source: draft-ietf-httpbis/latest/p2-semantics.xml @ 266

Last change on this file since 266 was 266, checked in by julian.reschke@…, 12 years ago

Enhance reference to definition of LINK/UNLINK/PATCH in RFC 2068.

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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 "June">
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  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
64]>
65<?rfc toc="yes" ?>
66<?rfc symrefs="yes" ?>
67<?rfc sortrefs="yes" ?>
68<?rfc compact="yes"?>
69<?rfc subcompact="no" ?>
70<?rfc linkmailto="no" ?>
71<?rfc editing="no" ?>
72<?rfc comments="yes"?>
73<?rfc inline="yes"?>
74<?rfc-ext allow-markup-in-artwork="yes" ?>
75<?rfc-ext include-references-in-index="yes" ?>
76<rfc obsoletes="2616" updates="2817" category="std"
77     ipr="full3978" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
78     xmlns:x='http://purl.org/net/xml2rfc/ext'>
79<front>
80
81  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
82
83  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
84    <organization abbrev="Day Software">Day Software</organization>
85    <address>
86      <postal>
87        <street>23 Corporate Plaza DR, Suite 280</street>
88        <city>Newport Beach</city>
89        <region>CA</region>
90        <code>92660</code>
91        <country>USA</country>
92      </postal>
93      <phone>+1-949-706-5300</phone>
94      <facsimile>+1-949-706-5305</facsimile>
95      <email>fielding@gbiv.com</email>
96      <uri>http://roy.gbiv.com/</uri>
97    </address>
98  </author>
99
100  <author initials="J." surname="Gettys" fullname="Jim Gettys">
101    <organization>One Laptop per Child</organization>
102    <address>
103      <postal>
104        <street>21 Oak Knoll Road</street>
105        <city>Carlisle</city>
106        <region>MA</region>
107        <code>01741</code>
108        <country>USA</country>
109      </postal>
110      <email>jg@laptop.org</email>
111      <uri>http://www.laptop.org/</uri>
112    </address>
113  </author>
114 
115  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
116    <organization abbrev="HP">Hewlett-Packard Company</organization>
117    <address>
118      <postal>
119        <street>HP Labs, Large Scale Systems Group</street>
120        <street>1501 Page Mill Road, MS 1177</street>
121        <city>Palo Alto</city>
122        <region>CA</region>
123        <code>94304</code>
124        <country>USA</country>
125      </postal>
126      <email>JeffMogul@acm.org</email>
127    </address>
128  </author>
129
130  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
131    <organization abbrev="Microsoft">Microsoft Corporation</organization>
132    <address>
133      <postal>
134        <street>1 Microsoft Way</street>
135        <city>Redmond</city>
136        <region>WA</region>
137        <code>98052</code>
138        <country>USA</country>
139      </postal>
140      <email>henrikn@microsoft.com</email>
141    </address>
142  </author>
143
144  <author initials="L." surname="Masinter" fullname="Larry Masinter">
145    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
146    <address>
147      <postal>
148        <street>345 Park Ave</street>
149        <city>San Jose</city>
150        <region>CA</region>
151        <code>95110</code>
152        <country>USA</country>
153      </postal>
154      <email>LMM@acm.org</email>
155      <uri>http://larry.masinter.net/</uri>
156    </address>
157  </author>
158 
159  <author initials="P." surname="Leach" fullname="Paul J. Leach">
160    <organization abbrev="Microsoft">Microsoft Corporation</organization>
161    <address>
162      <postal>
163        <street>1 Microsoft Way</street>
164        <city>Redmond</city>
165        <region>WA</region>
166        <code>98052</code>
167      </postal>
168      <email>paulle@microsoft.com</email>
169    </address>
170  </author>
171   
172  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
173    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
174    <address>
175      <postal>
176        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
177        <street>The Stata Center, Building 32</street>
178        <street>32 Vassar Street</street>
179        <city>Cambridge</city>
180        <region>MA</region>
181        <code>02139</code>
182        <country>USA</country>
183      </postal>
184      <email>timbl@w3.org</email>
185      <uri>http://www.w3.org/People/Berners-Lee/</uri>
186    </address>
187  </author>
188
189  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
190    <organization abbrev="W3C">World Wide Web Consortium</organization>
191    <address>
192      <postal>
193        <street>W3C / ERCIM</street>
194        <street>2004, rte des Lucioles</street>
195        <city>Sophia-Antipolis</city>
196        <region>AM</region>
197        <code>06902</code>
198        <country>France</country>
199      </postal>
200      <email>ylafon@w3.org</email>
201      <uri>http://www.raubacapeu.net/people/yves/</uri>
202    </address>
203  </author>
204
205  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
206    <organization abbrev="greenbytes">greenbytes GmbH</organization>
207    <address>
208      <postal>
209        <street>Hafenweg 16</street>
210        <city>Muenster</city><region>NW</region><code>48155</code>
211        <country>Germany</country>
212      </postal>
213      <phone>+49 251 2807760</phone>   
214      <facsimile>+49 251 2807761</facsimile>   
215      <email>julian.reschke@greenbytes.de</email>       
216      <uri>http://greenbytes.de/tech/webdav/</uri>     
217    </address>
218  </author>
219
220  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
221
222<abstract>
223<t>
224   The Hypertext Transfer Protocol (HTTP) is an application-level
225   protocol for distributed, collaborative, hypermedia information
226   systems. HTTP has been in use by the World Wide Web global information
227   initiative since 1990. This document is Part 2 of the seven-part specification
228   that defines the protocol referred to as "HTTP/1.1" and, taken together,
229   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
230   as expressed by request methods, request-header fields, response status codes,
231   and response-header fields.
232</t>
233</abstract>
234
235<note title="Editorial Note (To be removed by RFC Editor)">
236  <t>
237    Discussion of this draft should take place on the HTTPBIS working group
238    mailing list (ietf-http-wg@w3.org). The current issues list is
239    at <eref target="http://www.tools.ietf.org/wg/httpbis/trac/report/11"/>
240    and related documents (including fancy diffs) can be found at
241    <eref target="http://www.tools.ietf.org/wg/httpbis/"/>.
242  </t>
243  <t>
244    The changes in this draft are summarized in <xref target="changes.since.02"/>.
245  </t>
246</note>
247</front>
248<middle>
249<section title="Introduction" anchor="introduction">
250<t>
251   This document defines HTTP/1.1 request and response semantics.  Each HTTP
252   message, as defined in &messaging;, is in the form of either a request or
253   a response.  An HTTP server listens on a connection for HTTP requests and
254   responds to each request, in the order received on that connection, with
255   one or more HTTP response messages.  This document defines the commonly
256   agreed upon semantics of the HTTP uniform interface, the intentions defined
257   by each request method, and the various response messages that might be
258   expected as a result of applying that method for the requested resource.
259</t>
260<t>
261   This document is currently disorganized in order to minimize the changes
262   between drafts and enable reviewers to see the smaller errata changes.
263   The next draft will reorganize the sections to better reflect the content.
264   In particular, the sections will be ordered according to the typical
265   processing of an HTTP request message (after message parsing): resource
266   mapping, general header fields, methods, request modifiers, response
267   status, and resource metadata.  The current mess reflects how widely
268   dispersed these topics and associated requirements had become in
269   <xref target="RFC2616"/>.
270</t>
271
272<section title="Requirements" anchor="intro.requirements">
273<t>
274   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
275   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
276   document are to be interpreted as described in <xref target="RFC2119"/>.
277</t>
278<t>
279   An implementation is not compliant if it fails to satisfy one or more
280   of the &MUST; or &REQUIRED; level requirements for the protocols it
281   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
282   level and all the &SHOULD; level requirements for its protocols is said
283   to be "unconditionally compliant"; one that satisfies all the &MUST;
284   level requirements but not all the &SHOULD; level requirements for its
285   protocols is said to be "conditionally compliant."
286</t>
287</section>
288</section>
289
290<section title="Notational Conventions and Generic Grammar" anchor="notation">
291  <x:anchor-alias value="comment"/>
292  <x:anchor-alias value="DIGIT"/>
293  <x:anchor-alias value="quoted-string"/>
294  <x:anchor-alias value="token"/>
295<t>
296  This specification uses the ABNF syntax defined in &notation-abnf; and
297  the core rules defined in &basic-rules;:
298  <cref anchor="abnf.dep">ABNF syntax and basic rules will be adopted from RFC 5234, see
299  <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>.</cref>
300</t>
301<figure><artwork type="abnf2616">
302  <x:ref>DIGIT</x:ref>         = &lt;DIGIT, defined in &basic-rules;&gt;
303</artwork></figure>
304<figure><artwork type="abnf2616">
305  <x:anchor-alias value="Accept"/>
306  <x:ref>comment</x:ref>       = &lt;comment, defined in &basic-rules;&gt;
307  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &basic-rules;&gt;
308  <x:ref>token</x:ref>         = &lt;token, defined in &basic-rules;&gt;
309</artwork></figure>
310<t anchor="abnf.dependencies">
311  <x:anchor-alias value="absoluteURI"/>
312  <x:anchor-alias value="Accept"/>
313  <x:anchor-alias value="Accept-Charset"/>
314  <x:anchor-alias value="Accept-Encoding"/>
315  <x:anchor-alias value="Accept-Language"/>
316  <x:anchor-alias value="Accept-Ranges"/>
317  <x:anchor-alias value="Age"/>
318  <x:anchor-alias value="Authorization"/>
319  <x:anchor-alias value="ETag"/>
320  <x:anchor-alias value="fragment"/>
321  <x:anchor-alias value="Host"/>
322  <x:anchor-alias value="HTTP-date"/>
323  <x:anchor-alias value="If-Match"/>
324  <x:anchor-alias value="If-Modified-Since"/>
325  <x:anchor-alias value="If-None-Match"/>
326  <x:anchor-alias value="If-Range"/>
327  <x:anchor-alias value="If-Unmodified-Since"/>
328  <x:anchor-alias value="product"/>
329  <x:anchor-alias value="Proxy-Authenticate"/>
330  <x:anchor-alias value="Proxy-Authorization"/>
331  <x:anchor-alias value="Range"/>
332  <x:anchor-alias value="relativeURI"/>
333  <x:anchor-alias value="TE"/>
334  <x:anchor-alias value="Vary"/>
335  <x:anchor-alias value="WWW-Authenticate"/>
336  The ABNF rules below are defined in other parts:
337</t>
338<figure><!--Part1--><artwork type="abnf2616">
339  <x:ref>absoluteURI</x:ref>   = &lt;absoluteURI, defined in &general-syntax;&gt;
340  <x:ref>fragment</x:ref>      = &lt;fragment, defined in &general-syntax;&gt;
341  <x:ref>Host</x:ref>          = &lt;Host, defined in &header-host;&gt;
342  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
343  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
344  <x:ref>relativeURI</x:ref>   = &lt;relativeURI, defined in &general-syntax;&gt;
345  <x:ref>TE</x:ref>            = &lt;TE, defined in &header-te;&gt;
346</artwork></figure>
347<figure><!--Part3--><artwork type="abnf2616">
348  <x:ref>Accept</x:ref>        = &lt;Accept, defined in &header-accept;&gt;
349  <x:ref>Accept-Charset</x:ref> =
350             &lt;Accept-Charset, defined in &header-accept-charset;&gt;
351  <x:ref>Accept-Encoding</x:ref> =
352             &lt;Accept-Encoding, defined in &header-accept-encoding;&gt;
353  <x:ref>Accept-Language</x:ref> =
354             &lt;Accept-Language, defined in &header-accept-language;&gt;
355</artwork></figure>
356<figure><!--Part4--><artwork type="abnf2616">
357  <x:ref>ETag</x:ref>          = &lt;ETag, defined in &header-etag;&gt;
358  <x:ref>If-Match</x:ref>      = &lt;If-Match, defined in &header-if-match;&gt;
359  <x:ref>If-Modified-Since</x:ref> =
360             &lt;If-Modified-Since, defined in &header-if-modified-since;&gt;
361  <x:ref>If-None-Match</x:ref> = &lt;If-None-Match, defined in &header-if-none-match;&gt;
362  <x:ref>If-Unmodified-Since</x:ref> =
363             &lt;If-Unmodified-Since, defined in &header-if-unmodified-since;&gt;
364</artwork></figure>
365<figure><!--Part5--><artwork type="abnf2616">
366  <x:ref>Accept-Ranges</x:ref> = &lt;Accept-Ranges, defined in &header-accept-ranges;&gt;
367  <x:ref>If-Range</x:ref>      = &lt;If-Range, defined in &header-if-range;&gt;
368  <x:ref>Range</x:ref>         = &lt;Range, defined in &header-range;&gt;
369</artwork></figure>
370<figure><!--Part6--><artwork type="abnf2616">
371  <x:ref>Age</x:ref>           = &lt;Age, defined in &header-age;&gt;
372  <x:ref>Vary</x:ref>          = &lt;Vary, defined in &header-vary;&gt;
373</artwork><!--Part7--></figure>
374<figure><artwork type="abnf2616">
375  <x:ref>Authorization</x:ref> = &lt;Authorization, defined in &header-authorization;&gt;
376  <x:ref>Proxy-Authenticate</x:ref> =
377             &lt;Proxy-Authenticate, defined in &header-proxy-authenticate;&gt;
378  <x:ref>Proxy-Authorization</x:ref> =
379             &lt;Proxy-Authorization, defined in &header-proxy-authorization;&gt;
380  <x:ref>WWW-Authenticate</x:ref> =
381             &lt;WWW-Authenticate, defined in &header-www-authenticate;&gt;
382</artwork></figure>
383</section>
384
385<section title="Method" anchor="method">
386  <x:anchor-alias value="Method"/>
387  <x:anchor-alias value="extension-method"/>
388<t>
389   The Method  token indicates the method to be performed on the
390   resource identified by the Request-URI. The method is case-sensitive.
391</t>
392<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
393  <x:ref>Method</x:ref>         = %x4F.50.54.49.4F.4E.53   ; "OPTIONS", <xref target="OPTIONS"/>
394                 | %x47.45.54               ; "GET", <xref target="GET"/>
395                 | %x48.45.41.44            ; "HEAD", <xref target="HEAD"/>
396                 | %x50.4F.53.54            ; "POST", <xref target="POST"/>
397                 | %x50.55.54               ; "PUT", <xref target="PUT"/>
398                 | %x44.45.4C.45.54.45      ; "DELETE", <xref target="DELETE"/>
399                 | %x54.52.41.43.45         ; "TRACE", <xref target="TRACE"/>
400                 | %x43.4F.4E.4E.45.43.54   ; "CONNECT", <xref target="CONNECT"/>
401                 | <x:ref>extension-method</x:ref>
402  <x:ref>extension-method</x:ref> = <x:ref>token</x:ref>
403</artwork></figure>
404<t>
405   The list of methods allowed by a resource can be specified in an
406   Allow header field (<xref target="header.allow"/>). The return code of the response
407   always notifies the client whether a method is currently allowed on a
408   resource, since the set of allowed methods can change dynamically. An
409   origin server &SHOULD; return the status code 405 (Method Not Allowed)
410   if the method is known by the origin server but not allowed for the
411   requested resource, and 501 (Not Implemented) if the method is
412   unrecognized or not implemented by the origin server. The methods GET
413   and HEAD &MUST; be supported by all general-purpose servers. All other
414   methods are &OPTIONAL;; however, if the above methods are implemented,
415   they &MUST; be implemented with the same semantics as those specified
416   in <xref target="method.definitions"/>.
417</t>
418</section>
419
420<section title="Request Header Fields" anchor="request.header.fields">
421  <x:anchor-alias value="extension-code"/>
422  <x:anchor-alias value="request-header"/>
423<t>
424   The request-header fields allow the client to pass additional
425   information about the request, and about the client itself, to the
426   server. These fields act as request modifiers, with semantics
427   equivalent to the parameters on a programming language method
428   invocation.
429</t>
430<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
431  <x:ref>request-header</x:ref> = <x:ref>Accept</x:ref>                   ; &header-accept;
432                 | <x:ref>Accept-Charset</x:ref>           ; &header-accept-charset;
433                 | <x:ref>Accept-Encoding</x:ref>          ; &header-accept-encoding;
434                 | <x:ref>Accept-Language</x:ref>          ; &header-accept-language;
435                 | <x:ref>Authorization</x:ref>            ; &header-authorization;
436                 | <x:ref>Expect</x:ref>                   ; <xref target="header.expect"/>
437                 | <x:ref>From</x:ref>                     ; <xref target="header.from"/>
438                 | <x:ref>Host</x:ref>                     ; &header-host;
439                 | <x:ref>If-Match</x:ref>                 ; &header-if-match;
440                 | <x:ref>If-Modified-Since</x:ref>        ; &header-if-modified-since;
441                 | <x:ref>If-None-Match</x:ref>            ; &header-if-none-match;
442                 | <x:ref>If-Range</x:ref>                 ; &header-if-range;
443                 | <x:ref>If-Unmodified-Since</x:ref>      ; &header-if-unmodified-since;
444                 | <x:ref>Max-Forwards</x:ref>             ; <xref target="header.max-forwards"/>
445                 | <x:ref>Proxy-Authorization</x:ref>      ; &header-proxy-authorization;
446                 | <x:ref>Range</x:ref>                    ; &header-range;
447                 | <x:ref>Referer</x:ref>                  ; <xref target="header.referer"/>
448                 | <x:ref>TE</x:ref>                       ; &header-te;
449                 | <x:ref>User-Agent</x:ref>               ; <xref target="header.user-agent"/>
450</artwork></figure>
451<t>
452   Request-header field names can be extended reliably only in
453   combination with a change in the protocol version. However, new or
454   experimental header fields &MAY; be given the semantics of request-header
455   fields if all parties in the communication recognize them to
456   be request-header fields. Unrecognized header fields are treated as
457   entity-header fields.
458</t>
459</section>
460
461<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
462  <x:anchor-alias value="Reason-Phrase"/>
463  <x:anchor-alias value="Status-Code"/>
464<t>
465   The Status-Code element is a 3-digit integer result code of the
466   attempt to understand and satisfy the request. The status codes listed
467   below are defined in <xref target="status.codes"/>.
468   The Reason-Phrase is intended to give a short
469   textual description of the Status-Code. The Status-Code is intended
470   for use by automata and the Reason-Phrase is intended for the human
471   user. The client is not required to examine or display the Reason-Phrase.
472</t>
473<t> 
474   The individual values of the numeric status codes defined for
475   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
476   presented below. The reason phrases listed here are only
477   recommendations -- they &MAY; be replaced by local equivalents without
478   affecting the protocol.
479</t>
480<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"/>
481  <x:ref>Status-Code</x:ref>    =
482         "100"  ; <xref target="status.100"/>: Continue
483       | "101"  ; <xref target="status.101"/>: Switching Protocols
484       | "200"  ; <xref target="status.200"/>: OK
485       | "201"  ; <xref target="status.201"/>: Created
486       | "202"  ; <xref target="status.202"/>: Accepted
487       | "203"  ; <xref target="status.203"/>: Non-Authoritative Information
488       | "204"  ; <xref target="status.204"/>: No Content
489       | "205"  ; <xref target="status.205"/>: Reset Content
490       | "206"  ; <xref target="status.206"/>: Partial Content
491       | "300"  ; <xref target="status.300"/>: Multiple Choices
492       | "301"  ; <xref target="status.301"/>: Moved Permanently
493       | "302"  ; <xref target="status.302"/>: Found
494       | "303"  ; <xref target="status.303"/>: See Other
495       | "304"  ; <xref target="status.304"/>: Not Modified
496       | "305"  ; <xref target="status.305"/>: Use Proxy
497       | "307"  ; <xref target="status.307"/>: Temporary Redirect
498       | "400"  ; <xref target="status.400"/>: Bad Request
499       | "401"  ; <xref target="status.401"/>: Unauthorized
500       | "402"  ; <xref target="status.402"/>: Payment Required
501       | "403"  ; <xref target="status.403"/>: Forbidden
502       | "404"  ; <xref target="status.404"/>: Not Found
503       | "405"  ; <xref target="status.405"/>: Method Not Allowed
504       | "406"  ; <xref target="status.406"/>: Not Acceptable
505       | "407"  ; <xref target="status.407"/>: Proxy Authentication Required
506       | "408"  ; <xref target="status.408"/>: Request Time-out
507       | "409"  ; <xref target="status.409"/>: Conflict
508       | "410"  ; <xref target="status.410"/>: Gone
509       | "411"  ; <xref target="status.411"/>: Length Required
510       | "412"  ; <xref target="status.412"/>: Precondition Failed
511       | "413"  ; <xref target="status.413"/>: Request Entity Too Large
512       | "414"  ; <xref target="status.414"/>: Request-URI Too Large
513       | "415"  ; <xref target="status.415"/>: Unsupported Media Type
514       | "416"  ; <xref target="status.416"/>: Requested range not satisfiable
515       | "417"  ; <xref target="status.417"/>: Expectation Failed
516       | "500"  ; <xref target="status.500"/>: Internal Server Error
517       | "501"  ; <xref target="status.501"/>: Not Implemented
518       | "502"  ; <xref target="status.502"/>: Bad Gateway
519       | "503"  ; <xref target="status.503"/>: Service Unavailable
520       | "504"  ; <xref target="status.504"/>: Gateway Time-out
521       | "505"  ; <xref target="status.505"/>: HTTP Version not supported
522       | <x:ref>extension-code</x:ref>
523
524  <x:ref>extension-code</x:ref> = 3<x:ref>DIGIT</x:ref>
525  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
526</artwork></figure>
527<t>
528   HTTP status codes are extensible. HTTP applications are not required
529   to understand the meaning of all registered status codes, though such
530   understanding is obviously desirable. However, applications &MUST;
531   understand the class of any status code, as indicated by the first
532   digit, and treat any unrecognized response as being equivalent to the
533   x00 status code of that class, with the exception that an
534   unrecognized response &MUST-NOT; be cached. For example, if an
535   unrecognized status code of 431 is received by the client, it can
536   safely assume that there was something wrong with its request and
537   treat the response as if it had received a 400 status code. In such
538   cases, user agents &SHOULD; present to the user the entity returned
539   with the response, since that entity is likely to include human-readable
540   information which will explain the unusual status.
541</t>
542
543<section title="Status Code Registry" anchor="status.code.registry">
544<t>
545  The HTTP Status Code Registry defines the name space for the Status-Code
546  token in the Status line of an HTTP response.
547</t>
548<t>
549  Values to be added to this name space are subject to IETF review
550  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).  Any document registering
551  new status codes should be traceable through statuses of either 'Obsoletes'
552  or 'Updates' to this document.
553</t>
554<t>
555  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
556</t>
557</section>
558
559</section>
560
561<section title="Response Header Fields" anchor="response.header.fields">
562  <x:anchor-alias value="response-header"/>
563<t>
564   The response-header fields allow the server to pass additional
565   information about the response which cannot be placed in the Status-Line.
566   These header fields give information about the server and about
567   further access to the resource identified by the Request-URI.
568</t>
569<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
570  <x:ref>response-header</x:ref> = <x:ref>Accept-Ranges</x:ref>           ; &header-accept-ranges;
571                  | <x:ref>Age</x:ref>                     ; &header-age;
572                  | <x:ref>Allow</x:ref>                   ; <xref target="header.allow"/>
573                  | <x:ref>ETag</x:ref>                    ; &header-etag;
574                  | <x:ref>Location</x:ref>                ; <xref target="header.location"/>
575                  | <x:ref>Proxy-Authenticate</x:ref>      ; &header-proxy-authenticate;
576                  | <x:ref>Retry-After</x:ref>             ; <xref target="header.retry-after"/>
577                  | <x:ref>Server</x:ref>                  ; <xref target="header.server"/>
578                  | <x:ref>Vary</x:ref>                    ; &header-vary;
579                  | <x:ref>WWW-Authenticate</x:ref>        ; &header-www-authenticate;
580</artwork></figure>
581<t>
582   Response-header field names can be extended reliably only in
583   combination with a change in the protocol version. However, new or
584   experimental header fields &MAY; be given the semantics of response-header
585   fields if all parties in the communication recognize them to
586   be response-header fields. Unrecognized header fields are treated as
587   entity-header fields.
588</t>
589</section>
590
591<section title="Entity" anchor="entity">
592<t>
593   Request and Response messages &MAY; transfer an entity if not otherwise
594   restricted by the request method or response status code. An entity
595   consists of entity-header fields and an entity-body, although some
596   responses will only include the entity-headers. HTTP entity-body and
597   entity-header fields are defined in &payload;.
598</t>
599<t>
600   An entity-body is only present in a message when a message-body is
601   present, as described in &message-body;. The entity-body is obtained
602   from the message-body by decoding any Transfer-Encoding that might
603   have been applied to ensure safe and proper transfer of the message.
604</t>
605</section>
606
607
608<section title="Method Definitions" anchor="method.definitions">
609<t>
610   The set of common methods for HTTP/1.1 is defined below. Although
611   this set can be expanded, additional methods cannot be assumed to
612   share the same semantics for separately extended clients and servers.
613</t>
614
615<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
616
617<section title="Safe Methods" anchor="safe.methods">
618<t>
619   Implementors should be aware that the software represents the user in
620   their interactions over the Internet, and should be careful to allow
621   the user to be aware of any actions they might take which may have an
622   unexpected significance to themselves or others.
623</t>
624<t>
625   In particular, the convention has been established that the GET and
626   HEAD methods &SHOULD-NOT;  have the significance of taking an action
627   other than retrieval. These methods ought to be considered "safe".
628   This allows user agents to represent other methods, such as POST, PUT
629   and DELETE, in a special way, so that the user is made aware of the
630   fact that a possibly unsafe action is being requested.
631</t>
632<t>
633   Naturally, it is not possible to ensure that the server does not
634   generate side-effects as a result of performing a GET request; in
635   fact, some dynamic resources consider that a feature. The important
636   distinction here is that the user did not request the side-effects,
637   so therefore cannot be held accountable for them.
638</t>
639</section>
640
641<section title="Idempotent Methods" anchor="idempotent.methods">
642<t>
643   Methods can also have the property of "idempotence" in that (aside
644   from error or expiration issues) the side-effects of N &gt; 0 identical
645   requests is the same as for a single request. The methods GET, HEAD,
646   PUT and DELETE share this property. Also, the methods OPTIONS and
647   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
648</t>
649<t>
650   However, it is possible that a sequence of several requests is non-idempotent,
651   even if all of the methods executed in that sequence are
652   idempotent. (A sequence is idempotent if a single execution of the
653   entire sequence always yields a result that is not changed by a
654   reexecution of all, or part, of that sequence.) For example, a
655   sequence is non-idempotent if its result depends on a value that is
656   later modified in the same sequence.
657</t>
658<t>
659   A sequence that never has side effects is idempotent, by definition
660   (provided that no concurrent operations are being executed on the
661   same set of resources).
662</t>
663</section>
664</section>
665
666<section title="OPTIONS" anchor="OPTIONS">
667  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
668  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
669<t>
670   The OPTIONS method represents a request for information about the
671   communication options available on the request/response chain
672   identified by the Request-URI. This method allows the client to
673   determine the options and/or requirements associated with a resource,
674   or the capabilities of a server, without implying a resource action
675   or initiating a resource retrieval.
676</t>
677<t>
678   Responses to this method are not cacheable.
679</t>
680<t>
681   If the OPTIONS request includes an entity-body (as indicated by the
682   presence of Content-Length or Transfer-Encoding), then the media type
683   &MUST; be indicated by a Content-Type field. Although this
684   specification does not define any use for such a body, future
685   extensions to HTTP might use the OPTIONS body to make more detailed
686   queries on the server. A server that does not support such an
687   extension &MAY; discard the request body.
688</t>
689<t>
690   If the Request-URI is an asterisk ("*"), the OPTIONS request is
691   intended to apply to the server in general rather than to a specific
692   resource. Since a server's communication options typically depend on
693   the resource, the "*" request is only useful as a "ping" or "no-op"
694   type of method; it does nothing beyond allowing the client to test
695   the capabilities of the server. For example, this can be used to test
696   a proxy for HTTP/1.1 compliance (or lack thereof).
697</t>
698<t>
699   If the Request-URI is not an asterisk, the OPTIONS request applies
700   only to the options that are available when communicating with that
701   resource.
702</t>
703<t>
704   A 200 response &SHOULD; include any header fields that indicate
705   optional features implemented by the server and applicable to that
706   resource (e.g., Allow), possibly including extensions not defined by
707   this specification. The response body, if any, &SHOULD; also include
708   information about the communication options. The format for such a
709   body is not defined by this specification, but might be defined by
710   future extensions to HTTP. Content negotiation &MAY; be used to select
711   the appropriate response format. If no response body is included, the
712   response &MUST; include a Content-Length field with a field-value of
713   "0".
714</t>
715<t>
716   The Max-Forwards request-header field &MAY; be used to target a
717   specific proxy in the request chain. When a proxy receives an OPTIONS
718   request on an absoluteURI for which request forwarding is permitted,
719   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
720   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
721   instead, the proxy &SHOULD; respond with its own communication options.
722   If the Max-Forwards field-value is an integer greater than zero, the
723   proxy &MUST; decrement the field-value when it forwards the request. If
724   no Max-Forwards field is present in the request, then the forwarded
725   request &MUST-NOT; include a Max-Forwards field.
726</t>
727</section>
728
729<section title="GET" anchor="GET">
730  <iref primary="true" item="GET method" x:for-anchor=""/>
731  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
732<t>
733   The GET method means retrieve whatever information (in the form of an
734   entity) is identified by the Request-URI. If the Request-URI refers
735   to a data-producing process, it is the produced data which shall be
736   returned as the entity in the response and not the source text of the
737   process, unless that text happens to be the output of the process.
738</t>
739<t>
740   The semantics of the GET method change to a "conditional GET" if the
741   request message includes an If-Modified-Since, If-Unmodified-Since,
742   If-Match, If-None-Match, or If-Range header field. A conditional GET
743   method requests that the entity be transferred only under the
744   circumstances described by the conditional header field(s). The
745   conditional GET method is intended to reduce unnecessary network
746   usage by allowing cached entities to be refreshed without requiring
747   multiple requests or transferring data already held by the client.
748</t>
749<t>
750   The semantics of the GET method change to a "partial GET" if the
751   request message includes a Range header field. A partial GET requests
752   that only part of the entity be transferred, as described in &header-range;.
753   The partial GET method is intended to reduce unnecessary
754   network usage by allowing partially-retrieved entities to be
755   completed without transferring data already held by the client.
756</t>
757<t>
758   The response to a GET request is cacheable if and only if it meets
759   the requirements for HTTP caching described in &caching;.
760</t>
761<t>
762   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
763</t>
764</section>
765
766<section title="HEAD" anchor="HEAD">
767  <iref primary="true" item="HEAD method" x:for-anchor=""/>
768  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
769<t>
770   The HEAD method is identical to GET except that the server &MUST-NOT;
771   return a message-body in the response. The metainformation contained
772   in the HTTP headers in response to a HEAD request &SHOULD; be identical
773   to the information sent in response to a GET request. This method can
774   be used for obtaining metainformation about the entity implied by the
775   request without transferring the entity-body itself. This method is
776   often used for testing hypertext links for validity, accessibility,
777   and recent modification.
778</t>
779<t>
780   The response to a HEAD request &MAY; be cacheable in the sense that the
781   information contained in the response &MAY; be used to update a
782   previously cached entity from that resource. If the new field values
783   indicate that the cached entity differs from the current entity (as
784   would be indicated by a change in Content-Length, Content-MD5, ETag
785   or Last-Modified), then the cache &MUST; treat the cache entry as
786   stale.
787</t>
788</section>
789
790<section title="POST" anchor="POST">
791  <iref primary="true" item="POST method" x:for-anchor=""/>
792  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
793<t>
794   The POST method is used to request that the origin server accept the
795   entity enclosed in the request as data to be processed by the resource
796   identified by the Request-URI in the Request-Line. POST is designed
797   to allow a uniform method to cover the following functions:
798  <list style="symbols">
799    <t>
800      Annotation of existing resources;
801    </t>
802    <t>
803        Posting a message to a bulletin board, newsgroup, mailing list,
804        or similar group of articles;
805    </t>
806    <t>
807        Providing a block of data, such as the result of submitting a
808        form, to a data-handling process;
809    </t>
810    <t>
811        Extending a database through an append operation.
812    </t>
813  </list>
814</t>
815<t>
816   The actual function performed by the POST method is determined by the
817   server and is usually dependent on the Request-URI.
818</t>
819<t>
820   The action performed by the POST method might not result in a
821   resource that can be identified by a URI. In this case, either 200
822   (OK) or 204 (No Content) is the appropriate response status,
823   depending on whether or not the response includes an entity that
824   describes the result.
825</t>
826<t>
827   If a resource has been created on the origin server, the response
828   &SHOULD; be 201 (Created) and contain an entity which describes the
829   status of the request and refers to the new resource, and a Location
830   header (see <xref target="header.location"/>).
831</t>
832<t>
833   Responses to this method are not cacheable, unless the response
834   includes appropriate Cache-Control or Expires header fields. However,
835   the 303 (See Other) response can be used to direct the user agent to
836   retrieve a cacheable resource.
837</t>
838</section>
839
840<section title="PUT" anchor="PUT">
841  <iref primary="true" item="PUT method" x:for-anchor=""/>
842  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
843<t>
844   The PUT method requests that the enclosed entity be stored at the
845   supplied Request-URI. If the Request-URI refers to an already
846   existing resource, the enclosed entity &SHOULD; be considered as a
847   modified version of the one residing on the origin server. If the
848   Request-URI does not point to an existing resource, and that URI is
849   capable of being defined as a new resource by the requesting user
850   agent, the origin server can create the resource with that URI. If a
851   new resource is created at the Request-URI, the origin server &MUST;
852         inform the user agent
853   via the 201 (Created) response. If an existing resource is modified,
854   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
855   to indicate successful completion of the request. If the resource
856   could not be created or modified with the Request-URI, an appropriate
857   error response &SHOULD; be given that reflects the nature of the
858   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
859   (e.g. Content-Range) headers that it does not understand or implement
860   and &MUST; return a 501 (Not Implemented) response in such cases.
861</t>
862<t>
863   If the request passes through a cache and the Request-URI identifies
864   one or more currently cached entities, those entries &SHOULD; be
865   treated as stale. Responses to this method are not cacheable.
866</t>
867<t>
868   The fundamental difference between the POST and PUT requests is
869   reflected in the different meaning of the Request-URI. The URI in a
870   POST request identifies the resource that will handle the enclosed
871   entity. That resource might be a data-accepting process, a gateway to
872   some other protocol, or a separate entity that accepts annotations.
873   In contrast, the URI in a PUT request identifies the entity enclosed
874   with the request -- the user agent knows what URI is intended and the
875   server &MUST-NOT; attempt to apply the request to some other resource.
876   If the server desires that the request be applied to a different URI,
877   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
878   then make its own decision regarding whether or not to redirect the
879   request.
880</t>
881<t>
882   A single resource &MAY; be identified by many different URIs. For
883   example, an article might have a URI for identifying "the current
884   version" which is separate from the URI identifying each particular
885   version. In this case, a PUT request on a general URI might result in
886   several other URIs being defined by the origin server.
887</t>
888<t>
889   HTTP/1.1 does not define how a PUT method affects the state of an
890   origin server.
891</t>
892<t>
893   Unless otherwise specified for a particular entity-header, the
894   entity-headers in the PUT request &SHOULD; be applied to the resource
895   created or modified by the PUT.
896</t>
897</section>
898
899<section title="DELETE" anchor="DELETE">
900  <iref primary="true" item="DELETE method" x:for-anchor=""/>
901  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
902<t>
903   The DELETE method requests that the origin server delete the resource
904   identified by the Request-URI. This method &MAY; be overridden by human
905   intervention (or other means) on the origin server. The client cannot
906   be guaranteed that the operation has been carried out, even if the
907   status code returned from the origin server indicates that the action
908   has been completed successfully. However, the server &SHOULD-NOT; 
909   indicate success unless, at the time the response is given, it
910   intends to delete the resource or move it to an inaccessible
911   location.
912</t>
913<t>
914   A successful response &SHOULD; be 200 (OK) if the response includes an
915   entity describing the status, 202 (Accepted) if the action has not
916   yet been enacted, or 204 (No Content) if the action has been enacted
917   but the response does not include an entity.
918</t>
919<t>
920   If the request passes through a cache and the Request-URI identifies
921   one or more currently cached entities, those entries &SHOULD; be
922   treated as stale. Responses to this method are not cacheable.
923</t>
924</section>
925
926<section title="TRACE" anchor="TRACE">
927  <iref primary="true" item="TRACE method" x:for-anchor=""/>
928  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
929<t>
930   The TRACE method is used to invoke a remote, application-layer loop-back
931   of the request message. The final recipient of the request
932   &SHOULD; reflect the message received back to the client as the
933   entity-body of a 200 (OK) response. The final recipient is either the
934   origin server or the first proxy or gateway to receive a Max-Forwards
935   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
936   &MUST-NOT; include an entity.
937</t>
938<t>
939   TRACE allows the client to see what is being received at the other
940   end of the request chain and use that data for testing or diagnostic
941   information. The value of the Via header field (&header-via;) is of
942   particular interest, since it acts as a trace of the request chain.
943   Use of the Max-Forwards header field allows the client to limit the
944   length of the request chain, which is useful for testing a chain of
945   proxies forwarding messages in an infinite loop.
946</t>
947<t>
948   If the request is valid, the response &SHOULD; contain the entire
949   request message in the entity-body, with a Content-Type of
950   "message/http" (see &media-type-message-http;). Responses to this method
951   &MUST-NOT; be cached.
952</t>
953</section>
954
955<section title="CONNECT" anchor="CONNECT">
956  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
957  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
958<t>
959   This specification reserves the method name CONNECT for use with a
960   proxy that can dynamically switch to being a tunnel (e.g. SSL
961   tunneling <xref target="Luo1998"/>).
962</t>
963</section>
964</section>
965
966
967<section title="Status Code Definitions" anchor="status.codes">
968<t>
969   Each Status-Code is described below, including a description of which
970   method(s) it can follow and any metainformation required in the
971   response.
972</t>
973
974<section title="Informational 1xx" anchor="status.1xx">
975<t>
976   This class of status code indicates a provisional response,
977   consisting only of the Status-Line and optional headers, and is
978   terminated by an empty line. There are no required headers for this
979   class of status code. Since HTTP/1.0 did not define any 1xx status
980   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
981   except under experimental conditions.
982</t>
983<t>
984   A client &MUST; be prepared to accept one or more 1xx status responses
985   prior to a regular response, even if the client does not expect a 100
986   (Continue) status message. Unexpected 1xx status responses &MAY; be
987   ignored by a user agent.
988</t>
989<t>
990   Proxies &MUST; forward 1xx responses, unless the connection between the
991   proxy and its client has been closed, or unless the proxy itself
992   requested the generation of the 1xx response. (For example, if a
993   proxy adds a "Expect: 100-continue" field when it forwards a request,
994   then it need not forward the corresponding 100 (Continue)
995   response(s).)
996</t>
997
998<section title="100 Continue" anchor="status.100">
999  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1000  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1001<t>
1002   The client &SHOULD; continue with its request. This interim response is
1003   used to inform the client that the initial part of the request has
1004   been received and has not yet been rejected by the server. The client
1005   &SHOULD; continue by sending the remainder of the request or, if the
1006   request has already been completed, ignore this response. The server
1007   &MUST; send a final response after the request has been completed. See
1008   &use100; for detailed discussion of the use and handling of this
1009   status code.
1010</t>
1011</section>
1012
1013<section title="101 Switching Protocols" anchor="status.101">
1014  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1015  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1016<t>
1017   The server understands and is willing to comply with the client's
1018   request, via the Upgrade message header field (&header-upgrade;), for a
1019   change in the application protocol being used on this connection. The
1020   server will switch protocols to those defined by the response's
1021   Upgrade header field immediately after the empty line which
1022   terminates the 101 response.
1023</t>
1024<t>
1025   The protocol &SHOULD; be switched only when it is advantageous to do
1026   so. For example, switching to a newer version of HTTP is advantageous
1027   over older versions, and switching to a real-time, synchronous
1028   protocol might be advantageous when delivering resources that use
1029   such features.
1030</t>
1031</section>
1032</section>
1033
1034<section title="Successful 2xx" anchor="status.2xx">
1035<t>
1036   This class of status code indicates that the client's request was
1037   successfully received, understood, and accepted.
1038</t>
1039
1040<section title="200 OK" anchor="status.200">
1041  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1042  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1043<t>
1044   The request has succeeded. The information returned with the response
1045   is dependent on the method used in the request, for example:
1046  <list style="hanging">
1047    <t hangText="GET">
1048          an entity corresponding to the requested resource is sent in
1049          the response;
1050    </t>
1051    <t hangText="HEAD">
1052          the entity-header fields corresponding to the requested
1053          resource are sent in the response without any message-body;
1054    </t>
1055    <t hangText="POST">
1056      an entity describing or containing the result of the action;
1057    </t>
1058    <t hangText="TRACE">
1059      an entity containing the request message as received by the
1060      end server.
1061    </t>
1062  </list>
1063</t>
1064</section>
1065
1066<section title="201 Created" anchor="status.201">
1067  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1068  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1069<t>
1070   The request has been fulfilled and resulted in a new resource being
1071   created. The newly created resource can be referenced by the URI(s)
1072   returned in the entity of the response, with the most specific URI
1073   for the resource given by a Location header field. The response
1074   &SHOULD; include an entity containing a list of resource
1075   characteristics and location(s) from which the user or user agent can
1076   choose the one most appropriate. The entity format is specified by
1077   the media type given in the Content-Type header field. The origin
1078   server &MUST; create the resource before returning the 201 status code.
1079   If the action cannot be carried out immediately, the server &SHOULD;
1080   respond with 202 (Accepted) response instead.
1081</t>
1082<t>
1083   A 201 response &MAY; contain an ETag response header field indicating
1084   the current value of the entity tag for the requested variant just
1085   created, see &header-etag;.
1086</t>
1087</section>
1088
1089<section title="202 Accepted" anchor="status.202">
1090  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1091  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1092<t>
1093   The request has been accepted for processing, but the processing has
1094   not been completed.  The request might or might not eventually be
1095   acted upon, as it might be disallowed when processing actually takes
1096   place. There is no facility for re-sending a status code from an
1097   asynchronous operation such as this.
1098</t>
1099<t>
1100   The 202 response is intentionally non-committal. Its purpose is to
1101   allow a server to accept a request for some other process (perhaps a
1102   batch-oriented process that is only run once per day) without
1103   requiring that the user agent's connection to the server persist
1104   until the process is completed. The entity returned with this
1105   response &SHOULD; include an indication of the request's current status
1106   and either a pointer to a status monitor or some estimate of when the
1107   user can expect the request to be fulfilled.
1108</t>
1109</section>
1110
1111<section title="203 Non-Authoritative Information" anchor="status.203">
1112  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1113  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1114<t>
1115   The returned metainformation in the entity-header is not the
1116   definitive set as available from the origin server, but is gathered
1117   from a local or a third-party copy. The set presented &MAY; be a subset
1118   or superset of the original version. For example, including local
1119   annotation information about the resource might result in a superset
1120   of the metainformation known by the origin server. Use of this
1121   response code is not required and is only appropriate when the
1122   response would otherwise be 200 (OK).
1123</t>
1124</section>
1125
1126<section title="204 No Content" anchor="status.204">
1127  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1128  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1129<t>
1130   The server has fulfilled the request but does not need to return an
1131   entity-body, and might want to return updated metainformation. The
1132   response &MAY; include new or updated metainformation in the form of
1133   entity-headers, which if present &SHOULD; be associated with the
1134   requested variant.
1135</t>
1136<t>
1137   If the client is a user agent, it &SHOULD-NOT;  change its document view
1138   from that which caused the request to be sent. This response is
1139   primarily intended to allow input for actions to take place without
1140   causing a change to the user agent's active document view, although
1141   any new or updated metainformation &SHOULD; be applied to the document
1142   currently in the user agent's active view.
1143</t>
1144<t>
1145   The 204 response &MUST-NOT; include a message-body, and thus is always
1146   terminated by the first empty line after the header fields.
1147</t>
1148</section>
1149
1150<section title="205 Reset Content" anchor="status.205">
1151  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1152  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1153<t>
1154   The server has fulfilled the request and the user agent &SHOULD; reset
1155   the document view which caused the request to be sent. This response
1156   is primarily intended to allow input for actions to take place via
1157   user input, followed by a clearing of the form in which the input is
1158   given so that the user can easily initiate another input action. The
1159   response &MUST-NOT; include an entity.
1160</t>
1161</section>
1162
1163<section title="206 Partial Content" anchor="status.206">
1164  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1165  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1166<t>
1167   The server has fulfilled the partial GET request for the resource
1168   and the enclosed entity is a partial representation as defined in &range;.
1169</t>
1170</section>
1171</section>
1172
1173<section title="Redirection 3xx" anchor="status.3xx">
1174<t>
1175   This class of status code indicates that further action needs to be
1176   taken by the user agent in order to fulfill the request.  The action
1177   required &MAY; be carried out by the user agent without interaction
1178   with the user if and only if the method used in the second request is
1179   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1180   such loops generate network traffic for each redirection.
1181  <list><t>
1182      <x:h>Note:</x:h> previous versions of this specification recommended a
1183      maximum of five redirections. Content developers should be aware
1184      that there might be clients that implement such a fixed
1185      limitation.
1186  </t></list>
1187</t>
1188
1189<section title="300 Multiple Choices" anchor="status.300">
1190  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1191  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1192<t>
1193   The requested resource corresponds to any one of a set of
1194   representations, each with its own specific location, and agent-driven
1195   negotiation information (&content-negotiation;) is being provided so that
1196   the user (or user agent) can select a preferred representation and
1197   redirect its request to that location.
1198</t>
1199<t>
1200   Unless it was a HEAD request, the response &SHOULD; include an entity
1201   containing a list of resource characteristics and location(s) from
1202   which the user or user agent can choose the one most appropriate. The
1203   entity format is specified by the media type given in the Content-Type
1204   header field. Depending upon the format and the capabilities of
1205   the user agent, selection of the most appropriate choice &MAY; be
1206   performed automatically. However, this specification does not define
1207   any standard for such automatic selection.
1208</t>
1209<t>
1210   If the server has a preferred choice of representation, it &SHOULD;
1211   include the specific URI for that representation in the Location
1212   field; user agents &MAY; use the Location field value for automatic
1213   redirection. This response is cacheable unless indicated otherwise.
1214</t>
1215</section>
1216
1217<section title="301 Moved Permanently" anchor="status.301">
1218  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1219  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1220<t>
1221   The requested resource has been assigned a new permanent URI and any
1222   future references to this resource &SHOULD; use one of the returned
1223   URIs.  Clients with link editing capabilities ought to automatically
1224   re-link references to the Request-URI to one or more of the new
1225   references returned by the server, where possible. This response is
1226   cacheable unless indicated otherwise.
1227</t>
1228<t>
1229   The new permanent URI &SHOULD; be given by the Location field in the
1230   response. Unless the request method was HEAD, the entity of the
1231   response &SHOULD; contain a short hypertext note with a hyperlink to
1232   the new URI(s).
1233</t>
1234<t>
1235   If the 301 status code is received in response to a request method
1236   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1237   then the request &MAY; be automatically redirected by the user agent without
1238   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1239   request unless it can be confirmed by the user, since this might
1240   change the conditions under which the request was issued.
1241  <list><t>
1242      <x:h>Note:</x:h> When automatically redirecting a POST request after
1243      receiving a 301 status code, some existing HTTP/1.0 user agents
1244      will erroneously change it into a GET request.
1245  </t></list>
1246</t>
1247</section>
1248
1249<section title="302 Found" anchor="status.302">
1250  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1251  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1252<t>
1253   The requested resource resides temporarily under a different URI.
1254   Since the redirection might be altered on occasion, the client &SHOULD;
1255   continue to use the Request-URI for future requests.  This response
1256   is only cacheable if indicated by a Cache-Control or Expires header
1257   field.
1258</t>
1259<t>
1260   The temporary URI &SHOULD; be given by the Location field in the
1261   response. Unless the request method was HEAD, the entity of the
1262   response &SHOULD; contain a short hypertext note with a hyperlink to
1263   the new URI(s).
1264</t>
1265<t>
1266   If the 302 status code is received in response to a request method
1267   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1268   then the request &MAY; be automatically redirected by the user agent without
1269   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1270   request unless it can be confirmed by the user, since this might
1271   change the conditions under which the request was issued.
1272  <list><t>
1273      <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1274      to change the method on the redirected request.  However, most
1275      existing user agent implementations treat 302 as if it were a 303
1276      response, performing a GET on the Location field-value regardless
1277      of the original request method. The status codes 303 and 307 have
1278      been added for servers that wish to make unambiguously clear which
1279      kind of reaction is expected of the client.
1280  </t></list>
1281</t>
1282</section>
1283
1284<section title="303 See Other" anchor="status.303">
1285  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1286  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1287<t>
1288   The server directs the user agent to a different resource, indicated
1289   by a URI in the Location header field, that provides an indirect
1290   response to the original request.  The user agent &MAY; perform a GET
1291   request on the URI in the Location field in order to obtain a
1292   representation corresponding to the response, be redirected again,
1293   or end with an error status.  The Location URI is not a substitute
1294   reference for the originally requested resource.
1295</t>
1296<t>
1297   The 303 status is generally applicable to any HTTP method.  It is
1298   primarily used to allow the output of a POST action to redirect
1299   the user agent to a selected resource, since doing so provides the
1300   information corresponding to the POST response in a form that
1301   can be separately identified, bookmarked, and cached independent
1302   of the original request.
1303</t>
1304<t>
1305   A 303 response to a GET request indicates that the requested
1306   resource does not have a representation of its own that can be
1307   transferred by the server over HTTP.  The Location URI indicates a
1308   resource that is descriptive of the requested resource such that
1309   the follow-on representation may be useful without implying that
1310   it adequately represents the previously requested resource.
1311   Note that answers to the questions of what can be represented, what
1312   representations are adequate, and what might be a useful description
1313   are outside the scope of HTTP and thus entirely determined by the
1314   resource owner(s).
1315</t>
1316<t>
1317   A 303 response &SHOULD-NOT; be cached unless it is indicated as
1318   cacheable by Cache-Control or Expires header fields.  Except for
1319   responses to a HEAD request, the entity of a 303 response &SHOULD;
1320   contain a short hypertext note with a hyperlink to the Location URI.
1321</t>
1322</section>
1323
1324<section title="304 Not Modified" anchor="status.304">
1325  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1326  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1327<t>
1328   The response to the request has not been modified since the conditions
1329   indicated by the client's conditional GET request, as defined in &conditional;.
1330</t>
1331</section>
1332
1333<section title="305 Use Proxy" anchor="status.305">
1334  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1335  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1336<t>
1337   The 305 status was defined in a previous version of this specification
1338   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1339</t>
1340</section>
1341
1342<section title="306 (Unused)" anchor="status.306">
1343  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1344  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1345<t>
1346   The 306 status code was used in a previous version of the
1347   specification, is no longer used, and the code is reserved.
1348</t>
1349</section>
1350
1351<section title="307 Temporary Redirect" anchor="status.307">
1352  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1353  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1354<t>
1355   The requested resource resides temporarily under a different URI.
1356   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1357   continue to use the Request-URI for future requests.  This response
1358   is only cacheable if indicated by a Cache-Control or Expires header
1359   field.
1360</t>
1361<t>
1362   The temporary URI &SHOULD; be given by the Location field in the
1363   response. Unless the request method was HEAD, the entity of the
1364   response &SHOULD; contain a short hypertext note with a hyperlink to
1365   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1366   understand the 307 status. Therefore, the note &SHOULD; contain the
1367   information necessary for a user to repeat the original request on
1368   the new URI.
1369</t>
1370<t>
1371   If the 307 status code is received in response to a request method
1372   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1373   then the request &MAY; be automatically redirected by the user agent without
1374   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1375   request unless it can be confirmed by the user, since this might
1376   change the conditions under which the request was issued.
1377</t>
1378</section>
1379</section>
1380
1381<section title="Client Error 4xx" anchor="status.4xx">
1382<t>
1383   The 4xx class of status code is intended for cases in which the
1384   client seems to have erred. Except when responding to a HEAD request,
1385   the server &SHOULD; include an entity containing an explanation of the
1386   error situation, and whether it is a temporary or permanent
1387   condition. These status codes are applicable to any request method.
1388   User agents &SHOULD; display any included entity to the user.
1389</t>
1390<t>
1391   If the client is sending data, a server implementation using TCP
1392   &SHOULD; be careful to ensure that the client acknowledges receipt of
1393   the packet(s) containing the response, before the server closes the
1394   input connection. If the client continues sending data to the server
1395   after the close, the server's TCP stack will send a reset packet to
1396   the client, which may erase the client's unacknowledged input buffers
1397   before they can be read and interpreted by the HTTP application.
1398</t>
1399
1400<section title="400 Bad Request" anchor="status.400">
1401  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1402  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1403<t>
1404   The request could not be understood by the server due to malformed
1405   syntax. The client &SHOULD-NOT;  repeat the request without
1406   modifications.
1407</t>
1408</section>
1409
1410<section title="401 Unauthorized" anchor="status.401">
1411  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1412  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1413<t>
1414   The request requires user authentication (see &auth;).
1415</t>
1416</section>
1417
1418<section title="402 Payment Required" anchor="status.402">
1419  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1420  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1421<t>
1422   This code is reserved for future use.
1423</t>
1424</section>
1425
1426<section title="403 Forbidden" anchor="status.403">
1427  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1428  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1429<t>
1430   The server understood the request, but is refusing to fulfill it.
1431   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1432   If the request method was not HEAD and the server wishes to make
1433   public why the request has not been fulfilled, it &SHOULD; describe the
1434   reason for the refusal in the entity.  If the server does not wish to
1435   make this information available to the client, the status code 404
1436   (Not Found) can be used instead.
1437</t>
1438</section>
1439
1440<section title="404 Not Found" anchor="status.404">
1441  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1442  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1443<t>
1444   The server has not found anything matching the Request-URI. No
1445   indication is given of whether the condition is temporary or
1446   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1447   knows, through some internally configurable mechanism, that an old
1448   resource is permanently unavailable and has no forwarding address.
1449   This status code is commonly used when the server does not wish to
1450   reveal exactly why the request has been refused, or when no other
1451   response is applicable.
1452</t>
1453</section>
1454
1455<section title="405 Method Not Allowed" anchor="status.405">
1456  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1457  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1458<t>
1459   The method specified in the Request-Line is not allowed for the
1460   resource identified by the Request-URI. The response &MUST; include an
1461   Allow header containing a list of valid methods for the requested
1462   resource.
1463</t>
1464</section>
1465
1466<section title="406 Not Acceptable" anchor="status.406">
1467  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1468  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1469<t>
1470   The resource identified by the request is only capable of generating
1471   response entities which have content characteristics not acceptable
1472   according to the accept headers sent in the request.
1473</t>
1474<t>
1475   Unless it was a HEAD request, the response &SHOULD; include an entity
1476   containing a list of available entity characteristics and location(s)
1477   from which the user or user agent can choose the one most
1478   appropriate. The entity format is specified by the media type given
1479   in the Content-Type header field. Depending upon the format and the
1480   capabilities of the user agent, selection of the most appropriate
1481   choice &MAY; be performed automatically. However, this specification
1482   does not define any standard for such automatic selection.
1483  <list><t>
1484      <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1485      not acceptable according to the accept headers sent in the
1486      request. In some cases, this may even be preferable to sending a
1487      406 response. User agents are encouraged to inspect the headers of
1488      an incoming response to determine if it is acceptable.
1489  </t></list>
1490</t>
1491<t>
1492   If the response could be unacceptable, a user agent &SHOULD;
1493   temporarily stop receipt of more data and query the user for a
1494   decision on further actions.
1495</t>
1496</section>
1497
1498<section title="407 Proxy Authentication Required" anchor="status.407">
1499  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1500  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1501<t>
1502   This code is similar to 401 (Unauthorized), but indicates that the
1503   client must first authenticate itself with the proxy (see &auth;).
1504</t>
1505</section>
1506
1507<section title="408 Request Timeout" anchor="status.408">
1508  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1509  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1510<t>
1511   The client did not produce a request within the time that the server
1512   was prepared to wait. The client &MAY; repeat the request without
1513   modifications at any later time.
1514</t>
1515</section>
1516
1517<section title="409 Conflict" anchor="status.409">
1518  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1519  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1520<t>
1521   The request could not be completed due to a conflict with the current
1522   state of the resource. This code is only allowed in situations where
1523   it is expected that the user might be able to resolve the conflict
1524   and resubmit the request. The response body &SHOULD; include enough
1525   information for the user to recognize the source of the conflict.
1526   Ideally, the response entity would include enough information for the
1527   user or user agent to fix the problem; however, that might not be
1528   possible and is not required.
1529</t>
1530<t>
1531   Conflicts are most likely to occur in response to a PUT request. For
1532   example, if versioning were being used and the entity being PUT
1533   included changes to a resource which conflict with those made by an
1534   earlier (third-party) request, the server might use the 409 response
1535   to indicate that it can't complete the request. In this case, the
1536   response entity would likely contain a list of the differences
1537   between the two versions in a format defined by the response
1538   Content-Type.
1539</t>
1540</section>
1541
1542<section title="410 Gone" anchor="status.410">
1543  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1544  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1545<t>
1546   The requested resource is no longer available at the server and no
1547   forwarding address is known. This condition is expected to be
1548   considered permanent. Clients with link editing capabilities &SHOULD;
1549   delete references to the Request-URI after user approval. If the
1550   server does not know, or has no facility to determine, whether or not
1551   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1552   used instead. This response is cacheable unless indicated otherwise.
1553</t>
1554<t>
1555   The 410 response is primarily intended to assist the task of web
1556   maintenance by notifying the recipient that the resource is
1557   intentionally unavailable and that the server owners desire that
1558   remote links to that resource be removed. Such an event is common for
1559   limited-time, promotional services and for resources belonging to
1560   individuals no longer working at the server's site. It is not
1561   necessary to mark all permanently unavailable resources as "gone" or
1562   to keep the mark for any length of time -- that is left to the
1563   discretion of the server owner.
1564</t>
1565</section>
1566
1567<section title="411 Length Required" anchor="status.411">
1568  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1569  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1570<t>
1571   The server refuses to accept the request without a defined Content-Length.
1572   The client &MAY; repeat the request if it adds a valid
1573   Content-Length header field containing the length of the message-body
1574   in the request message.
1575</t>
1576</section>
1577
1578<section title="412 Precondition Failed" anchor="status.412">
1579  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1580  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1581<t>
1582   The precondition given in one or more of the request-header fields
1583   evaluated to false when it was tested on the server, as defined in
1584   &conditional;.
1585</t>
1586</section>
1587
1588<section title="413 Request Entity Too Large" anchor="status.413">
1589  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1590  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1591<t>
1592   The server is refusing to process a request because the request
1593   entity is larger than the server is willing or able to process. The
1594   server &MAY; close the connection to prevent the client from continuing
1595   the request.
1596</t>
1597<t>
1598   If the condition is temporary, the server &SHOULD; include a Retry-After
1599   header field to indicate that it is temporary and after what
1600   time the client &MAY; try again.
1601</t>
1602</section>
1603
1604<section title="414 Request-URI Too Long" anchor="status.414">
1605  <iref primary="true" item="414 Request-URI Too Long (status code)" x:for-anchor=""/>
1606  <iref primary="true" item="Status Codes" subitem="414 Request-URI Too Long" x:for-anchor=""/>
1607<t>
1608   The server is refusing to service the request because the Request-URI
1609   is longer than the server is willing to interpret. This rare
1610   condition is only likely to occur when a client has improperly
1611   converted a POST request to a GET request with long query
1612   information, when the client has descended into a URI "black hole" of
1613   redirection (e.g., a redirected URI prefix that points to a suffix of
1614   itself), or when the server is under attack by a client attempting to
1615   exploit security holes present in some servers using fixed-length
1616   buffers for reading or manipulating the Request-URI.
1617</t>
1618</section>
1619
1620<section title="415 Unsupported Media Type" anchor="status.415">
1621  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1622  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1623<t>
1624   The server is refusing to service the request because the entity of
1625   the request is in a format not supported by the requested resource
1626   for the requested method.
1627</t>
1628</section>
1629
1630<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1631  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1632  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1633<t>
1634   The request included a Range request-header field (&header-range;) and none of
1635   the range-specifier values in this field overlap the current extent
1636   of the selected resource.
1637</t>
1638</section>
1639
1640<section title="417 Expectation Failed" anchor="status.417">
1641  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1642  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1643<t>
1644   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1645   could not be met by this server, or, if the server is a proxy,
1646   the server has unambiguous evidence that the request could not be met
1647   by the next-hop server.
1648</t>
1649</section>
1650</section>
1651
1652<section title="Server Error 5xx" anchor="status.5xx">
1653<t>
1654   Response status codes beginning with the digit "5" indicate cases in
1655   which the server is aware that it has erred or is incapable of
1656   performing the request. Except when responding to a HEAD request, the
1657   server &SHOULD; include an entity containing an explanation of the
1658   error situation, and whether it is a temporary or permanent
1659   condition. User agents &SHOULD; display any included entity to the
1660   user. These response codes are applicable to any request method.
1661</t>
1662
1663<section title="500 Internal Server Error" anchor="status.500">
1664  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1665  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1666<t>
1667   The server encountered an unexpected condition which prevented it
1668   from fulfilling the request.
1669</t>
1670</section>
1671
1672<section title="501 Not Implemented" anchor="status.501">
1673  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1674  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1675<t>
1676   The server does not support the functionality required to fulfill the
1677   request. This is the appropriate response when the server does not
1678   recognize the request method and is not capable of supporting it for
1679   any resource.
1680</t>
1681</section>
1682
1683<section title="502 Bad Gateway" anchor="status.502">
1684  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1685  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1686<t>
1687   The server, while acting as a gateway or proxy, received an invalid
1688   response from the upstream server it accessed in attempting to
1689   fulfill the request.
1690</t>
1691</section>
1692
1693<section title="503 Service Unavailable" anchor="status.503">
1694  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1695  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1696<t>
1697   The server is currently unable to handle the request due to a
1698   temporary overloading or maintenance of the server. The implication
1699   is that this is a temporary condition which will be alleviated after
1700   some delay. If known, the length of the delay &MAY; be indicated in a
1701   Retry-After header. If no Retry-After is given, the client &SHOULD;
1702   handle the response as it would for a 500 response.
1703  <list><t>
1704      <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1705      server must use it when becoming overloaded. Some servers may wish
1706      to simply refuse the connection.
1707  </t></list>
1708</t>
1709</section>
1710
1711<section title="504 Gateway Timeout" anchor="status.504">
1712  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1713  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1714<t>
1715   The server, while acting as a gateway or proxy, did not receive a
1716   timely response from the upstream server specified by the URI (e.g.
1717   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1718   to access in attempting to complete the request.
1719  <list><t>
1720      <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1721      return 400 or 500 when DNS lookups time out.
1722  </t></list>
1723</t>
1724</section>
1725
1726<section title="505 HTTP Version Not Supported" anchor="status.505">
1727  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1728  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1729<t>
1730   The server does not support, or refuses to support, the protocol
1731   version that was used in the request message. The server is
1732   indicating that it is unable or unwilling to complete the request
1733   using the same major version as the client, as described in &http-version;,
1734   other than with this error message. The response &SHOULD; contain
1735   an entity describing why that version is not supported and what other
1736   protocols are supported by that server.
1737</t>
1738
1739</section>
1740</section>
1741</section>
1742
1743
1744<section title="Header Field Definitions" anchor="header.fields">
1745<t>
1746   This section defines the syntax and semantics of HTTP/1.1 header fields
1747   related to request and response semantics.
1748</t>
1749<t>
1750   For entity-header fields, both sender and recipient refer to either the
1751   client or the server, depending on who sends and who receives the entity.
1752</t>
1753
1754<section title="Allow" anchor="header.allow">
1755  <iref primary="true" item="Allow header" x:for-anchor=""/>
1756  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1757  <x:anchor-alias value="Allow"/>
1758<t>
1759      The Allow response-header field lists the set of methods advertised as
1760      supported by the resource identified by the Request-URI. The purpose of
1761      this field is strictly to inform the recipient of valid methods
1762      associated with the resource. An Allow header field &MUST; be
1763      present in a 405 (Method Not Allowed) response.
1764</t>
1765<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
1766  <x:ref>Allow</x:ref>   = "Allow" ":" #<x:ref>Method</x:ref>
1767</artwork></figure>
1768<t>
1769      Example of use:
1770</t>
1771<figure><artwork type="example">
1772       Allow: GET, HEAD, PUT
1773</artwork></figure>
1774<t>
1775      The actual set of allowed methods is defined
1776      by the origin server at the time of each request.
1777</t>
1778<t>
1779      A proxy &MUST-NOT; modify the Allow header field even if it does not
1780      understand all the methods specified, since the user agent might
1781      have other means of communicating with the origin server.
1782</t>
1783</section>
1784
1785<section title="Expect" anchor="header.expect">
1786  <iref primary="true" item="Expect header" x:for-anchor=""/>
1787  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1788  <x:anchor-alias value="Expect"/>
1789  <x:anchor-alias value="expectation"/>
1790  <x:anchor-alias value="expectation-extension"/>
1791  <x:anchor-alias value="expect-params"/>
1792<t>
1793   The Expect request-header field is used to indicate that particular
1794   server behaviors are required by the client.
1795</t>
1796<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"/>
1797  <x:ref>Expect</x:ref>       =  "Expect" ":" 1#<x:ref>expectation</x:ref>
1798 
1799  <x:ref>expectation</x:ref>  =  "100-continue" | <x:ref>expectation-extension</x:ref>
1800  <x:ref>expectation-extension</x:ref> =  <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> )
1801                           *<x:ref>expect-params</x:ref> ]
1802  <x:ref>expect-params</x:ref> =  ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> | <x:ref>quoted-string</x:ref> ) ]
1803</artwork></figure>
1804<t>
1805   A server that does not understand or is unable to comply with any of
1806   the expectation values in the Expect field of a request &MUST; respond
1807   with appropriate error status. The server &MUST; respond with a 417
1808   (Expectation Failed) status if any of the expectations cannot be met
1809   or, if there are other problems with the request, some other 4xx
1810   status.
1811</t>
1812<t>
1813   This header field is defined with extensible syntax to allow for
1814   future extensions. If a server receives a request containing an
1815   Expect field that includes an expectation-extension that it does not
1816   support, it &MUST; respond with a 417 (Expectation Failed) status.
1817</t>
1818<t>
1819   Comparison of expectation values is case-insensitive for unquoted
1820   tokens (including the 100-continue token), and is case-sensitive for
1821   quoted-string expectation-extensions.
1822</t>
1823<t>
1824   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1825   return a 417 (Expectation Failed) status if it receives a request
1826   with an expectation that it cannot meet. However, the Expect
1827   request-header itself is end-to-end; it &MUST; be forwarded if the
1828   request is forwarded.
1829</t>
1830<t>
1831   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1832   Expect header.
1833</t>
1834<t>
1835   See &use100; for the use of the 100 (Continue) status.
1836</t>
1837</section>
1838
1839<section title="From" anchor="header.from">
1840  <iref primary="true" item="From header" x:for-anchor=""/>
1841  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1842  <x:anchor-alias value="From"/>
1843  <x:anchor-alias value="mailbox"/>
1844<t>
1845   The From request-header field, if given, &SHOULD; contain an Internet
1846   e-mail address for the human user who controls the requesting user
1847   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1848   in <xref x:sec="3.4" x:fmt="of" target="RFC2822"/>:
1849</t>
1850<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
1851  <x:ref>From</x:ref>    = "From" ":" <x:ref>mailbox</x:ref>
1852 
1853  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC2822"/>&gt;
1854</artwork></figure>
1855<t>
1856   An example is:
1857</t>
1858<figure><artwork type="example">
1859    From: webmaster@example.org
1860</artwork></figure>
1861<t>
1862   This header field &MAY; be used for logging purposes and as a means for
1863   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1864   be used as an insecure form of access protection. The interpretation
1865   of this field is that the request is being performed on behalf of the
1866   person given, who accepts responsibility for the method performed. In
1867   particular, robot agents &SHOULD; include this header so that the
1868   person responsible for running the robot can be contacted if problems
1869   occur on the receiving end.
1870</t>
1871<t>
1872   The Internet e-mail address in this field &MAY; be separate from the
1873   Internet host which issued the request. For example, when a request
1874   is passed through a proxy the original issuer's address &SHOULD; be
1875   used.
1876</t>
1877<t>
1878   The client &SHOULD-NOT;  send the From header field without the user's
1879   approval, as it might conflict with the user's privacy interests or
1880   their site's security policy. It is strongly recommended that the
1881   user be able to disable, enable, and modify the value of this field
1882   at any time prior to a request.
1883</t>
1884</section>
1885
1886<section title="Location" anchor="header.location">
1887  <iref primary="true" item="Location header" x:for-anchor=""/>
1888  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1889  <x:anchor-alias value="Location"/>
1890<t>
1891   The Location response-header field is used for the identification of a
1892   new resource or to redirect the recipient to a location other than the
1893   Request-URI for completion of the request.  For 201 (Created)
1894   responses, the Location is that of the new resource which was created
1895   by the request. For 3xx responses, the location &SHOULD; indicate the
1896   server's preferred URI for automatic redirection to the resource. The
1897   field value consists of a single absolute URI.
1898</t>
1899<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
1900  <x:ref>Location</x:ref>       = "Location" ":" <x:ref>absoluteURI</x:ref> [ "#" <x:ref>fragment</x:ref> ]
1901</artwork></figure>
1902<t>
1903   An example is:
1904</t>
1905<figure><artwork type="example">
1906    Location: http://www.example.org/pub/WWW/People.html
1907</artwork></figure>
1908<t>
1909  <list><t>
1910      <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1911      from Location in that the Content-Location identifies the original
1912      location of the entity enclosed in the request. It is therefore
1913      possible for a response to contain header fields for both Location
1914      and Content-Location.
1915  </t></list>
1916</t>
1917<t>
1918   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1919   <list style="symbols">
1920      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
1921      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
1922      <t>With 305 Use Proxy.</t>
1923   </list>
1924</t>
1925</section>
1926
1927<section title="Max-Forwards" anchor="header.max-forwards">
1928  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
1929  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
1930  <x:anchor-alias value="Max-Forwards"/>
1931<t>
1932   The Max-Forwards request-header field provides a mechanism with the
1933   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
1934   number of proxies or gateways that can forward the request to the
1935   next inbound server. This can be useful when the client is attempting
1936   to trace a request chain which appears to be failing or looping in
1937   mid-chain.
1938</t>
1939<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
1940  <x:ref>Max-Forwards</x:ref>   = "Max-Forwards" ":" 1*<x:ref>DIGIT</x:ref>
1941</artwork></figure>
1942<t>
1943   The Max-Forwards value is a decimal integer indicating the remaining
1944   number of times this request message may be forwarded.
1945</t>
1946<t>
1947   Each proxy or gateway recipient of a TRACE or OPTIONS request
1948   containing a Max-Forwards header field &MUST; check and update its
1949   value prior to forwarding the request. If the received value is zero
1950   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
1951   respond as the final recipient. If the received Max-Forwards value is
1952   greater than zero, then the forwarded message &MUST; contain an updated
1953   Max-Forwards field with a value decremented by one (1).
1954</t>
1955<t>
1956   The Max-Forwards header field &MAY; be ignored for all other methods
1957   defined by this specification and for any extension methods for which
1958   it is not explicitly referred to as part of that method definition.
1959</t>
1960</section>
1961
1962<section title="Referer" anchor="header.referer">
1963  <iref primary="true" item="Referer header" x:for-anchor=""/>
1964  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
1965  <x:anchor-alias value="Referer"/>
1966<t>
1967   The Referer[sic] request-header field allows the client to specify,
1968   for the server's benefit, the address (URI) of the resource from
1969   which the Request-URI was obtained (the "referrer", although the
1970   header field is misspelled.) The Referer request-header allows a
1971   server to generate lists of back-links to resources for interest,
1972   logging, optimized caching, etc. It also allows obsolete or mistyped
1973   links to be traced for maintenance. The Referer field &MUST-NOT; be
1974   sent if the Request-URI was obtained from a source that does not have
1975   its own URI, such as input from the user keyboard.
1976</t>
1977<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
1978  <x:ref>Referer</x:ref>        = "Referer" ":" ( <x:ref>absoluteURI</x:ref> | <x:ref>relativeURI</x:ref> )
1979</artwork></figure>
1980<t>
1981   Example:
1982</t>
1983<figure><artwork type="example">
1984    Referer: http://www.example.org/hypertext/Overview.html
1985</artwork></figure>
1986<t>
1987   If the field value is a relative URI, it &SHOULD; be interpreted
1988   relative to the Request-URI. The URI &MUST-NOT; include a fragment. See
1989   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
1990</t>
1991</section>
1992
1993<section title="Retry-After" anchor="header.retry-after">
1994  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
1995  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
1996  <x:anchor-alias value="Retry-After"/>
1997<t>
1998   The Retry-After response-header field can be used with a 503 (Service
1999   Unavailable) response to indicate how long the service is expected to
2000   be unavailable to the requesting client. This field &MAY; also be used
2001   with any 3xx (Redirection) response to indicate the minimum time the
2002   user-agent is asked wait before issuing the redirected request. The
2003   value of this field can be either an HTTP-date or an integer number
2004   of seconds (in decimal) after the time of the response.
2005</t>
2006<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2007  <x:ref>Retry-After</x:ref>   = "Retry-After" ":" ( <x:ref>HTTP-date</x:ref> | <x:ref>delta-seconds</x:ref> )
2008</artwork></figure>
2009<t anchor="rule.delta-seconds">
2010  <x:anchor-alias value="delta-seconds"/>
2011   Time spans are non-negative decimal integers, representing time in
2012   seconds.
2013</t>
2014<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2015  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2016</artwork></figure>
2017<t>
2018   Two examples of its use are
2019</t>
2020<figure><artwork type="example">
2021    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2022    Retry-After: 120
2023</artwork></figure>
2024<t>
2025   In the latter example, the delay is 2 minutes.
2026</t>
2027</section>
2028
2029<section title="Server" anchor="header.server">
2030  <iref primary="true" item="Server header" x:for-anchor=""/>
2031  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
2032  <x:anchor-alias value="Server"/>
2033<t>
2034   The Server response-header field contains information about the
2035   software used by the origin server to handle the request. The field
2036   can contain multiple product tokens (&product-tokens;) and comments
2037   identifying the server and any significant subproducts. The product
2038   tokens are listed in order of their significance for identifying the
2039   application.
2040</t>
2041<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2042  <x:ref>Server</x:ref>         = "Server" ":" 1*( <x:ref>product</x:ref> | <x:ref>comment</x:ref> )
2043</artwork></figure>
2044<t>
2045   Example:
2046</t>
2047<figure><artwork type="example">
2048    Server: CERN/3.0 libwww/2.17
2049</artwork></figure>
2050<t>
2051   If the response is being forwarded through a proxy, the proxy
2052   application &MUST-NOT; modify the Server response-header. Instead, it
2053   &MUST; include a Via field (as described in &header-via;).
2054  <list><t>
2055      <x:h>Note:</x:h> Revealing the specific software version of the server might
2056      allow the server machine to become more vulnerable to attacks
2057      against software that is known to contain security holes. Server
2058      implementors are encouraged to make this field a configurable
2059      option.
2060  </t></list>
2061</t>
2062</section>
2063
2064<section title="User-Agent" anchor="header.user-agent">
2065  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
2066  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
2067  <x:anchor-alias value="User-Agent"/>
2068<t>
2069   The User-Agent request-header field contains information about the
2070   user agent originating the request. This is for statistical purposes,
2071   the tracing of protocol violations, and automated recognition of user
2072   agents for the sake of tailoring responses to avoid particular user
2073   agent limitations. User agents &SHOULD; include this field with
2074   requests. The field can contain multiple product tokens (&product-tokens;)
2075   and comments identifying the agent and any subproducts which form a
2076   significant part of the user agent. By convention, the product tokens
2077   are listed in order of their significance for identifying the
2078   application.
2079</t>
2080<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2081  <x:ref>User-Agent</x:ref>     = "User-Agent" ":" 1*( <x:ref>product</x:ref> | <x:ref>comment</x:ref> )
2082</artwork></figure>
2083<t>
2084   Example:
2085</t>
2086<figure><artwork type="example">
2087    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2088</artwork></figure>
2089</section>
2090
2091</section>
2092
2093<section title="IANA Considerations" anchor="IANA.considerations">
2094<section title="Status Code Registry" anchor="status.code.registration">
2095<t>
2096  The registration procedure for HTTP Status Codes -- previously defined
2097  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> -- is now defined
2098  by <xref target="status.code.registry"/> of this document.
2099</t>
2100<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2101<!--(START)-->
2102<t xmlns:x="http://purl.org/net/xml2rfc/ext">
2103    The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2104    should be updated with the registrations below:
2105  </t>
2106<texttable xmlns:x="http://purl.org/net/xml2rfc/ext">
2107   <ttcol>Value</ttcol>
2108   <ttcol>Description</ttcol>
2109   <ttcol>Reference</ttcol>
2110
2111   <c>100</c>
2112   <c>Continue</c>
2113   <c>
2114      <xref target="status.100"/>
2115   </c>
2116
2117   <c>101</c>
2118   <c>Switching Protocols</c>
2119   <c>
2120      <xref target="status.101"/>
2121   </c>
2122
2123   <c>200</c>
2124   <c>OK</c>
2125   <c>
2126      <xref target="status.200"/>
2127   </c>
2128
2129   <c>201</c>
2130   <c>Created</c>
2131   <c>
2132      <xref target="status.201"/>
2133   </c>
2134
2135   <c>202</c>
2136   <c>Accepted</c>
2137   <c>
2138      <xref target="status.202"/>
2139   </c>
2140
2141   <c>203</c>
2142   <c>Non-Authoritative Information</c>
2143   <c>
2144      <xref target="status.203"/>
2145   </c>
2146
2147   <c>204</c>
2148   <c>No Content</c>
2149   <c>
2150      <xref target="status.204"/>
2151   </c>
2152
2153   <c>205</c>
2154   <c>Reset Content</c>
2155   <c>
2156      <xref target="status.205"/>
2157   </c>
2158
2159   <c>206</c>
2160   <c>Partial Content</c>
2161   <c>
2162      <xref target="status.206"/>
2163   </c>
2164
2165   <c>300</c>
2166   <c>Multiple Choices</c>
2167   <c>
2168      <xref target="status.300"/>
2169   </c>
2170
2171   <c>301</c>
2172   <c>Moved Permanently</c>
2173   <c>
2174      <xref target="status.301"/>
2175   </c>
2176
2177   <c>302</c>
2178   <c>Found</c>
2179   <c>
2180      <xref target="status.302"/>
2181   </c>
2182
2183   <c>303</c>
2184   <c>See Other</c>
2185   <c>
2186      <xref target="status.303"/>
2187   </c>
2188
2189   <c>304</c>
2190   <c>Not Modified</c>
2191   <c>
2192      <xref target="status.304"/>
2193   </c>
2194
2195   <c>305</c>
2196   <c>Use Proxy</c>
2197   <c>
2198      <xref target="status.305"/>
2199   </c>
2200
2201   <c>306</c>
2202   <c>(Unused)</c>
2203   <c>
2204      <xref target="status.306"/>
2205   </c>
2206
2207   <c>307</c>
2208   <c>Temporary Redirect</c>
2209   <c>
2210      <xref target="status.307"/>
2211   </c>
2212
2213   <c>400</c>
2214   <c>Bad Request</c>
2215   <c>
2216      <xref target="status.400"/>
2217   </c>
2218
2219   <c>401</c>
2220   <c>Unauthorized</c>
2221   <c>
2222      <xref target="status.401"/>
2223   </c>
2224
2225   <c>402</c>
2226   <c>Payment Required</c>
2227   <c>
2228      <xref target="status.402"/>
2229   </c>
2230
2231   <c>403</c>
2232   <c>Forbidden</c>
2233   <c>
2234      <xref target="status.403"/>
2235   </c>
2236
2237   <c>404</c>
2238   <c>Not Found</c>
2239   <c>
2240      <xref target="status.404"/>
2241   </c>
2242
2243   <c>405</c>
2244   <c>Method Not Allowed</c>
2245   <c>
2246      <xref target="status.405"/>
2247   </c>
2248
2249   <c>406</c>
2250   <c>Not Acceptable</c>
2251   <c>
2252      <xref target="status.406"/>
2253   </c>
2254
2255   <c>407</c>
2256   <c>Proxy Authentication Required</c>
2257   <c>
2258      <xref target="status.407"/>
2259   </c>
2260
2261   <c>408</c>
2262   <c>Request Timeout</c>
2263   <c>
2264      <xref target="status.408"/>
2265   </c>
2266
2267   <c>409</c>
2268   <c>Conflict</c>
2269   <c>
2270      <xref target="status.409"/>
2271   </c>
2272
2273   <c>410</c>
2274   <c>Gone</c>
2275   <c>
2276      <xref target="status.410"/>
2277   </c>
2278
2279   <c>411</c>
2280   <c>Length Required</c>
2281   <c>
2282      <xref target="status.411"/>
2283   </c>
2284
2285   <c>412</c>
2286   <c>Precondition Failed</c>
2287   <c>
2288      <xref target="status.412"/>
2289   </c>
2290
2291   <c>413</c>
2292   <c>Request Entity Too Large</c>
2293   <c>
2294      <xref target="status.413"/>
2295   </c>
2296
2297   <c>414</c>
2298   <c>Request-URI Too Long</c>
2299   <c>
2300      <xref target="status.414"/>
2301   </c>
2302
2303   <c>415</c>
2304   <c>Unsupported Media Type</c>
2305   <c>
2306      <xref target="status.415"/>
2307   </c>
2308
2309   <c>416</c>
2310   <c>Requested Range Not Satisfiable</c>
2311   <c>
2312      <xref target="status.416"/>
2313   </c>
2314
2315   <c>417</c>
2316   <c>Expectation Failed</c>
2317   <c>
2318      <xref target="status.417"/>
2319   </c>
2320
2321   <c>500</c>
2322   <c>Internal Server Error</c>
2323   <c>
2324      <xref target="status.500"/>
2325   </c>
2326
2327   <c>501</c>
2328   <c>Not Implemented</c>
2329   <c>
2330      <xref target="status.501"/>
2331   </c>
2332
2333   <c>502</c>
2334   <c>Bad Gateway</c>
2335   <c>
2336      <xref target="status.502"/>
2337   </c>
2338
2339   <c>503</c>
2340   <c>Service Unavailable</c>
2341   <c>
2342      <xref target="status.503"/>
2343   </c>
2344
2345   <c>504</c>
2346   <c>Gateway Timeout</c>
2347   <c>
2348      <xref target="status.504"/>
2349   </c>
2350
2351   <c>505</c>
2352   <c>HTTP Version Not Supported</c>
2353   <c>
2354      <xref target="status.505"/>
2355   </c>
2356</texttable>
2357<!--(END)-->
2358</section>
2359<section title="Message Header Registration" anchor="message.header.registration">
2360<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2361<!--(START)-->
2362<t>
2363    The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2364    with the permanent registrations below (see <xref target="RFC3864"/>):
2365  </t>
2366<texttable>
2367   <ttcol>Header Field Name</ttcol>
2368   <ttcol>Protocol</ttcol>
2369   <ttcol>Status</ttcol>
2370   <ttcol>Reference</ttcol>
2371
2372   <c>Allow</c>
2373   <c>http</c>
2374   <c>standard</c>
2375   <c>
2376      <xref target="header.allow"/>
2377   </c>
2378
2379   <c>Expect</c>
2380   <c>http</c>
2381   <c>standard</c>
2382   <c>
2383      <xref target="header.expect"/>
2384   </c>
2385
2386   <c>From</c>
2387   <c>http</c>
2388   <c>standard</c>
2389   <c>
2390      <xref target="header.from"/>
2391   </c>
2392
2393   <c>Location</c>
2394   <c>http</c>
2395   <c>standard</c>
2396   <c>
2397      <xref target="header.location"/>
2398   </c>
2399
2400   <c>Max-Forwards</c>
2401   <c>http</c>
2402   <c>standard</c>
2403   <c>
2404      <xref target="header.max-forwards"/>
2405   </c>
2406
2407   <c>Referer</c>
2408   <c>http</c>
2409   <c>standard</c>
2410   <c>
2411      <xref target="header.referer"/>
2412   </c>
2413
2414   <c>Retry-After</c>
2415   <c>http</c>
2416   <c>standard</c>
2417   <c>
2418      <xref target="header.retry-after"/>
2419   </c>
2420
2421   <c>Server</c>
2422   <c>http</c>
2423   <c>standard</c>
2424   <c>
2425      <xref target="header.server"/>
2426   </c>
2427
2428   <c>User-Agent</c>
2429   <c>http</c>
2430   <c>standard</c>
2431   <c>
2432      <xref target="header.user-agent"/>
2433   </c>
2434</texttable>
2435<t>
2436    The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2437</t>
2438<!--(END)-->
2439</section>
2440</section>
2441
2442<section title="Security Considerations" anchor="security.considerations">
2443<t>
2444   This section is meant to inform application developers, information
2445   providers, and users of the security limitations in HTTP/1.1 as
2446   described by this document. The discussion does not include
2447   definitive solutions to the problems revealed, though it does make
2448   some suggestions for reducing security risks.
2449</t>
2450
2451<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2452<t>
2453   Like any generic data transfer protocol, HTTP cannot regulate the
2454   content of the data that is transferred, nor is there any a priori
2455   method of determining the sensitivity of any particular piece of
2456   information within the context of any given request. Therefore,
2457   applications &SHOULD; supply as much control over this information as
2458   possible to the provider of that information. Four header fields are
2459   worth special mention in this context: Server, Via, Referer and From.
2460</t>
2461<t>
2462   Revealing the specific software version of the server might allow the
2463   server machine to become more vulnerable to attacks against software
2464   that is known to contain security holes. Implementors &SHOULD; make the
2465   Server header field a configurable option.
2466</t>
2467<t>
2468   Proxies which serve as a portal through a network firewall &SHOULD;
2469   take special precautions regarding the transfer of header information
2470   that identifies the hosts behind the firewall. In particular, they
2471   &SHOULD; remove, or replace with sanitized versions, any Via fields
2472   generated behind the firewall.
2473</t>
2474<t>
2475   The Referer header allows reading patterns to be studied and reverse
2476   links drawn. Although it can be very useful, its power can be abused
2477   if user details are not separated from the information contained in
2478   the Referer. Even when the personal information has been removed, the
2479   Referer header might indicate a private document's URI whose
2480   publication would be inappropriate.
2481</t>
2482<t>
2483   The information sent in the From field might conflict with the user's
2484   privacy interests or their site's security policy, and hence it
2485   &SHOULD-NOT;  be transmitted without the user being able to disable,
2486   enable, and modify the contents of the field. The user &MUST; be able
2487   to set the contents of this field within a user preference or
2488   application defaults configuration.
2489</t>
2490<t>
2491   We suggest, though do not require, that a convenient toggle interface
2492   be provided for the user to enable or disable the sending of From and
2493   Referer information.
2494</t>
2495<t>
2496   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2497   fields can sometimes be used to determine that a specific client or
2498   server have a particular security hole which might be exploited.
2499   Unfortunately, this same information is often used for other valuable
2500   purposes for which HTTP currently has no better mechanism.
2501</t>
2502</section>
2503
2504<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2505<t>
2506   Because the source of a link might be private information or might
2507   reveal an otherwise private information source, it is strongly
2508   recommended that the user be able to select whether or not the
2509   Referer field is sent. For example, a browser client could have a
2510   toggle switch for browsing openly/anonymously, which would
2511   respectively enable/disable the sending of Referer and From
2512   information.
2513</t>
2514<t>
2515   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
2516   HTTP request if the referring page was transferred with a secure
2517   protocol.
2518</t>
2519<t>
2520   Authors of services should not use
2521   GET-based forms for the submission of sensitive data because that
2522   data will be encoded in the Request-URI. Many existing
2523   servers, proxies, and user agents log or display the Request-URI in
2524   places where it might be visible to third parties. Such services can
2525   use POST-based form submission instead.
2526</t>
2527</section>
2528
2529<section title="Location Headers and Spoofing" anchor="location.spoofing">
2530<t>
2531   If a single server supports multiple organizations that do not trust
2532   one another, then it &MUST; check the values of Location and Content-Location
2533   headers in responses that are generated under control of
2534   said organizations to make sure that they do not attempt to
2535   invalidate resources over which they have no authority.
2536</t>
2537</section>
2538
2539</section>
2540
2541<section title="Acknowledgments" anchor="ack">
2542</section>
2543</middle>
2544<back>
2545
2546<references title="Normative References">
2547
2548<reference anchor="Part1">
2549  <front>
2550    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2551    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2552      <organization abbrev="Day Software">Day Software</organization>
2553      <address><email>fielding@gbiv.com</email></address>
2554    </author>
2555    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2556      <organization>One Laptop per Child</organization>
2557      <address><email>jg@laptop.org</email></address>
2558    </author>
2559    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2560      <organization abbrev="HP">Hewlett-Packard Company</organization>
2561      <address><email>JeffMogul@acm.org</email></address>
2562    </author>
2563    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2564      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2565      <address><email>henrikn@microsoft.com</email></address>
2566    </author>
2567    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2568      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2569      <address><email>LMM@acm.org</email></address>
2570    </author>
2571    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2572      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2573      <address><email>paulle@microsoft.com</email></address>
2574    </author>
2575    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2576      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2577      <address><email>timbl@w3.org</email></address>
2578    </author>
2579    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2580      <organization abbrev="W3C">World Wide Web Consortium</organization>
2581      <address><email>ylafon@w3.org</email></address>
2582    </author>
2583    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2584      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2585      <address><email>julian.reschke@greenbytes.de</email></address>
2586    </author>
2587    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2588  </front>
2589  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2590  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2591</reference>
2592
2593<reference anchor="Part3">
2594  <front>
2595    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2596    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2597      <organization abbrev="Day Software">Day Software</organization>
2598      <address><email>fielding@gbiv.com</email></address>
2599    </author>
2600    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2601      <organization>One Laptop per Child</organization>
2602      <address><email>jg@laptop.org</email></address>
2603    </author>
2604    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2605      <organization abbrev="HP">Hewlett-Packard Company</organization>
2606      <address><email>JeffMogul@acm.org</email></address>
2607    </author>
2608    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2609      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2610      <address><email>henrikn@microsoft.com</email></address>
2611    </author>
2612    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2613      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2614      <address><email>LMM@acm.org</email></address>
2615    </author>
2616    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2617      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2618      <address><email>paulle@microsoft.com</email></address>
2619    </author>
2620    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2621      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2622      <address><email>timbl@w3.org</email></address>
2623    </author>
2624    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2625      <organization abbrev="W3C">World Wide Web Consortium</organization>
2626      <address><email>ylafon@w3.org</email></address>
2627    </author>
2628    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2629      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2630      <address><email>julian.reschke@greenbytes.de</email></address>
2631    </author>
2632    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2633  </front>
2634  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2635  <x:source href="p3-payload.xml" basename="p3-payload"/>
2636</reference>
2637
2638<reference anchor="Part4">
2639  <front>
2640    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2641    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2642      <organization abbrev="Day Software">Day Software</organization>
2643      <address><email>fielding@gbiv.com</email></address>
2644    </author>
2645    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2646      <organization>One Laptop per Child</organization>
2647      <address><email>jg@laptop.org</email></address>
2648    </author>
2649    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2650      <organization abbrev="HP">Hewlett-Packard Company</organization>
2651      <address><email>JeffMogul@acm.org</email></address>
2652    </author>
2653    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2654      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2655      <address><email>henrikn@microsoft.com</email></address>
2656    </author>
2657    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2658      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2659      <address><email>LMM@acm.org</email></address>
2660    </author>
2661    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2662      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2663      <address><email>paulle@microsoft.com</email></address>
2664    </author>
2665    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2666      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2667      <address><email>timbl@w3.org</email></address>
2668    </author>
2669    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2670      <organization abbrev="W3C">World Wide Web Consortium</organization>
2671      <address><email>ylafon@w3.org</email></address>
2672    </author>
2673    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2674      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2675      <address><email>julian.reschke@greenbytes.de</email></address>
2676    </author>
2677    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2678  </front>
2679  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2680  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2681</reference>
2682
2683<reference anchor="Part5">
2684  <front>
2685    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2686    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2687      <organization abbrev="Day Software">Day Software</organization>
2688      <address><email>fielding@gbiv.com</email></address>
2689    </author>
2690    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2691      <organization>One Laptop per Child</organization>
2692      <address><email>jg@laptop.org</email></address>
2693    </author>
2694    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2695      <organization abbrev="HP">Hewlett-Packard Company</organization>
2696      <address><email>JeffMogul@acm.org</email></address>
2697    </author>
2698    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2699      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2700      <address><email>henrikn@microsoft.com</email></address>
2701    </author>
2702    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2703      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2704      <address><email>LMM@acm.org</email></address>
2705    </author>
2706    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2707      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2708      <address><email>paulle@microsoft.com</email></address>
2709    </author>
2710    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2711      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2712      <address><email>timbl@w3.org</email></address>
2713    </author>
2714    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2715      <organization abbrev="W3C">World Wide Web Consortium</organization>
2716      <address><email>ylafon@w3.org</email></address>
2717    </author>
2718    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2719      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2720      <address><email>julian.reschke@greenbytes.de</email></address>
2721    </author>
2722    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2723  </front>
2724  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2725  <x:source href="p5-range.xml" basename="p5-range"/>
2726</reference>
2727
2728<reference anchor="Part6">
2729  <front>
2730    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2731    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2732      <organization abbrev="Day Software">Day Software</organization>
2733      <address><email>fielding@gbiv.com</email></address>
2734    </author>
2735    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2736      <organization>One Laptop per Child</organization>
2737      <address><email>jg@laptop.org</email></address>
2738    </author>
2739    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2740      <organization abbrev="HP">Hewlett-Packard Company</organization>
2741      <address><email>JeffMogul@acm.org</email></address>
2742    </author>
2743    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2744      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2745      <address><email>henrikn@microsoft.com</email></address>
2746    </author>
2747    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2748      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2749      <address><email>LMM@acm.org</email></address>
2750    </author>
2751    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2752      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2753      <address><email>paulle@microsoft.com</email></address>
2754    </author>
2755    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2756      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2757      <address><email>timbl@w3.org</email></address>
2758    </author>
2759    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2760      <organization abbrev="W3C">World Wide Web Consortium</organization>
2761      <address><email>ylafon@w3.org</email></address>
2762    </author>
2763    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2764      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2765      <address><email>julian.reschke@greenbytes.de</email></address>
2766    </author>
2767    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2768  </front>
2769  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2770  <x:source href="p6-cache.xml" basename="p6-cache"/>
2771</reference>
2772
2773<reference anchor="Part7">
2774  <front>
2775    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2776    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2777      <organization abbrev="Day Software">Day Software</organization>
2778      <address><email>fielding@gbiv.com</email></address>
2779    </author>
2780    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2781      <organization>One Laptop per Child</organization>
2782      <address><email>jg@laptop.org</email></address>
2783    </author>
2784    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2785      <organization abbrev="HP">Hewlett-Packard Company</organization>
2786      <address><email>JeffMogul@acm.org</email></address>
2787    </author>
2788    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2789      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2790      <address><email>henrikn@microsoft.com</email></address>
2791    </author>
2792    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2793      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2794      <address><email>LMM@acm.org</email></address>
2795    </author>
2796    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2797      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2798      <address><email>paulle@microsoft.com</email></address>
2799    </author>
2800    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2801      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2802      <address><email>timbl@w3.org</email></address>
2803    </author>
2804    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2805      <organization abbrev="W3C">World Wide Web Consortium</organization>
2806      <address><email>ylafon@w3.org</email></address>
2807    </author>
2808    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2809      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2810      <address><email>julian.reschke@greenbytes.de</email></address>
2811    </author>
2812    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2813  </front>
2814  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2815  <x:source href="p7-auth.xml" basename="p7-auth"/>
2816</reference>
2817
2818<reference anchor="RFC2119">
2819  <front>
2820    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2821    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2822      <organization>Harvard University</organization>
2823      <address><email>sob@harvard.edu</email></address>
2824    </author>
2825    <date month="March" year="1997"/>
2826  </front>
2827  <seriesInfo name="BCP" value="14"/>
2828  <seriesInfo name="RFC" value="2119"/>
2829</reference>
2830
2831</references>
2832
2833<references title="Informative References">
2834
2835<reference anchor="Luo1998">
2836  <front>
2837    <title>Tunneling TCP based protocols through Web proxy servers</title>
2838    <author initials="A." surname="Luotonen" fullname="A. Luotonen">
2839      <organization/>
2840    </author>
2841    <date year="1998" month="August"/>
2842  </front>
2843  <seriesInfo name="Internet-Draft" value="draft-luotonen-web-proxy-tunneling-01"/>
2844</reference>
2845
2846<reference anchor="RFC1945">
2847  <front>
2848    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2849    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2850      <organization>MIT, Laboratory for Computer Science</organization>
2851      <address><email>timbl@w3.org</email></address>
2852    </author>
2853    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2854      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2855      <address><email>fielding@ics.uci.edu</email></address>
2856    </author>
2857    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2858      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2859      <address><email>frystyk@w3.org</email></address>
2860    </author>
2861    <date month="May" year="1996"/>
2862  </front>
2863  <seriesInfo name="RFC" value="1945"/>
2864</reference>
2865
2866<reference anchor="RFC2068">
2867  <front>
2868    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
2869    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
2870      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2871      <address><email>fielding@ics.uci.edu</email></address>
2872    </author>
2873    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2874      <organization>MIT Laboratory for Computer Science</organization>
2875      <address><email>jg@w3.org</email></address>
2876    </author>
2877    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2878      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
2879      <address><email>mogul@wrl.dec.com</email></address>
2880    </author>
2881    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2882      <organization>MIT Laboratory for Computer Science</organization>
2883      <address><email>frystyk@w3.org</email></address>
2884    </author>
2885    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2886      <organization>MIT Laboratory for Computer Science</organization>
2887      <address><email>timbl@w3.org</email></address>
2888    </author>
2889    <date month="January" year="1997"/>
2890  </front>
2891  <seriesInfo name="RFC" value="2068"/>
2892</reference>
2893
2894<reference anchor="RFC2616">
2895  <front>
2896    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2897    <author initials="R." surname="Fielding" fullname="R. Fielding">
2898      <organization>University of California, Irvine</organization>
2899      <address><email>fielding@ics.uci.edu</email></address>
2900    </author>
2901    <author initials="J." surname="Gettys" fullname="J. Gettys">
2902      <organization>W3C</organization>
2903      <address><email>jg@w3.org</email></address>
2904    </author>
2905    <author initials="J." surname="Mogul" fullname="J. Mogul">
2906      <organization>Compaq Computer Corporation</organization>
2907      <address><email>mogul@wrl.dec.com</email></address>
2908    </author>
2909    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
2910      <organization>MIT Laboratory for Computer Science</organization>
2911      <address><email>frystyk@w3.org</email></address>
2912    </author>
2913    <author initials="L." surname="Masinter" fullname="L. Masinter">
2914      <organization>Xerox Corporation</organization>
2915      <address><email>masinter@parc.xerox.com</email></address>
2916    </author>
2917    <author initials="P." surname="Leach" fullname="P. Leach">
2918      <organization>Microsoft Corporation</organization>
2919      <address><email>paulle@microsoft.com</email></address>
2920    </author>
2921    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
2922      <organization>W3C</organization>
2923      <address><email>timbl@w3.org</email></address>
2924    </author>
2925    <date month="June" year="1999"/>
2926  </front>
2927  <seriesInfo name="RFC" value="2616"/>
2928</reference>
2929
2930<reference anchor='RFC2817'>
2931  <front>
2932    <title>Upgrading to TLS Within HTTP/1.1</title>
2933    <author initials='R.' surname='Khare' fullname='R. Khare'>
2934      <organization>4K Associates / UC Irvine</organization>
2935      <address><email>rohit@4K-associates.com</email></address>
2936    </author>
2937    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
2938      <organization>Agranat Systems, Inc.</organization>
2939      <address><email>lawrence@agranat.com</email></address>
2940    </author>
2941    <date year='2000' month='May' />
2942  </front>
2943  <seriesInfo name='RFC' value='2817' />
2944</reference>
2945
2946<reference anchor="RFC2822">
2947  <front>
2948    <title>Internet Message Format</title>
2949    <author initials="P." surname="Resnick" fullname="P. Resnick">
2950      <organization>QUALCOMM Incorporated</organization>
2951    </author>
2952    <date year="2001" month="April"/>
2953  </front> 
2954  <seriesInfo name="RFC" value="2822"/>
2955</reference>
2956
2957<reference anchor='RFC3864'>
2958  <front>
2959    <title>Registration Procedures for Message Header Fields</title>
2960    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
2961      <organization>Nine by Nine</organization>
2962      <address><email>GK-IETF@ninebynine.org</email></address>
2963    </author>
2964    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
2965      <organization>BEA Systems</organization>
2966      <address><email>mnot@pobox.com</email></address>
2967    </author>
2968    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
2969      <organization>HP Labs</organization>
2970      <address><email>JeffMogul@acm.org</email></address>
2971    </author>
2972    <date year='2004' month='September' />
2973  </front>
2974  <seriesInfo name='BCP' value='90' />
2975  <seriesInfo name='RFC' value='3864' />
2976</reference>
2977
2978<reference anchor='RFC5226'>
2979  <front>
2980    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2981    <author initials='T.' surname='Narten' fullname='T. Narten'>
2982      <organization>IBM</organization>
2983      <address><email>narten@us.ibm.com</email></address>
2984    </author>
2985    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
2986      <organization>Google</organization>
2987      <address><email>Harald@Alvestrand.no</email></address>
2988    </author>
2989    <date year='2008' month='May' />
2990  </front>
2991  <seriesInfo name='BCP' value='26' />
2992  <seriesInfo name='RFC' value='5226' />
2993</reference>
2994
2995</references>
2996
2997<section title="Compatibility with Previous Versions" anchor="compatibility">
2998<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
2999<t>
3000   Clarified which error code should be used for inbound server failures
3001   (e.g. DNS failures). (<xref target="status.504"/>).
3002</t>
3003<t>
3004   201 (Created) had a race that required an Etag be sent when a resource is
3005   first created. (<xref target="status.201"/>).
3006</t>
3007<t>
3008   Rewrite of message transmission requirements to make it much harder
3009   for implementors to get it wrong, as the consequences of errors here
3010   can have significant impact on the Internet, and to deal with the
3011   following problems:
3012  <list style="numbers">
3013      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
3014         this was incorrectly placing a requirement on the behavior of
3015         an implementation of a future version of HTTP/1.x</t>
3016
3017      <t>Made it clear that user-agents should retry requests, not
3018         "clients" in general.</t>
3019
3020      <t>Converted requirements for clients to ignore unexpected 100
3021         (Continue) responses, and for proxies to forward 100 responses,
3022         into a general requirement for 1xx responses.</t>
3023
3024      <t>Modified some TCP-specific language, to make it clearer that
3025         non-TCP transports are possible for HTTP.</t>
3026
3027      <t>Require that the origin server &MUST-NOT; wait for the request
3028         body before it sends a required 100 (Continue) response.</t>
3029
3030      <t>Allow, rather than require, a server to omit 100 (Continue) if
3031         it has already seen some of the request body.</t>
3032
3033      <t>Allow servers to defend against denial-of-service attacks and
3034         broken clients.</t>
3035  </list>
3036</t>
3037<t>
3038   This change adds the Expect header and 417 status code.
3039</t>
3040<t>
3041   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
3042   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
3043</t>
3044<t>
3045   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
3046   implemented in previous versions of this specification. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.1"/>.
3047</t>
3048</section>
3049
3050<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3051<t>
3052  This document takes over the Status Code Registry, previously defined
3053  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3054  (<xref target="status.code.registry"/>)
3055</t>
3056<t>
3057  Clarify definition of POST.
3058  (<xref target="POST"/>)
3059</t>
3060<t>
3061  Failed to consider that there are
3062  many other request methods that are safe to automatically redirect,
3063  and further that the user agent is able to make that determination
3064  based on the request method semantics.
3065  (Sections <xref format="counter" target="status.301"/>,
3066  <xref format="counter" target="status.302"/> and
3067  <xref format="counter" target="status.307"/>)
3068</t>
3069<t>
3070  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3071  It used to indicate that the requested resource must be accessed through the
3072  proxy given by the Location field. The Location field gave the URI of the
3073  proxy. The recipient was expected to repeat this single request via the proxy.
3074  (<xref target="status.305"/>)
3075</t>
3076<t>
3077  Reclassify Allow header as response header, removing the option to
3078  specify it in a PUT request.
3079  Relax the server requirement on the contents of the Allow header and
3080  remove requirement on clients to always trust the header value.
3081  (<xref target="header.allow"/>)
3082</t>
3083<t>
3084  Correct syntax of Location header to allow fragment,
3085  as referred symbol wasn't what was expected, and add some
3086  clarifications as to when it would not be appropriate.
3087  (<xref target="header.location"/>)
3088</t>
3089<t>
3090  In the description of the Server header, the Via field
3091  was described as a SHOULD. The requirement was and is stated
3092  correctly in the description of the Via header in &header-via;.
3093  (<xref target="header.server"/>)
3094</t>
3095</section>
3096
3097</section>
3098
3099<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3100
3101<section title="Since RFC2616">
3102<t>
3103  Extracted relevant partitions from <xref target="RFC2616"/>.
3104</t>
3105</section>
3106
3107<section title="Since draft-ietf-httpbis-p2-semantics-00">
3108<t>
3109  Closed issues:
3110  <list style="symbols"> 
3111    <t>
3112      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3113      "Via is a MUST"
3114      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3115    </t>
3116    <t>
3117      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3118      "Fragments allowed in Location"
3119      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3120    </t>
3121    <t>
3122      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3123      "Safe Methods vs Redirection"
3124      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3125    </t>
3126    <t>
3127      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3128      "Revise description of the POST method"
3129      (<eref target="http://purl.org/NET/http-errata#post"/>)
3130    </t>
3131    <t>
3132      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3133      "Normative and Informative references"
3134    </t>
3135    <t>
3136      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3137      "RFC2606 Compliance"
3138    </t>
3139    <t>
3140      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3141      "Informative references"
3142    </t>
3143    <t>
3144      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3145      "Redundant cross-references"
3146    </t>
3147  </list>
3148</t>
3149<t>
3150  Other changes:
3151  <list style="symbols"> 
3152    <t>
3153      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3154    </t>
3155  </list>
3156</t>
3157</section>
3158
3159<section title="Since draft-ietf-httpbis-p2-semantics-01">
3160<t>
3161  Closed issues:
3162  <list style="symbols"> 
3163    <t>
3164      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3165      "PUT side effects"
3166    </t>
3167    <t>
3168      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3169      "Duplicate Host header requirements"
3170    </t>
3171  </list>
3172</t>
3173<t>
3174  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3175  <list style="symbols"> 
3176    <t>
3177      Move "Product Tokens" section (back) into Part 1, as "token" is used
3178      in the definition of the Upgrade header.
3179    </t>
3180    <t>
3181      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3182    </t>
3183    <t>
3184      Copy definition of delta-seconds from Part6 instead of referencing it.
3185    </t>
3186  </list>
3187</t>
3188</section>
3189
3190<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3191<t>
3192  Closed issues:
3193  <list style="symbols"> 
3194    <t>
3195      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3196      "Requiring Allow in 405 responses"
3197    </t>
3198    <t>
3199      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3200      "Status Code Registry"
3201    </t>
3202    <t>
3203      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3204      "Redirection vs. Location"
3205    </t>
3206    <t>
3207      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3208      "Cacheability of 303 response"
3209    </t>
3210    <t>
3211      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3212      "305 Use Proxy"
3213    </t>
3214    <t>
3215      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3216      "Classification for Allow header"
3217    </t>
3218    <t>
3219      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3220      "PUT - 'store under' vs 'store at'"
3221    </t>
3222  </list>
3223</t>
3224<t>
3225  Ongoing work on IANA Message Header Registration (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3226  <list style="symbols"> 
3227    <t>
3228      Reference RFC 3984, and update header registrations for headers defined
3229      in this document.
3230    </t>
3231  </list>
3232</t>
3233<t>
3234  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3235  <list style="symbols"> 
3236    <t>
3237      Replace string literals when the string really is case-sensitive (method).
3238    </t>
3239  </list>
3240</t>
3241</section>
3242
3243</section>
3244
3245</back>
3246</rfc>
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