
825  <iref primary="true" item="PUT method" x:for-anchor=""/>
826  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
827<t>
828   The PUT method requests that the enclosed entity be stored under the
829   supplied Request-URI. If the Request-URI refers to an already
830   existing resource, the enclosed entity &SHOULD; be considered as a
831   modified version of the one residing on the origin server. If the
832   Request-URI does not point to an existing resource, and that URI is
833   capable of being defined as a new resource by the requesting user
834   agent, the origin server can create the resource with that URI. If a
835   new resource is created at the Request-URI, the origin server &MUST;
836         inform the user agent
837   via the 201 (Created) response. If an existing resource is modified,
838   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
839   to indicate successful completion of the request. If the resource
840   could not be created or modified with the Request-URI, an appropriate
841   error response &SHOULD; be given that reflects the nature of the
842   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
843   (e.g. Content-Range) headers that it does not understand or implement
844   and &MUST; return a 501 (Not Implemented) response in such cases.
845</t>
846<t>
847   If the request passes through a cache and the Request-URI identifies
848   one or more currently cached entities, those entries &SHOULD; be
849   treated as stale. Responses to this method are not cacheable.
850</t>
851<t>
852   The fundamental difference between the POST and PUT requests is
853   reflected in the different meaning of the Request-URI. The URI in a
854   POST request identifies the resource that will handle the enclosed
855   entity. That resource might be a data-accepting process, a gateway to
856   some other protocol, or a separate entity that accepts annotations.
857   In contrast, the URI in a PUT request identifies the entity enclosed
858   with the request -- the user agent knows what URI is intended and the
859   server &MUST-NOT; attempt to apply the request to some other resource.
860   If the server desires that the request be applied to a different URI,
861   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
862   then make its own decision regarding whether or not to redirect the
863   request.
864</t>
865<t>
866   A single resource &MAY; be identified by many different URIs. For
867   example, an article might have a URI for identifying "the current
868   version" which is separate from the URI identifying each particular
869   version. In this case, a PUT request on a general URI might result in
870   several other URIs being defined by the origin server.
871</t>
872<t>
873   HTTP/1.1 does not define how a PUT method affects the state of an
874   origin server.
875</t>
876<t>
877   Unless otherwise specified for a particular entity-header, the
878   entity-headers in the PUT request &SHOULD; be applied to the resource
879   created or modified by the PUT.
880</t>
881</section>
882
883<section title="DELETE" anchor="DELETE">
884  <iref primary="true" item="DELETE method" x:for-anchor=""/>
885  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
886<t>
887   The DELETE method requests that the origin server delete the resource
888   identified by the Request-URI. This method &MAY; be overridden by human
889   intervention (or other means) on the origin server. The client cannot
890   be guaranteed that the operation has been carried out, even if the
891   status code returned from the origin server indicates that the action
892   has been completed successfully. However, the server &SHOULD-NOT; 
893   indicate success unless, at the time the response is given, it
894   intends to delete the resource or move it to an inaccessible
895   location.
896</t>
897<t>
898   A successful response &SHOULD; be 200 (OK) if the response includes an
899   entity describing the status, 202 (Accepted) if the action has not
900   yet been enacted, or 204 (No Content) if the action has been enacted
901   but the response does not include an entity.
902</t>
903<t>
904   If the request passes through a cache and the Request-URI identifies
905   one or more currently cached entities, those entries &SHOULD; be
906   treated as stale. Responses to this method are not cacheable.
907</t>
908</section>
909
910<section title="TRACE" anchor="TRACE">
911  <iref primary="true" item="TRACE method" x:for-anchor=""/>
912  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
913<t>
914   The TRACE method is used to invoke a remote, application-layer loop-back
915   of the request message. The final recipient of the request
916   &SHOULD; reflect the message received back to the client as the
917   entity-body of a 200 (OK) response. The final recipient is either the
918   origin server or the first proxy or gateway to receive a Max-Forwards
919   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
920   &MUST-NOT; include an entity.
921</t>
922<t>
923   TRACE allows the client to see what is being received at the other
924   end of the request chain and use that data for testing or diagnostic
925   information. The value of the Via header field (&header-via;) is of
926   particular interest, since it acts as a trace of the request chain.
927   Use of the Max-Forwards header field allows the client to limit the
928   length of the request chain, which is useful for testing a chain of
929   proxies forwarding messages in an infinite loop.
930</t>
931<t>
932   If the request is valid, the response &SHOULD; contain the entire
933   request message in the entity-body, with a Content-Type of
934   "message/http". Responses to this method &MUST-NOT; be cached.
935</t>
936</section>
937
938<section title="CONNECT" anchor="CONNECT">
939  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
940  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
941<t>
942   This specification reserves the method name CONNECT for use with a
943   proxy that can dynamically switch to being a tunnel (e.g. SSL
944   tunneling <xref target="Luo1998"/>).
945</t>
946</section>
947</section>
948
949
950<section title="Status Code Definitions" anchor="status.codes">
951<t>
952   Each Status-Code is described below, including a description of which
953   method(s) it can follow and any metainformation required in the
954   response.
955</t>
956
957<section title="Informational 1xx" anchor="status.1xx">
958<t>
959   This class of status code indicates a provisional response,
960   consisting only of the Status-Line and optional headers, and is
961   terminated by an empty line. There are no required headers for this
962   class of status code. Since HTTP/1.0 did not define any 1xx status
963   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
964   except under experimental conditions.
965</t>
966<t>
967   A client &MUST; be prepared to accept one or more 1xx status responses
968   prior to a regular response, even if the client does not expect a 100
969   (Continue) status message. Unexpected 1xx status responses &MAY; be
970   ignored by a user agent.
971</t>
972<t>
973   Proxies &MUST; forward 1xx responses, unless the connection between the
974   proxy and its client has been closed, or unless the proxy itself
975   requested the generation of the 1xx response. (For example, if a
976   proxy adds a "Expect: 100-continue" field when it forwards a request,
977   then it need not forward the corresponding 100 (Continue)
978   response(s).)
979</t>
980
981<section title="100 Continue" anchor="status.100">
982  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
983  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
984<t>
985   The client &SHOULD; continue with its request. This interim response is
986   used to inform the client that the initial part of the request has
987   been received and has not yet been rejected by the server. The client
988   &SHOULD; continue by sending the remainder of the request or, if the
989   request has already been completed, ignore this response. The server
990   &MUST; send a final response after the request has been completed. See
991   &use100; for detailed discussion of the use and handling of this
992   status code.
993</t>
994</section>
995
996<section title="101 Switching Protocols" anchor="status.101">
997  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
998  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
999<t>
1000   The server understands and is willing to comply with the client's
1001   request, via the Upgrade message header field (&header-upgrade;), for a
1002   change in the application protocol being used on this connection. The
1003   server will switch protocols to those defined by the response's
1004   Upgrade header field immediately after the empty line which
1005   terminates the 101 response.
1006</t>
1007<t>
1008   The protocol &SHOULD; be switched only when it is advantageous to do
1009   so. For example, switching to a newer version of HTTP is advantageous
1010   over older versions, and switching to a real-time, synchronous
1011   protocol might be advantageous when delivering resources that use
1012   such features.
1013</t>
1014</section>
1015</section>
1016
1017<section title="Successful 2xx" anchor="status.2xx">
1018<t>
1019   This class of status code indicates that the client's request was
1020   successfully received, understood, and accepted.
1021</t>
1022
1023<section title="200 OK" anchor="status.200">
1024  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1025  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1026<t>
1027   The request has succeeded. The information returned with the response
1028   is dependent on the method used in the request, for example:
1029  <list style="hanging">
1030    <t hangText="GET">
1031          an entity corresponding to the requested resource is sent in
1032          the response;
1033    </t>
1034    <t hangText="HEAD">
1035          the entity-header fields corresponding to the requested
1036          resource are sent in the response without any message-body;
1037    </t>
1038    <t hangText="POST">
1039      an entity describing or containing the result of the action;
1040    </t>
1041    <t hangText="TRACE">
1042      an entity containing the request message as received by the
1043      end server.
1044    </t>
1045  </list>
1046</t>
1047</section>
1048
1049<section title="201 Created" anchor="status.201">
1050  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1051  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1052<t>
1053   The request has been fulfilled and resulted in a new resource being
1054   created. The newly created resource can be referenced by the URI(s)
1055   returned in the entity of the response, with the most specific URI
1056   for the resource given by a Location header field. The response
1057   &SHOULD; include an entity containing a list of resource
1058   characteristics and location(s) from which the user or user agent can
1059   choose the one most appropriate. The entity format is specified by
1060   the media type given in the Content-Type header field. The origin
1061   server &MUST; create the resource before returning the 201 status code.
1062   If the action cannot be carried out immediately, the server &SHOULD;
1063   respond with 202 (Accepted) response instead.
1064</t>
1065<t>
1066   A 201 response &MAY; contain an ETag response header field indicating
1067   the current value of the entity tag for the requested variant just
1068   created, see &header-etag;.
1069</t>
1070</section>
1071
1072<section title="202 Accepted" anchor="status.202">
1073  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1074  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1075<t>
1076   The request has been accepted for processing, but the processing has
1077   not been completed.  The request might or might not eventually be
1078   acted upon, as it might be disallowed when processing actually takes
1079   place. There is no facility for re-sending a status code from an
1080   asynchronous operation such as this.
1081</t>
1082<t>
1083   The 202 response is intentionally non-committal. Its purpose is to
1084   allow a server to accept a request for some other process (perhaps a
1085   batch-oriented process that is only run once per day) without
1086   requiring that the user agent's connection to the server persist
1087   until the process is completed. The entity returned with this
1088   response &SHOULD; include an indication of the request's current status
1089   and either a pointer to a status monitor or some estimate of when the
1090   user can expect the request to be fulfilled.
1091</t>
1092</section>
1093
1094<section title="203 Non-Authoritative Information" anchor="status.203">
1095  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1096  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1097<t>
1098   The returned metainformation in the entity-header is not the
1099   definitive set as available from the origin server, but is gathered
1100   from a local or a third-party copy. The set presented &MAY; be a subset
1101   or superset of the original version. For example, including local
1102   annotation information about the resource might result in a superset
1103   of the metainformation known by the origin server. Use of this
1104   response code is not required and is only appropriate when the
1105   response would otherwise be 200 (OK).
1106</t>
1107</section>
1108
1109<section title="204 No Content" anchor="status.204">
1110  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1111  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1112<t>
1113   The server has fulfilled the request but does not need to return an
1114   entity-body, and might want to return updated metainformation. The
1115   response &MAY; include new or updated metainformation in the form of
1116   entity-headers, which if present &SHOULD; be associated with the
1117   requested variant.
1118</t>
1119<t>
1120   If the client is a user agent, it &SHOULD-NOT;  change its document view
1121   from that which caused the request to be sent. This response is
1122   primarily intended to allow input for actions to take place without
1123   causing a change to the user agent's active document view, although
1124   any new or updated metainformation &SHOULD; be applied to the document
1125   currently in the user agent's active view.
1126</t>
1127<t>
1128   The 204 response &MUST-NOT; include a message-body, and thus is always
1129   terminated by the first empty line after the header fields.
1130</t>
1131</section>
1132
1133<section title="205 Reset Content" anchor="status.205">
1134  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1135  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1136<t>
1137   The server has fulfilled the request and the user agent &SHOULD; reset
1138   the document view which caused the request to be sent. This response
1139   is primarily intended to allow input for actions to take place via
1140   user input, followed by a clearing of the form in which the input is
1141   given so that the user can easily initiate another input action. The
1142   response &MUST-NOT; include an entity.
1143</t>
1144</section>
1145
1146<section title="206 Partial Content" anchor="status.206">
1147  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1148  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1149<t>
1150   The server has fulfilled the partial GET request for the resource
1151   and the enclosed entity is a partial representation as defined in &range;.
1152</t>
1153</section>
1154</section>
1155
1156<section title="Redirection 3xx" anchor="status.3xx">
1157<t>
1158   This class of status code indicates that further action needs to be
1159   taken by the user agent in order to fulfill the request.  The action
1160   required &MAY; be carried out by the user agent without interaction
1161   with the user if and only if the method used in the second request is
1162   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1163   such loops generate network traffic for each redirection.
1164  <list><t>
1165      <x:h>Note:</x:h> previous versions of this specification recommended a
1166      maximum of five redirections. Content developers should be aware
1167      that there might be clients that implement such a fixed
1168      limitation.
1169  </t></list>
1170</t>
1171
1172<section title="300 Multiple Choices" anchor="status.300">
1173  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1174  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1175<t>
1176   The requested resource corresponds to any one of a set of
1177   representations, each with its own specific location, and agent-driven
1178   negotiation information (&content-negotiation;) is being provided so that
1179   the user (or user agent) can select a preferred representation and
1180   redirect its request to that location.
1181</t>
1182<t>
1183   Unless it was a HEAD request, the response &SHOULD; include an entity
1184   containing a list of resource characteristics and location(s) from
1185   which the user or user agent can choose the one most appropriate. The
1186   entity format is specified by the media type given in the Content-Type
1187   header field. Depending upon the format and the capabilities of
1188   the user agent, selection of the most appropriate choice &MAY; be
1189   performed automatically. However, this specification does not define
1190   any standard for such automatic selection.
1191</t>
1192<t>
1193   If the server has a preferred choice of representation, it &SHOULD;
1194   include the specific URI for that representation in the Location
1195   field; user agents &MAY; use the Location field value for automatic
1196   redirection. This response is cacheable unless indicated otherwise.
1197</t>
1198</section>
1199
1200<section title="301 Moved Permanently" anchor="status.301">
1201  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1202  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1203<t>
1204   The requested resource has been assigned a new permanent URI and any
1205   future references to this resource &SHOULD; use one of the returned
1206   URIs.  Clients with link editing capabilities ought to automatically
1207   re-link references to the Request-URI to one or more of the new
1208   references returned by the server, where possible. This response is
1209   cacheable unless indicated otherwise.
1210</t>
1211<t>
1212   The new permanent URI &SHOULD; be given by the Location field in the
1213   response. Unless the request method was HEAD, the entity of the
1214   response &SHOULD; contain a short hypertext note with a hyperlink to
1215   the new URI(s).
1216</t>
1217<t>
1218   If the 301 status code is received in response to a request method
1219   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1220   then the request &MAY; be automatically redirected by the user agent without
1221   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1222   request unless it can be confirmed by the user, since this might
1223   change the conditions under which the request was issued.
1224  <list><t>
1225      <x:h>Note:</x:h> When automatically redirecting a POST request after
1226      receiving a 301 status code, some existing HTTP/1.0 user agents
1227      will erroneously change it into a GET request.
1228  </t></list>
1229</t>
1230</section>
1231
1232<section title="302 Found" anchor="status.302">
1233  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1234  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1235<t>
1236   The requested resource resides temporarily under a different URI.
1237   Since the redirection might be altered on occasion, the client &SHOULD;
1238   continue to use the Request-URI for future requests.  This response
1239   is only cacheable if indicated by a Cache-Control or Expires header
1240   field.
1241</t>
1242<t>
1243   The temporary URI &SHOULD; be given by the Location field in the
1244   response. Unless the request method was HEAD, the entity of the
1245   response &SHOULD; contain a short hypertext note with a hyperlink to
1246   the new URI(s).
1247</t>
1248<t>
1249   If the 302 status code is received in response to a request method
1250   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1251   then the request &MAY; be automatically redirected by the user agent without
1252   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1253   request unless it can be confirmed by the user, since this might
1254   change the conditions under which the request was issued.
1255  <list><t>
1256      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1257      to change the method on the redirected request.  However, most
1258      existing user agent implementations treat 302 as if it were a 303
1259      response, performing a GET on the Location field-value regardless
1260      of the original request method. The status codes 303 and 307 have
1261      been added for servers that wish to make unambiguously clear which
1262      kind of reaction is expected of the client.
1263  </t></list>
1264</t>
1265</section>
1266
1267<section title="303 See Other" anchor="status.303">
1268  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1269  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1270<t>
1271   The response to the request can be found under a different URI and
1272   &SHOULD; be retrieved using a GET method on that resource. This method
1273   exists primarily to allow the output of a POST-activated script to
1274   redirect the user agent to a selected resource. The new URI is not a
1275   substitute reference for the originally requested resource. The 303
1276   response &MUST-NOT; be cached, but the response to the second
1277   (redirected) request might be cacheable.
1278</t>
1279<t>
1280   The different URI &SHOULD; be given by the Location field in the
1281   response. Unless the request method was HEAD, the entity of the
1282   response &SHOULD; contain a short hypertext note with a hyperlink to
1283   the new URI(s).
1284  <list><t>
1285      <x:h>Note:</x:h> Many pre-HTTP/1.1 user agents do not understand the 303
1286      status. When interoperability with such clients is a concern, the
1287      302 status code may be used instead, since most user agents react
1288      to a 302 response as described here for 303.
1289  </t></list>
1290</t>
1291</section>
1292
1293<section title="304 Not Modified" anchor="status.304">
1294  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1295  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1296<t>
1297   The response to the request has not been modified since the conditions
1298   indicated by the client's conditional GET request, as defined in &conditional;.
1299</t>
1300</section>
1301
1302<section title="305 Use Proxy" anchor="status.305">
1303  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1304  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1305<t>
1306   The requested resource &MUST; be accessed through the proxy given by
1307   the Location field. The Location field gives the URI of the proxy.
1308   The recipient is expected to repeat this single request via the
1309   proxy. 305 responses &MUST; only be generated by origin servers.
1310  <list><t>
1311      <x:h>Note:</x:h> <xref target="RFC2068"/> was not clear that 305 was intended to redirect a
1312      single request, and to be generated by origin servers only.  Not
1313      observing these limitations has significant security consequences.
1314  </t></list>
1315</t>
1316</section>
1317
1318<section title="306 (Unused)" anchor="status.306">
1319  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1320  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1321<t>
1322   The 306 status code was used in a previous version of the
1323   specification, is no longer used, and the code is reserved.
1324</t>
1325</section>
1326
1327<section title="307 Temporary Redirect" anchor="status.307">
1328  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1329  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1330<t>
1331   The requested resource resides temporarily under a different URI.
1332   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1333   continue to use the Request-URI for future requests.  This response
1334   is only cacheable if indicated by a Cache-Control or Expires header
1335   field.
1336</t>
1337<t>
1338   The temporary URI &SHOULD; be given by the Location field in the
1339   response. Unless the request method was HEAD, the entity of the
1340   response &SHOULD; contain a short hypertext note with a hyperlink to
1341   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1342   understand the 307 status. Therefore, the note &SHOULD; contain the
1343   information necessary for a user to repeat the original request on
1344   the new URI.
1345</t>
1346<t>
1347   If the 307 status code is received in response to a request method
1348   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1349   then the request &MAY; be automatically redirected by the user agent without
1350   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1351   request unless it can be confirmed by the user, since this might
1352   change the conditions under which the request was issued.
1353</t>
1354</section>
1355</section>
1356
1357<section title="Client Error 4xx" anchor="status.4xx">
1358<t>
1359   The 4xx class of status code is intended for cases in which the
1360   client seems to have erred. Except when responding to a HEAD request,
1361   the server &SHOULD; include an entity containing an explanation of the
1362   error situation, and whether it is a temporary or permanent
1363   condition. These status codes are applicable to any request method.
1364   User agents &SHOULD; display any included entity to the user.
1365</t>
1366<t>
1367   If the client is sending data, a server implementation using TCP
1368   &SHOULD; be careful to ensure that the client acknowledges receipt of
1369   the packet(s) containing the response, before the server closes the
1370   input connection. If the client continues sending data to the server
1371   after the close, the server's TCP stack will send a reset packet to
1372   the client, which may erase the client's unacknowledged input buffers
1373   before they can be read and interpreted by the HTTP application.
1374</t>
1375
1376<section title="400 Bad Request" anchor="status.400">
1377  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1378  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1379<t>
1380   The request could not be understood by the server due to malformed
1381   syntax. The client &SHOULD-NOT;  repeat the request without
1382   modifications.
1383</t>
1384</section>
1385
1386<section title="401 Unauthorized" anchor="status.401">
1387  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1388  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1389<t>
1390   The request requires user authentication (see &auth;).
1391</t>
1392</section>
1393
1394<section title="402 Payment Required" anchor="status.402">
1395  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1396  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1397<t>
1398   This code is reserved for future use.
1399</t>
1400</section>
1401
1402<section title="403 Forbidden" anchor="status.403">
1403  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1404  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1405<t>
1406   The server understood the request, but is refusing to fulfill it.
1407   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1408   If the request method was not HEAD and the server wishes to make
1409   public why the request has not been fulfilled, it &SHOULD; describe the
1410   reason for the refusal in the entity.  If the server does not wish to
1411   make this information available to the client, the status code 404
1412   (Not Found) can be used instead.
1413</t>
1414</section>
1415
1416<section title="404 Not Found" anchor="status.404">
1417  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1418  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1419<t>
1420   The server has not found anything matching the Request-URI. No
1421   indication is given of whether the condition is temporary or
1422   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1423   knows, through some internally configurable mechanism, that an old
1424   resource is permanently unavailable and has no forwarding address.
1425   This status code is commonly used when the server does not wish to
1426   reveal exactly why the request has been refused, or when no other
1427   response is applicable.
1428</t>
1429</section>
1430
1431<section title="405 Method Not Allowed" anchor="status.405">
1432  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1433  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1434<t>
1435   The method specified in the Request-Line is not allowed for the
1436   resource identified by the Request-URI. The response &MUST; include an
1437   Allow header containing a list of valid methods for the requested
1438   resource.
1439</t>
1440</section>
1441
1442<section title="406 Not Acceptable" anchor="status.406">
1443  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1444  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1445<t>
1446   The resource identified by the request is only capable of generating
1447   response entities which have content characteristics not acceptable
1448   according to the accept headers sent in the request.
1449</t>
1450<t>
1451   Unless it was a HEAD request, the response &SHOULD; include an entity
1452   containing a list of available entity characteristics and location(s)
1453   from which the user or user agent can choose the one most
1454   appropriate. The entity format is specified by the media type given
1455   in the Content-Type header field. Depending upon the format and the
1456   capabilities of the user agent, selection of the most appropriate
1457   choice &MAY; be performed automatically. However, this specification
1458   does not define any standard for such automatic selection.
1459  <list><t>
1460      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1461      not acceptable according to the accept headers sent in the
1462      request. In some cases, this may even be preferable to sending a
1463      406 response. User agents are encouraged to inspect the headers of
1464      an incoming response to determine if it is acceptable.
1465  </t></list>
1466</t>
1467<t>
1468   If the response could be unacceptable, a user agent &SHOULD;
1469   temporarily stop receipt of more data and query the user for a
1470   decision on further actions.
1471</t>
1472</section>
1473
1474<section title="407 Proxy Authentication Required" anchor="status.407">
1475  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1476  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1477<t>
1478   This code is similar to 401 (Unauthorized), but indicates that the
1479   client must first authenticate itself with the proxy (see &auth;).
1480</t>
1481</section>
1482
1483<section title="408 Request Timeout" anchor="status.408">
1484  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1485  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1486<t>
1487   The client did not produce a request within the time that the server
1488   was prepared to wait. The client &MAY; repeat the request without
1489   modifications at any later time.
1490</t>
1491</section>
1492
1493<section title="409 Conflict" anchor="status.409">
1494  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1495  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1496<t>
1497   The request could not be completed due to a conflict with the current
1498   state of the resource. This code is only allowed in situations where
1499   it is expected that the user might be able to resolve the conflict
1500   and resubmit the request. The response body &SHOULD; include enough
1501   information for the user to recognize the source of the conflict.
1502   Ideally, the response entity would include enough information for the
1503   user or user agent to fix the problem; however, that might not be
1504   possible and is not required.
1505</t>
1506<t>
1507   Conflicts are most likely to occur in response to a PUT request. For
1508   example, if versioning were being used and the entity being PUT
1509   included changes to a resource which conflict with those made by an
1510   earlier (third-party) request, the server might use the 409 response
1511   to indicate that it can't complete the request. In this case, the
1512   response entity would likely contain a list of the differences
1513   between the two versions in a format defined by the response
1514   Content-Type.
1515</t>
1516</section>
1517
1518<section title="410 Gone" anchor="status.410">
1519  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1520  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1521<t>
1522   The requested resource is no longer available at the server and no
1523   forwarding address is known. This condition is expected to be
1524   considered permanent. Clients with link editing capabilities &SHOULD;
1525   delete references to the Request-URI after user approval. If the
1526   server does not know, or has no facility to determine, whether or not
1527   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1528   used instead. This response is cacheable unless indicated otherwise.
1529</t>
1530<t>
1531   The 410 response is primarily intended to assist the task of web
1532   maintenance by notifying the recipient that the resource is
1533   intentionally unavailable and that the server owners desire that
1534   remote links to that resource be removed. Such an event is common for
1535   limited-time, promotional services and for resources belonging to
1536   individuals no longer working at the server's site. It is not
1537   necessary to mark all permanently unavailable resources as "gone" or
1538   to keep the mark for any length of time -- that is left to the
1539   discretion of the server owner.
1540</t>
1541</section>
1542
1543<section title="411 Length Required" anchor="status.411">
1544  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1545  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1546<t>
1547   The server refuses to accept the request without a defined Content-Length.
1548   The client &MAY; repeat the request if it adds a valid
1549   Content-Length header field containing the length of the message-body
1550   in the request message.
1551</t>
1552</section>
1553
1554<section title="412 Precondition Failed" anchor="status.412">
1555  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1556  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1557<t>
1558   The precondition given in one or more of the request-header fields
1559   evaluated to false when it was tested on the server, as defined in
1560   &conditional;.
1561</t>
1562</section>
1563
1564<section title="413 Request Entity Too Large" anchor="status.413">
1565  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1566  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1567<t>
1568   The server is refusing to process a request because the request
1569   entity is larger than the server is willing or able to process. The
1570   server &MAY; close the connection to prevent the client from continuing
1571   the request.
1572</t>
1573<t>
1574   If the condition is temporary, the server &SHOULD; include a Retry-After
1575   header field to indicate that it is temporary and after what
1576   time the client &MAY; try again.
1577</t>
1578</section>
1579
1580<section title="414 Request-URI Too Long" anchor="status.414">
1581  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1582  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1583<t>
1584   The server is refusing to service the request because the Request-URI
1585   is longer than the server is willing to interpret. This rare
1586   condition is only likely to occur when a client has improperly
1587   converted a POST request to a GET request with long query
1588   information, when the client has descended into a URI "black hole" of
1589   redirection (e.g., a redirected URI prefix that points to a suffix of
1590   itself), or when the server is under attack by a client attempting to
1591   exploit security holes present in some servers using fixed-length
1592   buffers for reading or manipulating the Request-URI.
1593</t>
1594</section>
1595
1596<section title="415 Unsupported Media Type" anchor="status.415">
1597  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1598  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1599<t>
1600   The server is refusing to service the request because the entity of
1601   the request is in a format not supported by the requested resource
1602   for the requested method.
1603</t>
1604</section>
1605
1606<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1607  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1608  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1609<t>
1610   The request included a Range request-header field (&header-range;) and none of
1611   the range-specifier values in this field overlap the current extent
1612   of the selected resource.
1613</t>
1614</section>
1615
1616<section title="417 Expectation Failed" anchor="status.417">
1617  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1618  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1619<t>
1620   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1621   could not be met by this server, or, if the server is a proxy,
1622   the server has unambiguous evidence that the request could not be met
1623   by the next-hop server.
1624</t>
1625</section>
1626</section>
1627
1628<section title="Server Error 5xx" anchor="status.5xx">
1629<t>
1630   Response status codes beginning with the digit "5" indicate cases in
1631   which the server is aware that it has erred or is incapable of
1632   performing the request. Except when responding to a HEAD request, the
1633   server &SHOULD; include an entity containing an explanation of the
1634   error situation, and whether it is a temporary or permanent
1635   condition. User agents &SHOULD; display any included entity to the
1636   user. These response codes are applicable to any request method.
1637</t>
1638
1639<section title="500 Internal Server Error" anchor="status.500">
1640  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1641  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1642<t>
1643   The server encountered an unexpected condition which prevented it
1644   from fulfilling the request.
1645</t>
1646</section>
1647
1648<section title="501 Not Implemented" anchor="status.501">
1649  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1650  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1651<t>
1652   The server does not support the functionality required to fulfill the
1653   request. This is the appropriate response when the server does not
1654   recognize the request method and is not capable of supporting it for
1655   any resource.
1656</t>
1657</section>
1658
1659<section title="502 Bad Gateway" anchor="status.502">
1660  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1661  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1662<t>
1663   The server, while acting as a gateway or proxy, received an invalid
1664   response from the upstream server it accessed in attempting to
1665   fulfill the request.
1666</t>
1667</section>
1668
1669<section title="503 Service Unavailable" anchor="status.503">
1670  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1671  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1672<t>
1673   The server is currently unable to handle the request due to a
1674   temporary overloading or maintenance of the server. The implication
1675   is that this is a temporary condition which will be alleviated after
1676   some delay. If known, the length of the delay &MAY; be indicated in a
1677   Retry-After header. If no Retry-After is given, the client &SHOULD;
1678   handle the response as it would for a 500 response.
1679  <list><t>
1680      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1681      server must use it when becoming overloaded. Some servers may wish
1682      to simply refuse the connection.
1683  </t></list>
1684</t>
1685</section>
1686
1687<section title="504 Gateway Timeout" anchor="status.504">
1688  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1689  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1690<t>
1691   The server, while acting as a gateway or proxy, did not receive a
1692   timely response from the upstream server specified by the URI (e.g.
1693   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1694   to access in attempting to complete the request.
1695  <list><t>
1696      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1697      return 400 or 500 when DNS lookups time out.
1698  </t></list>
1699</t>
1700</section>
1701
1702<section title="505 HTTP Version Not Supported" anchor="status.505">
1703  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1704  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1705<t>
1706   The server does not support, or refuses to support, the protocol
1707   version that was used in the request message. The server is
1708   indicating that it is unable or unwilling to complete the request
1709   using the same major version as the client, as described in &http-version;,
1710   other than with this error message. The response &SHOULD; contain
1711   an entity describing why that version is not supported and what other
1712   protocols are supported by that server.
1713</t>
1714
1715</section>
1716</section>
1717</section>
1718
1719
1720<section title="Header Field Definitions" anchor="header.fields">
1721<t>
1722   This section defines the syntax and semantics of HTTP/1.1 header fields
1723   related to request and response semantics.
1724</t>
1725<t>
1726   For entity-header fields, both sender and recipient refer to either the
1727   client or the server, depending on who sends and who receives the entity.
1728</t>
1729
1730<section title="Allow" anchor="header.allow">
1731  <iref primary="true" item="Allow header" x:for-anchor=""/>
1732  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1733  <x:anchor-alias value="Allow"/>
1734<t>
1735      The Allow entity-header field lists the set of methods supported
1736      by the resource identified by the Request-URI. The purpose of this
1737      field is strictly to inform the recipient of valid methods
1738      associated with the resource. An Allow header field &MUST; be
1739      present in a 405 (Method Not Allowed) response.
1740</t>
1741<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1742  <x:ref>Allow</x:ref>   = "Allow" ":" #<x:ref>Method</x:ref>
1743</artwork></figure>
1744<t>
1745      Example of use:
1746</t>
1747<figure><artwork type="example">
1748       Allow: GET, HEAD, PUT
1749</artwork></figure>
1750<t>
1751      This field cannot prevent a client from trying other methods.
1752      However, the indications given by the Allow header field value
1753      &SHOULD; be followed. The actual set of allowed methods is defined
1754      by the origin server at the time of each request.
1755</t>
1756<t>
1757      The Allow header field &MAY; be provided with a PUT request to
1758      recommend the methods to be supported by the new or modified
1759      resource. The server is not required to support these methods and
1760      &SHOULD; include an Allow header in the response giving the actual
1761      supported methods.
1762</t>
1763<t>
1764      A proxy &MUST-NOT; modify the Allow header field even if it does not
1765      understand all the methods specified, since the user agent might
1766      have other means of communicating with the origin server.
1767</t>
1768</section>
1769
1770<section title="Expect" anchor="header.expect">
1771  <iref primary="true" item="Expect header" x:for-anchor=""/>
1772  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1773  <x:anchor-alias value="Expect"/>
1774  <x:anchor-alias value="expectation"/>
1775  <x:anchor-alias value="expectation-extension"/>
1776  <x:anchor-alias value="expect-params"/>
1777<t>
1778   The Expect request-header field is used to indicate that particular
1779   server behaviors are required by the client.
1780</t>
1781<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"/>
1782  <x:ref>Expect</x:ref>       =  "Expect" ":" 1#<x:ref>expectation</x:ref>
1783 
1784  <x:ref>expectation</x:ref>  =  "100-continue" | <x:ref>expectation-extension</x:ref>
1785  <x:ref>expectation-extension</x:ref> =  <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> )
1786                           *<x:ref>expect-params</x:ref> ]
1787  <x:ref>expect-params</x:ref> =  ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> ) ]
1788</artwork></figure>
1789<t>
1790   A server that does not understand or is unable to comply with any of
1791   the expectation values in the Expect field of a request &MUST; respond
1792   with appropriate error status. The server &MUST; respond with a 417
1793   (Expectation Failed) status if any of the expectations cannot be met
1794   or, if there are other problems with the request, some other 4xx
1795   status.
1796</t>
1797<t>
1798   This header field is defined with extensible syntax to allow for
1799   future extensions. If a server receives a request containing an
1800   Expect field that includes an expectation-extension that it does not
1801   support, it &MUST; respond with a 417 (Expectation Failed) status.
1802</t>
1803<t>
1804   Comparison of expectation values is case-insensitive for unquoted
1805   tokens (including the 100-continue token), and is case-sensitive for
1806   quoted-string expectation-extensions.
1807</t>
1808<t>
1809   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1810   return a 417 (Expectation Failed) status if it receives a request
1811   with an expectation that it cannot meet. However, the Expect
1812   request-header itself is end-to-end; it &MUST; be forwarded if the
1813   request is forwarded.
1814</t>
1815<t>
1816   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1817   Expect header.
1818</t>
1819<t>
1820   See &use100; for the use of the 100 (Continue) status.
1821</t>
1822</section>
1823
1824<section title="From" anchor="header.from">
1825  <iref primary="true" item="From header" x:for-anchor=""/>
1826  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1827  <x:anchor-alias value="From"/>
1828  <x:anchor-alias value="mailbox"/>
1829<t>
1830   The From request-header field, if given, &SHOULD; contain an Internet
1831   e-mail address for the human user who controls the requesting user
1832   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1833   in <xref x:sec="3.4" x:fmt="of" target="RFC2822"/>:
1834</t>
1835<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1836  <x:ref>From</x:ref>    = "From" ":" <x:ref>mailbox</x:ref>
1837 
1838  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC2822"/>&gt;
1839</artwork></figure>
1840<t>
1841   An example is:
1842</t>
1843<figure><artwork type="example">
1844    From: webmaster@example.org
1845</artwork></figure>
1846<t>
1847   This header field &MAY; be used for logging purposes and as a means for
1848   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1849   be used as an insecure form of access protection. The interpretation
1850   of this field is that the request is being performed on behalf of the
1851   person given, who accepts responsibility for the method performed. In
1852   particular, robot agents &SHOULD; include this header so that the
1853   person responsible for running the robot can be contacted if problems
1854   occur on the receiving end.
1855</t>
1856<t>
1857   The Internet e-mail address in this field &MAY; be separate from the
1858   Internet host which issued the request. For example, when a request
1859   is passed through a proxy the original issuer's address &SHOULD; be
1860   used.
1861</t>
1862<t>
1863   The client &SHOULD-NOT;  send the From header field without the user's
1864   approval, as it might conflict with the user's privacy interests or
1865   their site's security policy. It is strongly recommended that the
1866   user be able to disable, enable, and modify the value of this field
1867   at any time prior to a request.
1868</t>
1869</section>
1870
1871<section title="Location" anchor="header.location">
1872  <iref primary="true" item="Location header" x:for-anchor=""/>
1873  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1874  <x:anchor-alias value="Location"/>
1875<t>
1876   The Location response-header field is used to redirect the recipient
1877   to a location other than the Request-URI for completion of the
1878   request or identification of a new resource. For 201 (Created)
1879   responses, the Location is that of the new resource which was created
1880   by the request. For 3xx responses, the location &SHOULD; indicate the
1881   server's preferred URI for automatic redirection to the resource. The
1882   field value consists of a single absolute URI.
1883</t>
1884<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1885  <x:ref>Location</x:ref>       = "Location" ":" <x:ref>absoluteURI</x:ref> [ "#" <x:ref>fragment</x:ref> ]
1886</artwork></figure>
1887<t>
1888   An example is:
1889</t>
1890<figure><artwork type="example">
1891    Location: http://www.example.org/pub/WWW/People.html
1892</artwork></figure>
1893<t>
1894  <list><t>
1895      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1896      from Location in that the Content-Location identifies the original
1897      location of the entity enclosed in the request. It is therefore
1898      possible for a response to contain header fields for both Location
1899      and Content-Location.
1900  </t></list>
1901</t>
1902<t>
1903   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1904   <list style="symbols">
1905      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1906      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1907      <t>With 305 Use Proxy.</t>
1908   </list>
1909</t>
1910</section>
1911
1912<section title="Max-Forwards" anchor="header.max-forwards">
1913  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1914  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1915  <x:anchor-alias value="Max-Forwards"/>
1916<t>
1917   The Max-Forwards request-header field provides a mechanism with the
1918   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1919   number of proxies or gateways that can forward the request to the
1920   next inbound server. This can be useful when the client is attempting
1921   to trace a request chain which appears to be failing or looping in
1922   mid-chain.
1923</t>
1924<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1925  <x:ref>Max-Forwards</x:ref>   = "Max-Forwards" ":" 1*<x:ref>DIGIT</x:ref>
1926</artwork></figure>
1927<t>
1928   The Max-Forwards value is a decimal integer indicating the remaining
1929   number of times this request message may be forwarded.
1930</t>
1931<t>
1932   Each proxy or gateway recipient of a TRACE or OPTIONS request
1933   containing a Max-Forwards header field &MUST; check and update its
1934   value prior to forwarding the request. If the received value is zero
1935   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1936   respond as the final recipient. If the received Max-Forwards value is
1937   greater than zero, then the forwarded message &MUST; contain an updated
1938   Max-Forwards field with a value decremented by one (1).
1939</t>
1940<t>
1941   The Max-Forwards header field &MAY; be ignored for all other methods
1942   defined by this specification and for any extension methods for which
1943   it is not explicitly referred to as part of that method definition.
1944</t>
1945</section>
1946
1947<section title="Referer" anchor="header.referer">
1948  <iref primary="true" item="Referer header" x:for-anchor=""/>
1949  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1950  <x:anchor-alias value="Referer"/>
1951<t>
1952   The Referer[sic] request-header field allows the client to specify,
1953   for the server's benefit, the address (URI) of the resource from
1954   which the Request-URI was obtained (the "referrer", although the
1955   header field is misspelled.) The Referer request-header allows a
1956   server to generate lists of back-links to resources for interest,
1957   logging, optimized caching, etc. It also allows obsolete or mistyped
1958   links to be traced for maintenance. The Referer field &MUST-NOT; be
1959   sent if the Request-URI was obtained from a source that does not have
1960   its own URI, such as input from the user keyboard.
1961</t>
1962<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1963  <x:ref>Referer</x:ref>        = "Referer" ":" ( <x:ref>absoluteURI</x:ref> | <x:ref>relativeURI</x:ref> )
1964</artwork></figure>
1965<t>
1966   Example:
1967</t>
1968<figure><artwork type="example">
1969    Referer: http://www.example.org/hypertext/Overview.html
1970</artwork></figure>
1971<t>
1972   If the field value is a relative URI, it &SHOULD; be interpreted
1973   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1974   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1975</t>
1976</section>
1977
1978<section title="Retry-After" anchor="header.retry-after">
1979  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1980  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1981  <x:anchor-alias value="Retry-After"/>
1982<t>
1983   The Retry-After response-header field can be used with a 503 (Service
1984   Unavailable) response to indicate how long the service is expected to
1985   be unavailable to the requesting client. This field &MAY; also be used
1986   with any 3xx (Redirection) response to indicate the minimum time the
1987   user-agent is asked wait before issuing the redirected request. The
1988   value of this field can be either an HTTP-date or an integer number
1989   of seconds (in decimal) after the time of the response.
1990</t>
1991<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
1992  <x:ref>Retry-After</x:ref>   = "Retry-After" ":" ( <x:ref>HTTP-date</x:ref> | <x:ref>delta-seconds</x:ref> )
1993</artwork></figure>
1994<t anchor="rule.delta-seconds">
1995  <x:anchor-alias value="delta-seconds"/>
1996   Time spans are non-negative decimal integers, representing time in
1997   seconds.
1998</t>
1999<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2000  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2001</artwork></figure>
2002<t>
2003   Two examples of its use are
2004</t>
2005<figure><artwork type="example">
2006    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2007    Retry-After: 120
2008</artwork></figure>
2009<t>
2010   In the latter example, the delay is 2 minutes.
2011</t>
2012</section>
2013
2014<section title="Server" anchor="header.server">
2015  <iref primary="true" item="Server header" x:for-anchor=""/>
2016  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
2017  <x:anchor-alias value="Server"/>
2018<t>
2019   The Server response-header field contains information about the
2020   software used by the origin server to handle the request. The field
2021   can contain multiple product tokens (&product-tokens;) and comments
2022   identifying the server and any significant subproducts. The product
2023   tokens are listed in order of their significance for identifying the
2024   application.
2025</t>
2026<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2027  <x:ref>Server</x:ref>         = "Server" ":" 1*( <x:ref>product</x:ref> | <x:ref>comment</x:ref> )
2028</artwork></figure>
2029<t>
2030   Example:
2031</t>
2032<figure><artwork type="example">
2033    Server: CERN/3.0 libwww/2.17
2034</artwork></figure>
2035<t>
2036   If the response is being forwarded through a proxy, the proxy
2037   application &MUST-NOT; modify the Server response-header. Instead, it
2038   &MUST; include a Via field (as described in &header-via;).
2039  <list><t>
2040      <x:h>Note:</x:h> Revealing the specific software version of the server might
2041      allow the server machine to become more vulnerable to attacks
2042      against software that is known to contain security holes. Server
2043      implementors are encouraged to make this field a configurable
2044      option.
2045  </t></list>
2046</t>
2047</section>
2048
2049<section title="User-Agent" anchor="header.user-agent">
2050  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
2051  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
2052  <x:anchor-alias value="User-Agent"/>
2053<t>
2054   The User-Agent request-header field contains information about the
2055   user agent originating the request. This is for statistical purposes,
2056   the tracing of protocol violations, and automated recognition of user
2057   agents for the sake of tailoring responses to avoid particular user
2058   agent limitations. User agents &SHOULD; include this field with
2059   requests. The field can contain multiple product tokens (&product-tokens;)
2060   and comments identifying the agent and any subproducts which form a
2061   significant part of the user agent. By convention, the product tokens
2062   are listed in order of their significance for identifying the
2063   application.
2064</t>
2065<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2066  <x:ref>User-Agent</x:ref>     = "User-Agent" ":" 1*( <x:ref>product</x:ref> | <x:ref>comment</x:ref> )
2067</artwork></figure>
2068<t>
2069   Example:
2070</t>
2071<figure><artwork type="example">
2072    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2073</artwork></figure>
2074</section>
2075
2076</section>
2077
2078<section title="IANA Considerations" anchor="IANA.considerations">
2079<t>
2080   <cref>TBD.</cref>
2081</t>
2082</section>
2083
2084<section title="Security Considerations" anchor="security.considerations">
2085<t>
2086   This section is meant to inform application developers, information
2087   providers, and users of the security limitations in HTTP/1.1 as
2088   described by this document. The discussion does not include
2089   definitive solutions to the problems revealed, though it does make
2090   some suggestions for reducing security risks.
2091</t>
2092
2093<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2094<t>
2095   Like any generic data transfer protocol, HTTP cannot regulate the
2096   content of the data that is transferred, nor is there any a priori
2097   method of determining the sensitivity of any particular piece of
2098   information within the context of any given request. Therefore,
2099   applications &SHOULD; supply as much control over this information as
2100   possible to the provider of that information. Four header fields are
2101   worth special mention in this context: Server, Via, Referer and From.
2102</t>
2103<t>
2104   Revealing the specific software version of the server might allow the
2105   server machine to become more vulnerable to attacks against software
2106   that is known to contain security holes. Implementors &SHOULD; make the
2107   Server header field a configurable option.
2108</t>
2109<t>
2110   Proxies which serve as a portal through a network firewall &SHOULD;
2111   take special precautions regarding the transfer of header information
2112   that identifies the hosts behind the firewall. In particular, they
2113   &SHOULD; remove, or replace with sanitized versions, any Via fields
2114   generated behind the firewall.
2115</t>
2116<t>
2117   The Referer header allows reading patterns to be studied and reverse
2118   links drawn. Although it can be very useful, its power can be abused
2119   if user details are not separated from the information contained in
2120   the Referer. Even when the personal information has been removed, the
2121   Referer header might indicate a private document's URI whose
2122   publication would be inappropriate.
2123</t>
2124<t>
2125   The information sent in the From field might conflict with the user's
2126   privacy interests or their site's security policy, and hence it
2127   &SHOULD-NOT;  be transmitted without the user being able to disable,
2128   enable, and modify the contents of the field. The user &MUST; be able
2129   to set the contents of this field within a user preference or
2130   application defaults configuration.
2131</t>
2132<t>
2133   We suggest, though do not require, that a convenient toggle interface
2134   be provided for the user to enable or disable the sending of From and
2135   Referer information.
2136</t>
2137<t>
2138   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2139   fields can sometimes be used to determine that a specific client or
2140   server have a particular security hole which might be exploited.
2141   Unfortunately, this same information is often used for other valuable
2142   purposes for which HTTP currently has no better mechanism.
2143</t>
2144</section>
2145
2146<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2147<t>
2148   Because the source of a link might be private information or might
2149   reveal an otherwise private information source, it is strongly
2150   recommended that the user be able to select whether or not the
2151   Referer field is sent. For example, a browser client could have a
2152   toggle switch for browsing openly/anonymously, which would
2153   respectively enable/disable the sending of Referer and From
2154   information.
2155</t>
2156<t>
2157   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
2158   HTTP request if the referring page was transferred with a secure
2159   protocol.
2160</t>
2161<t>
2162   Authors of services should not use
2163   GET-based forms for the submission of sensitive data because that
2164   data will be encoded in the Request-URI. Many existing
2165   servers, proxies, and user agents log or display the Request-URI in
2166   places where it might be visible to third parties. Such services can
2167   use POST-based form submission instead.
2168</t>
2169</section>
2170
2171<section title="Location Headers and Spoofing" anchor="location.spoofing">
2172<t>
2173   If a single server supports multiple organizations that do not trust
2174   one another, then it &MUST; check the values of Location and Content-Location
2175   headers in responses that are generated under control of
2176   said organizations to make sure that they do not attempt to
2177   invalidate resources over which they have no authority.
2178</t>
2179</section>
2180
2181</section>
2182
2183<section title="Acknowledgments" anchor="ack">
2184</section>
2185</middle>
2186<back>
2187
2188<references title="Normative References">
2189
2190<reference anchor="Part1">
2191  <front>
2192    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2193    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2194      <organization abbrev="Day Software">Day Software</organization>
2195      <address><email>fielding@gbiv.com</email></address>
2196    </author>
2197    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2198      <organization>One Laptop per Child</organization>
2199      <address><email>jg@laptop.org</email></address>
2200    </author>
2201    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2202      <organization abbrev="HP">Hewlett-Packard Company</organization>
2203      <address><email>JeffMogul@acm.org</email></address>
2204    </author>
2205    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2206      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2207      <address><email>henrikn@microsoft.com</email></address>
2208    </author>
2209    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2210      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2211      <address><email>LMM@acm.org</email></address>
2212    </author>
2213    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2214      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2215      <address><email>paulle@microsoft.com</email></address>
2216    </author>
2217    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2218      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2219      <address><email>timbl@w3.org</email></address>
2220    </author>
2221    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2222      <organization abbrev="W3C">World Wide Web Consortium</organization>
2223      <address><email>ylafon@w3.org</email></address>
2224    </author>
2225    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2226      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2227      <address><email>julian.reschke@greenbytes.de</email></address>
2228    </author>
2229    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2230  </front>
2231  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2232  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2233</reference>
2234
2235<reference anchor="Part3">
2236  <front>
2237    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2238    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2239      <organization abbrev="Day Software">Day Software</organization>
2240      <address><email>fielding@gbiv.com</email></address>
2241    </author>
2242    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2243      <organization>One Laptop per Child</organization>
2244      <address><email>jg@laptop.org</email></address>
2245    </author>
2246    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2247      <organization abbrev="HP">Hewlett-Packard Company</organization>
2248      <address><email>JeffMogul@acm.org</email></address>
2249    </author>
2250    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2251      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2252      <address><email>henrikn@microsoft.com</email></address>
2253    </author>
2254    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2255      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2256      <address><email>LMM@acm.org</email></address>
2257    </author>
2258    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2259      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2260      <address><email>paulle@microsoft.com</email></address>
2261    </author>
2262    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2263      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2264      <address><email>timbl@w3.org</email></address>
2265    </author>
2266    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2267      <organization abbrev="W3C">World Wide Web Consortium</organization>
2268      <address><email>ylafon@w3.org</email></address>
2269    </author>
2270    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2271      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2272      <address><email>julian.reschke@greenbytes.de</email></address>
2273    </author>
2274    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2275  </front>
2276  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2277  <x:source href="p3-payload.xml" basename="p3-payload"/>
2278</reference>
2279
2280<reference anchor="Part4">
2281  <front>
2282    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2283    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2284      <organization abbrev="Day Software">Day Software</organization>
2285      <address><email>fielding@gbiv.com</email></address>
2286    </author>
2287    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2288      <organization>One Laptop per Child</organization>
2289      <address><email>jg@laptop.org</email></address>
2290    </author>
2291    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2292      <organization abbrev="HP">Hewlett-Packard Company</organization>
2293      <address><email>JeffMogul@acm.org</email></address>
2294    </author>
2295    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2296      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2297      <address><email>henrikn@microsoft.com</email></address>
2298    </author>
2299    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2300      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2301      <address><email>LMM@acm.org</email></address>
2302    </author>
2303    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2304      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2305      <address><email>paulle@microsoft.com</email></address>
2306    </author>
2307    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2308      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2309      <address><email>timbl@w3.org</email></address>
2310    </author>
2311    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2312      <organization abbrev="W3C">World Wide Web Consortium</organization>
2313      <address><email>ylafon@w3.org</email></address>
2314    </author>
2315    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2316      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2317      <address><email>julian.reschke@greenbytes.de</email></address>
2318    </author>
2319    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2320  </front>
2321  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2322  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2323</reference>
2324
2325<reference anchor="Part5">
2326  <front>
2327    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2328    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2329      <organization abbrev="Day Software">Day Software</organization>
2330      <address><email>fielding@gbiv.com</email></address>
2331    </author>
2332    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2333      <organization>One Laptop per Child</organization>
2334      <address><email>jg@laptop.org</email></address>
2335    </author>
2336    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2337      <organization abbrev="HP">Hewlett-Packard Company</organization>
2338      <address><email>JeffMogul@acm.org</email></address>
2339    </author>
2340    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2341      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2342      <address><email>henrikn@microsoft.com</email></address>
2343    </author>
2344    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2345      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2346      <address><email>LMM@acm.org</email></address>
2347    </author>
2348    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2349      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2350      <address><email>paulle@microsoft.com</email></address>
2351    </author>
2352    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2353      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2354      <address><email>timbl@w3.org</email></address>
2355    </author>
2356    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2357      <organization abbrev="W3C">World Wide Web Consortium</organization>
2358      <address><email>ylafon@w3.org</email></address>
2359    </author>
2360    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2361      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2362      <address><email>julian.reschke@greenbytes.de</email></address>
2363    </author>
2364    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2365  </front>
2366  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2367  <x:source href="p5-range.xml" basename="p5-range"/>
2368</reference>
2369
2370<reference anchor="Part6">
2371  <front>
2372    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2373    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2374      <organization abbrev="Day Software">Day Software</organization>
2375      <address><email>fielding@gbiv.com</email></address>
2376    </author>
2377    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2378      <organization>One Laptop per Child</organization>
2379      <address><email>jg@laptop.org</email></address>
2380    </author>
2381    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2382      <organization abbrev="HP">Hewlett-Packard Company</organization>
2383      <address><email>JeffMogul@acm.org</email></address>
2384    </author>
2385    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2386      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2387      <address><email>henrikn@microsoft.com</email></address>
2388    </author>
2389    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2390      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2391      <address><email>LMM@acm.org</email></address>
2392    </author>
2393    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2394      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2395      <address><email>paulle@microsoft.com</email></address>
2396    </author>
2397    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2398      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2399      <address><email>timbl@w3.org</email></address>
2400    </author>
2401    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2402      <organization abbrev="W3C">World Wide Web Consortium</organization>
2403      <address><email>ylafon@w3.org</email></address>
2404    </author>
2405    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2406      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2407      <address><email>julian.reschke@greenbytes.de</email></address>
2408    </author>
2409    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2410  </front>
2411  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2412  <x:source href="p6-cache.xml" basename="p6-cache"/>
2413</reference>
2414
2415<reference anchor="Part7">
2416  <front>
2417    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2418    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2419      <organization abbrev="Day Software">Day Software</organization>
2420      <address><email>fielding@gbiv.com</email></address>
2421    </author>
2422    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2423      <organization>One Laptop per Child</organization>
2424      <address><email>jg@laptop.org</email></address>
2425    </author>
2426    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2427      <organization abbrev="HP">Hewlett-Packard Company</organization>
2428      <address><email>JeffMogul@acm.org</email></address>
2429    </author>
2430    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2431      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2432      <address><email>henrikn@microsoft.com</email></address>
2433    </author>
2434    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2435      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2436      <address><email>LMM@acm.org</email></address>
2437    </author>
2438    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2439      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2440      <address><email>paulle@microsoft.com</email></address>
2441    </author>
2442    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2443      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2444      <address><email>timbl@w3.org</email></address>
2445    </author>
2446    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2447      <organization abbrev="W3C">World Wide Web Consortium</organization>
2448      <address><email>ylafon@w3.org</email></address>
2449    </author>
2450    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2451      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2452      <address><email>julian.reschke@greenbytes.de</email></address>
2453    </author>
2454    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2455  </front>
2456  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2457  <x:source href="p7-auth.xml" basename="p7-auth"/>
2458</reference>
2459
2460<reference anchor="RFC2119">
2461  <front>
2462    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2463    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2464      <organization>Harvard University</organization>
2465      <address><email>sob@harvard.edu</email></address>
2466    </author>
2467    <date month="March" year="1997"/>
2468  </front>
2469  <seriesInfo name="BCP" value="14"/>
2470  <seriesInfo name="RFC" value="2119"/>
2471</reference>
2472
2473</references>
2474
2475<references title="Informative References">
2476
2477<reference anchor="Luo1998">
2478  <front>
2479    <title>Tunneling TCP based protocols through Web proxy servers</title>
2480    <author initials="A." surname="Luotonen" fullname="A. Luotonen">
2481      <organization/>
2482    </author>
2483    <date year="1998" month="August"/>
2484  </front>
2485  <seriesInfo name="Internet-Draft" value="draft-luotonen-web-proxy-tunneling-01"/>
2486</reference>
2487
2488<reference anchor="RFC1945">
2489  <front>
2490    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2491    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2492      <organization>MIT, Laboratory for Computer Science</organization>
2493      <address><email>timbl@w3.org</email></address>
2494    </author>
2495    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2496      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2497      <address><email>fielding@ics.uci.edu</email></address>
2498    </author>
2499    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2500      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2501      <address><email>frystyk@w3.org</email></address>
2502    </author>
2503    <date month="May" year="1996"/>
2504  </front>
2505  <seriesInfo name="RFC" value="1945"/>
2506</reference>
2507
2508<reference anchor="RFC2068">
2509  <front>
2510    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2511    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2512      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2513      <address><email>fielding@ics.uci.edu</email></address>
2514    </author>
2515    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2516      <organization>MIT Laboratory for Computer Science</organization>
2517      <address><email>jg@w3.org</email></address>
2518    </author>
2519    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2520      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2521      <address><email>mogul@wrl.dec.com</email></address>
2522    </author>
2523    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2524      <organization>MIT Laboratory for Computer Science</organization>
2525      <address><email>frystyk@w3.org</email></address>
2526    </author>
2527    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2528      <organization>MIT Laboratory for Computer Science</organization>
2529      <address><email>timbl@w3.org</email></address>
2530    </author>
2531    <date month="January" year="1997"/>
2532  </front>
2533  <seriesInfo name="RFC" value="2068"/>
2534</reference>
2535
2536<reference anchor="RFC2616">
2537  <front>
2538    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2539    <author initials="R." surname="Fielding" fullname="R. Fielding">
2540      <organization>University of California, Irvine</organization>
2541      <address><email>fielding@ics.uci.edu</email></address>
2542    </author>
2543    <author initials="J." surname="Gettys" fullname="J. Gettys">
2544      <organization>W3C</organization>
2545      <address><email>jg@w3.org</email></address>
2546    </author>
2547    <author initials="J." surname="Mogul" fullname="J. Mogul">
2548      <organization>Compaq Computer Corporation</organization>
2549      <address><email>mogul@wrl.dec.com</email></address>
2550    </author>
2551    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2552      <organization>MIT Laboratory for Computer Science</organization>
2553      <address><email>frystyk@w3.org</email></address>
2554    </author>
2555    <author initials="L." surname="Masinter" fullname="L. Masinter">
2556      <organization>Xerox Corporation</organization>
2557      <address><email>masinter@parc.xerox.com</email></address>
2558    </author>
2559    <author initials="P." surname="Leach" fullname="P. Leach">
2560      <organization>Microsoft Corporation</organization>
2561      <address><email>paulle@microsoft.com</email></address>
2562    </author>
2563    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2564      <organization>W3C</organization>
2565      <address><email>timbl@w3.org</email></address>
2566    </author>
2567    <date month="June" year="1999"/>
2568  </front>
2569  <seriesInfo name="RFC" value="2616"/>
2570</reference>
2571
2572<reference anchor="RFC2822">
2573  <front>
2574    <title>Internet Message Format</title>
2575    <author initials="P." surname="Resnick" fullname="P. Resnick">
2576      <organization>QUALCOMM Incorporated</organization>
2577    </author>
2578    <date year="2001" month="April"/>
2579  </front> 
2580  <seriesInfo name="RFC" value="2822"/>
2581</reference>
2582
2583</references>
2584
2585<section title="Compatibility with Previous Versions" anchor="compatibility">
2586<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2587<t>
2588   Clarified which error code should be used for inbound server failures
2589   (e.g. DNS failures). (<xref target="status.504"/>).
2590</t>
2591<t>
2592   201 (Created) had a race that required an Etag be sent when a resource is
2593   first created. (<xref target="status.201"/>).
2594</t>
2595<t>
2596   Rewrite of message transmission requirements to make it much harder
2597   for implementors to get it wrong, as the consequences of errors here
2598   can have significant impact on the Internet, and to deal with the
2599   following problems:
2600  <list style="numbers">
2601      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
2602         this was incorrectly placing a requirement on the behavior of
2603         an implementation of a future version of HTTP/1.x</t>
2604
2605      <t>Made it clear that user-agents should retry requests, not
2606         "clients" in general.</t>
2607
2608      <t>Converted requirements for clients to ignore unexpected 100
2609         (Continue) responses, and for proxies to forward 100 responses,
2610         into a general requirement for 1xx responses.</t>
2611
2612      <t>Modified some TCP-specific language, to make it clearer that
2613         non-TCP transports are possible for HTTP.</t>
2614
2615      <t>Require that the origin server &MUST-NOT; wait for the request
2616         body before it sends a required 100 (Continue) response.</t>
2617
2618      <t>Allow, rather than require, a server to omit 100 (Continue) if
2619         it has already seen some of the request body.</t>
2620
2621      <t>Allow servers to defend against denial-of-service attacks and
2622         broken clients.</t>
2623  </list>
2624</t>
2625<t>
2626   This change adds the Expect header and 417 status code.
2627</t>
2628<t>
2629   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
2630   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
2631</t>
2632<t>
2633   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
2634   implemented in previous versions of this specification. See <xref target="RFC2068"/>.
2635</t>
2636</section>
2637
2638<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
2639<t>
2640  Clarify definition of POST.
2641  (<xref target="POST"/>)
2642</t>
2643<t>
2644  Failed to consider that there are
2645  many other request methods that are safe to automatically redirect,
2646  and further that the user agent is able to make that determination
2647  based on the request method semantics.
2648  (Sections <xref format="counter" target="status.301"/>,
2649  <xref format="counter" target="status.302"/> and
2650  <xref format="counter" target="status.307"/> )
2651</t>
2652<t>
2653  Correct syntax of Location header to allow fragment,
2654  as referred symbol wasn't what was expected, and add some
2655  clarifications as to when it would not be appropriate.
2656  (<xref target="header.location"/>)
2657</t>
2658<t>
2659  In the description of the Server header, the Via field
2660  was described as a SHOULD. The requirement was and is stated
2661  correctly in the description of the Via header in &header-via;.
2662  (<xref target="header.server"/>)
2663</t>
2664</section>
2665
2666</section>
2667
2668<section title="Change Log (to be removed by RFC Editor before publication)">
2669
2670<section title="Since RFC2616">
2671<t>
2672  Extracted relevant partitions from <xref target="RFC2616"/>.
2673</t>
2674</section>
2675
2676<section title="Since draft-ietf-httpbis-p2-semantics-00">
2677<t>
2678  Closed issues:
2679  <list style="symbols"> 
2680    <t>
2681      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
2682      "Via is a MUST"
2683      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
2684    </t>
2685    <t>
2686      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
2687      "Fragments allowed in Location"
2688      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
2689    </t>
2690    <t>
2691      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
2692      "Safe Methods vs Redirection"
2693      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
2694    </t>
2695    <t>
2696      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
2697      "Revise description of the POST method"
2698      (<eref target="http://purl.org/NET/http-errata#post"/>)
2699    </t>
2700    <t>
2701      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
2702      "Normative and Informative references"
2703    </t>
2704    <t>
2705      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
2706      "RFC2606 Compliance"
2707    </t>
2708    <t>
2709      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
2710      "Informative references"
2711    </t>
2712    <t>
2713      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
2714      "Redundant cross-references"
2715    </t>
2716  </list>
2717</t>
2718<t>
2719  Other changes:
2720  <list style="symbols"> 
2721    <t>
2722      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
2723    </t>
2724  </list>
2725</t>
2726</section>
2727
2728<section title="Since draft-ietf-httpbis-p2-semantics-01">
2729<t>
2730  Closed issues:
2731  <list style="symbols"> 
2732    <t>
2733      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
2734      "PUT side effects"
2735    </t>
2736    <t>
2737      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
2738      "Duplicate Host header requirements"
2739    </t>
2740  </list>
2741</t>
2742<t>
2743  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2744  <list style="symbols"> 
2745    <t>
2746      Move "Product Tokens" section (back) into Part 1, as "token" is used
2747      in the definition of the Upgrade header.
2748    </t>
2749    <t>
2750      Add explicit references to BNF syntax and rules imported from other parts of the specification.
2751    </t>
2752    <t>
2753      Copy definition of delta-seconds from Part6 instead of referencing it.
2754    </t>
2755  </list>
2756</t>
2757</section>
2758
2759<section title="Since draft-ietf-httpbis-p2-semantics-02">
2760<t>
2761</t>
2762</section>
2763
2764</section>
2765
2766</back>
2767</rfc>
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