source: draft-ietf-httpbis/07/p2-semantics.xml @ 653

Last change on this file since 653 was 609, checked in by julian.reschke@…, 10 years ago

HTAB cleanup (not even editorial)

  • Property svn:eol-style set to native
File size: 152.7 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "07">
15  <!ENTITY ID-MONTH "July">
16  <!ENTITY ID-YEAR "2009">
17  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' 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='#date.time.formats.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" x:maturity-level="draft"
77     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
78     xmlns:x='http://purl.org/net/xml2rfc/ext'
79     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
80<front>
81
82  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
83
84  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
85    <organization abbrev="Day Software">Day Software</organization>
86    <address>
87      <postal>
88        <street>23 Corporate Plaza DR, Suite 280</street>
89        <city>Newport Beach</city>
90        <region>CA</region>
91        <code>92660</code>
92        <country>USA</country>
93      </postal>
94      <phone>+1-949-706-5300</phone>
95      <facsimile>+1-949-706-5305</facsimile>
96      <email>fielding@gbiv.com</email>
97      <uri>http://roy.gbiv.com/</uri>
98    </address>
99  </author>
100
101  <author initials="J." surname="Gettys" fullname="Jim Gettys">
102    <organization>One Laptop per Child</organization>
103    <address>
104      <postal>
105        <street>21 Oak Knoll Road</street>
106        <city>Carlisle</city>
107        <region>MA</region>
108        <code>01741</code>
109        <country>USA</country>
110      </postal>
111      <email>jg@laptop.org</email>
112      <uri>http://www.laptop.org/</uri>
113    </address>
114  </author>
115 
116  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
117    <organization abbrev="HP">Hewlett-Packard Company</organization>
118    <address>
119      <postal>
120        <street>HP Labs, Large Scale Systems Group</street>
121        <street>1501 Page Mill Road, MS 1177</street>
122        <city>Palo Alto</city>
123        <region>CA</region>
124        <code>94304</code>
125        <country>USA</country>
126      </postal>
127      <email>JeffMogul@acm.org</email>
128    </address>
129  </author>
130
131  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
132    <organization abbrev="Microsoft">Microsoft Corporation</organization>
133    <address>
134      <postal>
135        <street>1 Microsoft Way</street>
136        <city>Redmond</city>
137        <region>WA</region>
138        <code>98052</code>
139        <country>USA</country>
140      </postal>
141      <email>henrikn@microsoft.com</email>
142    </address>
143  </author>
144
145  <author initials="L." surname="Masinter" fullname="Larry Masinter">
146    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
147    <address>
148      <postal>
149        <street>345 Park Ave</street>
150        <city>San Jose</city>
151        <region>CA</region>
152        <code>95110</code>
153        <country>USA</country>
154      </postal>
155      <email>LMM@acm.org</email>
156      <uri>http://larry.masinter.net/</uri>
157    </address>
158  </author>
159 
160  <author initials="P." surname="Leach" fullname="Paul J. Leach">
161    <organization abbrev="Microsoft">Microsoft Corporation</organization>
162    <address>
163      <postal>
164        <street>1 Microsoft Way</street>
165        <city>Redmond</city>
166        <region>WA</region>
167        <code>98052</code>
168      </postal>
169      <email>paulle@microsoft.com</email>
170    </address>
171  </author>
172   
173  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
174    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
175    <address>
176      <postal>
177        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
178        <street>The Stata Center, Building 32</street>
179        <street>32 Vassar Street</street>
180        <city>Cambridge</city>
181        <region>MA</region>
182        <code>02139</code>
183        <country>USA</country>
184      </postal>
185      <email>timbl@w3.org</email>
186      <uri>http://www.w3.org/People/Berners-Lee/</uri>
187    </address>
188  </author>
189
190  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
191    <organization abbrev="W3C">World Wide Web Consortium</organization>
192    <address>
193      <postal>
194        <street>W3C / ERCIM</street>
195        <street>2004, rte des Lucioles</street>
196        <city>Sophia-Antipolis</city>
197        <region>AM</region>
198        <code>06902</code>
199        <country>France</country>
200      </postal>
201      <email>ylafon@w3.org</email>
202      <uri>http://www.raubacapeu.net/people/yves/</uri>
203    </address>
204  </author>
205
206  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
207    <organization abbrev="greenbytes">greenbytes GmbH</organization>
208    <address>
209      <postal>
210        <street>Hafenweg 16</street>
211        <city>Muenster</city><region>NW</region><code>48155</code>
212        <country>Germany</country>
213      </postal>
214      <phone>+49 251 2807760</phone>
215      <facsimile>+49 251 2807761</facsimile>
216      <email>julian.reschke@greenbytes.de</email>
217      <uri>http://greenbytes.de/tech/webdav/</uri>
218    </address>
219  </author>
220
221  <date day="13" month="&ID-MONTH;" year="&ID-YEAR;"/>
222  <workgroup>HTTPbis Working Group</workgroup>
223
224<abstract>
225<t>
226   The Hypertext Transfer Protocol (HTTP) is an application-level
227   protocol for distributed, collaborative, hypermedia information
228   systems. HTTP has been in use by the World Wide Web global information
229   initiative since 1990. This document is Part 2 of the seven-part specification
230   that defines the protocol referred to as "HTTP/1.1" and, taken together,
231   obsoletes RFC 2616.  Part 2 defines the semantics of HTTP messages
232   as expressed by request methods, request-header fields, response status codes,
233   and response-header fields.
234</t>
235</abstract>
236
237<note title="Editorial Note (To be removed by RFC Editor)">
238  <t>
239    Discussion of this draft should take place on the HTTPBIS working group
240    mailing list (ietf-http-wg@w3.org). The current issues list is
241    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
242    and related documents (including fancy diffs) can be found at
243    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
244  </t>
245  <t>
246    The changes in this draft are summarized in <xref target="changes.since.06"/>.
247  </t>
248</note>
249</front>
250<middle>
251<section title="Introduction" anchor="introduction">
252<t>
253   This document defines HTTP/1.1 request and response semantics.  Each HTTP
254   message, as defined in &messaging;, is in the form of either a request or
255   a response.  An HTTP server listens on a connection for HTTP requests and
256   responds to each request, in the order received on that connection, with
257   one or more HTTP response messages.  This document defines the commonly
258   agreed upon semantics of the HTTP uniform interface, the intentions defined
259   by each request method, and the various response messages that might be
260   expected as a result of applying that method for the requested resource.
261</t>
262<t>
263   This document is currently disorganized in order to minimize the changes
264   between drafts and enable reviewers to see the smaller errata changes.
265   The next draft will reorganize the sections to better reflect the content.
266   In particular, the sections will be ordered according to the typical
267   processing of an HTTP request message (after message parsing): resource
268   mapping, general header fields, methods, request modifiers, response
269   status, and resource metadata.  The current mess reflects how widely
270   dispersed these topics and associated requirements had become in
271   <xref target="RFC2616"/>.
272</t>
273
274<section title="Requirements" anchor="intro.requirements">
275<t>
276   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
277   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
278   document are to be interpreted as described in <xref target="RFC2119"/>.
279</t>
280<t>
281   An implementation is not compliant if it fails to satisfy one or more
282   of the &MUST; or &REQUIRED; level requirements for the protocols it
283   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
284   level and all the &SHOULD; level requirements for its protocols is said
285   to be "unconditionally compliant"; one that satisfies all the &MUST;
286   level requirements but not all the &SHOULD; level requirements for its
287   protocols is said to be "conditionally compliant."
288</t>
289</section>
290
291<section title="Syntax Notation" anchor="notation">
292  <x:anchor-alias value="CR"/>
293  <x:anchor-alias value="DIGIT"/>
294  <x:anchor-alias value="LF"/>
295  <x:anchor-alias value="VCHAR"/>
296  <x:anchor-alias value="WSP"/>
297<t>
298  This specification uses the ABNF syntax defined in &notation; (which
299  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
300  <xref target="collected.abnf"/> shows the collected ABNF, with the list
301  rule expanded.
302</t>
303<t>
304  The following core rules are included by
305  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
306  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
307  DIGIT (decimal 0-9), DQUOTE (double quote),
308  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
309  OCTET (any 8-bit sequence of data), SP (space),
310  VCHAR (any visible USASCII character),
311  and WSP (whitespace).
312</t>
313
314<section title="Core Rules" anchor="core.rules">
315  <x:anchor-alias value="comment"/>
316  <x:anchor-alias value="obs-text"/>
317  <x:anchor-alias value="quoted-string"/>
318  <x:anchor-alias value="token"/>
319  <x:anchor-alias value="OWS"/>
320  <x:anchor-alias value="RWS"/>
321<t>
322  The core rules below are defined in &basic-rules;:
323</t>
324<figure><artwork type="abnf2616">
325  <x:ref>comment</x:ref>       = &lt;comment, defined in &basic-rules;&gt;
326  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &basic-rules;&gt;
327  <x:ref>token</x:ref>         = &lt;token, defined in &basic-rules;&gt;
328  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
329  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &basic-rules;&gt;
330  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &basic-rules;&gt;
331</artwork></figure>
332</section>
333
334<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
335  <x:anchor-alias value="absolute-URI"/>
336  <x:anchor-alias value="Accept"/>
337  <x:anchor-alias value="Accept-Charset"/>
338  <x:anchor-alias value="Accept-Encoding"/>
339  <x:anchor-alias value="Accept-Language"/>
340  <x:anchor-alias value="Accept-Ranges"/>
341  <x:anchor-alias value="Age"/>
342  <x:anchor-alias value="Authorization"/>
343  <x:anchor-alias value="ETag"/>
344  <x:anchor-alias value="fragment"/>
345  <x:anchor-alias value="Host"/>
346  <x:anchor-alias value="HTTP-date"/>
347  <x:anchor-alias value="If-Match"/>
348  <x:anchor-alias value="If-Modified-Since"/>
349  <x:anchor-alias value="If-None-Match"/>
350  <x:anchor-alias value="If-Range"/>
351  <x:anchor-alias value="If-Unmodified-Since"/>
352  <x:anchor-alias value="partial-URI"/>
353  <x:anchor-alias value="product"/>
354  <x:anchor-alias value="Proxy-Authenticate"/>
355  <x:anchor-alias value="Proxy-Authorization"/>
356  <x:anchor-alias value="Range"/>
357  <x:anchor-alias value="TE"/>
358  <x:anchor-alias value="Vary"/>
359  <x:anchor-alias value="WWW-Authenticate"/>
360<t>
361  The ABNF rules below are defined in other parts:
362</t>
363<figure><!--Part1--><artwork type="abnf2616">
364  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
365  <x:ref>fragment</x:ref>      = &lt;fragment, defined in &uri;&gt;
366  <x:ref>Host</x:ref>          = &lt;Host, defined in &uri;&gt;
367  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
368  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
369  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
370  <x:ref>TE</x:ref>            = &lt;TE, defined in &header-te;&gt;
371</artwork></figure>
372<figure><!--Part3--><artwork type="abnf2616">
373  <x:ref>Accept</x:ref>        = &lt;Accept, defined in &header-accept;&gt;
374  <x:ref>Accept-Charset</x:ref> =
375             &lt;Accept-Charset, defined in &header-accept-charset;&gt;
376  <x:ref>Accept-Encoding</x:ref> =
377             &lt;Accept-Encoding, defined in &header-accept-encoding;&gt;
378  <x:ref>Accept-Language</x:ref> =
379             &lt;Accept-Language, defined in &header-accept-language;&gt;
380</artwork></figure>
381<figure><!--Part4--><artwork type="abnf2616">
382  <x:ref>ETag</x:ref>          = &lt;ETag, defined in &header-etag;&gt;
383  <x:ref>If-Match</x:ref>      = &lt;If-Match, defined in &header-if-match;&gt;
384  <x:ref>If-Modified-Since</x:ref> =
385             &lt;If-Modified-Since, defined in &header-if-modified-since;&gt;
386  <x:ref>If-None-Match</x:ref> = &lt;If-None-Match, defined in &header-if-none-match;&gt;
387  <x:ref>If-Unmodified-Since</x:ref> =
388             &lt;If-Unmodified-Since, defined in &header-if-unmodified-since;&gt;
389</artwork></figure>
390<figure><!--Part5--><artwork type="abnf2616">
391  <x:ref>Accept-Ranges</x:ref> = &lt;Accept-Ranges, defined in &header-accept-ranges;&gt;
392  <x:ref>If-Range</x:ref>      = &lt;If-Range, defined in &header-if-range;&gt;
393  <x:ref>Range</x:ref>         = &lt;Range, defined in &header-range;&gt;
394</artwork></figure>
395<figure><!--Part6--><artwork type="abnf2616">
396  <x:ref>Age</x:ref>           = &lt;Age, defined in &header-age;&gt;
397  <x:ref>Vary</x:ref>          = &lt;Vary, defined in &header-vary;&gt;
398</artwork><!--Part7--></figure>
399<figure><artwork type="abnf2616">
400  <x:ref>Authorization</x:ref> = &lt;Authorization, defined in &header-authorization;&gt;
401  <x:ref>Proxy-Authenticate</x:ref> =
402             &lt;Proxy-Authenticate, defined in &header-proxy-authenticate;&gt;
403  <x:ref>Proxy-Authorization</x:ref> =
404             &lt;Proxy-Authorization, defined in &header-proxy-authorization;&gt;
405  <x:ref>WWW-Authenticate</x:ref> =
406             &lt;WWW-Authenticate, defined in &header-www-authenticate;&gt;
407</artwork></figure>
408</section>
409</section>
410</section>
411
412<section title="Method" anchor="method">
413  <x:anchor-alias value="Method"/>
414  <x:anchor-alias value="extension-method"/>
415<t>
416   The Method  token indicates the method to be performed on the
417   resource identified by the request-target. The method is case-sensitive.
418</t>
419<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
420  <x:ref>Method</x:ref>         = <x:abnf-char-sequence>"OPTIONS"</x:abnf-char-sequence>   ; "OPTIONS", <xref target="OPTIONS"/>
421                 / <x:abnf-char-sequence>"GET"</x:abnf-char-sequence>               ; "GET", <xref target="GET"/>
422                 / <x:abnf-char-sequence>"HEAD"</x:abnf-char-sequence>            ; "HEAD", <xref target="HEAD"/>
423                 / <x:abnf-char-sequence>"POST"</x:abnf-char-sequence>            ; "POST", <xref target="POST"/>
424                 / <x:abnf-char-sequence>"PUT"</x:abnf-char-sequence>               ; "PUT", <xref target="PUT"/>
425                 / <x:abnf-char-sequence>"DELETE"</x:abnf-char-sequence>      ; "DELETE", <xref target="DELETE"/>
426                 / <x:abnf-char-sequence>"TRACE"</x:abnf-char-sequence>         ; "TRACE", <xref target="TRACE"/>
427                 / <x:abnf-char-sequence>"CONNECT"</x:abnf-char-sequence>   ; "CONNECT", <xref target="CONNECT"/>
428                 / <x:ref>extension-method</x:ref>
429  <x:ref>extension-method</x:ref> = <x:ref>token</x:ref>
430</artwork></figure>
431<t>
432   The list of methods allowed by a resource can be specified in an
433   Allow header field (<xref target="header.allow"/>). The return code of the response
434   always notifies the client whether a method is currently allowed on a
435   resource, since the set of allowed methods can change dynamically. An
436   origin server &SHOULD; return the status code 405 (Method Not Allowed)
437   if the method is known by the origin server but not allowed for the
438   requested resource, and 501 (Not Implemented) if the method is
439   unrecognized or not implemented by the origin server. The methods GET
440   and HEAD &MUST; be supported by all general-purpose servers. All other
441   methods are &OPTIONAL;; however, if the above methods are implemented,
442   they &MUST; be implemented with the same semantics as those specified
443   in <xref target="method.definitions"/>.
444</t>
445
446<section title="Method Registry" anchor="method.registry">
447<t>
448  The HTTP Method Registry defines the name space for the Method token in the
449  Request line of an HTTP request.
450</t>
451<t>
452  Registrations &MUST; include the following fields:
453  <list style="symbols">
454    <t>Method Name (see <xref target="method"/>)</t>
455    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
456    <t>Pointer to specification text</t>
457  </list>
458</t>
459<t>
460  Values to be added to this name space are subject to IETF review
461  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
462</t>
463<t>
464  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
465</t>
466</section>
467</section>
468
469<section title="Request Header Fields" anchor="request.header.fields">
470  <x:anchor-alias value="request-header"/>
471<t>
472   The request-header fields allow the client to pass additional
473   information about the request, and about the client itself, to the
474   server. These fields act as request modifiers, with semantics
475   equivalent to the parameters on a programming language method
476   invocation.
477</t>
478<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-header"/>
479  <x:ref>request-header</x:ref> = <x:ref>Accept</x:ref>                   ; &header-accept;
480                 / <x:ref>Accept-Charset</x:ref>           ; &header-accept-charset;
481                 / <x:ref>Accept-Encoding</x:ref>          ; &header-accept-encoding;
482                 / <x:ref>Accept-Language</x:ref>          ; &header-accept-language;
483                 / <x:ref>Authorization</x:ref>            ; &header-authorization;
484                 / <x:ref>Expect</x:ref>                   ; <xref target="header.expect"/>
485                 / <x:ref>From</x:ref>                     ; <xref target="header.from"/>
486                 / <x:ref>Host</x:ref>                     ; &header-host;
487                 / <x:ref>If-Match</x:ref>                 ; &header-if-match;
488                 / <x:ref>If-Modified-Since</x:ref>        ; &header-if-modified-since;
489                 / <x:ref>If-None-Match</x:ref>            ; &header-if-none-match;
490                 / <x:ref>If-Range</x:ref>                 ; &header-if-range;
491                 / <x:ref>If-Unmodified-Since</x:ref>      ; &header-if-unmodified-since;
492                 / <x:ref>Max-Forwards</x:ref>             ; <xref target="header.max-forwards"/>
493                 / <x:ref>Proxy-Authorization</x:ref>      ; &header-proxy-authorization;
494                 / <x:ref>Range</x:ref>                    ; &header-range;
495                 / <x:ref>Referer</x:ref>                  ; <xref target="header.referer"/>
496                 / <x:ref>TE</x:ref>                       ; &header-te;
497                 / <x:ref>User-Agent</x:ref>               ; <xref target="header.user-agent"/>
498</artwork></figure>
499<t>
500   Request-header field names can be extended reliably only in
501   combination with a change in the protocol version. However, new or
502   experimental header fields &MAY; be given the semantics of request-header
503   fields if all parties in the communication recognize them to
504   be request-header fields. Unrecognized header fields are treated as
505   entity-header fields.
506</t>
507</section>
508
509<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
510  <x:anchor-alias value="Reason-Phrase"/>
511  <x:anchor-alias value="Status-Code"/>
512  <x:anchor-alias value="extension-code"/>
513<t>
514   The Status-Code element is a 3-digit integer result code of the
515   attempt to understand and satisfy the request. The status codes listed
516   below are defined in <xref target="status.codes"/>.
517   The Reason-Phrase is intended to give a short
518   textual description of the Status-Code. The Status-Code is intended
519   for use by automata and the Reason-Phrase is intended for the human
520   user. The client is not required to examine or display the Reason-Phrase.
521</t>
522<t> 
523   The individual values of the numeric status codes defined for
524   HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
525   presented below. The reason phrases listed here are only
526   recommendations -- they &MAY; be replaced by local equivalents without
527   affecting the protocol.
528</t>
529<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"/>
530  <x:ref>Status-Code</x:ref>    =
531         "100"  ; <xref target="status.100"/>: Continue
532       / "101"  ; <xref target="status.101"/>: Switching Protocols
533       / "200"  ; <xref target="status.200"/>: OK
534       / "201"  ; <xref target="status.201"/>: Created
535       / "202"  ; <xref target="status.202"/>: Accepted
536       / "203"  ; <xref target="status.203"/>: Non-Authoritative Information
537       / "204"  ; <xref target="status.204"/>: No Content
538       / "205"  ; <xref target="status.205"/>: Reset Content
539       / "206"  ; <xref target="status.206"/>: Partial Content
540       / "300"  ; <xref target="status.300"/>: Multiple Choices
541       / "301"  ; <xref target="status.301"/>: Moved Permanently
542       / "302"  ; <xref target="status.302"/>: Found
543       / "303"  ; <xref target="status.303"/>: See Other
544       / "304"  ; <xref target="status.304"/>: Not Modified
545       / "305"  ; <xref target="status.305"/>: Use Proxy
546       / "307"  ; <xref target="status.307"/>: Temporary Redirect
547       / "400"  ; <xref target="status.400"/>: Bad Request
548       / "401"  ; <xref target="status.401"/>: Unauthorized
549       / "402"  ; <xref target="status.402"/>: Payment Required
550       / "403"  ; <xref target="status.403"/>: Forbidden
551       / "404"  ; <xref target="status.404"/>: Not Found
552       / "405"  ; <xref target="status.405"/>: Method Not Allowed
553       / "406"  ; <xref target="status.406"/>: Not Acceptable
554       / "407"  ; <xref target="status.407"/>: Proxy Authentication Required
555       / "408"  ; <xref target="status.408"/>: Request Time-out
556       / "409"  ; <xref target="status.409"/>: Conflict
557       / "410"  ; <xref target="status.410"/>: Gone
558       / "411"  ; <xref target="status.411"/>: Length Required
559       / "412"  ; <xref target="status.412"/>: Precondition Failed
560       / "413"  ; <xref target="status.413"/>: Request Entity Too Large
561       / "414"  ; <xref target="status.414"/>: URI Too Long
562       / "415"  ; <xref target="status.415"/>: Unsupported Media Type
563       / "416"  ; <xref target="status.416"/>: Requested range not satisfiable
564       / "417"  ; <xref target="status.417"/>: Expectation Failed
565       / "500"  ; <xref target="status.500"/>: Internal Server Error
566       / "501"  ; <xref target="status.501"/>: Not Implemented
567       / "502"  ; <xref target="status.502"/>: Bad Gateway
568       / "503"  ; <xref target="status.503"/>: Service Unavailable
569       / "504"  ; <xref target="status.504"/>: Gateway Time-out
570       / "505"  ; <xref target="status.505"/>: HTTP Version not supported
571       / <x:ref>extension-code</x:ref>
572
573  <x:ref>extension-code</x:ref> = 3<x:ref>DIGIT</x:ref>
574  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
575</artwork></figure>
576<t>
577   HTTP status codes are extensible. HTTP applications are not required
578   to understand the meaning of all registered status codes, though such
579   understanding is obviously desirable. However, applications &MUST;
580   understand the class of any status code, as indicated by the first
581   digit, and treat any unrecognized response as being equivalent to the
582   x00 status code of that class, with the exception that an
583   unrecognized response &MUST-NOT; be cached. For example, if an
584   unrecognized status code of 431 is received by the client, it can
585   safely assume that there was something wrong with its request and
586   treat the response as if it had received a 400 status code. In such
587   cases, user agents &SHOULD; present to the user the entity returned
588   with the response, since that entity is likely to include human-readable
589   information which will explain the unusual status.
590</t>
591
592<section title="Status Code Registry" anchor="status.code.registry">
593<t>
594  The HTTP Status Code Registry defines the name space for the Status-Code
595  token in the Status line of an HTTP response.
596</t>
597<t>
598  Values to be added to this name space are subject to IETF review
599  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
600</t>
601<t>
602  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
603</t>
604</section>
605
606</section>
607
608<section title="Response Header Fields" anchor="response.header.fields">
609  <x:anchor-alias value="response-header"/>
610<t>
611   The response-header fields allow the server to pass additional
612   information about the response which cannot be placed in the Status-Line.
613   These header fields give information about the server and about
614   further access to the resource identified by the request-target.
615</t>
616<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="response-header"/>
617  <x:ref>response-header</x:ref> = <x:ref>Accept-Ranges</x:ref>           ; &header-accept-ranges;
618                  / <x:ref>Age</x:ref>                     ; &header-age;
619                  / <x:ref>Allow</x:ref>                   ; <xref target="header.allow"/>
620                  / <x:ref>ETag</x:ref>                    ; &header-etag;
621                  / <x:ref>Location</x:ref>                ; <xref target="header.location"/>
622                  / <x:ref>Proxy-Authenticate</x:ref>      ; &header-proxy-authenticate;
623                  / <x:ref>Retry-After</x:ref>             ; <xref target="header.retry-after"/>
624                  / <x:ref>Server</x:ref>                  ; <xref target="header.server"/>
625                  / <x:ref>Vary</x:ref>                    ; &header-vary;
626                  / <x:ref>WWW-Authenticate</x:ref>        ; &header-www-authenticate;
627</artwork></figure>
628<t>
629   Response-header field names can be extended reliably only in
630   combination with a change in the protocol version. However, new or
631   experimental header fields &MAY; be given the semantics of response-header
632   fields if all parties in the communication recognize them to
633   be response-header fields. Unrecognized header fields are treated as
634   entity-header fields.
635</t>
636</section>
637
638<section title="Entity" anchor="entity">
639<t>
640   Request and Response messages &MAY; transfer an entity if not otherwise
641   restricted by the request method or response status code. An entity
642   consists of entity-header fields and an entity-body, although some
643   responses will only include the entity-headers. HTTP entity-body and
644   entity-header fields are defined in &payload;.
645</t>
646<t>
647   An entity-body is only present in a message when a message-body is
648   present, as described in &message-body;. The entity-body is obtained
649   from the message-body by decoding any Transfer-Encoding that might
650   have been applied to ensure safe and proper transfer of the message.
651</t>
652</section>
653
654
655<section title="Method Definitions" anchor="method.definitions">
656<t>
657   The set of common methods for HTTP/1.1 is defined below. Although
658   this set can be expanded, additional methods cannot be assumed to
659   share the same semantics for separately extended clients and servers.
660</t>
661
662<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
663
664<section title="Safe Methods" anchor="safe.methods">
665<iref item="Safe Methods" primary="true"/>
666<t>
667   Implementors should be aware that the software represents the user in
668   their interactions over the Internet, and should be careful to allow
669   the user to be aware of any actions they might take which may have an
670   unexpected significance to themselves or others.
671</t>
672<t>
673   In particular, the convention has been established that the GET and
674   HEAD methods &SHOULD-NOT;  have the significance of taking an action
675   other than retrieval. These methods ought to be considered "<x:dfn anchor="safe">safe</x:dfn>".
676   This allows user agents to represent other methods, such as POST, PUT
677   and DELETE, in a special way, so that the user is made aware of the
678   fact that a possibly unsafe action is being requested.
679</t>
680<t>
681   Naturally, it is not possible to ensure that the server does not
682   generate side-effects as a result of performing a GET request; in
683   fact, some dynamic resources consider that a feature. The important
684   distinction here is that the user did not request the side-effects,
685   so therefore cannot be held accountable for them.
686</t>
687</section>
688
689<section title="Idempotent Methods" anchor="idempotent.methods">
690<iref item="Idempotent Methods" primary="true"/>
691<t>
692   Methods can also have the property of "idempotence" in that (aside
693   from error or expiration issues) the side-effects of N &gt; 0 identical
694   requests is the same as for a single request. The methods GET, HEAD,
695   PUT and DELETE share this property. Also, the methods OPTIONS and
696   TRACE &SHOULD-NOT;  have side effects, and so are inherently idempotent.
697</t>
698<t>
699   However, it is possible that a sequence of several requests is non-idempotent,
700   even if all of the methods executed in that sequence are
701   idempotent. (A sequence is idempotent if a single execution of the
702   entire sequence always yields a result that is not changed by a
703   reexecution of all, or part, of that sequence.) For example, a
704   sequence is non-idempotent if its result depends on a value that is
705   later modified in the same sequence.
706</t>
707<t>
708   A sequence that never has side effects is idempotent, by definition
709   (provided that no concurrent operations are being executed on the
710   same set of resources).
711</t>
712</section>
713</section>
714
715<section title="OPTIONS" anchor="OPTIONS">
716  <rdf:Description>
717    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
718  </rdf:Description>
719  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
720  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
721<t>
722   The OPTIONS method represents a request for information about the
723   communication options available on the request/response chain
724   identified by the request-target. This method allows the client to
725   determine the options and/or requirements associated with a resource,
726   or the capabilities of a server, without implying a resource action
727   or initiating a resource retrieval.
728</t>
729<t>
730   Responses to this method are not cacheable.
731</t>
732<t>
733   If the OPTIONS request includes an entity-body (as indicated by the
734   presence of Content-Length or Transfer-Encoding), then the media type
735   &MUST; be indicated by a Content-Type field. Although this
736   specification does not define any use for such a body, future
737   extensions to HTTP might use the OPTIONS body to make more detailed
738   queries on the server.
739</t>
740<t>
741   If the request-target is an asterisk ("*"), the OPTIONS request is
742   intended to apply to the server in general rather than to a specific
743   resource. Since a server's communication options typically depend on
744   the resource, the "*" request is only useful as a "ping" or "no-op"
745   type of method; it does nothing beyond allowing the client to test
746   the capabilities of the server. For example, this can be used to test
747   a proxy for HTTP/1.1 compliance (or lack thereof).
748</t>
749<t>
750   If the request-target is not an asterisk, the OPTIONS request applies
751   only to the options that are available when communicating with that
752   resource.
753</t>
754<t>
755   A 200 response &SHOULD; include any header fields that indicate
756   optional features implemented by the server and applicable to that
757   resource (e.g., Allow), possibly including extensions not defined by
758   this specification. The response body, if any, &SHOULD; also include
759   information about the communication options. The format for such a
760   body is not defined by this specification, but might be defined by
761   future extensions to HTTP. Content negotiation &MAY; be used to select
762   the appropriate response format. If no response body is included, the
763   response &MUST; include a Content-Length field with a field-value of
764   "0".
765</t>
766<t>
767   The Max-Forwards request-header field &MAY; be used to target a
768   specific proxy in the request chain. When a proxy receives an OPTIONS
769   request on an absolute-URI for which request forwarding is permitted,
770   the proxy &MUST; check for a Max-Forwards field. If the Max-Forwards
771   field-value is zero ("0"), the proxy &MUST-NOT; forward the message;
772   instead, the proxy &SHOULD; respond with its own communication options.
773   If the Max-Forwards field-value is an integer greater than zero, the
774   proxy &MUST; decrement the field-value when it forwards the request. If
775   no Max-Forwards field is present in the request, then the forwarded
776   request &MUST-NOT; include a Max-Forwards field.
777</t>
778</section>
779
780<section title="GET" anchor="GET">
781  <rdf:Description>
782    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
783  </rdf:Description>
784  <iref primary="true" item="GET method" x:for-anchor=""/>
785  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
786<t>
787   The GET method means retrieve whatever information (in the form of an
788   entity) is identified by the request-target. If the request-target refers
789   to a data-producing process, it is the produced data which shall be
790   returned as the entity in the response and not the source text of the
791   process, unless that text happens to be the output of the process.
792</t>
793<t>
794   The semantics of the GET method change to a "conditional GET" if the
795   request message includes an If-Modified-Since, If-Unmodified-Since,
796   If-Match, If-None-Match, or If-Range header field. A conditional GET
797   method requests that the entity be transferred only under the
798   circumstances described by the conditional header field(s). The
799   conditional GET method is intended to reduce unnecessary network
800   usage by allowing cached entities to be refreshed without requiring
801   multiple requests or transferring data already held by the client.
802</t>
803<t>
804   The semantics of the GET method change to a "partial GET" if the
805   request message includes a Range header field. A partial GET requests
806   that only part of the entity be transferred, as described in &header-range;.
807   The partial GET method is intended to reduce unnecessary
808   network usage by allowing partially-retrieved entities to be
809   completed without transferring data already held by the client.
810</t>
811<t>
812   The response to a GET request is cacheable if and only if it meets
813   the requirements for HTTP caching described in &caching;.
814</t>
815<t>
816   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
817</t>
818</section>
819
820<section title="HEAD" anchor="HEAD">
821  <rdf:Description>
822    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
823  </rdf:Description>
824  <iref primary="true" item="HEAD method" x:for-anchor=""/>
825  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
826<t>
827   The HEAD method is identical to GET except that the server &MUST-NOT;
828   return a message-body in the response. The metainformation contained
829   in the HTTP headers in response to a HEAD request &SHOULD; be identical
830   to the information sent in response to a GET request. This method can
831   be used for obtaining metainformation about the entity implied by the
832   request without transferring the entity-body itself. This method is
833   often used for testing hypertext links for validity, accessibility,
834   and recent modification.
835</t>
836<t>
837   The response to a HEAD request &MAY; be cacheable in the sense that the
838   information contained in the response &MAY; be used to update a
839   previously cached entity from that resource. If the new field values
840   indicate that the cached entity differs from the current entity (as
841   would be indicated by a change in Content-Length, Content-MD5, ETag
842   or Last-Modified), then the cache &MUST; treat the cache entry as
843   stale.
844</t>
845</section>
846
847<section title="POST" anchor="POST">
848  <iref primary="true" item="POST method" x:for-anchor=""/>
849  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
850<t>
851   The POST method is used to request that the origin server accept the
852   entity enclosed in the request as data to be processed by the resource
853   identified by the request-target in the Request-Line. POST is designed
854   to allow a uniform method to cover the following functions:
855  <list style="symbols">
856    <t>
857      Annotation of existing resources;
858    </t>
859    <t>
860        Posting a message to a bulletin board, newsgroup, mailing list,
861        or similar group of articles;
862    </t>
863    <t>
864        Providing a block of data, such as the result of submitting a
865        form, to a data-handling process;
866    </t>
867    <t>
868        Extending a database through an append operation.
869    </t>
870  </list>
871</t>
872<t>
873   The actual function performed by the POST method is determined by the
874   server and is usually dependent on the request-target.
875</t>
876<t>
877   The action performed by the POST method might not result in a
878   resource that can be identified by a URI. In this case, either 200
879   (OK) or 204 (No Content) is the appropriate response status,
880   depending on whether or not the response includes an entity that
881   describes the result.
882</t>
883<t>
884   If a resource has been created on the origin server, the response
885   &SHOULD; be 201 (Created) and contain an entity which describes the
886   status of the request and refers to the new resource, and a Location
887   header (see <xref target="header.location"/>).
888</t>
889<t>
890   Responses to this method are not cacheable, unless the response
891   includes appropriate Cache-Control or Expires header fields. However,
892   the 303 (See Other) response can be used to direct the user agent to
893   retrieve a cacheable resource.
894</t>
895</section>
896
897<section title="PUT" anchor="PUT">
898  <iref primary="true" item="PUT method" x:for-anchor=""/>
899  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
900<t>
901   The PUT method requests that the enclosed entity be stored at the
902   supplied request-target. If the request-target refers to an already
903   existing resource, the enclosed entity &SHOULD; be considered as a
904   modified version of the one residing on the origin server. If the
905   request-target does not point to an existing resource, and that URI is
906   capable of being defined as a new resource by the requesting user
907   agent, the origin server can create the resource with that URI. If a
908   new resource is created at the request-target, the origin server &MUST;
909   inform the user agent
910   via the 201 (Created) response. If an existing resource is modified,
911   either the 200 (OK) or 204 (No Content) response codes &SHOULD; be sent
912   to indicate successful completion of the request. If the resource
913   could not be created or modified with the request-target, an appropriate
914   error response &SHOULD; be given that reflects the nature of the
915   problem. The recipient of the entity &MUST-NOT; ignore any Content-*
916   headers (headers starting with the prefix 'Content-') that it does
917   not understand or implement
918   and &MUST; return a 501 (Not Implemented) response in such cases.
919</t>
920<t>
921   If the request passes through a cache and the request-target identifies
922   one or more currently cached entities, those entries &SHOULD; be
923   treated as stale. Responses to this method are not cacheable.
924</t>
925<t>
926   The fundamental difference between the POST and PUT requests is
927   reflected in the different meaning of the request-target. The URI in a
928   POST request identifies the resource that will handle the enclosed
929   entity. That resource might be a data-accepting process, a gateway to
930   some other protocol, or a separate entity that accepts annotations.
931   In contrast, the URI in a PUT request identifies the entity enclosed
932   with the request -- the user agent knows what URI is intended and the
933   server &MUST-NOT; attempt to apply the request to some other resource.
934   If the server desires that the request be applied to a different URI,
935   it &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
936   then make its own decision regarding whether or not to redirect the
937   request.
938</t>
939<t>
940   A single resource &MAY; be identified by many different URIs. For
941   example, an article might have a URI for identifying "the current
942   version" which is separate from the URI identifying each particular
943   version. In this case, a PUT request on a general URI might result in
944   several other URIs being defined by the origin server.
945</t>
946<t>
947   HTTP/1.1 does not define how a PUT method affects the state of an
948   origin server.
949</t>
950<t>
951   Unless otherwise specified for a particular entity-header, the
952   entity-headers in the PUT request &SHOULD; be applied to the resource
953   created or modified by the PUT.
954</t>
955</section>
956
957<section title="DELETE" anchor="DELETE">
958  <iref primary="true" item="DELETE method" x:for-anchor=""/>
959  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
960<t>
961   The DELETE method requests that the origin server delete the resource
962   identified by the request-target. This method &MAY; be overridden by human
963   intervention (or other means) on the origin server. The client cannot
964   be guaranteed that the operation has been carried out, even if the
965   status code returned from the origin server indicates that the action
966   has been completed successfully. However, the server &SHOULD-NOT; 
967   indicate success unless, at the time the response is given, it
968   intends to delete the resource or move it to an inaccessible
969   location.
970</t>
971<t>
972   A successful response &SHOULD; be 200 (OK) if the response includes an
973   entity describing the status, 202 (Accepted) if the action has not
974   yet been enacted, or 204 (No Content) if the action has been enacted
975   but the response does not include an entity.
976</t>
977<t>
978   If the request passes through a cache and the request-target identifies
979   one or more currently cached entities, those entries &SHOULD; be
980   treated as stale. Responses to this method are not cacheable.
981</t>
982</section>
983
984<section title="TRACE" anchor="TRACE">
985  <rdf:Description>
986    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
987  </rdf:Description>
988  <iref primary="true" item="TRACE method" x:for-anchor=""/>
989  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
990<t>
991   The TRACE method is used to invoke a remote, application-layer loop-back
992   of the request message. The final recipient of the request
993   &SHOULD; reflect the message received back to the client as the
994   entity-body of a 200 (OK) response. The final recipient is either the
995   origin server or the first proxy or gateway to receive a Max-Forwards
996   value of zero (0) in the request (see <xref target="header.max-forwards"/>). A TRACE request
997   &MUST-NOT; include an entity.
998</t>
999<t>
1000   TRACE allows the client to see what is being received at the other
1001   end of the request chain and use that data for testing or diagnostic
1002   information. The value of the Via header field (&header-via;) is of
1003   particular interest, since it acts as a trace of the request chain.
1004   Use of the Max-Forwards header field allows the client to limit the
1005   length of the request chain, which is useful for testing a chain of
1006   proxies forwarding messages in an infinite loop.
1007</t>
1008<t>
1009   If the request is valid, the response &SHOULD; contain the entire
1010   request message in the entity-body, with a Content-Type of
1011   "message/http" (see &media-type-message-http;). Responses to this method
1012   &MUST-NOT; be cached.
1013</t>
1014</section>
1015
1016<section title="CONNECT" anchor="CONNECT">
1017  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1018  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1019<t>
1020   This specification reserves the method name CONNECT for use with a
1021   proxy that can dynamically switch to being a tunnel (e.g. SSL
1022   tunneling <xref target="RFC2817"/>).
1023</t>
1024</section>
1025</section>
1026
1027
1028<section title="Status Code Definitions" anchor="status.codes">
1029<t>
1030   Each Status-Code is described below, including any metainformation required
1031   in the response.
1032</t>
1033
1034<section title="Informational 1xx" anchor="status.1xx">
1035<t>
1036   This class of status code indicates a provisional response,
1037   consisting only of the Status-Line and optional headers, and is
1038   terminated by an empty line. There are no required headers for this
1039   class of status code. Since HTTP/1.0 did not define any 1xx status
1040   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1041   except under experimental conditions.
1042</t>
1043<t>
1044   A client &MUST; be prepared to accept one or more 1xx status responses
1045   prior to a regular response, even if the client does not expect a 100
1046   (Continue) status message. Unexpected 1xx status responses &MAY; be
1047   ignored by a user agent.
1048</t>
1049<t>
1050   Proxies &MUST; forward 1xx responses, unless the connection between the
1051   proxy and its client has been closed, or unless the proxy itself
1052   requested the generation of the 1xx response. (For example, if a
1053   proxy adds a "Expect: 100-continue" field when it forwards a request,
1054   then it need not forward the corresponding 100 (Continue)
1055   response(s).)
1056</t>
1057
1058<section title="100 Continue" anchor="status.100">
1059  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1060  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1061<t>
1062   The client &SHOULD; continue with its request. This interim response is
1063   used to inform the client that the initial part of the request has
1064   been received and has not yet been rejected by the server. The client
1065   &SHOULD; continue by sending the remainder of the request or, if the
1066   request has already been completed, ignore this response. The server
1067   &MUST; send a final response after the request has been completed. See
1068   &use100; for detailed discussion of the use and handling of this
1069   status code.
1070</t>
1071</section>
1072
1073<section title="101 Switching Protocols" anchor="status.101">
1074  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1075  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1076<t>
1077   The server understands and is willing to comply with the client's
1078   request, via the Upgrade message header field (&header-upgrade;), for a
1079   change in the application protocol being used on this connection. The
1080   server will switch protocols to those defined by the response's
1081   Upgrade header field immediately after the empty line which
1082   terminates the 101 response.
1083</t>
1084<t>
1085   The protocol &SHOULD; be switched only when it is advantageous to do
1086   so. For example, switching to a newer version of HTTP is advantageous
1087   over older versions, and switching to a real-time, synchronous
1088   protocol might be advantageous when delivering resources that use
1089   such features.
1090</t>
1091</section>
1092</section>
1093
1094<section title="Successful 2xx" anchor="status.2xx">
1095<t>
1096   This class of status code indicates that the client's request was
1097   successfully received, understood, and accepted.
1098</t>
1099
1100<section title="200 OK" anchor="status.200">
1101  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1102  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1103<t>
1104   The request has succeeded. The information returned with the response
1105   is dependent on the method used in the request, for example:
1106  <list style="hanging">
1107    <t hangText="GET">
1108          an entity corresponding to the requested resource is sent in
1109          the response;
1110    </t>
1111    <t hangText="HEAD">
1112          the entity-header fields corresponding to the requested
1113          resource are sent in the response without any message-body;
1114    </t>
1115    <t hangText="POST">
1116      an entity describing or containing the result of the action;
1117    </t>
1118    <t hangText="TRACE">
1119      an entity containing the request message as received by the
1120      end server.
1121    </t>
1122  </list>
1123</t>
1124</section>
1125
1126<section title="201 Created" anchor="status.201">
1127  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1128  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1129<t>
1130   The request has been fulfilled and resulted in a new resource being
1131   created. The newly created resource can be referenced by the URI(s)
1132   returned in the entity of the response, with the most specific URI
1133   for the resource given by a Location header field. The response
1134   &SHOULD; include an entity containing a list of resource
1135   characteristics and location(s) from which the user or user agent can
1136   choose the one most appropriate. The entity format is specified by
1137   the media type given in the Content-Type header field. The origin
1138   server &MUST; create the resource before returning the 201 status code.
1139   If the action cannot be carried out immediately, the server &SHOULD;
1140   respond with 202 (Accepted) response instead.
1141</t>
1142<t>
1143   A 201 response &MAY; contain an ETag response header field indicating
1144   the current value of the entity tag for the requested variant just
1145   created, see &header-etag;.
1146</t>
1147</section>
1148
1149<section title="202 Accepted" anchor="status.202">
1150  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1151  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1152<t>
1153   The request has been accepted for processing, but the processing has
1154   not been completed.  The request might or might not eventually be
1155   acted upon, as it might be disallowed when processing actually takes
1156   place. There is no facility for re-sending a status code from an
1157   asynchronous operation such as this.
1158</t>
1159<t>
1160   The 202 response is intentionally non-committal. Its purpose is to
1161   allow a server to accept a request for some other process (perhaps a
1162   batch-oriented process that is only run once per day) without
1163   requiring that the user agent's connection to the server persist
1164   until the process is completed. The entity returned with this
1165   response &SHOULD; include an indication of the request's current status
1166   and either a pointer to a status monitor or some estimate of when the
1167   user can expect the request to be fulfilled.
1168</t>
1169</section>
1170
1171<section title="203 Non-Authoritative Information" anchor="status.203">
1172  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1173  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1174<t>
1175   The returned metainformation in the entity-header is not the
1176   definitive set as available from the origin server, but is gathered
1177   from a local or a third-party copy. The set presented &MAY; be a subset
1178   or superset of the original version. For example, including local
1179   annotation information about the resource might result in a superset
1180   of the metainformation known by the origin server. Use of this
1181   response code is not required and is only appropriate when the
1182   response would otherwise be 200 (OK).
1183</t>
1184</section>
1185
1186<section title="204 No Content" anchor="status.204">
1187  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1188  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1189<t>
1190   The server has fulfilled the request but does not need to return an
1191   entity-body, and might want to return updated metainformation. The
1192   response &MAY; include new or updated metainformation in the form of
1193   entity-headers, which if present &SHOULD; be associated with the
1194   requested variant.
1195</t>
1196<t>
1197   If the client is a user agent, it &SHOULD-NOT;  change its document view
1198   from that which caused the request to be sent. This response is
1199   primarily intended to allow input for actions to take place without
1200   causing a change to the user agent's active document view, although
1201   any new or updated metainformation &SHOULD; be applied to the document
1202   currently in the user agent's active view.
1203</t>
1204<t>
1205   The 204 response &MUST-NOT; include a message-body, and thus is always
1206   terminated by the first empty line after the header fields.
1207</t>
1208</section>
1209
1210<section title="205 Reset Content" anchor="status.205">
1211  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1212  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1213<t>
1214   The server has fulfilled the request and the user agent &SHOULD; reset
1215   the document view which caused the request to be sent. This response
1216   is primarily intended to allow input for actions to take place via
1217   user input, followed by a clearing of the form in which the input is
1218   given so that the user can easily initiate another input action. The
1219   response &MUST-NOT; include an entity.
1220</t>
1221</section>
1222
1223<section title="206 Partial Content" anchor="status.206">
1224  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1225  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1226<t>
1227   The server has fulfilled the partial GET request for the resource
1228   and the enclosed entity is a partial representation as defined in &range;.
1229</t>
1230</section>
1231</section>
1232
1233<section title="Redirection 3xx" anchor="status.3xx">
1234<t>
1235   This class of status code indicates that further action needs to be
1236   taken by the user agent in order to fulfill the request.  The action
1237   required &MAY; be carried out by the user agent without interaction
1238   with the user if and only if the method used in the second request is
1239   GET or HEAD. A client &SHOULD; detect infinite redirection loops, since
1240   such loops generate network traffic for each redirection.
1241</t>
1242<x:note>
1243  <t>
1244    <x:h>Note:</x:h> previous versions of this specification recommended a
1245    maximum of five redirections. Content developers should be aware
1246    that there might be clients that implement such a fixed
1247    limitation.
1248  </t>
1249</x:note>
1250
1251<section title="300 Multiple Choices" anchor="status.300">
1252  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1253  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1254<t>
1255   The requested resource corresponds to any one of a set of
1256   representations, each with its own specific location, and agent-driven
1257   negotiation information (&content-negotiation;) is being provided so that
1258   the user (or user agent) can select a preferred representation and
1259   redirect its request to that location.
1260</t>
1261<t>
1262   Unless it was a HEAD request, the response &SHOULD; include an entity
1263   containing a list of resource characteristics and location(s) from
1264   which the user or user agent can choose the one most appropriate. The
1265   entity format is specified by the media type given in the Content-Type
1266   header field. Depending upon the format and the capabilities of
1267   the user agent, selection of the most appropriate choice &MAY; be
1268   performed automatically. However, this specification does not define
1269   any standard for such automatic selection.
1270</t>
1271<t>
1272   If the server has a preferred choice of representation, it &SHOULD;
1273   include the specific URI for that representation in the Location
1274   field; user agents &MAY; use the Location field value for automatic
1275   redirection. This response is cacheable unless indicated otherwise.
1276</t>
1277</section>
1278
1279<section title="301 Moved Permanently" anchor="status.301">
1280  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1281  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1282<t>
1283   The requested resource has been assigned a new permanent URI and any
1284   future references to this resource &SHOULD; use one of the returned
1285   URIs.  Clients with link editing capabilities ought to automatically
1286   re-link references to the request-target to one or more of the new
1287   references returned by the server, where possible. This response is
1288   cacheable unless indicated otherwise.
1289</t>
1290<t>
1291   The new permanent URI &SHOULD; be given by the Location field in the
1292   response. Unless the request method was HEAD, the entity of the
1293   response &SHOULD; contain a short hypertext note with a hyperlink to
1294   the new URI(s).
1295</t>
1296<t>
1297   If the 301 status code is received in response to a request method
1298   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1299   then the request &MAY; be automatically redirected by the user agent without
1300   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1301   request unless it can be confirmed by the user, since this might
1302   change the conditions under which the request was issued.
1303</t>
1304<x:note>
1305  <t>
1306    <x:h>Note:</x:h> When automatically redirecting a POST request after
1307    receiving a 301 status code, some existing HTTP/1.0 user agents
1308    will erroneously change it into a GET request.
1309  </t>
1310</x:note>
1311</section>
1312
1313<section title="302 Found" anchor="status.302">
1314  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1315  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1316<t>
1317   The requested resource resides temporarily under a different URI.
1318   Since the redirection might be altered on occasion, the client &SHOULD;
1319   continue to use the request-target for future requests.  This response
1320   is only cacheable if indicated by a Cache-Control or Expires header
1321   field.
1322</t>
1323<t>
1324   The temporary URI &SHOULD; be given by the Location field in the
1325   response. Unless the request method was HEAD, the entity of the
1326   response &SHOULD; contain a short hypertext note with a hyperlink to
1327   the new URI(s).
1328</t>
1329<t>
1330   If the 302 status code is received in response to a request method
1331   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1332   then the request &MAY; be automatically redirected by the user agent without
1333   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1334   request unless it can be confirmed by the user, since this might
1335   change the conditions under which the request was issued.
1336</t>
1337<x:note>
1338  <t>
1339    <x:h>Note:</x:h> <xref target="RFC1945"/> and <xref target="RFC2068"/> specify that the client is not allowed
1340    to change the method on the redirected request.  However, most
1341    existing user agent implementations treat 302 as if it were a 303
1342    response, performing a GET on the Location field-value regardless
1343    of the original request method. The status codes 303 and 307 have
1344    been added for servers that wish to make unambiguously clear which
1345    kind of reaction is expected of the client.
1346  </t>
1347</x:note>
1348</section>
1349
1350<section title="303 See Other" anchor="status.303">
1351  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1352  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1353<t>
1354   The server directs the user agent to a different resource, indicated
1355   by a URI in the Location header field, that provides an indirect
1356   response to the original request.  The user agent &MAY; perform a GET
1357   request on the URI in the Location field in order to obtain a
1358   representation corresponding to the response, be redirected again,
1359   or end with an error status.  The Location URI is not a substitute
1360   reference for the originally requested resource.
1361</t>
1362<t>
1363   The 303 status is generally applicable to any HTTP method.  It is
1364   primarily used to allow the output of a POST action to redirect
1365   the user agent to a selected resource, since doing so provides the
1366   information corresponding to the POST response in a form that
1367   can be separately identified, bookmarked, and cached independent
1368   of the original request.
1369</t>
1370<t>
1371   A 303 response to a GET request indicates that the requested
1372   resource does not have a representation of its own that can be
1373   transferred by the server over HTTP.  The Location URI indicates a
1374   resource that is descriptive of the requested resource such that
1375   the follow-on representation may be useful without implying that
1376   it adequately represents the previously requested resource.
1377   Note that answers to the questions of what can be represented, what
1378   representations are adequate, and what might be a useful description
1379   are outside the scope of HTTP and thus entirely determined by the
1380   URI owner(s).
1381</t>
1382<t>
1383   A 303 response &SHOULD-NOT; be cached unless it is indicated as
1384   cacheable by Cache-Control or Expires header fields.  Except for
1385   responses to a HEAD request, the entity of a 303 response &SHOULD;
1386   contain a short hypertext note with a hyperlink to the Location URI.
1387</t>
1388</section>
1389
1390<section title="304 Not Modified" anchor="status.304">
1391  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1392  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1393<t>
1394   The response to the request has not been modified since the conditions
1395   indicated by the client's conditional GET request, as defined in &conditional;.
1396</t>
1397</section>
1398
1399<section title="305 Use Proxy" anchor="status.305">
1400  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1401  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1402<t>
1403   The 305 status was defined in a previous version of this specification
1404   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1405</t>
1406</section>
1407
1408<section title="306 (Unused)" anchor="status.306">
1409  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1410  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1411<t>
1412   The 306 status code was used in a previous version of the
1413   specification, is no longer used, and the code is reserved.
1414</t>
1415</section>
1416
1417<section title="307 Temporary Redirect" anchor="status.307">
1418  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1419  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1420<t>
1421   The requested resource resides temporarily under a different URI.
1422   Since the redirection &MAY; be altered on occasion, the client &SHOULD;
1423   continue to use the request-target for future requests.  This response
1424   is only cacheable if indicated by a Cache-Control or Expires header
1425   field.
1426</t>
1427<t>
1428   The temporary URI &SHOULD; be given by the Location field in the
1429   response. Unless the request method was HEAD, the entity of the
1430   response &SHOULD; contain a short hypertext note with a hyperlink to
1431   the new URI(s) , since many pre-HTTP/1.1 user agents do not
1432   understand the 307 status. Therefore, the note &SHOULD; contain the
1433   information necessary for a user to repeat the original request on
1434   the new URI.
1435</t>
1436<t>
1437   If the 307 status code is received in response to a request method
1438   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1439   then the request &MAY; be automatically redirected by the user agent without
1440   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1441   request unless it can be confirmed by the user, since this might
1442   change the conditions under which the request was issued.
1443</t>
1444</section>
1445</section>
1446
1447<section title="Client Error 4xx" anchor="status.4xx">
1448<t>
1449   The 4xx class of status code is intended for cases in which the
1450   client seems to have erred. Except when responding to a HEAD request,
1451   the server &SHOULD; include an entity containing an explanation of the
1452   error situation, and whether it is a temporary or permanent
1453   condition. These status codes are applicable to any request method.
1454   User agents &SHOULD; display any included entity to the user.
1455</t>
1456<t>
1457   If the client is sending data, a server implementation using TCP
1458   &SHOULD; be careful to ensure that the client acknowledges receipt of
1459   the packet(s) containing the response, before the server closes the
1460   input connection. If the client continues sending data to the server
1461   after the close, the server's TCP stack will send a reset packet to
1462   the client, which may erase the client's unacknowledged input buffers
1463   before they can be read and interpreted by the HTTP application.
1464</t>
1465
1466<section title="400 Bad Request" anchor="status.400">
1467  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1468  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1469<t>
1470   The request could not be understood by the server due to malformed
1471   syntax. The client &SHOULD-NOT;  repeat the request without
1472   modifications.
1473</t>
1474</section>
1475
1476<section title="401 Unauthorized" anchor="status.401">
1477  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1478  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1479<t>
1480   The request requires user authentication (see &auth;).
1481</t>
1482</section>
1483
1484<section title="402 Payment Required" anchor="status.402">
1485  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1486  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1487<t>
1488   This code is reserved for future use.
1489</t>
1490</section>
1491
1492<section title="403 Forbidden" anchor="status.403">
1493  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1494  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1495<t>
1496   The server understood the request, but is refusing to fulfill it.
1497   Authorization will not help and the request &SHOULD-NOT;  be repeated.
1498   If the request method was not HEAD and the server wishes to make
1499   public why the request has not been fulfilled, it &SHOULD; describe the
1500   reason for the refusal in the entity.  If the server does not wish to
1501   make this information available to the client, the status code 404
1502   (Not Found) can be used instead.
1503</t>
1504</section>
1505
1506<section title="404 Not Found" anchor="status.404">
1507  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1508  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1509<t>
1510   The server has not found anything matching the request-target. No
1511   indication is given of whether the condition is temporary or
1512   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1513   knows, through some internally configurable mechanism, that an old
1514   resource is permanently unavailable and has no forwarding address.
1515   This status code is commonly used when the server does not wish to
1516   reveal exactly why the request has been refused, or when no other
1517   response is applicable.
1518</t>
1519</section>
1520
1521<section title="405 Method Not Allowed" anchor="status.405">
1522  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1523  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1524<t>
1525   The method specified in the Request-Line is not allowed for the
1526   resource identified by the request-target. The response &MUST; include an
1527   Allow header containing a list of valid methods for the requested
1528   resource.
1529</t>
1530</section>
1531
1532<section title="406 Not Acceptable" anchor="status.406">
1533  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1534  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1535<t>
1536   The resource identified by the request is only capable of generating
1537   response entities which have content characteristics not acceptable
1538   according to the accept headers sent in the request.
1539</t>
1540<t>
1541   Unless it was a HEAD request, the response &SHOULD; include an entity
1542   containing a list of available entity characteristics and location(s)
1543   from which the user or user agent can choose the one most
1544   appropriate. The entity format is specified by the media type given
1545   in the Content-Type header field. Depending upon the format and the
1546   capabilities of the user agent, selection of the most appropriate
1547   choice &MAY; be performed automatically. However, this specification
1548   does not define any standard for such automatic selection.
1549</t>
1550<x:note>
1551  <t>
1552    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1553    not acceptable according to the accept headers sent in the
1554    request. In some cases, this may even be preferable to sending a
1555    406 response. User agents are encouraged to inspect the headers of
1556    an incoming response to determine if it is acceptable.
1557  </t>
1558</x:note>
1559<t>
1560   If the response could be unacceptable, a user agent &SHOULD;
1561   temporarily stop receipt of more data and query the user for a
1562   decision on further actions.
1563</t>
1564</section>
1565
1566<section title="407 Proxy Authentication Required" anchor="status.407">
1567  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1568  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1569<t>
1570   This code is similar to 401 (Unauthorized), but indicates that the
1571   client must first authenticate itself with the proxy (see &auth;).
1572</t>
1573</section>
1574
1575<section title="408 Request Timeout" anchor="status.408">
1576  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1577  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1578<t>
1579   The client did not produce a request within the time that the server
1580   was prepared to wait. The client &MAY; repeat the request without
1581   modifications at any later time.
1582</t>
1583</section>
1584
1585<section title="409 Conflict" anchor="status.409">
1586  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1587  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1588<t>
1589   The request could not be completed due to a conflict with the current
1590   state of the resource. This code is only allowed in situations where
1591   it is expected that the user might be able to resolve the conflict
1592   and resubmit the request. The response body &SHOULD; include enough
1593   information for the user to recognize the source of the conflict.
1594   Ideally, the response entity would include enough information for the
1595   user or user agent to fix the problem; however, that might not be
1596   possible and is not required.
1597</t>
1598<t>
1599   Conflicts are most likely to occur in response to a PUT request. For
1600   example, if versioning were being used and the entity being PUT
1601   included changes to a resource which conflict with those made by an
1602   earlier (third-party) request, the server might use the 409 response
1603   to indicate that it can't complete the request. In this case, the
1604   response entity would likely contain a list of the differences
1605   between the two versions in a format defined by the response
1606   Content-Type.
1607</t>
1608</section>
1609
1610<section title="410 Gone" anchor="status.410">
1611  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1612  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1613<t>
1614   The requested resource is no longer available at the server and no
1615   forwarding address is known. This condition is expected to be
1616   considered permanent. Clients with link editing capabilities &SHOULD;
1617   delete references to the request-target after user approval. If the
1618   server does not know, or has no facility to determine, whether or not
1619   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1620   used instead. This response is cacheable unless indicated otherwise.
1621</t>
1622<t>
1623   The 410 response is primarily intended to assist the task of web
1624   maintenance by notifying the recipient that the resource is
1625   intentionally unavailable and that the server owners desire that
1626   remote links to that resource be removed. Such an event is common for
1627   limited-time, promotional services and for resources belonging to
1628   individuals no longer working at the server's site. It is not
1629   necessary to mark all permanently unavailable resources as "gone" or
1630   to keep the mark for any length of time -- that is left to the
1631   discretion of the server owner.
1632</t>
1633</section>
1634
1635<section title="411 Length Required" anchor="status.411">
1636  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1637  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1638<t>
1639   The server refuses to accept the request without a defined Content-Length.
1640   The client &MAY; repeat the request if it adds a valid
1641   Content-Length header field containing the length of the message-body
1642   in the request message.
1643</t>
1644</section>
1645
1646<section title="412 Precondition Failed" anchor="status.412">
1647  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1648  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1649<t>
1650   The precondition given in one or more of the request-header fields
1651   evaluated to false when it was tested on the server, as defined in
1652   &conditional;.
1653</t>
1654</section>
1655
1656<section title="413 Request Entity Too Large" anchor="status.413">
1657  <iref primary="true" item="413 Request Entity Too Large (status code)" x:for-anchor=""/>
1658  <iref primary="true" item="Status Codes" subitem="413 Request Entity Too Large" x:for-anchor=""/>
1659<t>
1660   The server is refusing to process a request because the request
1661   entity is larger than the server is willing or able to process. The
1662   server &MAY; close the connection to prevent the client from continuing
1663   the request.
1664</t>
1665<t>
1666   If the condition is temporary, the server &SHOULD; include a Retry-After
1667   header field to indicate that it is temporary and after what
1668   time the client &MAY; try again.
1669</t>
1670</section>
1671
1672<section title="414 URI Too Long" anchor="status.414">
1673  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1674  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1675<t>
1676   The server is refusing to service the request because the request-target
1677   is longer than the server is willing to interpret. This rare
1678   condition is only likely to occur when a client has improperly
1679   converted a POST request to a GET request with long query
1680   information, when the client has descended into a URI "black hole" of
1681   redirection (e.g., a redirected URI prefix that points to a suffix of
1682   itself), or when the server is under attack by a client attempting to
1683   exploit security holes present in some servers using fixed-length
1684   buffers for reading or manipulating the request-target.
1685</t>
1686</section>
1687
1688<section title="415 Unsupported Media Type" anchor="status.415">
1689  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1690  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1691<t>
1692   The server is refusing to service the request because the entity of
1693   the request is in a format not supported by the requested resource
1694   for the requested method.
1695</t>
1696</section>
1697
1698<section title="416 Requested Range Not Satisfiable" anchor="status.416">
1699  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
1700  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
1701<t>
1702   The request included a Range request-header field (&header-range;) and none of
1703   the range-specifier values in this field overlap the current extent
1704   of the selected resource.
1705</t>
1706</section>
1707
1708<section title="417 Expectation Failed" anchor="status.417">
1709  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1710  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1711<t>
1712   The expectation given in an Expect request-header field (see <xref target="header.expect"/>)
1713   could not be met by this server, or, if the server is a proxy,
1714   the server has unambiguous evidence that the request could not be met
1715   by the next-hop server.
1716</t>
1717</section>
1718</section>
1719
1720<section title="Server Error 5xx" anchor="status.5xx">
1721<t>
1722   Response status codes beginning with the digit "5" indicate cases in
1723   which the server is aware that it has erred or is incapable of
1724   performing the request. Except when responding to a HEAD request, the
1725   server &SHOULD; include an entity containing an explanation of the
1726   error situation, and whether it is a temporary or permanent
1727   condition. User agents &SHOULD; display any included entity to the
1728   user. These response codes are applicable to any request method.
1729</t>
1730
1731<section title="500 Internal Server Error" anchor="status.500">
1732  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1733  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1734<t>
1735   The server encountered an unexpected condition which prevented it
1736   from fulfilling the request.
1737</t>
1738</section>
1739
1740<section title="501 Not Implemented" anchor="status.501">
1741  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1742  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1743<t>
1744   The server does not support the functionality required to fulfill the
1745   request. This is the appropriate response when the server does not
1746   recognize the request method and is not capable of supporting it for
1747   any resource.
1748</t>
1749</section>
1750
1751<section title="502 Bad Gateway" anchor="status.502">
1752  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1753  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1754<t>
1755   The server, while acting as a gateway or proxy, received an invalid
1756   response from the upstream server it accessed in attempting to
1757   fulfill the request.
1758</t>
1759</section>
1760
1761<section title="503 Service Unavailable" anchor="status.503">
1762  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1763  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1764<t>
1765   The server is currently unable to handle the request due to a
1766   temporary overloading or maintenance of the server. The implication
1767   is that this is a temporary condition which will be alleviated after
1768   some delay. If known, the length of the delay &MAY; be indicated in a
1769   Retry-After header. If no Retry-After is given, the client &SHOULD;
1770   handle the response as it would for a 500 response.
1771</t>
1772<x:note>
1773  <t>
1774    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
1775    server must use it when becoming overloaded. Some servers may wish
1776    to simply refuse the connection.
1777  </t>
1778</x:note>
1779</section>
1780
1781<section title="504 Gateway Timeout" anchor="status.504">
1782  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
1783  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
1784<t>
1785   The server, while acting as a gateway or proxy, did not receive a
1786   timely response from the upstream server specified by the URI (e.g.
1787   HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed
1788   to access in attempting to complete the request.
1789</t>
1790<x:note>
1791  <t>
1792    <x:h>Note:</x:h> Note to implementors: some deployed proxies are known to
1793    return 400 or 500 when DNS lookups time out.
1794  </t>
1795</x:note>
1796</section>
1797
1798<section title="505 HTTP Version Not Supported" anchor="status.505">
1799  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
1800  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
1801<t>
1802   The server does not support, or refuses to support, the protocol
1803   version that was used in the request message. The server is
1804   indicating that it is unable or unwilling to complete the request
1805   using the same major version as the client, as described in &http-version;,
1806   other than with this error message. The response &SHOULD; contain
1807   an entity describing why that version is not supported and what other
1808   protocols are supported by that server.
1809</t>
1810
1811</section>
1812</section>
1813</section>
1814
1815
1816<section title="Header Field Definitions" anchor="header.fields">
1817<t>
1818   This section defines the syntax and semantics of HTTP/1.1 header fields
1819   related to request and response semantics.
1820</t>
1821<t>
1822   For entity-header fields, both sender and recipient refer to either the
1823   client or the server, depending on who sends and who receives the entity.
1824</t>
1825
1826<section title="Allow" anchor="header.allow">
1827  <iref primary="true" item="Allow header" x:for-anchor=""/>
1828  <iref primary="true" item="Headers" subitem="Allow" x:for-anchor=""/>
1829  <x:anchor-alias value="Allow"/>
1830  <x:anchor-alias value="Allow-v"/>
1831<t>
1832      The response-header field "Allow" lists the set of methods advertised as
1833      supported by the resource identified by the request-target. The purpose of
1834      this field is strictly to inform the recipient of valid methods
1835      associated with the resource. An Allow header field &MUST; be
1836      present in a 405 (Method Not Allowed) response.
1837</t>
1838<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/><iref primary="true" item="Grammar" subitem="Allow-v"/>
1839  <x:ref>Allow</x:ref>   = "Allow" ":" <x:ref>OWS</x:ref> <x:ref>Allow-v</x:ref>
1840  <x:ref>Allow-v</x:ref> = #<x:ref>Method</x:ref>
1841</artwork></figure>
1842<t>
1843      Example of use:
1844</t>
1845<figure><artwork type="example">
1846  Allow: GET, HEAD, PUT
1847</artwork></figure>
1848<t>
1849      The actual set of allowed methods is defined
1850      by the origin server at the time of each request.
1851</t>
1852<t>
1853      A proxy &MUST-NOT; modify the Allow header field even if it does not
1854      understand all the methods specified, since the user agent might
1855      have other means of communicating with the origin server.
1856</t>
1857</section>
1858
1859<section title="Expect" anchor="header.expect">
1860  <iref primary="true" item="Expect header" x:for-anchor=""/>
1861  <iref primary="true" item="Headers" subitem="Expect" x:for-anchor=""/>
1862  <x:anchor-alias value="Expect"/>
1863  <x:anchor-alias value="Expect-v"/>
1864  <x:anchor-alias value="expectation"/>
1865  <x:anchor-alias value="expectation-extension"/>
1866  <x:anchor-alias value="expect-params"/>
1867<t>
1868   The request-header field "Expect" is used to indicate that particular
1869   server behaviors are required by the client.
1870</t>
1871<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="Expect-v"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/>
1872  <x:ref>Expect</x:ref>       = "Expect" ":" <x:ref>OWS</x:ref> <x:ref>Expect-v</x:ref>
1873  <x:ref>Expect-v</x:ref>     = 1#<x:ref>expectation</x:ref>
1874 
1875  <x:ref>expectation</x:ref>  = "100-continue" / <x:ref>expectation-extension</x:ref>
1876  <x:ref>expectation-extension</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
1877                           *<x:ref>expect-params</x:ref> ]
1878  <x:ref>expect-params</x:ref> = ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
1879</artwork></figure>
1880<t>
1881   A server that does not understand or is unable to comply with any of
1882   the expectation values in the Expect field of a request &MUST; respond
1883   with appropriate error status. The server &MUST; respond with a 417
1884   (Expectation Failed) status if any of the expectations cannot be met
1885   or, if there are other problems with the request, some other 4xx
1886   status.
1887</t>
1888<t>
1889   This header field is defined with extensible syntax to allow for
1890   future extensions. If a server receives a request containing an
1891   Expect field that includes an expectation-extension that it does not
1892   support, it &MUST; respond with a 417 (Expectation Failed) status.
1893</t>
1894<t>
1895   Comparison of expectation values is case-insensitive for unquoted
1896   tokens (including the 100-continue token), and is case-sensitive for
1897   quoted-string expectation-extensions.
1898</t>
1899<t>
1900   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
1901   return a 417 (Expectation Failed) status if it receives a request
1902   with an expectation that it cannot meet. However, the Expect
1903   request-header itself is end-to-end; it &MUST; be forwarded if the
1904   request is forwarded.
1905</t>
1906<t>
1907   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
1908   Expect header.
1909</t>
1910<t>
1911   See &use100; for the use of the 100 (Continue) status.
1912</t>
1913</section>
1914
1915<section title="From" anchor="header.from">
1916  <iref primary="true" item="From header" x:for-anchor=""/>
1917  <iref primary="true" item="Headers" subitem="From" x:for-anchor=""/>
1918  <x:anchor-alias value="From"/>
1919  <x:anchor-alias value="From-v"/>
1920  <x:anchor-alias value="mailbox"/>
1921<t>
1922   The request-header field "From", if given, &SHOULD; contain an Internet
1923   e-mail address for the human user who controls the requesting user
1924   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
1925   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
1926</t>
1927<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/><iref primary="true" item="Grammar" subitem="From-v"/>
1928  <x:ref>From</x:ref>    = "From" ":" <x:ref>OWS</x:ref> <x:ref>From-v</x:ref>
1929  <x:ref>From-v</x:ref>  = <x:ref>mailbox</x:ref>
1930 
1931  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
1932</artwork></figure>
1933<t>
1934   An example is:
1935</t>
1936<figure><artwork type="example">
1937  From: webmaster@example.org
1938</artwork></figure>
1939<t>
1940   This header field &MAY; be used for logging purposes and as a means for
1941   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
1942   be used as an insecure form of access protection. The interpretation
1943   of this field is that the request is being performed on behalf of the
1944   person given, who accepts responsibility for the method performed. In
1945   particular, robot agents &SHOULD; include this header so that the
1946   person responsible for running the robot can be contacted if problems
1947   occur on the receiving end.
1948</t>
1949<t>
1950   The Internet e-mail address in this field &MAY; be separate from the
1951   Internet host which issued the request. For example, when a request
1952   is passed through a proxy the original issuer's address &SHOULD; be
1953   used.
1954</t>
1955<t>
1956   The client &SHOULD-NOT;  send the From header field without the user's
1957   approval, as it might conflict with the user's privacy interests or
1958   their site's security policy. It is strongly recommended that the
1959   user be able to disable, enable, and modify the value of this field
1960   at any time prior to a request.
1961</t>
1962</section>
1963
1964<section title="Location" anchor="header.location">
1965  <iref primary="true" item="Location header" x:for-anchor=""/>
1966  <iref primary="true" item="Headers" subitem="Location" x:for-anchor=""/>
1967  <x:anchor-alias value="Location"/>
1968  <x:anchor-alias value="Location-v"/>
1969<t>
1970   The response-header field "Location" is used for the identification of a
1971   new resource or to redirect the recipient to a location other than the
1972   request-target for completion of the request.  For 201 (Created)
1973   responses, the Location is that of the new resource which was created
1974   by the request. For 3xx responses, the location &SHOULD; indicate the
1975   server's preferred URI for automatic redirection to the resource. The
1976   field value consists of a single absolute URI.
1977</t>
1978<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/><iref primary="true" item="Grammar" subitem="Location-v"/>
1979  <x:ref>Location</x:ref>       = "Location" ":" <x:ref>OWS</x:ref> <x:ref>Location-v</x:ref>
1980  <x:ref>Location-v</x:ref>     = <x:ref>absolute-URI</x:ref> [ "#" <x:ref>fragment</x:ref> ]
1981</artwork></figure>
1982<t>
1983   An example is:
1984</t>
1985<figure><artwork type="example">
1986  Location: http://www.example.org/pub/WWW/People.html
1987</artwork></figure>
1988<x:note>
1989  <t>
1990    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
1991    from Location in that the Content-Location identifies the original
1992    location of the entity enclosed in the response. It is therefore
1993    possible for a response to contain header fields for both Location
1994    and Content-Location.
1995  </t>
1996</x:note>
1997<t>
1998   There are circumstances in which a fragment identifier in a Location URL would not be appropriate:
1999   <list style="symbols">
2000      <t>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</t>
2001      <t>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment characteristics.</t>
2002      <t>With 305 Use Proxy.</t>
2003   </list>
2004</t>
2005</section>
2006
2007<section title="Max-Forwards" anchor="header.max-forwards">
2008  <iref primary="true" item="Max-Forwards header" x:for-anchor=""/>
2009  <iref primary="true" item="Headers" subitem="Max-Forwards" x:for-anchor=""/>
2010  <x:anchor-alias value="Max-Forwards"/>
2011  <x:anchor-alias value="Max-Forwards-v"/>
2012<t>
2013   The request-header "Max-Forwards" field provides a mechanism with the
2014   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>) methods to limit the
2015   number of proxies or gateways that can forward the request to the
2016   next inbound server. This can be useful when the client is attempting
2017   to trace a request chain which appears to be failing or looping in
2018   mid-chain.
2019</t>
2020<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/><iref primary="true" item="Grammar" subitem="Max-Forwards-v"/>
2021  <x:ref>Max-Forwards</x:ref>   = "Max-Forwards" ":" <x:ref>OWS</x:ref> <x:ref>Max-Forwards-v</x:ref>
2022  <x:ref>Max-Forwards-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2023</artwork></figure>
2024<t>
2025   The Max-Forwards value is a decimal integer indicating the remaining
2026   number of times this request message may be forwarded.
2027</t>
2028<t>
2029   Each proxy or gateway recipient of a TRACE or OPTIONS request
2030   containing a Max-Forwards header field &MUST; check and update its
2031   value prior to forwarding the request. If the received value is zero
2032   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2033   respond as the final recipient. If the received Max-Forwards value is
2034   greater than zero, then the forwarded message &MUST; contain an updated
2035   Max-Forwards field with a value decremented by one (1).
2036</t>
2037<t>
2038   The Max-Forwards header field &MAY; be ignored for all other methods
2039   defined by this specification and for any extension methods for which
2040   it is not explicitly referred to as part of that method definition.
2041</t>
2042</section>
2043
2044<section title="Referer" anchor="header.referer">
2045  <iref primary="true" item="Referer header" x:for-anchor=""/>
2046  <iref primary="true" item="Headers" subitem="Referer" x:for-anchor=""/>
2047  <x:anchor-alias value="Referer"/>
2048  <x:anchor-alias value="Referer-v"/>
2049<t>
2050   The request-header field "Referer" [sic] allows the client to specify, for
2051   the server's benefit, the address (URI) of the resource from which the
2052   request-target was obtained (the "referrer", although the header field is
2053   misspelled.).
2054</t>
2055<t>
2056   The Referer header allows servers to generate lists of back-links to
2057   resources for interest, logging, optimized caching, etc. It also allows
2058   obsolete or mistyped links to be traced for maintenance. Some servers use
2059   Referer as a means of controlling where they allow links from (so-called
2060   "deep linking"), but it should be noted that legitimate requests are not
2061   required to contain a Referer header field.
2062</t>
2063<t>
2064   If the request-target was obtained from a source that does not have its own
2065   URI (e.g., input from the user keyboard), the Referer field MUST either be
2066   sent with the value "about:blank", or not be sent at all. Note that this
2067   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2068</t>
2069<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/><iref primary="true" item="Grammar" subitem="Referer-v"/>
2070  <x:ref>Referer</x:ref>        = "Referer" ":" <x:ref>OWS</x:ref> <x:ref>Referer-v</x:ref>
2071  <x:ref>Referer-v</x:ref>      = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2072</artwork></figure>
2073<t>
2074   Example:
2075</t>
2076<figure><artwork type="example">
2077  Referer: http://www.example.org/hypertext/Overview.html
2078</artwork></figure>
2079<t>
2080   If the field value is a relative URI, it &SHOULD; be interpreted
2081   relative to the request-target. The URI &MUST-NOT; include a fragment. See
2082   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2083</t>
2084</section>
2085
2086<section title="Retry-After" anchor="header.retry-after">
2087  <iref primary="true" item="Retry-After header" x:for-anchor=""/>
2088  <iref primary="true" item="Headers" subitem="Retry-After" x:for-anchor=""/>
2089  <x:anchor-alias value="Retry-After"/>
2090  <x:anchor-alias value="Retry-After-v"/>
2091<t>
2092   The response-header "Retry-After" field can be used with a 503 (Service
2093   Unavailable) response to indicate how long the service is expected to
2094   be unavailable to the requesting client. This field &MAY; also be used
2095   with any 3xx (Redirection) response to indicate the minimum time the
2096   user-agent is asked wait before issuing the redirected request. The
2097   value of this field can be either an HTTP-date or an integer number
2098   of seconds (in decimal) after the time of the response.
2099</t>
2100<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/><iref primary="true" item="Grammar" subitem="Retry-After-v"/>
2101  <x:ref>Retry-After</x:ref>   = "Retry-After" ":" <x:ref>OWS</x:ref> <x:ref>Retry-After-v</x:ref>
2102  <x:ref>Retry-After-v</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2103</artwork></figure>
2104<t anchor="rule.delta-seconds">
2105  <x:anchor-alias value="delta-seconds"/>
2106   Time spans are non-negative decimal integers, representing time in
2107   seconds.
2108</t>
2109<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2110  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2111</artwork></figure>
2112<t>
2113   Two examples of its use are
2114</t>
2115<figure><artwork type="example">
2116  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2117  Retry-After: 120
2118</artwork></figure>
2119<t>
2120   In the latter example, the delay is 2 minutes.
2121</t>
2122</section>
2123
2124<section title="Server" anchor="header.server">
2125  <iref primary="true" item="Server header" x:for-anchor=""/>
2126  <iref primary="true" item="Headers" subitem="Server" x:for-anchor=""/>
2127  <x:anchor-alias value="Server"/>
2128  <x:anchor-alias value="Server-v"/>
2129<t>
2130   The response-header field "Server" contains information about the
2131   software used by the origin server to handle the request. The field
2132   can contain multiple product tokens (&product-tokens;) and comments
2133   identifying the server and any significant subproducts. The product
2134   tokens are listed in order of their significance for identifying the
2135   application.
2136</t>
2137<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/><iref primary="true" item="Grammar" subitem="Server-v"/>
2138  <x:ref>Server</x:ref>         = "Server" ":" <x:ref>OWS</x:ref> <x:ref>Server-v</x:ref>
2139  <x:ref>Server-v</x:ref>       = <x:ref>product</x:ref>
2140                   *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2141</artwork></figure>
2142<t>
2143   Example:
2144</t>
2145<figure><artwork type="example">
2146  Server: CERN/3.0 libwww/2.17
2147</artwork></figure>
2148<t>
2149   If the response is being forwarded through a proxy, the proxy
2150   application &MUST-NOT; modify the Server response-header. Instead, it
2151   &MUST; include a Via field (as described in &header-via;).
2152</t>
2153<x:note>
2154  <t>
2155    <x:h>Note:</x:h> Revealing the specific software version of the server might
2156    allow the server machine to become more vulnerable to attacks
2157    against software that is known to contain security holes. Server
2158    implementors are encouraged to make this field a configurable
2159    option.
2160  </t>
2161</x:note>
2162</section>
2163
2164<section title="User-Agent" anchor="header.user-agent">
2165  <iref primary="true" item="User-Agent header" x:for-anchor=""/>
2166  <iref primary="true" item="Headers" subitem="User-Agent" x:for-anchor=""/>
2167  <x:anchor-alias value="User-Agent"/>
2168  <x:anchor-alias value="User-Agent-v"/>
2169<t>
2170   The request-header field "User-Agent" contains information about the
2171   user agent originating the request. This is for statistical purposes,
2172   the tracing of protocol violations, and automated recognition of user
2173   agents for the sake of tailoring responses to avoid particular user
2174   agent limitations. User agents &SHOULD; include this field with
2175   requests. The field can contain multiple product tokens (&product-tokens;)
2176   and comments identifying the agent and any subproducts which form a
2177   significant part of the user agent. By convention, the product tokens
2178   are listed in order of their significance for identifying the
2179   application.
2180</t>
2181<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/><iref primary="true" item="Grammar" subitem="User-Agent-v"/>
2182  <x:ref>User-Agent</x:ref>     = "User-Agent" ":" <x:ref>OWS</x:ref> <x:ref>User-Agent-v</x:ref>
2183  <x:ref>User-Agent-v</x:ref>   = <x:ref>product</x:ref>
2184                   *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2185</artwork></figure>
2186<t>
2187   Example:
2188</t>
2189<figure><artwork type="example">
2190  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2191</artwork></figure>
2192</section>
2193
2194</section>
2195
2196<section title="IANA Considerations" anchor="IANA.considerations">
2197
2198<section title="Method Registry" anchor="method.registration">
2199<t>
2200  The registration procedure for HTTP Methods is defined by
2201  <xref target="method.registry"/> of this document.
2202</t>
2203<t>
2204   The HTTP Method Registry located at <eref target="http://www.iana.org/assignments/http-methods"/>
2205   should be populated with the registrations below:
2206</t>
2207<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2208<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2209   <ttcol>Method</ttcol>
2210   <ttcol>Safe</ttcol>
2211   <ttcol>Reference</ttcol>
2212   <c>CONNECT</c>
2213   <c>no</c>
2214   <c>
2215      <xref target="CONNECT"/>
2216   </c>
2217   <c>DELETE</c>
2218   <c>no</c>
2219   <c>
2220      <xref target="DELETE"/>
2221   </c>
2222   <c>GET</c>
2223   <c>yes</c>
2224   <c>
2225      <xref target="GET"/>
2226   </c>
2227   <c>HEAD</c>
2228   <c>yes</c>
2229   <c>
2230      <xref target="HEAD"/>
2231   </c>
2232   <c>OPTIONS</c>
2233   <c>yes</c>
2234   <c>
2235      <xref target="OPTIONS"/>
2236   </c>
2237   <c>POST</c>
2238   <c>no</c>
2239   <c>
2240      <xref target="POST"/>
2241   </c>
2242   <c>PUT</c>
2243   <c>no</c>
2244   <c>
2245      <xref target="PUT"/>
2246   </c>
2247   <c>TRACE</c>
2248   <c>yes</c>
2249   <c>
2250      <xref target="TRACE"/>
2251   </c>
2252</texttable>
2253<!--(END)-->
2254</section>
2255
2256<section title="Status Code Registry" anchor="status.code.registration">
2257<t>
2258   The registration procedure for HTTP Status Codes -- previously defined
2259   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> -- is now defined
2260   by <xref target="status.code.registry"/> of this document.
2261</t>
2262<t>
2263   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2264   should be updated with the registrations below:
2265</t>
2266<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2267<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2268   <ttcol>Value</ttcol>
2269   <ttcol>Description</ttcol>
2270   <ttcol>Reference</ttcol>
2271   <c>100</c>
2272   <c>Continue</c>
2273   <c>
2274      <xref target="status.100"/>
2275   </c>
2276   <c>101</c>
2277   <c>Switching Protocols</c>
2278   <c>
2279      <xref target="status.101"/>
2280   </c>
2281   <c>200</c>
2282   <c>OK</c>
2283   <c>
2284      <xref target="status.200"/>
2285   </c>
2286   <c>201</c>
2287   <c>Created</c>
2288   <c>
2289      <xref target="status.201"/>
2290   </c>
2291   <c>202</c>
2292   <c>Accepted</c>
2293   <c>
2294      <xref target="status.202"/>
2295   </c>
2296   <c>203</c>
2297   <c>Non-Authoritative Information</c>
2298   <c>
2299      <xref target="status.203"/>
2300   </c>
2301   <c>204</c>
2302   <c>No Content</c>
2303   <c>
2304      <xref target="status.204"/>
2305   </c>
2306   <c>205</c>
2307   <c>Reset Content</c>
2308   <c>
2309      <xref target="status.205"/>
2310   </c>
2311   <c>206</c>
2312   <c>Partial Content</c>
2313   <c>
2314      <xref target="status.206"/>
2315   </c>
2316   <c>300</c>
2317   <c>Multiple Choices</c>
2318   <c>
2319      <xref target="status.300"/>
2320   </c>
2321   <c>301</c>
2322   <c>Moved Permanently</c>
2323   <c>
2324      <xref target="status.301"/>
2325   </c>
2326   <c>302</c>
2327   <c>Found</c>
2328   <c>
2329      <xref target="status.302"/>
2330   </c>
2331   <c>303</c>
2332   <c>See Other</c>
2333   <c>
2334      <xref target="status.303"/>
2335   </c>
2336   <c>304</c>
2337   <c>Not Modified</c>
2338   <c>
2339      <xref target="status.304"/>
2340   </c>
2341   <c>305</c>
2342   <c>Use Proxy</c>
2343   <c>
2344      <xref target="status.305"/>
2345   </c>
2346   <c>306</c>
2347   <c>(Unused)</c>
2348   <c>
2349      <xref target="status.306"/>
2350   </c>
2351   <c>307</c>
2352   <c>Temporary Redirect</c>
2353   <c>
2354      <xref target="status.307"/>
2355   </c>
2356   <c>400</c>
2357   <c>Bad Request</c>
2358   <c>
2359      <xref target="status.400"/>
2360   </c>
2361   <c>401</c>
2362   <c>Unauthorized</c>
2363   <c>
2364      <xref target="status.401"/>
2365   </c>
2366   <c>402</c>
2367   <c>Payment Required</c>
2368   <c>
2369      <xref target="status.402"/>
2370   </c>
2371   <c>403</c>
2372   <c>Forbidden</c>
2373   <c>
2374      <xref target="status.403"/>
2375   </c>
2376   <c>404</c>
2377   <c>Not Found</c>
2378   <c>
2379      <xref target="status.404"/>
2380   </c>
2381   <c>405</c>
2382   <c>Method Not Allowed</c>
2383   <c>
2384      <xref target="status.405"/>
2385   </c>
2386   <c>406</c>
2387   <c>Not Acceptable</c>
2388   <c>
2389      <xref target="status.406"/>
2390   </c>
2391   <c>407</c>
2392   <c>Proxy Authentication Required</c>
2393   <c>
2394      <xref target="status.407"/>
2395   </c>
2396   <c>408</c>
2397   <c>Request Timeout</c>
2398   <c>
2399      <xref target="status.408"/>
2400   </c>
2401   <c>409</c>
2402   <c>Conflict</c>
2403   <c>
2404      <xref target="status.409"/>
2405   </c>
2406   <c>410</c>
2407   <c>Gone</c>
2408   <c>
2409      <xref target="status.410"/>
2410   </c>
2411   <c>411</c>
2412   <c>Length Required</c>
2413   <c>
2414      <xref target="status.411"/>
2415   </c>
2416   <c>412</c>
2417   <c>Precondition Failed</c>
2418   <c>
2419      <xref target="status.412"/>
2420   </c>
2421   <c>413</c>
2422   <c>Request Entity Too Large</c>
2423   <c>
2424      <xref target="status.413"/>
2425   </c>
2426   <c>414</c>
2427   <c>URI Too Long</c>
2428   <c>
2429      <xref target="status.414"/>
2430   </c>
2431   <c>415</c>
2432   <c>Unsupported Media Type</c>
2433   <c>
2434      <xref target="status.415"/>
2435   </c>
2436   <c>416</c>
2437   <c>Requested Range Not Satisfiable</c>
2438   <c>
2439      <xref target="status.416"/>
2440   </c>
2441   <c>417</c>
2442   <c>Expectation Failed</c>
2443   <c>
2444      <xref target="status.417"/>
2445   </c>
2446   <c>500</c>
2447   <c>Internal Server Error</c>
2448   <c>
2449      <xref target="status.500"/>
2450   </c>
2451   <c>501</c>
2452   <c>Not Implemented</c>
2453   <c>
2454      <xref target="status.501"/>
2455   </c>
2456   <c>502</c>
2457   <c>Bad Gateway</c>
2458   <c>
2459      <xref target="status.502"/>
2460   </c>
2461   <c>503</c>
2462   <c>Service Unavailable</c>
2463   <c>
2464      <xref target="status.503"/>
2465   </c>
2466   <c>504</c>
2467   <c>Gateway Timeout</c>
2468   <c>
2469      <xref target="status.504"/>
2470   </c>
2471   <c>505</c>
2472   <c>HTTP Version Not Supported</c>
2473   <c>
2474      <xref target="status.505"/>
2475   </c>
2476</texttable>
2477<!--(END)-->
2478</section>
2479<section title="Message Header Registration" anchor="message.header.registration">
2480<t>
2481   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2482   with the permanent registrations below (see <xref target="RFC3864"/>):
2483</t>
2484<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2485<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2486   <ttcol>Header Field Name</ttcol>
2487   <ttcol>Protocol</ttcol>
2488   <ttcol>Status</ttcol>
2489   <ttcol>Reference</ttcol>
2490   <c>Allow</c>
2491   <c>http</c>
2492   <c>standard</c>
2493   <c>
2494      <xref target="header.allow"/>
2495   </c>
2496   <c>Expect</c>
2497   <c>http</c>
2498   <c>standard</c>
2499   <c>
2500      <xref target="header.expect"/>
2501   </c>
2502   <c>From</c>
2503   <c>http</c>
2504   <c>standard</c>
2505   <c>
2506      <xref target="header.from"/>
2507   </c>
2508   <c>Location</c>
2509   <c>http</c>
2510   <c>standard</c>
2511   <c>
2512      <xref target="header.location"/>
2513   </c>
2514   <c>Max-Forwards</c>
2515   <c>http</c>
2516   <c>standard</c>
2517   <c>
2518      <xref target="header.max-forwards"/>
2519   </c>
2520   <c>Referer</c>
2521   <c>http</c>
2522   <c>standard</c>
2523   <c>
2524      <xref target="header.referer"/>
2525   </c>
2526   <c>Retry-After</c>
2527   <c>http</c>
2528   <c>standard</c>
2529   <c>
2530      <xref target="header.retry-after"/>
2531   </c>
2532   <c>Server</c>
2533   <c>http</c>
2534   <c>standard</c>
2535   <c>
2536      <xref target="header.server"/>
2537   </c>
2538   <c>User-Agent</c>
2539   <c>http</c>
2540   <c>standard</c>
2541   <c>
2542      <xref target="header.user-agent"/>
2543   </c>
2544</texttable>
2545<!--(END)-->
2546<t>
2547   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2548</t>
2549</section>
2550</section>
2551
2552<section title="Security Considerations" anchor="security.considerations">
2553<t>
2554   This section is meant to inform application developers, information
2555   providers, and users of the security limitations in HTTP/1.1 as
2556   described by this document. The discussion does not include
2557   definitive solutions to the problems revealed, though it does make
2558   some suggestions for reducing security risks.
2559</t>
2560
2561<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2562<t>
2563   Like any generic data transfer protocol, HTTP cannot regulate the
2564   content of the data that is transferred, nor is there any a priori
2565   method of determining the sensitivity of any particular piece of
2566   information within the context of any given request. Therefore,
2567   applications &SHOULD; supply as much control over this information as
2568   possible to the provider of that information. Four header fields are
2569   worth special mention in this context: Server, Via, Referer and From.
2570</t>
2571<t>
2572   Revealing the specific software version of the server might allow the
2573   server machine to become more vulnerable to attacks against software
2574   that is known to contain security holes. Implementors &SHOULD; make the
2575   Server header field a configurable option.
2576</t>
2577<t>
2578   Proxies which serve as a portal through a network firewall &SHOULD;
2579   take special precautions regarding the transfer of header information
2580   that identifies the hosts behind the firewall. In particular, they
2581   &SHOULD; remove, or replace with sanitized versions, any Via fields
2582   generated behind the firewall.
2583</t>
2584<t>
2585   The Referer header allows reading patterns to be studied and reverse
2586   links drawn. Although it can be very useful, its power can be abused
2587   if user details are not separated from the information contained in
2588   the Referer. Even when the personal information has been removed, the
2589   Referer header might indicate a private document's URI whose
2590   publication would be inappropriate.
2591</t>
2592<t>
2593   The information sent in the From field might conflict with the user's
2594   privacy interests or their site's security policy, and hence it
2595   &SHOULD-NOT;  be transmitted without the user being able to disable,
2596   enable, and modify the contents of the field. The user &MUST; be able
2597   to set the contents of this field within a user preference or
2598   application defaults configuration.
2599</t>
2600<t>
2601   We suggest, though do not require, that a convenient toggle interface
2602   be provided for the user to enable or disable the sending of From and
2603   Referer information.
2604</t>
2605<t>
2606   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref target="header.server"/>) header
2607   fields can sometimes be used to determine that a specific client or
2608   server have a particular security hole which might be exploited.
2609   Unfortunately, this same information is often used for other valuable
2610   purposes for which HTTP currently has no better mechanism.
2611</t>
2612</section>
2613
2614<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
2615<t>
2616   Because the source of a link might be private information or might
2617   reveal an otherwise private information source, it is strongly
2618   recommended that the user be able to select whether or not the
2619   Referer field is sent. For example, a browser client could have a
2620   toggle switch for browsing openly/anonymously, which would
2621   respectively enable/disable the sending of Referer and From
2622   information.
2623</t>
2624<t>
2625   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
2626   HTTP request if the referring page was transferred with a secure
2627   protocol.
2628</t>
2629<t>
2630   Authors of services should not use
2631   GET-based forms for the submission of sensitive data because that
2632   data will be encoded in the Request-target. Many existing
2633   servers, proxies, and user agents log or display the Request-target in
2634   places where it might be visible to third parties. Such services can
2635   use POST-based form submission instead.
2636</t>
2637</section>
2638
2639<section title="Location Headers and Spoofing" anchor="location.spoofing">
2640<t>
2641   If a single server supports multiple organizations that do not trust
2642   one another, then it &MUST; check the values of Location and Content-Location
2643   headers in responses that are generated under control of
2644   said organizations to make sure that they do not attempt to
2645   invalidate resources over which they have no authority.
2646</t>
2647</section>
2648
2649</section>
2650
2651<section title="Acknowledgments" anchor="ack">
2652</section>
2653</middle>
2654<back>
2655
2656<references title="Normative References">
2657
2658<reference anchor="Part1">
2659  <front>
2660    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
2661    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2662      <organization abbrev="Day Software">Day Software</organization>
2663      <address><email>fielding@gbiv.com</email></address>
2664    </author>
2665    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2666      <organization>One Laptop per Child</organization>
2667      <address><email>jg@laptop.org</email></address>
2668    </author>
2669    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2670      <organization abbrev="HP">Hewlett-Packard Company</organization>
2671      <address><email>JeffMogul@acm.org</email></address>
2672    </author>
2673    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2674      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2675      <address><email>henrikn@microsoft.com</email></address>
2676    </author>
2677    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2678      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2679      <address><email>LMM@acm.org</email></address>
2680    </author>
2681    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2682      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2683      <address><email>paulle@microsoft.com</email></address>
2684    </author>
2685    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2686      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2687      <address><email>timbl@w3.org</email></address>
2688    </author>
2689    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2690      <organization abbrev="W3C">World Wide Web Consortium</organization>
2691      <address><email>ylafon@w3.org</email></address>
2692    </author>
2693    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2694      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2695      <address><email>julian.reschke@greenbytes.de</email></address>
2696    </author>
2697    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2698  </front>
2699  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
2700  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
2701</reference>
2702
2703<reference anchor="Part3">
2704  <front>
2705    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
2706    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2707      <organization abbrev="Day Software">Day Software</organization>
2708      <address><email>fielding@gbiv.com</email></address>
2709    </author>
2710    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2711      <organization>One Laptop per Child</organization>
2712      <address><email>jg@laptop.org</email></address>
2713    </author>
2714    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2715      <organization abbrev="HP">Hewlett-Packard Company</organization>
2716      <address><email>JeffMogul@acm.org</email></address>
2717    </author>
2718    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2719      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2720      <address><email>henrikn@microsoft.com</email></address>
2721    </author>
2722    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2723      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2724      <address><email>LMM@acm.org</email></address>
2725    </author>
2726    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2727      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2728      <address><email>paulle@microsoft.com</email></address>
2729    </author>
2730    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2731      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2732      <address><email>timbl@w3.org</email></address>
2733    </author>
2734    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2735      <organization abbrev="W3C">World Wide Web Consortium</organization>
2736      <address><email>ylafon@w3.org</email></address>
2737    </author>
2738    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2739      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2740      <address><email>julian.reschke@greenbytes.de</email></address>
2741    </author>
2742    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2743  </front>
2744  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
2745  <x:source href="p3-payload.xml" basename="p3-payload"/>
2746</reference>
2747
2748<reference anchor="Part4">
2749  <front>
2750    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
2751    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2752      <organization abbrev="Day Software">Day Software</organization>
2753      <address><email>fielding@gbiv.com</email></address>
2754    </author>
2755    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2756      <organization>One Laptop per Child</organization>
2757      <address><email>jg@laptop.org</email></address>
2758    </author>
2759    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2760      <organization abbrev="HP">Hewlett-Packard Company</organization>
2761      <address><email>JeffMogul@acm.org</email></address>
2762    </author>
2763    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2764      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2765      <address><email>henrikn@microsoft.com</email></address>
2766    </author>
2767    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2768      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2769      <address><email>LMM@acm.org</email></address>
2770    </author>
2771    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2772      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2773      <address><email>paulle@microsoft.com</email></address>
2774    </author>
2775    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2776      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2777      <address><email>timbl@w3.org</email></address>
2778    </author>
2779    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2780      <organization abbrev="W3C">World Wide Web Consortium</organization>
2781      <address><email>ylafon@w3.org</email></address>
2782    </author>
2783    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2784      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2785      <address><email>julian.reschke@greenbytes.de</email></address>
2786    </author>
2787    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2788  </front>
2789  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
2790  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
2791</reference>
2792
2793<reference anchor="Part5">
2794  <front>
2795    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
2796    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2797      <organization abbrev="Day Software">Day Software</organization>
2798      <address><email>fielding@gbiv.com</email></address>
2799    </author>
2800    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2801      <organization>One Laptop per Child</organization>
2802      <address><email>jg@laptop.org</email></address>
2803    </author>
2804    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2805      <organization abbrev="HP">Hewlett-Packard Company</organization>
2806      <address><email>JeffMogul@acm.org</email></address>
2807    </author>
2808    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2809      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2810      <address><email>henrikn@microsoft.com</email></address>
2811    </author>
2812    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2813      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2814      <address><email>LMM@acm.org</email></address>
2815    </author>
2816    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2817      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2818      <address><email>paulle@microsoft.com</email></address>
2819    </author>
2820    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2821      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2822      <address><email>timbl@w3.org</email></address>
2823    </author>
2824    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2825      <organization abbrev="W3C">World Wide Web Consortium</organization>
2826      <address><email>ylafon@w3.org</email></address>
2827    </author>
2828    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2829      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2830      <address><email>julian.reschke@greenbytes.de</email></address>
2831    </author>
2832    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2833  </front>
2834  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
2835  <x:source href="p5-range.xml" basename="p5-range"/>
2836</reference>
2837
2838<reference anchor="Part6">
2839  <front>
2840    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
2841    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2842      <organization abbrev="Day Software">Day Software</organization>
2843      <address><email>fielding@gbiv.com</email></address>
2844    </author>
2845    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2846      <organization>One Laptop per Child</organization>
2847      <address><email>jg@laptop.org</email></address>
2848    </author>
2849    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2850      <organization abbrev="HP">Hewlett-Packard Company</organization>
2851      <address><email>JeffMogul@acm.org</email></address>
2852    </author>
2853    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2854      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2855      <address><email>henrikn@microsoft.com</email></address>
2856    </author>
2857    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2858      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2859      <address><email>LMM@acm.org</email></address>
2860    </author>
2861    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2862      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2863      <address><email>paulle@microsoft.com</email></address>
2864    </author>
2865    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2866      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2867      <address><email>timbl@w3.org</email></address>
2868    </author>
2869    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2870      <organization abbrev="W3C">World Wide Web Consortium</organization>
2871      <address><email>ylafon@w3.org</email></address>
2872    </author>
2873    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
2874      <organization />
2875      <address><email>mnot@mnot.net</email></address>
2876    </author>
2877    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2878      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2879      <address><email>julian.reschke@greenbytes.de</email></address>
2880    </author>
2881    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2882  </front>
2883  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
2884  <x:source href="p6-cache.xml" basename="p6-cache"/>
2885</reference>
2886
2887<reference anchor="Part7">
2888  <front>
2889    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2890    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
2891      <organization abbrev="Day Software">Day Software</organization>
2892      <address><email>fielding@gbiv.com</email></address>
2893    </author>
2894    <author initials="J." surname="Gettys" fullname="Jim Gettys">
2895      <organization>One Laptop per Child</organization>
2896      <address><email>jg@laptop.org</email></address>
2897    </author>
2898    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
2899      <organization abbrev="HP">Hewlett-Packard Company</organization>
2900      <address><email>JeffMogul@acm.org</email></address>
2901    </author>
2902    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
2903      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2904      <address><email>henrikn@microsoft.com</email></address>
2905    </author>
2906    <author initials="L." surname="Masinter" fullname="Larry Masinter">
2907      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2908      <address><email>LMM@acm.org</email></address>
2909    </author>
2910    <author initials="P." surname="Leach" fullname="Paul J. Leach">
2911      <organization abbrev="Microsoft">Microsoft Corporation</organization>
2912      <address><email>paulle@microsoft.com</email></address>
2913    </author>
2914    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2915      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2916      <address><email>timbl@w3.org</email></address>
2917    </author>
2918    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
2919      <organization abbrev="W3C">World Wide Web Consortium</organization>
2920      <address><email>ylafon@w3.org</email></address>
2921    </author>
2922    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
2923      <organization abbrev="greenbytes">greenbytes GmbH</organization>
2924      <address><email>julian.reschke@greenbytes.de</email></address>
2925    </author>
2926    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
2927  </front>
2928  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
2929  <x:source href="p7-auth.xml" basename="p7-auth"/>
2930</reference>
2931
2932<reference anchor="RFC2119">
2933  <front>
2934    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2935    <author initials="S." surname="Bradner" fullname="Scott Bradner">
2936      <organization>Harvard University</organization>
2937      <address><email>sob@harvard.edu</email></address>
2938    </author>
2939    <date month="March" year="1997"/>
2940  </front>
2941  <seriesInfo name="BCP" value="14"/>
2942  <seriesInfo name="RFC" value="2119"/>
2943</reference>
2944
2945<reference anchor="RFC5234">
2946  <front>
2947    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2948    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2949      <organization>Brandenburg InternetWorking</organization>
2950      <address>
2951      <postal>
2952      <street>675 Spruce Dr.</street>
2953      <city>Sunnyvale</city>
2954      <region>CA</region>
2955      <code>94086</code>
2956      <country>US</country></postal>
2957      <phone>+1.408.246.8253</phone>
2958      <email>dcrocker@bbiw.net</email></address> 
2959    </author>
2960    <author initials="P." surname="Overell" fullname="Paul Overell">
2961      <organization>THUS plc.</organization>
2962      <address>
2963      <postal>
2964      <street>1/2 Berkeley Square</street>
2965      <street>99 Berkely Street</street>
2966      <city>Glasgow</city>
2967      <code>G3 7HR</code>
2968      <country>UK</country></postal>
2969      <email>paul.overell@thus.net</email></address>
2970    </author>
2971    <date month="January" year="2008"/>
2972  </front>
2973  <seriesInfo name="STD" value="68"/>
2974  <seriesInfo name="RFC" value="5234"/>
2975</reference>
2976
2977</references>
2978
2979<references title="Informative References">
2980
2981<reference anchor="RFC1945">
2982  <front>
2983    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
2984    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
2985      <organization>MIT, Laboratory for Computer Science</organization>
2986      <address><email>timbl@w3.org</email></address>
2987    </author>
2988    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
2989      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
2990      <address><email>fielding@ics.uci.edu</email></address>
2991    </author>
2992    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
2993      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
2994      <address><email>frystyk@w3.org</email></address>
2995    </author>
2996    <date month="May" year="1996"/>
2997  </front>
2998  <seriesInfo name="RFC" value="1945"/>
2999</reference>
3000
3001<reference anchor="RFC2068">
3002  <front>
3003    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3004    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3005      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3006      <address><email>fielding@ics.uci.edu</email></address>
3007    </author>
3008    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3009      <organization>MIT Laboratory for Computer Science</organization>
3010      <address><email>jg@w3.org</email></address>
3011    </author>
3012    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3013      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3014      <address><email>mogul@wrl.dec.com</email></address>
3015    </author>
3016    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3017      <organization>MIT Laboratory for Computer Science</organization>
3018      <address><email>frystyk@w3.org</email></address>
3019    </author>
3020    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3021      <organization>MIT Laboratory for Computer Science</organization>
3022      <address><email>timbl@w3.org</email></address>
3023    </author>
3024    <date month="January" year="1997"/>
3025  </front>
3026  <seriesInfo name="RFC" value="2068"/>
3027</reference>
3028
3029<reference anchor="RFC2616">
3030  <front>
3031    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3032    <author initials="R." surname="Fielding" fullname="R. Fielding">
3033      <organization>University of California, Irvine</organization>
3034      <address><email>fielding@ics.uci.edu</email></address>
3035    </author>
3036    <author initials="J." surname="Gettys" fullname="J. Gettys">
3037      <organization>W3C</organization>
3038      <address><email>jg@w3.org</email></address>
3039    </author>
3040    <author initials="J." surname="Mogul" fullname="J. Mogul">
3041      <organization>Compaq Computer Corporation</organization>
3042      <address><email>mogul@wrl.dec.com</email></address>
3043    </author>
3044    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3045      <organization>MIT Laboratory for Computer Science</organization>
3046      <address><email>frystyk@w3.org</email></address>
3047    </author>
3048    <author initials="L." surname="Masinter" fullname="L. Masinter">
3049      <organization>Xerox Corporation</organization>
3050      <address><email>masinter@parc.xerox.com</email></address>
3051    </author>
3052    <author initials="P." surname="Leach" fullname="P. Leach">
3053      <organization>Microsoft Corporation</organization>
3054      <address><email>paulle@microsoft.com</email></address>
3055    </author>
3056    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3057      <organization>W3C</organization>
3058      <address><email>timbl@w3.org</email></address>
3059    </author>
3060    <date month="June" year="1999"/>
3061  </front>
3062  <seriesInfo name="RFC" value="2616"/>
3063</reference>
3064
3065<reference anchor='RFC2817'>
3066  <front>
3067    <title>Upgrading to TLS Within HTTP/1.1</title>
3068    <author initials='R.' surname='Khare' fullname='R. Khare'>
3069      <organization>4K Associates / UC Irvine</organization>
3070      <address><email>rohit@4K-associates.com</email></address>
3071    </author>
3072    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3073      <organization>Agranat Systems, Inc.</organization>
3074      <address><email>lawrence@agranat.com</email></address>
3075    </author>
3076    <date year='2000' month='May' />
3077  </front>
3078  <seriesInfo name='RFC' value='2817' />
3079</reference>
3080
3081<reference anchor='RFC3864'>
3082  <front>
3083    <title>Registration Procedures for Message Header Fields</title>
3084    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3085      <organization>Nine by Nine</organization>
3086      <address><email>GK-IETF@ninebynine.org</email></address>
3087    </author>
3088    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3089      <organization>BEA Systems</organization>
3090      <address><email>mnot@pobox.com</email></address>
3091    </author>
3092    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3093      <organization>HP Labs</organization>
3094      <address><email>JeffMogul@acm.org</email></address>
3095    </author>
3096    <date year='2004' month='September' />
3097  </front>
3098  <seriesInfo name='BCP' value='90' />
3099  <seriesInfo name='RFC' value='3864' />
3100</reference>
3101
3102<reference anchor='RFC5226'>
3103  <front>
3104    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3105    <author initials='T.' surname='Narten' fullname='T. Narten'>
3106      <organization>IBM</organization>
3107      <address><email>narten@us.ibm.com</email></address>
3108    </author>
3109    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3110      <organization>Google</organization>
3111      <address><email>Harald@Alvestrand.no</email></address>
3112    </author>
3113    <date year='2008' month='May' />
3114  </front>
3115  <seriesInfo name='BCP' value='26' />
3116  <seriesInfo name='RFC' value='5226' />
3117</reference>
3118
3119<reference anchor="RFC5322">
3120  <front>
3121    <title>Internet Message Format</title>
3122    <author initials="P." surname="Resnick" fullname="P. Resnick">
3123      <organization>Qualcomm Incorporated</organization>
3124    </author>
3125    <date year="2008" month="October"/>
3126  </front> 
3127  <seriesInfo name="RFC" value="5322"/>
3128</reference>
3129
3130</references>
3131
3132<section title="Compatibility with Previous Versions" anchor="compatibility">
3133<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3134<t>
3135   Clarified which error code should be used for inbound server failures
3136   (e.g. DNS failures). (<xref target="status.504"/>).
3137</t>
3138<t>
3139   201 (Created) had a race that required an Etag be sent when a resource is
3140   first created. (<xref target="status.201"/>).
3141</t>
3142<t>
3143   Rewrite of message transmission requirements to make it much harder
3144   for implementors to get it wrong, as the consequences of errors here
3145   can have significant impact on the Internet, and to deal with the
3146   following problems:
3147  <list style="numbers">
3148      <t>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
3149         this was incorrectly placing a requirement on the behavior of
3150         an implementation of a future version of HTTP/1.x</t>
3151
3152      <t>Made it clear that user-agents should retry requests, not
3153         "clients" in general.</t>
3154
3155      <t>Converted requirements for clients to ignore unexpected 100
3156         (Continue) responses, and for proxies to forward 100 responses,
3157         into a general requirement for 1xx responses.</t>
3158
3159      <t>Modified some TCP-specific language, to make it clearer that
3160         non-TCP transports are possible for HTTP.</t>
3161
3162      <t>Require that the origin server &MUST-NOT; wait for the request
3163         body before it sends a required 100 (Continue) response.</t>
3164
3165      <t>Allow, rather than require, a server to omit 100 (Continue) if
3166         it has already seen some of the request body.</t>
3167
3168      <t>Allow servers to defend against denial-of-service attacks and
3169         broken clients.</t>
3170  </list>
3171</t>
3172<t>
3173   This change adds the Expect header and 417 status code.
3174</t>
3175<t>
3176   Clean up confusion between 403 and 404 responses. (Section <xref target="status.403" format="counter"/>,
3177   <xref target="status.404" format="counter"/>, and <xref target="status.410" format="counter"/>)
3178</t>
3179<t>
3180   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
3181   implemented in previous versions of this specification. See <xref target="RFC2068" x:fmt="of" x:sec="19.6.1"/>.
3182</t>
3183</section>
3184
3185<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3186<t>
3187  This document takes over the Status Code Registry, previously defined
3188  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3189  (<xref target="status.code.registry"/>)
3190</t>
3191<t>
3192  Clarify definition of POST.
3193  (<xref target="POST"/>)
3194</t>
3195<t>
3196  Failed to consider that there are
3197  many other request methods that are safe to automatically redirect,
3198  and further that the user agent is able to make that determination
3199  based on the request method semantics.
3200  (Sections <xref format="counter" target="status.301"/>,
3201  <xref format="counter" target="status.302"/> and
3202  <xref format="counter" target="status.307"/>)
3203</t>
3204<t>
3205  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3206  It used to indicate that the requested resource must be accessed through the
3207  proxy given by the Location field. The Location field gave the URI of the
3208  proxy. The recipient was expected to repeat this single request via the proxy.
3209  (<xref target="status.305"/>)
3210</t>
3211<t>
3212  Reclassify Allow header as response header, removing the option to
3213  specify it in a PUT request.
3214  Relax the server requirement on the contents of the Allow header and
3215  remove requirement on clients to always trust the header value.
3216  (<xref target="header.allow"/>)
3217</t>
3218<t>
3219  Correct syntax of Location header to allow fragment,
3220  as referred symbol wasn't what was expected, and add some
3221  clarifications as to when it would not be appropriate.
3222  (<xref target="header.location"/>)
3223</t>
3224<t>
3225  Allow Referer value of "about:blank" as alternative to not specifying it.
3226  (<xref target="header.referer"/>)
3227</t>
3228<t>
3229  In the description of the Server header, the Via field
3230  was described as a SHOULD. The requirement was and is stated
3231  correctly in the description of the Via header in &header-via;.
3232  (<xref target="header.server"/>)
3233</t>
3234</section>
3235
3236</section>
3237
3238<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3239<figure>
3240<artwork type="abnf" name="p2-semantics.parsed-abnf">
3241<x:ref>Accept</x:ref> = &lt;Accept, defined in [Part3], Section 5.1&gt;
3242<x:ref>Accept-Charset</x:ref> = &lt;Accept-Charset, defined in [Part3], Section 5.2&gt;
3243<x:ref>Accept-Encoding</x:ref> = &lt;Accept-Encoding, defined in [Part3], Section 5.3&gt;
3244<x:ref>Accept-Language</x:ref> = &lt;Accept-Language, defined in [Part3], Section 5.4&gt;
3245<x:ref>Accept-Ranges</x:ref> = &lt;Accept-Ranges, defined in [Part5], Section 5.1&gt;
3246<x:ref>Age</x:ref> = &lt;Age, defined in [Part6], Section 3.1&gt;
3247<x:ref>Allow</x:ref> = "Allow:" OWS Allow-v
3248<x:ref>Allow-v</x:ref> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
3249<x:ref>Authorization</x:ref> = &lt;Authorization, defined in [Part7], Section 3.1&gt;
3250
3251<x:ref>ETag</x:ref> = &lt;ETag, defined in [Part4], Section 6.1&gt;
3252<x:ref>Expect</x:ref> = "Expect:" OWS Expect-v
3253<x:ref>Expect-v</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3254
3255<x:ref>From</x:ref> = "From:" OWS From-v
3256<x:ref>From-v</x:ref> = mailbox
3257
3258<x:ref>HTTP-date</x:ref> = &lt;HTTP-date, defined in [Part1], Section 3.2&gt;
3259<x:ref>Host</x:ref> = &lt;Host, defined in [Part1], Section 2.1&gt;
3260
3261<x:ref>If-Match</x:ref> = &lt;If-Match, defined in [Part4], Section 6.2&gt;
3262If-Modified-Since =
3263 &lt;If-Modified-Since, defined in [Part4], Section 6.3&gt;
3264<x:ref>If-None-Match</x:ref> = &lt;If-None-Match, defined in [Part4], Section 6.4&gt;
3265<x:ref>If-Range</x:ref> = &lt;If-Range, defined in [Part5], Section 5.3&gt;
3266If-Unmodified-Since =
3267 &lt;If-Unmodified-Since, defined in [Part4], Section 6.5&gt;
3268
3269<x:ref>Location</x:ref> = "Location:" OWS Location-v
3270<x:ref>Location-v</x:ref> = absolute-URI [ "#" fragment ]
3271
3272<x:ref>Max-Forwards</x:ref> = "Max-Forwards:" OWS Max-Forwards-v
3273<x:ref>Max-Forwards-v</x:ref> = 1*DIGIT
3274<x:ref>Method</x:ref> = %x4F.50.54.49.4F.4E.53 ; OPTIONS
3275 / %x47.45.54 ; GET
3276 / %x48.45.41.44 ; HEAD
3277 / %x50.4F.53.54 ; POST
3278 / %x50.55.54 ; PUT
3279 / %x44.45.4C.45.54.45 ; DELETE
3280 / %x54.52.41.43.45 ; TRACE
3281 / %x43.4F.4E.4E.45.43.54 ; CONNECT
3282 / extension-method
3283
3284<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
3285
3286Proxy-Authenticate =
3287 &lt;Proxy-Authenticate, defined in [Part7], Section 3.2&gt;
3288Proxy-Authorization =
3289 &lt;Proxy-Authorization, defined in [Part7], Section 3.3&gt;
3290
3291<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 1.2.2&gt;
3292<x:ref>Range</x:ref> = &lt;Range, defined in [Part5], Section 5.4&gt;
3293<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
3294<x:ref>Referer</x:ref> = "Referer:" OWS Referer-v
3295<x:ref>Referer-v</x:ref> = absolute-URI / partial-URI
3296<x:ref>Retry-After</x:ref> = "Retry-After:" OWS Retry-After-v
3297<x:ref>Retry-After-v</x:ref> = HTTP-date / delta-seconds
3298
3299<x:ref>Server</x:ref> = "Server:" OWS Server-v
3300<x:ref>Server-v</x:ref> = product *( RWS ( product / comment ) )
3301<x:ref>Status-Code</x:ref> = "100" / "101" / "200" / "201" / "202" / "203" / "204" /
3302 "205" / "206" / "300" / "301" / "302" / "303" / "304" / "305" /
3303 "307" / "400" / "401" / "402" / "403" / "404" / "405" / "406" /
3304 "407" / "408" / "409" / "410" / "411" / "412" / "413" / "414" /
3305 "415" / "416" / "417" / "500" / "501" / "502" / "503" / "504" /
3306 "505" / extension-code
3307
3308<x:ref>TE</x:ref> = &lt;TE, defined in [Part1], Section 8.8&gt;
3309
3310<x:ref>User-Agent</x:ref> = "User-Agent:" OWS User-Agent-v
3311<x:ref>User-Agent-v</x:ref> = product *( RWS ( product / comment ) )
3312
3313<x:ref>Vary</x:ref> = &lt;Vary, defined in [Part6], Section 3.5&gt;
3314
3315WWW-Authenticate =
3316 &lt;WWW-Authenticate, defined in [Part7], Section 3.4&gt;
3317
3318<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.1&gt;
3319
3320<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 1.2.2&gt;
3321
3322<x:ref>delta-seconds</x:ref> = 1*DIGIT
3323
3324<x:ref>expect-params</x:ref> = ";" token [ "=" ( token / quoted-string ) ]
3325<x:ref>expectation</x:ref> = "100-continue" / expectation-extension
3326<x:ref>expectation-extension</x:ref> = token [ "=" ( token / quoted-string )
3327 *expect-params ]
3328<x:ref>extension-code</x:ref> = 3DIGIT
3329<x:ref>extension-method</x:ref> = token
3330
3331<x:ref>fragment</x:ref> = &lt;fragment, defined in [Part1], Section 2.1&gt;
3332
3333<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
3334
3335<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 1.2.2&gt;
3336
3337<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.1&gt;
3338<x:ref>product</x:ref> = &lt;product, defined in [Part1], Section 3.4&gt;
3339
3340<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
3341
3342<x:ref>request-header</x:ref> = Accept / Accept-Charset / Accept-Encoding /
3343 Accept-Language / Authorization / Expect / From / Host / If-Match /
3344 If-Modified-Since / If-None-Match / If-Range / If-Unmodified-Since /
3345 Max-Forwards / Proxy-Authorization / Range / Referer / TE /
3346 User-Agent
3347<x:ref>response-header</x:ref> = Accept-Ranges / Age / Allow / ETag / Location /
3348 Proxy-Authenticate / Retry-After / Server / Vary / WWW-Authenticate
3349
3350<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 1.2.2&gt;
3351</artwork>
3352</figure>
3353<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
3354; Reason-Phrase defined but not used
3355; Status-Code defined but not used
3356; request-header defined but not used
3357; response-header defined but not used
3358</artwork></figure></section>
3359
3360<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3361
3362<section title="Since RFC2616">
3363<t>
3364  Extracted relevant partitions from <xref target="RFC2616"/>.
3365</t>
3366</section>
3367
3368<section title="Since draft-ietf-httpbis-p2-semantics-00">
3369<t>
3370  Closed issues:
3371  <list style="symbols"> 
3372    <t>
3373      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3374      "Via is a MUST"
3375      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3376    </t>
3377    <t>
3378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3379      "Fragments allowed in Location"
3380      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3381    </t>
3382    <t>
3383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3384      "Safe Methods vs Redirection"
3385      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3386    </t>
3387    <t>
3388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3389      "Revise description of the POST method"
3390      (<eref target="http://purl.org/NET/http-errata#post"/>)
3391    </t>
3392    <t>
3393      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3394      "Normative and Informative references"
3395    </t>
3396    <t>
3397      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3398      "RFC2606 Compliance"
3399    </t>
3400    <t>
3401      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3402      "Informative references"
3403    </t>
3404    <t>
3405      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3406      "Redundant cross-references"
3407    </t>
3408  </list>
3409</t>
3410<t>
3411  Other changes:
3412  <list style="symbols"> 
3413    <t>
3414      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3415    </t>
3416  </list>
3417</t>
3418</section>
3419
3420<section title="Since draft-ietf-httpbis-p2-semantics-01">
3421<t>
3422  Closed issues:
3423  <list style="symbols"> 
3424    <t>
3425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3426      "PUT side effects"
3427    </t>
3428    <t>
3429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3430      "Duplicate Host header requirements"
3431    </t>
3432  </list>
3433</t>
3434<t>
3435  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3436  <list style="symbols"> 
3437    <t>
3438      Move "Product Tokens" section (back) into Part 1, as "token" is used
3439      in the definition of the Upgrade header.
3440    </t>
3441    <t>
3442      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3443    </t>
3444    <t>
3445      Copy definition of delta-seconds from Part6 instead of referencing it.
3446    </t>
3447  </list>
3448</t>
3449</section>
3450
3451<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3452<t>
3453  Closed issues:
3454  <list style="symbols"> 
3455    <t>
3456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3457      "Requiring Allow in 405 responses"
3458    </t>
3459    <t>
3460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3461      "Status Code Registry"
3462    </t>
3463    <t>
3464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3465      "Redirection vs. Location"
3466    </t>
3467    <t>
3468      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3469      "Cacheability of 303 response"
3470    </t>
3471    <t>
3472      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3473      "305 Use Proxy"
3474    </t>
3475    <t>
3476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3477      "Classification for Allow header"
3478    </t>
3479    <t>
3480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3481      "PUT - 'store under' vs 'store at'"
3482    </t>
3483  </list>
3484</t>
3485<t>
3486  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3487  <list style="symbols"> 
3488    <t>
3489      Reference RFC 3984, and update header registrations for headers defined
3490      in this document.
3491    </t>
3492  </list>
3493</t>
3494<t>
3495  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3496  <list style="symbols"> 
3497    <t>
3498      Replace string literals when the string really is case-sensitive (method).
3499    </t>
3500  </list>
3501</t>
3502</section>
3503
3504<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
3505<t>
3506  Closed issues:
3507  <list style="symbols"> 
3508    <t>
3509      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
3510      "OPTIONS request bodies"
3511    </t>
3512    <t>
3513      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
3514      "Description of CONNECT should refer to RFC2817"
3515    </t>
3516    <t>
3517      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
3518      "Location Content-Location reference request/response mixup"
3519    </t>
3520  </list>
3521</t>
3522<t>
3523  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
3524  <list style="symbols"> 
3525    <t>
3526      Added initial proposal for registration process, plus initial
3527      content (non-HTTP/1.1 methods to be added by a separate specification).
3528    </t>
3529  </list>
3530</t>
3531</section>
3532
3533<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
3534<t>
3535  Closed issues:
3536  <list style="symbols"> 
3537    <t>
3538      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
3539      "Content-*"
3540    </t>
3541    <t>
3542      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3543      "RFC 2822 is updated by RFC 5322"
3544    </t>
3545  </list>
3546</t>
3547<t>
3548  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3549  <list style="symbols"> 
3550    <t>
3551      Use "/" instead of "|" for alternatives.
3552    </t>
3553    <t>
3554      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3555      whitespace ("OWS") and required whitespace ("RWS").
3556    </t>
3557    <t>
3558      Rewrite ABNFs to spell out whitespace rules, factor out
3559      header value format definitions.
3560    </t>
3561  </list>
3562</t>
3563</section>
3564
3565<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
3566<t>
3567  Closed issues:
3568  <list style="symbols"> 
3569    <t>
3570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
3571      "Reason-Phrase BNF"
3572    </t>
3573  </list>
3574</t>
3575<t>
3576  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3577  <list style="symbols"> 
3578    <t>
3579      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
3580    </t>
3581  </list>
3582</t>
3583</section>
3584
3585<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
3586<t>
3587  Closed issues:
3588  <list style="symbols"> 
3589    <t>
3590      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
3591      "Clarify when Referer is sent"
3592    </t>
3593    <t>
3594      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
3595      "status codes vs methods"
3596    </t>
3597    <t>
3598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
3599      "Do not require "updates" relation for specs that register status codes or method names"
3600    </t>
3601  </list>
3602</t>
3603</section>
3604
3605</section>
3606
3607</back>
3608</rfc>
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