source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1493

Last change on this file since 1493 was 1493, checked in by julian.reschke@…, 8 years ago

warn about things that look like quoted-strings but are not (see #329)

  • Property svn:eol-style set to native
File size: 194.2 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 "December">
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="proposed"
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<x:link rel="prev" basename="p1-messaging"/>
107<x:link rel="next" basename="p3-payload"/>
108<front>
109
110  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
111
112  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
113    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
114    <address>
115      <postal>
116        <street>345 Park Ave</street>
117        <city>San Jose</city>
118        <region>CA</region>
119        <code>95110</code>
120        <country>USA</country>
121      </postal>
122      <email>fielding@gbiv.com</email>
123      <uri>http://roy.gbiv.com/</uri>
124    </address>
125  </author>
126
127  <author initials="J." surname="Gettys" fullname="Jim Gettys">
128    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
129    <address>
130      <postal>
131        <street>21 Oak Knoll Road</street>
132        <city>Carlisle</city>
133        <region>MA</region>
134        <code>01741</code>
135        <country>USA</country>
136      </postal>
137      <email>jg@freedesktop.org</email>
138      <uri>http://gettys.wordpress.com/</uri>
139    </address>
140  </author>
141 
142  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
143    <organization abbrev="HP">Hewlett-Packard Company</organization>
144    <address>
145      <postal>
146        <street>HP Labs, Large Scale Systems Group</street>
147        <street>1501 Page Mill Road, MS 1177</street>
148        <city>Palo Alto</city>
149        <region>CA</region>
150        <code>94304</code>
151        <country>USA</country>
152      </postal>
153      <email>JeffMogul@acm.org</email>
154    </address>
155  </author>
156
157  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
158    <organization abbrev="Microsoft">Microsoft Corporation</organization>
159    <address>
160      <postal>
161        <street>1 Microsoft Way</street>
162        <city>Redmond</city>
163        <region>WA</region>
164        <code>98052</code>
165        <country>USA</country>
166      </postal>
167      <email>henrikn@microsoft.com</email>
168    </address>
169  </author>
170
171  <author initials="L." surname="Masinter" fullname="Larry Masinter">
172    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
173    <address>
174      <postal>
175        <street>345 Park Ave</street>
176        <city>San Jose</city>
177        <region>CA</region>
178        <code>95110</code>
179        <country>USA</country>
180      </postal>
181      <email>LMM@acm.org</email>
182      <uri>http://larry.masinter.net/</uri>
183    </address>
184  </author>
185 
186  <author initials="P." surname="Leach" fullname="Paul J. Leach">
187    <organization abbrev="Microsoft">Microsoft Corporation</organization>
188    <address>
189      <postal>
190        <street>1 Microsoft Way</street>
191        <city>Redmond</city>
192        <region>WA</region>
193        <code>98052</code>
194      </postal>
195      <email>paulle@microsoft.com</email>
196    </address>
197  </author>
198   
199  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
200    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
201    <address>
202      <postal>
203        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
204        <street>The Stata Center, Building 32</street>
205        <street>32 Vassar Street</street>
206        <city>Cambridge</city>
207        <region>MA</region>
208        <code>02139</code>
209        <country>USA</country>
210      </postal>
211      <email>timbl@w3.org</email>
212      <uri>http://www.w3.org/People/Berners-Lee/</uri>
213    </address>
214  </author>
215
216  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
217    <organization abbrev="W3C">World Wide Web Consortium</organization>
218    <address>
219      <postal>
220        <street>W3C / ERCIM</street>
221        <street>2004, rte des Lucioles</street>
222        <city>Sophia-Antipolis</city>
223        <region>AM</region>
224        <code>06902</code>
225        <country>France</country>
226      </postal>
227      <email>ylafon@w3.org</email>
228      <uri>http://www.raubacapeu.net/people/yves/</uri>
229    </address>
230  </author>
231
232  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
233    <organization abbrev="greenbytes">greenbytes GmbH</organization>
234    <address>
235      <postal>
236        <street>Hafenweg 16</street>
237        <city>Muenster</city><region>NW</region><code>48155</code>
238        <country>Germany</country>
239      </postal>
240      <phone>+49 251 2807760</phone>
241      <facsimile>+49 251 2807761</facsimile>
242      <email>julian.reschke@greenbytes.de</email>
243      <uri>http://greenbytes.de/tech/webdav/</uri>
244    </address>
245  </author>
246
247  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
248  <workgroup>HTTPbis Working Group</workgroup>
249
250<abstract>
251<t>
252   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
253   distributed, collaborative, hypertext information systems. HTTP has been in
254   use by the World Wide Web global information initiative since 1990. This
255   document is Part 2 of the seven-part specification that defines the protocol
256   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
257</t>
258<t>
259   Part 2 defines the semantics of HTTP messages as expressed by request
260   methods, request header fields, response status codes, and response header
261   fields.
262</t>
263</abstract>
264
265<note title="Editorial Note (To be removed by RFC Editor)">
266  <t>
267    Discussion of this draft should take place on the HTTPBIS working group
268    mailing list (ietf-http-wg@w3.org), which is archived at
269    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
270  </t>
271  <t>
272    The current issues list is at
273    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
274    documents (including fancy diffs) can be found at
275    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
276  </t>
277  <t>
278    The changes in this draft are summarized in <xref target="changes.since.17"/>.
279  </t>
280</note>
281</front>
282<middle>
283<section title="Introduction" anchor="introduction">
284<t>
285   This document defines HTTP/1.1 request and response semantics.  Each HTTP
286   message, as defined in &messaging;, is in the form of either a request or
287   a response.  An HTTP server listens on a connection for HTTP requests and
288   responds to each request, in the order received on that connection, with
289   one or more HTTP response messages.  This document defines the commonly
290   agreed upon semantics of the HTTP uniform interface, the intentions defined
291   by each request method, and the various response messages that might be
292   expected as a result of applying that method to the target resource.
293</t>
294<t>
295   This document is currently disorganized in order to minimize the changes
296   between drafts and enable reviewers to see the smaller errata changes.
297   A future draft will reorganize the sections to better reflect the content.
298   In particular, the sections will be ordered according to the typical
299   processing of an HTTP request message (after message parsing): resource
300   mapping, methods, request modifying header fields, response status,
301   status modifying header fields, and resource metadata.  The current mess
302   reflects how widely dispersed these topics and associated requirements
303   had become in <xref target="RFC2616"/>.
304</t>
305
306<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
307<t>
308   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
309   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
310   document are to be interpreted as described in <xref target="RFC2119"/>.
311</t>
312<t>
313   This document defines conformance criteria for several roles in HTTP
314   communication, including Senders, Recipients, Clients, Servers, User-Agents,
315   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
316   for definitions of these terms.
317</t>
318<t>
319   An implementation is considered conformant if it complies with all of the
320   requirements associated with its role(s). Note that SHOULD-level requirements
321   are relevant here, unless one of the documented exceptions is applicable.
322</t>
323<t>
324   This document also uses ABNF to define valid protocol elements
325   (<xref target="notation"/>). In addition to the prose requirements placed
326   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
327</t>
328<t>
329   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
330   protocol element from an invalid construct. However, HTTP does not define
331   specific error handling mechanisms, except in cases where it has direct
332   impact on security. This is because different uses of the protocol require
333   different error handling strategies; for example, a Web browser may wish to
334   transparently recover from a response where the Location header field
335   doesn't parse according to the ABNF, whereby in a systems control protocol
336   using HTTP, this type of error recovery could lead to dangerous consequences.
337</t>
338</section>
339
340<section title="Syntax Notation" anchor="notation">
341  <x:anchor-alias value="CR"/>
342  <x:anchor-alias value="DIGIT"/>
343  <x:anchor-alias value="LF"/>
344  <x:anchor-alias value="HTAB"/>
345  <x:anchor-alias value="VCHAR"/>
346  <x:anchor-alias value="SP"/>
347<t>
348  This specification uses the ABNF syntax defined in &notation; (which
349  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
350  <xref target="collected.abnf"/> shows the collected ABNF, with the list
351  rule expanded.
352</t>
353<t>
354  The following core rules are included by
355  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
356  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
357  DIGIT (decimal 0-9), DQUOTE (double quote),
358  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
359  OCTET (any 8-bit sequence of data), SP (space), and
360  VCHAR (any visible US-ASCII character).
361</t>
362
363<section title="Core Rules" anchor="core.rules">
364  <x:anchor-alias value="obs-text"/>
365  <x:anchor-alias value="quoted-string"/>
366  <x:anchor-alias value="token"/>
367  <x:anchor-alias value="OWS"/>
368  <x:anchor-alias value="RWS"/>
369<t>
370  The core rules below are defined in <xref target="Part1"/>:
371</t>
372<figure><artwork type="abnf2616">
373  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
374  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &basic-rules;&gt;
375  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &basic-rules;&gt;
376  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-rules;&gt;
377  <x:ref>token</x:ref>         = &lt;token, defined in &field-rules;&gt;
378</artwork></figure>
379</section>
380
381<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
382  <x:anchor-alias value="absolute-URI"/>
383  <x:anchor-alias value="comment"/>
384  <x:anchor-alias value="partial-URI"/>
385  <x:anchor-alias value="product"/>
386  <x:anchor-alias value="URI-reference"/>
387<t>
388  The ABNF rules below are defined in other parts:
389</t>
390<figure><!--Part1--><artwork type="abnf2616">
391  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
392  <x:ref>comment</x:ref>       = &lt;comment, defined in &header-fields;&gt;
393  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
394  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
395  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
396</artwork></figure>
397</section>
398</section>
399</section>
400
401<section title="Method" anchor="method">
402  <x:anchor-alias value="Method"/>
403  <x:anchor-alias value="extension-method"/>
404<t>
405   The Method token indicates the request method to be performed on the target
406   resource (&effective-request-uri;). The method is case-sensitive.
407</t>
408<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
409  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
410</artwork></figure>
411<t>
412   The list of methods allowed by a resource can be specified in an
413   Allow header field (<xref target="header.allow"/>). The status code of the response
414   always notifies the client whether a method is currently allowed on a
415   resource, since the set of allowed methods can change dynamically. An
416   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
417   if the method is known by the origin server but not allowed for the
418   resource, and 501 (Not Implemented) if the method is
419   unrecognized or not implemented by the origin server. The methods GET
420   and HEAD &MUST; be supported by all general-purpose servers. All other
421   methods are &OPTIONAL;; however, if the above methods are implemented,
422   they &MUST; be implemented with the same semantics as those specified
423   in <xref target="method.definitions"/>.
424</t>
425
426<section title="Overview of Methods" anchor="overview.of.methods">
427<t>
428  The methods listed below are defined in <xref target="method.definitions"/>.
429</t>
430<texttable align="left">
431  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
432 
433  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
434  <c>GET</c> <c><xref target="GET"/></c>
435  <c>HEAD</c> <c><xref target="HEAD"/></c>
436  <c>POST</c> <c><xref target="POST"/></c>
437  <c>PUT</c> <c><xref target="PUT"/></c>
438  <c>DELETE</c> <c><xref target="DELETE"/></c>
439  <c>TRACE</c> <c><xref target="TRACE"/></c>
440  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
441</texttable>
442<t>
443  Note that this list is not exhaustive &mdash; it does not include request methods defined
444  in other specifications.
445</t>
446</section>
447
448<section title="Method Registry" anchor="method.registry">
449<t>
450  The HTTP Method Registry defines the name space for the Method token in the
451  Request line of an HTTP request.
452</t>
453<t>
454  Registrations &MUST; include the following fields:
455  <list style="symbols">
456    <t>Method Name (see <xref target="method"/>)</t>
457    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
458    <t>Pointer to specification text</t>
459  </list>
460</t>
461<t>
462  Values to be added to this name space are subject to IETF review
463  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
464</t>
465<t>
466  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
467</t>
468
469<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
470<t>
471   When it is necessary to express new semantics for a HTTP request that
472   aren't specific to a single application or media type, and currently defined
473   methods are inadequate, it may be appropriate to register a new method.
474</t>
475<t>
476   HTTP methods are generic; that is, they are potentially applicable to any
477   resource, not just one particular media type, "type" of resource, or
478   application. As such, it is preferred that new HTTP methods be registered
479   in a document that isn't specific to a single application, so that this is
480   clear.
481</t>
482<t>
483   Due to the parsing rules defined in &message-body;, definitions of HTTP
484   methods cannot prohibit the presence of a message-body on either the request
485   or the response message (with responses to HEAD requests being the single
486   exception). Definitions of new methods cannot change this rule, but they can
487   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
488</t>
489<t>
490   New method definitions need to indicate whether they are safe (<xref
491   target="safe.methods"/>), what semantics (if any) the request body has,
492   and whether they are idempotent (<xref target="idempotent.methods"/>).
493   They also need to state whether they can be cached (&caching;); in
494   particular what conditions a cache may store the response, and under what
495   conditions such a stored response may be used to satisfy a subsequent
496   request.
497</t>
498</section>
499
500</section>
501</section>
502
503<section title="Header Fields" anchor="header.fields">
504<t>
505   Header fields are key value pairs that can be used to communicate data about
506   the message, its payload, the target resource, or about the connection
507   itself (i.e., control data).  See &header-fields; for a general definition
508   of their syntax.
509</t>
510
511<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
512<t>
513   New header fields are registered using the procedures described in
514   <xref target="RFC3864"/>.
515</t>
516<t>
517   The requirements for header field names are defined in
518   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
519   defining new fields are advised to keep the name as short as practical, and
520   not to prefix them with "X-" if they are to be registered (either
521   immediately or in the future).
522</t>
523<t>
524   New header field values typically have their syntax defined using ABNF
525   (<xref target="RFC5234"/>), using the extensions defined in &notation-abnf;
526   as necessary, and are usually constrained to the range of ASCII characters.
527   Header fields needing a greater range of characters can use an encoding
528   such as the one defined in <xref target="RFC5987"/>.
529</t>
530<t>
531   Because commas (",") are used as a generic delimiter between field-values,
532   they need to be treated with care if they are allowed in the field-value's
533   payload. Typically, components that might contain a comma are protected with
534   double-quotes using the quoted-string ABNF production (&field-rules;).
535</t>
536<t>
537   For example, a textual date and a URI (either of which might contain a comma)
538   could be safely carried in field-values like these:
539</t>
540<figure><artwork type="example">
541  Example-URI-Field: "http://example.com/a.html,foo",
542                     "http://without-a-comma.example.com/"
543  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
544</artwork></figure>
545<t>
546   Note that double quote delimiters almost always are used with the
547   quoted-string production; using a different syntax inside double quotes
548   will likely cause unnecessary confusion.
549</t>
550<t>
551   Many header fields use a format including (case-insensitively) named
552   parameters (for instance, Content-Type, defined in &header-content-type;).
553   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
554   parameter value enables recipients to use existing parser components. When
555   allowing both forms, the meaning of a parameter value ought to be
556   independent of the syntax used for it (for an example, see the notes on
557   parameter handling for media types in &media-types;).
558</t>
559<t>
560   Authors of specifications defining new header fields are advised to consider
561   documenting:
562  <list style="symbols">
563    <x:lt>
564      <t>Whether the field is a single value, or whether it can be a list
565      (delimited by commas; see &header-fields;).</t>
566      <t>If it does not use the list syntax, document how to treat messages
567      where the header field occurs multiple times (a sensible default would
568      be to ignore the header field, but this might not always be the right
569      choice).</t>
570      <t>Note that intermediaries and software libraries might combine
571      multiple header field instances into a single one, despite the header
572      field not allowing this. A robust format enables recipients to discover
573      these situations (good example: "Content-Type", as the comma can only
574      appear inside quoted strings; bad example: "Location", as a comma can
575      occur inside a URI).</t>
576    </x:lt>
577    <x:lt><t>Under what conditions the header field can be used; e.g., only in
578    responses or requests, in all messages, only on responses to a particular
579    request method.</t></x:lt>
580    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
581    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
582    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
583    field's value, insert or delete it.</t></x:lt>
584    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
585    <x:lt><t>Whether the header field is useful or allowable in trailers (see
586    &chunked-encoding;).</t></x:lt>
587    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
588  </list>
589</t>
590</section>
591
592<section title="Request Header Fields" anchor="request.header.fields">
593  <x:anchor-alias value="request-header"/>
594<t>
595   The request header fields allow the client to pass additional
596   information about the request, and about the client itself, to the
597   server. These fields act as request modifiers, with semantics
598   equivalent to the parameters on a programming language method
599   invocation.
600</t>
601<texttable align="left">
602  <ttcol>Header Field Name</ttcol>
603  <ttcol>Defined in...</ttcol>
604
605  <c>Accept</c> <c>&header-accept;</c>
606  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
607  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
608  <c>Accept-Language</c> <c>&header-accept-language;</c>
609  <c>Authorization</c> <c>&header-authorization;</c>
610  <c>Expect</c> <c><xref target="header.expect"/></c>
611  <c>From</c> <c><xref target="header.from"/></c>
612  <c>Host</c> <c>&header-host;</c>
613  <c>If-Match</c> <c>&header-if-match;</c>
614  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
615  <c>If-None-Match</c> <c>&header-if-none-match;</c>
616  <c>If-Range</c> <c>&header-if-range;</c>
617  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
618  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
619  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
620  <c>Range</c> <c>&header-range;</c>
621  <c>Referer</c> <c><xref target="header.referer"/></c>
622  <c>TE</c> <c>&header-te;</c>
623  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
624</texttable>
625</section>
626
627<section title="Response Header Fields" anchor="response.header.fields">
628  <x:anchor-alias value="response-header"/>
629<t>
630   The response header fields allow the server to pass additional
631   information about the response which cannot be placed in the Status-Line.
632   These header fields give information about the server and about
633   further access to the target resource (&effective-request-uri;).
634</t>
635<texttable align="left">
636  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
637
638  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
639  <c>Age</c> <c>&header-age;</c>
640  <c>Allow</c> <c><xref target="header.allow"/></c>
641  <c>Date</c> <c><xref target="header.date"/></c>
642  <c>ETag</c> <c>&header-etag;</c>
643  <c>Location</c> <c><xref target="header.location"/></c>
644  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
645  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
646  <c>Server</c> <c><xref target="header.server"/></c>
647  <c>Vary</c> <c>&header-vary;</c>
648  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
649</texttable>
650</section>
651
652</section>
653
654<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
655  <x:anchor-alias value="Reason-Phrase"/>
656  <x:anchor-alias value="Status-Code"/>
657  <x:anchor-alias value="extension-code"/>
658<t>
659   The Status-Code element is a 3-digit integer result code of the attempt to
660   understand and satisfy the request.
661</t>
662<t>
663   The Reason-Phrase is intended to give a short textual description of the
664   Status-Code and is intended for a human user. The client does not need
665   to examine or display the Reason-Phrase.
666</t>
667<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"/>
668  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
669  <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> )
670</artwork></figure>
671<t>
672   HTTP status codes are extensible. HTTP applications are not required
673   to understand the meaning of all registered status codes, though such
674   understanding is obviously desirable. However, applications &MUST;
675   understand the class of any status code, as indicated by the first
676   digit, and treat any unrecognized response as being equivalent to the
677   x00 status code of that class, with the exception that an
678   unrecognized response &MUST-NOT; be cached. For example, if an
679   unrecognized status code of 431 is received by the client, it can
680   safely assume that there was something wrong with its request and
681   treat the response as if it had received a 400 status code. In such
682   cases, user agents &SHOULD; present to the user the representation enclosed
683   with the response, since that representation is likely to include human-readable
684   information which will explain the unusual status.
685</t>
686
687<section title="Overview of Status Codes" anchor="overview.of.status.codes">
688<t> 
689   The status codes listed below are defined in <xref target="status.codes"/>
690   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
691   The reason phrases listed here are only recommendations &mdash; they can be
692   replaced by local equivalents without affecting the protocol.
693</t>
694<texttable align="left">
695  <ttcol>Status-Code</ttcol>
696  <ttcol>Reason-Phrase</ttcol>
697  <ttcol>Defined in...</ttcol>
698 
699  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
700  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
701
702  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
703  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
704  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
705  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
706  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
707  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
708  <c>206</c> <c>Partial Content</c> <c>&status-206;</c>
709
710  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
711  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
712  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
713  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
714  <c>304</c> <c>Not Modified</c> <c>&status-304;</c>
715  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
716  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
717
718  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
719  <c>401</c> <c>Unauthorized</c> <c>&status-401;</c>
720  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
721  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
722  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
723  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
724  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
725  <c>407</c> <c>Proxy Authentication Required</c> <c>&status-407;</c>
726  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
727  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
728  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
729  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
730  <c>412</c> <c>Precondition Failed</c> <c>&status-412;</c>
731  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
732  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
733  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
734  <c>416</c> <c>Requested range not satisfiable</c> <c>&status-416;</c>
735  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
736  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
737
738  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
739  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
740  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
741  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
742  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
743  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
744</texttable>
745<t>
746   Note that this list is not exhaustive &mdash; it does not include
747   extension status codes defined in other specifications.
748</t>
749</section>
750
751<section title="Status Code Registry" anchor="status.code.registry">
752<t>
753  The HTTP Status Code Registry defines the name space for the Status-Code
754  token in the Status-Line of an HTTP response.
755</t>
756<t>
757  Values to be added to this name space are subject to IETF review
758  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
759</t>
760<t>
761  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
762</t>
763
764<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
765<t>
766   When it is necessary to express new semantics for a HTTP response that
767   aren't specific to a single application or media type, and currently defined
768   status codes are inadequate, a new status code can be registered.
769</t>
770<t>
771   HTTP status codes are generic; that is, they are potentially applicable to
772   any resource, not just one particular media type, "type" of resource, or
773   application. As such, it is preferred that new HTTP status codes be
774   registered in a document that isn't specific to a single application, so
775   that this is clear.
776</t>
777<t>
778   Definitions of new HTTP status codes typically explain the request
779   conditions that produce a response containing the status code (e.g.,
780   combinations of request headers and/or method(s)), along with any
781   interactions with response headers (e.g., those that are required, those
782   that modify the semantics of the response).
783</t>
784<t>
785   New HTTP status codes are required to fall under one of the categories
786   defined in <xref target="status.codes"/>. To allow existing parsers to
787   properly handle them, new status codes cannot disallow a response body,
788   although they can mandate a zero-length response body. They can require the
789   presence of one or more particular HTTP response header(s).
790</t>
791<t>
792   Likewise, their definitions can specify that caches are allowed to use
793   heuristics to determine their freshness (see &caching;; by default, it is
794   not allowed), and can define how to determine the resource which they
795   carry a representation for (see <xref
796   target="identifying.response.associated.with.representation"/>; by default,
797   it is anonymous).
798</t>
799</section>
800
801</section>
802
803</section>
804
805<section title="Representation" anchor="representation">
806<t>
807   Request and Response messages &MAY; transfer a representation if not otherwise
808   restricted by the request method or response status code. A representation
809   consists of metadata (representation header fields) and data (representation
810   body).  When a complete or partial representation is enclosed in an HTTP message,
811   it is referred to as the payload of the message. HTTP representations
812   are defined in &payload;.
813</t>
814<t>
815   A representation body is only present in a message when a message-body is
816   present, as described in &message-body;. The representation body is obtained
817   from the message-body by decoding any Transfer-Encoding that might
818   have been applied to ensure safe and proper transfer of the message.
819</t>
820
821<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
822<t>
823   It is sometimes necessary to determine an identifier for the resource
824   associated with a representation.
825</t>
826<t>
827   An HTTP request representation, when present, is always associated with an
828   anonymous (i.e., unidentified) resource.
829</t>
830<t>
831   In the common case, an HTTP response is a representation of the target
832   resource (see &effective-request-uri;). However, this is not always the
833   case. To determine the URI of the resource a response is associated with,
834   the following rules are used (with the first applicable one being selected):
835</t>
836<t><list style="numbers">
837   <t>If the response status code is 200 or 203 and the request method was GET,
838   the response payload is a representation of the target resource.</t>
839   <t>If the response status code is 204, 206, or 304 and the request method was GET
840   or HEAD, the response payload is a partial representation of the target
841   resource.</t>
842   <t>If the response has a Content-Location header field, and that URI is the same
843   as the effective request URI, the response payload is a representation of the
844   target resource.</t>
845   <t>If the response has a Content-Location header field, and that URI is not the
846   same as the effective request URI, then the response asserts that its
847   payload is a representation of the resource identified by the
848   Content-Location URI. However, such an assertion cannot be trusted unless
849   it can be verified by other means (not defined by HTTP).</t>
850   <t>Otherwise, the response is a representation of an anonymous (i.e.,
851   unidentified) resource.</t>
852</list></t>
853<t>
854  <cref anchor="TODO-req-uri">
855   The comparison function is going to have to be defined somewhere,
856   because we already need to compare URIs for things like cache invalidation.</cref>
857</t>
858</section>
859
860</section>
861
862
863<section title="Method Definitions" anchor="method.definitions">
864<t>
865   The set of common request methods for HTTP/1.1 is defined below. Although
866   this set can be expanded, additional methods cannot be assumed to
867   share the same semantics for separately extended clients and servers.
868</t>
869
870<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
871
872<section title="Safe Methods" anchor="safe.methods">
873<iref item="Safe Methods" primary="true"/>
874<t>
875   Implementors need to be aware that the software represents the user in
876   their interactions over the Internet, and need to allow
877   the user to be aware of any actions they take which might have an
878   unexpected significance to themselves or others.
879</t>
880<t>
881   In particular, the convention has been established that the GET, HEAD,
882   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
883   of taking an action other than retrieval. These request methods ought
884   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
885   This allows user agents to represent other methods, such as POST, PUT
886   and DELETE, in a special way, so that the user is made aware of the
887   fact that a possibly unsafe action is being requested.
888</t>
889<t>
890   Naturally, it is not possible to ensure that the server does not
891   generate side-effects as a result of performing a GET request; in
892   fact, some dynamic resources consider that a feature. The important
893   distinction here is that the user did not request the side-effects,
894   so therefore cannot be held accountable for them.
895</t>
896</section>
897
898<section title="Idempotent Methods" anchor="idempotent.methods">
899<iref item="Idempotent Methods" primary="true"/>
900<t>
901   Request methods can also have the property of "idempotence" in that,
902   aside from error or expiration issues, the intended effect of multiple
903   identical requests is the same as for a single request.
904   PUT, DELETE, and all safe request methods are idempotent.
905   It is important to note that idempotence refers only to changes
906   requested by the client: a server is free to change its state due
907   to multiple requests for the purpose of tracking those requests,
908   versioning of results, etc.
909</t>
910</section>
911</section>
912
913<section title="OPTIONS" anchor="OPTIONS">
914  <rdf:Description>
915    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
916  </rdf:Description>
917  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
918  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
919<t>
920   The OPTIONS method requests information about the
921   communication options available on the request/response chain
922   identified by the effective request URI. This method allows a client to
923   determine the options and/or requirements associated with a resource,
924   or the capabilities of a server, without implying a resource action
925   or initiating a resource retrieval.
926</t>
927<t>
928   Responses to the OPTIONS method are not cacheable.
929</t>
930<t>
931   If the OPTIONS request includes a message-body (as indicated by the
932   presence of Content-Length or Transfer-Encoding), then the media type
933   &MUST; be indicated by a Content-Type field. Although this
934   specification does not define any use for such a body, future
935   extensions to HTTP might use the OPTIONS body to make more detailed
936   queries on the server.
937</t>
938<t>
939   If the request-target is an asterisk ("*"), the OPTIONS request is
940   intended to apply to the server in general rather than to a specific
941   resource. Since a server's communication options typically depend on
942   the resource, the "*" request is only useful as a "ping" or "no-op"
943   type of method; it does nothing beyond allowing the client to test
944   the capabilities of the server. For example, this can be used to test
945   a proxy for HTTP/1.1 compliance (or lack thereof).
946</t>
947<t>
948   If the request-target is not an asterisk, the OPTIONS request applies
949   only to the options that are available when communicating with that
950   resource.
951</t>
952<t>
953   A 200 response &SHOULD; include any header fields that indicate
954   optional features implemented by the server and applicable to that
955   resource (e.g., Allow), possibly including extensions not defined by
956   this specification. The response body, if any, &SHOULD; also include
957   information about the communication options. The format for such a
958   body is not defined by this specification, but might be defined by
959   future extensions to HTTP. Content negotiation &MAY; be used to select
960   the appropriate response format. If no response body is included, the
961   response &MUST; include a Content-Length field with a field-value of
962   "0".
963</t>
964<t>
965   The Max-Forwards header field &MAY; be used to target a
966   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
967   If no Max-Forwards field is present in the request, then the forwarded
968   request &MUST-NOT; include a Max-Forwards field.
969</t>
970</section>
971
972<section title="GET" anchor="GET">
973  <rdf:Description>
974    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
975  </rdf:Description>
976  <iref primary="true" item="GET method" x:for-anchor=""/>
977  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
978<t>
979   The GET method requests transfer of a current representation of
980   the target resource.
981</t>
982<t>   
983   If the target resource is a data-producing process, it is the
984   produced data which shall be returned as the representation in the response and not
985   the source text of the process, unless that text happens to be the output of
986   the process.
987</t>
988<t>
989   The semantics of the GET method change to a "conditional GET" if the
990   request message includes an If-Modified-Since, If-Unmodified-Since,
991   If-Match, If-None-Match, or If-Range header field. A conditional GET
992   requests that the representation be transferred only under the
993   circumstances described by the conditional header field(s). The
994   conditional GET request is intended to reduce unnecessary network
995   usage by allowing cached representations to be refreshed without requiring
996   multiple requests or transferring data already held by the client.
997</t>
998<t>
999   The semantics of the GET method change to a "partial GET" if the
1000   request message includes a Range header field. A partial GET requests
1001   that only part of the representation be transferred, as described in &header-range;.
1002   The partial GET request is intended to reduce unnecessary
1003   network usage by allowing partially-retrieved representations to be
1004   completed without transferring data already held by the client.
1005</t>
1006<t>
1007   Bodies on GET requests have no defined semantics. Note that sending a body
1008   on a GET request might cause some existing implementations to reject the
1009   request.
1010</t>
1011<t>
1012   The response to a GET request is cacheable and &MAY; be used to satisfy
1013   subsequent GET and HEAD requests (see &caching;).
1014</t>
1015<t>
1016   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
1017</t>
1018</section>
1019
1020<section title="HEAD" anchor="HEAD">
1021  <rdf:Description>
1022    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1023  </rdf:Description>
1024  <iref primary="true" item="HEAD method" x:for-anchor=""/>
1025  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
1026<t>
1027   The HEAD method is identical to GET except that the server &MUST-NOT;
1028   return a message-body in the response. The metadata contained
1029   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
1030   to the information sent in response to a GET request. This method can
1031   be used for obtaining metadata about the representation implied by the
1032   request without transferring the representation body. This method is
1033   often used for testing hypertext links for validity, accessibility,
1034   and recent modification.
1035</t>
1036<t>
1037   The response to a HEAD request is cacheable and &MAY; be used to satisfy
1038   a subsequent HEAD request; see &caching;. It also &MAY; be used to update a previously cached
1039   representation from that resource; if the new field values
1040   indicate that the cached representation differs from the current representation (as
1041   would be indicated by a change in Content-Length, ETag
1042   or Last-Modified), then the cache &MUST; treat the cache entry as
1043   stale.
1044</t>
1045<t>
1046   Bodies on HEAD requests have no defined semantics. Note that sending a body
1047   on a HEAD request might cause some existing implementations to reject the
1048   request.
1049</t>
1050</section>
1051
1052<section title="POST" anchor="POST">
1053  <iref primary="true" item="POST method" x:for-anchor=""/>
1054  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
1055<t>
1056   The POST method requests that the origin server accept the
1057   representation enclosed in the request as data to be processed by the
1058   target resource. POST is designed to allow a uniform method to cover the
1059   following functions:
1060  <list style="symbols">
1061    <t>
1062      Annotation of existing resources;
1063    </t>
1064    <t>
1065        Posting a message to a bulletin board, newsgroup, mailing list,
1066        or similar group of articles;
1067    </t>
1068    <t>
1069        Providing a block of data, such as the result of submitting a
1070        form, to a data-handling process;
1071    </t>
1072    <t>
1073        Extending a database through an append operation.
1074    </t>
1075  </list>
1076</t>
1077<t>
1078   The actual function performed by the POST method is determined by the
1079   server and is usually dependent on the effective request URI.
1080</t>
1081<t>
1082   The action performed by the POST method might not result in a
1083   resource that can be identified by a URI. In this case, either 200
1084   (OK) or 204 (No Content) is the appropriate response status code,
1085   depending on whether or not the response includes a representation that
1086   describes the result.
1087</t>
1088<t>
1089   If a resource has been created on the origin server, the response
1090   &SHOULD; be 201 (Created) and contain a representation which describes the
1091   status of the request and refers to the new resource, and a Location
1092   header field (see <xref target="header.location"/>).
1093</t>
1094<t>
1095   Responses to POST requests are only cacheable when they
1096   include explicit freshness information (see &p6-explicit;). A
1097   cached POST response with a Content-Location header field
1098   (see &header-content-location;) whose value is the effective
1099   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1100</t>
1101<t>
1102   Note that POST caching is not widely implemented.
1103   However, the 303 (See Other) response can be used to direct the
1104   user agent to retrieve a cacheable resource.
1105</t>
1106</section>
1107
1108<section title="PUT" anchor="PUT">
1109  <iref primary="true" item="PUT method" x:for-anchor=""/>
1110  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
1111<t>
1112   The PUT method requests that the state of the target resource
1113   be created or replaced with the state defined by the representation
1114   enclosed in the request message payload.  A successful PUT of a given
1115   representation would suggest that a subsequent GET on that same target
1116   resource will result in an equivalent representation being returned in
1117   a 200 (OK) response.  However, there is no guarantee that such a state
1118   change will be observable, since the target resource might be acted
1119   upon by other user agents in parallel, or might be subject to dynamic
1120   processing by the origin server, before any subsequent GET is received.
1121   A successful response only implies that the user agent's intent was
1122   achieved at the time of its processing by the origin server.
1123</t>
1124<t>   
1125   If the target resource does not have a current representation and
1126   the PUT successfully creates one, then the origin server &MUST; inform
1127   the user agent by sending a 201 (Created) response.  If the target
1128   resource does have a current representation and that representation is
1129   successfully modified in accordance with the state of the enclosed
1130   representation, then either a 200 (OK) or 204 (No Content) response
1131   &SHOULD; be sent to indicate successful completion of the request.
1132</t>
1133<t>
1134   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1135   as part of the resource state).
1136</t>
1137<t>
1138   An origin server &SHOULD; verify that the PUT representation is
1139   consistent with any constraints which the server has for the target
1140   resource that cannot or will not be changed by the PUT.  This is
1141   particularly important when the origin server uses internal
1142   configuration information related to the URI in order to set the
1143   values for representation metadata on GET responses.  When a PUT
1144   representation is inconsistent with the target resource, the origin
1145   server &SHOULD; either make them consistent, by transforming the
1146   representation or changing the resource configuration, or respond
1147   with an appropriate error message containing sufficient information
1148   to explain why the representation is unsuitable.  The 409 (Conflict)
1149   or 415 (Unsupported Media Type) status codes are suggested, with the
1150   latter being specific to constraints on Content-Type values.
1151</t>
1152<t>
1153   For example, if the target resource is configured to always have a
1154   Content-Type of "text/html" and the representation being PUT has a
1155   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1156   (a) reconfigure the target resource to reflect the new media type;
1157   (b) transform the PUT representation to a format consistent with that
1158   of the resource before saving it as the new resource state; or,
1159   (c) reject the request with a 415 response indicating that the target
1160   resource is limited to "text/html", perhaps including a link to a
1161   different resource that would be a suitable target for the new
1162   representation.
1163</t>
1164<t>
1165   HTTP does not define exactly how a PUT method affects the state
1166   of an origin server beyond what can be expressed by the intent of
1167   the user agent request and the semantics of the origin server response.
1168   It does not define what a resource might be, in any sense of that
1169   word, beyond the interface provided via HTTP.  It does not define
1170   how resource state is "stored", nor how such storage might change
1171   as a result of a change in resource state, nor how the origin server
1172   translates resource state into representations.  Generally speaking,
1173   all implementation details behind the resource interface are
1174   intentionally hidden by the server.
1175</t>
1176<t>
1177   The fundamental difference between the POST and PUT methods is
1178   highlighted by the different intent for the target resource.
1179   The target resource in a POST request is intended to handle the
1180   enclosed representation as a data-accepting process, such as for
1181   a gateway to some other protocol or a document that accepts annotations.
1182   In contrast, the target resource in a PUT request is intended to
1183   take the enclosed representation as a new or replacement value.
1184   Hence, the intent of PUT is idempotent and visible to intermediaries,
1185   even though the exact effect is only known by the origin server.
1186</t>
1187<t>
1188   Proper interpretation of a PUT request presumes that the user agent
1189   knows what target resource is desired.  A service that is intended
1190   to select a proper URI on behalf of the client, after receiving
1191   a state-changing request, &SHOULD; be implemented using the POST
1192   method rather than PUT.  If the origin server will not make the
1193   requested PUT state change to the target resource and instead
1194   wishes to have it applied to a different resource, such as when the
1195   resource has been moved to a different URI, then the origin server
1196   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
1197   then make its own decision regarding whether or not to redirect the
1198   request.
1199</t>
1200<t>
1201   A PUT request applied to the target resource &MAY; have side-effects
1202   on other resources.  For example, an article might have a URI for
1203   identifying "the current version" (a resource) which is separate
1204   from the URIs identifying each particular version (different
1205   resources that at one point shared the same state as the current version
1206   resource).  A successful PUT request on "the current version" URI might
1207   therefore create a new version resource in addition to changing the
1208   state of the target resource, and might also cause links to be added
1209   between the related resources.
1210</t>
1211<t>
1212   An origin server &SHOULD; reject any PUT request that contains a
1213   Content-Range header field, since it might be misinterpreted as
1214   partial content (or might be partial content that is being mistakenly
1215   PUT as a full representation).  Partial content updates are
1216   possible by targeting a separately identified resource with state
1217   that overlaps a portion of the larger resource, or by using a
1218   different method that has been specifically defined for partial
1219   updates (for example, the PATCH method defined in
1220   <xref target="RFC5789"/>).
1221</t>
1222<t>
1223   Responses to the PUT method are not cacheable. If a PUT request passes
1224   through a cache that has one or more stored responses for the effective
1225   request URI, those stored responses will be invalidated (see
1226   &p6-invalid;).
1227</t>
1228</section>
1229
1230<section title="DELETE" anchor="DELETE">
1231  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1232  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
1233<t>
1234   The DELETE method requests that the origin server delete the target
1235   resource. This method &MAY; be overridden by
1236   human intervention (or other means) on the origin server. The client cannot
1237   be guaranteed that the operation has been carried out, even if the
1238   status code returned from the origin server indicates that the action
1239   has been completed successfully. However, the server &SHOULD-NOT; 
1240   indicate success unless, at the time the response is given, it
1241   intends to delete the resource or move it to an inaccessible
1242   location.
1243</t>
1244<t>
1245   A successful response &SHOULD; be 200 (OK) if the response includes an
1246   representation describing the status, 202 (Accepted) if the action has not
1247   yet been enacted, or 204 (No Content) if the action has been enacted
1248   but the response does not include a representation.
1249</t>
1250<t>
1251   Bodies on DELETE requests have no defined semantics. Note that sending a body
1252   on a DELETE request might cause some existing implementations to reject the
1253   request.
1254</t>
1255<t>
1256   Responses to the DELETE method are not cacheable. If a DELETE request
1257   passes through a cache that has one or more stored responses for the
1258   effective request URI, those stored responses will be invalidated (see
1259   &p6-invalid;).
1260</t>
1261</section>
1262
1263<section title="TRACE" anchor="TRACE">
1264  <rdf:Description>
1265    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1266  </rdf:Description>
1267  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1268  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
1269<t>
1270   The TRACE method requests a remote, application-layer loop-back
1271   of the request message. The final recipient of the request
1272   &SHOULD; reflect the message received back to the client as the
1273   message-body of a 200 (OK) response. The final recipient is either the
1274   origin server or the first proxy to receive a Max-Forwards
1275   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1276   A TRACE request &MUST-NOT; include a message-body.
1277</t>
1278<t>
1279   TRACE allows the client to see what is being received at the other
1280   end of the request chain and use that data for testing or diagnostic
1281   information. The value of the Via header field (&header-via;) is of
1282   particular interest, since it acts as a trace of the request chain.
1283   Use of the Max-Forwards header field allows the client to limit the
1284   length of the request chain, which is useful for testing a chain of
1285   proxies forwarding messages in an infinite loop.
1286</t>
1287<t>
1288   If the request is valid, the response &SHOULD; have a Content-Type of
1289   "message/http" (see &media-type-message-http;) and contain a message-body
1290   that encloses a copy of the entire request message.
1291   Responses to the TRACE method are not cacheable.
1292</t>
1293</section>
1294
1295<section title="CONNECT" anchor="CONNECT">
1296  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1297  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1298<t>
1299   The CONNECT method requests that the proxy establish a tunnel
1300   to the request-target and then restrict its behavior to blind
1301   forwarding of packets until the connection is closed.
1302</t>
1303<t>
1304   When using CONNECT, the request-target &MUST; use the authority form
1305   (&request-target;); i.e., the request-target consists of only the
1306   host name and port number of the tunnel destination, separated by a colon.
1307   For example,
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
1312
1313</artwork></figure>
1314<t>
1315   Other HTTP mechanisms can be used normally with the CONNECT method &mdash;
1316   except end-to-end protocol Upgrade requests, since the
1317   tunnel must be established first.
1318</t>
1319<t>
1320   For example, proxy authentication might be used to establish the
1321   authority to create a tunnel:
1322</t>
1323<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1324CONNECT server.example.com:80 HTTP/1.1
1325Host: server.example.com:80
1326Proxy-Authorization: basic aGVsbG86d29ybGQ=
1327
1328</artwork></figure>
1329<t>
1330   Bodies on CONNECT requests have no defined semantics. Note that sending a body
1331   on a CONNECT request might cause some existing implementations to reject the
1332   request.
1333</t>
1334<t>
1335   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1336   sent immediately after the blank line. The usual caveats also apply:
1337   data may be discarded if the eventual response is negative, and the
1338   connection may be reset with no response if more than one TCP segment
1339   is outstanding.
1340</t>
1341
1342<section title="Establishing a Tunnel with CONNECT">
1343<t>
1344   Any successful (2xx) response to a CONNECT request indicates that the
1345   proxy has established a connection to the requested host and port,
1346   and has switched to tunneling the current connection to that server
1347   connection.
1348</t>
1349<t>
1350   It may be the case that the proxy itself can only reach the requested
1351   origin server through another proxy.  In this case, the first proxy
1352   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1353   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1354   unless it has either a direct or tunnel connection established to the
1355   authority.
1356</t>
1357<t>
1358   An origin server which receives a CONNECT request for itself &MAY;
1359   respond with a 2xx status code to indicate that a connection is
1360   established.
1361</t>
1362<t>
1363   If at any point either one of the peers gets disconnected, any
1364   outstanding data that came from that peer will be passed to the other
1365   one, and after that also the other connection will be terminated by
1366   the proxy. If there is outstanding data to that peer undelivered,
1367   that data will be discarded.
1368</t>
1369
1370</section>
1371</section>
1372</section>
1373
1374
1375<section title="Status Code Definitions" anchor="status.codes">
1376<t>
1377   The first digit of the Status-Code defines the class of response. The
1378   last two digits do not have any categorization role. There are 5
1379   values for the first digit:
1380  <list style="symbols">
1381    <t>
1382      1xx: Informational - Request received, continuing process
1383    </t>
1384    <t>
1385      2xx: Success - The action was successfully received,
1386        understood, and accepted
1387    </t>
1388    <t>
1389      3xx: Redirection - Further action must be taken in order to
1390        complete the request
1391    </t>
1392    <t>
1393      4xx: Client Error - The request contains bad syntax or cannot
1394        be fulfilled
1395    </t>
1396    <t>
1397      5xx: Server Error - The server failed to fulfill an apparently
1398        valid request
1399    </t>
1400  </list>
1401</t>
1402<t>
1403   Each Status-Code is described below, including any metadata required
1404   in the response.
1405</t>
1406
1407<section title="Informational 1xx" anchor="status.1xx">
1408<t>
1409   This class of status code indicates a provisional response,
1410   consisting only of the Status-Line and optional header fields, and is
1411   terminated by an empty line. There are no required header fields for this
1412   class of status code. Since HTTP/1.0 did not define any 1xx status
1413   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1414   except under experimental conditions.
1415</t>
1416<t>
1417   A client &MUST; be prepared to accept one or more 1xx status responses
1418   prior to a regular response, even if the client does not expect a 100
1419   (Continue) status message. Unexpected 1xx status responses &MAY; be
1420   ignored by a user agent.
1421</t>
1422<t>
1423   Proxies &MUST; forward 1xx responses, unless the connection between the
1424   proxy and its client has been closed, or unless the proxy itself
1425   requested the generation of the 1xx response. (For example, if a
1426   proxy adds a "Expect: 100-continue" field when it forwards a request,
1427   then it need not forward the corresponding 100 (Continue)
1428   response(s).)
1429</t>
1430
1431<section title="100 Continue" anchor="status.100">
1432  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1433  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1434<t>
1435   The client &SHOULD; continue with its request. This interim response is
1436   used to inform the client that the initial part of the request has
1437   been received and has not yet been rejected by the server. The client
1438   &SHOULD; continue by sending the remainder of the request or, if the
1439   request has already been completed, ignore this response. The server
1440   &MUST; send a final response after the request has been completed. See
1441   &use100; for detailed discussion of the use and handling of this
1442   status code.
1443</t>
1444</section>
1445
1446<section title="101 Switching Protocols" anchor="status.101">
1447  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1448  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1449<t>
1450   The server understands and is willing to comply with the client's
1451   request, via the Upgrade message header field (&header-upgrade;), for a
1452   change in the application protocol being used on this connection. The
1453   server will switch protocols to those defined by the response's
1454   Upgrade header field immediately after the empty line which
1455   terminates the 101 response.
1456</t>
1457<t>
1458   The protocol &SHOULD; be switched only when it is advantageous to do
1459   so. For example, switching to a newer version of HTTP is advantageous
1460   over older versions, and switching to a real-time, synchronous
1461   protocol might be advantageous when delivering resources that use
1462   such features.
1463</t>
1464</section>
1465</section>
1466
1467<section title="Successful 2xx" anchor="status.2xx">
1468<t>
1469   This class of status code indicates that the client's request was
1470   successfully received, understood, and accepted.
1471</t>
1472
1473<section title="200 OK" anchor="status.200">
1474  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1475  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1476<t>
1477   The request has succeeded. The payload returned with the response
1478   is dependent on the method used in the request, for example:
1479  <list style="hanging">
1480    <t hangText="GET">
1481      a representation of the target resource is sent in the response;
1482    </t>
1483    <t hangText="HEAD">
1484      the same representation as GET, except without the message-body;
1485    </t>
1486    <t hangText="POST">
1487      a representation describing or containing the result of the action;
1488    </t>
1489    <t hangText="TRACE">
1490      a representation containing the request message as received by the
1491      end server.
1492    </t>
1493  </list>
1494</t>
1495<t>
1496   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1497   freshness for 200 responses.
1498</t>
1499</section>
1500
1501<section title="201 Created" anchor="status.201">
1502  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1503  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1504<t>
1505   The request has been fulfilled and has resulted in a new resource being
1506   created. The newly created resource can be referenced by the URI(s)
1507   returned in the payload of the response, with the most specific URI
1508   for the resource given by a Location header field. The response
1509   &SHOULD; include a payload containing a list of resource
1510   characteristics and location(s) from which the user or user agent can
1511   choose the one most appropriate. The payload format is specified by
1512   the media type given in the Content-Type header field. The origin
1513   server &MUST; create the resource before returning the 201 status code.
1514   If the action cannot be carried out immediately, the server &SHOULD;
1515   respond with 202 (Accepted) response instead.
1516</t>
1517<t>
1518   A 201 response &MAY; contain an ETag response header field indicating
1519   the current value of the entity-tag for the representation of the resource
1520   just created (see &header-etag;).
1521</t>
1522</section>
1523
1524<section title="202 Accepted" anchor="status.202">
1525  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1526  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1527<t>
1528   The request has been accepted for processing, but the processing has
1529   not been completed.  The request might or might not eventually be
1530   acted upon, as it might be disallowed when processing actually takes
1531   place. There is no facility for re-sending a status code from an
1532   asynchronous operation such as this.
1533</t>
1534<t>
1535   The 202 response is intentionally non-committal. Its purpose is to
1536   allow a server to accept a request for some other process (perhaps a
1537   batch-oriented process that is only run once per day) without
1538   requiring that the user agent's connection to the server persist
1539   until the process is completed. The representation returned with this
1540   response &SHOULD; include an indication of the request's current status
1541   and either a pointer to a status monitor or some estimate of when the
1542   user can expect the request to be fulfilled.
1543</t>
1544</section>
1545
1546<section title="203 Non-Authoritative Information" anchor="status.203">
1547  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1548  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1549<t>
1550   The representation in the response has been transformed or otherwise
1551   modified by a transforming proxy (&intermediaries;).  Note that the
1552   behaviour of transforming intermediaries is controlled by the no-transform
1553   Cache-Control directive (&header-cache-control;).
1554</t>
1555<t>
1556   This status code is only appropriate when the response status code would
1557   have been 200 (OK) otherwise. When the status code before transformation
1558   would have been different, the 214 Transformation Applied warn-code
1559   (&header-warning;) is appropriate.
1560</t>
1561<t>
1562   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1563   freshness for 203 responses.
1564</t>
1565</section>
1566
1567<section title="204 No Content" anchor="status.204">
1568  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1569  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1570<t>
1571   The 204 (No Content) status code indicates that the server has
1572   successfully fulfilled the request and that there is no additional
1573   content to return in the response payload body.  Metadata in the
1574   response header fields refer to the target resource and its current
1575   representation after the requested action.
1576</t>
1577<t>
1578   For example, if a 204 status code is received in response to a PUT
1579   request and the response contains an ETag header field, then the PUT
1580   was successful and the ETag field-value contains the entity-tag for
1581   the new representation of that target resource.
1582</t>
1583<t>
1584   The 204 response allows a server to indicate that the action has been
1585   successfully applied to the target resource while implying that the
1586   user agent &SHOULD-NOT; traverse away from its current "document view"
1587   (if any).  The server assumes that the user agent will provide some
1588   indication of the success to its user, in accord with its own interface,
1589   and apply any new or updated metadata in the response to the active
1590   representation.
1591</t>
1592<t>
1593   For example, a 204 status code is commonly used with document editing
1594   interfaces corresponding to a "save" action, such that the document
1595   being saved remains available to the user for editing. It is also
1596   frequently used with interfaces that expect automated data transfers
1597   to be prevalent, such as within distributed version control systems.
1598</t>
1599<t>
1600   The 204 response &MUST-NOT; include a message-body, and thus is always
1601   terminated by the first empty line after the header fields.
1602</t>
1603</section>
1604
1605<section title="205 Reset Content" anchor="status.205">
1606  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1607  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1608<t>
1609   The server has fulfilled the request and the user agent &SHOULD; reset
1610   the document view which caused the request to be sent. This response
1611   is primarily intended to allow input for actions to take place via
1612   user input, followed by a clearing of the form in which the input is
1613   given so that the user can easily initiate another input action.
1614</t>
1615<t>   
1616   The message-body included with the response &MUST; be empty. Note that
1617   receivers still need to parse the response according to the algorithm defined
1618   in &message-body;.
1619</t>
1620</section>
1621
1622<section title="206 Partial Content" anchor="status.206">
1623  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1624  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1625  <rdf:Description>
1626    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
1627  </rdf:Description>
1628<t>
1629   The server has fulfilled the partial GET request for the resource
1630   and the enclosed payload is a partial representation as defined in &status-206;.
1631</t>
1632<t>
1633   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1634   freshness for 206 responses.
1635</t>
1636</section>
1637</section>
1638
1639<section title="Redirection 3xx" anchor="status.3xx">
1640<t>
1641   This class of status code indicates that further action needs to be
1642   taken by the user agent in order to fulfill the request.  If the required
1643   action involves a subsequent HTTP request, it &MAY; be carried out by the
1644   user agent without interaction with the user if and only if the method used
1645   in the second request is known to be "safe", as defined in
1646   <xref target="safe.methods"/>.
1647</t>
1648<t>
1649   There are several types of redirects:
1650   <list style="numbers">
1651      <x:lt>
1652        <t>
1653          Redirects of the request to another URI, either temporarily or
1654          permanently. The new URI is specified in the Location header field.
1655          In this specification, the status codes 301 (Moved Permanently),
1656          302 (Found), and 307 (Temporary Redirect) fall under this category.
1657        </t>
1658      </x:lt>
1659      <x:lt>
1660        <t>
1661          Redirection to a new location that represents an indirect response to
1662          the request, such as the result of a POST operation to be retrieved
1663          with a subsequent GET request. This is status code 303 (See Other).
1664        </t>
1665      </x:lt>
1666      <x:lt>
1667        <t>
1668          Redirection offering a choice of matching resources for use by
1669          agent-driven content negotiation (&agent-driven-negotiation;). This
1670          is status code 300 (Multiple Choices).
1671        </t>
1672      </x:lt>
1673      <x:lt>
1674        <t>
1675          Other kinds of redirection, such as to a cached result (status code 304
1676          (Not Modified)).
1677        </t>
1678      </x:lt>
1679   </list>
1680</t>
1681<x:note>
1682  <t>
1683    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1684    and 302 (Found) were defined for the first type of redirect, and the second
1685    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1686    However it turned out that web forms using POST expected redirects to change
1687    the operation for the subsequent request to retrieval (GET). To address this
1688    use case, HTTP/1.1 introduced the second type of redirect with the status
1689    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1690    As user agents did not change their behavior to maintain backwards
1691    compatibility, the first revision of HTTP/1.1 added yet another status code,
1692    307 (Temporary Redirect), for which the backwards compatibility problems did
1693    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1694    Over 10 years later, most user agents still do method rewriting for
1695    status codes 301 and 302, therefore this specification makes that behavior
1696    compliant in case the original request was POST.
1697  </t>
1698</x:note>
1699<t>
1700   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1701   "infinite" redirection loops).
1702</t>
1703<x:note>
1704  <t>
1705    <x:h>Note:</x:h> An earlier version of this specification recommended a
1706    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1707    Content developers need to be aware that some clients might
1708    implement such a fixed limitation.
1709  </t>
1710</x:note>
1711
1712<section title="300 Multiple Choices" anchor="status.300">
1713  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1714  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1715<t>
1716   The target resource has more than one
1717   representation, each with its own specific location, and agent-driven
1718   negotiation information (&content-negotiation;) is being provided so that
1719   the user (or user agent) can select a preferred representation by
1720   redirecting its request to that location.
1721</t>
1722<t>
1723   Unless it was a HEAD request, the response &SHOULD; include a representation
1724   containing a list of representation metadata and location(s) from
1725   which the user or user agent can choose the one most appropriate. The
1726   data format is specified by the media type given in the Content-Type
1727   header field. Depending upon the format and the capabilities of
1728   the user agent, selection of the most appropriate choice &MAY; be
1729   performed automatically. However, this specification does not define
1730   any standard for such automatic selection.
1731</t>
1732<t>
1733   If the server has a preferred choice of representation, it &SHOULD;
1734   include the specific URI for that representation in the Location
1735   field; user agents &MAY; use the Location field value for automatic
1736   redirection.
1737</t>
1738<t>
1739   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1740   freshness for 300 responses.
1741</t>
1742
1743</section>
1744
1745<section title="301 Moved Permanently" anchor="status.301">
1746  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1747  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1748<t>
1749   The target resource has been assigned a new permanent URI and any
1750   future references to this resource &SHOULD; use one of the returned
1751   URIs.  Clients with link editing capabilities ought to automatically
1752   re-link references to the effective request URI to one or more of the new
1753   references returned by the server, where possible.
1754</t>
1755<t>
1756   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1757   freshness for 301 responses.
1758</t>
1759<t>
1760   The new permanent URI &SHOULD; be given by the Location field in the
1761   response. Unless the request method was HEAD, the representation of the
1762   response &SHOULD; contain a short hypertext note with a hyperlink to
1763   the new URI(s).
1764</t>
1765<t>
1766   If the 301 status code is received in response to a request method
1767   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1768   then the request &MAY; be automatically redirected by the user agent without
1769   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1770   request unless it can be confirmed by the user, since this might
1771   change the conditions under which the request was issued.
1772</t>
1773<x:note>
1774  <t>
1775    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1776    request method from POST to GET for the subsequent request. If this
1777    behavior is undesired, status code 307 (Temporary Redirect) can be used
1778    instead.
1779  </t>
1780</x:note>
1781</section>
1782
1783<section title="302 Found" anchor="status.302">
1784  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1785  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1786<t>
1787   The target resource resides temporarily under a different URI.
1788   Since the redirection might be altered on occasion, the client &SHOULD;
1789   continue to use the effective request URI for future requests.
1790</t>
1791<t>
1792   The temporary URI &SHOULD; be given by the Location field in the
1793   response. Unless the request method was HEAD, the representation of the
1794   response &SHOULD; contain a short hypertext note with a hyperlink to
1795   the new URI(s).
1796</t>
1797<t>
1798   If the 302 status code is received in response to a request method
1799   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1800   then the request &MAY; be automatically redirected by the user agent without
1801   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1802   request unless it can be confirmed by the user, since this might
1803   change the conditions under which the request was issued.
1804</t>
1805<x:note>
1806  <t>
1807    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1808    request method from POST to GET for the subsequent request. If this
1809    behavior is undesired, status code 307 (Temporary Redirect) can be used
1810    instead.
1811    <cref anchor="issue312">but see <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/312"/></cref>
1812  </t>
1813</x:note>
1814</section>
1815
1816<section title="303 See Other" anchor="status.303">
1817  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1818  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1819<t>
1820   The 303 status code indicates that the server is redirecting the
1821   user agent to a different resource, as indicated by a URI in the
1822   Location header field, that is intended to provide an indirect
1823   response to the original request.  In order to satisfy the original
1824   request, a user agent &SHOULD; perform a retrieval request using the
1825   Location URI (a GET or HEAD request if using HTTP), which
1826   may itself be redirected further, and present the eventual result as an
1827   answer to the original request.
1828   Note that the new URI in the Location header field is not considered
1829   equivalent to the effective request URI.
1830</t>
1831<t>
1832   This status code is generally applicable to any HTTP method.  It is
1833   primarily used to allow the output of a POST action to redirect
1834   the user agent to a selected resource, since doing so provides the
1835   information corresponding to the POST response in a form that
1836   can be separately identified, bookmarked, and cached independent
1837   of the original request.
1838</t>
1839<t>
1840   A 303 response to a GET request indicates that the requested
1841   resource does not have a representation of its own that can be
1842   transferred by the server over HTTP.  The Location URI indicates a
1843   resource that is descriptive of the target resource, such that the
1844   follow-on representation might be useful to recipients without
1845   implying that it adequately represents the target resource.
1846   Note that answers to the questions of what can be represented, what
1847   representations are adequate, and what might be a useful description
1848   are outside the scope of HTTP and thus entirely determined by the
1849   URI owner(s).
1850</t>
1851<t>
1852   Except for responses to a HEAD request, the representation of a 303
1853   response &SHOULD; contain a short hypertext note with a hyperlink
1854   to the Location URI.
1855</t>
1856</section>
1857
1858<section title="304 Not Modified" anchor="status.304">
1859  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1860  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1861  <rdf:Description>
1862    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
1863  </rdf:Description>
1864<t>
1865   The response to the request has not been modified since the conditions
1866   indicated by the client's conditional GET request, as defined in &status-304;.
1867</t>
1868</section>
1869
1870<section title="305 Use Proxy" anchor="status.305">
1871  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1872  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1873<t>
1874   The 305 status code was defined in a previous version of this specification
1875   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1876</t>
1877</section>
1878
1879<section title="306 (Unused)" anchor="status.306">
1880  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1881  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1882<t>
1883   The 306 status code was used in a previous version of the
1884   specification, is no longer used, and the code is reserved.
1885</t>
1886</section>
1887
1888<section title="307 Temporary Redirect" anchor="status.307">
1889  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1890  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1891<t>
1892   The target resource resides temporarily under a different URI.
1893   Since the redirection can change over time, the client &SHOULD;
1894   continue to use the effective request URI for future requests.
1895</t>
1896<t>
1897   The temporary URI &SHOULD; be given by the Location field in the
1898   response. Unless the request method was HEAD, the representation of the
1899   response &SHOULD; contain a short hypertext note with a hyperlink to
1900   the new URI(s), since many pre-HTTP/1.1 user agents do not
1901   understand the 307 status code. Therefore, the note &SHOULD; contain the
1902   information necessary for a user to repeat the original request on
1903   the new URI.
1904</t>
1905<t>
1906   If the 307 status code is received in response to a request method
1907   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1908   then the request &MAY; be automatically redirected by the user agent without
1909   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1910   request unless it can be confirmed by the user, since this might
1911   change the conditions under which the request was issued.
1912</t>
1913<x:note>
1914  <t>
1915    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1916    it does not allow rewriting the request method from POST to GET. This
1917    specification defines no equivalent counterpart for 301 Moved Permanently.
1918  </t>
1919</x:note>
1920</section>
1921</section>
1922
1923<section title="Client Error 4xx" anchor="status.4xx">
1924<t>
1925   The 4xx class of status code is intended for cases in which the
1926   client seems to have erred. Except when responding to a HEAD request,
1927   the server &SHOULD; include a representation containing an explanation of the
1928   error situation, and whether it is a temporary or permanent
1929   condition. These status codes are applicable to any request method.
1930   User agents &SHOULD; display any included representation to the user.
1931</t>
1932<t>
1933   If the client is sending data, a server implementation using TCP
1934   &SHOULD; be careful to ensure that the client acknowledges receipt of
1935   the packet(s) containing the response, before the server closes the
1936   input connection. If the client continues sending data to the server
1937   after the close, the server's TCP stack will send a reset packet to
1938   the client, which might erase the client's unacknowledged input buffers
1939   before they can be read and interpreted by the HTTP application.
1940</t>
1941
1942<section title="400 Bad Request" anchor="status.400">
1943  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1944  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1945<t>
1946   The server cannot or will not process the request, due to a client error (e.g.,
1947   malformed syntax).</t>
1948</section>
1949
1950<section title="401 Unauthorized" anchor="status.401">
1951  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1952  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1953  <rdf:Description>
1954    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part7</redirects-to>
1955  </rdf:Description>
1956<t>
1957   The request requires user authentication (see &status-401;).
1958</t>
1959</section>
1960
1961<section title="402 Payment Required" anchor="status.402">
1962  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1963  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1964<t>
1965   This code is reserved for future use.
1966</t>
1967</section>
1968
1969<section title="403 Forbidden" anchor="status.403">
1970  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1971  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1972<t>
1973   The server understood the request, but refuses to authorize it. Providing
1974   different user authentication credentials might be successful, but any
1975   credentials that were provided in the request are insufficient. The request
1976   &SHOULD-NOT; be repeated with the same credentials.
1977</t>
1978<t>
1979   If the request method was not HEAD and the server wishes to make
1980   public why the request has not been fulfilled, it &SHOULD; describe the
1981   reason for the refusal in the representation.  If the server does not wish to
1982   make this information available to the client, the status code 404
1983   (Not Found) &MAY; be used instead.
1984</t>
1985</section>
1986
1987<section title="404 Not Found" anchor="status.404">
1988  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1989  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1990<t>
1991   The server has not found anything matching the effective request URI. No
1992   indication is given of whether the condition is temporary or
1993   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1994   knows, through some internally configurable mechanism, that an old
1995   resource is permanently unavailable and has no forwarding address.
1996   This status code is commonly used when the server does not wish to
1997   reveal exactly why the request has been refused, or when no other
1998   response is applicable.
1999</t>
2000</section>
2001
2002<section title="405 Method Not Allowed" anchor="status.405">
2003  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
2004  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
2005<t>
2006   The method specified in the Request-Line is not allowed for the target
2007   resource. The response &MUST; include an Allow header field containing a
2008   list of valid methods for the requested resource.
2009</t>
2010</section>
2011
2012<section title="406 Not Acceptable" anchor="status.406">
2013  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
2014  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
2015<t>
2016   The resource identified by the request is only capable of generating
2017   response representations which have content characteristics not acceptable
2018   according to the Accept and Accept-* header fields sent in the request
2019   (see &p3-header-fields;).
2020</t>
2021<t>
2022   Unless it was a HEAD request, the response &SHOULD; include a representation
2023   containing a list of available representation characteristics and location(s)
2024   from which the user or user agent can choose the one most
2025   appropriate. The data format is specified by the media type given
2026   in the Content-Type header field. Depending upon the format and the
2027   capabilities of the user agent, selection of the most appropriate
2028   choice &MAY; be performed automatically. However, this specification
2029   does not define any standard for such automatic selection.
2030</t>
2031<x:note>
2032  <t>
2033    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
2034    not acceptable according to the accept header fields sent in the
2035    request. In some cases, this might even be preferable to sending a
2036    406 response. User agents are encouraged to inspect the header fields of
2037    an incoming response to determine if it is acceptable.
2038  </t>
2039</x:note>
2040<t>
2041   If the response could be unacceptable, a user agent &SHOULD;
2042   temporarily stop receipt of more data and query the user for a
2043   decision on further actions.
2044</t>
2045</section>
2046
2047<section title="407 Proxy Authentication Required" anchor="status.407">
2048  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
2049  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
2050<t>
2051   This code is similar to 401 (Unauthorized), but indicates that the
2052   client must first authenticate itself with the proxy (see &status-407;).
2053</t>
2054</section>
2055
2056<section title="408 Request Timeout" anchor="status.408">
2057  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
2058  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
2059<t>
2060   The client did not produce a request within the time that the server
2061   was prepared to wait. The client &MAY; repeat the request without
2062   modifications at any later time.
2063</t>
2064</section>
2065
2066<section title="409 Conflict" anchor="status.409">
2067  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
2068  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
2069<t>
2070   The request could not be completed due to a conflict with the current
2071   state of the resource. This code is only allowed in situations where
2072   it is expected that the user might be able to resolve the conflict
2073   and resubmit the request. The response body &SHOULD; include enough
2074   information for the user to recognize the source of the conflict.
2075   Ideally, the response representation would include enough information for the
2076   user or user agent to fix the problem; however, that might not be
2077   possible and is not required.
2078</t>
2079<t>
2080   Conflicts are most likely to occur in response to a PUT request. For
2081   example, if versioning were being used and the representation being PUT
2082   included changes to a resource which conflict with those made by an
2083   earlier (third-party) request, the server might use the 409 response
2084   to indicate that it can't complete the request. In this case, the
2085   response representation would likely contain a list of the differences
2086   between the two versions in a format defined by the response
2087   Content-Type.
2088</t>
2089</section>
2090
2091<section title="410 Gone" anchor="status.410">
2092  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
2093  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
2094<t>
2095   The target resource is no longer available at the server and no
2096   forwarding address is known. This condition is expected to be
2097   considered permanent. Clients with link editing capabilities &SHOULD;
2098   delete references to the effective request URI after user approval. If the
2099   server does not know, or has no facility to determine, whether or not
2100   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
2101   used instead.
2102</t>
2103<t>
2104   The 410 response is primarily intended to assist the task of web
2105   maintenance by notifying the recipient that the resource is
2106   intentionally unavailable and that the server owners desire that
2107   remote links to that resource be removed. Such an event is common for
2108   limited-time, promotional services and for resources belonging to
2109   individuals no longer working at the server's site. It is not
2110   necessary to mark all permanently unavailable resources as "gone" or
2111   to keep the mark for any length of time &mdash; that is left to the
2112   discretion of the server owner.
2113</t>
2114<t>
2115   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
2116   for 410 responses.
2117</t>
2118
2119</section>
2120
2121<section title="411 Length Required" anchor="status.411">
2122  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
2123  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
2124<t>
2125   The server refuses to accept the request without a defined Content-Length.
2126   The client &MAY; repeat the request if it adds a valid
2127   Content-Length header field containing the length of the message-body
2128   in the request message.
2129</t>
2130</section>
2131
2132<section title="412 Precondition Failed" anchor="status.412">
2133  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
2134  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
2135  <rdf:Description>
2136    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
2137  </rdf:Description>
2138<t>
2139   The precondition given in one or more of the header fields
2140   evaluated to false when it was tested on the server, as defined in
2141   &status-412;.
2142</t>
2143</section>
2144
2145<section title="413 Request Representation Too Large" anchor="status.413">
2146  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2147  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2148<t>
2149   The server is refusing to process a request because the request
2150   representation is larger than the server is willing or able to process. The
2151   server &MAY; close the connection to prevent the client from continuing
2152   the request.
2153</t>
2154<t>
2155   If the condition is temporary, the server &SHOULD; include a Retry-After
2156   header field to indicate that it is temporary and after what
2157   time the client &MAY; try again.
2158</t>
2159</section>
2160
2161<section title="414 URI Too Long" anchor="status.414">
2162  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2163  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
2164<t>
2165   The server is refusing to service the request because the effective request URI
2166   is longer than the server is willing to interpret. This rare
2167   condition is only likely to occur when a client has improperly
2168   converted a POST request to a GET request with long query
2169   information, when the client has descended into a URI "black hole" of
2170   redirection (e.g., a redirected URI prefix that points to a suffix of
2171   itself), or when the server is under attack by a client attempting to
2172   exploit security holes present in some servers using fixed-length
2173   buffers for reading or manipulating the effective request URI.
2174</t>
2175</section>
2176
2177<section title="415 Unsupported Media Type" anchor="status.415">
2178  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2179  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2180<t>
2181   The server is refusing to service the request because the request
2182   payload is in a format not supported by this request method on the
2183   target resource.
2184</t>
2185</section>
2186
2187<section title="416 Requested Range Not Satisfiable" anchor="status.416">
2188  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
2189  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
2190  <rdf:Description>
2191    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
2192  </rdf:Description>
2193<t>
2194   The request included a Range header field (&header-range;) and none of
2195   the range-specifier values in this field overlap the current extent
2196   of the selected resource. See &status-416;.
2197</t>
2198</section>
2199
2200<section title="417 Expectation Failed" anchor="status.417">
2201  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2202  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2203<t>
2204   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2205   could not be met by this server, or, if the server is a proxy,
2206   the server has unambiguous evidence that the request could not be met
2207   by the next-hop server.
2208</t>
2209</section>
2210
2211<section title="426 Upgrade Required" anchor="status.426">
2212  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2213  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2214<t>
2215   The request can not be completed without a prior protocol upgrade. This
2216   response &MUST; include an Upgrade header field (&header-upgrade;)
2217   specifying the required protocols.
2218</t>
2219<figure>
2220<preamble>Example:</preamble>
2221<artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2222HTTP/1.1 426 Upgrade Required
2223Upgrade: HTTP/2.0
2224Connection: Upgrade
2225
2226</artwork></figure>
2227<t>
2228   The server &SHOULD; include a message body in the 426 response which
2229   indicates in human readable form the reason for the error and describes any
2230   alternative courses which may be available to the user.
2231</t>
2232</section>
2233</section>
2234
2235<section title="Server Error 5xx" anchor="status.5xx">
2236<t>
2237   Response status codes beginning with the digit "5" indicate cases in
2238   which the server is aware that it has erred or is incapable of
2239   performing the request. Except when responding to a HEAD request, the
2240   server &SHOULD; include a representation containing an explanation of the
2241   error situation, and whether it is a temporary or permanent
2242   condition. User agents &SHOULD; display any included representation to the
2243   user. These response codes are applicable to any request method.
2244</t>
2245
2246<section title="500 Internal Server Error" anchor="status.500">
2247  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2248  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2249<t>
2250   The server encountered an unexpected condition which prevented it
2251   from fulfilling the request.
2252</t>
2253</section>
2254
2255<section title="501 Not Implemented" anchor="status.501">
2256  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2257  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2258<t>
2259   The server does not support the functionality required to fulfill the
2260   request. This is the appropriate response when the server does not
2261   recognize the request method and is not capable of supporting it for
2262   any resource.
2263</t>
2264</section>
2265
2266<section title="502 Bad Gateway" anchor="status.502">
2267  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2268  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2269<t>
2270   The server, while acting as a gateway or proxy, received an invalid
2271   response from the upstream server it accessed in attempting to
2272   fulfill the request.
2273</t>
2274</section>
2275
2276<section title="503 Service Unavailable" anchor="status.503">
2277  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2278  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2279<t>
2280   The server is currently unable to handle the request due to a
2281   temporary overloading or maintenance of the server.
2282</t>
2283<t>
2284   The implication is that this is a temporary condition which will be
2285   alleviated after some delay. If known, the length of the delay &MAY; be
2286   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2287   If no Retry-After is given, the client &SHOULD; handle the response as it
2288   would for a 500 response.
2289</t>
2290<x:note>
2291  <t>
2292    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2293    server must use it when becoming overloaded. Some servers might wish
2294    to simply refuse the connection.
2295  </t>
2296</x:note>
2297</section>
2298
2299<section title="504 Gateway Timeout" anchor="status.504">
2300  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2301  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2302<t>
2303   The server, while acting as a gateway or proxy, did not receive a
2304   timely response from the upstream server specified by the URI (e.g.,
2305   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2306   to access in attempting to complete the request.
2307</t>
2308<x:note>
2309  <t>
2310    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2311    return 400 or 500 when DNS lookups time out.
2312  </t>
2313</x:note>
2314</section>
2315
2316<section title="505 HTTP Version Not Supported" anchor="status.505">
2317  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2318  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2319<t>
2320   The server does not support, or refuses to support, the protocol
2321   version that was used in the request message. The server is
2322   indicating that it is unable or unwilling to complete the request
2323   using the same major version as the client, as described in &http-version;,
2324   other than with this error message. The response &SHOULD; contain
2325   a representation describing why that version is not supported and what other
2326   protocols are supported by that server.
2327</t>
2328
2329</section>
2330</section>
2331</section>
2332
2333
2334<section title="Date/Time Formats" anchor="http.date">
2335  <x:anchor-alias value="HTTP-date"/>
2336<t>
2337   HTTP applications have historically allowed three different formats
2338   for date/time stamps. However, the preferred format is a fixed-length subset
2339   of that defined by <xref target="RFC1123"/>:
2340</t>
2341<figure><artwork type="example" x:indent-with="  ">
2342Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2343</artwork></figure>
2344<t>
2345   The other formats are described here only for compatibility with obsolete
2346   implementations.
2347</t>
2348<figure><artwork type="example" x:indent-with="  ">
2349Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2350Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2351</artwork></figure>
2352<t>
2353   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2354   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2355   only generate the RFC 1123 format for representing HTTP-date values
2356   in header fields.
2357</t>
2358<t>
2359   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2360   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2361   equal to UTC (Coordinated Universal Time). This is indicated in the
2362   first two formats by the inclusion of "GMT" as the three-letter
2363   abbreviation for time zone, and &MUST; be assumed when reading the
2364   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2365   additional whitespace beyond that specifically included as SP in the
2366   grammar.
2367</t>
2368<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2369  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2370</artwork></figure>
2371<t anchor="preferred.date.format">
2372  <x:anchor-alias value="rfc1123-date"/>
2373  <x:anchor-alias value="time-of-day"/>
2374  <x:anchor-alias value="hour"/>
2375  <x:anchor-alias value="minute"/>
2376  <x:anchor-alias value="second"/>
2377  <x:anchor-alias value="day-name"/>
2378  <x:anchor-alias value="day"/>
2379  <x:anchor-alias value="month"/>
2380  <x:anchor-alias value="year"/>
2381  <x:anchor-alias value="GMT"/>
2382  Preferred format:
2383</t>
2384<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"/>
2385  <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>
2386  ; fixed length subset of the format defined in
2387  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2388 
2389  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2390               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2391               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2392               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2393               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2394               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2395               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2396               
2397  <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>
2398               ; e.g., 02 Jun 1982
2399
2400  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2401  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2402               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2403               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2404               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2405               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2406               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2407               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2408               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2409               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2410               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2411               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2412               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2413  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2414
2415  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2416
2417  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2418                 ; 00:00:00 - 23:59:59
2419                 
2420  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2421  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2422  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2423</artwork></figure>
2424<t>
2425  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2426  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2427  same as those defined for the RFC 5322 constructs
2428  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2429</t>
2430<t anchor="obsolete.date.formats">
2431  <x:anchor-alias value="obs-date"/>
2432  <x:anchor-alias value="rfc850-date"/>
2433  <x:anchor-alias value="asctime-date"/>
2434  <x:anchor-alias value="date1"/>
2435  <x:anchor-alias value="date2"/>
2436  <x:anchor-alias value="date3"/>
2437  <x:anchor-alias value="rfc1123-date"/>
2438  <x:anchor-alias value="day-name-l"/>
2439  Obsolete formats:
2440</t>
2441<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2442  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2443</artwork></figure>
2444<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2445  <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>
2446  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2447                 ; day-month-year (e.g., 02-Jun-82)
2448
2449  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2450         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2451         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2452         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2453         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2454         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2455         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2456</artwork></figure>
2457<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2458  <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>
2459  <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> ))
2460                 ; month day (e.g., Jun  2)
2461</artwork></figure>
2462<x:note>
2463  <t>
2464    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2465    accepting date values that might have been sent by non-HTTP
2466    applications, as is sometimes the case when retrieving or posting
2467    messages via proxies/gateways to SMTP or NNTP.
2468  </t>
2469</x:note>
2470<x:note>
2471  <t>
2472    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2473    to their usage within the protocol stream. Clients and servers are
2474    not required to use these formats for user presentation, request
2475    logging, etc.
2476  </t>
2477</x:note>
2478</section>
2479
2480
2481<section title="Header Field Definitions" anchor="header.field.definitions">
2482<t>
2483   This section defines the syntax and semantics of HTTP/1.1 header fields
2484   related to request and response semantics.
2485</t>
2486
2487<section title="Allow" anchor="header.allow">
2488  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2489  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2490  <x:anchor-alias value="Allow"/>
2491<t>
2492   The "Allow" header field lists the set of methods advertised as
2493   supported by the target resource. The purpose of this field is strictly to
2494   inform the recipient of valid request methods associated with the resource.
2495</t>
2496<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2497  <x:ref>Allow</x:ref> = #<x:ref>Method</x:ref>
2498</artwork></figure>
2499<t>
2500   Example of use:
2501</t>
2502<figure><artwork type="example">
2503  Allow: GET, HEAD, PUT
2504</artwork></figure>
2505<t>
2506   The actual set of allowed methods is defined by the origin server at the
2507   time of each request.
2508</t>
2509<t>
2510   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2511   understand all the methods specified in order to handle them according to
2512   the generic message handling rules.
2513</t>
2514</section>
2515
2516<section title="Date" anchor="header.date">
2517  <iref primary="true" item="Date header field" x:for-anchor=""/>
2518  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2519  <x:anchor-alias value="Date"/>
2520<t>
2521   The "Date" header field represents the date and time at which
2522   the message was originated, having the same semantics as the Origination
2523   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2524   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2525   it &MUST; be sent in rfc1123-date format.
2526</t>
2527<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2528  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2529</artwork></figure>
2530<t>
2531   An example is
2532</t>
2533<figure><artwork type="example">
2534  Date: Tue, 15 Nov 1994 08:12:31 GMT
2535</artwork></figure>
2536<t>
2537   Origin servers &MUST; include a Date header field in all responses,
2538   except in these cases:
2539  <list style="numbers">
2540      <t>If the response status code is 100 (Continue) or 101 (Switching
2541         Protocols), the response &MAY; include a Date header field, at
2542         the server's option.</t>
2543
2544      <t>If the response status code conveys a server error, e.g., 500
2545         (Internal Server Error) or 503 (Service Unavailable), and it is
2546         inconvenient or impossible to generate a valid Date.</t>
2547
2548      <t>If the server does not have a clock that can provide a
2549         reasonable approximation of the current time, its responses
2550         &MUST-NOT; include a Date header field.</t>
2551  </list>
2552</t>
2553<t>
2554   A received message that does not have a Date header field &MUST; be
2555   assigned one by the recipient if the message will be cached by that
2556   recipient.
2557</t>
2558<t>
2559   Clients can use the Date header field as well; in order to keep request
2560   messages small, they are advised not to include it when it doesn't convey
2561   any useful information (as it is usually the case for requests that do not
2562   contain a payload).
2563</t>
2564<t>
2565   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2566   time subsequent to the generation of the message. It &SHOULD; represent
2567   the best available approximation of the date and time of message
2568   generation, unless the implementation has no means of generating a
2569   reasonably accurate date and time. In theory, the date ought to
2570   represent the moment just before the payload is generated. In
2571   practice, the date can be generated at any time during the message
2572   origination without affecting its semantic value.
2573</t>
2574</section>
2575
2576<section title="Expect" anchor="header.expect">
2577  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2578  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2579  <x:anchor-alias value="Expect"/>
2580  <x:anchor-alias value="expectation"/>
2581  <x:anchor-alias value="expectation-extension"/>
2582  <x:anchor-alias value="expect-param"/>
2583<t>
2584   The "Expect" header field is used to indicate that particular
2585   server behaviors are required by the client.
2586</t>
2587<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-param"/>
2588  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2589 
2590  <x:ref>expectation</x:ref>  = "100-continue" / <x:ref>expectation-extension</x:ref>
2591  <x:ref>expectation-extension</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2592                           *(";" <x:ref>expect-param</x:ref>) ]
2593  <x:ref>expect-param</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2594</artwork></figure>
2595<t>
2596   A server that does not understand or is unable to comply with any of
2597   the expectation values in the Expect field of a request &MUST; respond
2598   with appropriate error status code. The server &MUST; respond with a 417
2599   (Expectation Failed) status code if any of the expectations cannot be met
2600   or, if there are other problems with the request, some other 4xx
2601   status code.
2602</t>
2603<t>
2604   This header field is defined with extensible syntax to allow for
2605   future extensions. If a server receives a request containing an
2606   Expect field that includes an expectation-extension that it does not
2607   support, it &MUST; respond with a 417 (Expectation Failed) status code.
2608</t>
2609<t>
2610   Comparison of expectation values is case-insensitive for unquoted
2611   tokens (including the 100-continue token), and is case-sensitive for
2612   quoted-string expectation-extensions.
2613</t>
2614<t>
2615   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
2616   return a 417 (Expectation Failed) status code if it receives a request
2617   with an expectation that it cannot meet. However, the Expect
2618   header field itself is end-to-end; it &MUST; be forwarded if the
2619   request is forwarded.
2620</t>
2621<t>
2622   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
2623   Expect header field.
2624</t>
2625<t>
2626   See &use100; for the use of the 100 (Continue) status code.
2627</t>
2628</section>
2629
2630<section title="From" anchor="header.from">
2631  <iref primary="true" item="From header field" x:for-anchor=""/>
2632  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2633  <x:anchor-alias value="From"/>
2634  <x:anchor-alias value="mailbox"/>
2635<t>
2636   The "From" header field, if given, &SHOULD; contain an Internet
2637   e-mail address for the human user who controls the requesting user
2638   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2639   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2640</t>
2641<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2642  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2643 
2644  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2645</artwork></figure>
2646<t>
2647   An example is:
2648</t>
2649<figure><artwork type="example">
2650  From: webmaster@example.org
2651</artwork></figure>
2652<t>
2653   This header field &MAY; be used for logging purposes and as a means for
2654   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2655   be used as an insecure form of access protection. The interpretation
2656   of this field is that the request is being performed on behalf of the
2657   person given, who accepts responsibility for the method performed. In
2658   particular, robot agents &SHOULD; include this header field so that the
2659   person responsible for running the robot can be contacted if problems
2660   occur on the receiving end.
2661</t>
2662<t>
2663   The Internet e-mail address in this field &MAY; be separate from the
2664   Internet host which issued the request. For example, when a request
2665   is passed through a proxy the original issuer's address &SHOULD; be
2666   used.
2667</t>
2668<t>
2669   The client &SHOULD-NOT;  send the From header field without the user's
2670   approval, as it might conflict with the user's privacy interests or
2671   their site's security policy. It is strongly recommended that the
2672   user be able to disable, enable, and modify the value of this field
2673   at any time prior to a request.
2674</t>
2675</section>
2676
2677<section title="Location" anchor="header.location">
2678  <iref primary="true" item="Location header field" x:for-anchor=""/>
2679  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2680  <x:anchor-alias value="Location"/>
2681<t>
2682   The "Location" header field is used to identify a newly created
2683   resource, or to redirect the recipient to a different location for
2684   completion of the request.
2685</t>
2686<t>
2687   For 201 (Created) responses, the Location is the URI of the new resource
2688   which was created by the request. For 3xx responses, the location &SHOULD;
2689   indicate the server's preferred URI for automatic redirection to the
2690   resource.
2691</t>
2692<t>
2693   The field value consists of a single URI-reference. When it has the form
2694   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2695   the final value is computed by resolving it against the effective request
2696   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>).
2697</t>
2698<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2699  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2700</artwork></figure>
2701<figure>
2702<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2703<artwork type="example">
2704  Location: http://www.example.org/pub/WWW/People.html#tim
2705</artwork></figure><figure><artwork type="example">  Location: /index.html
2706</artwork></figure>
2707<t>
2708   There are circumstances in which a fragment identifier in a Location URI
2709   would not be appropriate. For instance, when it appears in a 201 Created
2710   response, where the Location header field specifies the URI for the entire
2711   created resource.
2712</t>
2713<x:note>
2714  <t>
2715    <x:h>Note:</x:h> This specification does not define precedence rules
2716    for the case where the original URI, as navigated to by the user
2717    agent, and the Location header field value both contain fragment
2718    identifiers. Thus be aware that including fragment identifiers might
2719    inconvenience anyone relying on the semantics of the original URI's
2720    fragment identifier.
2721  </t>
2722</x:note>
2723<x:note>
2724  <t>
2725    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2726    from Location in that the Content-Location identifies the most specific
2727    resource corresponding to the enclosed representation.
2728    It is therefore possible for a response to contain header fields for
2729    both Location and Content-Location.
2730  </t>
2731</x:note>
2732</section>
2733
2734<section title="Max-Forwards" anchor="header.max-forwards">
2735  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2736  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2737  <x:anchor-alias value="Max-Forwards"/>
2738<t>
2739   The "Max-Forwards" header field provides a mechanism with the
2740   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2741   methods to limit the number of times that the request is forwarded by
2742   proxies. This can be useful when the client is attempting to
2743   trace a request which appears to be failing or looping in mid-chain.
2744</t>
2745<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2746  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2747</artwork></figure>
2748<t>
2749   The Max-Forwards value is a decimal integer indicating the remaining
2750   number of times this request message can be forwarded.
2751</t>
2752<t>
2753   Each recipient of a TRACE or OPTIONS request
2754   containing a Max-Forwards header field &MUST; check and update its
2755   value prior to forwarding the request. If the received value is zero
2756   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2757   respond as the final recipient. If the received Max-Forwards value is
2758   greater than zero, then the forwarded message &MUST; contain an updated
2759   Max-Forwards field with a value decremented by one (1).
2760</t>
2761<t>
2762   The Max-Forwards header field &MAY; be ignored for all other request
2763   methods.
2764</t>
2765</section>
2766
2767<section title="Referer" anchor="header.referer">
2768  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2769  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2770  <x:anchor-alias value="Referer"/>
2771<t>
2772   The "Referer" [sic] header field allows the client to specify the
2773   URI of the resource from which the effective request URI was obtained (the
2774   "referrer", although the header field is misspelled.).
2775</t>
2776<t>
2777   The Referer header field allows servers to generate lists of back-links to
2778   resources for interest, logging, optimized caching, etc. It also allows
2779   obsolete or mistyped links to be traced for maintenance. Some servers use
2780   Referer as a means of controlling where they allow links from (so-called
2781   "deep linking"), but legitimate requests do not always
2782   contain a Referer header field.
2783</t>
2784<t>
2785   If the effective request URI was obtained from a source that does not have its own
2786   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2787   sent with the value "about:blank", or not be sent at all. Note that this
2788   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2789</t>
2790<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2791  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2792</artwork></figure>
2793<t>
2794   Example:
2795</t>
2796<figure><artwork type="example">
2797  Referer: http://www.example.org/hypertext/Overview.html
2798</artwork></figure>
2799<t>
2800   If the field value is a relative URI, it &SHOULD; be interpreted
2801   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2802   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2803</t>
2804</section>
2805
2806<section title="Retry-After" anchor="header.retry-after">
2807  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2808  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2809  <x:anchor-alias value="Retry-After"/>
2810<t>
2811   The header "Retry-After" field can be used with a 503 (Service
2812   Unavailable) response to indicate how long the service is expected to
2813   be unavailable to the requesting client. This field &MAY; also be used
2814   with any 3xx (Redirection) response to indicate the minimum time the
2815   user-agent is asked wait before issuing the redirected request.
2816</t>
2817<t>
2818   The value of this field can be either an HTTP-date or an integer number
2819   of seconds (in decimal) after the time of the response.
2820</t>
2821<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2822  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2823</artwork></figure>
2824<t anchor="rule.delta-seconds">
2825  <x:anchor-alias value="delta-seconds"/>
2826   Time spans are non-negative decimal integers, representing time in
2827   seconds.
2828</t>
2829<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2830  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2831</artwork></figure>
2832<t>
2833   Two examples of its use are
2834</t>
2835<figure><artwork type="example">
2836  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2837  Retry-After: 120
2838</artwork></figure>
2839<t>
2840   In the latter example, the delay is 2 minutes.
2841</t>
2842</section>
2843
2844<section title="Server" anchor="header.server">
2845  <iref primary="true" item="Server header field" x:for-anchor=""/>
2846  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2847  <x:anchor-alias value="Server"/>
2848<t>
2849   The "Server" header field contains information about the
2850   software used by the origin server to handle the request.
2851</t>
2852<t>
2853   The field can contain multiple product tokens (&product-tokens;) and
2854   comments (&header-fields;) identifying the server and any significant
2855   subproducts. The product tokens are listed in order of their significance
2856   for identifying the application.
2857</t>
2858<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2859  <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> ) )
2860</artwork></figure>
2861<t>
2862   Example:
2863</t>
2864<figure><artwork type="example">
2865  Server: CERN/3.0 libwww/2.17
2866</artwork></figure>
2867<t>
2868   If the response is being forwarded through a proxy, the proxy
2869   application &MUST-NOT; modify the Server header field. Instead, it
2870   &MUST; include a Via field (as described in &header-via;).
2871</t>
2872<x:note>
2873  <t>
2874    <x:h>Note:</x:h> Revealing the specific software version of the server might
2875    allow the server machine to become more vulnerable to attacks
2876    against software that is known to contain security holes. Server
2877    implementors are encouraged to make this field a configurable
2878    option.
2879  </t>
2880</x:note>
2881</section>
2882
2883<section title="User-Agent" anchor="header.user-agent">
2884  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2885  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2886  <x:anchor-alias value="User-Agent"/>
2887<t>
2888   The "User-Agent" header field contains information about the user
2889   agent originating the request. User agents &SHOULD; include this field with
2890   requests.
2891</t>
2892<t>
2893   Typically, it is used for statistical purposes, the tracing of protocol
2894   violations, and tailoring responses to avoid particular user agent
2895   limitations.
2896</t>
2897<t>
2898   The field can contain multiple product tokens (&product-tokens;)
2899   and comments (&header-fields;) identifying the agent and its
2900   significant subproducts. By convention, the product tokens are listed in
2901   order of their significance for identifying the application.
2902</t>
2903<t>
2904   Because this field is usually sent on every request a user agent makes,
2905   implementations are encouraged not to include needlessly fine-grained
2906   detail, and to limit (or even prohibit) the addition of subproducts by third
2907   parties. Overly long and detailed User-Agent field values make requests
2908   larger and can also be used to identify ("fingerprint") the user against
2909   their wishes.
2910</t>
2911<t>
2912   Likewise, implementations are encouraged not to use the product tokens of
2913   other implementations in order to declare compatibility with them, as this
2914   circumvents the purpose of the field. Finally, they are encouraged not to
2915   use comments to identify products; doing so makes the field value more
2916   difficult to parse.
2917</t>
2918<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2919  <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> ) )
2920</artwork></figure>
2921<t>
2922   Example:
2923</t>
2924<figure><artwork type="example">
2925  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2926</artwork></figure>
2927</section>
2928
2929</section>
2930
2931<section title="IANA Considerations" anchor="IANA.considerations">
2932
2933<section title="Method Registry" anchor="method.registration">
2934<t>
2935  The registration procedure for HTTP request methods is defined by
2936  <xref target="method.registry"/> of this document.
2937</t>
2938<t>
2939   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2940   and be populated with the registrations below:
2941</t>
2942<?BEGININC p2-semantics.iana-methods ?>
2943<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2944<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2945   <ttcol>Method</ttcol>
2946   <ttcol>Safe</ttcol>
2947   <ttcol>Reference</ttcol>
2948   <c>CONNECT</c>
2949   <c>no</c>
2950   <c>
2951      <xref target="CONNECT"/>
2952   </c>
2953   <c>DELETE</c>
2954   <c>no</c>
2955   <c>
2956      <xref target="DELETE"/>
2957   </c>
2958   <c>GET</c>
2959   <c>yes</c>
2960   <c>
2961      <xref target="GET"/>
2962   </c>
2963   <c>HEAD</c>
2964   <c>yes</c>
2965   <c>
2966      <xref target="HEAD"/>
2967   </c>
2968   <c>OPTIONS</c>
2969   <c>yes</c>
2970   <c>
2971      <xref target="OPTIONS"/>
2972   </c>
2973   <c>POST</c>
2974   <c>no</c>
2975   <c>
2976      <xref target="POST"/>
2977   </c>
2978   <c>PUT</c>
2979   <c>no</c>
2980   <c>
2981      <xref target="PUT"/>
2982   </c>
2983   <c>TRACE</c>
2984   <c>yes</c>
2985   <c>
2986      <xref target="TRACE"/>
2987   </c>
2988</texttable>
2989<!--(END)-->
2990<?ENDINC p2-semantics.iana-methods ?>
2991</section>
2992
2993<section title="Status Code Registry" anchor="status.code.registration">
2994<t>
2995   The registration procedure for HTTP Status Codes &mdash; previously defined
2996   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2997   by <xref target="status.code.registry"/> of this document.
2998</t>
2999<t>
3000   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
3001   shall be updated with the registrations below:
3002</t>
3003<?BEGININC p2-semantics.iana-status-codes ?>
3004<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
3005<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
3006   <ttcol>Value</ttcol>
3007   <ttcol>Description</ttcol>
3008   <ttcol>Reference</ttcol>
3009   <c>100</c>
3010   <c>Continue</c>
3011   <c>
3012      <xref target="status.100"/>
3013   </c>
3014   <c>101</c>
3015   <c>Switching Protocols</c>
3016   <c>
3017      <xref target="status.101"/>
3018   </c>
3019   <c>200</c>
3020   <c>OK</c>
3021   <c>
3022      <xref target="status.200"/>
3023   </c>
3024   <c>201</c>
3025   <c>Created</c>
3026   <c>
3027      <xref target="status.201"/>
3028   </c>
3029   <c>202</c>
3030   <c>Accepted</c>
3031   <c>
3032      <xref target="status.202"/>
3033   </c>
3034   <c>203</c>
3035   <c>Non-Authoritative Information</c>
3036   <c>
3037      <xref target="status.203"/>
3038   </c>
3039   <c>204</c>
3040   <c>No Content</c>
3041   <c>
3042      <xref target="status.204"/>
3043   </c>
3044   <c>205</c>
3045   <c>Reset Content</c>
3046   <c>
3047      <xref target="status.205"/>
3048   </c>
3049   <c>300</c>
3050   <c>Multiple Choices</c>
3051   <c>
3052      <xref target="status.300"/>
3053   </c>
3054   <c>301</c>
3055   <c>Moved Permanently</c>
3056   <c>
3057      <xref target="status.301"/>
3058   </c>
3059   <c>302</c>
3060   <c>Found</c>
3061   <c>
3062      <xref target="status.302"/>
3063   </c>
3064   <c>303</c>
3065   <c>See Other</c>
3066   <c>
3067      <xref target="status.303"/>
3068   </c>
3069   <c>305</c>
3070   <c>Use Proxy</c>
3071   <c>
3072      <xref target="status.305"/>
3073   </c>
3074   <c>306</c>
3075   <c>(Unused)</c>
3076   <c>
3077      <xref target="status.306"/>
3078   </c>
3079   <c>307</c>
3080   <c>Temporary Redirect</c>
3081   <c>
3082      <xref target="status.307"/>
3083   </c>
3084   <c>400</c>
3085   <c>Bad Request</c>
3086   <c>
3087      <xref target="status.400"/>
3088   </c>
3089   <c>402</c>
3090   <c>Payment Required</c>
3091   <c>
3092      <xref target="status.402"/>
3093   </c>
3094   <c>403</c>
3095   <c>Forbidden</c>
3096   <c>
3097      <xref target="status.403"/>
3098   </c>
3099   <c>404</c>
3100   <c>Not Found</c>
3101   <c>
3102      <xref target="status.404"/>
3103   </c>
3104   <c>405</c>
3105   <c>Method Not Allowed</c>
3106   <c>
3107      <xref target="status.405"/>
3108   </c>
3109   <c>406</c>
3110   <c>Not Acceptable</c>
3111   <c>
3112      <xref target="status.406"/>
3113   </c>
3114   <c>407</c>
3115   <c>Proxy Authentication Required</c>
3116   <c>
3117      <xref target="status.407"/>
3118   </c>
3119   <c>408</c>
3120   <c>Request Timeout</c>
3121   <c>
3122      <xref target="status.408"/>
3123   </c>
3124   <c>409</c>
3125   <c>Conflict</c>
3126   <c>
3127      <xref target="status.409"/>
3128   </c>
3129   <c>410</c>
3130   <c>Gone</c>
3131   <c>
3132      <xref target="status.410"/>
3133   </c>
3134   <c>411</c>
3135   <c>Length Required</c>
3136   <c>
3137      <xref target="status.411"/>
3138   </c>
3139   <c>413</c>
3140   <c>Request Representation Too Large</c>
3141   <c>
3142      <xref target="status.413"/>
3143   </c>
3144   <c>414</c>
3145   <c>URI Too Long</c>
3146   <c>
3147      <xref target="status.414"/>
3148   </c>
3149   <c>415</c>
3150   <c>Unsupported Media Type</c>
3151   <c>
3152      <xref target="status.415"/>
3153   </c>
3154   <c>417</c>
3155   <c>Expectation Failed</c>
3156   <c>
3157      <xref target="status.417"/>
3158   </c>
3159   <c>426</c>
3160   <c>Upgrade Required</c>
3161   <c>
3162      <xref target="status.426"/>
3163   </c>
3164   <c>500</c>
3165   <c>Internal Server Error</c>
3166   <c>
3167      <xref target="status.500"/>
3168   </c>
3169   <c>501</c>
3170   <c>Not Implemented</c>
3171   <c>
3172      <xref target="status.501"/>
3173   </c>
3174   <c>502</c>
3175   <c>Bad Gateway</c>
3176   <c>
3177      <xref target="status.502"/>
3178   </c>
3179   <c>503</c>
3180   <c>Service Unavailable</c>
3181   <c>
3182      <xref target="status.503"/>
3183   </c>
3184   <c>504</c>
3185   <c>Gateway Timeout</c>
3186   <c>
3187      <xref target="status.504"/>
3188   </c>
3189   <c>505</c>
3190   <c>HTTP Version Not Supported</c>
3191   <c>
3192      <xref target="status.505"/>
3193   </c>
3194</texttable>
3195<!--(END)-->
3196<?ENDINC p2-semantics.iana-status-codes ?>
3197</section>
3198<section title="Header Field Registration" anchor="header.field.registration">
3199<t>
3200   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3201   with the permanent registrations below (see <xref target="RFC3864"/>):
3202</t>
3203<?BEGININC p2-semantics.iana-headers ?>
3204<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3205<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3206   <ttcol>Header Field Name</ttcol>
3207   <ttcol>Protocol</ttcol>
3208   <ttcol>Status</ttcol>
3209   <ttcol>Reference</ttcol>
3210
3211   <c>Allow</c>
3212   <c>http</c>
3213   <c>standard</c>
3214   <c>
3215      <xref target="header.allow"/>
3216   </c>
3217   <c>Date</c>
3218   <c>http</c>
3219   <c>standard</c>
3220   <c>
3221      <xref target="header.date"/>
3222   </c>
3223   <c>Expect</c>
3224   <c>http</c>
3225   <c>standard</c>
3226   <c>
3227      <xref target="header.expect"/>
3228   </c>
3229   <c>From</c>
3230   <c>http</c>
3231   <c>standard</c>
3232   <c>
3233      <xref target="header.from"/>
3234   </c>
3235   <c>Location</c>
3236   <c>http</c>
3237   <c>standard</c>
3238   <c>
3239      <xref target="header.location"/>
3240   </c>
3241   <c>Max-Forwards</c>
3242   <c>http</c>
3243   <c>standard</c>
3244   <c>
3245      <xref target="header.max-forwards"/>
3246   </c>
3247   <c>Referer</c>
3248   <c>http</c>
3249   <c>standard</c>
3250   <c>
3251      <xref target="header.referer"/>
3252   </c>
3253   <c>Retry-After</c>
3254   <c>http</c>
3255   <c>standard</c>
3256   <c>
3257      <xref target="header.retry-after"/>
3258   </c>
3259   <c>Server</c>
3260   <c>http</c>
3261   <c>standard</c>
3262   <c>
3263      <xref target="header.server"/>
3264   </c>
3265   <c>User-Agent</c>
3266   <c>http</c>
3267   <c>standard</c>
3268   <c>
3269      <xref target="header.user-agent"/>
3270   </c>
3271</texttable>
3272<!--(END)-->
3273<?ENDINC p2-semantics.iana-headers ?>
3274<t>
3275   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3276</t>
3277</section>
3278</section>
3279
3280<section title="Security Considerations" anchor="security.considerations">
3281<t>
3282   This section is meant to inform application developers, information
3283   providers, and users of the security limitations in HTTP/1.1 as
3284   described by this document. The discussion does not include
3285   definitive solutions to the problems revealed, though it does make
3286   some suggestions for reducing security risks.
3287</t>
3288
3289<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3290<t>
3291   Like any generic data transfer protocol, HTTP cannot regulate the
3292   content of the data that is transferred, nor is there any a priori
3293   method of determining the sensitivity of any particular piece of
3294   information within the context of any given request. Therefore,
3295   applications &SHOULD; supply as much control over this information as
3296   possible to the provider of that information. Four header fields are
3297   worth special mention in this context: Server, Via, Referer and From.
3298</t>
3299<t>
3300   Revealing the specific software version of the server might allow the
3301   server machine to become more vulnerable to attacks against software
3302   that is known to contain security holes. Implementors &SHOULD; make the
3303   Server header field a configurable option.
3304</t>
3305<t>
3306   Proxies which serve as a portal through a network firewall &SHOULD;
3307   take special precautions regarding the transfer of header information
3308   that identifies the hosts behind the firewall. In particular, they
3309   &SHOULD; remove, or replace with sanitized versions, any Via fields
3310   generated behind the firewall.
3311</t>
3312<t>
3313   The Referer header field allows reading patterns to be studied and reverse
3314   links drawn. Although it can be very useful, its power can be abused
3315   if user details are not separated from the information contained in
3316   the Referer. Even when the personal information has been removed, the
3317   Referer header field might indicate a private document's URI whose
3318   publication would be inappropriate.
3319</t>
3320<t>
3321   The information sent in the From field might conflict with the user's
3322   privacy interests or their site's security policy, and hence it
3323   &SHOULD-NOT;  be transmitted without the user being able to disable,
3324   enable, and modify the contents of the field. The user &MUST; be able
3325   to set the contents of this field within a user preference or
3326   application defaults configuration.
3327</t>
3328<t>
3329   We suggest, though do not require, that a convenient toggle interface
3330   be provided for the user to enable or disable the sending of From and
3331   Referer information.
3332</t>
3333<t>
3334   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3335   target="header.server"/>) header fields can sometimes be used to determine
3336   that a specific client or server have a particular security hole which might
3337   be exploited. Unfortunately, this same information is often used for other
3338   valuable purposes for which HTTP currently has no better mechanism.
3339</t>
3340<t>
3341   Furthermore, the User-Agent header field may contain enough entropy to be
3342   used, possibly in conjunction with other material, to uniquely identify the
3343   user.
3344</t>
3345<t>
3346   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3347   that was sent in request header fields within the body of their response.
3348   Clients &SHOULD; be careful with sensitive information, like Cookies,
3349   Authorization credentials, and other header fields that might be used to
3350   collect data from the client.
3351</t> 
3352</section>
3353
3354<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3355<t>
3356   Because the source of a link might be private information or might
3357   reveal an otherwise private information source, it is strongly
3358   recommended that the user be able to select whether or not the
3359   Referer field is sent. For example, a browser client could have a
3360   toggle switch for browsing openly/anonymously, which would
3361   respectively enable/disable the sending of Referer and From
3362   information.
3363</t>
3364<t>
3365   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3366   HTTP request if the referring page was transferred with a secure
3367   protocol.
3368</t>
3369<t>
3370   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3371   sensitive data because that data will be placed in the request-target. Many
3372   existing servers, proxies, and user agents log or display the request-target
3373   in places where it might be visible to third parties. Such services can
3374   use POST-based form submission instead.
3375</t>
3376</section>
3377
3378<section title="Location Headers and Spoofing" anchor="location.spoofing">
3379<t>
3380   If a single server supports multiple organizations that do not trust
3381   one another, then it &MUST; check the values of Location and Content-Location
3382   header fields in responses that are generated under control of
3383   said organizations to make sure that they do not attempt to
3384   invalidate resources over which they have no authority.
3385</t>
3386</section>
3387
3388<section title="Security Considerations for CONNECT">
3389<t>
3390   Since tunneled data is opaque to the proxy, there are additional
3391   risks to tunneling to other well-known or reserved ports.
3392   A HTTP client CONNECTing to port 25 could relay spam
3393   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3394   access to a small number of known ports.
3395</t>
3396</section>
3397
3398</section>
3399
3400<section title="Acknowledgments" anchor="acks">
3401<t>
3402  See &acks;.
3403</t>
3404</section>
3405</middle>
3406<back>
3407
3408<references title="Normative References">
3409
3410<reference anchor="Part1">
3411  <front>
3412    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3413    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3414      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3415      <address><email>fielding@gbiv.com</email></address>
3416    </author>
3417    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3418      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3419      <address><email>jg@freedesktop.org</email></address>
3420    </author>
3421    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3422      <organization abbrev="HP">Hewlett-Packard Company</organization>
3423      <address><email>JeffMogul@acm.org</email></address>
3424    </author>
3425    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3426      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3427      <address><email>henrikn@microsoft.com</email></address>
3428    </author>
3429    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3430      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3431      <address><email>LMM@acm.org</email></address>
3432    </author>
3433    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3434      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3435      <address><email>paulle@microsoft.com</email></address>
3436    </author>
3437    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3438      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3439      <address><email>timbl@w3.org</email></address>
3440    </author>
3441    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3442      <organization abbrev="W3C">World Wide Web Consortium</organization>
3443      <address><email>ylafon@w3.org</email></address>
3444    </author>
3445    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3446      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3447      <address><email>julian.reschke@greenbytes.de</email></address>
3448    </author>
3449    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3450  </front>
3451  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3452  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3453</reference>
3454
3455<reference anchor="Part3">
3456  <front>
3457    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3458    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3459      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3460      <address><email>fielding@gbiv.com</email></address>
3461    </author>
3462    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3463      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3464      <address><email>jg@freedesktop.org</email></address>
3465    </author>
3466    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3467      <organization abbrev="HP">Hewlett-Packard Company</organization>
3468      <address><email>JeffMogul@acm.org</email></address>
3469    </author>
3470    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3471      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3472      <address><email>henrikn@microsoft.com</email></address>
3473    </author>
3474    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3475      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3476      <address><email>LMM@acm.org</email></address>
3477    </author>
3478    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3479      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3480      <address><email>paulle@microsoft.com</email></address>
3481    </author>
3482    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3483      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3484      <address><email>timbl@w3.org</email></address>
3485    </author>
3486    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3487      <organization abbrev="W3C">World Wide Web Consortium</organization>
3488      <address><email>ylafon@w3.org</email></address>
3489    </author>
3490    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3491      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3492      <address><email>julian.reschke@greenbytes.de</email></address>
3493    </author>
3494    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3495  </front>
3496  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3497  <x:source href="p3-payload.xml" basename="p3-payload"/>
3498</reference>
3499
3500<reference anchor="Part4">
3501  <front>
3502    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3503    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3504      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3505      <address><email>fielding@gbiv.com</email></address>
3506    </author>
3507    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3508      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3509      <address><email>jg@freedesktop.org</email></address>
3510    </author>
3511    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3512      <organization abbrev="HP">Hewlett-Packard Company</organization>
3513      <address><email>JeffMogul@acm.org</email></address>
3514    </author>
3515    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3516      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3517      <address><email>henrikn@microsoft.com</email></address>
3518    </author>
3519    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3520      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3521      <address><email>LMM@acm.org</email></address>
3522    </author>
3523    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3524      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3525      <address><email>paulle@microsoft.com</email></address>
3526    </author>
3527    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3528      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3529      <address><email>timbl@w3.org</email></address>
3530    </author>
3531    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3532      <organization abbrev="W3C">World Wide Web Consortium</organization>
3533      <address><email>ylafon@w3.org</email></address>
3534    </author>
3535    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3536      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3537      <address><email>julian.reschke@greenbytes.de</email></address>
3538    </author>
3539    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3540  </front>
3541  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3542  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3543</reference>
3544
3545<reference anchor="Part5">
3546  <front>
3547    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3548    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3549      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3550      <address><email>fielding@gbiv.com</email></address>
3551    </author>
3552    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3553      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3554      <address><email>jg@freedesktop.org</email></address>
3555    </author>
3556    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3557      <organization abbrev="HP">Hewlett-Packard Company</organization>
3558      <address><email>JeffMogul@acm.org</email></address>
3559    </author>
3560    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3561      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3562      <address><email>henrikn@microsoft.com</email></address>
3563    </author>
3564    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3565      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3566      <address><email>LMM@acm.org</email></address>
3567    </author>
3568    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3569      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3570      <address><email>paulle@microsoft.com</email></address>
3571    </author>
3572    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3573      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3574      <address><email>timbl@w3.org</email></address>
3575    </author>
3576    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3577      <organization abbrev="W3C">World Wide Web Consortium</organization>
3578      <address><email>ylafon@w3.org</email></address>
3579    </author>
3580    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3581      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3582      <address><email>julian.reschke@greenbytes.de</email></address>
3583    </author>
3584    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3585  </front>
3586  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3587  <x:source href="p5-range.xml" basename="p5-range"/>
3588</reference>
3589
3590<reference anchor="Part6">
3591  <front>
3592    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3593    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3594      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3595      <address><email>fielding@gbiv.com</email></address>
3596    </author>
3597    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3598      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3599      <address><email>jg@freedesktop.org</email></address>
3600    </author>
3601    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3602      <organization abbrev="HP">Hewlett-Packard Company</organization>
3603      <address><email>JeffMogul@acm.org</email></address>
3604    </author>
3605    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3606      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3607      <address><email>henrikn@microsoft.com</email></address>
3608    </author>
3609    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3610      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3611      <address><email>LMM@acm.org</email></address>
3612    </author>
3613    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3614      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3615      <address><email>paulle@microsoft.com</email></address>
3616    </author>
3617    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3618      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3619      <address><email>timbl@w3.org</email></address>
3620    </author>
3621    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3622      <organization abbrev="W3C">World Wide Web Consortium</organization>
3623      <address><email>ylafon@w3.org</email></address>
3624    </author>
3625    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3626      <organization>Rackspace</organization>
3627      <address><email>mnot@mnot.net</email></address>
3628    </author>
3629    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3630      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3631      <address><email>julian.reschke@greenbytes.de</email></address>
3632    </author>
3633    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3634  </front>
3635  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3636  <x:source href="p6-cache.xml" basename="p6-cache"/>
3637</reference>
3638
3639<reference anchor="Part7">
3640  <front>
3641    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3642    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3643      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3644      <address><email>fielding@gbiv.com</email></address>
3645    </author>
3646    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3647      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3648      <address><email>jg@freedesktop.org</email></address>
3649    </author>
3650    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3651      <organization abbrev="HP">Hewlett-Packard Company</organization>
3652      <address><email>JeffMogul@acm.org</email></address>
3653    </author>
3654    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3655      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3656      <address><email>henrikn@microsoft.com</email></address>
3657    </author>
3658    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3659      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3660      <address><email>LMM@acm.org</email></address>
3661    </author>
3662    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3663      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3664      <address><email>paulle@microsoft.com</email></address>
3665    </author>
3666    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3667      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3668      <address><email>timbl@w3.org</email></address>
3669    </author>
3670    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3671      <organization abbrev="W3C">World Wide Web Consortium</organization>
3672      <address><email>ylafon@w3.org</email></address>
3673    </author>
3674    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3675      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3676      <address><email>julian.reschke@greenbytes.de</email></address>
3677    </author>
3678    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3679  </front>
3680  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3681  <x:source href="p7-auth.xml" basename="p7-auth"/>
3682</reference>
3683
3684<reference anchor="RFC2119">
3685  <front>
3686    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3687    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3688      <organization>Harvard University</organization>
3689      <address><email>sob@harvard.edu</email></address>
3690    </author>
3691    <date month="March" year="1997"/>
3692  </front>
3693  <seriesInfo name="BCP" value="14"/>
3694  <seriesInfo name="RFC" value="2119"/>
3695</reference>
3696
3697<reference anchor="RFC3986">
3698 <front>
3699  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3700  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3701    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3702    <address>
3703       <email>timbl@w3.org</email>
3704       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3705    </address>
3706  </author>
3707  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3708    <organization abbrev="Day Software">Day Software</organization>
3709    <address>
3710      <email>fielding@gbiv.com</email>
3711      <uri>http://roy.gbiv.com/</uri>
3712    </address>
3713  </author>
3714  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3715    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3716    <address>
3717      <email>LMM@acm.org</email>
3718      <uri>http://larry.masinter.net/</uri>
3719    </address>
3720  </author>
3721  <date month='January' year='2005'></date>
3722 </front>
3723 <seriesInfo name="STD" value="66"/>
3724 <seriesInfo name="RFC" value="3986"/>
3725</reference>
3726
3727<reference anchor="RFC5234">
3728  <front>
3729    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3730    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3731      <organization>Brandenburg InternetWorking</organization>
3732      <address>
3733        <email>dcrocker@bbiw.net</email>
3734      </address> 
3735    </author>
3736    <author initials="P." surname="Overell" fullname="Paul Overell">
3737      <organization>THUS plc.</organization>
3738      <address>
3739        <email>paul.overell@thus.net</email>
3740      </address>
3741    </author>
3742    <date month="January" year="2008"/>
3743  </front>
3744  <seriesInfo name="STD" value="68"/>
3745  <seriesInfo name="RFC" value="5234"/>
3746</reference>
3747
3748</references>
3749
3750<references title="Informative References">
3751
3752<reference anchor="RFC1123">
3753  <front>
3754    <title>Requirements for Internet Hosts - Application and Support</title>
3755    <author initials="R." surname="Braden" fullname="Robert Braden">
3756      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3757      <address><email>Braden@ISI.EDU</email></address>
3758    </author>
3759    <date month="October" year="1989"/>
3760  </front>
3761  <seriesInfo name="STD" value="3"/>
3762  <seriesInfo name="RFC" value="1123"/>
3763</reference>
3764
3765<reference anchor="RFC1945">
3766  <front>
3767    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3768    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3769      <organization>MIT, Laboratory for Computer Science</organization>
3770      <address><email>timbl@w3.org</email></address>
3771    </author>
3772    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3773      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3774      <address><email>fielding@ics.uci.edu</email></address>
3775    </author>
3776    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3777      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3778      <address><email>frystyk@w3.org</email></address>
3779    </author>
3780    <date month="May" year="1996"/>
3781  </front>
3782  <seriesInfo name="RFC" value="1945"/>
3783</reference>
3784
3785<reference anchor="RFC2068">
3786  <front>
3787    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3788    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3789      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3790      <address><email>fielding@ics.uci.edu</email></address>
3791    </author>
3792    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3793      <organization>MIT Laboratory for Computer Science</organization>
3794      <address><email>jg@w3.org</email></address>
3795    </author>
3796    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3797      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3798      <address><email>mogul@wrl.dec.com</email></address>
3799    </author>
3800    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3801      <organization>MIT Laboratory for Computer Science</organization>
3802      <address><email>frystyk@w3.org</email></address>
3803    </author>
3804    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3805      <organization>MIT Laboratory for Computer Science</organization>
3806      <address><email>timbl@w3.org</email></address>
3807    </author>
3808    <date month="January" year="1997"/>
3809  </front>
3810  <seriesInfo name="RFC" value="2068"/>
3811</reference>
3812
3813<reference anchor="RFC2616">
3814  <front>
3815    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3816    <author initials="R." surname="Fielding" fullname="R. Fielding">
3817      <organization>University of California, Irvine</organization>
3818      <address><email>fielding@ics.uci.edu</email></address>
3819    </author>
3820    <author initials="J." surname="Gettys" fullname="J. Gettys">
3821      <organization>W3C</organization>
3822      <address><email>jg@w3.org</email></address>
3823    </author>
3824    <author initials="J." surname="Mogul" fullname="J. Mogul">
3825      <organization>Compaq Computer Corporation</organization>
3826      <address><email>mogul@wrl.dec.com</email></address>
3827    </author>
3828    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3829      <organization>MIT Laboratory for Computer Science</organization>
3830      <address><email>frystyk@w3.org</email></address>
3831    </author>
3832    <author initials="L." surname="Masinter" fullname="L. Masinter">
3833      <organization>Xerox Corporation</organization>
3834      <address><email>masinter@parc.xerox.com</email></address>
3835    </author>
3836    <author initials="P." surname="Leach" fullname="P. Leach">
3837      <organization>Microsoft Corporation</organization>
3838      <address><email>paulle@microsoft.com</email></address>
3839    </author>
3840    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3841      <organization>W3C</organization>
3842      <address><email>timbl@w3.org</email></address>
3843    </author>
3844    <date month="June" year="1999"/>
3845  </front>
3846  <seriesInfo name="RFC" value="2616"/>
3847</reference>
3848
3849<reference anchor='RFC2817'>
3850  <front>
3851    <title>Upgrading to TLS Within HTTP/1.1</title>
3852    <author initials='R.' surname='Khare' fullname='R. Khare'>
3853      <organization>4K Associates / UC Irvine</organization>
3854      <address><email>rohit@4K-associates.com</email></address>
3855    </author>
3856    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3857      <organization>Agranat Systems, Inc.</organization>
3858      <address><email>lawrence@agranat.com</email></address>
3859    </author>
3860    <date year='2000' month='May' />
3861  </front>
3862  <seriesInfo name='RFC' value='2817' />
3863</reference>
3864
3865<reference anchor='RFC3864'>
3866  <front>
3867    <title>Registration Procedures for Message Header Fields</title>
3868    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3869      <organization>Nine by Nine</organization>
3870      <address><email>GK-IETF@ninebynine.org</email></address>
3871    </author>
3872    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3873      <organization>BEA Systems</organization>
3874      <address><email>mnot@pobox.com</email></address>
3875    </author>
3876    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3877      <organization>HP Labs</organization>
3878      <address><email>JeffMogul@acm.org</email></address>
3879    </author>
3880    <date year='2004' month='September' />
3881  </front>
3882  <seriesInfo name='BCP' value='90' />
3883  <seriesInfo name='RFC' value='3864' />
3884</reference>
3885
3886<reference anchor='RFC5226'>
3887  <front>
3888    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3889    <author initials='T.' surname='Narten' fullname='T. Narten'>
3890      <organization>IBM</organization>
3891      <address><email>narten@us.ibm.com</email></address>
3892    </author>
3893    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3894      <organization>Google</organization>
3895      <address><email>Harald@Alvestrand.no</email></address>
3896    </author>
3897    <date year='2008' month='May' />
3898  </front>
3899  <seriesInfo name='BCP' value='26' />
3900  <seriesInfo name='RFC' value='5226' />
3901</reference>
3902
3903<reference anchor="RFC5322">
3904  <front>
3905    <title>Internet Message Format</title>
3906    <author initials="P." surname="Resnick" fullname="P. Resnick">
3907      <organization>Qualcomm Incorporated</organization>
3908    </author>
3909    <date year="2008" month="October"/>
3910  </front> 
3911  <seriesInfo name="RFC" value="5322"/>
3912</reference>
3913
3914<reference anchor='RFC5789'>
3915  <front>
3916    <title>PATCH Method for HTTP</title>
3917    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3918      <organization>Linden Lab</organization>
3919    </author>
3920    <author initials='J.' surname='Snell' fullname='J. Snell' />
3921    <date year='2010' month='March' />
3922  </front>
3923  <seriesInfo name='RFC' value='5789' />
3924</reference>
3925
3926<reference anchor="RFC5987">
3927        <front>
3928    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3929    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3930      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3931      <address>
3932        <postal>
3933          <street>Hafenweg 16</street>
3934          <city>Muenster</city><region>NW</region><code>48155</code>
3935          <country>Germany</country>
3936        </postal>
3937        <email>julian.reschke@greenbytes.de</email>     
3938        <uri>http://greenbytes.de/tech/webdav/</uri>   
3939      </address>
3940    </author>
3941    <date month="August" year="2010"/>
3942  </front>
3943  <seriesInfo name="RFC" value="5987"/>
3944</reference>
3945
3946</references>
3947
3948<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3949<t>
3950  This document takes over the Status Code Registry, previously defined
3951  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3952  (<xref target="status.code.registry"/>)
3953</t>
3954<t>
3955  Clarify definition of POST.
3956  (<xref target="POST"/>)
3957</t>
3958<t>
3959  Remove requirement to handle all Content-* header fields; ban use of
3960  Content-Range with PUT.
3961  (<xref target="PUT"/>)
3962</t>
3963<t>
3964  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3965  (<xref target="CONNECT"/>)
3966</t>
3967<t>
3968  Broadened the definition of 203 (Non-Authoritative Information) to include
3969  cases of payload transformations as well.
3970  (<xref target="status.203"/>)
3971</t>
3972<t>
3973  Failed to consider that there are many other request methods that are safe
3974  to automatically redirect, and further that the user agent is able to make
3975  that determination based on the request method semantics.
3976  Furthermore, allow user agents to rewrite the method from POST to GET
3977  for status codes 301 and 302.
3978  (Sections <xref format="counter" target="status.301"/>,
3979  <xref format="counter" target="status.302"/> and
3980  <xref format="counter" target="status.307"/>)
3981</t>
3982<t>
3983  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3984  It used to indicate that the target resource must be accessed through the
3985  proxy given by the Location field. The Location field gave the URI of the
3986  proxy. The recipient was expected to repeat this single request via the proxy.
3987  (<xref target="status.305"/>)
3988</t>
3989<t>
3990  Define status 426 (Upgrade Required) (this was incorporated from
3991  <xref target="RFC2817"/>).
3992  (<xref target="status.426"/>)
3993</t>
3994<t>
3995  Change ABNF productions for header fields to only define the field value.
3996  (<xref target="header.field.definitions"/>)
3997</t>
3998<t>
3999  Reclassify "Allow" as response header field, removing the option to
4000  specify it in a PUT request.
4001  Relax the server requirement on the contents of the Allow header field and
4002  remove requirement on clients to always trust the header field value.
4003  (<xref target="header.allow"/>)
4004</t>
4005<t>
4006  Correct syntax of Location header field to allow URI references (including
4007  relative references and fragments), as referred symbol "absoluteURI" wasn't
4008  what was expected, and add some clarifications as to when use of fragments
4009  would not be appropriate.
4010  (<xref target="header.location"/>)
4011</t>
4012<t>
4013  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
4014  extension methods could have used it as well).
4015  (<xref target="header.max-forwards"/>)
4016</t>
4017<t>
4018  Allow Referer field value of "about:blank" as alternative to not specifying it.
4019  (<xref target="header.referer"/>)
4020</t>
4021<t>
4022  In the description of the Server header field, the Via field
4023  was described as a SHOULD. The requirement was and is stated
4024  correctly in the description of the Via header field in &header-via;.
4025  (<xref target="header.server"/>)
4026</t>
4027</section>
4028
4029<?BEGININC p2-semantics.abnf-appendix ?>
4030<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4031<figure>
4032<artwork type="abnf" name="p2-semantics.parsed-abnf">
4033<x:ref>Allow</x:ref> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
4034
4035<x:ref>Date</x:ref> = HTTP-date
4036
4037<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
4038
4039<x:ref>From</x:ref> = mailbox
4040
4041<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4042
4043<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4044
4045<x:ref>Location</x:ref> = URI-reference
4046
4047<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4048<x:ref>Method</x:ref> = token
4049
4050<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
4051
4052<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 1.2.2&gt;
4053<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4054<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4055<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4056
4057<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4058<x:ref>Status-Code</x:ref> = 3DIGIT
4059
4060<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4061<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4062
4063<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4064<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4065
4066<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2&gt;
4067
4068<x:ref>date1</x:ref> = day SP month SP year
4069<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4070<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4071<x:ref>day</x:ref> = 2DIGIT
4072<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4073 / %x54.75.65 ; Tue
4074 / %x57.65.64 ; Wed
4075 / %x54.68.75 ; Thu
4076 / %x46.72.69 ; Fri
4077 / %x53.61.74 ; Sat
4078 / %x53.75.6E ; Sun
4079<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4080 / %x54.75.65.73.64.61.79 ; Tuesday
4081 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4082 / %x54.68.75.72.73.64.61.79 ; Thursday
4083 / %x46.72.69.64.61.79 ; Friday
4084 / %x53.61.74.75.72.64.61.79 ; Saturday
4085 / %x53.75.6E.64.61.79 ; Sunday
4086<x:ref>delta-seconds</x:ref> = 1*DIGIT
4087
4088<x:ref>expect-param</x:ref> = token [ "=" ( token / quoted-string ) ]
4089<x:ref>expectation</x:ref> = "100-continue" / expectation-extension
4090<x:ref>expectation-extension</x:ref> = token [ "=" ( token / quoted-string ) *( ";"
4091 expect-param ) ]
4092
4093<x:ref>hour</x:ref> = 2DIGIT
4094
4095<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4096<x:ref>minute</x:ref> = 2DIGIT
4097<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4098 / %x46.65.62 ; Feb
4099 / %x4D.61.72 ; Mar
4100 / %x41.70.72 ; Apr
4101 / %x4D.61.79 ; May
4102 / %x4A.75.6E ; Jun
4103 / %x4A.75.6C ; Jul
4104 / %x41.75.67 ; Aug
4105 / %x53.65.70 ; Sep
4106 / %x4F.63.74 ; Oct
4107 / %x4E.6F.76 ; Nov
4108 / %x44.65.63 ; Dec
4109
4110<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4111<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 1.2.2&gt;
4112
4113<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4114<x:ref>product</x:ref> = &lt;product, defined in [Part1], Section 5.2&gt;
4115
4116<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.3&gt;
4117
4118<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4119<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4120
4121<x:ref>second</x:ref> = 2DIGIT
4122
4123<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4124<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.3&gt;
4125
4126<x:ref>year</x:ref> = 4DIGIT
4127</artwork>
4128</figure>
4129<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4130; Allow defined but not used
4131; Date defined but not used
4132; Expect defined but not used
4133; From defined but not used
4134; Location defined but not used
4135; Max-Forwards defined but not used
4136; Reason-Phrase defined but not used
4137; Referer defined but not used
4138; Retry-After defined but not used
4139; Server defined but not used
4140; Status-Code defined but not used
4141; User-Agent defined but not used
4142</artwork></figure></section>
4143<?ENDINC p2-semantics.abnf-appendix ?>
4144
4145<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4146
4147<section title="Since RFC 2616">
4148<t>
4149  Extracted relevant partitions from <xref target="RFC2616"/>.
4150</t>
4151</section>
4152
4153<section title="Since draft-ietf-httpbis-p2-semantics-00">
4154<t>
4155  Closed issues:
4156  <list style="symbols"> 
4157    <t>
4158      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4159      "Via is a MUST"
4160      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4161    </t>
4162    <t>
4163      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4164      "Fragments allowed in Location"
4165      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4166    </t>
4167    <t>
4168      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4169      "Safe Methods vs Redirection"
4170      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4171    </t>
4172    <t>
4173      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4174      "Revise description of the POST method"
4175      (<eref target="http://purl.org/NET/http-errata#post"/>)
4176    </t>
4177    <t>
4178      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4179      "Normative and Informative references"
4180    </t>
4181    <t>
4182      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4183      "RFC2606 Compliance"
4184    </t>
4185    <t>
4186      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4187      "Informative references"
4188    </t>
4189    <t>
4190      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4191      "Redundant cross-references"
4192    </t>
4193  </list>
4194</t>
4195<t>
4196  Other changes:
4197  <list style="symbols"> 
4198    <t>
4199      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4200    </t>
4201  </list>
4202</t>
4203</section>
4204
4205<section title="Since draft-ietf-httpbis-p2-semantics-01">
4206<t>
4207  Closed issues:
4208  <list style="symbols"> 
4209    <t>
4210      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4211      "PUT side effects"
4212    </t>
4213    <t>
4214      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4215      "Duplicate Host header requirements"
4216    </t>
4217  </list>
4218</t>
4219<t>
4220  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4221  <list style="symbols"> 
4222    <t>
4223      Move "Product Tokens" section (back) into Part 1, as "token" is used
4224      in the definition of the Upgrade header field.
4225    </t>
4226    <t>
4227      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4228    </t>
4229    <t>
4230      Copy definition of delta-seconds from Part6 instead of referencing it.
4231    </t>
4232  </list>
4233</t>
4234</section>
4235
4236<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4237<t>
4238  Closed issues:
4239  <list style="symbols"> 
4240    <t>
4241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4242      "Requiring Allow in 405 responses"
4243    </t>
4244    <t>
4245      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4246      "Status Code Registry"
4247    </t>
4248    <t>
4249      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4250      "Redirection vs. Location"
4251    </t>
4252    <t>
4253      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4254      "Cacheability of 303 response"
4255    </t>
4256    <t>
4257      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4258      "305 Use Proxy"
4259    </t>
4260    <t>
4261      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4262      "Classification for Allow header"
4263    </t>
4264    <t>
4265      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4266      "PUT - 'store under' vs 'store at'"
4267    </t>
4268  </list>
4269</t>
4270<t>
4271  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4272  <list style="symbols"> 
4273    <t>
4274      Reference RFC 3984, and update header field registrations for headers defined
4275      in this document.
4276    </t>
4277  </list>
4278</t>
4279<t>
4280  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4281  <list style="symbols"> 
4282    <t>
4283      Replace string literals when the string really is case-sensitive (method).
4284    </t>
4285  </list>
4286</t>
4287</section>
4288
4289<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4290<t>
4291  Closed issues:
4292  <list style="symbols"> 
4293    <t>
4294      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4295      "OPTIONS request bodies"
4296    </t>
4297    <t>
4298      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4299      "Description of CONNECT should refer to RFC2817"
4300    </t>
4301    <t>
4302      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4303      "Location Content-Location reference request/response mixup"
4304    </t>
4305  </list>
4306</t>
4307<t>
4308  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4309  <list style="symbols"> 
4310    <t>
4311      Added initial proposal for registration process, plus initial
4312      content (non-HTTP/1.1 methods to be added by a separate specification).
4313    </t>
4314  </list>
4315</t>
4316</section>
4317
4318<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4319<t>
4320  Closed issues:
4321  <list style="symbols"> 
4322    <t>
4323      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4324      "Content-*"
4325    </t>
4326    <t>
4327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4328      "RFC 2822 is updated by RFC 5322"
4329    </t>
4330  </list>
4331</t>
4332<t>
4333  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4334  <list style="symbols"> 
4335    <t>
4336      Use "/" instead of "|" for alternatives.
4337    </t>
4338    <t>
4339      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4340      whitespace ("OWS") and required whitespace ("RWS").
4341    </t>
4342    <t>
4343      Rewrite ABNFs to spell out whitespace rules, factor out
4344      header field value format definitions.
4345    </t>
4346  </list>
4347</t>
4348</section>
4349
4350<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4351<t>
4352  Closed issues:
4353  <list style="symbols"> 
4354    <t>
4355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4356      "Reason-Phrase BNF"
4357    </t>
4358  </list>
4359</t>
4360<t>
4361  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4362  <list style="symbols"> 
4363    <t>
4364      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4365    </t>
4366  </list>
4367</t>
4368</section>
4369
4370<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4371<t>
4372  Closed issues:
4373  <list style="symbols"> 
4374    <t>
4375      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4376      "Clarify when Referer is sent"
4377    </t>
4378    <t>
4379      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4380      "status codes vs methods"
4381    </t>
4382    <t>
4383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4384      "Do not require "updates" relation for specs that register status codes or method names"
4385    </t>
4386  </list>
4387</t>
4388</section>
4389
4390<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4391<t>
4392  Closed issues:
4393  <list style="symbols"> 
4394    <t>
4395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4396      "Idempotency"
4397    </t>
4398    <t>
4399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4400      "TRACE security considerations"
4401    </t>
4402    <t>
4403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4404      "Clarify rules for determining what entities a response carries"
4405    </t>
4406    <t>
4407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4408      "update note citing RFC 1945 and 2068"
4409    </t>
4410    <t>
4411      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4412      "update note about redirect limit"
4413    </t>
4414    <t>
4415      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4416      "Location header ABNF should use 'URI'"
4417    </t>
4418    <t>
4419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4420      "fragments in Location vs status 303"
4421    </t>
4422    <t>
4423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4424      "move IANA registrations for optional status codes"
4425    </t>
4426  </list>
4427</t>
4428<t>
4429  Partly resolved issues:
4430  <list style="symbols"> 
4431    <t>
4432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4433      "Are OPTIONS and TRACE safe?"
4434    </t>
4435  </list>
4436</t>
4437</section>
4438
4439<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4440<t>
4441  Closed issues:
4442  <list style="symbols"> 
4443    <t>
4444      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4445      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4446      status codes when fixing this previously)
4447    </t>
4448  </list>
4449</t>
4450</section>
4451
4452<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4453<t>
4454  Closed issues:
4455  <list style="symbols"> 
4456    <t>
4457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4458      "Fragment combination / precedence during redirects"
4459    </t>
4460  </list>
4461</t>
4462<t>
4463  Partly resolved issues:
4464  <list style="symbols"> 
4465    <t>
4466      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4467      "Location header payload handling"
4468    </t>
4469    <t>
4470      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4471      "Term for the requested resource's URI"
4472    </t>
4473  </list>
4474</t>
4475</section>
4476
4477<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4478<t>
4479  Closed issues:
4480  <list style="symbols"> 
4481    <t>
4482      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4483      "Clarify 'Requested Variant'"
4484    </t>
4485    <t>
4486      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4487      "Clarify entity / representation / variant terminology"
4488    </t>
4489    <t>
4490      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4491      "Methods and Caching"
4492    </t>
4493    <t>
4494      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4495      "OPTIONS vs Max-Forwards"
4496    </t>
4497    <t>
4498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4499      "Status codes and caching"
4500    </t>
4501    <t>
4502      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4503      "consider removing the 'changes from 2068' sections"
4504    </t>
4505  </list>
4506</t>
4507</section>
4508
4509<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4510<t>
4511  Closed issues:
4512  <list style="symbols"> 
4513    <t>
4514      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4515      "Considerations for new status codes"
4516    </t>
4517    <t>
4518      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4519      "Considerations for new methods"
4520    </t>
4521    <t>
4522      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4523      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4524    </t>
4525  </list>
4526</t>
4527</section>
4528
4529<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4530<t>
4531  Closed issues:
4532  <list style="symbols"> 
4533    <t>
4534      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4535      "Fragment combination / precedence during redirects" (added warning
4536      about having a fragid on the redirect may cause inconvenience in
4537      some cases)
4538    </t>
4539    <t>
4540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4541      "Content-* vs. PUT"
4542    </t>
4543    <t>
4544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4545      "205 Bodies"
4546    </t>
4547    <t>
4548      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4549      "Understanding Content-* on non-PUT requests"
4550    </t>
4551    <t>
4552      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4553      "Content-*"
4554    </t>
4555    <t>
4556      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4557      "Header type defaulting"
4558    </t>
4559    <t>
4560      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4561      "PUT - 'store under' vs 'store at'"
4562    </t>
4563    <t>
4564      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4565      "duplicate ABNF for Reason-Phrase"
4566    </t>
4567    <t>
4568      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4569      "Note special status of Content-* prefix in header registration procedures"
4570    </t>
4571    <t>
4572      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4573      "Max-Forwards vs extension methods"
4574    </t>
4575    <t>
4576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4577      "What is the value space of HTTP status codes?" (actually fixed in
4578      draft-ietf-httpbis-p2-semantics-11)
4579    </t>
4580    <t>
4581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4582      "Header Classification"
4583    </t>
4584    <t>
4585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4586      "PUT side effect: invalidation or just stale?"
4587    </t>
4588    <t>
4589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4590      "proxies not supporting certain methods"
4591    </t>
4592    <t>
4593      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4594      "Migrate CONNECT from RFC2817 to p2"
4595    </t>
4596    <t>
4597      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4598      "Migrate Upgrade details from RFC2817"
4599    </t>
4600    <t>
4601      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4602      "clarify PUT semantics'"
4603    </t>
4604    <t>
4605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4606      "duplicate ABNF for 'Method'"
4607    </t>
4608    <t>
4609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4610      "untangle ABNFs for header fields"
4611    </t>
4612  </list>
4613</t>
4614</section>
4615
4616<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4617<t>
4618  Closed issues:
4619  <list style="symbols"> 
4620    <t>
4621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4622      "untangle ABNFs for header fields"
4623    </t>
4624    <t>
4625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4626      "message-body in CONNECT request"
4627    </t>
4628  </list>
4629</t>
4630</section>
4631
4632<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4633<t>
4634  Closed issues:
4635  <list style="symbols"> 
4636    <t>
4637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4638      "Clarify status code for rate limiting"
4639    </t>
4640    <t>
4641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4642      "clarify 403 forbidden"
4643    </t>
4644    <t>
4645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4646      "Clarify 203 Non-Authoritative Information"
4647    </t>
4648    <t>
4649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4650      "update default reason phrase for 413"
4651    </t>
4652  </list>
4653</t>
4654</section>
4655
4656<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4657<t>
4658  Closed issues:
4659  <list style="symbols"> 
4660    <t>
4661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4662      "Strength of requirements on Accept re: 406"
4663    </t>
4664    <t>
4665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4666      "400 response isn't generic"
4667    </t>
4668  </list>
4669</t>
4670</section>
4671
4672<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4673<t>
4674  Closed issues:
4675  <list style="symbols"> 
4676    <t>
4677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4678      "Redirects and non-GET methods"
4679    </t>
4680    <t>
4681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4682      "Document HTTP's error-handling philosophy"
4683    </t>
4684    <t>
4685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4686      "Considerations for new headers"
4687    </t>
4688    <t>
4689      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4690      "clarify 303 redirect on HEAD"
4691    </t>
4692  </list>
4693</t>
4694</section>
4695
4696<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4697<t>
4698  Closed issues:
4699  <list style="symbols"> 
4700    <t>
4701      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4702      "Clarify status code for rate limiting" (change backed out because
4703      a new status code is being defined for this purpose)
4704    </t>
4705    <t>
4706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4707      "should there be a permanent variant of 307"
4708    </t>
4709    <t>
4710      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4711      "header field considerations: quoted-string vs use of double quotes"
4712    </t>
4713  </list>
4714</t>
4715</section>
4716
4717</section>
4718
4719</back>
4720</rfc>
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