source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1428

Last change on this file since 1428 was 1428, checked in by julian.reschke@…, 8 years ago

explain types of redirects, history of changes, and allow POST->GET rewriting for 301/302 (see [160])

  • Property svn:eol-style set to native
File size: 177.0 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "September">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY agent-driven-negotiation    "<xref target='Part3' x:rel='#agent-driven.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY field-rules                "<xref target='Part1' x:rel='#field.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY intermediaries             "<xref target='Part1' x:rel='#intermediaries' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY chunked-encoding           "<xref target='Part1' x:rel='#chunked.encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY full-date                  "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY request-target             "<xref target='Part1' x:rel='#request-target' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-connection          "<xref target='Part1' x:rel='#header.connection' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-fields              "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
61  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
62  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
63  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
64  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
65  <!ENTITY header-upgrade             "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
66  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.te' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
67  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
68  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
69  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
70  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
71  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
72  <!ENTITY product-tokens             "<xref target='Part1' x:rel='#product.tokens' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
73  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
74  <!ENTITY status-206                 "<xref target='Part5' x:rel='#status.206' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
75  <!ENTITY status-304                 "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
76  <!ENTITY status-401                 "<xref target='Part7' x:rel='#status.401' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
77  <!ENTITY status-407                 "<xref target='Part7' x:rel='#status.407' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
78  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
79  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
80  <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
81  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
82  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
83  <!ENTITY p7-status-codes            "<xref target='Part7' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
84  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
85  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
86  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
87]>
88<?rfc toc="yes" ?>
89<?rfc symrefs="yes" ?>
90<?rfc sortrefs="yes" ?>
91<?rfc compact="yes"?>
92<?rfc subcompact="no" ?>
93<?rfc linkmailto="no" ?>
94<?rfc editing="no" ?>
95<?rfc comments="yes"?>
96<?rfc inline="yes"?>
97<?rfc rfcedstyle="yes"?>
98<?rfc-ext allow-markup-in-artwork="yes" ?>
99<?rfc-ext include-references-in-index="yes" ?>
100<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
101     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
102     xmlns:x='http://purl.org/net/xml2rfc/ext'
103     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
104<front>
105
106  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
107
108  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
109    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
110    <address>
111      <postal>
112        <street>345 Park Ave</street>
113        <city>San Jose</city>
114        <region>CA</region>
115        <code>95110</code>
116        <country>USA</country>
117      </postal>
118      <email>fielding@gbiv.com</email>
119      <uri>http://roy.gbiv.com/</uri>
120    </address>
121  </author>
122
123  <author initials="J." surname="Gettys" fullname="Jim Gettys">
124    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
125    <address>
126      <postal>
127        <street>21 Oak Knoll Road</street>
128        <city>Carlisle</city>
129        <region>MA</region>
130        <code>01741</code>
131        <country>USA</country>
132      </postal>
133      <email>jg@freedesktop.org</email>
134      <uri>http://gettys.wordpress.com/</uri>
135    </address>
136  </author>
137 
138  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
139    <organization abbrev="HP">Hewlett-Packard Company</organization>
140    <address>
141      <postal>
142        <street>HP Labs, Large Scale Systems Group</street>
143        <street>1501 Page Mill Road, MS 1177</street>
144        <city>Palo Alto</city>
145        <region>CA</region>
146        <code>94304</code>
147        <country>USA</country>
148      </postal>
149      <email>JeffMogul@acm.org</email>
150    </address>
151  </author>
152
153  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
154    <organization abbrev="Microsoft">Microsoft Corporation</organization>
155    <address>
156      <postal>
157        <street>1 Microsoft Way</street>
158        <city>Redmond</city>
159        <region>WA</region>
160        <code>98052</code>
161        <country>USA</country>
162      </postal>
163      <email>henrikn@microsoft.com</email>
164    </address>
165  </author>
166
167  <author initials="L." surname="Masinter" fullname="Larry Masinter">
168    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
169    <address>
170      <postal>
171        <street>345 Park Ave</street>
172        <city>San Jose</city>
173        <region>CA</region>
174        <code>95110</code>
175        <country>USA</country>
176      </postal>
177      <email>LMM@acm.org</email>
178      <uri>http://larry.masinter.net/</uri>
179    </address>
180  </author>
181 
182  <author initials="P." surname="Leach" fullname="Paul J. Leach">
183    <organization abbrev="Microsoft">Microsoft Corporation</organization>
184    <address>
185      <postal>
186        <street>1 Microsoft Way</street>
187        <city>Redmond</city>
188        <region>WA</region>
189        <code>98052</code>
190      </postal>
191      <email>paulle@microsoft.com</email>
192    </address>
193  </author>
194   
195  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
196    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
197    <address>
198      <postal>
199        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
200        <street>The Stata Center, Building 32</street>
201        <street>32 Vassar Street</street>
202        <city>Cambridge</city>
203        <region>MA</region>
204        <code>02139</code>
205        <country>USA</country>
206      </postal>
207      <email>timbl@w3.org</email>
208      <uri>http://www.w3.org/People/Berners-Lee/</uri>
209    </address>
210  </author>
211
212  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
213    <organization abbrev="W3C">World Wide Web Consortium</organization>
214    <address>
215      <postal>
216        <street>W3C / ERCIM</street>
217        <street>2004, rte des Lucioles</street>
218        <city>Sophia-Antipolis</city>
219        <region>AM</region>
220        <code>06902</code>
221        <country>France</country>
222      </postal>
223      <email>ylafon@w3.org</email>
224      <uri>http://www.raubacapeu.net/people/yves/</uri>
225    </address>
226  </author>
227
228  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
229    <organization abbrev="greenbytes">greenbytes GmbH</organization>
230    <address>
231      <postal>
232        <street>Hafenweg 16</street>
233        <city>Muenster</city><region>NW</region><code>48155</code>
234        <country>Germany</country>
235      </postal>
236      <phone>+49 251 2807760</phone>
237      <facsimile>+49 251 2807761</facsimile>
238      <email>julian.reschke@greenbytes.de</email>
239      <uri>http://greenbytes.de/tech/webdav/</uri>
240    </address>
241  </author>
242
243  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
244  <workgroup>HTTPbis Working Group</workgroup>
245
246<abstract>
247<t>
248   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
249   distributed, collaborative, hypertext information systems. HTTP has been in
250   use by the World Wide Web global information initiative since 1990. This
251   document is Part 2 of the seven-part specification that defines the protocol
252   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
253</t>
254<t>
255   Part 2 defines the semantics of HTTP messages as expressed by request
256   methods, request header fields, response status codes, and response header
257   fields.
258</t>
259</abstract>
260
261<note title="Editorial Note (To be removed by RFC Editor)">
262  <t>
263    Discussion of this draft should take place on the HTTPBIS working group
264    mailing list (ietf-http-wg@w3.org), which is archived at
265    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
266  </t>
267  <t>
268    The current issues list is at
269    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
270    documents (including fancy diffs) can be found at
271    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
272  </t>
273  <t>
274    The changes in this draft are summarized in <xref target="changes.since.16"/>.
275  </t>
276</note>
277</front>
278<middle>
279<section title="Introduction" anchor="introduction">
280<t>
281   This document defines HTTP/1.1 request and response semantics.  Each HTTP
282   message, as defined in &messaging;, is in the form of either a request or
283   a response.  An HTTP server listens on a connection for HTTP requests and
284   responds to each request, in the order received on that connection, with
285   one or more HTTP response messages.  This document defines the commonly
286   agreed upon semantics of the HTTP uniform interface, the intentions defined
287   by each request method, and the various response messages that might be
288   expected as a result of applying that method to the target resource.
289</t>
290<t>
291   This document is currently disorganized in order to minimize the changes
292   between drafts and enable reviewers to see the smaller errata changes.
293   A future draft will reorganize the sections to better reflect the content.
294   In particular, the sections will be ordered according to the typical
295   processing of an HTTP request message (after message parsing): resource
296   mapping, methods, request modifying header fields, response status,
297   status modifying header fields, and resource metadata.  The current mess
298   reflects how widely dispersed these topics and associated requirements
299   had become in <xref target="RFC2616"/>.
300</t>
301
302<section title="Requirements" anchor="intro.requirements">
303<t>
304   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
305   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
306   document are to be interpreted as described in <xref target="RFC2119"/>.
307</t>
308<t>
309   An implementation is not compliant if it fails to satisfy one or more
310   of the "MUST" or "REQUIRED" level requirements for the protocols it
311   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
312   level and all the "SHOULD" level requirements for its protocols is said
313   to be "unconditionally compliant"; one that satisfies all the "MUST"
314   level requirements but not all the "SHOULD" level requirements for its
315   protocols is said to be "conditionally compliant".
316</t>
317</section>
318
319<section title="Syntax Notation" anchor="notation">
320  <x:anchor-alias value="CR"/>
321  <x:anchor-alias value="DIGIT"/>
322  <x:anchor-alias value="LF"/>
323  <x:anchor-alias value="HTAB"/>
324  <x:anchor-alias value="VCHAR"/>
325  <x:anchor-alias value="SP"/>
326<t>
327  This specification uses the ABNF syntax defined in &notation; (which
328  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
329  <xref target="collected.abnf"/> shows the collected ABNF, with the list
330  rule expanded.
331</t>
332<t>
333  The following core rules are included by
334  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
335  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
336  DIGIT (decimal 0-9), DQUOTE (double quote),
337  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
338  OCTET (any 8-bit sequence of data), SP (space), and
339  VCHAR (any visible US-ASCII character).
340</t>
341
342<section title="Core Rules" anchor="core.rules">
343  <x:anchor-alias value="obs-text"/>
344  <x:anchor-alias value="quoted-string"/>
345  <x:anchor-alias value="token"/>
346  <x:anchor-alias value="OWS"/>
347  <x:anchor-alias value="RWS"/>
348<t>
349  The core rules below are defined in <xref target="Part1"/>:
350</t>
351<figure><artwork type="abnf2616">
352  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
353  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &basic-rules;&gt;
354  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &basic-rules;&gt;
355  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-rules;&gt;
356  <x:ref>token</x:ref>         = &lt;token, defined in &field-rules;&gt;
357</artwork></figure>
358</section>
359
360<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
361  <x:anchor-alias value="absolute-URI"/>
362  <x:anchor-alias value="comment"/>
363  <x:anchor-alias value="HTTP-date"/>
364  <x:anchor-alias value="partial-URI"/>
365  <x:anchor-alias value="product"/>
366  <x:anchor-alias value="URI-reference"/>
367<t>
368  The ABNF rules below are defined in other parts:
369</t>
370<figure><!--Part1--><artwork type="abnf2616">
371  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
372  <x:ref>comment</x:ref>       = &lt;comment, defined in &header-fields;&gt;
373  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
374  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
375  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
376  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
377</artwork></figure>
378</section>
379</section>
380</section>
381
382<section title="Method" anchor="method">
383  <x:anchor-alias value="Method"/>
384  <x:anchor-alias value="extension-method"/>
385<t>
386   The Method token indicates the request method to be performed on the target
387   resource (&effective-request-uri;). The method is case-sensitive.
388</t>
389<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
390  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
391</artwork></figure>
392<t>
393   The list of methods allowed by a resource can be specified in an
394   Allow header field (<xref target="header.allow"/>). The status code of the response
395   always notifies the client whether a method is currently allowed on a
396   resource, since the set of allowed methods can change dynamically. An
397   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
398   if the method is known by the origin server but not allowed for the
399   resource, and 501 (Not Implemented) if the method is
400   unrecognized or not implemented by the origin server. The methods GET
401   and HEAD &MUST; be supported by all general-purpose servers. All other
402   methods are &OPTIONAL;; however, if the above methods are implemented,
403   they &MUST; be implemented with the same semantics as those specified
404   in <xref target="method.definitions"/>.
405</t>
406
407<section title="Overview of Methods" anchor="overview.of.methods">
408<t>
409  The methods listed below are defined in <xref target="method.definitions"/>.
410</t>
411<texttable align="left">
412  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
413 
414  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
415  <c>GET</c> <c><xref target="GET"/></c>
416  <c>HEAD</c> <c><xref target="HEAD"/></c>
417  <c>POST</c> <c><xref target="POST"/></c>
418  <c>PUT</c> <c><xref target="PUT"/></c>
419  <c>DELETE</c> <c><xref target="DELETE"/></c>
420  <c>TRACE</c> <c><xref target="TRACE"/></c>
421  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
422</texttable>
423<t>
424  Note that this list is not exhaustive &mdash; it does not include request methods defined
425  in other specifications.
426</t>
427</section>
428
429<section title="Method Registry" anchor="method.registry">
430<t>
431  The HTTP Method Registry defines the name space for the Method token in the
432  Request line of an HTTP request.
433</t>
434<t>
435  Registrations &MUST; include the following fields:
436  <list style="symbols">
437    <t>Method Name (see <xref target="method"/>)</t>
438    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
439    <t>Pointer to specification text</t>
440  </list>
441</t>
442<t>
443  Values to be added to this name space are subject to IETF review
444  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
445</t>
446<t>
447  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
448</t>
449
450<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
451<t>
452   When it is necessary to express new semantics for a HTTP request that
453   aren't specific to a single application or media type, and currently defined
454   methods are inadequate, it may be appropriate to register a new method.
455</t>
456<t>
457   HTTP methods are generic; that is, they are potentially applicable to any
458   resource, not just one particular media type, "type" of resource, or
459   application. As such, it is preferred that new HTTP methods be registered
460   in a document that isn't specific to a single application, so that this is
461   clear.
462</t>
463<t>
464   Due to the parsing rules defined in &message-body;, definitions of HTTP
465   methods cannot prohibit the presence of a message-body on either the request
466   or the response message (with responses to HEAD requests being the single
467   exception). Definitions of new methods cannot change this rule, but they can
468   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
469</t>
470<t>
471   New method definitions need to indicate whether they are safe (<xref
472   target="safe.methods"/>), what semantics (if any) the request body has,
473   and whether they are idempotent (<xref target="idempotent.methods"/>).
474   They also need to state whether they can be cached (&caching;); in
475   particular what conditions a cache may store the response, and under what
476   conditions such a stored response may be used to satisfy a subsequent
477   request.
478</t>
479</section>
480
481</section>
482</section>
483
484<section title="Header Fields" anchor="header.fields">
485<t>
486   Header fields are key value pairs that can be used to communicate data about
487   the message, its payload, the target resource, or about the connection
488   itself (i.e., control data).  See &header-fields; for a general definition
489   of their syntax.
490</t>
491
492<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
493<t>
494   New header fields are registered using the procedures described in
495   <xref target="RFC3864"/>.
496</t>
497<t>
498   The requirements for header field names are defined in
499   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
500   defining new fields are advised to keep the name as short as practical, and
501   not to prefix them with "X-" if they are to be registered (either
502   immediately or in the future).
503</t>
504<t>
505   New header field values typically have their syntax defined using ABNF
506   (<xref target="RFC5234"/>), using the extensions defined in &notation-abnf;
507   as necessary, and are usually constrained to the range of ASCII characters.
508   Header fields needing a greater range of characters can use an encoding
509   such as the one defined in <xref target="RFC5987"/>.
510</t>
511<t>
512   Because commas (",") are used as a generic delimiter between field-values,
513   they need to be treated with care if they are allowed in the field-value's
514   payload. Typically, components that might contain a comma are protected with
515   double-quotes using the quoted-string ABNF production (&field-rules;).
516</t>
517<t>
518   For example, a textual date and a URI (either of which might contain a comma)
519   could be safely carried in field-values like these:
520</t>
521<figure><artwork type="example">
522  Example-URI-Field: "http://example.com/a.html,foo",
523                     "http://without-a-comma.example.com/"
524  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
525</artwork></figure>
526<t>
527   Authors of specifications defining new header fields are advised to consider
528   documenting:
529  <list style="symbols">
530    <t>Whether the field is a single value, or whether it can be a list
531    (delimited by commas; see &header-fields;).</t>
532    <t>Under what conditions the header field can be used; e.g., only i
533    responses or requests, in all messages, only on responses to a particular
534    request method.</t>
535    <t>Whether it is appropriate to list the field-name in the Connection header
536    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t>
537    <t>Under what conditions intermediaries are allowed to modify the header
538    field's value, insert or delete it.</t>
539    <t>How the header might interact with caching (see <xref target="Part6"/>).</t>
540    <t>Whether the header field is useful or allowable in trailers (see
541    &chunked-encoding;).</t>
542    <t>Whether the header field should be preserved across redirects.</t>
543  </list>
544</t>
545</section>
546
547<section title="Request Header Fields" anchor="request.header.fields">
548  <x:anchor-alias value="request-header"/>
549<t>
550   The request header fields allow the client to pass additional
551   information about the request, and about the client itself, to the
552   server. These fields act as request modifiers, with semantics
553   equivalent to the parameters on a programming language method
554   invocation.
555</t>
556<texttable align="left">
557  <ttcol>Header Field Name</ttcol>
558  <ttcol>Defined in...</ttcol>
559
560  <c>Accept</c> <c>&header-accept;</c>
561  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
562  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
563  <c>Accept-Language</c> <c>&header-accept-language;</c>
564  <c>Authorization</c> <c>&header-authorization;</c>
565  <c>Expect</c> <c><xref target="header.expect"/></c>
566  <c>From</c> <c><xref target="header.from"/></c>
567  <c>Host</c> <c>&header-host;</c>
568  <c>If-Match</c> <c>&header-if-match;</c>
569  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
570  <c>If-None-Match</c> <c>&header-if-none-match;</c>
571  <c>If-Range</c> <c>&header-if-range;</c>
572  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
573  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
574  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
575  <c>Range</c> <c>&header-range;</c>
576  <c>Referer</c> <c><xref target="header.referer"/></c>
577  <c>TE</c> <c>&header-te;</c>
578  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
579</texttable>
580</section>
581
582<section title="Response Header Fields" anchor="response.header.fields">
583  <x:anchor-alias value="response-header"/>
584<t>
585   The response header fields allow the server to pass additional
586   information about the response which cannot be placed in the Status-Line.
587   These header fields give information about the server and about
588   further access to the target resource (&effective-request-uri;).
589</t>
590<texttable align="left">
591  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
592
593  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
594  <c>Age</c> <c>&header-age;</c>
595  <c>Allow</c> <c><xref target="header.allow"/></c>
596  <c>ETag</c> <c>&header-etag;</c>
597  <c>Location</c> <c><xref target="header.location"/></c>
598  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
599  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
600  <c>Server</c> <c><xref target="header.server"/></c>
601  <c>Vary</c> <c>&header-vary;</c>
602  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
603</texttable>
604</section>
605
606</section>
607
608<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
609  <x:anchor-alias value="Reason-Phrase"/>
610  <x:anchor-alias value="Status-Code"/>
611  <x:anchor-alias value="extension-code"/>
612<t>
613   The Status-Code element is a 3-digit integer result code of the attempt to
614   understand and satisfy the request.
615</t>
616<t>
617   The Reason-Phrase is intended to give a short textual description of the
618   Status-Code and is intended for a human user. The client does not need
619   to examine or display the Reason-Phrase.
620</t>
621<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"/>
622  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
623  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
624</artwork></figure>
625<t>
626   HTTP status codes are extensible. HTTP applications are not required
627   to understand the meaning of all registered status codes, though such
628   understanding is obviously desirable. However, applications &MUST;
629   understand the class of any status code, as indicated by the first
630   digit, and treat any unrecognized response as being equivalent to the
631   x00 status code of that class, with the exception that an
632   unrecognized response &MUST-NOT; be cached. For example, if an
633   unrecognized status code of 431 is received by the client, it can
634   safely assume that there was something wrong with its request and
635   treat the response as if it had received a 400 status code. In such
636   cases, user agents &SHOULD; present to the user the representation enclosed
637   with the response, since that representation is likely to include human-readable
638   information which will explain the unusual status.
639</t>
640
641<section title="Overview of Status Codes" anchor="overview.of.status.codes">
642<t> 
643   The status codes listed below are defined in <xref target="status.codes"/>
644   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
645   The reason phrases listed here are only recommendations &mdash; they can be
646   replaced by local equivalents without affecting the protocol.
647</t>
648<texttable align="left">
649  <ttcol>Status-Code</ttcol>
650  <ttcol>Reason-Phrase</ttcol>
651  <ttcol>Defined in...</ttcol>
652 
653  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
654  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
655
656  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
657  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
658  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
659  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
660  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
661  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
662  <c>206</c> <c>Partial Content</c> <c>&status-206;</c>
663
664  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
665  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
666  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
667  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
668  <c>304</c> <c>Not Modified</c> <c>&status-304;</c>
669  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
670  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
671
672  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
673  <c>401</c> <c>Unauthorized</c> <c>&status-401;</c>
674  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
675  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
676  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
677  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
678  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
679  <c>407</c> <c>Proxy Authentication Required</c> <c>&status-407;</c>
680  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
681  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
682  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
683  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
684  <c>412</c> <c>Precondition Failed</c> <c>&status-412;</c>
685  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
686  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
687  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
688  <c>416</c> <c>Requested range not satisfiable</c> <c>&status-416;</c>
689  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
690  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
691
692  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
693  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
694  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
695  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
696  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
697  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
698</texttable>
699<t>
700   Note that this list is not exhaustive &mdash; it does not include
701   extension status codes defined in other specifications.
702</t>
703</section>
704
705<section title="Status Code Registry" anchor="status.code.registry">
706<t>
707  The HTTP Status Code Registry defines the name space for the Status-Code
708  token in the Status-Line of an HTTP response.
709</t>
710<t>
711  Values to be added to this name space are subject to IETF review
712  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
713</t>
714<t>
715  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
716</t>
717
718<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
719<t>
720   When it is necessary to express new semantics for a HTTP response that
721   aren't specific to a single application or media type, and currently defined
722   status codes are inadequate, a new status code can be registered.
723</t>
724<t>
725   HTTP status codes are generic; that is, they are potentially applicable to
726   any resource, not just one particular media type, "type" of resource, or
727   application. As such, it is preferred that new HTTP status codes be
728   registered in a document that isn't specific to a single application, so
729   that this is clear.
730</t>
731<t>
732   Definitions of new HTTP status codes typically explain the request
733   conditions that produce a response containing the status code (e.g.,
734   combinations of request headers and/or method(s)), along with any
735   interactions with response headers (e.g., those that are required, those
736   that modify the semantics of the response).
737</t>
738<t>
739   New HTTP status codes are required to fall under one of the categories
740   defined in <xref target="status.codes"/>. To allow existing parsers to
741   properly handle them, new status codes cannot disallow a response body,
742   although they can mandate a zero-length response body. They can require the
743   presence of one or more particular HTTP response header(s).
744</t>
745<t>
746   Likewise, their definitions can specify that caches are allowed to use
747   heuristics to determine their freshness (see &caching;; by default, it is
748   not allowed), and can define how to determine the resource which they
749   carry a representation for (see <xref
750   target="identifying.response.associated.with.representation"/>; by default,
751   it is anonymous).
752</t>
753</section>
754
755</section>
756
757</section>
758
759<section title="Representation" anchor="representation">
760<t>
761   Request and Response messages &MAY; transfer a representation if not otherwise
762   restricted by the request method or response status code. A representation
763   consists of metadata (representation header fields) and data (representation
764   body).  When a complete or partial representation is enclosed in an HTTP message,
765   it is referred to as the payload of the message. HTTP representations
766   are defined in &payload;.
767</t>
768<t>
769   A representation body is only present in a message when a message-body is
770   present, as described in &message-body;. The representation body is obtained
771   from the message-body by decoding any Transfer-Encoding that might
772   have been applied to ensure safe and proper transfer of the message.
773</t>
774
775<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
776<t>
777   It is sometimes necessary to determine an identifier for the resource
778   associated with a representation.
779</t>
780<t>
781   An HTTP request representation, when present, is always associated with an
782   anonymous (i.e., unidentified) resource.
783</t>
784<t>
785   In the common case, an HTTP response is a representation of the target
786   resource (see &effective-request-uri;). However, this is not always the
787   case. To determine the URI of the resource a response is associated with,
788   the following rules are used (with the first applicable one being selected):
789</t>
790<t><list style="numbers">
791   <t>If the response status code is 200 or 203 and the request method was GET,
792   the response payload is a representation of the target resource.</t>
793   <t>If the response status code is 204, 206, or 304 and the request method was GET
794   or HEAD, the response payload is a partial representation of the target
795   resource.</t>
796   <t>If the response has a Content-Location header field, and that URI is the same
797   as the effective request URI, the response payload is a representation of the
798   target resource.</t>
799   <t>If the response has a Content-Location header field, and that URI is not the
800   same as the effective request URI, then the response asserts that its
801   payload is a representation of the resource identified by the
802   Content-Location URI. However, such an assertion cannot be trusted unless
803   it can be verified by other means (not defined by HTTP).</t>
804   <t>Otherwise, the response is a representation of an anonymous (i.e.,
805   unidentified) resource.</t>
806</list></t>
807<t>
808  <cref anchor="TODO-req-uri">
809   The comparison function is going to have to be defined somewhere,
810   because we already need to compare URIs for things like cache invalidation.</cref>
811</t>
812</section>
813
814</section>
815
816
817<section title="Method Definitions" anchor="method.definitions">
818<t>
819   The set of common request methods for HTTP/1.1 is defined below. Although
820   this set can be expanded, additional methods cannot be assumed to
821   share the same semantics for separately extended clients and servers.
822</t>
823
824<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
825
826<section title="Safe Methods" anchor="safe.methods">
827<iref item="Safe Methods" primary="true"/>
828<t>
829   Implementors need to be aware that the software represents the user in
830   their interactions over the Internet, and need to allow
831   the user to be aware of any actions they take which might have an
832   unexpected significance to themselves or others.
833</t>
834<t>
835   In particular, the convention has been established that the GET, HEAD,
836   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
837   of taking an action other than retrieval. These request methods ought
838   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
839   This allows user agents to represent other methods, such as POST, PUT
840   and DELETE, in a special way, so that the user is made aware of the
841   fact that a possibly unsafe action is being requested.
842</t>
843<t>
844   Naturally, it is not possible to ensure that the server does not
845   generate side-effects as a result of performing a GET request; in
846   fact, some dynamic resources consider that a feature. The important
847   distinction here is that the user did not request the side-effects,
848   so therefore cannot be held accountable for them.
849</t>
850</section>
851
852<section title="Idempotent Methods" anchor="idempotent.methods">
853<iref item="Idempotent Methods" primary="true"/>
854<t>
855   Request methods can also have the property of "idempotence" in that,
856   aside from error or expiration issues, the intended effect of multiple
857   identical requests is the same as for a single request.
858   PUT, DELETE, and all safe request methods are idempotent.
859   It is important to note that idempotence refers only to changes
860   requested by the client: a server is free to change its state due
861   to multiple requests for the purpose of tracking those requests,
862   versioning of results, etc.
863</t>
864</section>
865</section>
866
867<section title="OPTIONS" anchor="OPTIONS">
868  <rdf:Description>
869    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
870  </rdf:Description>
871  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
872  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
873<t>
874   The OPTIONS method requests information about the
875   communication options available on the request/response chain
876   identified by the effective request URI. This method allows a client to
877   determine the options and/or requirements associated with a resource,
878   or the capabilities of a server, without implying a resource action
879   or initiating a resource retrieval.
880</t>
881<t>
882   Responses to the OPTIONS method are not cacheable.
883</t>
884<t>
885   If the OPTIONS request includes a message-body (as indicated by the
886   presence of Content-Length or Transfer-Encoding), then the media type
887   &MUST; be indicated by a Content-Type field. Although this
888   specification does not define any use for such a body, future
889   extensions to HTTP might use the OPTIONS body to make more detailed
890   queries on the server.
891</t>
892<t>
893   If the request-target is an asterisk ("*"), the OPTIONS request is
894   intended to apply to the server in general rather than to a specific
895   resource. Since a server's communication options typically depend on
896   the resource, the "*" request is only useful as a "ping" or "no-op"
897   type of method; it does nothing beyond allowing the client to test
898   the capabilities of the server. For example, this can be used to test
899   a proxy for HTTP/1.1 compliance (or lack thereof).
900</t>
901<t>
902   If the request-target is not an asterisk, the OPTIONS request applies
903   only to the options that are available when communicating with that
904   resource.
905</t>
906<t>
907   A 200 response &SHOULD; include any header fields that indicate
908   optional features implemented by the server and applicable to that
909   resource (e.g., Allow), possibly including extensions not defined by
910   this specification. The response body, if any, &SHOULD; also include
911   information about the communication options. The format for such a
912   body is not defined by this specification, but might be defined by
913   future extensions to HTTP. Content negotiation &MAY; be used to select
914   the appropriate response format. If no response body is included, the
915   response &MUST; include a Content-Length field with a field-value of
916   "0".
917</t>
918<t>
919   The Max-Forwards header field &MAY; be used to target a
920   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
921   If no Max-Forwards field is present in the request, then the forwarded
922   request &MUST-NOT; include a Max-Forwards field.
923</t>
924</section>
925
926<section title="GET" anchor="GET">
927  <rdf:Description>
928    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
929  </rdf:Description>
930  <iref primary="true" item="GET method" x:for-anchor=""/>
931  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
932<t>
933   The GET method requests transfer of a current representation of
934   the target resource.
935</t>
936<t>   
937   If the target resource is a data-producing process, it is the
938   produced data which shall be returned as the representation in the response and not
939   the source text of the process, unless that text happens to be the output of
940   the process.
941</t>
942<t>
943   The semantics of the GET method change to a "conditional GET" if the
944   request message includes an If-Modified-Since, If-Unmodified-Since,
945   If-Match, If-None-Match, or If-Range header field. A conditional GET
946   requests that the representation be transferred only under the
947   circumstances described by the conditional header field(s). The
948   conditional GET request is intended to reduce unnecessary network
949   usage by allowing cached representations to be refreshed without requiring
950   multiple requests or transferring data already held by the client.
951</t>
952<t>
953   The semantics of the GET method change to a "partial GET" if the
954   request message includes a Range header field. A partial GET requests
955   that only part of the representation be transferred, as described in &header-range;.
956   The partial GET request is intended to reduce unnecessary
957   network usage by allowing partially-retrieved representations to be
958   completed without transferring data already held by the client.
959</t>
960<t>
961   Bodies on GET requests have no defined semantics. Note that sending a body
962   on a GET request might cause some existing implementations to reject the
963   request.
964</t>
965<t>
966   The response to a GET request is cacheable and &MAY; be used to satisfy
967   subsequent GET and HEAD requests (see &caching;).
968</t>
969<t>
970   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
971</t>
972</section>
973
974<section title="HEAD" anchor="HEAD">
975  <rdf:Description>
976    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
977  </rdf:Description>
978  <iref primary="true" item="HEAD method" x:for-anchor=""/>
979  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
980<t>
981   The HEAD method is identical to GET except that the server &MUST-NOT;
982   return a message-body in the response. The metadata contained
983   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
984   to the information sent in response to a GET request. This method can
985   be used for obtaining metadata about the representation implied by the
986   request without transferring the representation body. This method is
987   often used for testing hypertext links for validity, accessibility,
988   and recent modification.
989</t>
990<t>
991   The response to a HEAD request is cacheable and &MAY; be used to satisfy
992   a subsequent HEAD request; see &caching;. It also &MAY; be used to update a previously cached
993   representation from that resource; if the new field values
994   indicate that the cached representation differs from the current representation (as
995   would be indicated by a change in Content-Length, ETag
996   or Last-Modified), then the cache &MUST; treat the cache entry as
997   stale.
998</t>
999<t>
1000   Bodies on HEAD requests have no defined semantics. Note that sending a body
1001   on a HEAD request might cause some existing implementations to reject the
1002   request.
1003</t>
1004</section>
1005
1006<section title="POST" anchor="POST">
1007  <iref primary="true" item="POST method" x:for-anchor=""/>
1008  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
1009<t>
1010   The POST method requests that the origin server accept the
1011   representation enclosed in the request as data to be processed by the
1012   target resource. POST is designed to allow a uniform method to cover the
1013   following functions:
1014  <list style="symbols">
1015    <t>
1016      Annotation of existing resources;
1017    </t>
1018    <t>
1019        Posting a message to a bulletin board, newsgroup, mailing list,
1020        or similar group of articles;
1021    </t>
1022    <t>
1023        Providing a block of data, such as the result of submitting a
1024        form, to a data-handling process;
1025    </t>
1026    <t>
1027        Extending a database through an append operation.
1028    </t>
1029  </list>
1030</t>
1031<t>
1032   The actual function performed by the POST method is determined by the
1033   server and is usually dependent on the effective request URI.
1034</t>
1035<t>
1036   The action performed by the POST method might not result in a
1037   resource that can be identified by a URI. In this case, either 200
1038   (OK) or 204 (No Content) is the appropriate response status code,
1039   depending on whether or not the response includes a representation that
1040   describes the result.
1041</t>
1042<t>
1043   If a resource has been created on the origin server, the response
1044   &SHOULD; be 201 (Created) and contain a representation which describes the
1045   status of the request and refers to the new resource, and a Location
1046   header field (see <xref target="header.location"/>).
1047</t>
1048<t>
1049   Responses to POST requests are only cacheable when they
1050   include explicit freshness information (see &p6-explicit;). A
1051   cached POST response with a Content-Location header field
1052   (see &header-content-location;) whose value is the effective
1053   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1054</t>
1055<t>
1056   Note that POST caching is not widely implemented.
1057   However, the 303 (See Other) response can be used to direct the
1058   user agent to retrieve a cacheable resource.
1059</t>
1060</section>
1061
1062<section title="PUT" anchor="PUT">
1063  <iref primary="true" item="PUT method" x:for-anchor=""/>
1064  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
1065<t>
1066   The PUT method requests that the state of the target resource
1067   be created or replaced with the state defined by the representation
1068   enclosed in the request message payload.  A successful PUT of a given
1069   representation would suggest that a subsequent GET on that same target
1070   resource will result in an equivalent representation being returned in
1071   a 200 (OK) response.  However, there is no guarantee that such a state
1072   change will be observable, since the target resource might be acted
1073   upon by other user agents in parallel, or might be subject to dynamic
1074   processing by the origin server, before any subsequent GET is received.
1075   A successful response only implies that the user agent's intent was
1076   achieved at the time of its processing by the origin server.
1077</t>
1078<t>   
1079   If the target resource does not have a current representation and
1080   the PUT successfully creates one, then the origin server &MUST; inform
1081   the user agent by sending a 201 (Created) response.  If the target
1082   resource does have a current representation and that representation is
1083   successfully modified in accordance with the state of the enclosed
1084   representation, then either a 200 (OK) or 204 (No Content) response
1085   &SHOULD; be sent to indicate successful completion of the request.
1086</t>
1087<t>
1088   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1089   as part of the resource state).
1090</t>
1091<t>
1092   An origin server &SHOULD; verify that the PUT representation is
1093   consistent with any constraints which the server has for the target
1094   resource that cannot or will not be changed by the PUT.  This is
1095   particularly important when the origin server uses internal
1096   configuration information related to the URI in order to set the
1097   values for representation metadata on GET responses.  When a PUT
1098   representation is inconsistent with the target resource, the origin
1099   server &SHOULD; either make them consistent, by transforming the
1100   representation or changing the resource configuration, or respond
1101   with an appropriate error message containing sufficient information
1102   to explain why the representation is unsuitable.  The 409 (Conflict)
1103   or 415 (Unsupported Media Type) status codes are suggested, with the
1104   latter being specific to constraints on Content-Type values.
1105</t>
1106<t>
1107   For example, if the target resource is configured to always have a
1108   Content-Type of "text/html" and the representation being PUT has a
1109   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1110   (a) reconfigure the target resource to reflect the new media type;
1111   (b) transform the PUT representation to a format consistent with that
1112   of the resource before saving it as the new resource state; or,
1113   (c) reject the request with a 415 response indicating that the target
1114   resource is limited to "text/html", perhaps including a link to a
1115   different resource that would be a suitable target for the new
1116   representation.
1117</t>
1118<t>
1119   HTTP does not define exactly how a PUT method affects the state
1120   of an origin server beyond what can be expressed by the intent of
1121   the user agent request and the semantics of the origin server response.
1122   It does not define what a resource might be, in any sense of that
1123   word, beyond the interface provided via HTTP.  It does not define
1124   how resource state is "stored", nor how such storage might change
1125   as a result of a change in resource state, nor how the origin server
1126   translates resource state into representations.  Generally speaking,
1127   all implementation details behind the resource interface are
1128   intentionally hidden by the server.
1129</t>
1130<t>
1131   The fundamental difference between the POST and PUT methods is
1132   highlighted by the different intent for the target resource.
1133   The target resource in a POST request is intended to handle the
1134   enclosed representation as a data-accepting process, such as for
1135   a gateway to some other protocol or a document that accepts annotations.
1136   In contrast, the target resource in a PUT request is intended to
1137   take the enclosed representation as a new or replacement value.
1138   Hence, the intent of PUT is idempotent and visible to intermediaries,
1139   even though the exact effect is only known by the origin server.
1140</t>
1141<t>
1142   Proper interpretation of a PUT request presumes that the user agent
1143   knows what target resource is desired.  A service that is intended
1144   to select a proper URI on behalf of the client, after receiving
1145   a state-changing request, &SHOULD; be implemented using the POST
1146   method rather than PUT.  If the origin server will not make the
1147   requested PUT state change to the target resource and instead
1148   wishes to have it applied to a different resource, such as when the
1149   resource has been moved to a different URI, then the origin server
1150   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
1151   then make its own decision regarding whether or not to redirect the
1152   request.
1153</t>
1154<t>
1155   A PUT request applied to the target resource &MAY; have side-effects
1156   on other resources.  For example, an article might have a URI for
1157   identifying "the current version" (a resource) which is separate
1158   from the URIs identifying each particular version (different
1159   resources that at one point shared the same state as the current version
1160   resource).  A successful PUT request on "the current version" URI might
1161   therefore create a new version resource in addition to changing the
1162   state of the target resource, and might also cause links to be added
1163   between the related resources.
1164</t>
1165<t>
1166   An origin server &SHOULD; reject any PUT request that contains a
1167   Content-Range header field, since it might be misinterpreted as
1168   partial content (or might be partial content that is being mistakenly
1169   PUT as a full representation).  Partial content updates are
1170   possible by targeting a separately identified resource with state
1171   that overlaps a portion of the larger resource, or by using a
1172   different method that has been specifically defined for partial
1173   updates (for example, the PATCH method defined in
1174   <xref target="RFC5789"/>).
1175</t>
1176<t>
1177   Responses to the PUT method are not cacheable. If a PUT request passes
1178   through a cache that has one or more stored responses for the effective
1179   request URI, those stored responses will be invalidated (see
1180   &p6-invalid;).
1181</t>
1182</section>
1183
1184<section title="DELETE" anchor="DELETE">
1185  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1186  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
1187<t>
1188   The DELETE method requests that the origin server delete the target
1189   resource. This method &MAY; be overridden by
1190   human intervention (or other means) on the origin server. The client cannot
1191   be guaranteed that the operation has been carried out, even if the
1192   status code returned from the origin server indicates that the action
1193   has been completed successfully. However, the server &SHOULD-NOT; 
1194   indicate success unless, at the time the response is given, it
1195   intends to delete the resource or move it to an inaccessible
1196   location.
1197</t>
1198<t>
1199   A successful response &SHOULD; be 200 (OK) if the response includes an
1200   representation describing the status, 202 (Accepted) if the action has not
1201   yet been enacted, or 204 (No Content) if the action has been enacted
1202   but the response does not include a representation.
1203</t>
1204<t>
1205   Bodies on DELETE requests have no defined semantics. Note that sending a body
1206   on a DELETE request might cause some existing implementations to reject the
1207   request.
1208</t>
1209<t>
1210   Responses to the DELETE method are not cacheable. If a DELETE request
1211   passes through a cache that has one or more stored responses for the
1212   effective request URI, those stored responses will be invalidated (see
1213   &p6-invalid;).
1214</t>
1215</section>
1216
1217<section title="TRACE" anchor="TRACE">
1218  <rdf:Description>
1219    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1220  </rdf:Description>
1221  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1222  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
1223<t>
1224   The TRACE method requests a remote, application-layer loop-back
1225   of the request message. The final recipient of the request
1226   &SHOULD; reflect the message received back to the client as the
1227   message-body of a 200 (OK) response. The final recipient is either the
1228   origin server or the first proxy to receive a Max-Forwards
1229   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1230   A TRACE request &MUST-NOT; include a message-body.
1231</t>
1232<t>
1233   TRACE allows the client to see what is being received at the other
1234   end of the request chain and use that data for testing or diagnostic
1235   information. The value of the Via header field (&header-via;) is of
1236   particular interest, since it acts as a trace of the request chain.
1237   Use of the Max-Forwards header field allows the client to limit the
1238   length of the request chain, which is useful for testing a chain of
1239   proxies forwarding messages in an infinite loop.
1240</t>
1241<t>
1242   If the request is valid, the response &SHOULD; have a Content-Type of
1243   "message/http" (see &media-type-message-http;) and contain a message-body
1244   that encloses a copy of the entire request message.
1245   Responses to the TRACE method are not cacheable.
1246</t>
1247</section>
1248
1249<section title="CONNECT" anchor="CONNECT">
1250  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1251  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1252<t>
1253   The CONNECT method requests that the proxy establish a tunnel
1254   to the request-target and then restrict its behavior to blind
1255   forwarding of packets until the connection is closed.
1256</t>
1257<t>
1258   When using CONNECT, the request-target &MUST; use the authority form
1259   (&request-target;); i.e., the request-target consists of only the
1260   host name and port number of the tunnel destination, separated by a colon.
1261   For example,
1262</t>
1263<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1264CONNECT server.example.com:80 HTTP/1.1
1265Host: server.example.com:80
1266
1267</artwork></figure>
1268<t>
1269   Other HTTP mechanisms can be used normally with the CONNECT method &mdash;
1270   except end-to-end protocol Upgrade requests, since the
1271   tunnel must be established first.
1272</t>
1273<t>
1274   For example, proxy authentication might be used to establish the
1275   authority to create a tunnel:
1276</t>
1277<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1278CONNECT server.example.com:80 HTTP/1.1
1279Host: server.example.com:80
1280Proxy-Authorization: basic aGVsbG86d29ybGQ=
1281
1282</artwork></figure>
1283<t>
1284   Bodies on CONNECT requests have no defined semantics. Note that sending a body
1285   on a CONNECT request might cause some existing implementations to reject the
1286   request.
1287</t>
1288<t>
1289   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1290   sent immediately after the blank line. The usual caveats also apply:
1291   data may be discarded if the eventual response is negative, and the
1292   connection may be reset with no response if more than one TCP segment
1293   is outstanding.
1294</t>
1295
1296<section title="Establishing a Tunnel with CONNECT">
1297<t>
1298   Any successful (2xx) response to a CONNECT request indicates that the
1299   proxy has established a connection to the requested host and port,
1300   and has switched to tunneling the current connection to that server
1301   connection.
1302</t>
1303<t>
1304   It may be the case that the proxy itself can only reach the requested
1305   origin server through another proxy.  In this case, the first proxy
1306   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1307   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1308   unless it has either a direct or tunnel connection established to the
1309   authority.
1310</t>
1311<t>
1312   An origin server which receives a CONNECT request for itself &MAY;
1313   respond with a 2xx status code to indicate that a connection is
1314   established.
1315</t>
1316<t>
1317   If at any point either one of the peers gets disconnected, any
1318   outstanding data that came from that peer will be passed to the other
1319   one, and after that also the other connection will be terminated by
1320   the proxy. If there is outstanding data to that peer undelivered,
1321   that data will be discarded.
1322</t>
1323
1324</section>
1325</section>
1326</section>
1327
1328
1329<section title="Status Code Definitions" anchor="status.codes">
1330<t>
1331   Each Status-Code is described below, including any metadata required
1332   in the response.
1333</t>
1334
1335<section title="Informational 1xx" anchor="status.1xx">
1336<t>
1337   This class of status code indicates a provisional response,
1338   consisting only of the Status-Line and optional header fields, and is
1339   terminated by an empty line. There are no required header fields for this
1340   class of status code. Since HTTP/1.0 did not define any 1xx status
1341   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1342   except under experimental conditions.
1343</t>
1344<t>
1345   A client &MUST; be prepared to accept one or more 1xx status responses
1346   prior to a regular response, even if the client does not expect a 100
1347   (Continue) status message. Unexpected 1xx status responses &MAY; be
1348   ignored by a user agent.
1349</t>
1350<t>
1351   Proxies &MUST; forward 1xx responses, unless the connection between the
1352   proxy and its client has been closed, or unless the proxy itself
1353   requested the generation of the 1xx response. (For example, if a
1354   proxy adds a "Expect: 100-continue" field when it forwards a request,
1355   then it need not forward the corresponding 100 (Continue)
1356   response(s).)
1357</t>
1358
1359<section title="100 Continue" anchor="status.100">
1360  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1361  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1362<t>
1363   The client &SHOULD; continue with its request. This interim response is
1364   used to inform the client that the initial part of the request has
1365   been received and has not yet been rejected by the server. The client
1366   &SHOULD; continue by sending the remainder of the request or, if the
1367   request has already been completed, ignore this response. The server
1368   &MUST; send a final response after the request has been completed. See
1369   &use100; for detailed discussion of the use and handling of this
1370   status code.
1371</t>
1372</section>
1373
1374<section title="101 Switching Protocols" anchor="status.101">
1375  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1376  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1377<t>
1378   The server understands and is willing to comply with the client's
1379   request, via the Upgrade message header field (&header-upgrade;), for a
1380   change in the application protocol being used on this connection. The
1381   server will switch protocols to those defined by the response's
1382   Upgrade header field immediately after the empty line which
1383   terminates the 101 response.
1384</t>
1385<t>
1386   The protocol &SHOULD; be switched only when it is advantageous to do
1387   so. For example, switching to a newer version of HTTP is advantageous
1388   over older versions, and switching to a real-time, synchronous
1389   protocol might be advantageous when delivering resources that use
1390   such features.
1391</t>
1392</section>
1393</section>
1394
1395<section title="Successful 2xx" anchor="status.2xx">
1396<t>
1397   This class of status code indicates that the client's request was
1398   successfully received, understood, and accepted.
1399</t>
1400
1401<section title="200 OK" anchor="status.200">
1402  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1403  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1404<t>
1405   The request has succeeded. The payload returned with the response
1406   is dependent on the method used in the request, for example:
1407  <list style="hanging">
1408    <t hangText="GET">
1409      a representation of the target resource is sent in the response;
1410    </t>
1411    <t hangText="HEAD">
1412      the same representation as GET, except without the message-body;
1413    </t>
1414    <t hangText="POST">
1415      a representation describing or containing the result of the action;
1416    </t>
1417    <t hangText="TRACE">
1418      a representation containing the request message as received by the
1419      end server.
1420    </t>
1421  </list>
1422</t>
1423<t>
1424   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1425   freshness for 200 responses.
1426</t>
1427</section>
1428
1429<section title="201 Created" anchor="status.201">
1430  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1431  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1432<t>
1433   The request has been fulfilled and has resulted in a new resource being
1434   created. The newly created resource can be referenced by the URI(s)
1435   returned in the payload of the response, with the most specific URI
1436   for the resource given by a Location header field. The response
1437   &SHOULD; include a payload containing a list of resource
1438   characteristics and location(s) from which the user or user agent can
1439   choose the one most appropriate. The payload format is specified by
1440   the media type given in the Content-Type header field. The origin
1441   server &MUST; create the resource before returning the 201 status code.
1442   If the action cannot be carried out immediately, the server &SHOULD;
1443   respond with 202 (Accepted) response instead.
1444</t>
1445<t>
1446   A 201 response &MAY; contain an ETag response header field indicating
1447   the current value of the entity-tag for the representation of the resource
1448   just created (see &header-etag;).
1449</t>
1450</section>
1451
1452<section title="202 Accepted" anchor="status.202">
1453  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1454  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1455<t>
1456   The request has been accepted for processing, but the processing has
1457   not been completed.  The request might or might not eventually be
1458   acted upon, as it might be disallowed when processing actually takes
1459   place. There is no facility for re-sending a status code from an
1460   asynchronous operation such as this.
1461</t>
1462<t>
1463   The 202 response is intentionally non-committal. Its purpose is to
1464   allow a server to accept a request for some other process (perhaps a
1465   batch-oriented process that is only run once per day) without
1466   requiring that the user agent's connection to the server persist
1467   until the process is completed. The representation returned with this
1468   response &SHOULD; include an indication of the request's current status
1469   and either a pointer to a status monitor or some estimate of when the
1470   user can expect the request to be fulfilled.
1471</t>
1472</section>
1473
1474<section title="203 Non-Authoritative Information" anchor="status.203">
1475  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1476  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1477<t>
1478   The representation in the response has been transformed or otherwise
1479   modified by a transforming proxy (&intermediaries;).  Note that the
1480   behaviour of transforming intermediaries is controlled by the no-transform
1481   Cache-Control directive (&header-cache-control;).
1482</t>
1483<t>
1484   This status code is only appropriate when the response status code would
1485   have been 200 (OK) otherwise. When the status code before transformation
1486   would have been different, the 214 Transformation Applied warn-code
1487   (&header-warning;) is appropriate.
1488</t>
1489<t>
1490   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1491   freshness for 203 responses.
1492</t>
1493</section>
1494
1495<section title="204 No Content" anchor="status.204">
1496  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1497  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1498<t>
1499   The 204 (No Content) status code indicates that the server has
1500   successfully fulfilled the request and that there is no additional
1501   content to return in the response payload body.  Metadata in the
1502   response header fields refer to the target resource and its current
1503   representation after the requested action.
1504</t>
1505<t>
1506   For example, if a 204 status code is received in response to a PUT
1507   request and the response contains an ETag header field, then the PUT
1508   was successful and the ETag field-value contains the entity-tag for
1509   the new representation of that target resource.
1510</t>
1511<t>
1512   The 204 response allows a server to indicate that the action has been
1513   successfully applied to the target resource while implying that the
1514   user agent &SHOULD-NOT; traverse away from its current "document view"
1515   (if any).  The server assumes that the user agent will provide some
1516   indication of the success to its user, in accord with its own interface,
1517   and apply any new or updated metadata in the response to the active
1518   representation.
1519</t>
1520<t>
1521   For example, a 204 status code is commonly used with document editing
1522   interfaces corresponding to a "save" action, such that the document
1523   being saved remains available to the user for editing. It is also
1524   frequently used with interfaces that expect automated data transfers
1525   to be prevalent, such as within distributed version control systems.
1526</t>
1527<t>
1528   The 204 response &MUST-NOT; include a message-body, and thus is always
1529   terminated by the first empty line after the header fields.
1530</t>
1531</section>
1532
1533<section title="205 Reset Content" anchor="status.205">
1534  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1535  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1536<t>
1537   The server has fulfilled the request and the user agent &SHOULD; reset
1538   the document view which caused the request to be sent. This response
1539   is primarily intended to allow input for actions to take place via
1540   user input, followed by a clearing of the form in which the input is
1541   given so that the user can easily initiate another input action.
1542</t>
1543<t>   
1544   The message-body included with the response &MUST; be empty. Note that
1545   receivers still need to parse the response according to the algorithm defined
1546   in &message-body;.
1547</t>
1548</section>
1549
1550<section title="206 Partial Content" anchor="status.206">
1551  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1552  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1553  <rdf:Description>
1554    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
1555  </rdf:Description>
1556<t>
1557   The server has fulfilled the partial GET request for the resource
1558   and the enclosed payload is a partial representation as defined in &status-206;.
1559</t>
1560<t>
1561   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1562   freshness for 206 responses.
1563</t>
1564</section>
1565</section>
1566
1567<section title="Redirection 3xx" anchor="status.3xx">
1568<t>
1569   This class of status code indicates that further action needs to be
1570   taken by the user agent in order to fulfill the request.  If the required
1571   action involves a subsequent HTTP request, it &MAY; be carried out by the
1572   user agent without interaction with the user if and only if the method used
1573   in the second request is known to be "safe", as defined in
1574   <xref target="safe.methods"/>.
1575</t>
1576<t>
1577   There are several types of redirects:
1578   <list style="numbers">
1579      <x:lt>
1580        <t>
1581          Redirects of the request to another URI, either temporarily or
1582          permanently. The new URI is specified in the Location header field.
1583          In this specification, the status codes 301 (Moved Permanently),
1584          302 (Found), and 307 (Temporary Redirect) fall under this category.
1585        </t>
1586      </x:lt>
1587      <x:lt>
1588        <t>
1589          Redirection to a new location that represents an indirect response to
1590          the request, such as the result of a POST operation to be retrieved
1591          with a subsequent GET request. This is status code 303 (See Other).
1592        </t>
1593      </x:lt>
1594      <x:lt>
1595        <t>
1596          Redirection offering a choice of matching resources for use by
1597          agent-driven content negotiation (&agent-driven-negotiation;). This
1598          is status code 300 (Multiple Choices).
1599        </t>
1600      </x:lt>
1601      <x:lt>
1602        <t>
1603          Other kinds of redirection, such as to a cached result (status code 304
1604          (Not Modified)).
1605        </t>
1606      </x:lt>
1607   </list>
1608</t>
1609<x:note>
1610  <t>
1611    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1612    and 302 (Found) were defined for the first type of redirect, and the second
1613    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1614    However it turned out that web forms using POST expected redirects to change
1615    the operation for the subsequent request to retrieval (GET). To address this
1616    use case, HTTP/1.1 introduced the second type of redirect with the status
1617    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1618    As user agents did not change their behavior to maintain backwards
1619    compatibility, the first revision of HTTP/1.1 added yet another status code,
1620    307 (Temporary Redirect), for which the backwards compatibility problems did
1621    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1622    Over 10 years later, most user agents still do method rewriting for
1623    status codes 301 and 302, therefore this specification makes that behavior
1624    compliant in case the original request was POST.
1625  </t>
1626</x:note>
1627<t>
1628   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1629   "infinite" redirection loops).
1630</t>
1631<x:note>
1632  <t>
1633    <x:h>Note:</x:h> An earlier version of this specification recommended a
1634    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1635    Content developers need to be aware that some clients might
1636    implement such a fixed limitation.
1637  </t>
1638</x:note>
1639
1640<section title="300 Multiple Choices" anchor="status.300">
1641  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1642  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1643<t>
1644   The target resource has more than one
1645   representation, each with its own specific location, and agent-driven
1646   negotiation information (&content-negotiation;) is being provided so that
1647   the user (or user agent) can select a preferred representation by
1648   redirecting its request to that location.
1649</t>
1650<t>
1651   Unless it was a HEAD request, the response &SHOULD; include a representation
1652   containing a list of representation metadata and location(s) from
1653   which the user or user agent can choose the one most appropriate. The
1654   data format is specified by the media type given in the Content-Type
1655   header field. Depending upon the format and the capabilities of
1656   the user agent, selection of the most appropriate choice &MAY; be
1657   performed automatically. However, this specification does not define
1658   any standard for such automatic selection.
1659</t>
1660<t>
1661   If the server has a preferred choice of representation, it &SHOULD;
1662   include the specific URI for that representation in the Location
1663   field; user agents &MAY; use the Location field value for automatic
1664   redirection.
1665</t>
1666<t>
1667   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1668   freshness for 300 responses.
1669</t>
1670
1671</section>
1672
1673<section title="301 Moved Permanently" anchor="status.301">
1674  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1675  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1676<t>
1677   The target resource has been assigned a new permanent URI and any
1678   future references to this resource &SHOULD; use one of the returned
1679   URIs.  Clients with link editing capabilities ought to automatically
1680   re-link references to the effective request URI to one or more of the new
1681   references returned by the server, where possible.
1682</t>
1683<t>
1684   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1685   freshness for 301 responses.
1686</t>
1687<t>
1688   The new permanent URI &SHOULD; be given by the Location field in the
1689   response. Unless the request method was HEAD, the representation of the
1690   response &SHOULD; contain a short hypertext note with a hyperlink to
1691   the new URI(s).
1692</t>
1693<t>
1694   If the 301 status code is received in response to a request method
1695   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1696   then the request &MAY; be automatically redirected by the user agent without
1697   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1698   request unless it can be confirmed by the user, since this might
1699   change the conditions under which the request was issued.
1700</t>
1701<x:note>
1702  <t>
1703    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1704    request method from POST to GET for the subsequent request. If this
1705    behavior is undesired, status code 307 (Temporary Redirect) can be used
1706    instead.
1707  </t>
1708</x:note>
1709</section>
1710
1711<section title="302 Found" anchor="status.302">
1712  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1713  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1714<t>
1715   The target resource resides temporarily under a different URI.
1716   Since the redirection might be altered on occasion, the client &SHOULD;
1717   continue to use the effective request URI for future requests.
1718</t>
1719<t>
1720   The temporary URI &SHOULD; be given by the Location field in the
1721   response. Unless the request method was HEAD, the representation of the
1722   response &SHOULD; contain a short hypertext note with a hyperlink to
1723   the new URI(s).
1724</t>
1725<t>
1726   If the 302 status code is received in response to a request method
1727   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1728   then the request &MAY; be automatically redirected by the user agent without
1729   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1730   request unless it can be confirmed by the user, since this might
1731   change the conditions under which the request was issued.
1732</t>
1733<x:note>
1734  <t>
1735    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1736    request method from POST to GET for the subsequent request. If this
1737    behavior is undesired, status code 307 (Temporary Redirect) can be used
1738    instead.
1739    <cref anchor="issue312">but see <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/312"/></cref>
1740  </t>
1741</x:note>
1742</section>
1743
1744<section title="303 See Other" anchor="status.303">
1745  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1746  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1747<t>
1748   The 303 status code indicates that the server is redirecting the
1749   user agent to a different resource, as indicated by a URI in the
1750   Location header field, that is intended to provide an indirect
1751   response to the original request.  In order to satisfy the original
1752   request, a user agent &SHOULD; perform a retrieval request using the
1753   Location URI, which may itself be redirected further, and present
1754   the eventual result as an answer to the original request.
1755   Note that the new URI in the Location header field is not considered
1756   equivalent to the effective request URI.
1757</t>
1758<t>
1759   This status code is generally applicable to any HTTP method.  It is
1760   primarily used to allow the output of a POST action to redirect
1761   the user agent to a selected resource, since doing so provides the
1762   information corresponding to the POST response in a form that
1763   can be separately identified, bookmarked, and cached independent
1764   of the original request.
1765</t>
1766<t>
1767   A 303 response to a GET request indicates that the requested
1768   resource does not have a representation of its own that can be
1769   transferred by the server over HTTP.  The Location URI indicates a
1770   resource that is descriptive of the target resource, such that the
1771   follow-on representation might be useful to recipients without
1772   implying that it adequately represents the target resource.
1773   Note that answers to the questions of what can be represented, what
1774   representations are adequate, and what might be a useful description
1775   are outside the scope of HTTP and thus entirely determined by the
1776   URI owner(s).
1777</t>
1778<t>
1779   Except for responses to a HEAD request, the representation of a 303
1780   response &SHOULD; contain a short hypertext note with a hyperlink
1781   to the Location URI.
1782</t>
1783</section>
1784
1785<section title="304 Not Modified" anchor="status.304">
1786  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1787  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1788  <rdf:Description>
1789    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
1790  </rdf:Description>
1791<t>
1792   The response to the request has not been modified since the conditions
1793   indicated by the client's conditional GET request, as defined in &status-304;.
1794</t>
1795</section>
1796
1797<section title="305 Use Proxy" anchor="status.305">
1798  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1799  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1800<t>
1801   The 305 status code was defined in a previous version of this specification
1802   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1803</t>
1804</section>
1805
1806<section title="306 (Unused)" anchor="status.306">
1807  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1808  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1809<t>
1810   The 306 status code was used in a previous version of the
1811   specification, is no longer used, and the code is reserved.
1812</t>
1813</section>
1814
1815<section title="307 Temporary Redirect" anchor="status.307">
1816  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1817  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1818<t>
1819   The target resource resides temporarily under a different URI.
1820   Since the redirection can change over time, the client &SHOULD;
1821   continue to use the effective request URI for future requests.
1822</t>
1823<t>
1824   The temporary URI &SHOULD; be given by the Location field in the
1825   response. Unless the request method was HEAD, the representation of the
1826   response &SHOULD; contain a short hypertext note with a hyperlink to
1827   the new URI(s), since many pre-HTTP/1.1 user agents do not
1828   understand the 307 status code. Therefore, the note &SHOULD; contain the
1829   information necessary for a user to repeat the original request on
1830   the new URI.
1831</t>
1832<t>
1833   If the 307 status code is received in response to a request method
1834   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1835   then the request &MAY; be automatically redirected by the user agent without
1836   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1837   request unless it can be confirmed by the user, since this might
1838   change the conditions under which the request was issued.
1839</t>
1840</section>
1841</section>
1842
1843<section title="Client Error 4xx" anchor="status.4xx">
1844<t>
1845   The 4xx class of status code is intended for cases in which the
1846   client seems to have erred. Except when responding to a HEAD request,
1847   the server &SHOULD; include a representation containing an explanation of the
1848   error situation, and whether it is a temporary or permanent
1849   condition. These status codes are applicable to any request method.
1850   User agents &SHOULD; display any included representation to the user.
1851</t>
1852<t>
1853   If the client is sending data, a server implementation using TCP
1854   &SHOULD; be careful to ensure that the client acknowledges receipt of
1855   the packet(s) containing the response, before the server closes the
1856   input connection. If the client continues sending data to the server
1857   after the close, the server's TCP stack will send a reset packet to
1858   the client, which might erase the client's unacknowledged input buffers
1859   before they can be read and interpreted by the HTTP application.
1860</t>
1861
1862<section title="400 Bad Request" anchor="status.400">
1863  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1864  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1865<t>
1866   The server cannot or will not process the request, due to a client error (e.g.,
1867   malformed syntax).</t>
1868</section>
1869
1870<section title="401 Unauthorized" anchor="status.401">
1871  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1872  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1873  <rdf:Description>
1874    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part7</redirects-to>
1875  </rdf:Description>
1876<t>
1877   The request requires user authentication (see &status-401;).
1878</t>
1879</section>
1880
1881<section title="402 Payment Required" anchor="status.402">
1882  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1883  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1884<t>
1885   This code is reserved for future use.
1886</t>
1887</section>
1888
1889<section title="403 Forbidden" anchor="status.403">
1890  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1891  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1892<t>
1893   The server understood the request, but refuses to authorize it. Providing
1894   different user authentication credentials might be successful, but any
1895   credentials that were provided in the request are insufficient. The request
1896   &SHOULD-NOT; be repeated with the same credentials.
1897</t>
1898<t>
1899   If the request method was not HEAD and the server wishes to make
1900   public why the request has not been fulfilled, it &SHOULD; describe the
1901   reason for the refusal in the representation.  If the server does not wish to
1902   make this information available to the client, the status code 404
1903   (Not Found) &MAY; be used instead.
1904</t>
1905</section>
1906
1907<section title="404 Not Found" anchor="status.404">
1908  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1909  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1910<t>
1911   The server has not found anything matching the effective request URI. No
1912   indication is given of whether the condition is temporary or
1913   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1914   knows, through some internally configurable mechanism, that an old
1915   resource is permanently unavailable and has no forwarding address.
1916   This status code is commonly used when the server does not wish to
1917   reveal exactly why the request has been refused, or when no other
1918   response is applicable.
1919</t>
1920</section>
1921
1922<section title="405 Method Not Allowed" anchor="status.405">
1923  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1924  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1925<t>
1926   The method specified in the Request-Line is not allowed for the target
1927   resource. The response &MUST; include an Allow header field containing a
1928   list of valid methods for the requested resource.
1929</t>
1930</section>
1931
1932<section title="406 Not Acceptable" anchor="status.406">
1933  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1934  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1935<t>
1936   The resource identified by the request is only capable of generating
1937   response representations which have content characteristics not acceptable
1938   according to the Accept and Accept-* header fields sent in the request
1939   (see &p3-header-fields;).
1940</t>
1941<t>
1942   Unless it was a HEAD request, the response &SHOULD; include a representation
1943   containing a list of available representation characteristics and location(s)
1944   from which the user or user agent can choose the one most
1945   appropriate. The data format is specified by the media type given
1946   in the Content-Type header field. Depending upon the format and the
1947   capabilities of the user agent, selection of the most appropriate
1948   choice &MAY; be performed automatically. However, this specification
1949   does not define any standard for such automatic selection.
1950</t>
1951<x:note>
1952  <t>
1953    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1954    not acceptable according to the accept header fields sent in the
1955    request. In some cases, this might even be preferable to sending a
1956    406 response. User agents are encouraged to inspect the header fields of
1957    an incoming response to determine if it is acceptable.
1958  </t>
1959</x:note>
1960<t>
1961   If the response could be unacceptable, a user agent &SHOULD;
1962   temporarily stop receipt of more data and query the user for a
1963   decision on further actions.
1964</t>
1965</section>
1966
1967<section title="407 Proxy Authentication Required" anchor="status.407">
1968  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1969  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1970<t>
1971   This code is similar to 401 (Unauthorized), but indicates that the
1972   client must first authenticate itself with the proxy (see &status-407;).
1973</t>
1974</section>
1975
1976<section title="408 Request Timeout" anchor="status.408">
1977  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1978  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1979<t>
1980   The client did not produce a request within the time that the server
1981   was prepared to wait. The client &MAY; repeat the request without
1982   modifications at any later time.
1983</t>
1984</section>
1985
1986<section title="409 Conflict" anchor="status.409">
1987  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1988  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1989<t>
1990   The request could not be completed due to a conflict with the current
1991   state of the resource. This code is only allowed in situations where
1992   it is expected that the user might be able to resolve the conflict
1993   and resubmit the request. The response body &SHOULD; include enough
1994   information for the user to recognize the source of the conflict.
1995   Ideally, the response representation would include enough information for the
1996   user or user agent to fix the problem; however, that might not be
1997   possible and is not required.
1998</t>
1999<t>
2000   Conflicts are most likely to occur in response to a PUT request. For
2001   example, if versioning were being used and the representation being PUT
2002   included changes to a resource which conflict with those made by an
2003   earlier (third-party) request, the server might use the 409 response
2004   to indicate that it can't complete the request. In this case, the
2005   response representation would likely contain a list of the differences
2006   between the two versions in a format defined by the response
2007   Content-Type.
2008</t>
2009</section>
2010
2011<section title="410 Gone" anchor="status.410">
2012  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
2013  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
2014<t>
2015   The target resource is no longer available at the server and no
2016   forwarding address is known. This condition is expected to be
2017   considered permanent. Clients with link editing capabilities &SHOULD;
2018   delete references to the effective request URI after user approval. If the
2019   server does not know, or has no facility to determine, whether or not
2020   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
2021   used instead.
2022</t>
2023<t>
2024   The 410 response is primarily intended to assist the task of web
2025   maintenance by notifying the recipient that the resource is
2026   intentionally unavailable and that the server owners desire that
2027   remote links to that resource be removed. Such an event is common for
2028   limited-time, promotional services and for resources belonging to
2029   individuals no longer working at the server's site. It is not
2030   necessary to mark all permanently unavailable resources as "gone" or
2031   to keep the mark for any length of time &mdash; that is left to the
2032   discretion of the server owner.
2033</t>
2034<t>
2035   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
2036   for 410 responses.
2037</t>
2038
2039</section>
2040
2041<section title="411 Length Required" anchor="status.411">
2042  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
2043  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
2044<t>
2045   The server refuses to accept the request without a defined Content-Length.
2046   The client &MAY; repeat the request if it adds a valid
2047   Content-Length header field containing the length of the message-body
2048   in the request message.
2049</t>
2050</section>
2051
2052<section title="412 Precondition Failed" anchor="status.412">
2053  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
2054  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
2055  <rdf:Description>
2056    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
2057  </rdf:Description>
2058<t>
2059   The precondition given in one or more of the header fields
2060   evaluated to false when it was tested on the server, as defined in
2061   &status-412;.
2062</t>
2063</section>
2064
2065<section title="413 Request Representation Too Large" anchor="status.413">
2066  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2067  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2068<t>
2069   The server is refusing to process a request because the request
2070   representation is larger than the server is willing or able to process. The
2071   server &MAY; close the connection to prevent the client from continuing
2072   the request.
2073</t>
2074<t>
2075   If the condition is temporary, the server &SHOULD; include a Retry-After
2076   header field to indicate that it is temporary and after what
2077   time the client &MAY; try again.
2078</t>
2079</section>
2080
2081<section title="414 URI Too Long" anchor="status.414">
2082  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2083  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
2084<t>
2085   The server is refusing to service the request because the effective request URI
2086   is longer than the server is willing to interpret. This rare
2087   condition is only likely to occur when a client has improperly
2088   converted a POST request to a GET request with long query
2089   information, when the client has descended into a URI "black hole" of
2090   redirection (e.g., a redirected URI prefix that points to a suffix of
2091   itself), or when the server is under attack by a client attempting to
2092   exploit security holes present in some servers using fixed-length
2093   buffers for reading or manipulating the effective request URI.
2094</t>
2095</section>
2096
2097<section title="415 Unsupported Media Type" anchor="status.415">
2098  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2099  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2100<t>
2101   The server is refusing to service the request because the request
2102   payload is in a format not supported by this request method on the
2103   target resource.
2104</t>
2105</section>
2106
2107<section title="416 Requested Range Not Satisfiable" anchor="status.416">
2108  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
2109  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
2110  <rdf:Description>
2111    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
2112  </rdf:Description>
2113<t>
2114   The request included a Range header field (&header-range;) and none of
2115   the range-specifier values in this field overlap the current extent
2116   of the selected resource. See &status-416;.
2117</t>
2118</section>
2119
2120<section title="417 Expectation Failed" anchor="status.417">
2121  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2122  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2123<t>
2124   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2125   could not be met by this server, or, if the server is a proxy,
2126   the server has unambiguous evidence that the request could not be met
2127   by the next-hop server.
2128</t>
2129</section>
2130
2131<section title="426 Upgrade Required" anchor="status.426">
2132  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2133  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2134<t>
2135   The request can not be completed without a prior protocol upgrade. This
2136   response &MUST; include an Upgrade header field (&header-upgrade;)
2137   specifying the required protocols.
2138</t>
2139<figure>
2140<preamble>Example:</preamble>
2141<artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2142HTTP/1.1 426 Upgrade Required
2143Upgrade: HTTP/2.0
2144Connection: Upgrade
2145
2146</artwork></figure>
2147<t>
2148   The server &SHOULD; include a message body in the 426 response which
2149   indicates in human readable form the reason for the error and describes any
2150   alternative courses which may be available to the user.
2151</t>
2152</section>
2153</section>
2154
2155<section title="Server Error 5xx" anchor="status.5xx">
2156<t>
2157   Response status codes beginning with the digit "5" indicate cases in
2158   which the server is aware that it has erred or is incapable of
2159   performing the request. Except when responding to a HEAD request, the
2160   server &SHOULD; include a representation containing an explanation of the
2161   error situation, and whether it is a temporary or permanent
2162   condition. User agents &SHOULD; display any included representation to the
2163   user. These response codes are applicable to any request method.
2164</t>
2165
2166<section title="500 Internal Server Error" anchor="status.500">
2167  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2168  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2169<t>
2170   The server encountered an unexpected condition which prevented it
2171   from fulfilling the request.
2172</t>
2173</section>
2174
2175<section title="501 Not Implemented" anchor="status.501">
2176  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2177  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2178<t>
2179   The server does not support the functionality required to fulfill the
2180   request. This is the appropriate response when the server does not
2181   recognize the request method and is not capable of supporting it for
2182   any resource.
2183</t>
2184</section>
2185
2186<section title="502 Bad Gateway" anchor="status.502">
2187  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2188  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2189<t>
2190   The server, while acting as a gateway or proxy, received an invalid
2191   response from the upstream server it accessed in attempting to
2192   fulfill the request.
2193</t>
2194</section>
2195
2196<section title="503 Service Unavailable" anchor="status.503">
2197  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2198  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2199<t>
2200   The server is currently unable or unwilling to handle the request due to
2201   reasons such as temporary overloading, maintenance of the server, or rate
2202   limiting of the client.
2203</t>
2204<t>
2205   The implication is that this is a temporary condition which will be
2206   alleviated after some delay. If known, the length of the delay &MAY; be
2207   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2208   If no Retry-After is given, the client &SHOULD; handle the response as it
2209   would for a 500 response.
2210</t>
2211<x:note>
2212  <t>
2213    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2214    server must use it when becoming overloaded. Some servers might wish
2215    to simply refuse the connection.
2216  </t>
2217</x:note>
2218</section>
2219
2220<section title="504 Gateway Timeout" anchor="status.504">
2221  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2222  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2223<t>
2224   The server, while acting as a gateway or proxy, did not receive a
2225   timely response from the upstream server specified by the URI (e.g.,
2226   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2227   to access in attempting to complete the request.
2228</t>
2229<x:note>
2230  <t>
2231    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2232    return 400 or 500 when DNS lookups time out.
2233  </t>
2234</x:note>
2235</section>
2236
2237<section title="505 HTTP Version Not Supported" anchor="status.505">
2238  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2239  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2240<t>
2241   The server does not support, or refuses to support, the protocol
2242   version that was used in the request message. The server is
2243   indicating that it is unable or unwilling to complete the request
2244   using the same major version as the client, as described in &http-version;,
2245   other than with this error message. The response &SHOULD; contain
2246   a representation describing why that version is not supported and what other
2247   protocols are supported by that server.
2248</t>
2249
2250</section>
2251</section>
2252</section>
2253
2254
2255<section title="Header Field Definitions" anchor="header.field.definitions">
2256<t>
2257   This section defines the syntax and semantics of HTTP/1.1 header fields
2258   related to request and response semantics.
2259</t>
2260
2261<section title="Allow" anchor="header.allow">
2262  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2263  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2264  <x:anchor-alias value="Allow"/>
2265<t>
2266   The "Allow" header field lists the set of methods advertised as
2267   supported by the target resource. The purpose of this field is strictly to
2268   inform the recipient of valid request methods associated with the resource.
2269</t>
2270<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2271  <x:ref>Allow</x:ref> = #<x:ref>Method</x:ref>
2272</artwork></figure>
2273<t>
2274   Example of use:
2275</t>
2276<figure><artwork type="example">
2277  Allow: GET, HEAD, PUT
2278</artwork></figure>
2279<t>
2280   The actual set of allowed methods is defined by the origin server at the
2281   time of each request.
2282</t>
2283<t>
2284   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2285   understand all the methods specified in order to handle them according to
2286   the generic message handling rules.
2287</t>
2288</section>
2289
2290<section title="Expect" anchor="header.expect">
2291  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2292  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2293  <x:anchor-alias value="Expect"/>
2294  <x:anchor-alias value="expectation"/>
2295  <x:anchor-alias value="expectation-extension"/>
2296  <x:anchor-alias value="expect-params"/>
2297<t>
2298   The "Expect" header field is used to indicate that particular
2299   server behaviors are required by the client.
2300</t>
2301<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/>
2302  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2303 
2304  <x:ref>expectation</x:ref>  = "100-continue" / <x:ref>expectation-extension</x:ref>
2305  <x:ref>expectation-extension</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2306                           *<x:ref>expect-params</x:ref> ]
2307  <x:ref>expect-params</x:ref> = ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2308</artwork></figure>
2309<t>
2310   A server that does not understand or is unable to comply with any of
2311   the expectation values in the Expect field of a request &MUST; respond
2312   with appropriate error status code. The server &MUST; respond with a 417
2313   (Expectation Failed) status code if any of the expectations cannot be met
2314   or, if there are other problems with the request, some other 4xx
2315   status code.
2316</t>
2317<t>
2318   This header field is defined with extensible syntax to allow for
2319   future extensions. If a server receives a request containing an
2320   Expect field that includes an expectation-extension that it does not
2321   support, it &MUST; respond with a 417 (Expectation Failed) status code.
2322</t>
2323<t>
2324   Comparison of expectation values is case-insensitive for unquoted
2325   tokens (including the 100-continue token), and is case-sensitive for
2326   quoted-string expectation-extensions.
2327</t>
2328<t>
2329   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
2330   return a 417 (Expectation Failed) status code if it receives a request
2331   with an expectation that it cannot meet. However, the Expect
2332   header field itself is end-to-end; it &MUST; be forwarded if the
2333   request is forwarded.
2334</t>
2335<t>
2336   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
2337   Expect header field.
2338</t>
2339<t>
2340   See &use100; for the use of the 100 (Continue) status code.
2341</t>
2342</section>
2343
2344<section title="From" anchor="header.from">
2345  <iref primary="true" item="From header field" x:for-anchor=""/>
2346  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2347  <x:anchor-alias value="From"/>
2348  <x:anchor-alias value="mailbox"/>
2349<t>
2350   The "From" header field, if given, &SHOULD; contain an Internet
2351   e-mail address for the human user who controls the requesting user
2352   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2353   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2354</t>
2355<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2356  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2357 
2358  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2359</artwork></figure>
2360<t>
2361   An example is:
2362</t>
2363<figure><artwork type="example">
2364  From: webmaster@example.org
2365</artwork></figure>
2366<t>
2367   This header field &MAY; be used for logging purposes and as a means for
2368   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2369   be used as an insecure form of access protection. The interpretation
2370   of this field is that the request is being performed on behalf of the
2371   person given, who accepts responsibility for the method performed. In
2372   particular, robot agents &SHOULD; include this header field so that the
2373   person responsible for running the robot can be contacted if problems
2374   occur on the receiving end.
2375</t>
2376<t>
2377   The Internet e-mail address in this field &MAY; be separate from the
2378   Internet host which issued the request. For example, when a request
2379   is passed through a proxy the original issuer's address &SHOULD; be
2380   used.
2381</t>
2382<t>
2383   The client &SHOULD-NOT;  send the From header field without the user's
2384   approval, as it might conflict with the user's privacy interests or
2385   their site's security policy. It is strongly recommended that the
2386   user be able to disable, enable, and modify the value of this field
2387   at any time prior to a request.
2388</t>
2389</section>
2390
2391<section title="Location" anchor="header.location">
2392  <iref primary="true" item="Location header field" x:for-anchor=""/>
2393  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2394  <x:anchor-alias value="Location"/>
2395<t>
2396   The "Location" header field is used to identify a newly created
2397   resource, or to redirect the recipient to a different location for
2398   completion of the request.
2399</t>
2400<t>
2401   For 201 (Created) responses, the Location is the URI of the new resource
2402   which was created by the request. For 3xx responses, the location &SHOULD;
2403   indicate the server's preferred URI for automatic redirection to the
2404   resource.
2405</t>
2406<t>
2407   The field value consists of a single URI-reference. When it has the form
2408   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2409   the final value is computed by resolving it against the effective request
2410   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>).
2411</t>
2412<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2413  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2414</artwork></figure>
2415<figure>
2416<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2417<artwork type="example">
2418  Location: http://www.example.org/pub/WWW/People.html#tim
2419</artwork></figure><figure><artwork type="example">  Location: /index.html
2420</artwork></figure>
2421<t>
2422   There are circumstances in which a fragment identifier in a Location URI
2423   would not be appropriate. For instance, when it appears in a 201 Created
2424   response, where the Location header field specifies the URI for the entire
2425   created resource.
2426</t>
2427<x:note>
2428  <t>
2429    <x:h>Note:</x:h> This specification does not define precedence rules
2430    for the case where the original URI, as navigated to by the user
2431    agent, and the Location header field value both contain fragment
2432    identifiers. Thus be aware that including fragment identifiers might
2433    inconvenience anyone relying on the semantics of the original URI's
2434    fragment identifier.
2435  </t>
2436</x:note>
2437<x:note>
2438  <t>
2439    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2440    from Location in that the Content-Location identifies the most specific
2441    resource corresponding to the enclosed representation.
2442    It is therefore possible for a response to contain header fields for
2443    both Location and Content-Location.
2444  </t>
2445</x:note>
2446</section>
2447
2448<section title="Max-Forwards" anchor="header.max-forwards">
2449  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2450  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2451  <x:anchor-alias value="Max-Forwards"/>
2452<t>
2453   The "Max-Forwards" header field provides a mechanism with the
2454   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2455   methods to limit the number of times that the request is forwarded by
2456   proxies. This can be useful when the client is attempting to
2457   trace a request which appears to be failing or looping in mid-chain.
2458</t>
2459<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2460  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2461</artwork></figure>
2462<t>
2463   The Max-Forwards value is a decimal integer indicating the remaining
2464   number of times this request message can be forwarded.
2465</t>
2466<t>
2467   Each recipient of a TRACE or OPTIONS request
2468   containing a Max-Forwards header field &MUST; check and update its
2469   value prior to forwarding the request. If the received value is zero
2470   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2471   respond as the final recipient. If the received Max-Forwards value is
2472   greater than zero, then the forwarded message &MUST; contain an updated
2473   Max-Forwards field with a value decremented by one (1).
2474</t>
2475<t>
2476   The Max-Forwards header field &MAY; be ignored for all other request
2477   methods.
2478</t>
2479</section>
2480
2481<section title="Referer" anchor="header.referer">
2482  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2483  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2484  <x:anchor-alias value="Referer"/>
2485<t>
2486   The "Referer" [sic] header field allows the client to specify the
2487   URI of the resource from which the effective request URI was obtained (the
2488   "referrer", although the header field is misspelled.).
2489</t>
2490<t>
2491   The Referer header field allows servers to generate lists of back-links to
2492   resources for interest, logging, optimized caching, etc. It also allows
2493   obsolete or mistyped links to be traced for maintenance. Some servers use
2494   Referer as a means of controlling where they allow links from (so-called
2495   "deep linking"), but legitimate requests do not always
2496   contain a Referer header field.
2497</t>
2498<t>
2499   If the effective request URI was obtained from a source that does not have its own
2500   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2501   sent with the value "about:blank", or not be sent at all. Note that this
2502   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2503</t>
2504<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2505  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2506</artwork></figure>
2507<t>
2508   Example:
2509</t>
2510<figure><artwork type="example">
2511  Referer: http://www.example.org/hypertext/Overview.html
2512</artwork></figure>
2513<t>
2514   If the field value is a relative URI, it &SHOULD; be interpreted
2515   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2516   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2517</t>
2518</section>
2519
2520<section title="Retry-After" anchor="header.retry-after">
2521  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2522  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2523  <x:anchor-alias value="Retry-After"/>
2524<t>
2525   The header "Retry-After" field can be used with a 503 (Service
2526   Unavailable) response to indicate how long the service is expected to
2527   be unavailable to the requesting client. This field &MAY; also be used
2528   with any 3xx (Redirection) response to indicate the minimum time the
2529   user-agent is asked wait before issuing the redirected request.
2530</t>
2531<t>
2532   The value of this field can be either an HTTP-date or an integer number
2533   of seconds (in decimal) after the time of the response.
2534</t>
2535<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2536  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2537</artwork></figure>
2538<t anchor="rule.delta-seconds">
2539  <x:anchor-alias value="delta-seconds"/>
2540   Time spans are non-negative decimal integers, representing time in
2541   seconds.
2542</t>
2543<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2544  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2545</artwork></figure>
2546<t>
2547   Two examples of its use are
2548</t>
2549<figure><artwork type="example">
2550  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2551  Retry-After: 120
2552</artwork></figure>
2553<t>
2554   In the latter example, the delay is 2 minutes.
2555</t>
2556</section>
2557
2558<section title="Server" anchor="header.server">
2559  <iref primary="true" item="Server header field" x:for-anchor=""/>
2560  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2561  <x:anchor-alias value="Server"/>
2562<t>
2563   The "Server" header field contains information about the
2564   software used by the origin server to handle the request.
2565</t>
2566<t>
2567   The field can contain multiple product tokens (&product-tokens;) and
2568   comments (&header-fields;) identifying the server and any significant
2569   subproducts. The product tokens are listed in order of their significance
2570   for identifying the application.
2571</t>
2572<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2573  <x:ref>Server</x:ref> = <x:ref>product</x:ref> *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2574</artwork></figure>
2575<t>
2576   Example:
2577</t>
2578<figure><artwork type="example">
2579  Server: CERN/3.0 libwww/2.17
2580</artwork></figure>
2581<t>
2582   If the response is being forwarded through a proxy, the proxy
2583   application &MUST-NOT; modify the Server header field. Instead, it
2584   &MUST; include a Via field (as described in &header-via;).
2585</t>
2586<x:note>
2587  <t>
2588    <x:h>Note:</x:h> Revealing the specific software version of the server might
2589    allow the server machine to become more vulnerable to attacks
2590    against software that is known to contain security holes. Server
2591    implementors are encouraged to make this field a configurable
2592    option.
2593  </t>
2594</x:note>
2595</section>
2596
2597<section title="User-Agent" anchor="header.user-agent">
2598  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2599  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2600  <x:anchor-alias value="User-Agent"/>
2601<t>
2602   The "User-Agent" header field contains information about the user
2603   agent originating the request. User agents &SHOULD; include this field with
2604   requests.
2605</t>
2606<t>
2607   Typically, it is used for statistical purposes, the tracing of protocol
2608   violations, and tailoring responses to avoid particular user agent
2609   limitations.
2610</t>
2611<t>
2612   The field can contain multiple product tokens (&product-tokens;)
2613   and comments (&header-fields;) identifying the agent and its
2614   significant subproducts. By convention, the product tokens are listed in
2615   order of their significance for identifying the application.
2616</t>
2617<t>
2618   Because this field is usually sent on every request a user agent makes,
2619   implementations are encouraged not to include needlessly fine-grained
2620   detail, and to limit (or even prohibit) the addition of subproducts by third
2621   parties. Overly long and detailed User-Agent field values make requests
2622   larger and can also be used to identify ("fingerprint") the user against
2623   their wishes.
2624</t>
2625<t>
2626   Likewise, implementations are encouraged not to use the product tokens of
2627   other implementations in order to declare compatibility with them, as this
2628   circumvents the purpose of the field. Finally, they are encouraged not to
2629   use comments to identify products; doing so makes the field value more
2630   difficult to parse.
2631</t>
2632<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2633  <x:ref>User-Agent</x:ref> = <x:ref>product</x:ref> *( <x:ref>RWS</x:ref> ( <x:ref>product</x:ref> / <x:ref>comment</x:ref> ) )
2634</artwork></figure>
2635<t>
2636   Example:
2637</t>
2638<figure><artwork type="example">
2639  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2640</artwork></figure>
2641</section>
2642
2643</section>
2644
2645<section title="IANA Considerations" anchor="IANA.considerations">
2646
2647<section title="Method Registry" anchor="method.registration">
2648<t>
2649  The registration procedure for HTTP request methods is defined by
2650  <xref target="method.registry"/> of this document.
2651</t>
2652<t>
2653   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2654   and be populated with the registrations below:
2655</t>
2656<?BEGININC p2-semantics.iana-methods ?>
2657<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2658<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2659   <ttcol>Method</ttcol>
2660   <ttcol>Safe</ttcol>
2661   <ttcol>Reference</ttcol>
2662   <c>CONNECT</c>
2663   <c>no</c>
2664   <c>
2665      <xref target="CONNECT"/>
2666   </c>
2667   <c>DELETE</c>
2668   <c>no</c>
2669   <c>
2670      <xref target="DELETE"/>
2671   </c>
2672   <c>GET</c>
2673   <c>yes</c>
2674   <c>
2675      <xref target="GET"/>
2676   </c>
2677   <c>HEAD</c>
2678   <c>yes</c>
2679   <c>
2680      <xref target="HEAD"/>
2681   </c>
2682   <c>OPTIONS</c>
2683   <c>yes</c>
2684   <c>
2685      <xref target="OPTIONS"/>
2686   </c>
2687   <c>POST</c>
2688   <c>no</c>
2689   <c>
2690      <xref target="POST"/>
2691   </c>
2692   <c>PUT</c>
2693   <c>no</c>
2694   <c>
2695      <xref target="PUT"/>
2696   </c>
2697   <c>TRACE</c>
2698   <c>yes</c>
2699   <c>
2700      <xref target="TRACE"/>
2701   </c>
2702</texttable>
2703<!--(END)-->
2704<?ENDINC p2-semantics.iana-methods ?>
2705</section>
2706
2707<section title="Status Code Registry" anchor="status.code.registration">
2708<t>
2709   The registration procedure for HTTP Status Codes &mdash; previously defined
2710   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2711   by <xref target="status.code.registry"/> of this document.
2712</t>
2713<t>
2714   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2715   shall be updated with the registrations below:
2716</t>
2717<?BEGININC p2-semantics.iana-status-codes ?>
2718<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2719<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2720   <ttcol>Value</ttcol>
2721   <ttcol>Description</ttcol>
2722   <ttcol>Reference</ttcol>
2723   <c>100</c>
2724   <c>Continue</c>
2725   <c>
2726      <xref target="status.100"/>
2727   </c>
2728   <c>101</c>
2729   <c>Switching Protocols</c>
2730   <c>
2731      <xref target="status.101"/>
2732   </c>
2733   <c>200</c>
2734   <c>OK</c>
2735   <c>
2736      <xref target="status.200"/>
2737   </c>
2738   <c>201</c>
2739   <c>Created</c>
2740   <c>
2741      <xref target="status.201"/>
2742   </c>
2743   <c>202</c>
2744   <c>Accepted</c>
2745   <c>
2746      <xref target="status.202"/>
2747   </c>
2748   <c>203</c>
2749   <c>Non-Authoritative Information</c>
2750   <c>
2751      <xref target="status.203"/>
2752   </c>
2753   <c>204</c>
2754   <c>No Content</c>
2755   <c>
2756      <xref target="status.204"/>
2757   </c>
2758   <c>205</c>
2759   <c>Reset Content</c>
2760   <c>
2761      <xref target="status.205"/>
2762   </c>
2763   <c>300</c>
2764   <c>Multiple Choices</c>
2765   <c>
2766      <xref target="status.300"/>
2767   </c>
2768   <c>301</c>
2769   <c>Moved Permanently</c>
2770   <c>
2771      <xref target="status.301"/>
2772   </c>
2773   <c>302</c>
2774   <c>Found</c>
2775   <c>
2776      <xref target="status.302"/>
2777   </c>
2778   <c>303</c>
2779   <c>See Other</c>
2780   <c>
2781      <xref target="status.303"/>
2782   </c>
2783   <c>305</c>
2784   <c>Use Proxy</c>
2785   <c>
2786      <xref target="status.305"/>
2787   </c>
2788   <c>306</c>
2789   <c>(Unused)</c>
2790   <c>
2791      <xref target="status.306"/>
2792   </c>
2793   <c>307</c>
2794   <c>Temporary Redirect</c>
2795   <c>
2796      <xref target="status.307"/>
2797   </c>
2798   <c>400</c>
2799   <c>Bad Request</c>
2800   <c>
2801      <xref target="status.400"/>
2802   </c>
2803   <c>402</c>
2804   <c>Payment Required</c>
2805   <c>
2806      <xref target="status.402"/>
2807   </c>
2808   <c>403</c>
2809   <c>Forbidden</c>
2810   <c>
2811      <xref target="status.403"/>
2812   </c>
2813   <c>404</c>
2814   <c>Not Found</c>
2815   <c>
2816      <xref target="status.404"/>
2817   </c>
2818   <c>405</c>
2819   <c>Method Not Allowed</c>
2820   <c>
2821      <xref target="status.405"/>
2822   </c>
2823   <c>406</c>
2824   <c>Not Acceptable</c>
2825   <c>
2826      <xref target="status.406"/>
2827   </c>
2828   <c>407</c>
2829   <c>Proxy Authentication Required</c>
2830   <c>
2831      <xref target="status.407"/>
2832   </c>
2833   <c>408</c>
2834   <c>Request Timeout</c>
2835   <c>
2836      <xref target="status.408"/>
2837   </c>
2838   <c>409</c>
2839   <c>Conflict</c>
2840   <c>
2841      <xref target="status.409"/>
2842   </c>
2843   <c>410</c>
2844   <c>Gone</c>
2845   <c>
2846      <xref target="status.410"/>
2847   </c>
2848   <c>411</c>
2849   <c>Length Required</c>
2850   <c>
2851      <xref target="status.411"/>
2852   </c>
2853   <c>413</c>
2854   <c>Request Representation Too Large</c>
2855   <c>
2856      <xref target="status.413"/>
2857   </c>
2858   <c>414</c>
2859   <c>URI Too Long</c>
2860   <c>
2861      <xref target="status.414"/>
2862   </c>
2863   <c>415</c>
2864   <c>Unsupported Media Type</c>
2865   <c>
2866      <xref target="status.415"/>
2867   </c>
2868   <c>417</c>
2869   <c>Expectation Failed</c>
2870   <c>
2871      <xref target="status.417"/>
2872   </c>
2873   <c>426</c>
2874   <c>Upgrade Required</c>
2875   <c>
2876      <xref target="status.426"/>
2877   </c>
2878   <c>500</c>
2879   <c>Internal Server Error</c>
2880   <c>
2881      <xref target="status.500"/>
2882   </c>
2883   <c>501</c>
2884   <c>Not Implemented</c>
2885   <c>
2886      <xref target="status.501"/>
2887   </c>
2888   <c>502</c>
2889   <c>Bad Gateway</c>
2890   <c>
2891      <xref target="status.502"/>
2892   </c>
2893   <c>503</c>
2894   <c>Service Unavailable</c>
2895   <c>
2896      <xref target="status.503"/>
2897   </c>
2898   <c>504</c>
2899   <c>Gateway Timeout</c>
2900   <c>
2901      <xref target="status.504"/>
2902   </c>
2903   <c>505</c>
2904   <c>HTTP Version Not Supported</c>
2905   <c>
2906      <xref target="status.505"/>
2907   </c>
2908</texttable>
2909<!--(END)-->
2910<?ENDINC p2-semantics.iana-status-codes ?>
2911</section>
2912<section title="Header Field Registration" anchor="header.field.registration">
2913<t>
2914   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
2915   with the permanent registrations below (see <xref target="RFC3864"/>):
2916</t>
2917<?BEGININC p2-semantics.iana-headers ?>
2918<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2919<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2920   <ttcol>Header Field Name</ttcol>
2921   <ttcol>Protocol</ttcol>
2922   <ttcol>Status</ttcol>
2923   <ttcol>Reference</ttcol>
2924
2925   <c>Allow</c>
2926   <c>http</c>
2927   <c>standard</c>
2928   <c>
2929      <xref target="header.allow"/>
2930   </c>
2931   <c>Expect</c>
2932   <c>http</c>
2933   <c>standard</c>
2934   <c>
2935      <xref target="header.expect"/>
2936   </c>
2937   <c>From</c>
2938   <c>http</c>
2939   <c>standard</c>
2940   <c>
2941      <xref target="header.from"/>
2942   </c>
2943   <c>Location</c>
2944   <c>http</c>
2945   <c>standard</c>
2946   <c>
2947      <xref target="header.location"/>
2948   </c>
2949   <c>Max-Forwards</c>
2950   <c>http</c>
2951   <c>standard</c>
2952   <c>
2953      <xref target="header.max-forwards"/>
2954   </c>
2955   <c>Referer</c>
2956   <c>http</c>
2957   <c>standard</c>
2958   <c>
2959      <xref target="header.referer"/>
2960   </c>
2961   <c>Retry-After</c>
2962   <c>http</c>
2963   <c>standard</c>
2964   <c>
2965      <xref target="header.retry-after"/>
2966   </c>
2967   <c>Server</c>
2968   <c>http</c>
2969   <c>standard</c>
2970   <c>
2971      <xref target="header.server"/>
2972   </c>
2973   <c>User-Agent</c>
2974   <c>http</c>
2975   <c>standard</c>
2976   <c>
2977      <xref target="header.user-agent"/>
2978   </c>
2979</texttable>
2980<!--(END)-->
2981<?ENDINC p2-semantics.iana-headers ?>
2982<t>
2983   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2984</t>
2985</section>
2986</section>
2987
2988<section title="Security Considerations" anchor="security.considerations">
2989<t>
2990   This section is meant to inform application developers, information
2991   providers, and users of the security limitations in HTTP/1.1 as
2992   described by this document. The discussion does not include
2993   definitive solutions to the problems revealed, though it does make
2994   some suggestions for reducing security risks.
2995</t>
2996
2997<section title="Transfer of Sensitive Information" anchor="security.sensitive">
2998<t>
2999   Like any generic data transfer protocol, HTTP cannot regulate the
3000   content of the data that is transferred, nor is there any a priori
3001   method of determining the sensitivity of any particular piece of
3002   information within the context of any given request. Therefore,
3003   applications &SHOULD; supply as much control over this information as
3004   possible to the provider of that information. Four header fields are
3005   worth special mention in this context: Server, Via, Referer and From.
3006</t>
3007<t>
3008   Revealing the specific software version of the server might allow the
3009   server machine to become more vulnerable to attacks against software
3010   that is known to contain security holes. Implementors &SHOULD; make the
3011   Server header field a configurable option.
3012</t>
3013<t>
3014   Proxies which serve as a portal through a network firewall &SHOULD;
3015   take special precautions regarding the transfer of header information
3016   that identifies the hosts behind the firewall. In particular, they
3017   &SHOULD; remove, or replace with sanitized versions, any Via fields
3018   generated behind the firewall.
3019</t>
3020<t>
3021   The Referer header field allows reading patterns to be studied and reverse
3022   links drawn. Although it can be very useful, its power can be abused
3023   if user details are not separated from the information contained in
3024   the Referer. Even when the personal information has been removed, the
3025   Referer header field might indicate a private document's URI whose
3026   publication would be inappropriate.
3027</t>
3028<t>
3029   The information sent in the From field might conflict with the user's
3030   privacy interests or their site's security policy, and hence it
3031   &SHOULD-NOT;  be transmitted without the user being able to disable,
3032   enable, and modify the contents of the field. The user &MUST; be able
3033   to set the contents of this field within a user preference or
3034   application defaults configuration.
3035</t>
3036<t>
3037   We suggest, though do not require, that a convenient toggle interface
3038   be provided for the user to enable or disable the sending of From and
3039   Referer information.
3040</t>
3041<t>
3042   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3043   target="header.server"/>) header fields can sometimes be used to determine
3044   that a specific client or server have a particular security hole which might
3045   be exploited. Unfortunately, this same information is often used for other
3046   valuable purposes for which HTTP currently has no better mechanism.
3047</t>
3048<t>
3049   Furthermore, the User-Agent header field may contain enough entropy to be
3050   used, possibly in conjunction with other material, to uniquely identify the
3051   user.
3052</t>
3053<t>
3054   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3055   that was sent in request header fields within the body of their response.
3056   Clients &SHOULD; be careful with sensitive information, like Cookies,
3057   Authorization credentials, and other header fields that might be used to
3058   collect data from the client.
3059</t> 
3060</section>
3061
3062<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3063<t>
3064   Because the source of a link might be private information or might
3065   reveal an otherwise private information source, it is strongly
3066   recommended that the user be able to select whether or not the
3067   Referer field is sent. For example, a browser client could have a
3068   toggle switch for browsing openly/anonymously, which would
3069   respectively enable/disable the sending of Referer and From
3070   information.
3071</t>
3072<t>
3073   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3074   HTTP request if the referring page was transferred with a secure
3075   protocol.
3076</t>
3077<t>
3078   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3079   sensitive data because that data will be placed in the request-target. Many
3080   existing servers, proxies, and user agents log or display the request-target
3081   in places where it might be visible to third parties. Such services can
3082   use POST-based form submission instead.
3083</t>
3084</section>
3085
3086<section title="Location Headers and Spoofing" anchor="location.spoofing">
3087<t>
3088   If a single server supports multiple organizations that do not trust
3089   one another, then it &MUST; check the values of Location and Content-Location
3090   header fields in responses that are generated under control of
3091   said organizations to make sure that they do not attempt to
3092   invalidate resources over which they have no authority.
3093</t>
3094</section>
3095
3096<section title="Security Considerations for CONNECT">
3097<t>
3098   Since tunneled data is opaque to the proxy, there are additional
3099   risks to tunneling to other well-known or reserved ports.
3100   A HTTP client CONNECTing to port 25 could relay spam
3101   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3102   access to a small number of known ports.
3103</t>
3104</section>
3105
3106</section>
3107
3108<section title="Acknowledgments" anchor="acks">
3109<t>
3110  See &acks;.
3111</t>
3112</section>
3113</middle>
3114<back>
3115
3116<references title="Normative References">
3117
3118<reference anchor="Part1">
3119  <front>
3120    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3121    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3122      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3123      <address><email>fielding@gbiv.com</email></address>
3124    </author>
3125    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3126      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3127      <address><email>jg@freedesktop.org</email></address>
3128    </author>
3129    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3130      <organization abbrev="HP">Hewlett-Packard Company</organization>
3131      <address><email>JeffMogul@acm.org</email></address>
3132    </author>
3133    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3134      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3135      <address><email>henrikn@microsoft.com</email></address>
3136    </author>
3137    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3138      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3139      <address><email>LMM@acm.org</email></address>
3140    </author>
3141    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3142      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3143      <address><email>paulle@microsoft.com</email></address>
3144    </author>
3145    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3146      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3147      <address><email>timbl@w3.org</email></address>
3148    </author>
3149    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3150      <organization abbrev="W3C">World Wide Web Consortium</organization>
3151      <address><email>ylafon@w3.org</email></address>
3152    </author>
3153    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3154      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3155      <address><email>julian.reschke@greenbytes.de</email></address>
3156    </author>
3157    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3158  </front>
3159  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3160  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3161</reference>
3162
3163<reference anchor="Part3">
3164  <front>
3165    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3166    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3167      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3168      <address><email>fielding@gbiv.com</email></address>
3169    </author>
3170    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3171      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3172      <address><email>jg@freedesktop.org</email></address>
3173    </author>
3174    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3175      <organization abbrev="HP">Hewlett-Packard Company</organization>
3176      <address><email>JeffMogul@acm.org</email></address>
3177    </author>
3178    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3179      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3180      <address><email>henrikn@microsoft.com</email></address>
3181    </author>
3182    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3183      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3184      <address><email>LMM@acm.org</email></address>
3185    </author>
3186    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3187      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3188      <address><email>paulle@microsoft.com</email></address>
3189    </author>
3190    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3191      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3192      <address><email>timbl@w3.org</email></address>
3193    </author>
3194    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3195      <organization abbrev="W3C">World Wide Web Consortium</organization>
3196      <address><email>ylafon@w3.org</email></address>
3197    </author>
3198    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3199      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3200      <address><email>julian.reschke@greenbytes.de</email></address>
3201    </author>
3202    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3203  </front>
3204  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3205  <x:source href="p3-payload.xml" basename="p3-payload"/>
3206</reference>
3207
3208<reference anchor="Part4">
3209  <front>
3210    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3211    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3212      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3213      <address><email>fielding@gbiv.com</email></address>
3214    </author>
3215    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3216      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3217      <address><email>jg@freedesktop.org</email></address>
3218    </author>
3219    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3220      <organization abbrev="HP">Hewlett-Packard Company</organization>
3221      <address><email>JeffMogul@acm.org</email></address>
3222    </author>
3223    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3224      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3225      <address><email>henrikn@microsoft.com</email></address>
3226    </author>
3227    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3228      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3229      <address><email>LMM@acm.org</email></address>
3230    </author>
3231    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3232      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3233      <address><email>paulle@microsoft.com</email></address>
3234    </author>
3235    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3236      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3237      <address><email>timbl@w3.org</email></address>
3238    </author>
3239    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3240      <organization abbrev="W3C">World Wide Web Consortium</organization>
3241      <address><email>ylafon@w3.org</email></address>
3242    </author>
3243    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3244      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3245      <address><email>julian.reschke@greenbytes.de</email></address>
3246    </author>
3247    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3248  </front>
3249  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3250  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3251</reference>
3252
3253<reference anchor="Part5">
3254  <front>
3255    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3256    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3257      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3258      <address><email>fielding@gbiv.com</email></address>
3259    </author>
3260    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3261      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3262      <address><email>jg@freedesktop.org</email></address>
3263    </author>
3264    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3265      <organization abbrev="HP">Hewlett-Packard Company</organization>
3266      <address><email>JeffMogul@acm.org</email></address>
3267    </author>
3268    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3269      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3270      <address><email>henrikn@microsoft.com</email></address>
3271    </author>
3272    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3273      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3274      <address><email>LMM@acm.org</email></address>
3275    </author>
3276    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3277      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3278      <address><email>paulle@microsoft.com</email></address>
3279    </author>
3280    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3281      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3282      <address><email>timbl@w3.org</email></address>
3283    </author>
3284    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3285      <organization abbrev="W3C">World Wide Web Consortium</organization>
3286      <address><email>ylafon@w3.org</email></address>
3287    </author>
3288    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3289      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3290      <address><email>julian.reschke@greenbytes.de</email></address>
3291    </author>
3292    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3293  </front>
3294  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3295  <x:source href="p5-range.xml" basename="p5-range"/>
3296</reference>
3297
3298<reference anchor="Part6">
3299  <front>
3300    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3301    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3302      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3303      <address><email>fielding@gbiv.com</email></address>
3304    </author>
3305    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3306      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3307      <address><email>jg@freedesktop.org</email></address>
3308    </author>
3309    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3310      <organization abbrev="HP">Hewlett-Packard Company</organization>
3311      <address><email>JeffMogul@acm.org</email></address>
3312    </author>
3313    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3314      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3315      <address><email>henrikn@microsoft.com</email></address>
3316    </author>
3317    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3318      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3319      <address><email>LMM@acm.org</email></address>
3320    </author>
3321    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3322      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3323      <address><email>paulle@microsoft.com</email></address>
3324    </author>
3325    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3326      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3327      <address><email>timbl@w3.org</email></address>
3328    </author>
3329    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3330      <organization abbrev="W3C">World Wide Web Consortium</organization>
3331      <address><email>ylafon@w3.org</email></address>
3332    </author>
3333    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3334      <address><email>mnot@mnot.net</email></address>
3335    </author>
3336    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3337      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3338      <address><email>julian.reschke@greenbytes.de</email></address>
3339    </author>
3340    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3341  </front>
3342  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3343  <x:source href="p6-cache.xml" basename="p6-cache"/>
3344</reference>
3345
3346<reference anchor="Part7">
3347  <front>
3348    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3349    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3350      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3351      <address><email>fielding@gbiv.com</email></address>
3352    </author>
3353    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3354      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3355      <address><email>jg@freedesktop.org</email></address>
3356    </author>
3357    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3358      <organization abbrev="HP">Hewlett-Packard Company</organization>
3359      <address><email>JeffMogul@acm.org</email></address>
3360    </author>
3361    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3362      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3363      <address><email>henrikn@microsoft.com</email></address>
3364    </author>
3365    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3366      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3367      <address><email>LMM@acm.org</email></address>
3368    </author>
3369    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3370      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3371      <address><email>paulle@microsoft.com</email></address>
3372    </author>
3373    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3374      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3375      <address><email>timbl@w3.org</email></address>
3376    </author>
3377    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3378      <organization abbrev="W3C">World Wide Web Consortium</organization>
3379      <address><email>ylafon@w3.org</email></address>
3380    </author>
3381    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3382      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3383      <address><email>julian.reschke@greenbytes.de</email></address>
3384    </author>
3385    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3386  </front>
3387  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3388  <x:source href="p7-auth.xml" basename="p7-auth"/>
3389</reference>
3390
3391<reference anchor="RFC2119">
3392  <front>
3393    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3394    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3395      <organization>Harvard University</organization>
3396      <address><email>sob@harvard.edu</email></address>
3397    </author>
3398    <date month="March" year="1997"/>
3399  </front>
3400  <seriesInfo name="BCP" value="14"/>
3401  <seriesInfo name="RFC" value="2119"/>
3402</reference>
3403
3404<reference anchor="RFC3986">
3405 <front>
3406  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3407  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3408    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3409    <address>
3410       <email>timbl@w3.org</email>
3411       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3412    </address>
3413  </author>
3414  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3415    <organization abbrev="Day Software">Day Software</organization>
3416    <address>
3417      <email>fielding@gbiv.com</email>
3418      <uri>http://roy.gbiv.com/</uri>
3419    </address>
3420  </author>
3421  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3422    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3423    <address>
3424      <email>LMM@acm.org</email>
3425      <uri>http://larry.masinter.net/</uri>
3426    </address>
3427  </author>
3428  <date month='January' year='2005'></date>
3429 </front>
3430 <seriesInfo name="STD" value="66"/>
3431 <seriesInfo name="RFC" value="3986"/>
3432</reference>
3433
3434<reference anchor="RFC5234">
3435  <front>
3436    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3437    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3438      <organization>Brandenburg InternetWorking</organization>
3439      <address>
3440        <email>dcrocker@bbiw.net</email>
3441      </address> 
3442    </author>
3443    <author initials="P." surname="Overell" fullname="Paul Overell">
3444      <organization>THUS plc.</organization>
3445      <address>
3446        <email>paul.overell@thus.net</email>
3447      </address>
3448    </author>
3449    <date month="January" year="2008"/>
3450  </front>
3451  <seriesInfo name="STD" value="68"/>
3452  <seriesInfo name="RFC" value="5234"/>
3453</reference>
3454
3455</references>
3456
3457<references title="Informative References">
3458
3459<reference anchor="RFC1945">
3460  <front>
3461    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3462    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3463      <organization>MIT, Laboratory for Computer Science</organization>
3464      <address><email>timbl@w3.org</email></address>
3465    </author>
3466    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3467      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3468      <address><email>fielding@ics.uci.edu</email></address>
3469    </author>
3470    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3471      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3472      <address><email>frystyk@w3.org</email></address>
3473    </author>
3474    <date month="May" year="1996"/>
3475  </front>
3476  <seriesInfo name="RFC" value="1945"/>
3477</reference>
3478
3479<reference anchor="RFC2068">
3480  <front>
3481    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3482    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3483      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3484      <address><email>fielding@ics.uci.edu</email></address>
3485    </author>
3486    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3487      <organization>MIT Laboratory for Computer Science</organization>
3488      <address><email>jg@w3.org</email></address>
3489    </author>
3490    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3491      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3492      <address><email>mogul@wrl.dec.com</email></address>
3493    </author>
3494    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3495      <organization>MIT Laboratory for Computer Science</organization>
3496      <address><email>frystyk@w3.org</email></address>
3497    </author>
3498    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3499      <organization>MIT Laboratory for Computer Science</organization>
3500      <address><email>timbl@w3.org</email></address>
3501    </author>
3502    <date month="January" year="1997"/>
3503  </front>
3504  <seriesInfo name="RFC" value="2068"/>
3505</reference>
3506
3507<reference anchor="RFC2616">
3508  <front>
3509    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3510    <author initials="R." surname="Fielding" fullname="R. Fielding">
3511      <organization>University of California, Irvine</organization>
3512      <address><email>fielding@ics.uci.edu</email></address>
3513    </author>
3514    <author initials="J." surname="Gettys" fullname="J. Gettys">
3515      <organization>W3C</organization>
3516      <address><email>jg@w3.org</email></address>
3517    </author>
3518    <author initials="J." surname="Mogul" fullname="J. Mogul">
3519      <organization>Compaq Computer Corporation</organization>
3520      <address><email>mogul@wrl.dec.com</email></address>
3521    </author>
3522    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3523      <organization>MIT Laboratory for Computer Science</organization>
3524      <address><email>frystyk@w3.org</email></address>
3525    </author>
3526    <author initials="L." surname="Masinter" fullname="L. Masinter">
3527      <organization>Xerox Corporation</organization>
3528      <address><email>masinter@parc.xerox.com</email></address>
3529    </author>
3530    <author initials="P." surname="Leach" fullname="P. Leach">
3531      <organization>Microsoft Corporation</organization>
3532      <address><email>paulle@microsoft.com</email></address>
3533    </author>
3534    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3535      <organization>W3C</organization>
3536      <address><email>timbl@w3.org</email></address>
3537    </author>
3538    <date month="June" year="1999"/>
3539  </front>
3540  <seriesInfo name="RFC" value="2616"/>
3541</reference>
3542
3543<reference anchor='RFC2817'>
3544  <front>
3545    <title>Upgrading to TLS Within HTTP/1.1</title>
3546    <author initials='R.' surname='Khare' fullname='R. Khare'>
3547      <organization>4K Associates / UC Irvine</organization>
3548      <address><email>rohit@4K-associates.com</email></address>
3549    </author>
3550    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3551      <organization>Agranat Systems, Inc.</organization>
3552      <address><email>lawrence@agranat.com</email></address>
3553    </author>
3554    <date year='2000' month='May' />
3555  </front>
3556  <seriesInfo name='RFC' value='2817' />
3557</reference>
3558
3559<reference anchor='RFC3864'>
3560  <front>
3561    <title>Registration Procedures for Message Header Fields</title>
3562    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3563      <organization>Nine by Nine</organization>
3564      <address><email>GK-IETF@ninebynine.org</email></address>
3565    </author>
3566    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3567      <organization>BEA Systems</organization>
3568      <address><email>mnot@pobox.com</email></address>
3569    </author>
3570    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3571      <organization>HP Labs</organization>
3572      <address><email>JeffMogul@acm.org</email></address>
3573    </author>
3574    <date year='2004' month='September' />
3575  </front>
3576  <seriesInfo name='BCP' value='90' />
3577  <seriesInfo name='RFC' value='3864' />
3578</reference>
3579
3580<reference anchor='RFC5226'>
3581  <front>
3582    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3583    <author initials='T.' surname='Narten' fullname='T. Narten'>
3584      <organization>IBM</organization>
3585      <address><email>narten@us.ibm.com</email></address>
3586    </author>
3587    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3588      <organization>Google</organization>
3589      <address><email>Harald@Alvestrand.no</email></address>
3590    </author>
3591    <date year='2008' month='May' />
3592  </front>
3593  <seriesInfo name='BCP' value='26' />
3594  <seriesInfo name='RFC' value='5226' />
3595</reference>
3596
3597<reference anchor="RFC5322">
3598  <front>
3599    <title>Internet Message Format</title>
3600    <author initials="P." surname="Resnick" fullname="P. Resnick">
3601      <organization>Qualcomm Incorporated</organization>
3602    </author>
3603    <date year="2008" month="October"/>
3604  </front> 
3605  <seriesInfo name="RFC" value="5322"/>
3606</reference>
3607
3608<reference anchor='RFC5789'>
3609  <front>
3610    <title>PATCH Method for HTTP</title>
3611    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3612      <organization>Linden Lab</organization>
3613    </author>
3614    <author initials='J.' surname='Snell' fullname='J. Snell' />
3615    <date year='2010' month='March' />
3616  </front>
3617  <seriesInfo name='RFC' value='5789' />
3618</reference>
3619
3620<reference anchor="RFC5987">
3621        <front>
3622    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3623    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3624      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3625      <address>
3626        <postal>
3627          <street>Hafenweg 16</street>
3628          <city>Muenster</city><region>NW</region><code>48155</code>
3629          <country>Germany</country>
3630        </postal>
3631        <email>julian.reschke@greenbytes.de</email>     
3632        <uri>http://greenbytes.de/tech/webdav/</uri>   
3633      </address>
3634    </author>
3635    <date month="August" year="2010"/>
3636  </front>
3637  <seriesInfo name="RFC" value="5987"/>
3638</reference>
3639
3640</references>
3641
3642<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3643<t>
3644  This document takes over the Status Code Registry, previously defined
3645  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3646  (<xref target="status.code.registry"/>)
3647</t>
3648<t>
3649  Clarify definition of POST.
3650  (<xref target="POST"/>)
3651</t>
3652<t>
3653  Remove requirement to handle all Content-* header fields; ban use of
3654  Content-Range with PUT.
3655  (<xref target="PUT"/>)
3656</t>
3657<t>
3658  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3659  (<xref target="CONNECT"/>)
3660</t>
3661<t>
3662  Broadened the definition of 203 (Non-Authoritative Information) to include
3663  cases of payload transformations as well.
3664  (<xref target="status.203"/>)
3665</t>
3666<t>
3667  Failed to consider that there are many other request methods that are safe
3668  to automatically redirect, and further that the user agent is able to make
3669  that determination based on the request method semantics.
3670  Furthermore, allow user agents to rewrite the method from POST to GET
3671  for status codes 301 and 302.
3672  (Sections <xref format="counter" target="status.301"/>,
3673  <xref format="counter" target="status.302"/> and
3674  <xref format="counter" target="status.307"/>)
3675</t>
3676<t>
3677  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3678  It used to indicate that the target resource must be accessed through the
3679  proxy given by the Location field. The Location field gave the URI of the
3680  proxy. The recipient was expected to repeat this single request via the proxy.
3681  (<xref target="status.305"/>)
3682</t>
3683<t>
3684  Define status 426 (Upgrade Required) (this was incorporated from
3685  <xref target="RFC2817"/>).
3686  (<xref target="status.426"/>)
3687</t>
3688<t>
3689  Change ABNF productions for header fields to only define the field value.
3690  (<xref target="header.field.definitions"/>)
3691</t>
3692<t>
3693  Reclassify "Allow" as response header field, removing the option to
3694  specify it in a PUT request.
3695  Relax the server requirement on the contents of the Allow header field and
3696  remove requirement on clients to always trust the header field value.
3697  (<xref target="header.allow"/>)
3698</t>
3699<t>
3700  Correct syntax of Location header field to allow URI references (including
3701  relative references and fragments), as referred symbol "absoluteURI" wasn't
3702  what was expected, and add some clarifications as to when use of fragments
3703  would not be appropriate.
3704  (<xref target="header.location"/>)
3705</t>
3706<t>
3707  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3708  extension methods could have used it as well).
3709  (<xref target="header.max-forwards"/>)
3710</t>
3711<t>
3712  Allow Referer field value of "about:blank" as alternative to not specifying it.
3713  (<xref target="header.referer"/>)
3714</t>
3715<t>
3716  In the description of the Server header field, the Via field
3717  was described as a SHOULD. The requirement was and is stated
3718  correctly in the description of the Via header field in &header-via;.
3719  (<xref target="header.server"/>)
3720</t>
3721</section>
3722
3723<?BEGININC p2-semantics.abnf-appendix ?>
3724<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3725<figure>
3726<artwork type="abnf" name="p2-semantics.parsed-abnf">
3727<x:ref>Allow</x:ref> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
3728
3729<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3730
3731<x:ref>From</x:ref> = mailbox
3732
3733<x:ref>HTTP-date</x:ref> = &lt;HTTP-date, defined in [Part1], Section 6.1&gt;
3734
3735<x:ref>Location</x:ref> = URI-reference
3736
3737<x:ref>Max-Forwards</x:ref> = 1*DIGIT
3738<x:ref>Method</x:ref> = token
3739
3740<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
3741
3742<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 1.2.2&gt;
3743<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
3744<x:ref>Referer</x:ref> = absolute-URI / partial-URI
3745<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
3746
3747<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
3748<x:ref>Status-Code</x:ref> = 3DIGIT
3749
3750<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
3751<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
3752
3753<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
3754
3755<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2&gt;
3756
3757<x:ref>delta-seconds</x:ref> = 1*DIGIT
3758
3759<x:ref>expect-params</x:ref> = ";" token [ "=" ( token / quoted-string ) ]
3760<x:ref>expectation</x:ref> = "100-continue" / expectation-extension
3761<x:ref>expectation-extension</x:ref> = token [ "=" ( token / quoted-string )
3762 *expect-params ]
3763
3764<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
3765
3766<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 1.2.2&gt;
3767
3768<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
3769<x:ref>product</x:ref> = &lt;product, defined in [Part1], Section 6.3&gt;
3770
3771<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.3&gt;
3772
3773<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.3&gt;
3774</artwork>
3775</figure>
3776<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
3777; Allow defined but not used
3778; Expect defined but not used
3779; From defined but not used
3780; Location defined but not used
3781; Max-Forwards defined but not used
3782; Reason-Phrase defined but not used
3783; Referer defined but not used
3784; Retry-After defined but not used
3785; Server defined but not used
3786; Status-Code defined but not used
3787; User-Agent defined but not used
3788</artwork></figure></section>
3789<?ENDINC p2-semantics.abnf-appendix ?>
3790
3791<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3792
3793<section title="Since RFC 2616">
3794<t>
3795  Extracted relevant partitions from <xref target="RFC2616"/>.
3796</t>
3797</section>
3798
3799<section title="Since draft-ietf-httpbis-p2-semantics-00">
3800<t>
3801  Closed issues:
3802  <list style="symbols"> 
3803    <t>
3804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3805      "Via is a MUST"
3806      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3807    </t>
3808    <t>
3809      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3810      "Fragments allowed in Location"
3811      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3812    </t>
3813    <t>
3814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3815      "Safe Methods vs Redirection"
3816      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3817    </t>
3818    <t>
3819      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3820      "Revise description of the POST method"
3821      (<eref target="http://purl.org/NET/http-errata#post"/>)
3822    </t>
3823    <t>
3824      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3825      "Normative and Informative references"
3826    </t>
3827    <t>
3828      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3829      "RFC2606 Compliance"
3830    </t>
3831    <t>
3832      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3833      "Informative references"
3834    </t>
3835    <t>
3836      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3837      "Redundant cross-references"
3838    </t>
3839  </list>
3840</t>
3841<t>
3842  Other changes:
3843  <list style="symbols"> 
3844    <t>
3845      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3846    </t>
3847  </list>
3848</t>
3849</section>
3850
3851<section title="Since draft-ietf-httpbis-p2-semantics-01">
3852<t>
3853  Closed issues:
3854  <list style="symbols"> 
3855    <t>
3856      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3857      "PUT side effects"
3858    </t>
3859    <t>
3860      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3861      "Duplicate Host header requirements"
3862    </t>
3863  </list>
3864</t>
3865<t>
3866  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3867  <list style="symbols"> 
3868    <t>
3869      Move "Product Tokens" section (back) into Part 1, as "token" is used
3870      in the definition of the Upgrade header field.
3871    </t>
3872    <t>
3873      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3874    </t>
3875    <t>
3876      Copy definition of delta-seconds from Part6 instead of referencing it.
3877    </t>
3878  </list>
3879</t>
3880</section>
3881
3882<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3883<t>
3884  Closed issues:
3885  <list style="symbols"> 
3886    <t>
3887      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3888      "Requiring Allow in 405 responses"
3889    </t>
3890    <t>
3891      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3892      "Status Code Registry"
3893    </t>
3894    <t>
3895      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3896      "Redirection vs. Location"
3897    </t>
3898    <t>
3899      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3900      "Cacheability of 303 response"
3901    </t>
3902    <t>
3903      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3904      "305 Use Proxy"
3905    </t>
3906    <t>
3907      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3908      "Classification for Allow header"
3909    </t>
3910    <t>
3911      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3912      "PUT - 'store under' vs 'store at'"
3913    </t>
3914  </list>
3915</t>
3916<t>
3917  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3918  <list style="symbols"> 
3919    <t>
3920      Reference RFC 3984, and update header field registrations for headers defined
3921      in this document.
3922    </t>
3923  </list>
3924</t>
3925<t>
3926  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3927  <list style="symbols"> 
3928    <t>
3929      Replace string literals when the string really is case-sensitive (method).
3930    </t>
3931  </list>
3932</t>
3933</section>
3934
3935<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
3936<t>
3937  Closed issues:
3938  <list style="symbols"> 
3939    <t>
3940      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
3941      "OPTIONS request bodies"
3942    </t>
3943    <t>
3944      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
3945      "Description of CONNECT should refer to RFC2817"
3946    </t>
3947    <t>
3948      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
3949      "Location Content-Location reference request/response mixup"
3950    </t>
3951  </list>
3952</t>
3953<t>
3954  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
3955  <list style="symbols"> 
3956    <t>
3957      Added initial proposal for registration process, plus initial
3958      content (non-HTTP/1.1 methods to be added by a separate specification).
3959    </t>
3960  </list>
3961</t>
3962</section>
3963
3964<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
3965<t>
3966  Closed issues:
3967  <list style="symbols"> 
3968    <t>
3969      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
3970      "Content-*"
3971    </t>
3972    <t>
3973      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
3974      "RFC 2822 is updated by RFC 5322"
3975    </t>
3976  </list>
3977</t>
3978<t>
3979  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3980  <list style="symbols"> 
3981    <t>
3982      Use "/" instead of "|" for alternatives.
3983    </t>
3984    <t>
3985      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
3986      whitespace ("OWS") and required whitespace ("RWS").
3987    </t>
3988    <t>
3989      Rewrite ABNFs to spell out whitespace rules, factor out
3990      header field value format definitions.
3991    </t>
3992  </list>
3993</t>
3994</section>
3995
3996<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
3997<t>
3998  Closed issues:
3999  <list style="symbols"> 
4000    <t>
4001      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4002      "Reason-Phrase BNF"
4003    </t>
4004  </list>
4005</t>
4006<t>
4007  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4008  <list style="symbols"> 
4009    <t>
4010      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4011    </t>
4012  </list>
4013</t>
4014</section>
4015
4016<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4017<t>
4018  Closed issues:
4019  <list style="symbols"> 
4020    <t>
4021      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4022      "Clarify when Referer is sent"
4023    </t>
4024    <t>
4025      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4026      "status codes vs methods"
4027    </t>
4028    <t>
4029      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4030      "Do not require "updates" relation for specs that register status codes or method names"
4031    </t>
4032  </list>
4033</t>
4034</section>
4035
4036<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4037<t>
4038  Closed issues:
4039  <list style="symbols"> 
4040    <t>
4041      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4042      "Idempotency"
4043    </t>
4044    <t>
4045      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4046      "TRACE security considerations"
4047    </t>
4048    <t>
4049      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4050      "Clarify rules for determining what entities a response carries"
4051    </t>
4052    <t>
4053      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4054      "update note citing RFC 1945 and 2068"
4055    </t>
4056    <t>
4057      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4058      "update note about redirect limit"
4059    </t>
4060    <t>
4061      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4062      "Location header ABNF should use 'URI'"
4063    </t>
4064    <t>
4065      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4066      "fragments in Location vs status 303"
4067    </t>
4068    <t>
4069      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4070      "move IANA registrations for optional status codes"
4071    </t>
4072  </list>
4073</t>
4074<t>
4075  Partly resolved issues:
4076  <list style="symbols"> 
4077    <t>
4078      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4079      "Are OPTIONS and TRACE safe?"
4080    </t>
4081  </list>
4082</t>
4083</section>
4084
4085<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4086<t>
4087  Closed issues:
4088  <list style="symbols"> 
4089    <t>
4090      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4091      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4092      status codes when fixing this previously)
4093    </t>
4094  </list>
4095</t>
4096</section>
4097
4098<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4099<t>
4100  Closed issues:
4101  <list style="symbols"> 
4102    <t>
4103      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4104      "Fragment combination / precedence during redirects"
4105    </t>
4106  </list>
4107</t>
4108<t>
4109  Partly resolved issues:
4110  <list style="symbols"> 
4111    <t>
4112      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4113      "Location header payload handling"
4114    </t>
4115    <t>
4116      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4117      "Term for the requested resource's URI"
4118    </t>
4119  </list>
4120</t>
4121</section>
4122
4123<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4124<t>
4125  Closed issues:
4126  <list style="symbols"> 
4127    <t>
4128      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4129      "Clarify 'Requested Variant'"
4130    </t>
4131    <t>
4132      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4133      "Clarify entity / representation / variant terminology"
4134    </t>
4135    <t>
4136      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4137      "Methods and Caching"
4138    </t>
4139    <t>
4140      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4141      "OPTIONS vs Max-Forwards"
4142    </t>
4143    <t>
4144      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4145      "Status codes and caching"
4146    </t>
4147    <t>
4148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4149      "consider removing the 'changes from 2068' sections"
4150    </t>
4151  </list>
4152</t>
4153</section>
4154
4155<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4156<t>
4157  Closed issues:
4158  <list style="symbols"> 
4159    <t>
4160      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4161      "Considerations for new status codes"
4162    </t>
4163    <t>
4164      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4165      "Considerations for new methods"
4166    </t>
4167    <t>
4168      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4169      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4170    </t>
4171  </list>
4172</t>
4173</section>
4174
4175<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4176<t>
4177  Closed issues:
4178  <list style="symbols"> 
4179    <t>
4180      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4181      "Fragment combination / precedence during redirects" (added warning
4182      about having a fragid on the redirect may cause inconvenience in
4183      some cases)
4184    </t>
4185    <t>
4186      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4187      "Content-* vs. PUT"
4188    </t>
4189    <t>
4190      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4191      "205 Bodies"
4192    </t>
4193    <t>
4194      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4195      "Understanding Content-* on non-PUT requests"
4196    </t>
4197    <t>
4198      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4199      "Content-*"
4200    </t>
4201    <t>
4202      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4203      "Header type defaulting"
4204    </t>
4205    <t>
4206      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4207      "PUT - 'store under' vs 'store at'"
4208    </t>
4209    <t>
4210      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4211      "duplicate ABNF for Reason-Phrase"
4212    </t>
4213    <t>
4214      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4215      "Note special status of Content-* prefix in header registration procedures"
4216    </t>
4217    <t>
4218      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4219      "Max-Forwards vs extension methods"
4220    </t>
4221    <t>
4222      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4223      "What is the value space of HTTP status codes?" (actually fixed in
4224      draft-ietf-httpbis-p2-semantics-11)
4225    </t>
4226    <t>
4227      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4228      "Header Classification"
4229    </t>
4230    <t>
4231      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4232      "PUT side effect: invalidation or just stale?"
4233    </t>
4234    <t>
4235      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4236      "proxies not supporting certain methods"
4237    </t>
4238    <t>
4239      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4240      "Migrate CONNECT from RFC2817 to p2"
4241    </t>
4242    <t>
4243      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4244      "Migrate Upgrade details from RFC2817"
4245    </t>
4246    <t>
4247      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4248      "clarify PUT semantics'"
4249    </t>
4250    <t>
4251      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4252      "duplicate ABNF for 'Method'"
4253    </t>
4254    <t>
4255      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4256      "untangle ABNFs for header fields"
4257    </t>
4258  </list>
4259</t>
4260</section>
4261
4262<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4263<t>
4264  Closed issues:
4265  <list style="symbols"> 
4266    <t>
4267      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4268      "untangle ABNFs for header fields"
4269    </t>
4270    <t>
4271      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4272      "message-body in CONNECT request"
4273    </t>
4274  </list>
4275</t>
4276</section>
4277
4278<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4279<t>
4280  Closed issues:
4281  <list style="symbols"> 
4282    <t>
4283      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4284      "Clarify status code for rate limiting"
4285    </t>
4286    <t>
4287      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4288      "clarify 403 forbidden"
4289    </t>
4290    <t>
4291      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4292      "Clarify 203 Non-Authoritative Information"
4293    </t>
4294    <t>
4295      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4296      "update default reason phrase for 413"
4297    </t>
4298  </list>
4299</t>
4300</section>
4301
4302<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4303<t>
4304  Closed issues:
4305  <list style="symbols"> 
4306    <t>
4307      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4308      "Strength of requirements on Accept re: 406"
4309    </t>
4310    <t>
4311      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4312      "400 response isn't generic"
4313    </t>
4314  </list>
4315</t>
4316</section>
4317
4318<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4319<t>
4320  Closed issues:
4321  <list style="symbols"> 
4322    <t>
4323      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4324      "Redirects and non-GET methods"
4325    </t>
4326    <t>
4327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4328      "clarify 303 redirect on HEAD"
4329    </t>
4330  </list>
4331</t>
4332<t>
4333  Work-in-progress:
4334  <list style="symbols"> 
4335    <t>
4336      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4337      "Considerations for new headers"
4338    </t>
4339  </list>
4340</t>
4341</section>
4342
4343</section>
4344
4345</back>
4346</rfc>
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