source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1435

Last change on this file since 1435 was 1435, checked in by fielding@…, 8 years ago

(editorial) Remove sections and ABNF defining Request and Response and
move status code semantics to p2. Add more xrefs to architecture intro.

  • Property svn:eol-style set to native
File size: 177.7 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "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   The first digit of the Status-Code defines the class of response. The
1332   last two digits do not have any categorization role. There are 5
1333   values for the first digit:
1334  <list style="symbols">
1335    <t>
1336      1xx: Informational - Request received, continuing process
1337    </t>
1338    <t>
1339      2xx: Success - The action was successfully received,
1340        understood, and accepted
1341    </t>
1342    <t>
1343      3xx: Redirection - Further action must be taken in order to
1344        complete the request
1345    </t>
1346    <t>
1347      4xx: Client Error - The request contains bad syntax or cannot
1348        be fulfilled
1349    </t>
1350    <t>
1351      5xx: Server Error - The server failed to fulfill an apparently
1352        valid request
1353    </t>
1354  </list>
1355</t>
1356<t>
1357   Each Status-Code is described below, including any metadata required
1358   in the response.
1359</t>
1360
1361<section title="Informational 1xx" anchor="status.1xx">
1362<t>
1363   This class of status code indicates a provisional response,
1364   consisting only of the Status-Line and optional header fields, and is
1365   terminated by an empty line. There are no required header fields for this
1366   class of status code. Since HTTP/1.0 did not define any 1xx status
1367   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1368   except under experimental conditions.
1369</t>
1370<t>
1371   A client &MUST; be prepared to accept one or more 1xx status responses
1372   prior to a regular response, even if the client does not expect a 100
1373   (Continue) status message. Unexpected 1xx status responses &MAY; be
1374   ignored by a user agent.
1375</t>
1376<t>
1377   Proxies &MUST; forward 1xx responses, unless the connection between the
1378   proxy and its client has been closed, or unless the proxy itself
1379   requested the generation of the 1xx response. (For example, if a
1380   proxy adds a "Expect: 100-continue" field when it forwards a request,
1381   then it need not forward the corresponding 100 (Continue)
1382   response(s).)
1383</t>
1384
1385<section title="100 Continue" anchor="status.100">
1386  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1387  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1388<t>
1389   The client &SHOULD; continue with its request. This interim response is
1390   used to inform the client that the initial part of the request has
1391   been received and has not yet been rejected by the server. The client
1392   &SHOULD; continue by sending the remainder of the request or, if the
1393   request has already been completed, ignore this response. The server
1394   &MUST; send a final response after the request has been completed. See
1395   &use100; for detailed discussion of the use and handling of this
1396   status code.
1397</t>
1398</section>
1399
1400<section title="101 Switching Protocols" anchor="status.101">
1401  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1402  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1403<t>
1404   The server understands and is willing to comply with the client's
1405   request, via the Upgrade message header field (&header-upgrade;), for a
1406   change in the application protocol being used on this connection. The
1407   server will switch protocols to those defined by the response's
1408   Upgrade header field immediately after the empty line which
1409   terminates the 101 response.
1410</t>
1411<t>
1412   The protocol &SHOULD; be switched only when it is advantageous to do
1413   so. For example, switching to a newer version of HTTP is advantageous
1414   over older versions, and switching to a real-time, synchronous
1415   protocol might be advantageous when delivering resources that use
1416   such features.
1417</t>
1418</section>
1419</section>
1420
1421<section title="Successful 2xx" anchor="status.2xx">
1422<t>
1423   This class of status code indicates that the client's request was
1424   successfully received, understood, and accepted.
1425</t>
1426
1427<section title="200 OK" anchor="status.200">
1428  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1429  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1430<t>
1431   The request has succeeded. The payload returned with the response
1432   is dependent on the method used in the request, for example:
1433  <list style="hanging">
1434    <t hangText="GET">
1435      a representation of the target resource is sent in the response;
1436    </t>
1437    <t hangText="HEAD">
1438      the same representation as GET, except without the message-body;
1439    </t>
1440    <t hangText="POST">
1441      a representation describing or containing the result of the action;
1442    </t>
1443    <t hangText="TRACE">
1444      a representation containing the request message as received by the
1445      end server.
1446    </t>
1447  </list>
1448</t>
1449<t>
1450   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1451   freshness for 200 responses.
1452</t>
1453</section>
1454
1455<section title="201 Created" anchor="status.201">
1456  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1457  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1458<t>
1459   The request has been fulfilled and has resulted in a new resource being
1460   created. The newly created resource can be referenced by the URI(s)
1461   returned in the payload of the response, with the most specific URI
1462   for the resource given by a Location header field. The response
1463   &SHOULD; include a payload containing a list of resource
1464   characteristics and location(s) from which the user or user agent can
1465   choose the one most appropriate. The payload format is specified by
1466   the media type given in the Content-Type header field. The origin
1467   server &MUST; create the resource before returning the 201 status code.
1468   If the action cannot be carried out immediately, the server &SHOULD;
1469   respond with 202 (Accepted) response instead.
1470</t>
1471<t>
1472   A 201 response &MAY; contain an ETag response header field indicating
1473   the current value of the entity-tag for the representation of the resource
1474   just created (see &header-etag;).
1475</t>
1476</section>
1477
1478<section title="202 Accepted" anchor="status.202">
1479  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1480  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1481<t>
1482   The request has been accepted for processing, but the processing has
1483   not been completed.  The request might or might not eventually be
1484   acted upon, as it might be disallowed when processing actually takes
1485   place. There is no facility for re-sending a status code from an
1486   asynchronous operation such as this.
1487</t>
1488<t>
1489   The 202 response is intentionally non-committal. Its purpose is to
1490   allow a server to accept a request for some other process (perhaps a
1491   batch-oriented process that is only run once per day) without
1492   requiring that the user agent's connection to the server persist
1493   until the process is completed. The representation returned with this
1494   response &SHOULD; include an indication of the request's current status
1495   and either a pointer to a status monitor or some estimate of when the
1496   user can expect the request to be fulfilled.
1497</t>
1498</section>
1499
1500<section title="203 Non-Authoritative Information" anchor="status.203">
1501  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1502  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1503<t>
1504   The representation in the response has been transformed or otherwise
1505   modified by a transforming proxy (&intermediaries;).  Note that the
1506   behaviour of transforming intermediaries is controlled by the no-transform
1507   Cache-Control directive (&header-cache-control;).
1508</t>
1509<t>
1510   This status code is only appropriate when the response status code would
1511   have been 200 (OK) otherwise. When the status code before transformation
1512   would have been different, the 214 Transformation Applied warn-code
1513   (&header-warning;) is appropriate.
1514</t>
1515<t>
1516   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1517   freshness for 203 responses.
1518</t>
1519</section>
1520
1521<section title="204 No Content" anchor="status.204">
1522  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1523  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1524<t>
1525   The 204 (No Content) status code indicates that the server has
1526   successfully fulfilled the request and that there is no additional
1527   content to return in the response payload body.  Metadata in the
1528   response header fields refer to the target resource and its current
1529   representation after the requested action.
1530</t>
1531<t>
1532   For example, if a 204 status code is received in response to a PUT
1533   request and the response contains an ETag header field, then the PUT
1534   was successful and the ETag field-value contains the entity-tag for
1535   the new representation of that target resource.
1536</t>
1537<t>
1538   The 204 response allows a server to indicate that the action has been
1539   successfully applied to the target resource while implying that the
1540   user agent &SHOULD-NOT; traverse away from its current "document view"
1541   (if any).  The server assumes that the user agent will provide some
1542   indication of the success to its user, in accord with its own interface,
1543   and apply any new or updated metadata in the response to the active
1544   representation.
1545</t>
1546<t>
1547   For example, a 204 status code is commonly used with document editing
1548   interfaces corresponding to a "save" action, such that the document
1549   being saved remains available to the user for editing. It is also
1550   frequently used with interfaces that expect automated data transfers
1551   to be prevalent, such as within distributed version control systems.
1552</t>
1553<t>
1554   The 204 response &MUST-NOT; include a message-body, and thus is always
1555   terminated by the first empty line after the header fields.
1556</t>
1557</section>
1558
1559<section title="205 Reset Content" anchor="status.205">
1560  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1561  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1562<t>
1563   The server has fulfilled the request and the user agent &SHOULD; reset
1564   the document view which caused the request to be sent. This response
1565   is primarily intended to allow input for actions to take place via
1566   user input, followed by a clearing of the form in which the input is
1567   given so that the user can easily initiate another input action.
1568</t>
1569<t>   
1570   The message-body included with the response &MUST; be empty. Note that
1571   receivers still need to parse the response according to the algorithm defined
1572   in &message-body;.
1573</t>
1574</section>
1575
1576<section title="206 Partial Content" anchor="status.206">
1577  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1578  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1579  <rdf:Description>
1580    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
1581  </rdf:Description>
1582<t>
1583   The server has fulfilled the partial GET request for the resource
1584   and the enclosed payload is a partial representation as defined in &status-206;.
1585</t>
1586<t>
1587   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1588   freshness for 206 responses.
1589</t>
1590</section>
1591</section>
1592
1593<section title="Redirection 3xx" anchor="status.3xx">
1594<t>
1595   This class of status code indicates that further action needs to be
1596   taken by the user agent in order to fulfill the request.  If the required
1597   action involves a subsequent HTTP request, it &MAY; be carried out by the
1598   user agent without interaction with the user if and only if the method used
1599   in the second request is known to be "safe", as defined in
1600   <xref target="safe.methods"/>.
1601</t>
1602<t>
1603   There are several types of redirects:
1604   <list style="numbers">
1605      <x:lt>
1606        <t>
1607          Redirects of the request to another URI, either temporarily or
1608          permanently. The new URI is specified in the Location header field.
1609          In this specification, the status codes 301 (Moved Permanently),
1610          302 (Found), and 307 (Temporary Redirect) fall under this category.
1611        </t>
1612      </x:lt>
1613      <x:lt>
1614        <t>
1615          Redirection to a new location that represents an indirect response to
1616          the request, such as the result of a POST operation to be retrieved
1617          with a subsequent GET request. This is status code 303 (See Other).
1618        </t>
1619      </x:lt>
1620      <x:lt>
1621        <t>
1622          Redirection offering a choice of matching resources for use by
1623          agent-driven content negotiation (&agent-driven-negotiation;). This
1624          is status code 300 (Multiple Choices).
1625        </t>
1626      </x:lt>
1627      <x:lt>
1628        <t>
1629          Other kinds of redirection, such as to a cached result (status code 304
1630          (Not Modified)).
1631        </t>
1632      </x:lt>
1633   </list>
1634</t>
1635<x:note>
1636  <t>
1637    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1638    and 302 (Found) were defined for the first type of redirect, and the second
1639    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1640    However it turned out that web forms using POST expected redirects to change
1641    the operation for the subsequent request to retrieval (GET). To address this
1642    use case, HTTP/1.1 introduced the second type of redirect with the status
1643    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1644    As user agents did not change their behavior to maintain backwards
1645    compatibility, the first revision of HTTP/1.1 added yet another status code,
1646    307 (Temporary Redirect), for which the backwards compatibility problems did
1647    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1648    Over 10 years later, most user agents still do method rewriting for
1649    status codes 301 and 302, therefore this specification makes that behavior
1650    compliant in case the original request was POST.
1651  </t>
1652</x:note>
1653<t>
1654   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1655   "infinite" redirection loops).
1656</t>
1657<x:note>
1658  <t>
1659    <x:h>Note:</x:h> An earlier version of this specification recommended a
1660    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1661    Content developers need to be aware that some clients might
1662    implement such a fixed limitation.
1663  </t>
1664</x:note>
1665
1666<section title="300 Multiple Choices" anchor="status.300">
1667  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1668  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1669<t>
1670   The target resource has more than one
1671   representation, each with its own specific location, and agent-driven
1672   negotiation information (&content-negotiation;) is being provided so that
1673   the user (or user agent) can select a preferred representation by
1674   redirecting its request to that location.
1675</t>
1676<t>
1677   Unless it was a HEAD request, the response &SHOULD; include a representation
1678   containing a list of representation metadata and location(s) from
1679   which the user or user agent can choose the one most appropriate. The
1680   data format is specified by the media type given in the Content-Type
1681   header field. Depending upon the format and the capabilities of
1682   the user agent, selection of the most appropriate choice &MAY; be
1683   performed automatically. However, this specification does not define
1684   any standard for such automatic selection.
1685</t>
1686<t>
1687   If the server has a preferred choice of representation, it &SHOULD;
1688   include the specific URI for that representation in the Location
1689   field; user agents &MAY; use the Location field value for automatic
1690   redirection.
1691</t>
1692<t>
1693   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1694   freshness for 300 responses.
1695</t>
1696
1697</section>
1698
1699<section title="301 Moved Permanently" anchor="status.301">
1700  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1701  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1702<t>
1703   The target resource has been assigned a new permanent URI and any
1704   future references to this resource &SHOULD; use one of the returned
1705   URIs.  Clients with link editing capabilities ought to automatically
1706   re-link references to the effective request URI to one or more of the new
1707   references returned by the server, where possible.
1708</t>
1709<t>
1710   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1711   freshness for 301 responses.
1712</t>
1713<t>
1714   The new permanent URI &SHOULD; be given by the Location field in the
1715   response. Unless the request method was HEAD, the representation of the
1716   response &SHOULD; contain a short hypertext note with a hyperlink to
1717   the new URI(s).
1718</t>
1719<t>
1720   If the 301 status code is received in response to a request method
1721   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1722   then the request &MAY; be automatically redirected by the user agent without
1723   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1724   request unless it can be confirmed by the user, since this might
1725   change the conditions under which the request was issued.
1726</t>
1727<x:note>
1728  <t>
1729    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1730    request method from POST to GET for the subsequent request. If this
1731    behavior is undesired, status code 307 (Temporary Redirect) can be used
1732    instead.
1733  </t>
1734</x:note>
1735</section>
1736
1737<section title="302 Found" anchor="status.302">
1738  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1739  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1740<t>
1741   The target resource resides temporarily under a different URI.
1742   Since the redirection might be altered on occasion, the client &SHOULD;
1743   continue to use the effective request URI for future requests.
1744</t>
1745<t>
1746   The temporary URI &SHOULD; be given by the Location field in the
1747   response. Unless the request method was HEAD, the representation of the
1748   response &SHOULD; contain a short hypertext note with a hyperlink to
1749   the new URI(s).
1750</t>
1751<t>
1752   If the 302 status code is received in response to a request method
1753   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1754   then the request &MAY; be automatically redirected by the user agent without
1755   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1756   request unless it can be confirmed by the user, since this might
1757   change the conditions under which the request was issued.
1758</t>
1759<x:note>
1760  <t>
1761    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1762    request method from POST to GET for the subsequent request. If this
1763    behavior is undesired, status code 307 (Temporary Redirect) can be used
1764    instead.
1765    <cref anchor="issue312">but see <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/312"/></cref>
1766  </t>
1767</x:note>
1768</section>
1769
1770<section title="303 See Other" anchor="status.303">
1771  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1772  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1773<t>
1774   The 303 status code indicates that the server is redirecting the
1775   user agent to a different resource, as indicated by a URI in the
1776   Location header field, that is intended to provide an indirect
1777   response to the original request.  In order to satisfy the original
1778   request, a user agent &SHOULD; perform a retrieval request using the
1779   Location URI (a GET or HEAD request if using HTTP), which
1780   may itself be redirected further, and present the eventual result as an
1781   answer to the original request.
1782   Note that the new URI in the Location header field is not considered
1783   equivalent to the effective request URI.
1784</t>
1785<t>
1786   This status code is generally applicable to any HTTP method.  It is
1787   primarily used to allow the output of a POST action to redirect
1788   the user agent to a selected resource, since doing so provides the
1789   information corresponding to the POST response in a form that
1790   can be separately identified, bookmarked, and cached independent
1791   of the original request.
1792</t>
1793<t>
1794   A 303 response to a GET request indicates that the requested
1795   resource does not have a representation of its own that can be
1796   transferred by the server over HTTP.  The Location URI indicates a
1797   resource that is descriptive of the target resource, such that the
1798   follow-on representation might be useful to recipients without
1799   implying that it adequately represents the target resource.
1800   Note that answers to the questions of what can be represented, what
1801   representations are adequate, and what might be a useful description
1802   are outside the scope of HTTP and thus entirely determined by the
1803   URI owner(s).
1804</t>
1805<t>
1806   Except for responses to a HEAD request, the representation of a 303
1807   response &SHOULD; contain a short hypertext note with a hyperlink
1808   to the Location URI.
1809</t>
1810</section>
1811
1812<section title="304 Not Modified" anchor="status.304">
1813  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1814  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1815  <rdf:Description>
1816    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
1817  </rdf:Description>
1818<t>
1819   The response to the request has not been modified since the conditions
1820   indicated by the client's conditional GET request, as defined in &status-304;.
1821</t>
1822</section>
1823
1824<section title="305 Use Proxy" anchor="status.305">
1825  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1826  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1827<t>
1828   The 305 status code was defined in a previous version of this specification
1829   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1830</t>
1831</section>
1832
1833<section title="306 (Unused)" anchor="status.306">
1834  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1835  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1836<t>
1837   The 306 status code was used in a previous version of the
1838   specification, is no longer used, and the code is reserved.
1839</t>
1840</section>
1841
1842<section title="307 Temporary Redirect" anchor="status.307">
1843  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1844  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1845<t>
1846   The target resource resides temporarily under a different URI.
1847   Since the redirection can change over time, the client &SHOULD;
1848   continue to use the effective request URI for future requests.
1849</t>
1850<t>
1851   The temporary URI &SHOULD; be given by the Location field in the
1852   response. Unless the request method was HEAD, the representation of the
1853   response &SHOULD; contain a short hypertext note with a hyperlink to
1854   the new URI(s), since many pre-HTTP/1.1 user agents do not
1855   understand the 307 status code. Therefore, the note &SHOULD; contain the
1856   information necessary for a user to repeat the original request on
1857   the new URI.
1858</t>
1859<t>
1860   If the 307 status code is received in response to a request method
1861   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1862   then the request &MAY; be automatically redirected by the user agent without
1863   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1864   request unless it can be confirmed by the user, since this might
1865   change the conditions under which the request was issued.
1866</t>
1867</section>
1868</section>
1869
1870<section title="Client Error 4xx" anchor="status.4xx">
1871<t>
1872   The 4xx class of status code is intended for cases in which the
1873   client seems to have erred. Except when responding to a HEAD request,
1874   the server &SHOULD; include a representation containing an explanation of the
1875   error situation, and whether it is a temporary or permanent
1876   condition. These status codes are applicable to any request method.
1877   User agents &SHOULD; display any included representation to the user.
1878</t>
1879<t>
1880   If the client is sending data, a server implementation using TCP
1881   &SHOULD; be careful to ensure that the client acknowledges receipt of
1882   the packet(s) containing the response, before the server closes the
1883   input connection. If the client continues sending data to the server
1884   after the close, the server's TCP stack will send a reset packet to
1885   the client, which might erase the client's unacknowledged input buffers
1886   before they can be read and interpreted by the HTTP application.
1887</t>
1888
1889<section title="400 Bad Request" anchor="status.400">
1890  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1891  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1892<t>
1893   The server cannot or will not process the request, due to a client error (e.g.,
1894   malformed syntax).</t>
1895</section>
1896
1897<section title="401 Unauthorized" anchor="status.401">
1898  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1899  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1900  <rdf:Description>
1901    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part7</redirects-to>
1902  </rdf:Description>
1903<t>
1904   The request requires user authentication (see &status-401;).
1905</t>
1906</section>
1907
1908<section title="402 Payment Required" anchor="status.402">
1909  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1910  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1911<t>
1912   This code is reserved for future use.
1913</t>
1914</section>
1915
1916<section title="403 Forbidden" anchor="status.403">
1917  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1918  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1919<t>
1920   The server understood the request, but refuses to authorize it. Providing
1921   different user authentication credentials might be successful, but any
1922   credentials that were provided in the request are insufficient. The request
1923   &SHOULD-NOT; be repeated with the same credentials.
1924</t>
1925<t>
1926   If the request method was not HEAD and the server wishes to make
1927   public why the request has not been fulfilled, it &SHOULD; describe the
1928   reason for the refusal in the representation.  If the server does not wish to
1929   make this information available to the client, the status code 404
1930   (Not Found) &MAY; be used instead.
1931</t>
1932</section>
1933
1934<section title="404 Not Found" anchor="status.404">
1935  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1936  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1937<t>
1938   The server has not found anything matching the effective request URI. No
1939   indication is given of whether the condition is temporary or
1940   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1941   knows, through some internally configurable mechanism, that an old
1942   resource is permanently unavailable and has no forwarding address.
1943   This status code is commonly used when the server does not wish to
1944   reveal exactly why the request has been refused, or when no other
1945   response is applicable.
1946</t>
1947</section>
1948
1949<section title="405 Method Not Allowed" anchor="status.405">
1950  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1951  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1952<t>
1953   The method specified in the Request-Line is not allowed for the target
1954   resource. The response &MUST; include an Allow header field containing a
1955   list of valid methods for the requested resource.
1956</t>
1957</section>
1958
1959<section title="406 Not Acceptable" anchor="status.406">
1960  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1961  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1962<t>
1963   The resource identified by the request is only capable of generating
1964   response representations which have content characteristics not acceptable
1965   according to the Accept and Accept-* header fields sent in the request
1966   (see &p3-header-fields;).
1967</t>
1968<t>
1969   Unless it was a HEAD request, the response &SHOULD; include a representation
1970   containing a list of available representation characteristics and location(s)
1971   from which the user or user agent can choose the one most
1972   appropriate. The data format is specified by the media type given
1973   in the Content-Type header field. Depending upon the format and the
1974   capabilities of the user agent, selection of the most appropriate
1975   choice &MAY; be performed automatically. However, this specification
1976   does not define any standard for such automatic selection.
1977</t>
1978<x:note>
1979  <t>
1980    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1981    not acceptable according to the accept header fields sent in the
1982    request. In some cases, this might even be preferable to sending a
1983    406 response. User agents are encouraged to inspect the header fields of
1984    an incoming response to determine if it is acceptable.
1985  </t>
1986</x:note>
1987<t>
1988   If the response could be unacceptable, a user agent &SHOULD;
1989   temporarily stop receipt of more data and query the user for a
1990   decision on further actions.
1991</t>
1992</section>
1993
1994<section title="407 Proxy Authentication Required" anchor="status.407">
1995  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
1996  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
1997<t>
1998   This code is similar to 401 (Unauthorized), but indicates that the
1999   client must first authenticate itself with the proxy (see &status-407;).
2000</t>
2001</section>
2002
2003<section title="408 Request Timeout" anchor="status.408">
2004  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
2005  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
2006<t>
2007   The client did not produce a request within the time that the server
2008   was prepared to wait. The client &MAY; repeat the request without
2009   modifications at any later time.
2010</t>
2011</section>
2012
2013<section title="409 Conflict" anchor="status.409">
2014  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
2015  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
2016<t>
2017   The request could not be completed due to a conflict with the current
2018   state of the resource. This code is only allowed in situations where
2019   it is expected that the user might be able to resolve the conflict
2020   and resubmit the request. The response body &SHOULD; include enough
2021   information for the user to recognize the source of the conflict.
2022   Ideally, the response representation would include enough information for the
2023   user or user agent to fix the problem; however, that might not be
2024   possible and is not required.
2025</t>
2026<t>
2027   Conflicts are most likely to occur in response to a PUT request. For
2028   example, if versioning were being used and the representation being PUT
2029   included changes to a resource which conflict with those made by an
2030   earlier (third-party) request, the server might use the 409 response
2031   to indicate that it can't complete the request. In this case, the
2032   response representation would likely contain a list of the differences
2033   between the two versions in a format defined by the response
2034   Content-Type.
2035</t>
2036</section>
2037
2038<section title="410 Gone" anchor="status.410">
2039  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
2040  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
2041<t>
2042   The target resource is no longer available at the server and no
2043   forwarding address is known. This condition is expected to be
2044   considered permanent. Clients with link editing capabilities &SHOULD;
2045   delete references to the effective request URI after user approval. If the
2046   server does not know, or has no facility to determine, whether or not
2047   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
2048   used instead.
2049</t>
2050<t>
2051   The 410 response is primarily intended to assist the task of web
2052   maintenance by notifying the recipient that the resource is
2053   intentionally unavailable and that the server owners desire that
2054   remote links to that resource be removed. Such an event is common for
2055   limited-time, promotional services and for resources belonging to
2056   individuals no longer working at the server's site. It is not
2057   necessary to mark all permanently unavailable resources as "gone" or
2058   to keep the mark for any length of time &mdash; that is left to the
2059   discretion of the server owner.
2060</t>
2061<t>
2062   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
2063   for 410 responses.
2064</t>
2065
2066</section>
2067
2068<section title="411 Length Required" anchor="status.411">
2069  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
2070  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
2071<t>
2072   The server refuses to accept the request without a defined Content-Length.
2073   The client &MAY; repeat the request if it adds a valid
2074   Content-Length header field containing the length of the message-body
2075   in the request message.
2076</t>
2077</section>
2078
2079<section title="412 Precondition Failed" anchor="status.412">
2080  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
2081  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
2082  <rdf:Description>
2083    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
2084  </rdf:Description>
2085<t>
2086   The precondition given in one or more of the header fields
2087   evaluated to false when it was tested on the server, as defined in
2088   &status-412;.
2089</t>
2090</section>
2091
2092<section title="413 Request Representation Too Large" anchor="status.413">
2093  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2094  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2095<t>
2096   The server is refusing to process a request because the request
2097   representation is larger than the server is willing or able to process. The
2098   server &MAY; close the connection to prevent the client from continuing
2099   the request.
2100</t>
2101<t>
2102   If the condition is temporary, the server &SHOULD; include a Retry-After
2103   header field to indicate that it is temporary and after what
2104   time the client &MAY; try again.
2105</t>
2106</section>
2107
2108<section title="414 URI Too Long" anchor="status.414">
2109  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2110  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
2111<t>
2112   The server is refusing to service the request because the effective request URI
2113   is longer than the server is willing to interpret. This rare
2114   condition is only likely to occur when a client has improperly
2115   converted a POST request to a GET request with long query
2116   information, when the client has descended into a URI "black hole" of
2117   redirection (e.g., a redirected URI prefix that points to a suffix of
2118   itself), or when the server is under attack by a client attempting to
2119   exploit security holes present in some servers using fixed-length
2120   buffers for reading or manipulating the effective request URI.
2121</t>
2122</section>
2123
2124<section title="415 Unsupported Media Type" anchor="status.415">
2125  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2126  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2127<t>
2128   The server is refusing to service the request because the request
2129   payload is in a format not supported by this request method on the
2130   target resource.
2131</t>
2132</section>
2133
2134<section title="416 Requested Range Not Satisfiable" anchor="status.416">
2135  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
2136  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
2137  <rdf:Description>
2138    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
2139  </rdf:Description>
2140<t>
2141   The request included a Range header field (&header-range;) and none of
2142   the range-specifier values in this field overlap the current extent
2143   of the selected resource. See &status-416;.
2144</t>
2145</section>
2146
2147<section title="417 Expectation Failed" anchor="status.417">
2148  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2149  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2150<t>
2151   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2152   could not be met by this server, or, if the server is a proxy,
2153   the server has unambiguous evidence that the request could not be met
2154   by the next-hop server.
2155</t>
2156</section>
2157
2158<section title="426 Upgrade Required" anchor="status.426">
2159  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2160  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2161<t>
2162   The request can not be completed without a prior protocol upgrade. This
2163   response &MUST; include an Upgrade header field (&header-upgrade;)
2164   specifying the required protocols.
2165</t>
2166<figure>
2167<preamble>Example:</preamble>
2168<artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2169HTTP/1.1 426 Upgrade Required
2170Upgrade: HTTP/2.0
2171Connection: Upgrade
2172
2173</artwork></figure>
2174<t>
2175   The server &SHOULD; include a message body in the 426 response which
2176   indicates in human readable form the reason for the error and describes any
2177   alternative courses which may be available to the user.
2178</t>
2179</section>
2180</section>
2181
2182<section title="Server Error 5xx" anchor="status.5xx">
2183<t>
2184   Response status codes beginning with the digit "5" indicate cases in
2185   which the server is aware that it has erred or is incapable of
2186   performing the request. Except when responding to a HEAD request, the
2187   server &SHOULD; include a representation containing an explanation of the
2188   error situation, and whether it is a temporary or permanent
2189   condition. User agents &SHOULD; display any included representation to the
2190   user. These response codes are applicable to any request method.
2191</t>
2192
2193<section title="500 Internal Server Error" anchor="status.500">
2194  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2195  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2196<t>
2197   The server encountered an unexpected condition which prevented it
2198   from fulfilling the request.
2199</t>
2200</section>
2201
2202<section title="501 Not Implemented" anchor="status.501">
2203  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2204  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2205<t>
2206   The server does not support the functionality required to fulfill the
2207   request. This is the appropriate response when the server does not
2208   recognize the request method and is not capable of supporting it for
2209   any resource.
2210</t>
2211</section>
2212
2213<section title="502 Bad Gateway" anchor="status.502">
2214  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2215  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2216<t>
2217   The server, while acting as a gateway or proxy, received an invalid
2218   response from the upstream server it accessed in attempting to
2219   fulfill the request.
2220</t>
2221</section>
2222
2223<section title="503 Service Unavailable" anchor="status.503">
2224  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2225  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2226<t>
2227   The server is currently unable or unwilling to handle the request due to
2228   reasons such as temporary overloading, maintenance of the server, or rate
2229   limiting of the client.
2230</t>
2231<t>
2232   The implication is that this is a temporary condition which will be
2233   alleviated after some delay. If known, the length of the delay &MAY; be
2234   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2235   If no Retry-After is given, the client &SHOULD; handle the response as it
2236   would for a 500 response.
2237</t>
2238<x:note>
2239  <t>
2240    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2241    server must use it when becoming overloaded. Some servers might wish
2242    to simply refuse the connection.
2243  </t>
2244</x:note>
2245</section>
2246
2247<section title="504 Gateway Timeout" anchor="status.504">
2248  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2249  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2250<t>
2251   The server, while acting as a gateway or proxy, did not receive a
2252   timely response from the upstream server specified by the URI (e.g.,
2253   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2254   to access in attempting to complete the request.
2255</t>
2256<x:note>
2257  <t>
2258    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2259    return 400 or 500 when DNS lookups time out.
2260  </t>
2261</x:note>
2262</section>
2263
2264<section title="505 HTTP Version Not Supported" anchor="status.505">
2265  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2266  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2267<t>
2268   The server does not support, or refuses to support, the protocol
2269   version that was used in the request message. The server is
2270   indicating that it is unable or unwilling to complete the request
2271   using the same major version as the client, as described in &http-version;,
2272   other than with this error message. The response &SHOULD; contain
2273   a representation describing why that version is not supported and what other
2274   protocols are supported by that server.
2275</t>
2276
2277</section>
2278</section>
2279</section>
2280
2281
2282<section title="Header Field Definitions" anchor="header.field.definitions">
2283<t>
2284   This section defines the syntax and semantics of HTTP/1.1 header fields
2285   related to request and response semantics.
2286</t>
2287
2288<section title="Allow" anchor="header.allow">
2289  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2290  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2291  <x:anchor-alias value="Allow"/>
2292<t>
2293   The "Allow" header field lists the set of methods advertised as
2294   supported by the target resource. The purpose of this field is strictly to
2295   inform the recipient of valid request methods associated with the resource.
2296</t>
2297<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2298  <x:ref>Allow</x:ref> = #<x:ref>Method</x:ref>
2299</artwork></figure>
2300<t>
2301   Example of use:
2302</t>
2303<figure><artwork type="example">
2304  Allow: GET, HEAD, PUT
2305</artwork></figure>
2306<t>
2307   The actual set of allowed methods is defined by the origin server at the
2308   time of each request.
2309</t>
2310<t>
2311   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2312   understand all the methods specified in order to handle them according to
2313   the generic message handling rules.
2314</t>
2315</section>
2316
2317<section title="Expect" anchor="header.expect">
2318  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2319  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2320  <x:anchor-alias value="Expect"/>
2321  <x:anchor-alias value="expectation"/>
2322  <x:anchor-alias value="expectation-extension"/>
2323  <x:anchor-alias value="expect-params"/>
2324<t>
2325   The "Expect" header field is used to indicate that particular
2326   server behaviors are required by the client.
2327</t>
2328<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"/>
2329  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2330 
2331  <x:ref>expectation</x:ref>  = "100-continue" / <x:ref>expectation-extension</x:ref>
2332  <x:ref>expectation-extension</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2333                           *<x:ref>expect-params</x:ref> ]
2334  <x:ref>expect-params</x:ref> = ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2335</artwork></figure>
2336<t>
2337   A server that does not understand or is unable to comply with any of
2338   the expectation values in the Expect field of a request &MUST; respond
2339   with appropriate error status code. The server &MUST; respond with a 417
2340   (Expectation Failed) status code if any of the expectations cannot be met
2341   or, if there are other problems with the request, some other 4xx
2342   status code.
2343</t>
2344<t>
2345   This header field is defined with extensible syntax to allow for
2346   future extensions. If a server receives a request containing an
2347   Expect field that includes an expectation-extension that it does not
2348   support, it &MUST; respond with a 417 (Expectation Failed) status code.
2349</t>
2350<t>
2351   Comparison of expectation values is case-insensitive for unquoted
2352   tokens (including the 100-continue token), and is case-sensitive for
2353   quoted-string expectation-extensions.
2354</t>
2355<t>
2356   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
2357   return a 417 (Expectation Failed) status code if it receives a request
2358   with an expectation that it cannot meet. However, the Expect
2359   header field itself is end-to-end; it &MUST; be forwarded if the
2360   request is forwarded.
2361</t>
2362<t>
2363   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
2364   Expect header field.
2365</t>
2366<t>
2367   See &use100; for the use of the 100 (Continue) status code.
2368</t>
2369</section>
2370
2371<section title="From" anchor="header.from">
2372  <iref primary="true" item="From header field" x:for-anchor=""/>
2373  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2374  <x:anchor-alias value="From"/>
2375  <x:anchor-alias value="mailbox"/>
2376<t>
2377   The "From" header field, if given, &SHOULD; contain an Internet
2378   e-mail address for the human user who controls the requesting user
2379   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2380   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2381</t>
2382<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2383  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2384 
2385  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2386</artwork></figure>
2387<t>
2388   An example is:
2389</t>
2390<figure><artwork type="example">
2391  From: webmaster@example.org
2392</artwork></figure>
2393<t>
2394   This header field &MAY; be used for logging purposes and as a means for
2395   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2396   be used as an insecure form of access protection. The interpretation
2397   of this field is that the request is being performed on behalf of the
2398   person given, who accepts responsibility for the method performed. In
2399   particular, robot agents &SHOULD; include this header field so that the
2400   person responsible for running the robot can be contacted if problems
2401   occur on the receiving end.
2402</t>
2403<t>
2404   The Internet e-mail address in this field &MAY; be separate from the
2405   Internet host which issued the request. For example, when a request
2406   is passed through a proxy the original issuer's address &SHOULD; be
2407   used.
2408</t>
2409<t>
2410   The client &SHOULD-NOT;  send the From header field without the user's
2411   approval, as it might conflict with the user's privacy interests or
2412   their site's security policy. It is strongly recommended that the
2413   user be able to disable, enable, and modify the value of this field
2414   at any time prior to a request.
2415</t>
2416</section>
2417
2418<section title="Location" anchor="header.location">
2419  <iref primary="true" item="Location header field" x:for-anchor=""/>
2420  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2421  <x:anchor-alias value="Location"/>
2422<t>
2423   The "Location" header field is used to identify a newly created
2424   resource, or to redirect the recipient to a different location for
2425   completion of the request.
2426</t>
2427<t>
2428   For 201 (Created) responses, the Location is the URI of the new resource
2429   which was created by the request. For 3xx responses, the location &SHOULD;
2430   indicate the server's preferred URI for automatic redirection to the
2431   resource.
2432</t>
2433<t>
2434   The field value consists of a single URI-reference. When it has the form
2435   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2436   the final value is computed by resolving it against the effective request
2437   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>).
2438</t>
2439<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2440  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2441</artwork></figure>
2442<figure>
2443<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2444<artwork type="example">
2445  Location: http://www.example.org/pub/WWW/People.html#tim
2446</artwork></figure><figure><artwork type="example">  Location: /index.html
2447</artwork></figure>
2448<t>
2449   There are circumstances in which a fragment identifier in a Location URI
2450   would not be appropriate. For instance, when it appears in a 201 Created
2451   response, where the Location header field specifies the URI for the entire
2452   created resource.
2453</t>
2454<x:note>
2455  <t>
2456    <x:h>Note:</x:h> This specification does not define precedence rules
2457    for the case where the original URI, as navigated to by the user
2458    agent, and the Location header field value both contain fragment
2459    identifiers. Thus be aware that including fragment identifiers might
2460    inconvenience anyone relying on the semantics of the original URI's
2461    fragment identifier.
2462  </t>
2463</x:note>
2464<x:note>
2465  <t>
2466    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2467    from Location in that the Content-Location identifies the most specific
2468    resource corresponding to the enclosed representation.
2469    It is therefore possible for a response to contain header fields for
2470    both Location and Content-Location.
2471  </t>
2472</x:note>
2473</section>
2474
2475<section title="Max-Forwards" anchor="header.max-forwards">
2476  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2477  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2478  <x:anchor-alias value="Max-Forwards"/>
2479<t>
2480   The "Max-Forwards" header field provides a mechanism with the
2481   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2482   methods to limit the number of times that the request is forwarded by
2483   proxies. This can be useful when the client is attempting to
2484   trace a request which appears to be failing or looping in mid-chain.
2485</t>
2486<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2487  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2488</artwork></figure>
2489<t>
2490   The Max-Forwards value is a decimal integer indicating the remaining
2491   number of times this request message can be forwarded.
2492</t>
2493<t>
2494   Each recipient of a TRACE or OPTIONS request
2495   containing a Max-Forwards header field &MUST; check and update its
2496   value prior to forwarding the request. If the received value is zero
2497   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2498   respond as the final recipient. If the received Max-Forwards value is
2499   greater than zero, then the forwarded message &MUST; contain an updated
2500   Max-Forwards field with a value decremented by one (1).
2501</t>
2502<t>
2503   The Max-Forwards header field &MAY; be ignored for all other request
2504   methods.
2505</t>
2506</section>
2507
2508<section title="Referer" anchor="header.referer">
2509  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2510  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2511  <x:anchor-alias value="Referer"/>
2512<t>
2513   The "Referer" [sic] header field allows the client to specify the
2514   URI of the resource from which the effective request URI was obtained (the
2515   "referrer", although the header field is misspelled.).
2516</t>
2517<t>
2518   The Referer header field allows servers to generate lists of back-links to
2519   resources for interest, logging, optimized caching, etc. It also allows
2520   obsolete or mistyped links to be traced for maintenance. Some servers use
2521   Referer as a means of controlling where they allow links from (so-called
2522   "deep linking"), but legitimate requests do not always
2523   contain a Referer header field.
2524</t>
2525<t>
2526   If the effective request URI was obtained from a source that does not have its own
2527   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2528   sent with the value "about:blank", or not be sent at all. Note that this
2529   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2530</t>
2531<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2532  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2533</artwork></figure>
2534<t>
2535   Example:
2536</t>
2537<figure><artwork type="example">
2538  Referer: http://www.example.org/hypertext/Overview.html
2539</artwork></figure>
2540<t>
2541   If the field value is a relative URI, it &SHOULD; be interpreted
2542   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2543   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2544</t>
2545</section>
2546
2547<section title="Retry-After" anchor="header.retry-after">
2548  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2549  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2550  <x:anchor-alias value="Retry-After"/>
2551<t>
2552   The header "Retry-After" field can be used with a 503 (Service
2553   Unavailable) response to indicate how long the service is expected to
2554   be unavailable to the requesting client. This field &MAY; also be used
2555   with any 3xx (Redirection) response to indicate the minimum time the
2556   user-agent is asked wait before issuing the redirected request.
2557</t>
2558<t>
2559   The value of this field can be either an HTTP-date or an integer number
2560   of seconds (in decimal) after the time of the response.
2561</t>
2562<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2563  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2564</artwork></figure>
2565<t anchor="rule.delta-seconds">
2566  <x:anchor-alias value="delta-seconds"/>
2567   Time spans are non-negative decimal integers, representing time in
2568   seconds.
2569</t>
2570<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2571  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2572</artwork></figure>
2573<t>
2574   Two examples of its use are
2575</t>
2576<figure><artwork type="example">
2577  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2578  Retry-After: 120
2579</artwork></figure>
2580<t>
2581   In the latter example, the delay is 2 minutes.
2582</t>
2583</section>
2584
2585<section title="Server" anchor="header.server">
2586  <iref primary="true" item="Server header field" x:for-anchor=""/>
2587  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2588  <x:anchor-alias value="Server"/>
2589<t>
2590   The "Server" header field contains information about the
2591   software used by the origin server to handle the request.
2592</t>
2593<t>
2594   The field can contain multiple product tokens (&product-tokens;) and
2595   comments (&header-fields;) identifying the server and any significant
2596   subproducts. The product tokens are listed in order of their significance
2597   for identifying the application.
2598</t>
2599<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2600  <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> ) )
2601</artwork></figure>
2602<t>
2603   Example:
2604</t>
2605<figure><artwork type="example">
2606  Server: CERN/3.0 libwww/2.17
2607</artwork></figure>
2608<t>
2609   If the response is being forwarded through a proxy, the proxy
2610   application &MUST-NOT; modify the Server header field. Instead, it
2611   &MUST; include a Via field (as described in &header-via;).
2612</t>
2613<x:note>
2614  <t>
2615    <x:h>Note:</x:h> Revealing the specific software version of the server might
2616    allow the server machine to become more vulnerable to attacks
2617    against software that is known to contain security holes. Server
2618    implementors are encouraged to make this field a configurable
2619    option.
2620  </t>
2621</x:note>
2622</section>
2623
2624<section title="User-Agent" anchor="header.user-agent">
2625  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2626  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2627  <x:anchor-alias value="User-Agent"/>
2628<t>
2629   The "User-Agent" header field contains information about the user
2630   agent originating the request. User agents &SHOULD; include this field with
2631   requests.
2632</t>
2633<t>
2634   Typically, it is used for statistical purposes, the tracing of protocol
2635   violations, and tailoring responses to avoid particular user agent
2636   limitations.
2637</t>
2638<t>
2639   The field can contain multiple product tokens (&product-tokens;)
2640   and comments (&header-fields;) identifying the agent and its
2641   significant subproducts. By convention, the product tokens are listed in
2642   order of their significance for identifying the application.
2643</t>
2644<t>
2645   Because this field is usually sent on every request a user agent makes,
2646   implementations are encouraged not to include needlessly fine-grained
2647   detail, and to limit (or even prohibit) the addition of subproducts by third
2648   parties. Overly long and detailed User-Agent field values make requests
2649   larger and can also be used to identify ("fingerprint") the user against
2650   their wishes.
2651</t>
2652<t>
2653   Likewise, implementations are encouraged not to use the product tokens of
2654   other implementations in order to declare compatibility with them, as this
2655   circumvents the purpose of the field. Finally, they are encouraged not to
2656   use comments to identify products; doing so makes the field value more
2657   difficult to parse.
2658</t>
2659<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2660  <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> ) )
2661</artwork></figure>
2662<t>
2663   Example:
2664</t>
2665<figure><artwork type="example">
2666  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2667</artwork></figure>
2668</section>
2669
2670</section>
2671
2672<section title="IANA Considerations" anchor="IANA.considerations">
2673
2674<section title="Method Registry" anchor="method.registration">
2675<t>
2676  The registration procedure for HTTP request methods is defined by
2677  <xref target="method.registry"/> of this document.
2678</t>
2679<t>
2680   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2681   and be populated with the registrations below:
2682</t>
2683<?BEGININC p2-semantics.iana-methods ?>
2684<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2685<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2686   <ttcol>Method</ttcol>
2687   <ttcol>Safe</ttcol>
2688   <ttcol>Reference</ttcol>
2689   <c>CONNECT</c>
2690   <c>no</c>
2691   <c>
2692      <xref target="CONNECT"/>
2693   </c>
2694   <c>DELETE</c>
2695   <c>no</c>
2696   <c>
2697      <xref target="DELETE"/>
2698   </c>
2699   <c>GET</c>
2700   <c>yes</c>
2701   <c>
2702      <xref target="GET"/>
2703   </c>
2704   <c>HEAD</c>
2705   <c>yes</c>
2706   <c>
2707      <xref target="HEAD"/>
2708   </c>
2709   <c>OPTIONS</c>
2710   <c>yes</c>
2711   <c>
2712      <xref target="OPTIONS"/>
2713   </c>
2714   <c>POST</c>
2715   <c>no</c>
2716   <c>
2717      <xref target="POST"/>
2718   </c>
2719   <c>PUT</c>
2720   <c>no</c>
2721   <c>
2722      <xref target="PUT"/>
2723   </c>
2724   <c>TRACE</c>
2725   <c>yes</c>
2726   <c>
2727      <xref target="TRACE"/>
2728   </c>
2729</texttable>
2730<!--(END)-->
2731<?ENDINC p2-semantics.iana-methods ?>
2732</section>
2733
2734<section title="Status Code Registry" anchor="status.code.registration">
2735<t>
2736   The registration procedure for HTTP Status Codes &mdash; previously defined
2737   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2738   by <xref target="status.code.registry"/> of this document.
2739</t>
2740<t>
2741   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2742   shall be updated with the registrations below:
2743</t>
2744<?BEGININC p2-semantics.iana-status-codes ?>
2745<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2746<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2747   <ttcol>Value</ttcol>
2748   <ttcol>Description</ttcol>
2749   <ttcol>Reference</ttcol>
2750   <c>100</c>
2751   <c>Continue</c>
2752   <c>
2753      <xref target="status.100"/>
2754   </c>
2755   <c>101</c>
2756   <c>Switching Protocols</c>
2757   <c>
2758      <xref target="status.101"/>
2759   </c>
2760   <c>200</c>
2761   <c>OK</c>
2762   <c>
2763      <xref target="status.200"/>
2764   </c>
2765   <c>201</c>
2766   <c>Created</c>
2767   <c>
2768      <xref target="status.201"/>
2769   </c>
2770   <c>202</c>
2771   <c>Accepted</c>
2772   <c>
2773      <xref target="status.202"/>
2774   </c>
2775   <c>203</c>
2776   <c>Non-Authoritative Information</c>
2777   <c>
2778      <xref target="status.203"/>
2779   </c>
2780   <c>204</c>
2781   <c>No Content</c>
2782   <c>
2783      <xref target="status.204"/>
2784   </c>
2785   <c>205</c>
2786   <c>Reset Content</c>
2787   <c>
2788      <xref target="status.205"/>
2789   </c>
2790   <c>300</c>
2791   <c>Multiple Choices</c>
2792   <c>
2793      <xref target="status.300"/>
2794   </c>
2795   <c>301</c>
2796   <c>Moved Permanently</c>
2797   <c>
2798      <xref target="status.301"/>
2799   </c>
2800   <c>302</c>
2801   <c>Found</c>
2802   <c>
2803      <xref target="status.302"/>
2804   </c>
2805   <c>303</c>
2806   <c>See Other</c>
2807   <c>
2808      <xref target="status.303"/>
2809   </c>
2810   <c>305</c>
2811   <c>Use Proxy</c>
2812   <c>
2813      <xref target="status.305"/>
2814   </c>
2815   <c>306</c>
2816   <c>(Unused)</c>
2817   <c>
2818      <xref target="status.306"/>
2819   </c>
2820   <c>307</c>
2821   <c>Temporary Redirect</c>
2822   <c>
2823      <xref target="status.307"/>
2824   </c>
2825   <c>400</c>
2826   <c>Bad Request</c>
2827   <c>
2828      <xref target="status.400"/>
2829   </c>
2830   <c>402</c>
2831   <c>Payment Required</c>
2832   <c>
2833      <xref target="status.402"/>
2834   </c>
2835   <c>403</c>
2836   <c>Forbidden</c>
2837   <c>
2838      <xref target="status.403"/>
2839   </c>
2840   <c>404</c>
2841   <c>Not Found</c>
2842   <c>
2843      <xref target="status.404"/>
2844   </c>
2845   <c>405</c>
2846   <c>Method Not Allowed</c>
2847   <c>
2848      <xref target="status.405"/>
2849   </c>
2850   <c>406</c>
2851   <c>Not Acceptable</c>
2852   <c>
2853      <xref target="status.406"/>
2854   </c>
2855   <c>407</c>
2856   <c>Proxy Authentication Required</c>
2857   <c>
2858      <xref target="status.407"/>
2859   </c>
2860   <c>408</c>
2861   <c>Request Timeout</c>
2862   <c>
2863      <xref target="status.408"/>
2864   </c>
2865   <c>409</c>
2866   <c>Conflict</c>
2867   <c>
2868      <xref target="status.409"/>
2869   </c>
2870   <c>410</c>
2871   <c>Gone</c>
2872   <c>
2873      <xref target="status.410"/>
2874   </c>
2875   <c>411</c>
2876   <c>Length Required</c>
2877   <c>
2878      <xref target="status.411"/>
2879   </c>
2880   <c>413</c>
2881   <c>Request Representation Too Large</c>
2882   <c>
2883      <xref target="status.413"/>
2884   </c>
2885   <c>414</c>
2886   <c>URI Too Long</c>
2887   <c>
2888      <xref target="status.414"/>
2889   </c>
2890   <c>415</c>
2891   <c>Unsupported Media Type</c>
2892   <c>
2893      <xref target="status.415"/>
2894   </c>
2895   <c>417</c>
2896   <c>Expectation Failed</c>
2897   <c>
2898      <xref target="status.417"/>
2899   </c>
2900   <c>426</c>
2901   <c>Upgrade Required</c>
2902   <c>
2903      <xref target="status.426"/>
2904   </c>
2905   <c>500</c>
2906   <c>Internal Server Error</c>
2907   <c>
2908      <xref target="status.500"/>
2909   </c>
2910   <c>501</c>
2911   <c>Not Implemented</c>
2912   <c>
2913      <xref target="status.501"/>
2914   </c>
2915   <c>502</c>
2916   <c>Bad Gateway</c>
2917   <c>
2918      <xref target="status.502"/>
2919   </c>
2920   <c>503</c>
2921   <c>Service Unavailable</c>
2922   <c>
2923      <xref target="status.503"/>
2924   </c>
2925   <c>504</c>
2926   <c>Gateway Timeout</c>
2927   <c>
2928      <xref target="status.504"/>
2929   </c>
2930   <c>505</c>
2931   <c>HTTP Version Not Supported</c>
2932   <c>
2933      <xref target="status.505"/>
2934   </c>
2935</texttable>
2936<!--(END)-->
2937<?ENDINC p2-semantics.iana-status-codes ?>
2938</section>
2939<section title="Header Field Registration" anchor="header.field.registration">
2940<t>
2941   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
2942   with the permanent registrations below (see <xref target="RFC3864"/>):
2943</t>
2944<?BEGININC p2-semantics.iana-headers ?>
2945<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2946<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2947   <ttcol>Header Field Name</ttcol>
2948   <ttcol>Protocol</ttcol>
2949   <ttcol>Status</ttcol>
2950   <ttcol>Reference</ttcol>
2951
2952   <c>Allow</c>
2953   <c>http</c>
2954   <c>standard</c>
2955   <c>
2956      <xref target="header.allow"/>
2957   </c>
2958   <c>Expect</c>
2959   <c>http</c>
2960   <c>standard</c>
2961   <c>
2962      <xref target="header.expect"/>
2963   </c>
2964   <c>From</c>
2965   <c>http</c>
2966   <c>standard</c>
2967   <c>
2968      <xref target="header.from"/>
2969   </c>
2970   <c>Location</c>
2971   <c>http</c>
2972   <c>standard</c>
2973   <c>
2974      <xref target="header.location"/>
2975   </c>
2976   <c>Max-Forwards</c>
2977   <c>http</c>
2978   <c>standard</c>
2979   <c>
2980      <xref target="header.max-forwards"/>
2981   </c>
2982   <c>Referer</c>
2983   <c>http</c>
2984   <c>standard</c>
2985   <c>
2986      <xref target="header.referer"/>
2987   </c>
2988   <c>Retry-After</c>
2989   <c>http</c>
2990   <c>standard</c>
2991   <c>
2992      <xref target="header.retry-after"/>
2993   </c>
2994   <c>Server</c>
2995   <c>http</c>
2996   <c>standard</c>
2997   <c>
2998      <xref target="header.server"/>
2999   </c>
3000   <c>User-Agent</c>
3001   <c>http</c>
3002   <c>standard</c>
3003   <c>
3004      <xref target="header.user-agent"/>
3005   </c>
3006</texttable>
3007<!--(END)-->
3008<?ENDINC p2-semantics.iana-headers ?>
3009<t>
3010   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3011</t>
3012</section>
3013</section>
3014
3015<section title="Security Considerations" anchor="security.considerations">
3016<t>
3017   This section is meant to inform application developers, information
3018   providers, and users of the security limitations in HTTP/1.1 as
3019   described by this document. The discussion does not include
3020   definitive solutions to the problems revealed, though it does make
3021   some suggestions for reducing security risks.
3022</t>
3023
3024<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3025<t>
3026   Like any generic data transfer protocol, HTTP cannot regulate the
3027   content of the data that is transferred, nor is there any a priori
3028   method of determining the sensitivity of any particular piece of
3029   information within the context of any given request. Therefore,
3030   applications &SHOULD; supply as much control over this information as
3031   possible to the provider of that information. Four header fields are
3032   worth special mention in this context: Server, Via, Referer and From.
3033</t>
3034<t>
3035   Revealing the specific software version of the server might allow the
3036   server machine to become more vulnerable to attacks against software
3037   that is known to contain security holes. Implementors &SHOULD; make the
3038   Server header field a configurable option.
3039</t>
3040<t>
3041   Proxies which serve as a portal through a network firewall &SHOULD;
3042   take special precautions regarding the transfer of header information
3043   that identifies the hosts behind the firewall. In particular, they
3044   &SHOULD; remove, or replace with sanitized versions, any Via fields
3045   generated behind the firewall.
3046</t>
3047<t>
3048   The Referer header field allows reading patterns to be studied and reverse
3049   links drawn. Although it can be very useful, its power can be abused
3050   if user details are not separated from the information contained in
3051   the Referer. Even when the personal information has been removed, the
3052   Referer header field might indicate a private document's URI whose
3053   publication would be inappropriate.
3054</t>
3055<t>
3056   The information sent in the From field might conflict with the user's
3057   privacy interests or their site's security policy, and hence it
3058   &SHOULD-NOT;  be transmitted without the user being able to disable,
3059   enable, and modify the contents of the field. The user &MUST; be able
3060   to set the contents of this field within a user preference or
3061   application defaults configuration.
3062</t>
3063<t>
3064   We suggest, though do not require, that a convenient toggle interface
3065   be provided for the user to enable or disable the sending of From and
3066   Referer information.
3067</t>
3068<t>
3069   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3070   target="header.server"/>) header fields can sometimes be used to determine
3071   that a specific client or server have a particular security hole which might
3072   be exploited. Unfortunately, this same information is often used for other
3073   valuable purposes for which HTTP currently has no better mechanism.
3074</t>
3075<t>
3076   Furthermore, the User-Agent header field may contain enough entropy to be
3077   used, possibly in conjunction with other material, to uniquely identify the
3078   user.
3079</t>
3080<t>
3081   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3082   that was sent in request header fields within the body of their response.
3083   Clients &SHOULD; be careful with sensitive information, like Cookies,
3084   Authorization credentials, and other header fields that might be used to
3085   collect data from the client.
3086</t> 
3087</section>
3088
3089<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3090<t>
3091   Because the source of a link might be private information or might
3092   reveal an otherwise private information source, it is strongly
3093   recommended that the user be able to select whether or not the
3094   Referer field is sent. For example, a browser client could have a
3095   toggle switch for browsing openly/anonymously, which would
3096   respectively enable/disable the sending of Referer and From
3097   information.
3098</t>
3099<t>
3100   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3101   HTTP request if the referring page was transferred with a secure
3102   protocol.
3103</t>
3104<t>
3105   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3106   sensitive data because that data will be placed in the request-target. Many
3107   existing servers, proxies, and user agents log or display the request-target
3108   in places where it might be visible to third parties. Such services can
3109   use POST-based form submission instead.
3110</t>
3111</section>
3112
3113<section title="Location Headers and Spoofing" anchor="location.spoofing">
3114<t>
3115   If a single server supports multiple organizations that do not trust
3116   one another, then it &MUST; check the values of Location and Content-Location
3117   header fields in responses that are generated under control of
3118   said organizations to make sure that they do not attempt to
3119   invalidate resources over which they have no authority.
3120</t>
3121</section>
3122
3123<section title="Security Considerations for CONNECT">
3124<t>
3125   Since tunneled data is opaque to the proxy, there are additional
3126   risks to tunneling to other well-known or reserved ports.
3127   A HTTP client CONNECTing to port 25 could relay spam
3128   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3129   access to a small number of known ports.
3130</t>
3131</section>
3132
3133</section>
3134
3135<section title="Acknowledgments" anchor="acks">
3136<t>
3137  See &acks;.
3138</t>
3139</section>
3140</middle>
3141<back>
3142
3143<references title="Normative References">
3144
3145<reference anchor="Part1">
3146  <front>
3147    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3148    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3149      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3150      <address><email>fielding@gbiv.com</email></address>
3151    </author>
3152    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3153      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3154      <address><email>jg@freedesktop.org</email></address>
3155    </author>
3156    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3157      <organization abbrev="HP">Hewlett-Packard Company</organization>
3158      <address><email>JeffMogul@acm.org</email></address>
3159    </author>
3160    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3161      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3162      <address><email>henrikn@microsoft.com</email></address>
3163    </author>
3164    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3165      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3166      <address><email>LMM@acm.org</email></address>
3167    </author>
3168    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3169      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3170      <address><email>paulle@microsoft.com</email></address>
3171    </author>
3172    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3173      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3174      <address><email>timbl@w3.org</email></address>
3175    </author>
3176    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3177      <organization abbrev="W3C">World Wide Web Consortium</organization>
3178      <address><email>ylafon@w3.org</email></address>
3179    </author>
3180    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3181      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3182      <address><email>julian.reschke@greenbytes.de</email></address>
3183    </author>
3184    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3185  </front>
3186  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3187  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3188</reference>
3189
3190<reference anchor="Part3">
3191  <front>
3192    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3193    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3194      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3195      <address><email>fielding@gbiv.com</email></address>
3196    </author>
3197    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3198      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3199      <address><email>jg@freedesktop.org</email></address>
3200    </author>
3201    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3202      <organization abbrev="HP">Hewlett-Packard Company</organization>
3203      <address><email>JeffMogul@acm.org</email></address>
3204    </author>
3205    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3206      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3207      <address><email>henrikn@microsoft.com</email></address>
3208    </author>
3209    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3210      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3211      <address><email>LMM@acm.org</email></address>
3212    </author>
3213    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3214      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3215      <address><email>paulle@microsoft.com</email></address>
3216    </author>
3217    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3218      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3219      <address><email>timbl@w3.org</email></address>
3220    </author>
3221    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3222      <organization abbrev="W3C">World Wide Web Consortium</organization>
3223      <address><email>ylafon@w3.org</email></address>
3224    </author>
3225    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3226      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3227      <address><email>julian.reschke@greenbytes.de</email></address>
3228    </author>
3229    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3230  </front>
3231  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3232  <x:source href="p3-payload.xml" basename="p3-payload"/>
3233</reference>
3234
3235<reference anchor="Part4">
3236  <front>
3237    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3238    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3239      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3240      <address><email>fielding@gbiv.com</email></address>
3241    </author>
3242    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3243      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3244      <address><email>jg@freedesktop.org</email></address>
3245    </author>
3246    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3247      <organization abbrev="HP">Hewlett-Packard Company</organization>
3248      <address><email>JeffMogul@acm.org</email></address>
3249    </author>
3250    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3251      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3252      <address><email>henrikn@microsoft.com</email></address>
3253    </author>
3254    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3255      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3256      <address><email>LMM@acm.org</email></address>
3257    </author>
3258    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3259      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3260      <address><email>paulle@microsoft.com</email></address>
3261    </author>
3262    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3263      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3264      <address><email>timbl@w3.org</email></address>
3265    </author>
3266    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3267      <organization abbrev="W3C">World Wide Web Consortium</organization>
3268      <address><email>ylafon@w3.org</email></address>
3269    </author>
3270    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3271      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3272      <address><email>julian.reschke@greenbytes.de</email></address>
3273    </author>
3274    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3275  </front>
3276  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3277  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3278</reference>
3279
3280<reference anchor="Part5">
3281  <front>
3282    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3283    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3284      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3285      <address><email>fielding@gbiv.com</email></address>
3286    </author>
3287    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3288      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3289      <address><email>jg@freedesktop.org</email></address>
3290    </author>
3291    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3292      <organization abbrev="HP">Hewlett-Packard Company</organization>
3293      <address><email>JeffMogul@acm.org</email></address>
3294    </author>
3295    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3296      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3297      <address><email>henrikn@microsoft.com</email></address>
3298    </author>
3299    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3300      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3301      <address><email>LMM@acm.org</email></address>
3302    </author>
3303    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3304      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3305      <address><email>paulle@microsoft.com</email></address>
3306    </author>
3307    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3308      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3309      <address><email>timbl@w3.org</email></address>
3310    </author>
3311    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3312      <organization abbrev="W3C">World Wide Web Consortium</organization>
3313      <address><email>ylafon@w3.org</email></address>
3314    </author>
3315    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3316      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3317      <address><email>julian.reschke@greenbytes.de</email></address>
3318    </author>
3319    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3320  </front>
3321  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3322  <x:source href="p5-range.xml" basename="p5-range"/>
3323</reference>
3324
3325<reference anchor="Part6">
3326  <front>
3327    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3328    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3329      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3330      <address><email>fielding@gbiv.com</email></address>
3331    </author>
3332    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3333      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3334      <address><email>jg@freedesktop.org</email></address>
3335    </author>
3336    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3337      <organization abbrev="HP">Hewlett-Packard Company</organization>
3338      <address><email>JeffMogul@acm.org</email></address>
3339    </author>
3340    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3341      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3342      <address><email>henrikn@microsoft.com</email></address>
3343    </author>
3344    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3345      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3346      <address><email>LMM@acm.org</email></address>
3347    </author>
3348    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3349      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3350      <address><email>paulle@microsoft.com</email></address>
3351    </author>
3352    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3353      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3354      <address><email>timbl@w3.org</email></address>
3355    </author>
3356    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3357      <organization abbrev="W3C">World Wide Web Consortium</organization>
3358      <address><email>ylafon@w3.org</email></address>
3359    </author>
3360    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3361      <address><email>mnot@mnot.net</email></address>
3362    </author>
3363    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3364      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3365      <address><email>julian.reschke@greenbytes.de</email></address>
3366    </author>
3367    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3368  </front>
3369  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3370  <x:source href="p6-cache.xml" basename="p6-cache"/>
3371</reference>
3372
3373<reference anchor="Part7">
3374  <front>
3375    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3376    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3377      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3378      <address><email>fielding@gbiv.com</email></address>
3379    </author>
3380    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3381      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3382      <address><email>jg@freedesktop.org</email></address>
3383    </author>
3384    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3385      <organization abbrev="HP">Hewlett-Packard Company</organization>
3386      <address><email>JeffMogul@acm.org</email></address>
3387    </author>
3388    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3389      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3390      <address><email>henrikn@microsoft.com</email></address>
3391    </author>
3392    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3393      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3394      <address><email>LMM@acm.org</email></address>
3395    </author>
3396    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3397      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3398      <address><email>paulle@microsoft.com</email></address>
3399    </author>
3400    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3401      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3402      <address><email>timbl@w3.org</email></address>
3403    </author>
3404    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3405      <organization abbrev="W3C">World Wide Web Consortium</organization>
3406      <address><email>ylafon@w3.org</email></address>
3407    </author>
3408    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3409      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3410      <address><email>julian.reschke@greenbytes.de</email></address>
3411    </author>
3412    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3413  </front>
3414  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3415  <x:source href="p7-auth.xml" basename="p7-auth"/>
3416</reference>
3417
3418<reference anchor="RFC2119">
3419  <front>
3420    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3421    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3422      <organization>Harvard University</organization>
3423      <address><email>sob@harvard.edu</email></address>
3424    </author>
3425    <date month="March" year="1997"/>
3426  </front>
3427  <seriesInfo name="BCP" value="14"/>
3428  <seriesInfo name="RFC" value="2119"/>
3429</reference>
3430
3431<reference anchor="RFC3986">
3432 <front>
3433  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3434  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3435    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3436    <address>
3437       <email>timbl@w3.org</email>
3438       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3439    </address>
3440  </author>
3441  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3442    <organization abbrev="Day Software">Day Software</organization>
3443    <address>
3444      <email>fielding@gbiv.com</email>
3445      <uri>http://roy.gbiv.com/</uri>
3446    </address>
3447  </author>
3448  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3449    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3450    <address>
3451      <email>LMM@acm.org</email>
3452      <uri>http://larry.masinter.net/</uri>
3453    </address>
3454  </author>
3455  <date month='January' year='2005'></date>
3456 </front>
3457 <seriesInfo name="STD" value="66"/>
3458 <seriesInfo name="RFC" value="3986"/>
3459</reference>
3460
3461<reference anchor="RFC5234">
3462  <front>
3463    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3464    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3465      <organization>Brandenburg InternetWorking</organization>
3466      <address>
3467        <email>dcrocker@bbiw.net</email>
3468      </address> 
3469    </author>
3470    <author initials="P." surname="Overell" fullname="Paul Overell">
3471      <organization>THUS plc.</organization>
3472      <address>
3473        <email>paul.overell@thus.net</email>
3474      </address>
3475    </author>
3476    <date month="January" year="2008"/>
3477  </front>
3478  <seriesInfo name="STD" value="68"/>
3479  <seriesInfo name="RFC" value="5234"/>
3480</reference>
3481
3482</references>
3483
3484<references title="Informative References">
3485
3486<reference anchor="RFC1945">
3487  <front>
3488    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3489    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3490      <organization>MIT, Laboratory for Computer Science</organization>
3491      <address><email>timbl@w3.org</email></address>
3492    </author>
3493    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3494      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3495      <address><email>fielding@ics.uci.edu</email></address>
3496    </author>
3497    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3498      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3499      <address><email>frystyk@w3.org</email></address>
3500    </author>
3501    <date month="May" year="1996"/>
3502  </front>
3503  <seriesInfo name="RFC" value="1945"/>
3504</reference>
3505
3506<reference anchor="RFC2068">
3507  <front>
3508    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3509    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3510      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3511      <address><email>fielding@ics.uci.edu</email></address>
3512    </author>
3513    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3514      <organization>MIT Laboratory for Computer Science</organization>
3515      <address><email>jg@w3.org</email></address>
3516    </author>
3517    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3518      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3519      <address><email>mogul@wrl.dec.com</email></address>
3520    </author>
3521    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3522      <organization>MIT Laboratory for Computer Science</organization>
3523      <address><email>frystyk@w3.org</email></address>
3524    </author>
3525    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3526      <organization>MIT Laboratory for Computer Science</organization>
3527      <address><email>timbl@w3.org</email></address>
3528    </author>
3529    <date month="January" year="1997"/>
3530  </front>
3531  <seriesInfo name="RFC" value="2068"/>
3532</reference>
3533
3534<reference anchor="RFC2616">
3535  <front>
3536    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3537    <author initials="R." surname="Fielding" fullname="R. Fielding">
3538      <organization>University of California, Irvine</organization>
3539      <address><email>fielding@ics.uci.edu</email></address>
3540    </author>
3541    <author initials="J." surname="Gettys" fullname="J. Gettys">
3542      <organization>W3C</organization>
3543      <address><email>jg@w3.org</email></address>
3544    </author>
3545    <author initials="J." surname="Mogul" fullname="J. Mogul">
3546      <organization>Compaq Computer Corporation</organization>
3547      <address><email>mogul@wrl.dec.com</email></address>
3548    </author>
3549    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3550      <organization>MIT Laboratory for Computer Science</organization>
3551      <address><email>frystyk@w3.org</email></address>
3552    </author>
3553    <author initials="L." surname="Masinter" fullname="L. Masinter">
3554      <organization>Xerox Corporation</organization>
3555      <address><email>masinter@parc.xerox.com</email></address>
3556    </author>
3557    <author initials="P." surname="Leach" fullname="P. Leach">
3558      <organization>Microsoft Corporation</organization>
3559      <address><email>paulle@microsoft.com</email></address>
3560    </author>
3561    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3562      <organization>W3C</organization>
3563      <address><email>timbl@w3.org</email></address>
3564    </author>
3565    <date month="June" year="1999"/>
3566  </front>
3567  <seriesInfo name="RFC" value="2616"/>
3568</reference>
3569
3570<reference anchor='RFC2817'>
3571  <front>
3572    <title>Upgrading to TLS Within HTTP/1.1</title>
3573    <author initials='R.' surname='Khare' fullname='R. Khare'>
3574      <organization>4K Associates / UC Irvine</organization>
3575      <address><email>rohit@4K-associates.com</email></address>
3576    </author>
3577    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3578      <organization>Agranat Systems, Inc.</organization>
3579      <address><email>lawrence@agranat.com</email></address>
3580    </author>
3581    <date year='2000' month='May' />
3582  </front>
3583  <seriesInfo name='RFC' value='2817' />
3584</reference>
3585
3586<reference anchor='RFC3864'>
3587  <front>
3588    <title>Registration Procedures for Message Header Fields</title>
3589    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3590      <organization>Nine by Nine</organization>
3591      <address><email>GK-IETF@ninebynine.org</email></address>
3592    </author>
3593    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3594      <organization>BEA Systems</organization>
3595      <address><email>mnot@pobox.com</email></address>
3596    </author>
3597    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3598      <organization>HP Labs</organization>
3599      <address><email>JeffMogul@acm.org</email></address>
3600    </author>
3601    <date year='2004' month='September' />
3602  </front>
3603  <seriesInfo name='BCP' value='90' />
3604  <seriesInfo name='RFC' value='3864' />
3605</reference>
3606
3607<reference anchor='RFC5226'>
3608  <front>
3609    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3610    <author initials='T.' surname='Narten' fullname='T. Narten'>
3611      <organization>IBM</organization>
3612      <address><email>narten@us.ibm.com</email></address>
3613    </author>
3614    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3615      <organization>Google</organization>
3616      <address><email>Harald@Alvestrand.no</email></address>
3617    </author>
3618    <date year='2008' month='May' />
3619  </front>
3620  <seriesInfo name='BCP' value='26' />
3621  <seriesInfo name='RFC' value='5226' />
3622</reference>
3623
3624<reference anchor="RFC5322">
3625  <front>
3626    <title>Internet Message Format</title>
3627    <author initials="P." surname="Resnick" fullname="P. Resnick">
3628      <organization>Qualcomm Incorporated</organization>
3629    </author>
3630    <date year="2008" month="October"/>
3631  </front> 
3632  <seriesInfo name="RFC" value="5322"/>
3633</reference>
3634
3635<reference anchor='RFC5789'>
3636  <front>
3637    <title>PATCH Method for HTTP</title>
3638    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3639      <organization>Linden Lab</organization>
3640    </author>
3641    <author initials='J.' surname='Snell' fullname='J. Snell' />
3642    <date year='2010' month='March' />
3643  </front>
3644  <seriesInfo name='RFC' value='5789' />
3645</reference>
3646
3647<reference anchor="RFC5987">
3648        <front>
3649    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3650    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3651      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3652      <address>
3653        <postal>
3654          <street>Hafenweg 16</street>
3655          <city>Muenster</city><region>NW</region><code>48155</code>
3656          <country>Germany</country>
3657        </postal>
3658        <email>julian.reschke@greenbytes.de</email>     
3659        <uri>http://greenbytes.de/tech/webdav/</uri>   
3660      </address>
3661    </author>
3662    <date month="August" year="2010"/>
3663  </front>
3664  <seriesInfo name="RFC" value="5987"/>
3665</reference>
3666
3667</references>
3668
3669<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3670<t>
3671  This document takes over the Status Code Registry, previously defined
3672  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3673  (<xref target="status.code.registry"/>)
3674</t>
3675<t>
3676  Clarify definition of POST.
3677  (<xref target="POST"/>)
3678</t>
3679<t>
3680  Remove requirement to handle all Content-* header fields; ban use of
3681  Content-Range with PUT.
3682  (<xref target="PUT"/>)
3683</t>
3684<t>
3685  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3686  (<xref target="CONNECT"/>)
3687</t>
3688<t>
3689  Broadened the definition of 203 (Non-Authoritative Information) to include
3690  cases of payload transformations as well.
3691  (<xref target="status.203"/>)
3692</t>
3693<t>
3694  Failed to consider that there are many other request methods that are safe
3695  to automatically redirect, and further that the user agent is able to make
3696  that determination based on the request method semantics.
3697  Furthermore, allow user agents to rewrite the method from POST to GET
3698  for status codes 301 and 302.
3699  (Sections <xref format="counter" target="status.301"/>,
3700  <xref format="counter" target="status.302"/> and
3701  <xref format="counter" target="status.307"/>)
3702</t>
3703<t>
3704  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3705  It used to indicate that the target resource must be accessed through the
3706  proxy given by the Location field. The Location field gave the URI of the
3707  proxy. The recipient was expected to repeat this single request via the proxy.
3708  (<xref target="status.305"/>)
3709</t>
3710<t>
3711  Define status 426 (Upgrade Required) (this was incorporated from
3712  <xref target="RFC2817"/>).
3713  (<xref target="status.426"/>)
3714</t>
3715<t>
3716  Change ABNF productions for header fields to only define the field value.
3717  (<xref target="header.field.definitions"/>)
3718</t>
3719<t>
3720  Reclassify "Allow" as response header field, removing the option to
3721  specify it in a PUT request.
3722  Relax the server requirement on the contents of the Allow header field and
3723  remove requirement on clients to always trust the header field value.
3724  (<xref target="header.allow"/>)
3725</t>
3726<t>
3727  Correct syntax of Location header field to allow URI references (including
3728  relative references and fragments), as referred symbol "absoluteURI" wasn't
3729  what was expected, and add some clarifications as to when use of fragments
3730  would not be appropriate.
3731  (<xref target="header.location"/>)
3732</t>
3733<t>
3734  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3735  extension methods could have used it as well).
3736  (<xref target="header.max-forwards"/>)
3737</t>
3738<t>
3739  Allow Referer field value of "about:blank" as alternative to not specifying it.
3740  (<xref target="header.referer"/>)
3741</t>
3742<t>
3743  In the description of the Server header field, the Via field
3744  was described as a SHOULD. The requirement was and is stated
3745  correctly in the description of the Via header field in &header-via;.
3746  (<xref target="header.server"/>)
3747</t>
3748</section>
3749
3750<?BEGININC p2-semantics.abnf-appendix ?>
3751<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3752<figure>
3753<artwork type="abnf" name="p2-semantics.parsed-abnf">
3754<x:ref>Allow</x:ref> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
3755
3756<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3757
3758<x:ref>From</x:ref> = mailbox
3759
3760<x:ref>HTTP-date</x:ref> = &lt;HTTP-date, defined in [Part1], Section 5.1&gt;
3761
3762<x:ref>Location</x:ref> = URI-reference
3763
3764<x:ref>Max-Forwards</x:ref> = 1*DIGIT
3765<x:ref>Method</x:ref> = token
3766
3767<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
3768
3769<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 1.2.2&gt;
3770<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
3771<x:ref>Referer</x:ref> = absolute-URI / partial-URI
3772<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
3773
3774<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
3775<x:ref>Status-Code</x:ref> = 3DIGIT
3776
3777<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
3778<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
3779
3780<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
3781
3782<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2&gt;
3783
3784<x:ref>delta-seconds</x:ref> = 1*DIGIT
3785
3786<x:ref>expect-params</x:ref> = ";" token [ "=" ( token / quoted-string ) ]
3787<x:ref>expectation</x:ref> = "100-continue" / expectation-extension
3788<x:ref>expectation-extension</x:ref> = token [ "=" ( token / quoted-string )
3789 *expect-params ]
3790
3791<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
3792
3793<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 1.2.2&gt;
3794
3795<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
3796<x:ref>product</x:ref> = &lt;product, defined in [Part1], Section 5.3&gt;
3797
3798<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.3&gt;
3799
3800<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.3&gt;
3801</artwork>
3802</figure>
3803<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
3804; Allow defined but not used
3805; Expect defined but not used
3806; From defined but not used
3807; Location defined but not used
3808; Max-Forwards defined but not used
3809; Reason-Phrase defined but not used
3810; Referer defined but not used
3811; Retry-After defined but not used
3812; Server defined but not used
3813; Status-Code defined but not used
3814; User-Agent defined but not used
3815</artwork></figure></section>
3816<?ENDINC p2-semantics.abnf-appendix ?>
3817
3818<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3819
3820<section title="Since RFC 2616">
3821<t>
3822  Extracted relevant partitions from <xref target="RFC2616"/>.
3823</t>
3824</section>
3825
3826<section title="Since draft-ietf-httpbis-p2-semantics-00">
3827<t>
3828  Closed issues:
3829  <list style="symbols"> 
3830    <t>
3831      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3832      "Via is a MUST"
3833      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3834    </t>
3835    <t>
3836      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3837      "Fragments allowed in Location"
3838      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3839    </t>
3840    <t>
3841      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3842      "Safe Methods vs Redirection"
3843      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3844    </t>
3845    <t>
3846      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3847      "Revise description of the POST method"
3848      (<eref target="http://purl.org/NET/http-errata#post"/>)
3849    </t>
3850    <t>
3851      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3852      "Normative and Informative references"
3853    </t>
3854    <t>
3855      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3856      "RFC2606 Compliance"
3857    </t>
3858    <t>
3859      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3860      "Informative references"
3861    </t>
3862    <t>
3863      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3864      "Redundant cross-references"
3865    </t>
3866  </list>
3867</t>
3868<t>
3869  Other changes:
3870  <list style="symbols"> 
3871    <t>
3872      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3873    </t>
3874  </list>
3875</t>
3876</section>
3877
3878<section title="Since draft-ietf-httpbis-p2-semantics-01">
3879<t>
3880  Closed issues:
3881  <list style="symbols"> 
3882    <t>
3883      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3884      "PUT side effects"
3885    </t>
3886    <t>
3887      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3888      "Duplicate Host header requirements"
3889    </t>
3890  </list>
3891</t>
3892<t>
3893  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3894  <list style="symbols"> 
3895    <t>
3896      Move "Product Tokens" section (back) into Part 1, as "token" is used
3897      in the definition of the Upgrade header field.
3898    </t>
3899    <t>
3900      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3901    </t>
3902    <t>
3903      Copy definition of delta-seconds from Part6 instead of referencing it.
3904    </t>
3905  </list>
3906</t>
3907</section>
3908
3909<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3910<t>
3911  Closed issues:
3912  <list style="symbols"> 
3913    <t>
3914      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3915      "Requiring Allow in 405 responses"
3916    </t>
3917    <t>
3918      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3919      "Status Code Registry"
3920    </t>
3921    <t>
3922      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3923      "Redirection vs. Location"
3924    </t>
3925    <t>
3926      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3927      "Cacheability of 303 response"
3928    </t>
3929    <t>
3930      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3931      "305 Use Proxy"
3932    </t>
3933    <t>
3934      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3935      "Classification for Allow header"
3936    </t>
3937    <t>
3938      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3939      "PUT - 'store under' vs 'store at'"
3940    </t>
3941  </list>
3942</t>
3943<t>
3944  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3945  <list style="symbols"> 
3946    <t>
3947      Reference RFC 3984, and update header field registrations for headers defined
3948      in this document.
3949    </t>
3950  </list>
3951</t>
3952<t>
3953  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3954  <list style="symbols"> 
3955    <t>
3956      Replace string literals when the string really is case-sensitive (method).
3957    </t>
3958  </list>
3959</t>
3960</section>
3961
3962<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
3963<t>
3964  Closed issues:
3965  <list style="symbols"> 
3966    <t>
3967      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
3968      "OPTIONS request bodies"
3969    </t>
3970    <t>
3971      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
3972      "Description of CONNECT should refer to RFC2817"
3973    </t>
3974    <t>
3975      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
3976      "Location Content-Location reference request/response mixup"
3977    </t>
3978  </list>
3979</t>
3980<t>
3981  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
3982  <list style="symbols"> 
3983    <t>
3984      Added initial proposal for registration process, plus initial
3985      content (non-HTTP/1.1 methods to be added by a separate specification).
3986    </t>
3987  </list>
3988</t>
3989</section>
3990
3991<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
3992<t>
3993  Closed issues:
3994  <list style="symbols"> 
3995    <t>
3996      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
3997      "Content-*"
3998    </t>
3999    <t>
4000      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4001      "RFC 2822 is updated by RFC 5322"
4002    </t>
4003  </list>
4004</t>
4005<t>
4006  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4007  <list style="symbols"> 
4008    <t>
4009      Use "/" instead of "|" for alternatives.
4010    </t>
4011    <t>
4012      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4013      whitespace ("OWS") and required whitespace ("RWS").
4014    </t>
4015    <t>
4016      Rewrite ABNFs to spell out whitespace rules, factor out
4017      header field value format definitions.
4018    </t>
4019  </list>
4020</t>
4021</section>
4022
4023<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4024<t>
4025  Closed issues:
4026  <list style="symbols"> 
4027    <t>
4028      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4029      "Reason-Phrase BNF"
4030    </t>
4031  </list>
4032</t>
4033<t>
4034  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4035  <list style="symbols"> 
4036    <t>
4037      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4038    </t>
4039  </list>
4040</t>
4041</section>
4042
4043<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4044<t>
4045  Closed issues:
4046  <list style="symbols"> 
4047    <t>
4048      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4049      "Clarify when Referer is sent"
4050    </t>
4051    <t>
4052      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4053      "status codes vs methods"
4054    </t>
4055    <t>
4056      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4057      "Do not require "updates" relation for specs that register status codes or method names"
4058    </t>
4059  </list>
4060</t>
4061</section>
4062
4063<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4064<t>
4065  Closed issues:
4066  <list style="symbols"> 
4067    <t>
4068      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4069      "Idempotency"
4070    </t>
4071    <t>
4072      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4073      "TRACE security considerations"
4074    </t>
4075    <t>
4076      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4077      "Clarify rules for determining what entities a response carries"
4078    </t>
4079    <t>
4080      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4081      "update note citing RFC 1945 and 2068"
4082    </t>
4083    <t>
4084      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4085      "update note about redirect limit"
4086    </t>
4087    <t>
4088      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4089      "Location header ABNF should use 'URI'"
4090    </t>
4091    <t>
4092      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4093      "fragments in Location vs status 303"
4094    </t>
4095    <t>
4096      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4097      "move IANA registrations for optional status codes"
4098    </t>
4099  </list>
4100</t>
4101<t>
4102  Partly resolved issues:
4103  <list style="symbols"> 
4104    <t>
4105      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4106      "Are OPTIONS and TRACE safe?"
4107    </t>
4108  </list>
4109</t>
4110</section>
4111
4112<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4113<t>
4114  Closed issues:
4115  <list style="symbols"> 
4116    <t>
4117      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4118      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4119      status codes when fixing this previously)
4120    </t>
4121  </list>
4122</t>
4123</section>
4124
4125<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4126<t>
4127  Closed issues:
4128  <list style="symbols"> 
4129    <t>
4130      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4131      "Fragment combination / precedence during redirects"
4132    </t>
4133  </list>
4134</t>
4135<t>
4136  Partly resolved issues:
4137  <list style="symbols"> 
4138    <t>
4139      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4140      "Location header payload handling"
4141    </t>
4142    <t>
4143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4144      "Term for the requested resource's URI"
4145    </t>
4146  </list>
4147</t>
4148</section>
4149
4150<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4151<t>
4152  Closed issues:
4153  <list style="symbols"> 
4154    <t>
4155      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4156      "Clarify 'Requested Variant'"
4157    </t>
4158    <t>
4159      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4160      "Clarify entity / representation / variant terminology"
4161    </t>
4162    <t>
4163      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4164      "Methods and Caching"
4165    </t>
4166    <t>
4167      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4168      "OPTIONS vs Max-Forwards"
4169    </t>
4170    <t>
4171      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4172      "Status codes and caching"
4173    </t>
4174    <t>
4175      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4176      "consider removing the 'changes from 2068' sections"
4177    </t>
4178  </list>
4179</t>
4180</section>
4181
4182<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4183<t>
4184  Closed issues:
4185  <list style="symbols"> 
4186    <t>
4187      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4188      "Considerations for new status codes"
4189    </t>
4190    <t>
4191      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4192      "Considerations for new methods"
4193    </t>
4194    <t>
4195      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4196      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4197    </t>
4198  </list>
4199</t>
4200</section>
4201
4202<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4203<t>
4204  Closed issues:
4205  <list style="symbols"> 
4206    <t>
4207      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4208      "Fragment combination / precedence during redirects" (added warning
4209      about having a fragid on the redirect may cause inconvenience in
4210      some cases)
4211    </t>
4212    <t>
4213      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4214      "Content-* vs. PUT"
4215    </t>
4216    <t>
4217      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4218      "205 Bodies"
4219    </t>
4220    <t>
4221      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4222      "Understanding Content-* on non-PUT requests"
4223    </t>
4224    <t>
4225      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4226      "Content-*"
4227    </t>
4228    <t>
4229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4230      "Header type defaulting"
4231    </t>
4232    <t>
4233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4234      "PUT - 'store under' vs 'store at'"
4235    </t>
4236    <t>
4237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4238      "duplicate ABNF for Reason-Phrase"
4239    </t>
4240    <t>
4241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4242      "Note special status of Content-* prefix in header registration procedures"
4243    </t>
4244    <t>
4245      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4246      "Max-Forwards vs extension methods"
4247    </t>
4248    <t>
4249      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4250      "What is the value space of HTTP status codes?" (actually fixed in
4251      draft-ietf-httpbis-p2-semantics-11)
4252    </t>
4253    <t>
4254      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4255      "Header Classification"
4256    </t>
4257    <t>
4258      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4259      "PUT side effect: invalidation or just stale?"
4260    </t>
4261    <t>
4262      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4263      "proxies not supporting certain methods"
4264    </t>
4265    <t>
4266      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4267      "Migrate CONNECT from RFC2817 to p2"
4268    </t>
4269    <t>
4270      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4271      "Migrate Upgrade details from RFC2817"
4272    </t>
4273    <t>
4274      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4275      "clarify PUT semantics'"
4276    </t>
4277    <t>
4278      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4279      "duplicate ABNF for 'Method'"
4280    </t>
4281    <t>
4282      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4283      "untangle ABNFs for header fields"
4284    </t>
4285  </list>
4286</t>
4287</section>
4288
4289<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4290<t>
4291  Closed issues:
4292  <list style="symbols"> 
4293    <t>
4294      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4295      "untangle ABNFs for header fields"
4296    </t>
4297    <t>
4298      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4299      "message-body in CONNECT request"
4300    </t>
4301  </list>
4302</t>
4303</section>
4304
4305<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4306<t>
4307  Closed issues:
4308  <list style="symbols"> 
4309    <t>
4310      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4311      "Clarify status code for rate limiting"
4312    </t>
4313    <t>
4314      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4315      "clarify 403 forbidden"
4316    </t>
4317    <t>
4318      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4319      "Clarify 203 Non-Authoritative Information"
4320    </t>
4321    <t>
4322      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4323      "update default reason phrase for 413"
4324    </t>
4325  </list>
4326</t>
4327</section>
4328
4329<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4330<t>
4331  Closed issues:
4332  <list style="symbols"> 
4333    <t>
4334      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4335      "Strength of requirements on Accept re: 406"
4336    </t>
4337    <t>
4338      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4339      "400 response isn't generic"
4340    </t>
4341  </list>
4342</t>
4343</section>
4344
4345<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4346<t>
4347  Closed issues:
4348  <list style="symbols"> 
4349    <t>
4350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4351      "Redirects and non-GET methods"
4352    </t>
4353    <t>
4354      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4355      "clarify 303 redirect on HEAD"
4356    </t>
4357  </list>
4358</t>
4359<t>
4360  Work-in-progress:
4361  <list style="symbols"> 
4362    <t>
4363      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4364      "Considerations for new headers"
4365    </t>
4366  </list>
4367</t>
4368</section>
4369
4370</section>
4371
4372</back>
4373</rfc>
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