source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1454

Last change on this file since 1454 was 1452, checked in by julian.reschke@…, 8 years ago

Rephrase description of conformance; explain how the spec handles error handling (see #186)

  • Property svn:eol-style set to native
File size: 192.7 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "October">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY architecture               "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY agent-driven-negotiation   "<xref target='Part3' x:rel='#agent-driven.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY field-rules                "<xref target='Part1' x:rel='#field.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY intermediaries             "<xref target='Part1' x:rel='#intermediaries' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY chunked-encoding           "<xref target='Part1' x:rel='#chunked.encoding' 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-content-type        "<xref target='Part3' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-fields              "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
61  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
62  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
63  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
64  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
65  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
66  <!ENTITY header-upgrade             "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
67  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.te' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
68  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
69  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
70  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
71  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
72  <!ENTITY media-types                "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
73  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
74  <!ENTITY product-tokens             "<xref target='Part1' x:rel='#product.tokens' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
75  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
76  <!ENTITY status-206                 "<xref target='Part5' x:rel='#status.206' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
77  <!ENTITY status-304                 "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
78  <!ENTITY status-401                 "<xref target='Part7' x:rel='#status.401' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
79  <!ENTITY status-407                 "<xref target='Part7' x:rel='#status.407' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
80  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
81  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
82  <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
83  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
84  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
85  <!ENTITY p7-status-codes            "<xref target='Part7' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
86  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
87  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
88  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
89]>
90<?rfc toc="yes" ?>
91<?rfc symrefs="yes" ?>
92<?rfc sortrefs="yes" ?>
93<?rfc compact="yes"?>
94<?rfc subcompact="no" ?>
95<?rfc linkmailto="no" ?>
96<?rfc editing="no" ?>
97<?rfc comments="yes"?>
98<?rfc inline="yes"?>
99<?rfc rfcedstyle="yes"?>
100<?rfc-ext allow-markup-in-artwork="yes" ?>
101<?rfc-ext include-references-in-index="yes" ?>
102<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
103     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
104     xmlns:x='http://purl.org/net/xml2rfc/ext'
105     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
106<front>
107
108  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
109
110  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
111    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
112    <address>
113      <postal>
114        <street>345 Park Ave</street>
115        <city>San Jose</city>
116        <region>CA</region>
117        <code>95110</code>
118        <country>USA</country>
119      </postal>
120      <email>fielding@gbiv.com</email>
121      <uri>http://roy.gbiv.com/</uri>
122    </address>
123  </author>
124
125  <author initials="J." surname="Gettys" fullname="Jim Gettys">
126    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
127    <address>
128      <postal>
129        <street>21 Oak Knoll Road</street>
130        <city>Carlisle</city>
131        <region>MA</region>
132        <code>01741</code>
133        <country>USA</country>
134      </postal>
135      <email>jg@freedesktop.org</email>
136      <uri>http://gettys.wordpress.com/</uri>
137    </address>
138  </author>
139 
140  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
141    <organization abbrev="HP">Hewlett-Packard Company</organization>
142    <address>
143      <postal>
144        <street>HP Labs, Large Scale Systems Group</street>
145        <street>1501 Page Mill Road, MS 1177</street>
146        <city>Palo Alto</city>
147        <region>CA</region>
148        <code>94304</code>
149        <country>USA</country>
150      </postal>
151      <email>JeffMogul@acm.org</email>
152    </address>
153  </author>
154
155  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
156    <organization abbrev="Microsoft">Microsoft Corporation</organization>
157    <address>
158      <postal>
159        <street>1 Microsoft Way</street>
160        <city>Redmond</city>
161        <region>WA</region>
162        <code>98052</code>
163        <country>USA</country>
164      </postal>
165      <email>henrikn@microsoft.com</email>
166    </address>
167  </author>
168
169  <author initials="L." surname="Masinter" fullname="Larry Masinter">
170    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
171    <address>
172      <postal>
173        <street>345 Park Ave</street>
174        <city>San Jose</city>
175        <region>CA</region>
176        <code>95110</code>
177        <country>USA</country>
178      </postal>
179      <email>LMM@acm.org</email>
180      <uri>http://larry.masinter.net/</uri>
181    </address>
182  </author>
183 
184  <author initials="P." surname="Leach" fullname="Paul J. Leach">
185    <organization abbrev="Microsoft">Microsoft Corporation</organization>
186    <address>
187      <postal>
188        <street>1 Microsoft Way</street>
189        <city>Redmond</city>
190        <region>WA</region>
191        <code>98052</code>
192      </postal>
193      <email>paulle@microsoft.com</email>
194    </address>
195  </author>
196   
197  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
198    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
199    <address>
200      <postal>
201        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
202        <street>The Stata Center, Building 32</street>
203        <street>32 Vassar Street</street>
204        <city>Cambridge</city>
205        <region>MA</region>
206        <code>02139</code>
207        <country>USA</country>
208      </postal>
209      <email>timbl@w3.org</email>
210      <uri>http://www.w3.org/People/Berners-Lee/</uri>
211    </address>
212  </author>
213
214  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
215    <organization abbrev="W3C">World Wide Web Consortium</organization>
216    <address>
217      <postal>
218        <street>W3C / ERCIM</street>
219        <street>2004, rte des Lucioles</street>
220        <city>Sophia-Antipolis</city>
221        <region>AM</region>
222        <code>06902</code>
223        <country>France</country>
224      </postal>
225      <email>ylafon@w3.org</email>
226      <uri>http://www.raubacapeu.net/people/yves/</uri>
227    </address>
228  </author>
229
230  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
231    <organization abbrev="greenbytes">greenbytes GmbH</organization>
232    <address>
233      <postal>
234        <street>Hafenweg 16</street>
235        <city>Muenster</city><region>NW</region><code>48155</code>
236        <country>Germany</country>
237      </postal>
238      <phone>+49 251 2807760</phone>
239      <facsimile>+49 251 2807761</facsimile>
240      <email>julian.reschke@greenbytes.de</email>
241      <uri>http://greenbytes.de/tech/webdav/</uri>
242    </address>
243  </author>
244
245  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
246  <workgroup>HTTPbis Working Group</workgroup>
247
248<abstract>
249<t>
250   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
251   distributed, collaborative, hypertext information systems. HTTP has been in
252   use by the World Wide Web global information initiative since 1990. This
253   document is Part 2 of the seven-part specification that defines the protocol
254   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
255</t>
256<t>
257   Part 2 defines the semantics of HTTP messages as expressed by request
258   methods, request header fields, response status codes, and response header
259   fields.
260</t>
261</abstract>
262
263<note title="Editorial Note (To be removed by RFC Editor)">
264  <t>
265    Discussion of this draft should take place on the HTTPBIS working group
266    mailing list (ietf-http-wg@w3.org), which is archived at
267    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
268  </t>
269  <t>
270    The current issues list is at
271    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
272    documents (including fancy diffs) can be found at
273    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
274  </t>
275  <t>
276    The changes in this draft are summarized in <xref target="changes.since.16"/>.
277  </t>
278</note>
279</front>
280<middle>
281<section title="Introduction" anchor="introduction">
282<t>
283   This document defines HTTP/1.1 request and response semantics.  Each HTTP
284   message, as defined in &messaging;, is in the form of either a request or
285   a response.  An HTTP server listens on a connection for HTTP requests and
286   responds to each request, in the order received on that connection, with
287   one or more HTTP response messages.  This document defines the commonly
288   agreed upon semantics of the HTTP uniform interface, the intentions defined
289   by each request method, and the various response messages that might be
290   expected as a result of applying that method to the target resource.
291</t>
292<t>
293   This document is currently disorganized in order to minimize the changes
294   between drafts and enable reviewers to see the smaller errata changes.
295   A future draft will reorganize the sections to better reflect the content.
296   In particular, the sections will be ordered according to the typical
297   processing of an HTTP request message (after message parsing): resource
298   mapping, methods, request modifying header fields, response status,
299   status modifying header fields, and resource metadata.  The current mess
300   reflects how widely dispersed these topics and associated requirements
301   had become in <xref target="RFC2616"/>.
302</t>
303
304<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
305<t>
306   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
307   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
308   document are to be interpreted as described in <xref target="RFC2119"/>.
309</t>
310<t>
311   This document defines conformance criteria for several roles in HTTP
312   communication, including Senders, Recipients, Clients, Servers, User-Agents,
313   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
314   for definitions of these terms.
315</t>
316<t>
317   An implementation is considered conformant if it complies with all of the
318   requirements associated with its role(s). Note that SHOULD-level requirements
319   are relevant here, unless one of the documented exceptions is applicable.
320</t>
321<t>
322   This document also uses ABNF to define valid protocol elements
323   (<xref target="notation"/>). In addition to the prose requirements placed
324   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
325</t>
326<t>
327   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
328   protocol element from an invalid construct. However, HTTP does not define
329   specific error handling mechanisms, except in cases where it has direct
330   impact on security. This is because different uses of the protocol require
331   different error handling strategies; for example, a Web browser may wish to
332   transparently recover from a response where the Location header field
333   doesn't parse according to the ABNF, whereby in a systems control protocol
334   using HTTP, this type of error recovery could lead to dangerous consequences.
335</t>
336</section>
337
338<section title="Syntax Notation" anchor="notation">
339  <x:anchor-alias value="CR"/>
340  <x:anchor-alias value="DIGIT"/>
341  <x:anchor-alias value="LF"/>
342  <x:anchor-alias value="HTAB"/>
343  <x:anchor-alias value="VCHAR"/>
344  <x:anchor-alias value="SP"/>
345<t>
346  This specification uses the ABNF syntax defined in &notation; (which
347  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
348  <xref target="collected.abnf"/> shows the collected ABNF, with the list
349  rule expanded.
350</t>
351<t>
352  The following core rules are included by
353  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
354  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
355  DIGIT (decimal 0-9), DQUOTE (double quote),
356  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
357  OCTET (any 8-bit sequence of data), SP (space), and
358  VCHAR (any visible US-ASCII character).
359</t>
360
361<section title="Core Rules" anchor="core.rules">
362  <x:anchor-alias value="obs-text"/>
363  <x:anchor-alias value="quoted-string"/>
364  <x:anchor-alias value="token"/>
365  <x:anchor-alias value="OWS"/>
366  <x:anchor-alias value="RWS"/>
367<t>
368  The core rules below are defined in <xref target="Part1"/>:
369</t>
370<figure><artwork type="abnf2616">
371  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
372  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &basic-rules;&gt;
373  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &basic-rules;&gt;
374  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-rules;&gt;
375  <x:ref>token</x:ref>         = &lt;token, defined in &field-rules;&gt;
376</artwork></figure>
377</section>
378
379<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
380  <x:anchor-alias value="absolute-URI"/>
381  <x:anchor-alias value="comment"/>
382  <x:anchor-alias value="partial-URI"/>
383  <x:anchor-alias value="product"/>
384  <x:anchor-alias value="URI-reference"/>
385<t>
386  The ABNF rules below are defined in other parts:
387</t>
388<figure><!--Part1--><artwork type="abnf2616">
389  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
390  <x:ref>comment</x:ref>       = &lt;comment, defined in &header-fields;&gt;
391  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
392  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
393  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
394</artwork></figure>
395</section>
396</section>
397</section>
398
399<section title="Method" anchor="method">
400  <x:anchor-alias value="Method"/>
401  <x:anchor-alias value="extension-method"/>
402<t>
403   The Method token indicates the request method to be performed on the target
404   resource (&effective-request-uri;). The method is case-sensitive.
405</t>
406<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
407  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
408</artwork></figure>
409<t>
410   The list of methods allowed by a resource can be specified in an
411   Allow header field (<xref target="header.allow"/>). The status code of the response
412   always notifies the client whether a method is currently allowed on a
413   resource, since the set of allowed methods can change dynamically. An
414   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
415   if the method is known by the origin server but not allowed for the
416   resource, and 501 (Not Implemented) if the method is
417   unrecognized or not implemented by the origin server. The methods GET
418   and HEAD &MUST; be supported by all general-purpose servers. All other
419   methods are &OPTIONAL;; however, if the above methods are implemented,
420   they &MUST; be implemented with the same semantics as those specified
421   in <xref target="method.definitions"/>.
422</t>
423
424<section title="Overview of Methods" anchor="overview.of.methods">
425<t>
426  The methods listed below are defined in <xref target="method.definitions"/>.
427</t>
428<texttable align="left">
429  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
430 
431  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
432  <c>GET</c> <c><xref target="GET"/></c>
433  <c>HEAD</c> <c><xref target="HEAD"/></c>
434  <c>POST</c> <c><xref target="POST"/></c>
435  <c>PUT</c> <c><xref target="PUT"/></c>
436  <c>DELETE</c> <c><xref target="DELETE"/></c>
437  <c>TRACE</c> <c><xref target="TRACE"/></c>
438  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
439</texttable>
440<t>
441  Note that this list is not exhaustive &mdash; it does not include request methods defined
442  in other specifications.
443</t>
444</section>
445
446<section title="Method Registry" anchor="method.registry">
447<t>
448  The HTTP Method Registry defines the name space for the Method token in the
449  Request line of an HTTP request.
450</t>
451<t>
452  Registrations &MUST; include the following fields:
453  <list style="symbols">
454    <t>Method Name (see <xref target="method"/>)</t>
455    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
456    <t>Pointer to specification text</t>
457  </list>
458</t>
459<t>
460  Values to be added to this name space are subject to IETF review
461  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
462</t>
463<t>
464  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
465</t>
466
467<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
468<t>
469   When it is necessary to express new semantics for a HTTP request that
470   aren't specific to a single application or media type, and currently defined
471   methods are inadequate, it may be appropriate to register a new method.
472</t>
473<t>
474   HTTP methods are generic; that is, they are potentially applicable to any
475   resource, not just one particular media type, "type" of resource, or
476   application. As such, it is preferred that new HTTP methods be registered
477   in a document that isn't specific to a single application, so that this is
478   clear.
479</t>
480<t>
481   Due to the parsing rules defined in &message-body;, definitions of HTTP
482   methods cannot prohibit the presence of a message-body on either the request
483   or the response message (with responses to HEAD requests being the single
484   exception). Definitions of new methods cannot change this rule, but they can
485   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
486</t>
487<t>
488   New method definitions need to indicate whether they are safe (<xref
489   target="safe.methods"/>), what semantics (if any) the request body has,
490   and whether they are idempotent (<xref target="idempotent.methods"/>).
491   They also need to state whether they can be cached (&caching;); in
492   particular what conditions a cache may store the response, and under what
493   conditions such a stored response may be used to satisfy a subsequent
494   request.
495</t>
496</section>
497
498</section>
499</section>
500
501<section title="Header Fields" anchor="header.fields">
502<t>
503   Header fields are key value pairs that can be used to communicate data about
504   the message, its payload, the target resource, or about the connection
505   itself (i.e., control data).  See &header-fields; for a general definition
506   of their syntax.
507</t>
508
509<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
510<t>
511   New header fields are registered using the procedures described in
512   <xref target="RFC3864"/>.
513</t>
514<t>
515   The requirements for header field names are defined in
516   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
517   defining new fields are advised to keep the name as short as practical, and
518   not to prefix them with "X-" if they are to be registered (either
519   immediately or in the future).
520</t>
521<t>
522   New header field values typically have their syntax defined using ABNF
523   (<xref target="RFC5234"/>), using the extensions defined in &notation-abnf;
524   as necessary, and are usually constrained to the range of ASCII characters.
525   Header fields needing a greater range of characters can use an encoding
526   such as the one defined in <xref target="RFC5987"/>.
527</t>
528<t>
529   Because commas (",") are used as a generic delimiter between field-values,
530   they need to be treated with care if they are allowed in the field-value's
531   payload. Typically, components that might contain a comma are protected with
532   double-quotes using the quoted-string ABNF production (&field-rules;).
533</t>
534<t>
535   For example, a textual date and a URI (either of which might contain a comma)
536   could be safely carried in field-values like these:
537</t>
538<figure><artwork type="example">
539  Example-URI-Field: "http://example.com/a.html,foo",
540                     "http://without-a-comma.example.com/"
541  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
542</artwork></figure>
543<t>
544   Many header fields use a format including (case-insensitively) named
545   parameters (for instance, Content-Type, defined in &header-content-type;).
546   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
547   parameter value enables recipients to use existing parser components. Also,
548   the meaning of a value ought to be independent of the syntax variant used
549   for it (for an example, see the notes on parameter handling for media types
550   in &media-types;).
551</t>
552<t>
553   Authors of specifications defining new header fields are advised to consider
554   documenting:
555  <list style="symbols">
556    <x:lt>
557      <t>Whether the field is a single value, or whether it can be a list
558      (delimited by commas; see &header-fields;).</t>
559      <t>If it does not use the list syntax, how to treat messages where the
560      header field occurs multiple times (a sensible default would be to ignore
561      the header field, but this might not always be the right choice).</t>
562    </x:lt>
563    <x:lt><t>Under what conditions the header field can be used; e.g., only in
564    responses or requests, in all messages, only on responses to a particular
565    request method.</t></x:lt>
566    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
567    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
568    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
569    field's value, insert or delete it.</t></x:lt>
570    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
571    <x:lt><t>Whether the header field is useful or allowable in trailers (see
572    &chunked-encoding;).</t></x:lt>
573    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
574  </list>
575</t>
576</section>
577
578<section title="Request Header Fields" anchor="request.header.fields">
579  <x:anchor-alias value="request-header"/>
580<t>
581   The request header fields allow the client to pass additional
582   information about the request, and about the client itself, to the
583   server. These fields act as request modifiers, with semantics
584   equivalent to the parameters on a programming language method
585   invocation.
586</t>
587<texttable align="left">
588  <ttcol>Header Field Name</ttcol>
589  <ttcol>Defined in...</ttcol>
590
591  <c>Accept</c> <c>&header-accept;</c>
592  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
593  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
594  <c>Accept-Language</c> <c>&header-accept-language;</c>
595  <c>Authorization</c> <c>&header-authorization;</c>
596  <c>Expect</c> <c><xref target="header.expect"/></c>
597  <c>From</c> <c><xref target="header.from"/></c>
598  <c>Host</c> <c>&header-host;</c>
599  <c>If-Match</c> <c>&header-if-match;</c>
600  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
601  <c>If-None-Match</c> <c>&header-if-none-match;</c>
602  <c>If-Range</c> <c>&header-if-range;</c>
603  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
604  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
605  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
606  <c>Range</c> <c>&header-range;</c>
607  <c>Referer</c> <c><xref target="header.referer"/></c>
608  <c>TE</c> <c>&header-te;</c>
609  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
610</texttable>
611</section>
612
613<section title="Response Header Fields" anchor="response.header.fields">
614  <x:anchor-alias value="response-header"/>
615<t>
616   The response header fields allow the server to pass additional
617   information about the response which cannot be placed in the Status-Line.
618   These header fields give information about the server and about
619   further access to the target resource (&effective-request-uri;).
620</t>
621<texttable align="left">
622  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
623
624  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
625  <c>Age</c> <c>&header-age;</c>
626  <c>Allow</c> <c><xref target="header.allow"/></c>
627  <c>Date</c> <c><xref target="header.date"/></c>
628  <c>ETag</c> <c>&header-etag;</c>
629  <c>Location</c> <c><xref target="header.location"/></c>
630  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
631  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
632  <c>Server</c> <c><xref target="header.server"/></c>
633  <c>Vary</c> <c>&header-vary;</c>
634  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
635</texttable>
636</section>
637
638</section>
639
640<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
641  <x:anchor-alias value="Reason-Phrase"/>
642  <x:anchor-alias value="Status-Code"/>
643  <x:anchor-alias value="extension-code"/>
644<t>
645   The Status-Code element is a 3-digit integer result code of the attempt to
646   understand and satisfy the request.
647</t>
648<t>
649   The Reason-Phrase is intended to give a short textual description of the
650   Status-Code and is intended for a human user. The client does not need
651   to examine or display the Reason-Phrase.
652</t>
653<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"/>
654  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
655  <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> )
656</artwork></figure>
657<t>
658   HTTP status codes are extensible. HTTP applications are not required
659   to understand the meaning of all registered status codes, though such
660   understanding is obviously desirable. However, applications &MUST;
661   understand the class of any status code, as indicated by the first
662   digit, and treat any unrecognized response as being equivalent to the
663   x00 status code of that class, with the exception that an
664   unrecognized response &MUST-NOT; be cached. For example, if an
665   unrecognized status code of 431 is received by the client, it can
666   safely assume that there was something wrong with its request and
667   treat the response as if it had received a 400 status code. In such
668   cases, user agents &SHOULD; present to the user the representation enclosed
669   with the response, since that representation is likely to include human-readable
670   information which will explain the unusual status.
671</t>
672
673<section title="Overview of Status Codes" anchor="overview.of.status.codes">
674<t> 
675   The status codes listed below are defined in <xref target="status.codes"/>
676   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
677   The reason phrases listed here are only recommendations &mdash; they can be
678   replaced by local equivalents without affecting the protocol.
679</t>
680<texttable align="left">
681  <ttcol>Status-Code</ttcol>
682  <ttcol>Reason-Phrase</ttcol>
683  <ttcol>Defined in...</ttcol>
684 
685  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
686  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
687
688  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
689  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
690  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
691  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
692  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
693  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
694  <c>206</c> <c>Partial Content</c> <c>&status-206;</c>
695
696  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
697  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
698  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
699  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
700  <c>304</c> <c>Not Modified</c> <c>&status-304;</c>
701  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
702  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
703
704  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
705  <c>401</c> <c>Unauthorized</c> <c>&status-401;</c>
706  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
707  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
708  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
709  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
710  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
711  <c>407</c> <c>Proxy Authentication Required</c> <c>&status-407;</c>
712  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
713  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
714  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
715  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
716  <c>412</c> <c>Precondition Failed</c> <c>&status-412;</c>
717  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
718  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
719  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
720  <c>416</c> <c>Requested range not satisfiable</c> <c>&status-416;</c>
721  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
722  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
723
724  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
725  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
726  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
727  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
728  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
729  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
730</texttable>
731<t>
732   Note that this list is not exhaustive &mdash; it does not include
733   extension status codes defined in other specifications.
734</t>
735</section>
736
737<section title="Status Code Registry" anchor="status.code.registry">
738<t>
739  The HTTP Status Code Registry defines the name space for the Status-Code
740  token in the Status-Line of an HTTP response.
741</t>
742<t>
743  Values to be added to this name space are subject to IETF review
744  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
745</t>
746<t>
747  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
748</t>
749
750<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
751<t>
752   When it is necessary to express new semantics for a HTTP response that
753   aren't specific to a single application or media type, and currently defined
754   status codes are inadequate, a new status code can be registered.
755</t>
756<t>
757   HTTP status codes are generic; that is, they are potentially applicable to
758   any resource, not just one particular media type, "type" of resource, or
759   application. As such, it is preferred that new HTTP status codes be
760   registered in a document that isn't specific to a single application, so
761   that this is clear.
762</t>
763<t>
764   Definitions of new HTTP status codes typically explain the request
765   conditions that produce a response containing the status code (e.g.,
766   combinations of request headers and/or method(s)), along with any
767   interactions with response headers (e.g., those that are required, those
768   that modify the semantics of the response).
769</t>
770<t>
771   New HTTP status codes are required to fall under one of the categories
772   defined in <xref target="status.codes"/>. To allow existing parsers to
773   properly handle them, new status codes cannot disallow a response body,
774   although they can mandate a zero-length response body. They can require the
775   presence of one or more particular HTTP response header(s).
776</t>
777<t>
778   Likewise, their definitions can specify that caches are allowed to use
779   heuristics to determine their freshness (see &caching;; by default, it is
780   not allowed), and can define how to determine the resource which they
781   carry a representation for (see <xref
782   target="identifying.response.associated.with.representation"/>; by default,
783   it is anonymous).
784</t>
785</section>
786
787</section>
788
789</section>
790
791<section title="Representation" anchor="representation">
792<t>
793   Request and Response messages &MAY; transfer a representation if not otherwise
794   restricted by the request method or response status code. A representation
795   consists of metadata (representation header fields) and data (representation
796   body).  When a complete or partial representation is enclosed in an HTTP message,
797   it is referred to as the payload of the message. HTTP representations
798   are defined in &payload;.
799</t>
800<t>
801   A representation body is only present in a message when a message-body is
802   present, as described in &message-body;. The representation body is obtained
803   from the message-body by decoding any Transfer-Encoding that might
804   have been applied to ensure safe and proper transfer of the message.
805</t>
806
807<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
808<t>
809   It is sometimes necessary to determine an identifier for the resource
810   associated with a representation.
811</t>
812<t>
813   An HTTP request representation, when present, is always associated with an
814   anonymous (i.e., unidentified) resource.
815</t>
816<t>
817   In the common case, an HTTP response is a representation of the target
818   resource (see &effective-request-uri;). However, this is not always the
819   case. To determine the URI of the resource a response is associated with,
820   the following rules are used (with the first applicable one being selected):
821</t>
822<t><list style="numbers">
823   <t>If the response status code is 200 or 203 and the request method was GET,
824   the response payload is a representation of the target resource.</t>
825   <t>If the response status code is 204, 206, or 304 and the request method was GET
826   or HEAD, the response payload is a partial representation of the target
827   resource.</t>
828   <t>If the response has a Content-Location header field, and that URI is the same
829   as the effective request URI, the response payload is a representation of the
830   target resource.</t>
831   <t>If the response has a Content-Location header field, and that URI is not the
832   same as the effective request URI, then the response asserts that its
833   payload is a representation of the resource identified by the
834   Content-Location URI. However, such an assertion cannot be trusted unless
835   it can be verified by other means (not defined by HTTP).</t>
836   <t>Otherwise, the response is a representation of an anonymous (i.e.,
837   unidentified) resource.</t>
838</list></t>
839<t>
840  <cref anchor="TODO-req-uri">
841   The comparison function is going to have to be defined somewhere,
842   because we already need to compare URIs for things like cache invalidation.</cref>
843</t>
844</section>
845
846</section>
847
848
849<section title="Method Definitions" anchor="method.definitions">
850<t>
851   The set of common request methods for HTTP/1.1 is defined below. Although
852   this set can be expanded, additional methods cannot be assumed to
853   share the same semantics for separately extended clients and servers.
854</t>
855
856<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
857
858<section title="Safe Methods" anchor="safe.methods">
859<iref item="Safe Methods" primary="true"/>
860<t>
861   Implementors need to be aware that the software represents the user in
862   their interactions over the Internet, and need to allow
863   the user to be aware of any actions they take which might have an
864   unexpected significance to themselves or others.
865</t>
866<t>
867   In particular, the convention has been established that the GET, HEAD,
868   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
869   of taking an action other than retrieval. These request methods ought
870   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
871   This allows user agents to represent other methods, such as POST, PUT
872   and DELETE, in a special way, so that the user is made aware of the
873   fact that a possibly unsafe action is being requested.
874</t>
875<t>
876   Naturally, it is not possible to ensure that the server does not
877   generate side-effects as a result of performing a GET request; in
878   fact, some dynamic resources consider that a feature. The important
879   distinction here is that the user did not request the side-effects,
880   so therefore cannot be held accountable for them.
881</t>
882</section>
883
884<section title="Idempotent Methods" anchor="idempotent.methods">
885<iref item="Idempotent Methods" primary="true"/>
886<t>
887   Request methods can also have the property of "idempotence" in that,
888   aside from error or expiration issues, the intended effect of multiple
889   identical requests is the same as for a single request.
890   PUT, DELETE, and all safe request methods are idempotent.
891   It is important to note that idempotence refers only to changes
892   requested by the client: a server is free to change its state due
893   to multiple requests for the purpose of tracking those requests,
894   versioning of results, etc.
895</t>
896</section>
897</section>
898
899<section title="OPTIONS" anchor="OPTIONS">
900  <rdf:Description>
901    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
902  </rdf:Description>
903  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
904  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
905<t>
906   The OPTIONS method requests information about the
907   communication options available on the request/response chain
908   identified by the effective request URI. This method allows a client to
909   determine the options and/or requirements associated with a resource,
910   or the capabilities of a server, without implying a resource action
911   or initiating a resource retrieval.
912</t>
913<t>
914   Responses to the OPTIONS method are not cacheable.
915</t>
916<t>
917   If the OPTIONS request includes a message-body (as indicated by the
918   presence of Content-Length or Transfer-Encoding), then the media type
919   &MUST; be indicated by a Content-Type field. Although this
920   specification does not define any use for such a body, future
921   extensions to HTTP might use the OPTIONS body to make more detailed
922   queries on the server.
923</t>
924<t>
925   If the request-target is an asterisk ("*"), the OPTIONS request is
926   intended to apply to the server in general rather than to a specific
927   resource. Since a server's communication options typically depend on
928   the resource, the "*" request is only useful as a "ping" or "no-op"
929   type of method; it does nothing beyond allowing the client to test
930   the capabilities of the server. For example, this can be used to test
931   a proxy for HTTP/1.1 compliance (or lack thereof).
932</t>
933<t>
934   If the request-target is not an asterisk, the OPTIONS request applies
935   only to the options that are available when communicating with that
936   resource.
937</t>
938<t>
939   A 200 response &SHOULD; include any header fields that indicate
940   optional features implemented by the server and applicable to that
941   resource (e.g., Allow), possibly including extensions not defined by
942   this specification. The response body, if any, &SHOULD; also include
943   information about the communication options. The format for such a
944   body is not defined by this specification, but might be defined by
945   future extensions to HTTP. Content negotiation &MAY; be used to select
946   the appropriate response format. If no response body is included, the
947   response &MUST; include a Content-Length field with a field-value of
948   "0".
949</t>
950<t>
951   The Max-Forwards header field &MAY; be used to target a
952   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
953   If no Max-Forwards field is present in the request, then the forwarded
954   request &MUST-NOT; include a Max-Forwards field.
955</t>
956</section>
957
958<section title="GET" anchor="GET">
959  <rdf:Description>
960    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
961  </rdf:Description>
962  <iref primary="true" item="GET method" x:for-anchor=""/>
963  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
964<t>
965   The GET method requests transfer of a current representation of
966   the target resource.
967</t>
968<t>   
969   If the target resource is a data-producing process, it is the
970   produced data which shall be returned as the representation in the response and not
971   the source text of the process, unless that text happens to be the output of
972   the process.
973</t>
974<t>
975   The semantics of the GET method change to a "conditional GET" if the
976   request message includes an If-Modified-Since, If-Unmodified-Since,
977   If-Match, If-None-Match, or If-Range header field. A conditional GET
978   requests that the representation be transferred only under the
979   circumstances described by the conditional header field(s). The
980   conditional GET request is intended to reduce unnecessary network
981   usage by allowing cached representations to be refreshed without requiring
982   multiple requests or transferring data already held by the client.
983</t>
984<t>
985   The semantics of the GET method change to a "partial GET" if the
986   request message includes a Range header field. A partial GET requests
987   that only part of the representation be transferred, as described in &header-range;.
988   The partial GET request is intended to reduce unnecessary
989   network usage by allowing partially-retrieved representations to be
990   completed without transferring data already held by the client.
991</t>
992<t>
993   Bodies on GET requests have no defined semantics. Note that sending a body
994   on a GET request might cause some existing implementations to reject the
995   request.
996</t>
997<t>
998   The response to a GET request is cacheable and &MAY; be used to satisfy
999   subsequent GET and HEAD requests (see &caching;).
1000</t>
1001<t>
1002   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
1003</t>
1004</section>
1005
1006<section title="HEAD" anchor="HEAD">
1007  <rdf:Description>
1008    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1009  </rdf:Description>
1010  <iref primary="true" item="HEAD method" x:for-anchor=""/>
1011  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
1012<t>
1013   The HEAD method is identical to GET except that the server &MUST-NOT;
1014   return a message-body in the response. The metadata contained
1015   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
1016   to the information sent in response to a GET request. This method can
1017   be used for obtaining metadata about the representation implied by the
1018   request without transferring the representation body. This method is
1019   often used for testing hypertext links for validity, accessibility,
1020   and recent modification.
1021</t>
1022<t>
1023   The response to a HEAD request is cacheable and &MAY; be used to satisfy
1024   a subsequent HEAD request; see &caching;. It also &MAY; be used to update a previously cached
1025   representation from that resource; if the new field values
1026   indicate that the cached representation differs from the current representation (as
1027   would be indicated by a change in Content-Length, ETag
1028   or Last-Modified), then the cache &MUST; treat the cache entry as
1029   stale.
1030</t>
1031<t>
1032   Bodies on HEAD requests have no defined semantics. Note that sending a body
1033   on a HEAD request might cause some existing implementations to reject the
1034   request.
1035</t>
1036</section>
1037
1038<section title="POST" anchor="POST">
1039  <iref primary="true" item="POST method" x:for-anchor=""/>
1040  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
1041<t>
1042   The POST method requests that the origin server accept the
1043   representation enclosed in the request as data to be processed by the
1044   target resource. POST is designed to allow a uniform method to cover the
1045   following functions:
1046  <list style="symbols">
1047    <t>
1048      Annotation of existing resources;
1049    </t>
1050    <t>
1051        Posting a message to a bulletin board, newsgroup, mailing list,
1052        or similar group of articles;
1053    </t>
1054    <t>
1055        Providing a block of data, such as the result of submitting a
1056        form, to a data-handling process;
1057    </t>
1058    <t>
1059        Extending a database through an append operation.
1060    </t>
1061  </list>
1062</t>
1063<t>
1064   The actual function performed by the POST method is determined by the
1065   server and is usually dependent on the effective request URI.
1066</t>
1067<t>
1068   The action performed by the POST method might not result in a
1069   resource that can be identified by a URI. In this case, either 200
1070   (OK) or 204 (No Content) is the appropriate response status code,
1071   depending on whether or not the response includes a representation that
1072   describes the result.
1073</t>
1074<t>
1075   If a resource has been created on the origin server, the response
1076   &SHOULD; be 201 (Created) and contain a representation which describes the
1077   status of the request and refers to the new resource, and a Location
1078   header field (see <xref target="header.location"/>).
1079</t>
1080<t>
1081   Responses to POST requests are only cacheable when they
1082   include explicit freshness information (see &p6-explicit;). A
1083   cached POST response with a Content-Location header field
1084   (see &header-content-location;) whose value is the effective
1085   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1086</t>
1087<t>
1088   Note that POST caching is not widely implemented.
1089   However, the 303 (See Other) response can be used to direct the
1090   user agent to retrieve a cacheable resource.
1091</t>
1092</section>
1093
1094<section title="PUT" anchor="PUT">
1095  <iref primary="true" item="PUT method" x:for-anchor=""/>
1096  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
1097<t>
1098   The PUT method requests that the state of the target resource
1099   be created or replaced with the state defined by the representation
1100   enclosed in the request message payload.  A successful PUT of a given
1101   representation would suggest that a subsequent GET on that same target
1102   resource will result in an equivalent representation being returned in
1103   a 200 (OK) response.  However, there is no guarantee that such a state
1104   change will be observable, since the target resource might be acted
1105   upon by other user agents in parallel, or might be subject to dynamic
1106   processing by the origin server, before any subsequent GET is received.
1107   A successful response only implies that the user agent's intent was
1108   achieved at the time of its processing by the origin server.
1109</t>
1110<t>   
1111   If the target resource does not have a current representation and
1112   the PUT successfully creates one, then the origin server &MUST; inform
1113   the user agent by sending a 201 (Created) response.  If the target
1114   resource does have a current representation and that representation is
1115   successfully modified in accordance with the state of the enclosed
1116   representation, then either a 200 (OK) or 204 (No Content) response
1117   &SHOULD; be sent to indicate successful completion of the request.
1118</t>
1119<t>
1120   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1121   as part of the resource state).
1122</t>
1123<t>
1124   An origin server &SHOULD; verify that the PUT representation is
1125   consistent with any constraints which the server has for the target
1126   resource that cannot or will not be changed by the PUT.  This is
1127   particularly important when the origin server uses internal
1128   configuration information related to the URI in order to set the
1129   values for representation metadata on GET responses.  When a PUT
1130   representation is inconsistent with the target resource, the origin
1131   server &SHOULD; either make them consistent, by transforming the
1132   representation or changing the resource configuration, or respond
1133   with an appropriate error message containing sufficient information
1134   to explain why the representation is unsuitable.  The 409 (Conflict)
1135   or 415 (Unsupported Media Type) status codes are suggested, with the
1136   latter being specific to constraints on Content-Type values.
1137</t>
1138<t>
1139   For example, if the target resource is configured to always have a
1140   Content-Type of "text/html" and the representation being PUT has a
1141   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1142   (a) reconfigure the target resource to reflect the new media type;
1143   (b) transform the PUT representation to a format consistent with that
1144   of the resource before saving it as the new resource state; or,
1145   (c) reject the request with a 415 response indicating that the target
1146   resource is limited to "text/html", perhaps including a link to a
1147   different resource that would be a suitable target for the new
1148   representation.
1149</t>
1150<t>
1151   HTTP does not define exactly how a PUT method affects the state
1152   of an origin server beyond what can be expressed by the intent of
1153   the user agent request and the semantics of the origin server response.
1154   It does not define what a resource might be, in any sense of that
1155   word, beyond the interface provided via HTTP.  It does not define
1156   how resource state is "stored", nor how such storage might change
1157   as a result of a change in resource state, nor how the origin server
1158   translates resource state into representations.  Generally speaking,
1159   all implementation details behind the resource interface are
1160   intentionally hidden by the server.
1161</t>
1162<t>
1163   The fundamental difference between the POST and PUT methods is
1164   highlighted by the different intent for the target resource.
1165   The target resource in a POST request is intended to handle the
1166   enclosed representation as a data-accepting process, such as for
1167   a gateway to some other protocol or a document that accepts annotations.
1168   In contrast, the target resource in a PUT request is intended to
1169   take the enclosed representation as a new or replacement value.
1170   Hence, the intent of PUT is idempotent and visible to intermediaries,
1171   even though the exact effect is only known by the origin server.
1172</t>
1173<t>
1174   Proper interpretation of a PUT request presumes that the user agent
1175   knows what target resource is desired.  A service that is intended
1176   to select a proper URI on behalf of the client, after receiving
1177   a state-changing request, &SHOULD; be implemented using the POST
1178   method rather than PUT.  If the origin server will not make the
1179   requested PUT state change to the target resource and instead
1180   wishes to have it applied to a different resource, such as when the
1181   resource has been moved to a different URI, then the origin server
1182   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
1183   then make its own decision regarding whether or not to redirect the
1184   request.
1185</t>
1186<t>
1187   A PUT request applied to the target resource &MAY; have side-effects
1188   on other resources.  For example, an article might have a URI for
1189   identifying "the current version" (a resource) which is separate
1190   from the URIs identifying each particular version (different
1191   resources that at one point shared the same state as the current version
1192   resource).  A successful PUT request on "the current version" URI might
1193   therefore create a new version resource in addition to changing the
1194   state of the target resource, and might also cause links to be added
1195   between the related resources.
1196</t>
1197<t>
1198   An origin server &SHOULD; reject any PUT request that contains a
1199   Content-Range header field, since it might be misinterpreted as
1200   partial content (or might be partial content that is being mistakenly
1201   PUT as a full representation).  Partial content updates are
1202   possible by targeting a separately identified resource with state
1203   that overlaps a portion of the larger resource, or by using a
1204   different method that has been specifically defined for partial
1205   updates (for example, the PATCH method defined in
1206   <xref target="RFC5789"/>).
1207</t>
1208<t>
1209   Responses to the PUT method are not cacheable. If a PUT request passes
1210   through a cache that has one or more stored responses for the effective
1211   request URI, those stored responses will be invalidated (see
1212   &p6-invalid;).
1213</t>
1214</section>
1215
1216<section title="DELETE" anchor="DELETE">
1217  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1218  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
1219<t>
1220   The DELETE method requests that the origin server delete the target
1221   resource. This method &MAY; be overridden by
1222   human intervention (or other means) on the origin server. The client cannot
1223   be guaranteed that the operation has been carried out, even if the
1224   status code returned from the origin server indicates that the action
1225   has been completed successfully. However, the server &SHOULD-NOT; 
1226   indicate success unless, at the time the response is given, it
1227   intends to delete the resource or move it to an inaccessible
1228   location.
1229</t>
1230<t>
1231   A successful response &SHOULD; be 200 (OK) if the response includes an
1232   representation describing the status, 202 (Accepted) if the action has not
1233   yet been enacted, or 204 (No Content) if the action has been enacted
1234   but the response does not include a representation.
1235</t>
1236<t>
1237   Bodies on DELETE requests have no defined semantics. Note that sending a body
1238   on a DELETE request might cause some existing implementations to reject the
1239   request.
1240</t>
1241<t>
1242   Responses to the DELETE method are not cacheable. If a DELETE request
1243   passes through a cache that has one or more stored responses for the
1244   effective request URI, those stored responses will be invalidated (see
1245   &p6-invalid;).
1246</t>
1247</section>
1248
1249<section title="TRACE" anchor="TRACE">
1250  <rdf:Description>
1251    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1252  </rdf:Description>
1253  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1254  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
1255<t>
1256   The TRACE method requests a remote, application-layer loop-back
1257   of the request message. The final recipient of the request
1258   &SHOULD; reflect the message received back to the client as the
1259   message-body of a 200 (OK) response. The final recipient is either the
1260   origin server or the first proxy to receive a Max-Forwards
1261   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1262   A TRACE request &MUST-NOT; include a message-body.
1263</t>
1264<t>
1265   TRACE allows the client to see what is being received at the other
1266   end of the request chain and use that data for testing or diagnostic
1267   information. The value of the Via header field (&header-via;) is of
1268   particular interest, since it acts as a trace of the request chain.
1269   Use of the Max-Forwards header field allows the client to limit the
1270   length of the request chain, which is useful for testing a chain of
1271   proxies forwarding messages in an infinite loop.
1272</t>
1273<t>
1274   If the request is valid, the response &SHOULD; have a Content-Type of
1275   "message/http" (see &media-type-message-http;) and contain a message-body
1276   that encloses a copy of the entire request message.
1277   Responses to the TRACE method are not cacheable.
1278</t>
1279</section>
1280
1281<section title="CONNECT" anchor="CONNECT">
1282  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1283  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1284<t>
1285   The CONNECT method requests that the proxy establish a tunnel
1286   to the request-target and then restrict its behavior to blind
1287   forwarding of packets until the connection is closed.
1288</t>
1289<t>
1290   When using CONNECT, the request-target &MUST; use the authority form
1291   (&request-target;); i.e., the request-target consists of only the
1292   host name and port number of the tunnel destination, separated by a colon.
1293   For example,
1294</t>
1295<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1296CONNECT server.example.com:80 HTTP/1.1
1297Host: server.example.com:80
1298
1299</artwork></figure>
1300<t>
1301   Other HTTP mechanisms can be used normally with the CONNECT method &mdash;
1302   except end-to-end protocol Upgrade requests, since the
1303   tunnel must be established first.
1304</t>
1305<t>
1306   For example, proxy authentication might be used to establish the
1307   authority to create a tunnel:
1308</t>
1309<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1310CONNECT server.example.com:80 HTTP/1.1
1311Host: server.example.com:80
1312Proxy-Authorization: basic aGVsbG86d29ybGQ=
1313
1314</artwork></figure>
1315<t>
1316   Bodies on CONNECT requests have no defined semantics. Note that sending a body
1317   on a CONNECT request might cause some existing implementations to reject the
1318   request.
1319</t>
1320<t>
1321   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1322   sent immediately after the blank line. The usual caveats also apply:
1323   data may be discarded if the eventual response is negative, and the
1324   connection may be reset with no response if more than one TCP segment
1325   is outstanding.
1326</t>
1327
1328<section title="Establishing a Tunnel with CONNECT">
1329<t>
1330   Any successful (2xx) response to a CONNECT request indicates that the
1331   proxy has established a connection to the requested host and port,
1332   and has switched to tunneling the current connection to that server
1333   connection.
1334</t>
1335<t>
1336   It may be the case that the proxy itself can only reach the requested
1337   origin server through another proxy.  In this case, the first proxy
1338   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1339   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1340   unless it has either a direct or tunnel connection established to the
1341   authority.
1342</t>
1343<t>
1344   An origin server which receives a CONNECT request for itself &MAY;
1345   respond with a 2xx status code to indicate that a connection is
1346   established.
1347</t>
1348<t>
1349   If at any point either one of the peers gets disconnected, any
1350   outstanding data that came from that peer will be passed to the other
1351   one, and after that also the other connection will be terminated by
1352   the proxy. If there is outstanding data to that peer undelivered,
1353   that data will be discarded.
1354</t>
1355
1356</section>
1357</section>
1358</section>
1359
1360
1361<section title="Status Code Definitions" anchor="status.codes">
1362<t>
1363   The first digit of the Status-Code defines the class of response. The
1364   last two digits do not have any categorization role. There are 5
1365   values for the first digit:
1366  <list style="symbols">
1367    <t>
1368      1xx: Informational - Request received, continuing process
1369    </t>
1370    <t>
1371      2xx: Success - The action was successfully received,
1372        understood, and accepted
1373    </t>
1374    <t>
1375      3xx: Redirection - Further action must be taken in order to
1376        complete the request
1377    </t>
1378    <t>
1379      4xx: Client Error - The request contains bad syntax or cannot
1380        be fulfilled
1381    </t>
1382    <t>
1383      5xx: Server Error - The server failed to fulfill an apparently
1384        valid request
1385    </t>
1386  </list>
1387</t>
1388<t>
1389   Each Status-Code is described below, including any metadata required
1390   in the response.
1391</t>
1392
1393<section title="Informational 1xx" anchor="status.1xx">
1394<t>
1395   This class of status code indicates a provisional response,
1396   consisting only of the Status-Line and optional header fields, and is
1397   terminated by an empty line. There are no required header fields for this
1398   class of status code. Since HTTP/1.0 did not define any 1xx status
1399   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1400   except under experimental conditions.
1401</t>
1402<t>
1403   A client &MUST; be prepared to accept one or more 1xx status responses
1404   prior to a regular response, even if the client does not expect a 100
1405   (Continue) status message. Unexpected 1xx status responses &MAY; be
1406   ignored by a user agent.
1407</t>
1408<t>
1409   Proxies &MUST; forward 1xx responses, unless the connection between the
1410   proxy and its client has been closed, or unless the proxy itself
1411   requested the generation of the 1xx response. (For example, if a
1412   proxy adds a "Expect: 100-continue" field when it forwards a request,
1413   then it need not forward the corresponding 100 (Continue)
1414   response(s).)
1415</t>
1416
1417<section title="100 Continue" anchor="status.100">
1418  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1419  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1420<t>
1421   The client &SHOULD; continue with its request. This interim response is
1422   used to inform the client that the initial part of the request has
1423   been received and has not yet been rejected by the server. The client
1424   &SHOULD; continue by sending the remainder of the request or, if the
1425   request has already been completed, ignore this response. The server
1426   &MUST; send a final response after the request has been completed. See
1427   &use100; for detailed discussion of the use and handling of this
1428   status code.
1429</t>
1430</section>
1431
1432<section title="101 Switching Protocols" anchor="status.101">
1433  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1434  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1435<t>
1436   The server understands and is willing to comply with the client's
1437   request, via the Upgrade message header field (&header-upgrade;), for a
1438   change in the application protocol being used on this connection. The
1439   server will switch protocols to those defined by the response's
1440   Upgrade header field immediately after the empty line which
1441   terminates the 101 response.
1442</t>
1443<t>
1444   The protocol &SHOULD; be switched only when it is advantageous to do
1445   so. For example, switching to a newer version of HTTP is advantageous
1446   over older versions, and switching to a real-time, synchronous
1447   protocol might be advantageous when delivering resources that use
1448   such features.
1449</t>
1450</section>
1451</section>
1452
1453<section title="Successful 2xx" anchor="status.2xx">
1454<t>
1455   This class of status code indicates that the client's request was
1456   successfully received, understood, and accepted.
1457</t>
1458
1459<section title="200 OK" anchor="status.200">
1460  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1461  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1462<t>
1463   The request has succeeded. The payload returned with the response
1464   is dependent on the method used in the request, for example:
1465  <list style="hanging">
1466    <t hangText="GET">
1467      a representation of the target resource is sent in the response;
1468    </t>
1469    <t hangText="HEAD">
1470      the same representation as GET, except without the message-body;
1471    </t>
1472    <t hangText="POST">
1473      a representation describing or containing the result of the action;
1474    </t>
1475    <t hangText="TRACE">
1476      a representation containing the request message as received by the
1477      end server.
1478    </t>
1479  </list>
1480</t>
1481<t>
1482   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1483   freshness for 200 responses.
1484</t>
1485</section>
1486
1487<section title="201 Created" anchor="status.201">
1488  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1489  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1490<t>
1491   The request has been fulfilled and has resulted in a new resource being
1492   created. The newly created resource can be referenced by the URI(s)
1493   returned in the payload of the response, with the most specific URI
1494   for the resource given by a Location header field. The response
1495   &SHOULD; include a payload containing a list of resource
1496   characteristics and location(s) from which the user or user agent can
1497   choose the one most appropriate. The payload format is specified by
1498   the media type given in the Content-Type header field. The origin
1499   server &MUST; create the resource before returning the 201 status code.
1500   If the action cannot be carried out immediately, the server &SHOULD;
1501   respond with 202 (Accepted) response instead.
1502</t>
1503<t>
1504   A 201 response &MAY; contain an ETag response header field indicating
1505   the current value of the entity-tag for the representation of the resource
1506   just created (see &header-etag;).
1507</t>
1508</section>
1509
1510<section title="202 Accepted" anchor="status.202">
1511  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1512  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1513<t>
1514   The request has been accepted for processing, but the processing has
1515   not been completed.  The request might or might not eventually be
1516   acted upon, as it might be disallowed when processing actually takes
1517   place. There is no facility for re-sending a status code from an
1518   asynchronous operation such as this.
1519</t>
1520<t>
1521   The 202 response is intentionally non-committal. Its purpose is to
1522   allow a server to accept a request for some other process (perhaps a
1523   batch-oriented process that is only run once per day) without
1524   requiring that the user agent's connection to the server persist
1525   until the process is completed. The representation returned with this
1526   response &SHOULD; include an indication of the request's current status
1527   and either a pointer to a status monitor or some estimate of when the
1528   user can expect the request to be fulfilled.
1529</t>
1530</section>
1531
1532<section title="203 Non-Authoritative Information" anchor="status.203">
1533  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1534  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1535<t>
1536   The representation in the response has been transformed or otherwise
1537   modified by a transforming proxy (&intermediaries;).  Note that the
1538   behaviour of transforming intermediaries is controlled by the no-transform
1539   Cache-Control directive (&header-cache-control;).
1540</t>
1541<t>
1542   This status code is only appropriate when the response status code would
1543   have been 200 (OK) otherwise. When the status code before transformation
1544   would have been different, the 214 Transformation Applied warn-code
1545   (&header-warning;) is appropriate.
1546</t>
1547<t>
1548   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1549   freshness for 203 responses.
1550</t>
1551</section>
1552
1553<section title="204 No Content" anchor="status.204">
1554  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1555  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1556<t>
1557   The 204 (No Content) status code indicates that the server has
1558   successfully fulfilled the request and that there is no additional
1559   content to return in the response payload body.  Metadata in the
1560   response header fields refer to the target resource and its current
1561   representation after the requested action.
1562</t>
1563<t>
1564   For example, if a 204 status code is received in response to a PUT
1565   request and the response contains an ETag header field, then the PUT
1566   was successful and the ETag field-value contains the entity-tag for
1567   the new representation of that target resource.
1568</t>
1569<t>
1570   The 204 response allows a server to indicate that the action has been
1571   successfully applied to the target resource while implying that the
1572   user agent &SHOULD-NOT; traverse away from its current "document view"
1573   (if any).  The server assumes that the user agent will provide some
1574   indication of the success to its user, in accord with its own interface,
1575   and apply any new or updated metadata in the response to the active
1576   representation.
1577</t>
1578<t>
1579   For example, a 204 status code is commonly used with document editing
1580   interfaces corresponding to a "save" action, such that the document
1581   being saved remains available to the user for editing. It is also
1582   frequently used with interfaces that expect automated data transfers
1583   to be prevalent, such as within distributed version control systems.
1584</t>
1585<t>
1586   The 204 response &MUST-NOT; include a message-body, and thus is always
1587   terminated by the first empty line after the header fields.
1588</t>
1589</section>
1590
1591<section title="205 Reset Content" anchor="status.205">
1592  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1593  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1594<t>
1595   The server has fulfilled the request and the user agent &SHOULD; reset
1596   the document view which caused the request to be sent. This response
1597   is primarily intended to allow input for actions to take place via
1598   user input, followed by a clearing of the form in which the input is
1599   given so that the user can easily initiate another input action.
1600</t>
1601<t>   
1602   The message-body included with the response &MUST; be empty. Note that
1603   receivers still need to parse the response according to the algorithm defined
1604   in &message-body;.
1605</t>
1606</section>
1607
1608<section title="206 Partial Content" anchor="status.206">
1609  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1610  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1611  <rdf:Description>
1612    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
1613  </rdf:Description>
1614<t>
1615   The server has fulfilled the partial GET request for the resource
1616   and the enclosed payload is a partial representation as defined in &status-206;.
1617</t>
1618<t>
1619   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1620   freshness for 206 responses.
1621</t>
1622</section>
1623</section>
1624
1625<section title="Redirection 3xx" anchor="status.3xx">
1626<t>
1627   This class of status code indicates that further action needs to be
1628   taken by the user agent in order to fulfill the request.  If the required
1629   action involves a subsequent HTTP request, it &MAY; be carried out by the
1630   user agent without interaction with the user if and only if the method used
1631   in the second request is known to be "safe", as defined in
1632   <xref target="safe.methods"/>.
1633</t>
1634<t>
1635   There are several types of redirects:
1636   <list style="numbers">
1637      <x:lt>
1638        <t>
1639          Redirects of the request to another URI, either temporarily or
1640          permanently. The new URI is specified in the Location header field.
1641          In this specification, the status codes 301 (Moved Permanently),
1642          302 (Found), and 307 (Temporary Redirect) fall under this category.
1643        </t>
1644      </x:lt>
1645      <x:lt>
1646        <t>
1647          Redirection to a new location that represents an indirect response to
1648          the request, such as the result of a POST operation to be retrieved
1649          with a subsequent GET request. This is status code 303 (See Other).
1650        </t>
1651      </x:lt>
1652      <x:lt>
1653        <t>
1654          Redirection offering a choice of matching resources for use by
1655          agent-driven content negotiation (&agent-driven-negotiation;). This
1656          is status code 300 (Multiple Choices).
1657        </t>
1658      </x:lt>
1659      <x:lt>
1660        <t>
1661          Other kinds of redirection, such as to a cached result (status code 304
1662          (Not Modified)).
1663        </t>
1664      </x:lt>
1665   </list>
1666</t>
1667<x:note>
1668  <t>
1669    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1670    and 302 (Found) were defined for the first type of redirect, and the second
1671    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1672    However it turned out that web forms using POST expected redirects to change
1673    the operation for the subsequent request to retrieval (GET). To address this
1674    use case, HTTP/1.1 introduced the second type of redirect with the status
1675    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1676    As user agents did not change their behavior to maintain backwards
1677    compatibility, the first revision of HTTP/1.1 added yet another status code,
1678    307 (Temporary Redirect), for which the backwards compatibility problems did
1679    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1680    Over 10 years later, most user agents still do method rewriting for
1681    status codes 301 and 302, therefore this specification makes that behavior
1682    compliant in case the original request was POST.
1683  </t>
1684</x:note>
1685<t>
1686   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1687   "infinite" redirection loops).
1688</t>
1689<x:note>
1690  <t>
1691    <x:h>Note:</x:h> An earlier version of this specification recommended a
1692    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1693    Content developers need to be aware that some clients might
1694    implement such a fixed limitation.
1695  </t>
1696</x:note>
1697
1698<section title="300 Multiple Choices" anchor="status.300">
1699  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1700  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1701<t>
1702   The target resource has more than one
1703   representation, each with its own specific location, and agent-driven
1704   negotiation information (&content-negotiation;) is being provided so that
1705   the user (or user agent) can select a preferred representation by
1706   redirecting its request to that location.
1707</t>
1708<t>
1709   Unless it was a HEAD request, the response &SHOULD; include a representation
1710   containing a list of representation metadata and location(s) from
1711   which the user or user agent can choose the one most appropriate. The
1712   data format is specified by the media type given in the Content-Type
1713   header field. Depending upon the format and the capabilities of
1714   the user agent, selection of the most appropriate choice &MAY; be
1715   performed automatically. However, this specification does not define
1716   any standard for such automatic selection.
1717</t>
1718<t>
1719   If the server has a preferred choice of representation, it &SHOULD;
1720   include the specific URI for that representation in the Location
1721   field; user agents &MAY; use the Location field value for automatic
1722   redirection.
1723</t>
1724<t>
1725   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1726   freshness for 300 responses.
1727</t>
1728
1729</section>
1730
1731<section title="301 Moved Permanently" anchor="status.301">
1732  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1733  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1734<t>
1735   The target resource has been assigned a new permanent URI and any
1736   future references to this resource &SHOULD; use one of the returned
1737   URIs.  Clients with link editing capabilities ought to automatically
1738   re-link references to the effective request URI to one or more of the new
1739   references returned by the server, where possible.
1740</t>
1741<t>
1742   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1743   freshness for 301 responses.
1744</t>
1745<t>
1746   The new permanent 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 301 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  </t>
1766</x:note>
1767</section>
1768
1769<section title="302 Found" anchor="status.302">
1770  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1771  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1772<t>
1773   The target resource resides temporarily under a different URI.
1774   Since the redirection might be altered on occasion, the client &SHOULD;
1775   continue to use the effective request URI for future requests.
1776</t>
1777<t>
1778   The temporary URI &SHOULD; be given by the Location field in the
1779   response. Unless the request method was HEAD, the representation of the
1780   response &SHOULD; contain a short hypertext note with a hyperlink to
1781   the new URI(s).
1782</t>
1783<t>
1784   If the 302 status code is received in response to a request method
1785   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1786   then the request &MAY; be automatically redirected by the user agent without
1787   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1788   request unless it can be confirmed by the user, since this might
1789   change the conditions under which the request was issued.
1790</t>
1791<x:note>
1792  <t>
1793    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1794    request method from POST to GET for the subsequent request. If this
1795    behavior is undesired, status code 307 (Temporary Redirect) can be used
1796    instead.
1797    <cref anchor="issue312">but see <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/312"/></cref>
1798  </t>
1799</x:note>
1800</section>
1801
1802<section title="303 See Other" anchor="status.303">
1803  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1804  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1805<t>
1806   The 303 status code indicates that the server is redirecting the
1807   user agent to a different resource, as indicated by a URI in the
1808   Location header field, that is intended to provide an indirect
1809   response to the original request.  In order to satisfy the original
1810   request, a user agent &SHOULD; perform a retrieval request using the
1811   Location URI (a GET or HEAD request if using HTTP), which
1812   may itself be redirected further, and present the eventual result as an
1813   answer to the original request.
1814   Note that the new URI in the Location header field is not considered
1815   equivalent to the effective request URI.
1816</t>
1817<t>
1818   This status code is generally applicable to any HTTP method.  It is
1819   primarily used to allow the output of a POST action to redirect
1820   the user agent to a selected resource, since doing so provides the
1821   information corresponding to the POST response in a form that
1822   can be separately identified, bookmarked, and cached independent
1823   of the original request.
1824</t>
1825<t>
1826   A 303 response to a GET request indicates that the requested
1827   resource does not have a representation of its own that can be
1828   transferred by the server over HTTP.  The Location URI indicates a
1829   resource that is descriptive of the target resource, such that the
1830   follow-on representation might be useful to recipients without
1831   implying that it adequately represents the target resource.
1832   Note that answers to the questions of what can be represented, what
1833   representations are adequate, and what might be a useful description
1834   are outside the scope of HTTP and thus entirely determined by the
1835   URI owner(s).
1836</t>
1837<t>
1838   Except for responses to a HEAD request, the representation of a 303
1839   response &SHOULD; contain a short hypertext note with a hyperlink
1840   to the Location URI.
1841</t>
1842</section>
1843
1844<section title="304 Not Modified" anchor="status.304">
1845  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1846  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1847  <rdf:Description>
1848    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
1849  </rdf:Description>
1850<t>
1851   The response to the request has not been modified since the conditions
1852   indicated by the client's conditional GET request, as defined in &status-304;.
1853</t>
1854</section>
1855
1856<section title="305 Use Proxy" anchor="status.305">
1857  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1858  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1859<t>
1860   The 305 status code was defined in a previous version of this specification
1861   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1862</t>
1863</section>
1864
1865<section title="306 (Unused)" anchor="status.306">
1866  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1867  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1868<t>
1869   The 306 status code was used in a previous version of the
1870   specification, is no longer used, and the code is reserved.
1871</t>
1872</section>
1873
1874<section title="307 Temporary Redirect" anchor="status.307">
1875  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1876  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1877<t>
1878   The target resource resides temporarily under a different URI.
1879   Since the redirection can change over time, the client &SHOULD;
1880   continue to use the effective request URI for future requests.
1881</t>
1882<t>
1883   The temporary URI &SHOULD; be given by the Location field in the
1884   response. Unless the request method was HEAD, the representation of the
1885   response &SHOULD; contain a short hypertext note with a hyperlink to
1886   the new URI(s), since many pre-HTTP/1.1 user agents do not
1887   understand the 307 status code. Therefore, the note &SHOULD; contain the
1888   information necessary for a user to repeat the original request on
1889   the new URI.
1890</t>
1891<t>
1892   If the 307 status code is received in response to a request method
1893   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1894   then the request &MAY; be automatically redirected by the user agent without
1895   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1896   request unless it can be confirmed by the user, since this might
1897   change the conditions under which the request was issued.
1898</t>
1899</section>
1900</section>
1901
1902<section title="Client Error 4xx" anchor="status.4xx">
1903<t>
1904   The 4xx class of status code is intended for cases in which the
1905   client seems to have erred. Except when responding to a HEAD request,
1906   the server &SHOULD; include a representation containing an explanation of the
1907   error situation, and whether it is a temporary or permanent
1908   condition. These status codes are applicable to any request method.
1909   User agents &SHOULD; display any included representation to the user.
1910</t>
1911<t>
1912   If the client is sending data, a server implementation using TCP
1913   &SHOULD; be careful to ensure that the client acknowledges receipt of
1914   the packet(s) containing the response, before the server closes the
1915   input connection. If the client continues sending data to the server
1916   after the close, the server's TCP stack will send a reset packet to
1917   the client, which might erase the client's unacknowledged input buffers
1918   before they can be read and interpreted by the HTTP application.
1919</t>
1920
1921<section title="400 Bad Request" anchor="status.400">
1922  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1923  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1924<t>
1925   The server cannot or will not process the request, due to a client error (e.g.,
1926   malformed syntax).</t>
1927</section>
1928
1929<section title="401 Unauthorized" anchor="status.401">
1930  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1931  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1932  <rdf:Description>
1933    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part7</redirects-to>
1934  </rdf:Description>
1935<t>
1936   The request requires user authentication (see &status-401;).
1937</t>
1938</section>
1939
1940<section title="402 Payment Required" anchor="status.402">
1941  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1942  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1943<t>
1944   This code is reserved for future use.
1945</t>
1946</section>
1947
1948<section title="403 Forbidden" anchor="status.403">
1949  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1950  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1951<t>
1952   The server understood the request, but refuses to authorize it. Providing
1953   different user authentication credentials might be successful, but any
1954   credentials that were provided in the request are insufficient. The request
1955   &SHOULD-NOT; be repeated with the same credentials.
1956</t>
1957<t>
1958   If the request method was not HEAD and the server wishes to make
1959   public why the request has not been fulfilled, it &SHOULD; describe the
1960   reason for the refusal in the representation.  If the server does not wish to
1961   make this information available to the client, the status code 404
1962   (Not Found) &MAY; be used instead.
1963</t>
1964</section>
1965
1966<section title="404 Not Found" anchor="status.404">
1967  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1968  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1969<t>
1970   The server has not found anything matching the effective request URI. No
1971   indication is given of whether the condition is temporary or
1972   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1973   knows, through some internally configurable mechanism, that an old
1974   resource is permanently unavailable and has no forwarding address.
1975   This status code is commonly used when the server does not wish to
1976   reveal exactly why the request has been refused, or when no other
1977   response is applicable.
1978</t>
1979</section>
1980
1981<section title="405 Method Not Allowed" anchor="status.405">
1982  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1983  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1984<t>
1985   The method specified in the Request-Line is not allowed for the target
1986   resource. The response &MUST; include an Allow header field containing a
1987   list of valid methods for the requested resource.
1988</t>
1989</section>
1990
1991<section title="406 Not Acceptable" anchor="status.406">
1992  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1993  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1994<t>
1995   The resource identified by the request is only capable of generating
1996   response representations which have content characteristics not acceptable
1997   according to the Accept and Accept-* header fields sent in the request
1998   (see &p3-header-fields;).
1999</t>
2000<t>
2001   Unless it was a HEAD request, the response &SHOULD; include a representation
2002   containing a list of available representation characteristics and location(s)
2003   from which the user or user agent can choose the one most
2004   appropriate. The data format is specified by the media type given
2005   in the Content-Type header field. Depending upon the format and the
2006   capabilities of the user agent, selection of the most appropriate
2007   choice &MAY; be performed automatically. However, this specification
2008   does not define any standard for such automatic selection.
2009</t>
2010<x:note>
2011  <t>
2012    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
2013    not acceptable according to the accept header fields sent in the
2014    request. In some cases, this might even be preferable to sending a
2015    406 response. User agents are encouraged to inspect the header fields of
2016    an incoming response to determine if it is acceptable.
2017  </t>
2018</x:note>
2019<t>
2020   If the response could be unacceptable, a user agent &SHOULD;
2021   temporarily stop receipt of more data and query the user for a
2022   decision on further actions.
2023</t>
2024</section>
2025
2026<section title="407 Proxy Authentication Required" anchor="status.407">
2027  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
2028  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
2029<t>
2030   This code is similar to 401 (Unauthorized), but indicates that the
2031   client must first authenticate itself with the proxy (see &status-407;).
2032</t>
2033</section>
2034
2035<section title="408 Request Timeout" anchor="status.408">
2036  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
2037  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
2038<t>
2039   The client did not produce a request within the time that the server
2040   was prepared to wait. The client &MAY; repeat the request without
2041   modifications at any later time.
2042</t>
2043</section>
2044
2045<section title="409 Conflict" anchor="status.409">
2046  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
2047  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
2048<t>
2049   The request could not be completed due to a conflict with the current
2050   state of the resource. This code is only allowed in situations where
2051   it is expected that the user might be able to resolve the conflict
2052   and resubmit the request. The response body &SHOULD; include enough
2053   information for the user to recognize the source of the conflict.
2054   Ideally, the response representation would include enough information for the
2055   user or user agent to fix the problem; however, that might not be
2056   possible and is not required.
2057</t>
2058<t>
2059   Conflicts are most likely to occur in response to a PUT request. For
2060   example, if versioning were being used and the representation being PUT
2061   included changes to a resource which conflict with those made by an
2062   earlier (third-party) request, the server might use the 409 response
2063   to indicate that it can't complete the request. In this case, the
2064   response representation would likely contain a list of the differences
2065   between the two versions in a format defined by the response
2066   Content-Type.
2067</t>
2068</section>
2069
2070<section title="410 Gone" anchor="status.410">
2071  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
2072  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
2073<t>
2074   The target resource is no longer available at the server and no
2075   forwarding address is known. This condition is expected to be
2076   considered permanent. Clients with link editing capabilities &SHOULD;
2077   delete references to the effective request URI after user approval. If the
2078   server does not know, or has no facility to determine, whether or not
2079   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
2080   used instead.
2081</t>
2082<t>
2083   The 410 response is primarily intended to assist the task of web
2084   maintenance by notifying the recipient that the resource is
2085   intentionally unavailable and that the server owners desire that
2086   remote links to that resource be removed. Such an event is common for
2087   limited-time, promotional services and for resources belonging to
2088   individuals no longer working at the server's site. It is not
2089   necessary to mark all permanently unavailable resources as "gone" or
2090   to keep the mark for any length of time &mdash; that is left to the
2091   discretion of the server owner.
2092</t>
2093<t>
2094   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
2095   for 410 responses.
2096</t>
2097
2098</section>
2099
2100<section title="411 Length Required" anchor="status.411">
2101  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
2102  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
2103<t>
2104   The server refuses to accept the request without a defined Content-Length.
2105   The client &MAY; repeat the request if it adds a valid
2106   Content-Length header field containing the length of the message-body
2107   in the request message.
2108</t>
2109</section>
2110
2111<section title="412 Precondition Failed" anchor="status.412">
2112  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
2113  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
2114  <rdf:Description>
2115    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
2116  </rdf:Description>
2117<t>
2118   The precondition given in one or more of the header fields
2119   evaluated to false when it was tested on the server, as defined in
2120   &status-412;.
2121</t>
2122</section>
2123
2124<section title="413 Request Representation Too Large" anchor="status.413">
2125  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2126  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2127<t>
2128   The server is refusing to process a request because the request
2129   representation is larger than the server is willing or able to process. The
2130   server &MAY; close the connection to prevent the client from continuing
2131   the request.
2132</t>
2133<t>
2134   If the condition is temporary, the server &SHOULD; include a Retry-After
2135   header field to indicate that it is temporary and after what
2136   time the client &MAY; try again.
2137</t>
2138</section>
2139
2140<section title="414 URI Too Long" anchor="status.414">
2141  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2142  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
2143<t>
2144   The server is refusing to service the request because the effective request URI
2145   is longer than the server is willing to interpret. This rare
2146   condition is only likely to occur when a client has improperly
2147   converted a POST request to a GET request with long query
2148   information, when the client has descended into a URI "black hole" of
2149   redirection (e.g., a redirected URI prefix that points to a suffix of
2150   itself), or when the server is under attack by a client attempting to
2151   exploit security holes present in some servers using fixed-length
2152   buffers for reading or manipulating the effective request URI.
2153</t>
2154</section>
2155
2156<section title="415 Unsupported Media Type" anchor="status.415">
2157  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2158  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2159<t>
2160   The server is refusing to service the request because the request
2161   payload is in a format not supported by this request method on the
2162   target resource.
2163</t>
2164</section>
2165
2166<section title="416 Requested Range Not Satisfiable" anchor="status.416">
2167  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
2168  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
2169  <rdf:Description>
2170    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
2171  </rdf:Description>
2172<t>
2173   The request included a Range header field (&header-range;) and none of
2174   the range-specifier values in this field overlap the current extent
2175   of the selected resource. See &status-416;.
2176</t>
2177</section>
2178
2179<section title="417 Expectation Failed" anchor="status.417">
2180  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2181  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2182<t>
2183   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2184   could not be met by this server, or, if the server is a proxy,
2185   the server has unambiguous evidence that the request could not be met
2186   by the next-hop server.
2187</t>
2188</section>
2189
2190<section title="426 Upgrade Required" anchor="status.426">
2191  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2192  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2193<t>
2194   The request can not be completed without a prior protocol upgrade. This
2195   response &MUST; include an Upgrade header field (&header-upgrade;)
2196   specifying the required protocols.
2197</t>
2198<figure>
2199<preamble>Example:</preamble>
2200<artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2201HTTP/1.1 426 Upgrade Required
2202Upgrade: HTTP/2.0
2203Connection: Upgrade
2204
2205</artwork></figure>
2206<t>
2207   The server &SHOULD; include a message body in the 426 response which
2208   indicates in human readable form the reason for the error and describes any
2209   alternative courses which may be available to the user.
2210</t>
2211</section>
2212</section>
2213
2214<section title="Server Error 5xx" anchor="status.5xx">
2215<t>
2216   Response status codes beginning with the digit "5" indicate cases in
2217   which the server is aware that it has erred or is incapable of
2218   performing the request. Except when responding to a HEAD request, the
2219   server &SHOULD; include a representation containing an explanation of the
2220   error situation, and whether it is a temporary or permanent
2221   condition. User agents &SHOULD; display any included representation to the
2222   user. These response codes are applicable to any request method.
2223</t>
2224
2225<section title="500 Internal Server Error" anchor="status.500">
2226  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2227  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2228<t>
2229   The server encountered an unexpected condition which prevented it
2230   from fulfilling the request.
2231</t>
2232</section>
2233
2234<section title="501 Not Implemented" anchor="status.501">
2235  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2236  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2237<t>
2238   The server does not support the functionality required to fulfill the
2239   request. This is the appropriate response when the server does not
2240   recognize the request method and is not capable of supporting it for
2241   any resource.
2242</t>
2243</section>
2244
2245<section title="502 Bad Gateway" anchor="status.502">
2246  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2247  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2248<t>
2249   The server, while acting as a gateway or proxy, received an invalid
2250   response from the upstream server it accessed in attempting to
2251   fulfill the request.
2252</t>
2253</section>
2254
2255<section title="503 Service Unavailable" anchor="status.503">
2256  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2257  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2258<t>
2259   The server is currently unable or unwilling to handle the request due to
2260   reasons such as temporary overloading, maintenance of the server, or rate
2261   limiting of the client.
2262</t>
2263<t>
2264   The implication is that this is a temporary condition which will be
2265   alleviated after some delay. If known, the length of the delay &MAY; be
2266   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2267   If no Retry-After is given, the client &SHOULD; handle the response as it
2268   would for a 500 response.
2269</t>
2270<x:note>
2271  <t>
2272    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2273    server must use it when becoming overloaded. Some servers might wish
2274    to simply refuse the connection.
2275  </t>
2276</x:note>
2277</section>
2278
2279<section title="504 Gateway Timeout" anchor="status.504">
2280  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2281  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2282<t>
2283   The server, while acting as a gateway or proxy, did not receive a
2284   timely response from the upstream server specified by the URI (e.g.,
2285   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2286   to access in attempting to complete the request.
2287</t>
2288<x:note>
2289  <t>
2290    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2291    return 400 or 500 when DNS lookups time out.
2292  </t>
2293</x:note>
2294</section>
2295
2296<section title="505 HTTP Version Not Supported" anchor="status.505">
2297  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2298  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2299<t>
2300   The server does not support, or refuses to support, the protocol
2301   version that was used in the request message. The server is
2302   indicating that it is unable or unwilling to complete the request
2303   using the same major version as the client, as described in &http-version;,
2304   other than with this error message. The response &SHOULD; contain
2305   a representation describing why that version is not supported and what other
2306   protocols are supported by that server.
2307</t>
2308
2309</section>
2310</section>
2311</section>
2312
2313
2314<section title="Date/Time Formats" anchor="http.date">
2315  <x:anchor-alias value="HTTP-date"/>
2316<t>
2317   HTTP applications have historically allowed three different formats
2318   for date/time stamps. However, the preferred format is a fixed-length subset
2319   of that defined by <xref target="RFC1123"/>:
2320</t>
2321<figure><artwork type="example" x:indent-with="  ">
2322Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2323</artwork></figure>
2324<t>
2325   The other formats are described here only for compatibility with obsolete
2326   implementations.
2327</t>
2328<figure><artwork type="example" x:indent-with="  ">
2329Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2330Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2331</artwork></figure>
2332<t>
2333   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2334   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2335   only generate the RFC 1123 format for representing HTTP-date values
2336   in header fields.
2337</t>
2338<t>
2339   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2340   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2341   equal to UTC (Coordinated Universal Time). This is indicated in the
2342   first two formats by the inclusion of "GMT" as the three-letter
2343   abbreviation for time zone, and &MUST; be assumed when reading the
2344   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2345   additional whitespace beyond that specifically included as SP in the
2346   grammar.
2347</t>
2348<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2349  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2350</artwork></figure>
2351<t anchor="preferred.date.format">
2352  <x:anchor-alias value="rfc1123-date"/>
2353  <x:anchor-alias value="time-of-day"/>
2354  <x:anchor-alias value="hour"/>
2355  <x:anchor-alias value="minute"/>
2356  <x:anchor-alias value="second"/>
2357  <x:anchor-alias value="day-name"/>
2358  <x:anchor-alias value="day"/>
2359  <x:anchor-alias value="month"/>
2360  <x:anchor-alias value="year"/>
2361  <x:anchor-alias value="GMT"/>
2362  Preferred format:
2363</t>
2364<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
2365  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
2366  ; fixed length subset of the format defined in
2367  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2368 
2369  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2370               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2371               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2372               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2373               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2374               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2375               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2376               
2377  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2378               ; e.g., 02 Jun 1982
2379
2380  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2381  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2382               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2383               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2384               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2385               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2386               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2387               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2388               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2389               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2390               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2391               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2392               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2393  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2394
2395  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2396
2397  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2398                 ; 00:00:00 - 23:59:59
2399                 
2400  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2401  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2402  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2403</artwork></figure>
2404<t>
2405  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2406  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2407  same as those defined for the RFC 5322 constructs
2408  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2409</t>
2410<t anchor="obsolete.date.formats">
2411  <x:anchor-alias value="obs-date"/>
2412  <x:anchor-alias value="rfc850-date"/>
2413  <x:anchor-alias value="asctime-date"/>
2414  <x:anchor-alias value="date1"/>
2415  <x:anchor-alias value="date2"/>
2416  <x:anchor-alias value="date3"/>
2417  <x:anchor-alias value="rfc1123-date"/>
2418  <x:anchor-alias value="day-name-l"/>
2419  Obsolete formats:
2420</t>
2421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2422  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2423</artwork></figure>
2424<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2425  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
2426  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2427                 ; day-month-year (e.g., 02-Jun-82)
2428
2429  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2430         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2431         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2432         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2433         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2434         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2435         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2436</artwork></figure>
2437<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2438  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2439  <x:ref>date3</x:ref>        = <x:ref>month</x:ref> <x:ref>SP</x:ref> ( 2<x:ref>DIGIT</x:ref> / ( <x:ref>SP</x:ref> 1<x:ref>DIGIT</x:ref> ))
2440                 ; month day (e.g., Jun  2)
2441</artwork></figure>
2442<x:note>
2443  <t>
2444    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2445    accepting date values that might have been sent by non-HTTP
2446    applications, as is sometimes the case when retrieving or posting
2447    messages via proxies/gateways to SMTP or NNTP.
2448  </t>
2449</x:note>
2450<x:note>
2451  <t>
2452    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2453    to their usage within the protocol stream. Clients and servers are
2454    not required to use these formats for user presentation, request
2455    logging, etc.
2456  </t>
2457</x:note>
2458</section>
2459
2460
2461<section title="Header Field Definitions" anchor="header.field.definitions">
2462<t>
2463   This section defines the syntax and semantics of HTTP/1.1 header fields
2464   related to request and response semantics.
2465</t>
2466
2467<section title="Allow" anchor="header.allow">
2468  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2469  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2470  <x:anchor-alias value="Allow"/>
2471<t>
2472   The "Allow" header field lists the set of methods advertised as
2473   supported by the target resource. The purpose of this field is strictly to
2474   inform the recipient of valid request methods associated with the resource.
2475</t>
2476<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2477  <x:ref>Allow</x:ref> = #<x:ref>Method</x:ref>
2478</artwork></figure>
2479<t>
2480   Example of use:
2481</t>
2482<figure><artwork type="example">
2483  Allow: GET, HEAD, PUT
2484</artwork></figure>
2485<t>
2486   The actual set of allowed methods is defined by the origin server at the
2487   time of each request.
2488</t>
2489<t>
2490   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2491   understand all the methods specified in order to handle them according to
2492   the generic message handling rules.
2493</t>
2494</section>
2495
2496<section title="Date" anchor="header.date">
2497  <iref primary="true" item="Date header field" x:for-anchor=""/>
2498  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2499  <x:anchor-alias value="Date"/>
2500<t>
2501   The "Date" header field represents the date and time at which
2502   the message was originated, having the same semantics as the Origination
2503   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2504   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2505   it &MUST; be sent in rfc1123-date format.
2506</t>
2507<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2508  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2509</artwork></figure>
2510<t>
2511   An example is
2512</t>
2513<figure><artwork type="example">
2514  Date: Tue, 15 Nov 1994 08:12:31 GMT
2515</artwork></figure>
2516<t>
2517   Origin servers &MUST; include a Date header field in all responses,
2518   except in these cases:
2519  <list style="numbers">
2520      <t>If the response status code is 100 (Continue) or 101 (Switching
2521         Protocols), the response &MAY; include a Date header field, at
2522         the server's option.</t>
2523
2524      <t>If the response status code conveys a server error, e.g., 500
2525         (Internal Server Error) or 503 (Service Unavailable), and it is
2526         inconvenient or impossible to generate a valid Date.</t>
2527
2528      <t>If the server does not have a clock that can provide a
2529         reasonable approximation of the current time, its responses
2530         &MUST-NOT; include a Date header field.</t>
2531  </list>
2532</t>
2533<t>
2534   A received message that does not have a Date header field &MUST; be
2535   assigned one by the recipient if the message will be cached by that
2536   recipient.
2537</t>
2538<t>
2539   Clients can use the Date header field as well; in order to keep request
2540   messages small, they are advised not to include it when it doesn't convey
2541   any useful information (as it is usually the case for requests that do not
2542   contain a payload).
2543</t>
2544<t>
2545   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2546   time subsequent to the generation of the message. It &SHOULD; represent
2547   the best available approximation of the date and time of message
2548   generation, unless the implementation has no means of generating a
2549   reasonably accurate date and time. In theory, the date ought to
2550   represent the moment just before the payload is generated. In
2551   practice, the date can be generated at any time during the message
2552   origination without affecting its semantic value.
2553</t>
2554</section>
2555
2556<section title="Expect" anchor="header.expect">
2557  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2558  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2559  <x:anchor-alias value="Expect"/>
2560  <x:anchor-alias value="expectation"/>
2561  <x:anchor-alias value="expectation-extension"/>
2562  <x:anchor-alias value="expect-params"/>
2563<t>
2564   The "Expect" header field is used to indicate that particular
2565   server behaviors are required by the client.
2566</t>
2567<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"/>
2568  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2569 
2570  <x:ref>expectation</x:ref>  = "100-continue" / <x:ref>expectation-extension</x:ref>
2571  <x:ref>expectation-extension</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2572                           *<x:ref>expect-params</x:ref> ]
2573  <x:ref>expect-params</x:ref> = ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2574</artwork></figure>
2575<t>
2576   A server that does not understand or is unable to comply with any of
2577   the expectation values in the Expect field of a request &MUST; respond
2578   with appropriate error status code. The server &MUST; respond with a 417
2579   (Expectation Failed) status code if any of the expectations cannot be met
2580   or, if there are other problems with the request, some other 4xx
2581   status code.
2582</t>
2583<t>
2584   This header field is defined with extensible syntax to allow for
2585   future extensions. If a server receives a request containing an
2586   Expect field that includes an expectation-extension that it does not
2587   support, it &MUST; respond with a 417 (Expectation Failed) status code.
2588</t>
2589<t>
2590   Comparison of expectation values is case-insensitive for unquoted
2591   tokens (including the 100-continue token), and is case-sensitive for
2592   quoted-string expectation-extensions.
2593</t>
2594<t>
2595   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
2596   return a 417 (Expectation Failed) status code if it receives a request
2597   with an expectation that it cannot meet. However, the Expect
2598   header field itself is end-to-end; it &MUST; be forwarded if the
2599   request is forwarded.
2600</t>
2601<t>
2602   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
2603   Expect header field.
2604</t>
2605<t>
2606   See &use100; for the use of the 100 (Continue) status code.
2607</t>
2608</section>
2609
2610<section title="From" anchor="header.from">
2611  <iref primary="true" item="From header field" x:for-anchor=""/>
2612  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2613  <x:anchor-alias value="From"/>
2614  <x:anchor-alias value="mailbox"/>
2615<t>
2616   The "From" header field, if given, &SHOULD; contain an Internet
2617   e-mail address for the human user who controls the requesting user
2618   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2619   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2620</t>
2621<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2622  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2623 
2624  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2625</artwork></figure>
2626<t>
2627   An example is:
2628</t>
2629<figure><artwork type="example">
2630  From: webmaster@example.org
2631</artwork></figure>
2632<t>
2633   This header field &MAY; be used for logging purposes and as a means for
2634   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2635   be used as an insecure form of access protection. The interpretation
2636   of this field is that the request is being performed on behalf of the
2637   person given, who accepts responsibility for the method performed. In
2638   particular, robot agents &SHOULD; include this header field so that the
2639   person responsible for running the robot can be contacted if problems
2640   occur on the receiving end.
2641</t>
2642<t>
2643   The Internet e-mail address in this field &MAY; be separate from the
2644   Internet host which issued the request. For example, when a request
2645   is passed through a proxy the original issuer's address &SHOULD; be
2646   used.
2647</t>
2648<t>
2649   The client &SHOULD-NOT;  send the From header field without the user's
2650   approval, as it might conflict with the user's privacy interests or
2651   their site's security policy. It is strongly recommended that the
2652   user be able to disable, enable, and modify the value of this field
2653   at any time prior to a request.
2654</t>
2655</section>
2656
2657<section title="Location" anchor="header.location">
2658  <iref primary="true" item="Location header field" x:for-anchor=""/>
2659  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2660  <x:anchor-alias value="Location"/>
2661<t>
2662   The "Location" header field is used to identify a newly created
2663   resource, or to redirect the recipient to a different location for
2664   completion of the request.
2665</t>
2666<t>
2667   For 201 (Created) responses, the Location is the URI of the new resource
2668   which was created by the request. For 3xx responses, the location &SHOULD;
2669   indicate the server's preferred URI for automatic redirection to the
2670   resource.
2671</t>
2672<t>
2673   The field value consists of a single URI-reference. When it has the form
2674   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2675   the final value is computed by resolving it against the effective request
2676   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>).
2677</t>
2678<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2679  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2680</artwork></figure>
2681<figure>
2682<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2683<artwork type="example">
2684  Location: http://www.example.org/pub/WWW/People.html#tim
2685</artwork></figure><figure><artwork type="example">  Location: /index.html
2686</artwork></figure>
2687<t>
2688   There are circumstances in which a fragment identifier in a Location URI
2689   would not be appropriate. For instance, when it appears in a 201 Created
2690   response, where the Location header field specifies the URI for the entire
2691   created resource.
2692</t>
2693<x:note>
2694  <t>
2695    <x:h>Note:</x:h> This specification does not define precedence rules
2696    for the case where the original URI, as navigated to by the user
2697    agent, and the Location header field value both contain fragment
2698    identifiers. Thus be aware that including fragment identifiers might
2699    inconvenience anyone relying on the semantics of the original URI's
2700    fragment identifier.
2701  </t>
2702</x:note>
2703<x:note>
2704  <t>
2705    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2706    from Location in that the Content-Location identifies the most specific
2707    resource corresponding to the enclosed representation.
2708    It is therefore possible for a response to contain header fields for
2709    both Location and Content-Location.
2710  </t>
2711</x:note>
2712</section>
2713
2714<section title="Max-Forwards" anchor="header.max-forwards">
2715  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2716  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2717  <x:anchor-alias value="Max-Forwards"/>
2718<t>
2719   The "Max-Forwards" header field provides a mechanism with the
2720   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2721   methods to limit the number of times that the request is forwarded by
2722   proxies. This can be useful when the client is attempting to
2723   trace a request which appears to be failing or looping in mid-chain.
2724</t>
2725<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2726  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2727</artwork></figure>
2728<t>
2729   The Max-Forwards value is a decimal integer indicating the remaining
2730   number of times this request message can be forwarded.
2731</t>
2732<t>
2733   Each recipient of a TRACE or OPTIONS request
2734   containing a Max-Forwards header field &MUST; check and update its
2735   value prior to forwarding the request. If the received value is zero
2736   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2737   respond as the final recipient. If the received Max-Forwards value is
2738   greater than zero, then the forwarded message &MUST; contain an updated
2739   Max-Forwards field with a value decremented by one (1).
2740</t>
2741<t>
2742   The Max-Forwards header field &MAY; be ignored for all other request
2743   methods.
2744</t>
2745</section>
2746
2747<section title="Referer" anchor="header.referer">
2748  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2749  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2750  <x:anchor-alias value="Referer"/>
2751<t>
2752   The "Referer" [sic] header field allows the client to specify the
2753   URI of the resource from which the effective request URI was obtained (the
2754   "referrer", although the header field is misspelled.).
2755</t>
2756<t>
2757   The Referer header field allows servers to generate lists of back-links to
2758   resources for interest, logging, optimized caching, etc. It also allows
2759   obsolete or mistyped links to be traced for maintenance. Some servers use
2760   Referer as a means of controlling where they allow links from (so-called
2761   "deep linking"), but legitimate requests do not always
2762   contain a Referer header field.
2763</t>
2764<t>
2765   If the effective request URI was obtained from a source that does not have its own
2766   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2767   sent with the value "about:blank", or not be sent at all. Note that this
2768   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2769</t>
2770<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2771  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2772</artwork></figure>
2773<t>
2774   Example:
2775</t>
2776<figure><artwork type="example">
2777  Referer: http://www.example.org/hypertext/Overview.html
2778</artwork></figure>
2779<t>
2780   If the field value is a relative URI, it &SHOULD; be interpreted
2781   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2782   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2783</t>
2784</section>
2785
2786<section title="Retry-After" anchor="header.retry-after">
2787  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2788  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2789  <x:anchor-alias value="Retry-After"/>
2790<t>
2791   The header "Retry-After" field can be used with a 503 (Service
2792   Unavailable) response to indicate how long the service is expected to
2793   be unavailable to the requesting client. This field &MAY; also be used
2794   with any 3xx (Redirection) response to indicate the minimum time the
2795   user-agent is asked wait before issuing the redirected request.
2796</t>
2797<t>
2798   The value of this field can be either an HTTP-date or an integer number
2799   of seconds (in decimal) after the time of the response.
2800</t>
2801<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2802  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2803</artwork></figure>
2804<t anchor="rule.delta-seconds">
2805  <x:anchor-alias value="delta-seconds"/>
2806   Time spans are non-negative decimal integers, representing time in
2807   seconds.
2808</t>
2809<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2810  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2811</artwork></figure>
2812<t>
2813   Two examples of its use are
2814</t>
2815<figure><artwork type="example">
2816  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2817  Retry-After: 120
2818</artwork></figure>
2819<t>
2820   In the latter example, the delay is 2 minutes.
2821</t>
2822</section>
2823
2824<section title="Server" anchor="header.server">
2825  <iref primary="true" item="Server header field" x:for-anchor=""/>
2826  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2827  <x:anchor-alias value="Server"/>
2828<t>
2829   The "Server" header field contains information about the
2830   software used by the origin server to handle the request.
2831</t>
2832<t>
2833   The field can contain multiple product tokens (&product-tokens;) and
2834   comments (&header-fields;) identifying the server and any significant
2835   subproducts. The product tokens are listed in order of their significance
2836   for identifying the application.
2837</t>
2838<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2839  <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> ) )
2840</artwork></figure>
2841<t>
2842   Example:
2843</t>
2844<figure><artwork type="example">
2845  Server: CERN/3.0 libwww/2.17
2846</artwork></figure>
2847<t>
2848   If the response is being forwarded through a proxy, the proxy
2849   application &MUST-NOT; modify the Server header field. Instead, it
2850   &MUST; include a Via field (as described in &header-via;).
2851</t>
2852<x:note>
2853  <t>
2854    <x:h>Note:</x:h> Revealing the specific software version of the server might
2855    allow the server machine to become more vulnerable to attacks
2856    against software that is known to contain security holes. Server
2857    implementors are encouraged to make this field a configurable
2858    option.
2859  </t>
2860</x:note>
2861</section>
2862
2863<section title="User-Agent" anchor="header.user-agent">
2864  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2865  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2866  <x:anchor-alias value="User-Agent"/>
2867<t>
2868   The "User-Agent" header field contains information about the user
2869   agent originating the request. User agents &SHOULD; include this field with
2870   requests.
2871</t>
2872<t>
2873   Typically, it is used for statistical purposes, the tracing of protocol
2874   violations, and tailoring responses to avoid particular user agent
2875   limitations.
2876</t>
2877<t>
2878   The field can contain multiple product tokens (&product-tokens;)
2879   and comments (&header-fields;) identifying the agent and its
2880   significant subproducts. By convention, the product tokens are listed in
2881   order of their significance for identifying the application.
2882</t>
2883<t>
2884   Because this field is usually sent on every request a user agent makes,
2885   implementations are encouraged not to include needlessly fine-grained
2886   detail, and to limit (or even prohibit) the addition of subproducts by third
2887   parties. Overly long and detailed User-Agent field values make requests
2888   larger and can also be used to identify ("fingerprint") the user against
2889   their wishes.
2890</t>
2891<t>
2892   Likewise, implementations are encouraged not to use the product tokens of
2893   other implementations in order to declare compatibility with them, as this
2894   circumvents the purpose of the field. Finally, they are encouraged not to
2895   use comments to identify products; doing so makes the field value more
2896   difficult to parse.
2897</t>
2898<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2899  <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> ) )
2900</artwork></figure>
2901<t>
2902   Example:
2903</t>
2904<figure><artwork type="example">
2905  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2906</artwork></figure>
2907</section>
2908
2909</section>
2910
2911<section title="IANA Considerations" anchor="IANA.considerations">
2912
2913<section title="Method Registry" anchor="method.registration">
2914<t>
2915  The registration procedure for HTTP request methods is defined by
2916  <xref target="method.registry"/> of this document.
2917</t>
2918<t>
2919   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2920   and be populated with the registrations below:
2921</t>
2922<?BEGININC p2-semantics.iana-methods ?>
2923<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2924<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2925   <ttcol>Method</ttcol>
2926   <ttcol>Safe</ttcol>
2927   <ttcol>Reference</ttcol>
2928   <c>CONNECT</c>
2929   <c>no</c>
2930   <c>
2931      <xref target="CONNECT"/>
2932   </c>
2933   <c>DELETE</c>
2934   <c>no</c>
2935   <c>
2936      <xref target="DELETE"/>
2937   </c>
2938   <c>GET</c>
2939   <c>yes</c>
2940   <c>
2941      <xref target="GET"/>
2942   </c>
2943   <c>HEAD</c>
2944   <c>yes</c>
2945   <c>
2946      <xref target="HEAD"/>
2947   </c>
2948   <c>OPTIONS</c>
2949   <c>yes</c>
2950   <c>
2951      <xref target="OPTIONS"/>
2952   </c>
2953   <c>POST</c>
2954   <c>no</c>
2955   <c>
2956      <xref target="POST"/>
2957   </c>
2958   <c>PUT</c>
2959   <c>no</c>
2960   <c>
2961      <xref target="PUT"/>
2962   </c>
2963   <c>TRACE</c>
2964   <c>yes</c>
2965   <c>
2966      <xref target="TRACE"/>
2967   </c>
2968</texttable>
2969<!--(END)-->
2970<?ENDINC p2-semantics.iana-methods ?>
2971</section>
2972
2973<section title="Status Code Registry" anchor="status.code.registration">
2974<t>
2975   The registration procedure for HTTP Status Codes &mdash; previously defined
2976   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2977   by <xref target="status.code.registry"/> of this document.
2978</t>
2979<t>
2980   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2981   shall be updated with the registrations below:
2982</t>
2983<?BEGININC p2-semantics.iana-status-codes ?>
2984<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2985<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2986   <ttcol>Value</ttcol>
2987   <ttcol>Description</ttcol>
2988   <ttcol>Reference</ttcol>
2989   <c>100</c>
2990   <c>Continue</c>
2991   <c>
2992      <xref target="status.100"/>
2993   </c>
2994   <c>101</c>
2995   <c>Switching Protocols</c>
2996   <c>
2997      <xref target="status.101"/>
2998   </c>
2999   <c>200</c>
3000   <c>OK</c>
3001   <c>
3002      <xref target="status.200"/>
3003   </c>
3004   <c>201</c>
3005   <c>Created</c>
3006   <c>
3007      <xref target="status.201"/>
3008   </c>
3009   <c>202</c>
3010   <c>Accepted</c>
3011   <c>
3012      <xref target="status.202"/>
3013   </c>
3014   <c>203</c>
3015   <c>Non-Authoritative Information</c>
3016   <c>
3017      <xref target="status.203"/>
3018   </c>
3019   <c>204</c>
3020   <c>No Content</c>
3021   <c>
3022      <xref target="status.204"/>
3023   </c>
3024   <c>205</c>
3025   <c>Reset Content</c>
3026   <c>
3027      <xref target="status.205"/>
3028   </c>
3029   <c>300</c>
3030   <c>Multiple Choices</c>
3031   <c>
3032      <xref target="status.300"/>
3033   </c>
3034   <c>301</c>
3035   <c>Moved Permanently</c>
3036   <c>
3037      <xref target="status.301"/>
3038   </c>
3039   <c>302</c>
3040   <c>Found</c>
3041   <c>
3042      <xref target="status.302"/>
3043   </c>
3044   <c>303</c>
3045   <c>See Other</c>
3046   <c>
3047      <xref target="status.303"/>
3048   </c>
3049   <c>305</c>
3050   <c>Use Proxy</c>
3051   <c>
3052      <xref target="status.305"/>
3053   </c>
3054   <c>306</c>
3055   <c>(Unused)</c>
3056   <c>
3057      <xref target="status.306"/>
3058   </c>
3059   <c>307</c>
3060   <c>Temporary Redirect</c>
3061   <c>
3062      <xref target="status.307"/>
3063   </c>
3064   <c>400</c>
3065   <c>Bad Request</c>
3066   <c>
3067      <xref target="status.400"/>
3068   </c>
3069   <c>402</c>
3070   <c>Payment Required</c>
3071   <c>
3072      <xref target="status.402"/>
3073   </c>
3074   <c>403</c>
3075   <c>Forbidden</c>
3076   <c>
3077      <xref target="status.403"/>
3078   </c>
3079   <c>404</c>
3080   <c>Not Found</c>
3081   <c>
3082      <xref target="status.404"/>
3083   </c>
3084   <c>405</c>
3085   <c>Method Not Allowed</c>
3086   <c>
3087      <xref target="status.405"/>
3088   </c>
3089   <c>406</c>
3090   <c>Not Acceptable</c>
3091   <c>
3092      <xref target="status.406"/>
3093   </c>
3094   <c>407</c>
3095   <c>Proxy Authentication Required</c>
3096   <c>
3097      <xref target="status.407"/>
3098   </c>
3099   <c>408</c>
3100   <c>Request Timeout</c>
3101   <c>
3102      <xref target="status.408"/>
3103   </c>
3104   <c>409</c>
3105   <c>Conflict</c>
3106   <c>
3107      <xref target="status.409"/>
3108   </c>
3109   <c>410</c>
3110   <c>Gone</c>
3111   <c>
3112      <xref target="status.410"/>
3113   </c>
3114   <c>411</c>
3115   <c>Length Required</c>
3116   <c>
3117      <xref target="status.411"/>
3118   </c>
3119   <c>413</c>
3120   <c>Request Representation Too Large</c>
3121   <c>
3122      <xref target="status.413"/>
3123   </c>
3124   <c>414</c>
3125   <c>URI Too Long</c>
3126   <c>
3127      <xref target="status.414"/>
3128   </c>
3129   <c>415</c>
3130   <c>Unsupported Media Type</c>
3131   <c>
3132      <xref target="status.415"/>
3133   </c>
3134   <c>417</c>
3135   <c>Expectation Failed</c>
3136   <c>
3137      <xref target="status.417"/>
3138   </c>
3139   <c>426</c>
3140   <c>Upgrade Required</c>
3141   <c>
3142      <xref target="status.426"/>
3143   </c>
3144   <c>500</c>
3145   <c>Internal Server Error</c>
3146   <c>
3147      <xref target="status.500"/>
3148   </c>
3149   <c>501</c>
3150   <c>Not Implemented</c>
3151   <c>
3152      <xref target="status.501"/>
3153   </c>
3154   <c>502</c>
3155   <c>Bad Gateway</c>
3156   <c>
3157      <xref target="status.502"/>
3158   </c>
3159   <c>503</c>
3160   <c>Service Unavailable</c>
3161   <c>
3162      <xref target="status.503"/>
3163   </c>
3164   <c>504</c>
3165   <c>Gateway Timeout</c>
3166   <c>
3167      <xref target="status.504"/>
3168   </c>
3169   <c>505</c>
3170   <c>HTTP Version Not Supported</c>
3171   <c>
3172      <xref target="status.505"/>
3173   </c>
3174</texttable>
3175<!--(END)-->
3176<?ENDINC p2-semantics.iana-status-codes ?>
3177</section>
3178<section title="Header Field Registration" anchor="header.field.registration">
3179<t>
3180   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3181   with the permanent registrations below (see <xref target="RFC3864"/>):
3182</t>
3183<?BEGININC p2-semantics.iana-headers ?>
3184<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3185<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3186   <ttcol>Header Field Name</ttcol>
3187   <ttcol>Protocol</ttcol>
3188   <ttcol>Status</ttcol>
3189   <ttcol>Reference</ttcol>
3190
3191   <c>Allow</c>
3192   <c>http</c>
3193   <c>standard</c>
3194   <c>
3195      <xref target="header.allow"/>
3196   </c>
3197   <c>Date</c>
3198   <c>http</c>
3199   <c>standard</c>
3200   <c>
3201      <xref target="header.date"/>
3202   </c>
3203   <c>Expect</c>
3204   <c>http</c>
3205   <c>standard</c>
3206   <c>
3207      <xref target="header.expect"/>
3208   </c>
3209   <c>From</c>
3210   <c>http</c>
3211   <c>standard</c>
3212   <c>
3213      <xref target="header.from"/>
3214   </c>
3215   <c>Location</c>
3216   <c>http</c>
3217   <c>standard</c>
3218   <c>
3219      <xref target="header.location"/>
3220   </c>
3221   <c>Max-Forwards</c>
3222   <c>http</c>
3223   <c>standard</c>
3224   <c>
3225      <xref target="header.max-forwards"/>
3226   </c>
3227   <c>Referer</c>
3228   <c>http</c>
3229   <c>standard</c>
3230   <c>
3231      <xref target="header.referer"/>
3232   </c>
3233   <c>Retry-After</c>
3234   <c>http</c>
3235   <c>standard</c>
3236   <c>
3237      <xref target="header.retry-after"/>
3238   </c>
3239   <c>Server</c>
3240   <c>http</c>
3241   <c>standard</c>
3242   <c>
3243      <xref target="header.server"/>
3244   </c>
3245   <c>User-Agent</c>
3246   <c>http</c>
3247   <c>standard</c>
3248   <c>
3249      <xref target="header.user-agent"/>
3250   </c>
3251</texttable>
3252<!--(END)-->
3253<?ENDINC p2-semantics.iana-headers ?>
3254<t>
3255   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3256</t>
3257</section>
3258</section>
3259
3260<section title="Security Considerations" anchor="security.considerations">
3261<t>
3262   This section is meant to inform application developers, information
3263   providers, and users of the security limitations in HTTP/1.1 as
3264   described by this document. The discussion does not include
3265   definitive solutions to the problems revealed, though it does make
3266   some suggestions for reducing security risks.
3267</t>
3268
3269<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3270<t>
3271   Like any generic data transfer protocol, HTTP cannot regulate the
3272   content of the data that is transferred, nor is there any a priori
3273   method of determining the sensitivity of any particular piece of
3274   information within the context of any given request. Therefore,
3275   applications &SHOULD; supply as much control over this information as
3276   possible to the provider of that information. Four header fields are
3277   worth special mention in this context: Server, Via, Referer and From.
3278</t>
3279<t>
3280   Revealing the specific software version of the server might allow the
3281   server machine to become more vulnerable to attacks against software
3282   that is known to contain security holes. Implementors &SHOULD; make the
3283   Server header field a configurable option.
3284</t>
3285<t>
3286   Proxies which serve as a portal through a network firewall &SHOULD;
3287   take special precautions regarding the transfer of header information
3288   that identifies the hosts behind the firewall. In particular, they
3289   &SHOULD; remove, or replace with sanitized versions, any Via fields
3290   generated behind the firewall.
3291</t>
3292<t>
3293   The Referer header field allows reading patterns to be studied and reverse
3294   links drawn. Although it can be very useful, its power can be abused
3295   if user details are not separated from the information contained in
3296   the Referer. Even when the personal information has been removed, the
3297   Referer header field might indicate a private document's URI whose
3298   publication would be inappropriate.
3299</t>
3300<t>
3301   The information sent in the From field might conflict with the user's
3302   privacy interests or their site's security policy, and hence it
3303   &SHOULD-NOT;  be transmitted without the user being able to disable,
3304   enable, and modify the contents of the field. The user &MUST; be able
3305   to set the contents of this field within a user preference or
3306   application defaults configuration.
3307</t>
3308<t>
3309   We suggest, though do not require, that a convenient toggle interface
3310   be provided for the user to enable or disable the sending of From and
3311   Referer information.
3312</t>
3313<t>
3314   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3315   target="header.server"/>) header fields can sometimes be used to determine
3316   that a specific client or server have a particular security hole which might
3317   be exploited. Unfortunately, this same information is often used for other
3318   valuable purposes for which HTTP currently has no better mechanism.
3319</t>
3320<t>
3321   Furthermore, the User-Agent header field may contain enough entropy to be
3322   used, possibly in conjunction with other material, to uniquely identify the
3323   user.
3324</t>
3325<t>
3326   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3327   that was sent in request header fields within the body of their response.
3328   Clients &SHOULD; be careful with sensitive information, like Cookies,
3329   Authorization credentials, and other header fields that might be used to
3330   collect data from the client.
3331</t> 
3332</section>
3333
3334<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3335<t>
3336   Because the source of a link might be private information or might
3337   reveal an otherwise private information source, it is strongly
3338   recommended that the user be able to select whether or not the
3339   Referer field is sent. For example, a browser client could have a
3340   toggle switch for browsing openly/anonymously, which would
3341   respectively enable/disable the sending of Referer and From
3342   information.
3343</t>
3344<t>
3345   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3346   HTTP request if the referring page was transferred with a secure
3347   protocol.
3348</t>
3349<t>
3350   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3351   sensitive data because that data will be placed in the request-target. Many
3352   existing servers, proxies, and user agents log or display the request-target
3353   in places where it might be visible to third parties. Such services can
3354   use POST-based form submission instead.
3355</t>
3356</section>
3357
3358<section title="Location Headers and Spoofing" anchor="location.spoofing">
3359<t>
3360   If a single server supports multiple organizations that do not trust
3361   one another, then it &MUST; check the values of Location and Content-Location
3362   header fields in responses that are generated under control of
3363   said organizations to make sure that they do not attempt to
3364   invalidate resources over which they have no authority.
3365</t>
3366</section>
3367
3368<section title="Security Considerations for CONNECT">
3369<t>
3370   Since tunneled data is opaque to the proxy, there are additional
3371   risks to tunneling to other well-known or reserved ports.
3372   A HTTP client CONNECTing to port 25 could relay spam
3373   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3374   access to a small number of known ports.
3375</t>
3376</section>
3377
3378</section>
3379
3380<section title="Acknowledgments" anchor="acks">
3381<t>
3382  See &acks;.
3383</t>
3384</section>
3385</middle>
3386<back>
3387
3388<references title="Normative References">
3389
3390<reference anchor="Part1">
3391  <front>
3392    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3393    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3394      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3395      <address><email>fielding@gbiv.com</email></address>
3396    </author>
3397    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3398      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3399      <address><email>jg@freedesktop.org</email></address>
3400    </author>
3401    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3402      <organization abbrev="HP">Hewlett-Packard Company</organization>
3403      <address><email>JeffMogul@acm.org</email></address>
3404    </author>
3405    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3406      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3407      <address><email>henrikn@microsoft.com</email></address>
3408    </author>
3409    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3410      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3411      <address><email>LMM@acm.org</email></address>
3412    </author>
3413    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3414      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3415      <address><email>paulle@microsoft.com</email></address>
3416    </author>
3417    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3418      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3419      <address><email>timbl@w3.org</email></address>
3420    </author>
3421    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3422      <organization abbrev="W3C">World Wide Web Consortium</organization>
3423      <address><email>ylafon@w3.org</email></address>
3424    </author>
3425    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3426      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3427      <address><email>julian.reschke@greenbytes.de</email></address>
3428    </author>
3429    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3430  </front>
3431  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3432  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3433</reference>
3434
3435<reference anchor="Part3">
3436  <front>
3437    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3438    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3439      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3440      <address><email>fielding@gbiv.com</email></address>
3441    </author>
3442    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3443      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3444      <address><email>jg@freedesktop.org</email></address>
3445    </author>
3446    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3447      <organization abbrev="HP">Hewlett-Packard Company</organization>
3448      <address><email>JeffMogul@acm.org</email></address>
3449    </author>
3450    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3451      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3452      <address><email>henrikn@microsoft.com</email></address>
3453    </author>
3454    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3455      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3456      <address><email>LMM@acm.org</email></address>
3457    </author>
3458    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3459      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3460      <address><email>paulle@microsoft.com</email></address>
3461    </author>
3462    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3463      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3464      <address><email>timbl@w3.org</email></address>
3465    </author>
3466    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3467      <organization abbrev="W3C">World Wide Web Consortium</organization>
3468      <address><email>ylafon@w3.org</email></address>
3469    </author>
3470    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3471      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3472      <address><email>julian.reschke@greenbytes.de</email></address>
3473    </author>
3474    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3475  </front>
3476  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3477  <x:source href="p3-payload.xml" basename="p3-payload"/>
3478</reference>
3479
3480<reference anchor="Part4">
3481  <front>
3482    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3483    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3484      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3485      <address><email>fielding@gbiv.com</email></address>
3486    </author>
3487    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3488      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3489      <address><email>jg@freedesktop.org</email></address>
3490    </author>
3491    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3492      <organization abbrev="HP">Hewlett-Packard Company</organization>
3493      <address><email>JeffMogul@acm.org</email></address>
3494    </author>
3495    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3496      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3497      <address><email>henrikn@microsoft.com</email></address>
3498    </author>
3499    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3500      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3501      <address><email>LMM@acm.org</email></address>
3502    </author>
3503    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3504      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3505      <address><email>paulle@microsoft.com</email></address>
3506    </author>
3507    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3508      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3509      <address><email>timbl@w3.org</email></address>
3510    </author>
3511    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3512      <organization abbrev="W3C">World Wide Web Consortium</organization>
3513      <address><email>ylafon@w3.org</email></address>
3514    </author>
3515    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3516      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3517      <address><email>julian.reschke@greenbytes.de</email></address>
3518    </author>
3519    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3520  </front>
3521  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3522  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3523</reference>
3524
3525<reference anchor="Part5">
3526  <front>
3527    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3528    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3529      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3530      <address><email>fielding@gbiv.com</email></address>
3531    </author>
3532    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3533      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3534      <address><email>jg@freedesktop.org</email></address>
3535    </author>
3536    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3537      <organization abbrev="HP">Hewlett-Packard Company</organization>
3538      <address><email>JeffMogul@acm.org</email></address>
3539    </author>
3540    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3541      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3542      <address><email>henrikn@microsoft.com</email></address>
3543    </author>
3544    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3545      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3546      <address><email>LMM@acm.org</email></address>
3547    </author>
3548    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3549      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3550      <address><email>paulle@microsoft.com</email></address>
3551    </author>
3552    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3553      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3554      <address><email>timbl@w3.org</email></address>
3555    </author>
3556    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3557      <organization abbrev="W3C">World Wide Web Consortium</organization>
3558      <address><email>ylafon@w3.org</email></address>
3559    </author>
3560    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3561      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3562      <address><email>julian.reschke@greenbytes.de</email></address>
3563    </author>
3564    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3565  </front>
3566  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3567  <x:source href="p5-range.xml" basename="p5-range"/>
3568</reference>
3569
3570<reference anchor="Part6">
3571  <front>
3572    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3573    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3574      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3575      <address><email>fielding@gbiv.com</email></address>
3576    </author>
3577    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3578      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3579      <address><email>jg@freedesktop.org</email></address>
3580    </author>
3581    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3582      <organization abbrev="HP">Hewlett-Packard Company</organization>
3583      <address><email>JeffMogul@acm.org</email></address>
3584    </author>
3585    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3586      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3587      <address><email>henrikn@microsoft.com</email></address>
3588    </author>
3589    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3590      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3591      <address><email>LMM@acm.org</email></address>
3592    </author>
3593    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3594      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3595      <address><email>paulle@microsoft.com</email></address>
3596    </author>
3597    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3598      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3599      <address><email>timbl@w3.org</email></address>
3600    </author>
3601    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3602      <organization abbrev="W3C">World Wide Web Consortium</organization>
3603      <address><email>ylafon@w3.org</email></address>
3604    </author>
3605    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3606      <organization>Rackspace</organization>
3607      <address><email>mnot@mnot.net</email></address>
3608    </author>
3609    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3610      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3611      <address><email>julian.reschke@greenbytes.de</email></address>
3612    </author>
3613    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3614  </front>
3615  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3616  <x:source href="p6-cache.xml" basename="p6-cache"/>
3617</reference>
3618
3619<reference anchor="Part7">
3620  <front>
3621    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3622    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3623      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3624      <address><email>fielding@gbiv.com</email></address>
3625    </author>
3626    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3627      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3628      <address><email>jg@freedesktop.org</email></address>
3629    </author>
3630    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3631      <organization abbrev="HP">Hewlett-Packard Company</organization>
3632      <address><email>JeffMogul@acm.org</email></address>
3633    </author>
3634    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3635      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3636      <address><email>henrikn@microsoft.com</email></address>
3637    </author>
3638    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3639      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3640      <address><email>LMM@acm.org</email></address>
3641    </author>
3642    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3643      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3644      <address><email>paulle@microsoft.com</email></address>
3645    </author>
3646    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3647      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3648      <address><email>timbl@w3.org</email></address>
3649    </author>
3650    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3651      <organization abbrev="W3C">World Wide Web Consortium</organization>
3652      <address><email>ylafon@w3.org</email></address>
3653    </author>
3654    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3655      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3656      <address><email>julian.reschke@greenbytes.de</email></address>
3657    </author>
3658    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3659  </front>
3660  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3661  <x:source href="p7-auth.xml" basename="p7-auth"/>
3662</reference>
3663
3664<reference anchor="RFC2119">
3665  <front>
3666    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3667    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3668      <organization>Harvard University</organization>
3669      <address><email>sob@harvard.edu</email></address>
3670    </author>
3671    <date month="March" year="1997"/>
3672  </front>
3673  <seriesInfo name="BCP" value="14"/>
3674  <seriesInfo name="RFC" value="2119"/>
3675</reference>
3676
3677<reference anchor="RFC3986">
3678 <front>
3679  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3680  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3681    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3682    <address>
3683       <email>timbl@w3.org</email>
3684       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3685    </address>
3686  </author>
3687  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3688    <organization abbrev="Day Software">Day Software</organization>
3689    <address>
3690      <email>fielding@gbiv.com</email>
3691      <uri>http://roy.gbiv.com/</uri>
3692    </address>
3693  </author>
3694  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3695    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3696    <address>
3697      <email>LMM@acm.org</email>
3698      <uri>http://larry.masinter.net/</uri>
3699    </address>
3700  </author>
3701  <date month='January' year='2005'></date>
3702 </front>
3703 <seriesInfo name="STD" value="66"/>
3704 <seriesInfo name="RFC" value="3986"/>
3705</reference>
3706
3707<reference anchor="RFC5234">
3708  <front>
3709    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3710    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3711      <organization>Brandenburg InternetWorking</organization>
3712      <address>
3713        <email>dcrocker@bbiw.net</email>
3714      </address> 
3715    </author>
3716    <author initials="P." surname="Overell" fullname="Paul Overell">
3717      <organization>THUS plc.</organization>
3718      <address>
3719        <email>paul.overell@thus.net</email>
3720      </address>
3721    </author>
3722    <date month="January" year="2008"/>
3723  </front>
3724  <seriesInfo name="STD" value="68"/>
3725  <seriesInfo name="RFC" value="5234"/>
3726</reference>
3727
3728</references>
3729
3730<references title="Informative References">
3731
3732<reference anchor="RFC1123">
3733  <front>
3734    <title>Requirements for Internet Hosts - Application and Support</title>
3735    <author initials="R." surname="Braden" fullname="Robert Braden">
3736      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3737      <address><email>Braden@ISI.EDU</email></address>
3738    </author>
3739    <date month="October" year="1989"/>
3740  </front>
3741  <seriesInfo name="STD" value="3"/>
3742  <seriesInfo name="RFC" value="1123"/>
3743</reference>
3744
3745<reference anchor="RFC1945">
3746  <front>
3747    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3748    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3749      <organization>MIT, Laboratory for Computer Science</organization>
3750      <address><email>timbl@w3.org</email></address>
3751    </author>
3752    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3753      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3754      <address><email>fielding@ics.uci.edu</email></address>
3755    </author>
3756    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3757      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3758      <address><email>frystyk@w3.org</email></address>
3759    </author>
3760    <date month="May" year="1996"/>
3761  </front>
3762  <seriesInfo name="RFC" value="1945"/>
3763</reference>
3764
3765<reference anchor="RFC2068">
3766  <front>
3767    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3768    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3769      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3770      <address><email>fielding@ics.uci.edu</email></address>
3771    </author>
3772    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3773      <organization>MIT Laboratory for Computer Science</organization>
3774      <address><email>jg@w3.org</email></address>
3775    </author>
3776    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3777      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3778      <address><email>mogul@wrl.dec.com</email></address>
3779    </author>
3780    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3781      <organization>MIT Laboratory for Computer Science</organization>
3782      <address><email>frystyk@w3.org</email></address>
3783    </author>
3784    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3785      <organization>MIT Laboratory for Computer Science</organization>
3786      <address><email>timbl@w3.org</email></address>
3787    </author>
3788    <date month="January" year="1997"/>
3789  </front>
3790  <seriesInfo name="RFC" value="2068"/>
3791</reference>
3792
3793<reference anchor="RFC2616">
3794  <front>
3795    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3796    <author initials="R." surname="Fielding" fullname="R. Fielding">
3797      <organization>University of California, Irvine</organization>
3798      <address><email>fielding@ics.uci.edu</email></address>
3799    </author>
3800    <author initials="J." surname="Gettys" fullname="J. Gettys">
3801      <organization>W3C</organization>
3802      <address><email>jg@w3.org</email></address>
3803    </author>
3804    <author initials="J." surname="Mogul" fullname="J. Mogul">
3805      <organization>Compaq Computer Corporation</organization>
3806      <address><email>mogul@wrl.dec.com</email></address>
3807    </author>
3808    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3809      <organization>MIT Laboratory for Computer Science</organization>
3810      <address><email>frystyk@w3.org</email></address>
3811    </author>
3812    <author initials="L." surname="Masinter" fullname="L. Masinter">
3813      <organization>Xerox Corporation</organization>
3814      <address><email>masinter@parc.xerox.com</email></address>
3815    </author>
3816    <author initials="P." surname="Leach" fullname="P. Leach">
3817      <organization>Microsoft Corporation</organization>
3818      <address><email>paulle@microsoft.com</email></address>
3819    </author>
3820    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3821      <organization>W3C</organization>
3822      <address><email>timbl@w3.org</email></address>
3823    </author>
3824    <date month="June" year="1999"/>
3825  </front>
3826  <seriesInfo name="RFC" value="2616"/>
3827</reference>
3828
3829<reference anchor='RFC2817'>
3830  <front>
3831    <title>Upgrading to TLS Within HTTP/1.1</title>
3832    <author initials='R.' surname='Khare' fullname='R. Khare'>
3833      <organization>4K Associates / UC Irvine</organization>
3834      <address><email>rohit@4K-associates.com</email></address>
3835    </author>
3836    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3837      <organization>Agranat Systems, Inc.</organization>
3838      <address><email>lawrence@agranat.com</email></address>
3839    </author>
3840    <date year='2000' month='May' />
3841  </front>
3842  <seriesInfo name='RFC' value='2817' />
3843</reference>
3844
3845<reference anchor='RFC3864'>
3846  <front>
3847    <title>Registration Procedures for Message Header Fields</title>
3848    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3849      <organization>Nine by Nine</organization>
3850      <address><email>GK-IETF@ninebynine.org</email></address>
3851    </author>
3852    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3853      <organization>BEA Systems</organization>
3854      <address><email>mnot@pobox.com</email></address>
3855    </author>
3856    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3857      <organization>HP Labs</organization>
3858      <address><email>JeffMogul@acm.org</email></address>
3859    </author>
3860    <date year='2004' month='September' />
3861  </front>
3862  <seriesInfo name='BCP' value='90' />
3863  <seriesInfo name='RFC' value='3864' />
3864</reference>
3865
3866<reference anchor='RFC5226'>
3867  <front>
3868    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3869    <author initials='T.' surname='Narten' fullname='T. Narten'>
3870      <organization>IBM</organization>
3871      <address><email>narten@us.ibm.com</email></address>
3872    </author>
3873    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3874      <organization>Google</organization>
3875      <address><email>Harald@Alvestrand.no</email></address>
3876    </author>
3877    <date year='2008' month='May' />
3878  </front>
3879  <seriesInfo name='BCP' value='26' />
3880  <seriesInfo name='RFC' value='5226' />
3881</reference>
3882
3883<reference anchor="RFC5322">
3884  <front>
3885    <title>Internet Message Format</title>
3886    <author initials="P." surname="Resnick" fullname="P. Resnick">
3887      <organization>Qualcomm Incorporated</organization>
3888    </author>
3889    <date year="2008" month="October"/>
3890  </front> 
3891  <seriesInfo name="RFC" value="5322"/>
3892</reference>
3893
3894<reference anchor='RFC5789'>
3895  <front>
3896    <title>PATCH Method for HTTP</title>
3897    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3898      <organization>Linden Lab</organization>
3899    </author>
3900    <author initials='J.' surname='Snell' fullname='J. Snell' />
3901    <date year='2010' month='March' />
3902  </front>
3903  <seriesInfo name='RFC' value='5789' />
3904</reference>
3905
3906<reference anchor="RFC5987">
3907        <front>
3908    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3909    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3910      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3911      <address>
3912        <postal>
3913          <street>Hafenweg 16</street>
3914          <city>Muenster</city><region>NW</region><code>48155</code>
3915          <country>Germany</country>
3916        </postal>
3917        <email>julian.reschke@greenbytes.de</email>     
3918        <uri>http://greenbytes.de/tech/webdav/</uri>   
3919      </address>
3920    </author>
3921    <date month="August" year="2010"/>
3922  </front>
3923  <seriesInfo name="RFC" value="5987"/>
3924</reference>
3925
3926</references>
3927
3928<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3929<t>
3930  This document takes over the Status Code Registry, previously defined
3931  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3932  (<xref target="status.code.registry"/>)
3933</t>
3934<t>
3935  Clarify definition of POST.
3936  (<xref target="POST"/>)
3937</t>
3938<t>
3939  Remove requirement to handle all Content-* header fields; ban use of
3940  Content-Range with PUT.
3941  (<xref target="PUT"/>)
3942</t>
3943<t>
3944  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3945  (<xref target="CONNECT"/>)
3946</t>
3947<t>
3948  Broadened the definition of 203 (Non-Authoritative Information) to include
3949  cases of payload transformations as well.
3950  (<xref target="status.203"/>)
3951</t>
3952<t>
3953  Failed to consider that there are many other request methods that are safe
3954  to automatically redirect, and further that the user agent is able to make
3955  that determination based on the request method semantics.
3956  Furthermore, allow user agents to rewrite the method from POST to GET
3957  for status codes 301 and 302.
3958  (Sections <xref format="counter" target="status.301"/>,
3959  <xref format="counter" target="status.302"/> and
3960  <xref format="counter" target="status.307"/>)
3961</t>
3962<t>
3963  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3964  It used to indicate that the target resource must be accessed through the
3965  proxy given by the Location field. The Location field gave the URI of the
3966  proxy. The recipient was expected to repeat this single request via the proxy.
3967  (<xref target="status.305"/>)
3968</t>
3969<t>
3970  Define status 426 (Upgrade Required) (this was incorporated from
3971  <xref target="RFC2817"/>).
3972  (<xref target="status.426"/>)
3973</t>
3974<t>
3975  Change ABNF productions for header fields to only define the field value.
3976  (<xref target="header.field.definitions"/>)
3977</t>
3978<t>
3979  Reclassify "Allow" as response header field, removing the option to
3980  specify it in a PUT request.
3981  Relax the server requirement on the contents of the Allow header field and
3982  remove requirement on clients to always trust the header field value.
3983  (<xref target="header.allow"/>)
3984</t>
3985<t>
3986  Correct syntax of Location header field to allow URI references (including
3987  relative references and fragments), as referred symbol "absoluteURI" wasn't
3988  what was expected, and add some clarifications as to when use of fragments
3989  would not be appropriate.
3990  (<xref target="header.location"/>)
3991</t>
3992<t>
3993  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3994  extension methods could have used it as well).
3995  (<xref target="header.max-forwards"/>)
3996</t>
3997<t>
3998  Allow Referer field value of "about:blank" as alternative to not specifying it.
3999  (<xref target="header.referer"/>)
4000</t>
4001<t>
4002  In the description of the Server header field, the Via field
4003  was described as a SHOULD. The requirement was and is stated
4004  correctly in the description of the Via header field in &header-via;.
4005  (<xref target="header.server"/>)
4006</t>
4007</section>
4008
4009<?BEGININC p2-semantics.abnf-appendix ?>
4010<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4011<figure>
4012<artwork type="abnf" name="p2-semantics.parsed-abnf">
4013<x:ref>Allow</x:ref> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
4014
4015<x:ref>Date</x:ref> = HTTP-date
4016
4017<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
4018
4019<x:ref>From</x:ref> = mailbox
4020
4021<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4022
4023<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4024
4025<x:ref>Location</x:ref> = URI-reference
4026
4027<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4028<x:ref>Method</x:ref> = token
4029
4030<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
4031
4032<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 1.2.2&gt;
4033<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4034<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4035<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4036
4037<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4038<x:ref>Status-Code</x:ref> = 3DIGIT
4039
4040<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4041<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4042
4043<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4044<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4045
4046<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2&gt;
4047
4048<x:ref>date1</x:ref> = day SP month SP year
4049<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4050<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4051<x:ref>day</x:ref> = 2DIGIT
4052<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4053 / %x54.75.65 ; Tue
4054 / %x57.65.64 ; Wed
4055 / %x54.68.75 ; Thu
4056 / %x46.72.69 ; Fri
4057 / %x53.61.74 ; Sat
4058 / %x53.75.6E ; Sun
4059<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4060 / %x54.75.65.73.64.61.79 ; Tuesday
4061 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4062 / %x54.68.75.72.73.64.61.79 ; Thursday
4063 / %x46.72.69.64.61.79 ; Friday
4064 / %x53.61.74.75.72.64.61.79 ; Saturday
4065 / %x53.75.6E.64.61.79 ; Sunday
4066<x:ref>delta-seconds</x:ref> = 1*DIGIT
4067
4068<x:ref>expect-params</x:ref> = ";" token [ "=" ( token / quoted-string ) ]
4069<x:ref>expectation</x:ref> = "100-continue" / expectation-extension
4070<x:ref>expectation-extension</x:ref> = token [ "=" ( token / quoted-string )
4071 *expect-params ]
4072
4073<x:ref>hour</x:ref> = 2DIGIT
4074
4075<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4076<x:ref>minute</x:ref> = 2DIGIT
4077<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4078 / %x46.65.62 ; Feb
4079 / %x4D.61.72 ; Mar
4080 / %x41.70.72 ; Apr
4081 / %x4D.61.79 ; May
4082 / %x4A.75.6E ; Jun
4083 / %x4A.75.6C ; Jul
4084 / %x41.75.67 ; Aug
4085 / %x53.65.70 ; Sep
4086 / %x4F.63.74 ; Oct
4087 / %x4E.6F.76 ; Nov
4088 / %x44.65.63 ; Dec
4089
4090<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4091<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 1.2.2&gt;
4092
4093<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4094<x:ref>product</x:ref> = &lt;product, defined in [Part1], Section 5.2&gt;
4095
4096<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.3&gt;
4097
4098<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4099<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4100
4101<x:ref>second</x:ref> = 2DIGIT
4102
4103<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4104<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.3&gt;
4105
4106<x:ref>year</x:ref> = 4DIGIT
4107</artwork>
4108</figure>
4109<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4110; Allow defined but not used
4111; Date defined but not used
4112; Expect defined but not used
4113; From defined but not used
4114; Location defined but not used
4115; Max-Forwards defined but not used
4116; Reason-Phrase defined but not used
4117; Referer defined but not used
4118; Retry-After defined but not used
4119; Server defined but not used
4120; Status-Code defined but not used
4121; User-Agent defined but not used
4122</artwork></figure></section>
4123<?ENDINC p2-semantics.abnf-appendix ?>
4124
4125<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4126
4127<section title="Since RFC 2616">
4128<t>
4129  Extracted relevant partitions from <xref target="RFC2616"/>.
4130</t>
4131</section>
4132
4133<section title="Since draft-ietf-httpbis-p2-semantics-00">
4134<t>
4135  Closed issues:
4136  <list style="symbols"> 
4137    <t>
4138      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4139      "Via is a MUST"
4140      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4141    </t>
4142    <t>
4143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4144      "Fragments allowed in Location"
4145      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4146    </t>
4147    <t>
4148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4149      "Safe Methods vs Redirection"
4150      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4151    </t>
4152    <t>
4153      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4154      "Revise description of the POST method"
4155      (<eref target="http://purl.org/NET/http-errata#post"/>)
4156    </t>
4157    <t>
4158      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4159      "Normative and Informative references"
4160    </t>
4161    <t>
4162      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4163      "RFC2606 Compliance"
4164    </t>
4165    <t>
4166      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4167      "Informative references"
4168    </t>
4169    <t>
4170      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4171      "Redundant cross-references"
4172    </t>
4173  </list>
4174</t>
4175<t>
4176  Other changes:
4177  <list style="symbols"> 
4178    <t>
4179      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4180    </t>
4181  </list>
4182</t>
4183</section>
4184
4185<section title="Since draft-ietf-httpbis-p2-semantics-01">
4186<t>
4187  Closed issues:
4188  <list style="symbols"> 
4189    <t>
4190      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4191      "PUT side effects"
4192    </t>
4193    <t>
4194      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4195      "Duplicate Host header requirements"
4196    </t>
4197  </list>
4198</t>
4199<t>
4200  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4201  <list style="symbols"> 
4202    <t>
4203      Move "Product Tokens" section (back) into Part 1, as "token" is used
4204      in the definition of the Upgrade header field.
4205    </t>
4206    <t>
4207      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4208    </t>
4209    <t>
4210      Copy definition of delta-seconds from Part6 instead of referencing it.
4211    </t>
4212  </list>
4213</t>
4214</section>
4215
4216<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4217<t>
4218  Closed issues:
4219  <list style="symbols"> 
4220    <t>
4221      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4222      "Requiring Allow in 405 responses"
4223    </t>
4224    <t>
4225      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4226      "Status Code Registry"
4227    </t>
4228    <t>
4229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4230      "Redirection vs. Location"
4231    </t>
4232    <t>
4233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4234      "Cacheability of 303 response"
4235    </t>
4236    <t>
4237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4238      "305 Use Proxy"
4239    </t>
4240    <t>
4241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4242      "Classification for Allow header"
4243    </t>
4244    <t>
4245      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4246      "PUT - 'store under' vs 'store at'"
4247    </t>
4248  </list>
4249</t>
4250<t>
4251  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4252  <list style="symbols"> 
4253    <t>
4254      Reference RFC 3984, and update header field registrations for headers defined
4255      in this document.
4256    </t>
4257  </list>
4258</t>
4259<t>
4260  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4261  <list style="symbols"> 
4262    <t>
4263      Replace string literals when the string really is case-sensitive (method).
4264    </t>
4265  </list>
4266</t>
4267</section>
4268
4269<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4270<t>
4271  Closed issues:
4272  <list style="symbols"> 
4273    <t>
4274      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4275      "OPTIONS request bodies"
4276    </t>
4277    <t>
4278      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4279      "Description of CONNECT should refer to RFC2817"
4280    </t>
4281    <t>
4282      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4283      "Location Content-Location reference request/response mixup"
4284    </t>
4285  </list>
4286</t>
4287<t>
4288  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4289  <list style="symbols"> 
4290    <t>
4291      Added initial proposal for registration process, plus initial
4292      content (non-HTTP/1.1 methods to be added by a separate specification).
4293    </t>
4294  </list>
4295</t>
4296</section>
4297
4298<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4299<t>
4300  Closed issues:
4301  <list style="symbols"> 
4302    <t>
4303      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4304      "Content-*"
4305    </t>
4306    <t>
4307      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4308      "RFC 2822 is updated by RFC 5322"
4309    </t>
4310  </list>
4311</t>
4312<t>
4313  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4314  <list style="symbols"> 
4315    <t>
4316      Use "/" instead of "|" for alternatives.
4317    </t>
4318    <t>
4319      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4320      whitespace ("OWS") and required whitespace ("RWS").
4321    </t>
4322    <t>
4323      Rewrite ABNFs to spell out whitespace rules, factor out
4324      header field value format definitions.
4325    </t>
4326  </list>
4327</t>
4328</section>
4329
4330<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4331<t>
4332  Closed issues:
4333  <list style="symbols"> 
4334    <t>
4335      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4336      "Reason-Phrase BNF"
4337    </t>
4338  </list>
4339</t>
4340<t>
4341  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4342  <list style="symbols"> 
4343    <t>
4344      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4345    </t>
4346  </list>
4347</t>
4348</section>
4349
4350<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4351<t>
4352  Closed issues:
4353  <list style="symbols"> 
4354    <t>
4355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4356      "Clarify when Referer is sent"
4357    </t>
4358    <t>
4359      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4360      "status codes vs methods"
4361    </t>
4362    <t>
4363      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4364      "Do not require "updates" relation for specs that register status codes or method names"
4365    </t>
4366  </list>
4367</t>
4368</section>
4369
4370<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4371<t>
4372  Closed issues:
4373  <list style="symbols"> 
4374    <t>
4375      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4376      "Idempotency"
4377    </t>
4378    <t>
4379      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4380      "TRACE security considerations"
4381    </t>
4382    <t>
4383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4384      "Clarify rules for determining what entities a response carries"
4385    </t>
4386    <t>
4387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4388      "update note citing RFC 1945 and 2068"
4389    </t>
4390    <t>
4391      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4392      "update note about redirect limit"
4393    </t>
4394    <t>
4395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4396      "Location header ABNF should use 'URI'"
4397    </t>
4398    <t>
4399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4400      "fragments in Location vs status 303"
4401    </t>
4402    <t>
4403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4404      "move IANA registrations for optional status codes"
4405    </t>
4406  </list>
4407</t>
4408<t>
4409  Partly resolved issues:
4410  <list style="symbols"> 
4411    <t>
4412      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4413      "Are OPTIONS and TRACE safe?"
4414    </t>
4415  </list>
4416</t>
4417</section>
4418
4419<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4420<t>
4421  Closed issues:
4422  <list style="symbols"> 
4423    <t>
4424      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4425      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4426      status codes when fixing this previously)
4427    </t>
4428  </list>
4429</t>
4430</section>
4431
4432<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4433<t>
4434  Closed issues:
4435  <list style="symbols"> 
4436    <t>
4437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4438      "Fragment combination / precedence during redirects"
4439    </t>
4440  </list>
4441</t>
4442<t>
4443  Partly resolved issues:
4444  <list style="symbols"> 
4445    <t>
4446      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4447      "Location header payload handling"
4448    </t>
4449    <t>
4450      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4451      "Term for the requested resource's URI"
4452    </t>
4453  </list>
4454</t>
4455</section>
4456
4457<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4458<t>
4459  Closed issues:
4460  <list style="symbols"> 
4461    <t>
4462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4463      "Clarify 'Requested Variant'"
4464    </t>
4465    <t>
4466      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4467      "Clarify entity / representation / variant terminology"
4468    </t>
4469    <t>
4470      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4471      "Methods and Caching"
4472    </t>
4473    <t>
4474      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4475      "OPTIONS vs Max-Forwards"
4476    </t>
4477    <t>
4478      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4479      "Status codes and caching"
4480    </t>
4481    <t>
4482      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4483      "consider removing the 'changes from 2068' sections"
4484    </t>
4485  </list>
4486</t>
4487</section>
4488
4489<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4490<t>
4491  Closed issues:
4492  <list style="symbols"> 
4493    <t>
4494      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4495      "Considerations for new status codes"
4496    </t>
4497    <t>
4498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4499      "Considerations for new methods"
4500    </t>
4501    <t>
4502      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4503      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4504    </t>
4505  </list>
4506</t>
4507</section>
4508
4509<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4510<t>
4511  Closed issues:
4512  <list style="symbols"> 
4513    <t>
4514      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4515      "Fragment combination / precedence during redirects" (added warning
4516      about having a fragid on the redirect may cause inconvenience in
4517      some cases)
4518    </t>
4519    <t>
4520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4521      "Content-* vs. PUT"
4522    </t>
4523    <t>
4524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4525      "205 Bodies"
4526    </t>
4527    <t>
4528      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4529      "Understanding Content-* on non-PUT requests"
4530    </t>
4531    <t>
4532      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4533      "Content-*"
4534    </t>
4535    <t>
4536      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4537      "Header type defaulting"
4538    </t>
4539    <t>
4540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4541      "PUT - 'store under' vs 'store at'"
4542    </t>
4543    <t>
4544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4545      "duplicate ABNF for Reason-Phrase"
4546    </t>
4547    <t>
4548      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4549      "Note special status of Content-* prefix in header registration procedures"
4550    </t>
4551    <t>
4552      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4553      "Max-Forwards vs extension methods"
4554    </t>
4555    <t>
4556      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4557      "What is the value space of HTTP status codes?" (actually fixed in
4558      draft-ietf-httpbis-p2-semantics-11)
4559    </t>
4560    <t>
4561      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4562      "Header Classification"
4563    </t>
4564    <t>
4565      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4566      "PUT side effect: invalidation or just stale?"
4567    </t>
4568    <t>
4569      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4570      "proxies not supporting certain methods"
4571    </t>
4572    <t>
4573      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4574      "Migrate CONNECT from RFC2817 to p2"
4575    </t>
4576    <t>
4577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4578      "Migrate Upgrade details from RFC2817"
4579    </t>
4580    <t>
4581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4582      "clarify PUT semantics'"
4583    </t>
4584    <t>
4585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4586      "duplicate ABNF for 'Method'"
4587    </t>
4588    <t>
4589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4590      "untangle ABNFs for header fields"
4591    </t>
4592  </list>
4593</t>
4594</section>
4595
4596<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4597<t>
4598  Closed issues:
4599  <list style="symbols"> 
4600    <t>
4601      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4602      "untangle ABNFs for header fields"
4603    </t>
4604    <t>
4605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4606      "message-body in CONNECT request"
4607    </t>
4608  </list>
4609</t>
4610</section>
4611
4612<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4613<t>
4614  Closed issues:
4615  <list style="symbols"> 
4616    <t>
4617      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4618      "Clarify status code for rate limiting"
4619    </t>
4620    <t>
4621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4622      "clarify 403 forbidden"
4623    </t>
4624    <t>
4625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4626      "Clarify 203 Non-Authoritative Information"
4627    </t>
4628    <t>
4629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4630      "update default reason phrase for 413"
4631    </t>
4632  </list>
4633</t>
4634</section>
4635
4636<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4637<t>
4638  Closed issues:
4639  <list style="symbols"> 
4640    <t>
4641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4642      "Strength of requirements on Accept re: 406"
4643    </t>
4644    <t>
4645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4646      "400 response isn't generic"
4647    </t>
4648  </list>
4649</t>
4650</section>
4651
4652<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4653<t>
4654  Closed issues:
4655  <list style="symbols"> 
4656    <t>
4657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4658      "Redirects and non-GET methods"
4659    </t>
4660    <t>
4661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4662      "Document HTTP's error-handling philosophy"
4663    </t>
4664    <t>
4665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4666      "clarify 303 redirect on HEAD"
4667    </t>
4668  </list>
4669</t>
4670<t>
4671  Work-in-progress:
4672  <list style="symbols"> 
4673    <t>
4674      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4675      "Considerations for new headers"
4676    </t>
4677  </list>
4678</t>
4679</section>
4680
4681</section>
4682
4683</back>
4684</rfc>
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