source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1489

Last change on this file since 1489 was 1489, checked in by julian.reschke@…, 8 years ago

sanitize Expect grammar (editorial)

  • Property svn:eol-style set to native
File size: 193.9 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "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   Many header fields use a format including (case-insensitively) named
547   parameters (for instance, Content-Type, defined in &header-content-type;).
548   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
549   parameter value enables recipients to use existing parser components. When
550   allowing both forms, the meaning of a parameter value ought to be
551   independent of the syntax used for it (for an example, see the notes on
552   parameter handling for media types in &media-types;).
553</t>
554<t>
555   Authors of specifications defining new header fields are advised to consider
556   documenting:
557  <list style="symbols">
558    <x:lt>
559      <t>Whether the field is a single value, or whether it can be a list
560      (delimited by commas; see &header-fields;).</t>
561      <t>If it does not use the list syntax, document how to treat messages
562      where the header field occurs multiple times (a sensible default would
563      be to ignore the header field, but this might not always be the right
564      choice).</t>
565      <t>Note that intermediaries and software libraries might combine
566      multiple header field instances into a single one, despite the header
567      field not allowing this. A robust format enables recipients to discover
568      these situations (good example: "Content-Type", as the comma can only
569      appear inside quoted strings; bad example: "Location", as a comma can
570      occur inside a URI).</t>
571    </x:lt>
572    <x:lt><t>Under what conditions the header field can be used; e.g., only in
573    responses or requests, in all messages, only on responses to a particular
574    request method.</t></x:lt>
575    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
576    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
577    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
578    field's value, insert or delete it.</t></x:lt>
579    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
580    <x:lt><t>Whether the header field is useful or allowable in trailers (see
581    &chunked-encoding;).</t></x:lt>
582    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
583  </list>
584</t>
585</section>
586
587<section title="Request Header Fields" anchor="request.header.fields">
588  <x:anchor-alias value="request-header"/>
589<t>
590   The request header fields allow the client to pass additional
591   information about the request, and about the client itself, to the
592   server. These fields act as request modifiers, with semantics
593   equivalent to the parameters on a programming language method
594   invocation.
595</t>
596<texttable align="left">
597  <ttcol>Header Field Name</ttcol>
598  <ttcol>Defined in...</ttcol>
599
600  <c>Accept</c> <c>&header-accept;</c>
601  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
602  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
603  <c>Accept-Language</c> <c>&header-accept-language;</c>
604  <c>Authorization</c> <c>&header-authorization;</c>
605  <c>Expect</c> <c><xref target="header.expect"/></c>
606  <c>From</c> <c><xref target="header.from"/></c>
607  <c>Host</c> <c>&header-host;</c>
608  <c>If-Match</c> <c>&header-if-match;</c>
609  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
610  <c>If-None-Match</c> <c>&header-if-none-match;</c>
611  <c>If-Range</c> <c>&header-if-range;</c>
612  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
613  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
614  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
615  <c>Range</c> <c>&header-range;</c>
616  <c>Referer</c> <c><xref target="header.referer"/></c>
617  <c>TE</c> <c>&header-te;</c>
618  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
619</texttable>
620</section>
621
622<section title="Response Header Fields" anchor="response.header.fields">
623  <x:anchor-alias value="response-header"/>
624<t>
625   The response header fields allow the server to pass additional
626   information about the response which cannot be placed in the Status-Line.
627   These header fields give information about the server and about
628   further access to the target resource (&effective-request-uri;).
629</t>
630<texttable align="left">
631  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
632
633  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
634  <c>Age</c> <c>&header-age;</c>
635  <c>Allow</c> <c><xref target="header.allow"/></c>
636  <c>Date</c> <c><xref target="header.date"/></c>
637  <c>ETag</c> <c>&header-etag;</c>
638  <c>Location</c> <c><xref target="header.location"/></c>
639  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
640  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
641  <c>Server</c> <c><xref target="header.server"/></c>
642  <c>Vary</c> <c>&header-vary;</c>
643  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
644</texttable>
645</section>
646
647</section>
648
649<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
650  <x:anchor-alias value="Reason-Phrase"/>
651  <x:anchor-alias value="Status-Code"/>
652  <x:anchor-alias value="extension-code"/>
653<t>
654   The Status-Code element is a 3-digit integer result code of the attempt to
655   understand and satisfy the request.
656</t>
657<t>
658   The Reason-Phrase is intended to give a short textual description of the
659   Status-Code and is intended for a human user. The client does not need
660   to examine or display the Reason-Phrase.
661</t>
662<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"/>
663  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
664  <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> )
665</artwork></figure>
666<t>
667   HTTP status codes are extensible. HTTP applications are not required
668   to understand the meaning of all registered status codes, though such
669   understanding is obviously desirable. However, applications &MUST;
670   understand the class of any status code, as indicated by the first
671   digit, and treat any unrecognized response as being equivalent to the
672   x00 status code of that class, with the exception that an
673   unrecognized response &MUST-NOT; be cached. For example, if an
674   unrecognized status code of 431 is received by the client, it can
675   safely assume that there was something wrong with its request and
676   treat the response as if it had received a 400 status code. In such
677   cases, user agents &SHOULD; present to the user the representation enclosed
678   with the response, since that representation is likely to include human-readable
679   information which will explain the unusual status.
680</t>
681
682<section title="Overview of Status Codes" anchor="overview.of.status.codes">
683<t> 
684   The status codes listed below are defined in <xref target="status.codes"/>
685   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
686   The reason phrases listed here are only recommendations &mdash; they can be
687   replaced by local equivalents without affecting the protocol.
688</t>
689<texttable align="left">
690  <ttcol>Status-Code</ttcol>
691  <ttcol>Reason-Phrase</ttcol>
692  <ttcol>Defined in...</ttcol>
693 
694  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
695  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
696
697  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
698  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
699  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
700  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
701  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
702  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
703  <c>206</c> <c>Partial Content</c> <c>&status-206;</c>
704
705  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
706  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
707  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
708  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
709  <c>304</c> <c>Not Modified</c> <c>&status-304;</c>
710  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
711  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
712
713  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
714  <c>401</c> <c>Unauthorized</c> <c>&status-401;</c>
715  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
716  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
717  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
718  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
719  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
720  <c>407</c> <c>Proxy Authentication Required</c> <c>&status-407;</c>
721  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
722  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
723  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
724  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
725  <c>412</c> <c>Precondition Failed</c> <c>&status-412;</c>
726  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
727  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
728  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
729  <c>416</c> <c>Requested range not satisfiable</c> <c>&status-416;</c>
730  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
731  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
732
733  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
734  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
735  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
736  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
737  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
738  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
739</texttable>
740<t>
741   Note that this list is not exhaustive &mdash; it does not include
742   extension status codes defined in other specifications.
743</t>
744</section>
745
746<section title="Status Code Registry" anchor="status.code.registry">
747<t>
748  The HTTP Status Code Registry defines the name space for the Status-Code
749  token in the Status-Line of an HTTP response.
750</t>
751<t>
752  Values to be added to this name space are subject to IETF review
753  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
754</t>
755<t>
756  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
757</t>
758
759<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
760<t>
761   When it is necessary to express new semantics for a HTTP response that
762   aren't specific to a single application or media type, and currently defined
763   status codes are inadequate, a new status code can be registered.
764</t>
765<t>
766   HTTP status codes are generic; that is, they are potentially applicable to
767   any resource, not just one particular media type, "type" of resource, or
768   application. As such, it is preferred that new HTTP status codes be
769   registered in a document that isn't specific to a single application, so
770   that this is clear.
771</t>
772<t>
773   Definitions of new HTTP status codes typically explain the request
774   conditions that produce a response containing the status code (e.g.,
775   combinations of request headers and/or method(s)), along with any
776   interactions with response headers (e.g., those that are required, those
777   that modify the semantics of the response).
778</t>
779<t>
780   New HTTP status codes are required to fall under one of the categories
781   defined in <xref target="status.codes"/>. To allow existing parsers to
782   properly handle them, new status codes cannot disallow a response body,
783   although they can mandate a zero-length response body. They can require the
784   presence of one or more particular HTTP response header(s).
785</t>
786<t>
787   Likewise, their definitions can specify that caches are allowed to use
788   heuristics to determine their freshness (see &caching;; by default, it is
789   not allowed), and can define how to determine the resource which they
790   carry a representation for (see <xref
791   target="identifying.response.associated.with.representation"/>; by default,
792   it is anonymous).
793</t>
794</section>
795
796</section>
797
798</section>
799
800<section title="Representation" anchor="representation">
801<t>
802   Request and Response messages &MAY; transfer a representation if not otherwise
803   restricted by the request method or response status code. A representation
804   consists of metadata (representation header fields) and data (representation
805   body).  When a complete or partial representation is enclosed in an HTTP message,
806   it is referred to as the payload of the message. HTTP representations
807   are defined in &payload;.
808</t>
809<t>
810   A representation body is only present in a message when a message-body is
811   present, as described in &message-body;. The representation body is obtained
812   from the message-body by decoding any Transfer-Encoding that might
813   have been applied to ensure safe and proper transfer of the message.
814</t>
815
816<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
817<t>
818   It is sometimes necessary to determine an identifier for the resource
819   associated with a representation.
820</t>
821<t>
822   An HTTP request representation, when present, is always associated with an
823   anonymous (i.e., unidentified) resource.
824</t>
825<t>
826   In the common case, an HTTP response is a representation of the target
827   resource (see &effective-request-uri;). However, this is not always the
828   case. To determine the URI of the resource a response is associated with,
829   the following rules are used (with the first applicable one being selected):
830</t>
831<t><list style="numbers">
832   <t>If the response status code is 200 or 203 and the request method was GET,
833   the response payload is a representation of the target resource.</t>
834   <t>If the response status code is 204, 206, or 304 and the request method was GET
835   or HEAD, the response payload is a partial representation of the target
836   resource.</t>
837   <t>If the response has a Content-Location header field, and that URI is the same
838   as the effective request URI, the response payload is a representation of the
839   target resource.</t>
840   <t>If the response has a Content-Location header field, and that URI is not the
841   same as the effective request URI, then the response asserts that its
842   payload is a representation of the resource identified by the
843   Content-Location URI. However, such an assertion cannot be trusted unless
844   it can be verified by other means (not defined by HTTP).</t>
845   <t>Otherwise, the response is a representation of an anonymous (i.e.,
846   unidentified) resource.</t>
847</list></t>
848<t>
849  <cref anchor="TODO-req-uri">
850   The comparison function is going to have to be defined somewhere,
851   because we already need to compare URIs for things like cache invalidation.</cref>
852</t>
853</section>
854
855</section>
856
857
858<section title="Method Definitions" anchor="method.definitions">
859<t>
860   The set of common request methods for HTTP/1.1 is defined below. Although
861   this set can be expanded, additional methods cannot be assumed to
862   share the same semantics for separately extended clients and servers.
863</t>
864
865<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
866
867<section title="Safe Methods" anchor="safe.methods">
868<iref item="Safe Methods" primary="true"/>
869<t>
870   Implementors need to be aware that the software represents the user in
871   their interactions over the Internet, and need to allow
872   the user to be aware of any actions they take which might have an
873   unexpected significance to themselves or others.
874</t>
875<t>
876   In particular, the convention has been established that the GET, HEAD,
877   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
878   of taking an action other than retrieval. These request methods ought
879   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
880   This allows user agents to represent other methods, such as POST, PUT
881   and DELETE, in a special way, so that the user is made aware of the
882   fact that a possibly unsafe action is being requested.
883</t>
884<t>
885   Naturally, it is not possible to ensure that the server does not
886   generate side-effects as a result of performing a GET request; in
887   fact, some dynamic resources consider that a feature. The important
888   distinction here is that the user did not request the side-effects,
889   so therefore cannot be held accountable for them.
890</t>
891</section>
892
893<section title="Idempotent Methods" anchor="idempotent.methods">
894<iref item="Idempotent Methods" primary="true"/>
895<t>
896   Request methods can also have the property of "idempotence" in that,
897   aside from error or expiration issues, the intended effect of multiple
898   identical requests is the same as for a single request.
899   PUT, DELETE, and all safe request methods are idempotent.
900   It is important to note that idempotence refers only to changes
901   requested by the client: a server is free to change its state due
902   to multiple requests for the purpose of tracking those requests,
903   versioning of results, etc.
904</t>
905</section>
906</section>
907
908<section title="OPTIONS" anchor="OPTIONS">
909  <rdf:Description>
910    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
911  </rdf:Description>
912  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
913  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
914<t>
915   The OPTIONS method requests information about the
916   communication options available on the request/response chain
917   identified by the effective request URI. This method allows a client to
918   determine the options and/or requirements associated with a resource,
919   or the capabilities of a server, without implying a resource action
920   or initiating a resource retrieval.
921</t>
922<t>
923   Responses to the OPTIONS method are not cacheable.
924</t>
925<t>
926   If the OPTIONS request includes a message-body (as indicated by the
927   presence of Content-Length or Transfer-Encoding), then the media type
928   &MUST; be indicated by a Content-Type field. Although this
929   specification does not define any use for such a body, future
930   extensions to HTTP might use the OPTIONS body to make more detailed
931   queries on the server.
932</t>
933<t>
934   If the request-target is an asterisk ("*"), the OPTIONS request is
935   intended to apply to the server in general rather than to a specific
936   resource. Since a server's communication options typically depend on
937   the resource, the "*" request is only useful as a "ping" or "no-op"
938   type of method; it does nothing beyond allowing the client to test
939   the capabilities of the server. For example, this can be used to test
940   a proxy for HTTP/1.1 compliance (or lack thereof).
941</t>
942<t>
943   If the request-target is not an asterisk, the OPTIONS request applies
944   only to the options that are available when communicating with that
945   resource.
946</t>
947<t>
948   A 200 response &SHOULD; include any header fields that indicate
949   optional features implemented by the server and applicable to that
950   resource (e.g., Allow), possibly including extensions not defined by
951   this specification. The response body, if any, &SHOULD; also include
952   information about the communication options. The format for such a
953   body is not defined by this specification, but might be defined by
954   future extensions to HTTP. Content negotiation &MAY; be used to select
955   the appropriate response format. If no response body is included, the
956   response &MUST; include a Content-Length field with a field-value of
957   "0".
958</t>
959<t>
960   The Max-Forwards header field &MAY; be used to target a
961   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
962   If no Max-Forwards field is present in the request, then the forwarded
963   request &MUST-NOT; include a Max-Forwards field.
964</t>
965</section>
966
967<section title="GET" anchor="GET">
968  <rdf:Description>
969    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
970  </rdf:Description>
971  <iref primary="true" item="GET method" x:for-anchor=""/>
972  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
973<t>
974   The GET method requests transfer of a current representation of
975   the target resource.
976</t>
977<t>   
978   If the target resource is a data-producing process, it is the
979   produced data which shall be returned as the representation in the response and not
980   the source text of the process, unless that text happens to be the output of
981   the process.
982</t>
983<t>
984   The semantics of the GET method change to a "conditional GET" if the
985   request message includes an If-Modified-Since, If-Unmodified-Since,
986   If-Match, If-None-Match, or If-Range header field. A conditional GET
987   requests that the representation be transferred only under the
988   circumstances described by the conditional header field(s). The
989   conditional GET request is intended to reduce unnecessary network
990   usage by allowing cached representations to be refreshed without requiring
991   multiple requests or transferring data already held by the client.
992</t>
993<t>
994   The semantics of the GET method change to a "partial GET" if the
995   request message includes a Range header field. A partial GET requests
996   that only part of the representation be transferred, as described in &header-range;.
997   The partial GET request is intended to reduce unnecessary
998   network usage by allowing partially-retrieved representations to be
999   completed without transferring data already held by the client.
1000</t>
1001<t>
1002   Bodies on GET requests have no defined semantics. Note that sending a body
1003   on a GET request might cause some existing implementations to reject the
1004   request.
1005</t>
1006<t>
1007   The response to a GET request is cacheable and &MAY; be used to satisfy
1008   subsequent GET and HEAD requests (see &caching;).
1009</t>
1010<t>
1011   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
1012</t>
1013</section>
1014
1015<section title="HEAD" anchor="HEAD">
1016  <rdf:Description>
1017    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1018  </rdf:Description>
1019  <iref primary="true" item="HEAD method" x:for-anchor=""/>
1020  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
1021<t>
1022   The HEAD method is identical to GET except that the server &MUST-NOT;
1023   return a message-body in the response. The metadata contained
1024   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
1025   to the information sent in response to a GET request. This method can
1026   be used for obtaining metadata about the representation implied by the
1027   request without transferring the representation body. This method is
1028   often used for testing hypertext links for validity, accessibility,
1029   and recent modification.
1030</t>
1031<t>
1032   The response to a HEAD request is cacheable and &MAY; be used to satisfy
1033   a subsequent HEAD request; see &caching;. It also &MAY; be used to update a previously cached
1034   representation from that resource; if the new field values
1035   indicate that the cached representation differs from the current representation (as
1036   would be indicated by a change in Content-Length, ETag
1037   or Last-Modified), then the cache &MUST; treat the cache entry as
1038   stale.
1039</t>
1040<t>
1041   Bodies on HEAD requests have no defined semantics. Note that sending a body
1042   on a HEAD request might cause some existing implementations to reject the
1043   request.
1044</t>
1045</section>
1046
1047<section title="POST" anchor="POST">
1048  <iref primary="true" item="POST method" x:for-anchor=""/>
1049  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
1050<t>
1051   The POST method requests that the origin server accept the
1052   representation enclosed in the request as data to be processed by the
1053   target resource. POST is designed to allow a uniform method to cover the
1054   following functions:
1055  <list style="symbols">
1056    <t>
1057      Annotation of existing resources;
1058    </t>
1059    <t>
1060        Posting a message to a bulletin board, newsgroup, mailing list,
1061        or similar group of articles;
1062    </t>
1063    <t>
1064        Providing a block of data, such as the result of submitting a
1065        form, to a data-handling process;
1066    </t>
1067    <t>
1068        Extending a database through an append operation.
1069    </t>
1070  </list>
1071</t>
1072<t>
1073   The actual function performed by the POST method is determined by the
1074   server and is usually dependent on the effective request URI.
1075</t>
1076<t>
1077   The action performed by the POST method might not result in a
1078   resource that can be identified by a URI. In this case, either 200
1079   (OK) or 204 (No Content) is the appropriate response status code,
1080   depending on whether or not the response includes a representation that
1081   describes the result.
1082</t>
1083<t>
1084   If a resource has been created on the origin server, the response
1085   &SHOULD; be 201 (Created) and contain a representation which describes the
1086   status of the request and refers to the new resource, and a Location
1087   header field (see <xref target="header.location"/>).
1088</t>
1089<t>
1090   Responses to POST requests are only cacheable when they
1091   include explicit freshness information (see &p6-explicit;). A
1092   cached POST response with a Content-Location header field
1093   (see &header-content-location;) whose value is the effective
1094   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1095</t>
1096<t>
1097   Note that POST caching is not widely implemented.
1098   However, the 303 (See Other) response can be used to direct the
1099   user agent to retrieve a cacheable resource.
1100</t>
1101</section>
1102
1103<section title="PUT" anchor="PUT">
1104  <iref primary="true" item="PUT method" x:for-anchor=""/>
1105  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
1106<t>
1107   The PUT method requests that the state of the target resource
1108   be created or replaced with the state defined by the representation
1109   enclosed in the request message payload.  A successful PUT of a given
1110   representation would suggest that a subsequent GET on that same target
1111   resource will result in an equivalent representation being returned in
1112   a 200 (OK) response.  However, there is no guarantee that such a state
1113   change will be observable, since the target resource might be acted
1114   upon by other user agents in parallel, or might be subject to dynamic
1115   processing by the origin server, before any subsequent GET is received.
1116   A successful response only implies that the user agent's intent was
1117   achieved at the time of its processing by the origin server.
1118</t>
1119<t>   
1120   If the target resource does not have a current representation and
1121   the PUT successfully creates one, then the origin server &MUST; inform
1122   the user agent by sending a 201 (Created) response.  If the target
1123   resource does have a current representation and that representation is
1124   successfully modified in accordance with the state of the enclosed
1125   representation, then either a 200 (OK) or 204 (No Content) response
1126   &SHOULD; be sent to indicate successful completion of the request.
1127</t>
1128<t>
1129   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1130   as part of the resource state).
1131</t>
1132<t>
1133   An origin server &SHOULD; verify that the PUT representation is
1134   consistent with any constraints which the server has for the target
1135   resource that cannot or will not be changed by the PUT.  This is
1136   particularly important when the origin server uses internal
1137   configuration information related to the URI in order to set the
1138   values for representation metadata on GET responses.  When a PUT
1139   representation is inconsistent with the target resource, the origin
1140   server &SHOULD; either make them consistent, by transforming the
1141   representation or changing the resource configuration, or respond
1142   with an appropriate error message containing sufficient information
1143   to explain why the representation is unsuitable.  The 409 (Conflict)
1144   or 415 (Unsupported Media Type) status codes are suggested, with the
1145   latter being specific to constraints on Content-Type values.
1146</t>
1147<t>
1148   For example, if the target resource is configured to always have a
1149   Content-Type of "text/html" and the representation being PUT has a
1150   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1151   (a) reconfigure the target resource to reflect the new media type;
1152   (b) transform the PUT representation to a format consistent with that
1153   of the resource before saving it as the new resource state; or,
1154   (c) reject the request with a 415 response indicating that the target
1155   resource is limited to "text/html", perhaps including a link to a
1156   different resource that would be a suitable target for the new
1157   representation.
1158</t>
1159<t>
1160   HTTP does not define exactly how a PUT method affects the state
1161   of an origin server beyond what can be expressed by the intent of
1162   the user agent request and the semantics of the origin server response.
1163   It does not define what a resource might be, in any sense of that
1164   word, beyond the interface provided via HTTP.  It does not define
1165   how resource state is "stored", nor how such storage might change
1166   as a result of a change in resource state, nor how the origin server
1167   translates resource state into representations.  Generally speaking,
1168   all implementation details behind the resource interface are
1169   intentionally hidden by the server.
1170</t>
1171<t>
1172   The fundamental difference between the POST and PUT methods is
1173   highlighted by the different intent for the target resource.
1174   The target resource in a POST request is intended to handle the
1175   enclosed representation as a data-accepting process, such as for
1176   a gateway to some other protocol or a document that accepts annotations.
1177   In contrast, the target resource in a PUT request is intended to
1178   take the enclosed representation as a new or replacement value.
1179   Hence, the intent of PUT is idempotent and visible to intermediaries,
1180   even though the exact effect is only known by the origin server.
1181</t>
1182<t>
1183   Proper interpretation of a PUT request presumes that the user agent
1184   knows what target resource is desired.  A service that is intended
1185   to select a proper URI on behalf of the client, after receiving
1186   a state-changing request, &SHOULD; be implemented using the POST
1187   method rather than PUT.  If the origin server will not make the
1188   requested PUT state change to the target resource and instead
1189   wishes to have it applied to a different resource, such as when the
1190   resource has been moved to a different URI, then the origin server
1191   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
1192   then make its own decision regarding whether or not to redirect the
1193   request.
1194</t>
1195<t>
1196   A PUT request applied to the target resource &MAY; have side-effects
1197   on other resources.  For example, an article might have a URI for
1198   identifying "the current version" (a resource) which is separate
1199   from the URIs identifying each particular version (different
1200   resources that at one point shared the same state as the current version
1201   resource).  A successful PUT request on "the current version" URI might
1202   therefore create a new version resource in addition to changing the
1203   state of the target resource, and might also cause links to be added
1204   between the related resources.
1205</t>
1206<t>
1207   An origin server &SHOULD; reject any PUT request that contains a
1208   Content-Range header field, since it might be misinterpreted as
1209   partial content (or might be partial content that is being mistakenly
1210   PUT as a full representation).  Partial content updates are
1211   possible by targeting a separately identified resource with state
1212   that overlaps a portion of the larger resource, or by using a
1213   different method that has been specifically defined for partial
1214   updates (for example, the PATCH method defined in
1215   <xref target="RFC5789"/>).
1216</t>
1217<t>
1218   Responses to the PUT method are not cacheable. If a PUT request passes
1219   through a cache that has one or more stored responses for the effective
1220   request URI, those stored responses will be invalidated (see
1221   &p6-invalid;).
1222</t>
1223</section>
1224
1225<section title="DELETE" anchor="DELETE">
1226  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1227  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
1228<t>
1229   The DELETE method requests that the origin server delete the target
1230   resource. This method &MAY; be overridden by
1231   human intervention (or other means) on the origin server. The client cannot
1232   be guaranteed that the operation has been carried out, even if the
1233   status code returned from the origin server indicates that the action
1234   has been completed successfully. However, the server &SHOULD-NOT; 
1235   indicate success unless, at the time the response is given, it
1236   intends to delete the resource or move it to an inaccessible
1237   location.
1238</t>
1239<t>
1240   A successful response &SHOULD; be 200 (OK) if the response includes an
1241   representation describing the status, 202 (Accepted) if the action has not
1242   yet been enacted, or 204 (No Content) if the action has been enacted
1243   but the response does not include a representation.
1244</t>
1245<t>
1246   Bodies on DELETE requests have no defined semantics. Note that sending a body
1247   on a DELETE request might cause some existing implementations to reject the
1248   request.
1249</t>
1250<t>
1251   Responses to the DELETE method are not cacheable. If a DELETE request
1252   passes through a cache that has one or more stored responses for the
1253   effective request URI, those stored responses will be invalidated (see
1254   &p6-invalid;).
1255</t>
1256</section>
1257
1258<section title="TRACE" anchor="TRACE">
1259  <rdf:Description>
1260    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1261  </rdf:Description>
1262  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1263  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
1264<t>
1265   The TRACE method requests a remote, application-layer loop-back
1266   of the request message. The final recipient of the request
1267   &SHOULD; reflect the message received back to the client as the
1268   message-body of a 200 (OK) response. The final recipient is either the
1269   origin server or the first proxy to receive a Max-Forwards
1270   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1271   A TRACE request &MUST-NOT; include a message-body.
1272</t>
1273<t>
1274   TRACE allows the client to see what is being received at the other
1275   end of the request chain and use that data for testing or diagnostic
1276   information. The value of the Via header field (&header-via;) is of
1277   particular interest, since it acts as a trace of the request chain.
1278   Use of the Max-Forwards header field allows the client to limit the
1279   length of the request chain, which is useful for testing a chain of
1280   proxies forwarding messages in an infinite loop.
1281</t>
1282<t>
1283   If the request is valid, the response &SHOULD; have a Content-Type of
1284   "message/http" (see &media-type-message-http;) and contain a message-body
1285   that encloses a copy of the entire request message.
1286   Responses to the TRACE method are not cacheable.
1287</t>
1288</section>
1289
1290<section title="CONNECT" anchor="CONNECT">
1291  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1292  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1293<t>
1294   The CONNECT method requests that the proxy establish a tunnel
1295   to the request-target and then restrict its behavior to blind
1296   forwarding of packets until the connection is closed.
1297</t>
1298<t>
1299   When using CONNECT, the request-target &MUST; use the authority form
1300   (&request-target;); i.e., the request-target consists of only the
1301   host name and port number of the tunnel destination, separated by a colon.
1302   For example,
1303</t>
1304<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1305CONNECT server.example.com:80 HTTP/1.1
1306Host: server.example.com:80
1307
1308</artwork></figure>
1309<t>
1310   Other HTTP mechanisms can be used normally with the CONNECT method &mdash;
1311   except end-to-end protocol Upgrade requests, since the
1312   tunnel must be established first.
1313</t>
1314<t>
1315   For example, proxy authentication might be used to establish the
1316   authority to create a tunnel:
1317</t>
1318<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1319CONNECT server.example.com:80 HTTP/1.1
1320Host: server.example.com:80
1321Proxy-Authorization: basic aGVsbG86d29ybGQ=
1322
1323</artwork></figure>
1324<t>
1325   Bodies on CONNECT requests have no defined semantics. Note that sending a body
1326   on a CONNECT request might cause some existing implementations to reject the
1327   request.
1328</t>
1329<t>
1330   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1331   sent immediately after the blank line. The usual caveats also apply:
1332   data may be discarded if the eventual response is negative, and the
1333   connection may be reset with no response if more than one TCP segment
1334   is outstanding.
1335</t>
1336
1337<section title="Establishing a Tunnel with CONNECT">
1338<t>
1339   Any successful (2xx) response to a CONNECT request indicates that the
1340   proxy has established a connection to the requested host and port,
1341   and has switched to tunneling the current connection to that server
1342   connection.
1343</t>
1344<t>
1345   It may be the case that the proxy itself can only reach the requested
1346   origin server through another proxy.  In this case, the first proxy
1347   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1348   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1349   unless it has either a direct or tunnel connection established to the
1350   authority.
1351</t>
1352<t>
1353   An origin server which receives a CONNECT request for itself &MAY;
1354   respond with a 2xx status code to indicate that a connection is
1355   established.
1356</t>
1357<t>
1358   If at any point either one of the peers gets disconnected, any
1359   outstanding data that came from that peer will be passed to the other
1360   one, and after that also the other connection will be terminated by
1361   the proxy. If there is outstanding data to that peer undelivered,
1362   that data will be discarded.
1363</t>
1364
1365</section>
1366</section>
1367</section>
1368
1369
1370<section title="Status Code Definitions" anchor="status.codes">
1371<t>
1372   The first digit of the Status-Code defines the class of response. The
1373   last two digits do not have any categorization role. There are 5
1374   values for the first digit:
1375  <list style="symbols">
1376    <t>
1377      1xx: Informational - Request received, continuing process
1378    </t>
1379    <t>
1380      2xx: Success - The action was successfully received,
1381        understood, and accepted
1382    </t>
1383    <t>
1384      3xx: Redirection - Further action must be taken in order to
1385        complete the request
1386    </t>
1387    <t>
1388      4xx: Client Error - The request contains bad syntax or cannot
1389        be fulfilled
1390    </t>
1391    <t>
1392      5xx: Server Error - The server failed to fulfill an apparently
1393        valid request
1394    </t>
1395  </list>
1396</t>
1397<t>
1398   Each Status-Code is described below, including any metadata required
1399   in the response.
1400</t>
1401
1402<section title="Informational 1xx" anchor="status.1xx">
1403<t>
1404   This class of status code indicates a provisional response,
1405   consisting only of the Status-Line and optional header fields, and is
1406   terminated by an empty line. There are no required header fields for this
1407   class of status code. Since HTTP/1.0 did not define any 1xx status
1408   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1409   except under experimental conditions.
1410</t>
1411<t>
1412   A client &MUST; be prepared to accept one or more 1xx status responses
1413   prior to a regular response, even if the client does not expect a 100
1414   (Continue) status message. Unexpected 1xx status responses &MAY; be
1415   ignored by a user agent.
1416</t>
1417<t>
1418   Proxies &MUST; forward 1xx responses, unless the connection between the
1419   proxy and its client has been closed, or unless the proxy itself
1420   requested the generation of the 1xx response. (For example, if a
1421   proxy adds a "Expect: 100-continue" field when it forwards a request,
1422   then it need not forward the corresponding 100 (Continue)
1423   response(s).)
1424</t>
1425
1426<section title="100 Continue" anchor="status.100">
1427  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1428  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1429<t>
1430   The client &SHOULD; continue with its request. This interim response is
1431   used to inform the client that the initial part of the request has
1432   been received and has not yet been rejected by the server. The client
1433   &SHOULD; continue by sending the remainder of the request or, if the
1434   request has already been completed, ignore this response. The server
1435   &MUST; send a final response after the request has been completed. See
1436   &use100; for detailed discussion of the use and handling of this
1437   status code.
1438</t>
1439</section>
1440
1441<section title="101 Switching Protocols" anchor="status.101">
1442  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1443  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1444<t>
1445   The server understands and is willing to comply with the client's
1446   request, via the Upgrade message header field (&header-upgrade;), for a
1447   change in the application protocol being used on this connection. The
1448   server will switch protocols to those defined by the response's
1449   Upgrade header field immediately after the empty line which
1450   terminates the 101 response.
1451</t>
1452<t>
1453   The protocol &SHOULD; be switched only when it is advantageous to do
1454   so. For example, switching to a newer version of HTTP is advantageous
1455   over older versions, and switching to a real-time, synchronous
1456   protocol might be advantageous when delivering resources that use
1457   such features.
1458</t>
1459</section>
1460</section>
1461
1462<section title="Successful 2xx" anchor="status.2xx">
1463<t>
1464   This class of status code indicates that the client's request was
1465   successfully received, understood, and accepted.
1466</t>
1467
1468<section title="200 OK" anchor="status.200">
1469  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1470  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1471<t>
1472   The request has succeeded. The payload returned with the response
1473   is dependent on the method used in the request, for example:
1474  <list style="hanging">
1475    <t hangText="GET">
1476      a representation of the target resource is sent in the response;
1477    </t>
1478    <t hangText="HEAD">
1479      the same representation as GET, except without the message-body;
1480    </t>
1481    <t hangText="POST">
1482      a representation describing or containing the result of the action;
1483    </t>
1484    <t hangText="TRACE">
1485      a representation containing the request message as received by the
1486      end server.
1487    </t>
1488  </list>
1489</t>
1490<t>
1491   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1492   freshness for 200 responses.
1493</t>
1494</section>
1495
1496<section title="201 Created" anchor="status.201">
1497  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1498  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1499<t>
1500   The request has been fulfilled and has resulted in a new resource being
1501   created. The newly created resource can be referenced by the URI(s)
1502   returned in the payload of the response, with the most specific URI
1503   for the resource given by a Location header field. The response
1504   &SHOULD; include a payload containing a list of resource
1505   characteristics and location(s) from which the user or user agent can
1506   choose the one most appropriate. The payload format is specified by
1507   the media type given in the Content-Type header field. The origin
1508   server &MUST; create the resource before returning the 201 status code.
1509   If the action cannot be carried out immediately, the server &SHOULD;
1510   respond with 202 (Accepted) response instead.
1511</t>
1512<t>
1513   A 201 response &MAY; contain an ETag response header field indicating
1514   the current value of the entity-tag for the representation of the resource
1515   just created (see &header-etag;).
1516</t>
1517</section>
1518
1519<section title="202 Accepted" anchor="status.202">
1520  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1521  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1522<t>
1523   The request has been accepted for processing, but the processing has
1524   not been completed.  The request might or might not eventually be
1525   acted upon, as it might be disallowed when processing actually takes
1526   place. There is no facility for re-sending a status code from an
1527   asynchronous operation such as this.
1528</t>
1529<t>
1530   The 202 response is intentionally non-committal. Its purpose is to
1531   allow a server to accept a request for some other process (perhaps a
1532   batch-oriented process that is only run once per day) without
1533   requiring that the user agent's connection to the server persist
1534   until the process is completed. The representation returned with this
1535   response &SHOULD; include an indication of the request's current status
1536   and either a pointer to a status monitor or some estimate of when the
1537   user can expect the request to be fulfilled.
1538</t>
1539</section>
1540
1541<section title="203 Non-Authoritative Information" anchor="status.203">
1542  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1543  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1544<t>
1545   The representation in the response has been transformed or otherwise
1546   modified by a transforming proxy (&intermediaries;).  Note that the
1547   behaviour of transforming intermediaries is controlled by the no-transform
1548   Cache-Control directive (&header-cache-control;).
1549</t>
1550<t>
1551   This status code is only appropriate when the response status code would
1552   have been 200 (OK) otherwise. When the status code before transformation
1553   would have been different, the 214 Transformation Applied warn-code
1554   (&header-warning;) is appropriate.
1555</t>
1556<t>
1557   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1558   freshness for 203 responses.
1559</t>
1560</section>
1561
1562<section title="204 No Content" anchor="status.204">
1563  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1564  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1565<t>
1566   The 204 (No Content) status code indicates that the server has
1567   successfully fulfilled the request and that there is no additional
1568   content to return in the response payload body.  Metadata in the
1569   response header fields refer to the target resource and its current
1570   representation after the requested action.
1571</t>
1572<t>
1573   For example, if a 204 status code is received in response to a PUT
1574   request and the response contains an ETag header field, then the PUT
1575   was successful and the ETag field-value contains the entity-tag for
1576   the new representation of that target resource.
1577</t>
1578<t>
1579   The 204 response allows a server to indicate that the action has been
1580   successfully applied to the target resource while implying that the
1581   user agent &SHOULD-NOT; traverse away from its current "document view"
1582   (if any).  The server assumes that the user agent will provide some
1583   indication of the success to its user, in accord with its own interface,
1584   and apply any new or updated metadata in the response to the active
1585   representation.
1586</t>
1587<t>
1588   For example, a 204 status code is commonly used with document editing
1589   interfaces corresponding to a "save" action, such that the document
1590   being saved remains available to the user for editing. It is also
1591   frequently used with interfaces that expect automated data transfers
1592   to be prevalent, such as within distributed version control systems.
1593</t>
1594<t>
1595   The 204 response &MUST-NOT; include a message-body, and thus is always
1596   terminated by the first empty line after the header fields.
1597</t>
1598</section>
1599
1600<section title="205 Reset Content" anchor="status.205">
1601  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1602  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1603<t>
1604   The server has fulfilled the request and the user agent &SHOULD; reset
1605   the document view which caused the request to be sent. This response
1606   is primarily intended to allow input for actions to take place via
1607   user input, followed by a clearing of the form in which the input is
1608   given so that the user can easily initiate another input action.
1609</t>
1610<t>   
1611   The message-body included with the response &MUST; be empty. Note that
1612   receivers still need to parse the response according to the algorithm defined
1613   in &message-body;.
1614</t>
1615</section>
1616
1617<section title="206 Partial Content" anchor="status.206">
1618  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1619  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1620  <rdf:Description>
1621    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
1622  </rdf:Description>
1623<t>
1624   The server has fulfilled the partial GET request for the resource
1625   and the enclosed payload is a partial representation as defined in &status-206;.
1626</t>
1627<t>
1628   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1629   freshness for 206 responses.
1630</t>
1631</section>
1632</section>
1633
1634<section title="Redirection 3xx" anchor="status.3xx">
1635<t>
1636   This class of status code indicates that further action needs to be
1637   taken by the user agent in order to fulfill the request.  If the required
1638   action involves a subsequent HTTP request, it &MAY; be carried out by the
1639   user agent without interaction with the user if and only if the method used
1640   in the second request is known to be "safe", as defined in
1641   <xref target="safe.methods"/>.
1642</t>
1643<t>
1644   There are several types of redirects:
1645   <list style="numbers">
1646      <x:lt>
1647        <t>
1648          Redirects of the request to another URI, either temporarily or
1649          permanently. The new URI is specified in the Location header field.
1650          In this specification, the status codes 301 (Moved Permanently),
1651          302 (Found), and 307 (Temporary Redirect) fall under this category.
1652        </t>
1653      </x:lt>
1654      <x:lt>
1655        <t>
1656          Redirection to a new location that represents an indirect response to
1657          the request, such as the result of a POST operation to be retrieved
1658          with a subsequent GET request. This is status code 303 (See Other).
1659        </t>
1660      </x:lt>
1661      <x:lt>
1662        <t>
1663          Redirection offering a choice of matching resources for use by
1664          agent-driven content negotiation (&agent-driven-negotiation;). This
1665          is status code 300 (Multiple Choices).
1666        </t>
1667      </x:lt>
1668      <x:lt>
1669        <t>
1670          Other kinds of redirection, such as to a cached result (status code 304
1671          (Not Modified)).
1672        </t>
1673      </x:lt>
1674   </list>
1675</t>
1676<x:note>
1677  <t>
1678    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1679    and 302 (Found) were defined for the first type of redirect, and the second
1680    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1681    However it turned out that web forms using POST expected redirects to change
1682    the operation for the subsequent request to retrieval (GET). To address this
1683    use case, HTTP/1.1 introduced the second type of redirect with the status
1684    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1685    As user agents did not change their behavior to maintain backwards
1686    compatibility, the first revision of HTTP/1.1 added yet another status code,
1687    307 (Temporary Redirect), for which the backwards compatibility problems did
1688    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1689    Over 10 years later, most user agents still do method rewriting for
1690    status codes 301 and 302, therefore this specification makes that behavior
1691    compliant in case the original request was POST.
1692  </t>
1693</x:note>
1694<t>
1695   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1696   "infinite" redirection loops).
1697</t>
1698<x:note>
1699  <t>
1700    <x:h>Note:</x:h> An earlier version of this specification recommended a
1701    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1702    Content developers need to be aware that some clients might
1703    implement such a fixed limitation.
1704  </t>
1705</x:note>
1706
1707<section title="300 Multiple Choices" anchor="status.300">
1708  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1709  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1710<t>
1711   The target resource has more than one
1712   representation, each with its own specific location, and agent-driven
1713   negotiation information (&content-negotiation;) is being provided so that
1714   the user (or user agent) can select a preferred representation by
1715   redirecting its request to that location.
1716</t>
1717<t>
1718   Unless it was a HEAD request, the response &SHOULD; include a representation
1719   containing a list of representation metadata and location(s) from
1720   which the user or user agent can choose the one most appropriate. The
1721   data format is specified by the media type given in the Content-Type
1722   header field. Depending upon the format and the capabilities of
1723   the user agent, selection of the most appropriate choice &MAY; be
1724   performed automatically. However, this specification does not define
1725   any standard for such automatic selection.
1726</t>
1727<t>
1728   If the server has a preferred choice of representation, it &SHOULD;
1729   include the specific URI for that representation in the Location
1730   field; user agents &MAY; use the Location field value for automatic
1731   redirection.
1732</t>
1733<t>
1734   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1735   freshness for 300 responses.
1736</t>
1737
1738</section>
1739
1740<section title="301 Moved Permanently" anchor="status.301">
1741  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1742  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1743<t>
1744   The target resource has been assigned a new permanent URI and any
1745   future references to this resource &SHOULD; use one of the returned
1746   URIs.  Clients with link editing capabilities ought to automatically
1747   re-link references to the effective request URI to one or more of the new
1748   references returned by the server, where possible.
1749</t>
1750<t>
1751   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1752   freshness for 301 responses.
1753</t>
1754<t>
1755   The new permanent URI &SHOULD; be given by the Location field in the
1756   response. Unless the request method was HEAD, the representation of the
1757   response &SHOULD; contain a short hypertext note with a hyperlink to
1758   the new URI(s).
1759</t>
1760<t>
1761   If the 301 status code is received in response to a request method
1762   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1763   then the request &MAY; be automatically redirected by the user agent without
1764   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1765   request unless it can be confirmed by the user, since this might
1766   change the conditions under which the request was issued.
1767</t>
1768<x:note>
1769  <t>
1770    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1771    request method from POST to GET for the subsequent request. If this
1772    behavior is undesired, status code 307 (Temporary Redirect) can be used
1773    instead.
1774  </t>
1775</x:note>
1776</section>
1777
1778<section title="302 Found" anchor="status.302">
1779  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1780  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1781<t>
1782   The target resource resides temporarily under a different URI.
1783   Since the redirection might be altered on occasion, the client &SHOULD;
1784   continue to use the effective request URI for future requests.
1785</t>
1786<t>
1787   The temporary URI &SHOULD; be given by the Location field in the
1788   response. Unless the request method was HEAD, the representation of the
1789   response &SHOULD; contain a short hypertext note with a hyperlink to
1790   the new URI(s).
1791</t>
1792<t>
1793   If the 302 status code is received in response to a request method
1794   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1795   then the request &MAY; be automatically redirected by the user agent without
1796   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1797   request unless it can be confirmed by the user, since this might
1798   change the conditions under which the request was issued.
1799</t>
1800<x:note>
1801  <t>
1802    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1803    request method from POST to GET for the subsequent request. If this
1804    behavior is undesired, status code 307 (Temporary Redirect) can be used
1805    instead.
1806    <cref anchor="issue312">but see <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/312"/></cref>
1807  </t>
1808</x:note>
1809</section>
1810
1811<section title="303 See Other" anchor="status.303">
1812  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1813  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1814<t>
1815   The 303 status code indicates that the server is redirecting the
1816   user agent to a different resource, as indicated by a URI in the
1817   Location header field, that is intended to provide an indirect
1818   response to the original request.  In order to satisfy the original
1819   request, a user agent &SHOULD; perform a retrieval request using the
1820   Location URI (a GET or HEAD request if using HTTP), which
1821   may itself be redirected further, and present the eventual result as an
1822   answer to the original request.
1823   Note that the new URI in the Location header field is not considered
1824   equivalent to the effective request URI.
1825</t>
1826<t>
1827   This status code is generally applicable to any HTTP method.  It is
1828   primarily used to allow the output of a POST action to redirect
1829   the user agent to a selected resource, since doing so provides the
1830   information corresponding to the POST response in a form that
1831   can be separately identified, bookmarked, and cached independent
1832   of the original request.
1833</t>
1834<t>
1835   A 303 response to a GET request indicates that the requested
1836   resource does not have a representation of its own that can be
1837   transferred by the server over HTTP.  The Location URI indicates a
1838   resource that is descriptive of the target resource, such that the
1839   follow-on representation might be useful to recipients without
1840   implying that it adequately represents the target resource.
1841   Note that answers to the questions of what can be represented, what
1842   representations are adequate, and what might be a useful description
1843   are outside the scope of HTTP and thus entirely determined by the
1844   URI owner(s).
1845</t>
1846<t>
1847   Except for responses to a HEAD request, the representation of a 303
1848   response &SHOULD; contain a short hypertext note with a hyperlink
1849   to the Location URI.
1850</t>
1851</section>
1852
1853<section title="304 Not Modified" anchor="status.304">
1854  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1855  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1856  <rdf:Description>
1857    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
1858  </rdf:Description>
1859<t>
1860   The response to the request has not been modified since the conditions
1861   indicated by the client's conditional GET request, as defined in &status-304;.
1862</t>
1863</section>
1864
1865<section title="305 Use Proxy" anchor="status.305">
1866  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1867  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1868<t>
1869   The 305 status code was defined in a previous version of this specification
1870   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1871</t>
1872</section>
1873
1874<section title="306 (Unused)" anchor="status.306">
1875  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1876  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1877<t>
1878   The 306 status code was used in a previous version of the
1879   specification, is no longer used, and the code is reserved.
1880</t>
1881</section>
1882
1883<section title="307 Temporary Redirect" anchor="status.307">
1884  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1885  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1886<t>
1887   The target resource resides temporarily under a different URI.
1888   Since the redirection can change over time, the client &SHOULD;
1889   continue to use the effective request URI for future requests.
1890</t>
1891<t>
1892   The temporary URI &SHOULD; be given by the Location field in the
1893   response. Unless the request method was HEAD, the representation of the
1894   response &SHOULD; contain a short hypertext note with a hyperlink to
1895   the new URI(s), since many pre-HTTP/1.1 user agents do not
1896   understand the 307 status code. Therefore, the note &SHOULD; contain the
1897   information necessary for a user to repeat the original request on
1898   the new URI.
1899</t>
1900<t>
1901   If the 307 status code is received in response to a request method
1902   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1903   then the request &MAY; be automatically redirected by the user agent without
1904   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1905   request unless it can be confirmed by the user, since this might
1906   change the conditions under which the request was issued.
1907</t>
1908<x:note>
1909  <t>
1910    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1911    it does not allow rewriting the request method from POST to GET. This
1912    specification defines no equivalent counterpart for 301 Moved Permanently.
1913  </t>
1914</x:note>
1915</section>
1916</section>
1917
1918<section title="Client Error 4xx" anchor="status.4xx">
1919<t>
1920   The 4xx class of status code is intended for cases in which the
1921   client seems to have erred. Except when responding to a HEAD request,
1922   the server &SHOULD; include a representation containing an explanation of the
1923   error situation, and whether it is a temporary or permanent
1924   condition. These status codes are applicable to any request method.
1925   User agents &SHOULD; display any included representation to the user.
1926</t>
1927<t>
1928   If the client is sending data, a server implementation using TCP
1929   &SHOULD; be careful to ensure that the client acknowledges receipt of
1930   the packet(s) containing the response, before the server closes the
1931   input connection. If the client continues sending data to the server
1932   after the close, the server's TCP stack will send a reset packet to
1933   the client, which might erase the client's unacknowledged input buffers
1934   before they can be read and interpreted by the HTTP application.
1935</t>
1936
1937<section title="400 Bad Request" anchor="status.400">
1938  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1939  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1940<t>
1941   The server cannot or will not process the request, due to a client error (e.g.,
1942   malformed syntax).</t>
1943</section>
1944
1945<section title="401 Unauthorized" anchor="status.401">
1946  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1947  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1948  <rdf:Description>
1949    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part7</redirects-to>
1950  </rdf:Description>
1951<t>
1952   The request requires user authentication (see &status-401;).
1953</t>
1954</section>
1955
1956<section title="402 Payment Required" anchor="status.402">
1957  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1958  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1959<t>
1960   This code is reserved for future use.
1961</t>
1962</section>
1963
1964<section title="403 Forbidden" anchor="status.403">
1965  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1966  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1967<t>
1968   The server understood the request, but refuses to authorize it. Providing
1969   different user authentication credentials might be successful, but any
1970   credentials that were provided in the request are insufficient. The request
1971   &SHOULD-NOT; be repeated with the same credentials.
1972</t>
1973<t>
1974   If the request method was not HEAD and the server wishes to make
1975   public why the request has not been fulfilled, it &SHOULD; describe the
1976   reason for the refusal in the representation.  If the server does not wish to
1977   make this information available to the client, the status code 404
1978   (Not Found) &MAY; be used instead.
1979</t>
1980</section>
1981
1982<section title="404 Not Found" anchor="status.404">
1983  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1984  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1985<t>
1986   The server has not found anything matching the effective request URI. No
1987   indication is given of whether the condition is temporary or
1988   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1989   knows, through some internally configurable mechanism, that an old
1990   resource is permanently unavailable and has no forwarding address.
1991   This status code is commonly used when the server does not wish to
1992   reveal exactly why the request has been refused, or when no other
1993   response is applicable.
1994</t>
1995</section>
1996
1997<section title="405 Method Not Allowed" anchor="status.405">
1998  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1999  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
2000<t>
2001   The method specified in the Request-Line is not allowed for the target
2002   resource. The response &MUST; include an Allow header field containing a
2003   list of valid methods for the requested resource.
2004</t>
2005</section>
2006
2007<section title="406 Not Acceptable" anchor="status.406">
2008  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
2009  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
2010<t>
2011   The resource identified by the request is only capable of generating
2012   response representations which have content characteristics not acceptable
2013   according to the Accept and Accept-* header fields sent in the request
2014   (see &p3-header-fields;).
2015</t>
2016<t>
2017   Unless it was a HEAD request, the response &SHOULD; include a representation
2018   containing a list of available representation characteristics and location(s)
2019   from which the user or user agent can choose the one most
2020   appropriate. The data format is specified by the media type given
2021   in the Content-Type header field. Depending upon the format and the
2022   capabilities of the user agent, selection of the most appropriate
2023   choice &MAY; be performed automatically. However, this specification
2024   does not define any standard for such automatic selection.
2025</t>
2026<x:note>
2027  <t>
2028    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
2029    not acceptable according to the accept header fields sent in the
2030    request. In some cases, this might even be preferable to sending a
2031    406 response. User agents are encouraged to inspect the header fields of
2032    an incoming response to determine if it is acceptable.
2033  </t>
2034</x:note>
2035<t>
2036   If the response could be unacceptable, a user agent &SHOULD;
2037   temporarily stop receipt of more data and query the user for a
2038   decision on further actions.
2039</t>
2040</section>
2041
2042<section title="407 Proxy Authentication Required" anchor="status.407">
2043  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
2044  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
2045<t>
2046   This code is similar to 401 (Unauthorized), but indicates that the
2047   client must first authenticate itself with the proxy (see &status-407;).
2048</t>
2049</section>
2050
2051<section title="408 Request Timeout" anchor="status.408">
2052  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
2053  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
2054<t>
2055   The client did not produce a request within the time that the server
2056   was prepared to wait. The client &MAY; repeat the request without
2057   modifications at any later time.
2058</t>
2059</section>
2060
2061<section title="409 Conflict" anchor="status.409">
2062  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
2063  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
2064<t>
2065   The request could not be completed due to a conflict with the current
2066   state of the resource. This code is only allowed in situations where
2067   it is expected that the user might be able to resolve the conflict
2068   and resubmit the request. The response body &SHOULD; include enough
2069   information for the user to recognize the source of the conflict.
2070   Ideally, the response representation would include enough information for the
2071   user or user agent to fix the problem; however, that might not be
2072   possible and is not required.
2073</t>
2074<t>
2075   Conflicts are most likely to occur in response to a PUT request. For
2076   example, if versioning were being used and the representation being PUT
2077   included changes to a resource which conflict with those made by an
2078   earlier (third-party) request, the server might use the 409 response
2079   to indicate that it can't complete the request. In this case, the
2080   response representation would likely contain a list of the differences
2081   between the two versions in a format defined by the response
2082   Content-Type.
2083</t>
2084</section>
2085
2086<section title="410 Gone" anchor="status.410">
2087  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
2088  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
2089<t>
2090   The target resource is no longer available at the server and no
2091   forwarding address is known. This condition is expected to be
2092   considered permanent. Clients with link editing capabilities &SHOULD;
2093   delete references to the effective request URI after user approval. If the
2094   server does not know, or has no facility to determine, whether or not
2095   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
2096   used instead.
2097</t>
2098<t>
2099   The 410 response is primarily intended to assist the task of web
2100   maintenance by notifying the recipient that the resource is
2101   intentionally unavailable and that the server owners desire that
2102   remote links to that resource be removed. Such an event is common for
2103   limited-time, promotional services and for resources belonging to
2104   individuals no longer working at the server's site. It is not
2105   necessary to mark all permanently unavailable resources as "gone" or
2106   to keep the mark for any length of time &mdash; that is left to the
2107   discretion of the server owner.
2108</t>
2109<t>
2110   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
2111   for 410 responses.
2112</t>
2113
2114</section>
2115
2116<section title="411 Length Required" anchor="status.411">
2117  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
2118  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
2119<t>
2120   The server refuses to accept the request without a defined Content-Length.
2121   The client &MAY; repeat the request if it adds a valid
2122   Content-Length header field containing the length of the message-body
2123   in the request message.
2124</t>
2125</section>
2126
2127<section title="412 Precondition Failed" anchor="status.412">
2128  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
2129  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
2130  <rdf:Description>
2131    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
2132  </rdf:Description>
2133<t>
2134   The precondition given in one or more of the header fields
2135   evaluated to false when it was tested on the server, as defined in
2136   &status-412;.
2137</t>
2138</section>
2139
2140<section title="413 Request Representation Too Large" anchor="status.413">
2141  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2142  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2143<t>
2144   The server is refusing to process a request because the request
2145   representation is larger than the server is willing or able to process. The
2146   server &MAY; close the connection to prevent the client from continuing
2147   the request.
2148</t>
2149<t>
2150   If the condition is temporary, the server &SHOULD; include a Retry-After
2151   header field to indicate that it is temporary and after what
2152   time the client &MAY; try again.
2153</t>
2154</section>
2155
2156<section title="414 URI Too Long" anchor="status.414">
2157  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2158  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
2159<t>
2160   The server is refusing to service the request because the effective request URI
2161   is longer than the server is willing to interpret. This rare
2162   condition is only likely to occur when a client has improperly
2163   converted a POST request to a GET request with long query
2164   information, when the client has descended into a URI "black hole" of
2165   redirection (e.g., a redirected URI prefix that points to a suffix of
2166   itself), or when the server is under attack by a client attempting to
2167   exploit security holes present in some servers using fixed-length
2168   buffers for reading or manipulating the effective request URI.
2169</t>
2170</section>
2171
2172<section title="415 Unsupported Media Type" anchor="status.415">
2173  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2174  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2175<t>
2176   The server is refusing to service the request because the request
2177   payload is in a format not supported by this request method on the
2178   target resource.
2179</t>
2180</section>
2181
2182<section title="416 Requested Range Not Satisfiable" anchor="status.416">
2183  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
2184  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
2185  <rdf:Description>
2186    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
2187  </rdf:Description>
2188<t>
2189   The request included a Range header field (&header-range;) and none of
2190   the range-specifier values in this field overlap the current extent
2191   of the selected resource. See &status-416;.
2192</t>
2193</section>
2194
2195<section title="417 Expectation Failed" anchor="status.417">
2196  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2197  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2198<t>
2199   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2200   could not be met by this server, or, if the server is a proxy,
2201   the server has unambiguous evidence that the request could not be met
2202   by the next-hop server.
2203</t>
2204</section>
2205
2206<section title="426 Upgrade Required" anchor="status.426">
2207  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2208  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2209<t>
2210   The request can not be completed without a prior protocol upgrade. This
2211   response &MUST; include an Upgrade header field (&header-upgrade;)
2212   specifying the required protocols.
2213</t>
2214<figure>
2215<preamble>Example:</preamble>
2216<artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2217HTTP/1.1 426 Upgrade Required
2218Upgrade: HTTP/2.0
2219Connection: Upgrade
2220
2221</artwork></figure>
2222<t>
2223   The server &SHOULD; include a message body in the 426 response which
2224   indicates in human readable form the reason for the error and describes any
2225   alternative courses which may be available to the user.
2226</t>
2227</section>
2228</section>
2229
2230<section title="Server Error 5xx" anchor="status.5xx">
2231<t>
2232   Response status codes beginning with the digit "5" indicate cases in
2233   which the server is aware that it has erred or is incapable of
2234   performing the request. Except when responding to a HEAD request, the
2235   server &SHOULD; include a representation containing an explanation of the
2236   error situation, and whether it is a temporary or permanent
2237   condition. User agents &SHOULD; display any included representation to the
2238   user. These response codes are applicable to any request method.
2239</t>
2240
2241<section title="500 Internal Server Error" anchor="status.500">
2242  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2243  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2244<t>
2245   The server encountered an unexpected condition which prevented it
2246   from fulfilling the request.
2247</t>
2248</section>
2249
2250<section title="501 Not Implemented" anchor="status.501">
2251  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2252  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2253<t>
2254   The server does not support the functionality required to fulfill the
2255   request. This is the appropriate response when the server does not
2256   recognize the request method and is not capable of supporting it for
2257   any resource.
2258</t>
2259</section>
2260
2261<section title="502 Bad Gateway" anchor="status.502">
2262  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2263  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2264<t>
2265   The server, while acting as a gateway or proxy, received an invalid
2266   response from the upstream server it accessed in attempting to
2267   fulfill the request.
2268</t>
2269</section>
2270
2271<section title="503 Service Unavailable" anchor="status.503">
2272  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2273  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2274<t>
2275   The server is currently unable to handle the request due to a
2276   temporary overloading or maintenance of the server.
2277</t>
2278<t>
2279   The implication is that this is a temporary condition which will be
2280   alleviated after some delay. If known, the length of the delay &MAY; be
2281   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2282   If no Retry-After is given, the client &SHOULD; handle the response as it
2283   would for a 500 response.
2284</t>
2285<x:note>
2286  <t>
2287    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2288    server must use it when becoming overloaded. Some servers might wish
2289    to simply refuse the connection.
2290  </t>
2291</x:note>
2292</section>
2293
2294<section title="504 Gateway Timeout" anchor="status.504">
2295  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2296  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2297<t>
2298   The server, while acting as a gateway or proxy, did not receive a
2299   timely response from the upstream server specified by the URI (e.g.,
2300   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2301   to access in attempting to complete the request.
2302</t>
2303<x:note>
2304  <t>
2305    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2306    return 400 or 500 when DNS lookups time out.
2307  </t>
2308</x:note>
2309</section>
2310
2311<section title="505 HTTP Version Not Supported" anchor="status.505">
2312  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2313  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2314<t>
2315   The server does not support, or refuses to support, the protocol
2316   version that was used in the request message. The server is
2317   indicating that it is unable or unwilling to complete the request
2318   using the same major version as the client, as described in &http-version;,
2319   other than with this error message. The response &SHOULD; contain
2320   a representation describing why that version is not supported and what other
2321   protocols are supported by that server.
2322</t>
2323
2324</section>
2325</section>
2326</section>
2327
2328
2329<section title="Date/Time Formats" anchor="http.date">
2330  <x:anchor-alias value="HTTP-date"/>
2331<t>
2332   HTTP applications have historically allowed three different formats
2333   for date/time stamps. However, the preferred format is a fixed-length subset
2334   of that defined by <xref target="RFC1123"/>:
2335</t>
2336<figure><artwork type="example" x:indent-with="  ">
2337Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2338</artwork></figure>
2339<t>
2340   The other formats are described here only for compatibility with obsolete
2341   implementations.
2342</t>
2343<figure><artwork type="example" x:indent-with="  ">
2344Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2345Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2346</artwork></figure>
2347<t>
2348   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2349   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2350   only generate the RFC 1123 format for representing HTTP-date values
2351   in header fields.
2352</t>
2353<t>
2354   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2355   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2356   equal to UTC (Coordinated Universal Time). This is indicated in the
2357   first two formats by the inclusion of "GMT" as the three-letter
2358   abbreviation for time zone, and &MUST; be assumed when reading the
2359   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2360   additional whitespace beyond that specifically included as SP in the
2361   grammar.
2362</t>
2363<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2364  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2365</artwork></figure>
2366<t anchor="preferred.date.format">
2367  <x:anchor-alias value="rfc1123-date"/>
2368  <x:anchor-alias value="time-of-day"/>
2369  <x:anchor-alias value="hour"/>
2370  <x:anchor-alias value="minute"/>
2371  <x:anchor-alias value="second"/>
2372  <x:anchor-alias value="day-name"/>
2373  <x:anchor-alias value="day"/>
2374  <x:anchor-alias value="month"/>
2375  <x:anchor-alias value="year"/>
2376  <x:anchor-alias value="GMT"/>
2377  Preferred format:
2378</t>
2379<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"/>
2380  <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>
2381  ; fixed length subset of the format defined in
2382  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2383 
2384  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2385               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2386               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2387               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2388               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2389               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2390               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2391               
2392  <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>
2393               ; e.g., 02 Jun 1982
2394
2395  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2396  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2397               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2398               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2399               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2400               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2401               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2402               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2403               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2404               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2405               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2406               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2407               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2408  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2409
2410  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2411
2412  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2413                 ; 00:00:00 - 23:59:59
2414                 
2415  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2416  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2417  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2418</artwork></figure>
2419<t>
2420  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2421  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2422  same as those defined for the RFC 5322 constructs
2423  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2424</t>
2425<t anchor="obsolete.date.formats">
2426  <x:anchor-alias value="obs-date"/>
2427  <x:anchor-alias value="rfc850-date"/>
2428  <x:anchor-alias value="asctime-date"/>
2429  <x:anchor-alias value="date1"/>
2430  <x:anchor-alias value="date2"/>
2431  <x:anchor-alias value="date3"/>
2432  <x:anchor-alias value="rfc1123-date"/>
2433  <x:anchor-alias value="day-name-l"/>
2434  Obsolete formats:
2435</t>
2436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2437  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2438</artwork></figure>
2439<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2440  <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>
2441  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2442                 ; day-month-year (e.g., 02-Jun-82)
2443
2444  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2445         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2446         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2447         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2448         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2449         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2450         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2451</artwork></figure>
2452<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2453  <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>
2454  <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> ))
2455                 ; month day (e.g., Jun  2)
2456</artwork></figure>
2457<x:note>
2458  <t>
2459    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2460    accepting date values that might have been sent by non-HTTP
2461    applications, as is sometimes the case when retrieving or posting
2462    messages via proxies/gateways to SMTP or NNTP.
2463  </t>
2464</x:note>
2465<x:note>
2466  <t>
2467    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2468    to their usage within the protocol stream. Clients and servers are
2469    not required to use these formats for user presentation, request
2470    logging, etc.
2471  </t>
2472</x:note>
2473</section>
2474
2475
2476<section title="Header Field Definitions" anchor="header.field.definitions">
2477<t>
2478   This section defines the syntax and semantics of HTTP/1.1 header fields
2479   related to request and response semantics.
2480</t>
2481
2482<section title="Allow" anchor="header.allow">
2483  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2484  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2485  <x:anchor-alias value="Allow"/>
2486<t>
2487   The "Allow" header field lists the set of methods advertised as
2488   supported by the target resource. The purpose of this field is strictly to
2489   inform the recipient of valid request methods associated with the resource.
2490</t>
2491<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2492  <x:ref>Allow</x:ref> = #<x:ref>Method</x:ref>
2493</artwork></figure>
2494<t>
2495   Example of use:
2496</t>
2497<figure><artwork type="example">
2498  Allow: GET, HEAD, PUT
2499</artwork></figure>
2500<t>
2501   The actual set of allowed methods is defined by the origin server at the
2502   time of each request.
2503</t>
2504<t>
2505   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2506   understand all the methods specified in order to handle them according to
2507   the generic message handling rules.
2508</t>
2509</section>
2510
2511<section title="Date" anchor="header.date">
2512  <iref primary="true" item="Date header field" x:for-anchor=""/>
2513  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2514  <x:anchor-alias value="Date"/>
2515<t>
2516   The "Date" header field represents the date and time at which
2517   the message was originated, having the same semantics as the Origination
2518   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2519   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2520   it &MUST; be sent in rfc1123-date format.
2521</t>
2522<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2523  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2524</artwork></figure>
2525<t>
2526   An example is
2527</t>
2528<figure><artwork type="example">
2529  Date: Tue, 15 Nov 1994 08:12:31 GMT
2530</artwork></figure>
2531<t>
2532   Origin servers &MUST; include a Date header field in all responses,
2533   except in these cases:
2534  <list style="numbers">
2535      <t>If the response status code is 100 (Continue) or 101 (Switching
2536         Protocols), the response &MAY; include a Date header field, at
2537         the server's option.</t>
2538
2539      <t>If the response status code conveys a server error, e.g., 500
2540         (Internal Server Error) or 503 (Service Unavailable), and it is
2541         inconvenient or impossible to generate a valid Date.</t>
2542
2543      <t>If the server does not have a clock that can provide a
2544         reasonable approximation of the current time, its responses
2545         &MUST-NOT; include a Date header field.</t>
2546  </list>
2547</t>
2548<t>
2549   A received message that does not have a Date header field &MUST; be
2550   assigned one by the recipient if the message will be cached by that
2551   recipient.
2552</t>
2553<t>
2554   Clients can use the Date header field as well; in order to keep request
2555   messages small, they are advised not to include it when it doesn't convey
2556   any useful information (as it is usually the case for requests that do not
2557   contain a payload).
2558</t>
2559<t>
2560   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2561   time subsequent to the generation of the message. It &SHOULD; represent
2562   the best available approximation of the date and time of message
2563   generation, unless the implementation has no means of generating a
2564   reasonably accurate date and time. In theory, the date ought to
2565   represent the moment just before the payload is generated. In
2566   practice, the date can be generated at any time during the message
2567   origination without affecting its semantic value.
2568</t>
2569</section>
2570
2571<section title="Expect" anchor="header.expect">
2572  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2573  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2574  <x:anchor-alias value="Expect"/>
2575  <x:anchor-alias value="expectation"/>
2576  <x:anchor-alias value="expectation-extension"/>
2577  <x:anchor-alias value="expect-param"/>
2578<t>
2579   The "Expect" header field is used to indicate that particular
2580   server behaviors are required by the client.
2581</t>
2582<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"/>
2583  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2584 
2585  <x:ref>expectation</x:ref>  = "100-continue" / <x:ref>expectation-extension</x:ref>
2586  <x:ref>expectation-extension</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2587                           *(";" <x:ref>expect-param</x:ref>) ]
2588  <x:ref>expect-param</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2589</artwork></figure>
2590<t>
2591   A server that does not understand or is unable to comply with any of
2592   the expectation values in the Expect field of a request &MUST; respond
2593   with appropriate error status code. The server &MUST; respond with a 417
2594   (Expectation Failed) status code if any of the expectations cannot be met
2595   or, if there are other problems with the request, some other 4xx
2596   status code.
2597</t>
2598<t>
2599   This header field is defined with extensible syntax to allow for
2600   future extensions. If a server receives a request containing an
2601   Expect field that includes an expectation-extension that it does not
2602   support, it &MUST; respond with a 417 (Expectation Failed) status code.
2603</t>
2604<t>
2605   Comparison of expectation values is case-insensitive for unquoted
2606   tokens (including the 100-continue token), and is case-sensitive for
2607   quoted-string expectation-extensions.
2608</t>
2609<t>
2610   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
2611   return a 417 (Expectation Failed) status code if it receives a request
2612   with an expectation that it cannot meet. However, the Expect
2613   header field itself is end-to-end; it &MUST; be forwarded if the
2614   request is forwarded.
2615</t>
2616<t>
2617   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
2618   Expect header field.
2619</t>
2620<t>
2621   See &use100; for the use of the 100 (Continue) status code.
2622</t>
2623</section>
2624
2625<section title="From" anchor="header.from">
2626  <iref primary="true" item="From header field" x:for-anchor=""/>
2627  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2628  <x:anchor-alias value="From"/>
2629  <x:anchor-alias value="mailbox"/>
2630<t>
2631   The "From" header field, if given, &SHOULD; contain an Internet
2632   e-mail address for the human user who controls the requesting user
2633   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2634   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2635</t>
2636<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2637  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2638 
2639  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2640</artwork></figure>
2641<t>
2642   An example is:
2643</t>
2644<figure><artwork type="example">
2645  From: webmaster@example.org
2646</artwork></figure>
2647<t>
2648   This header field &MAY; be used for logging purposes and as a means for
2649   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2650   be used as an insecure form of access protection. The interpretation
2651   of this field is that the request is being performed on behalf of the
2652   person given, who accepts responsibility for the method performed. In
2653   particular, robot agents &SHOULD; include this header field so that the
2654   person responsible for running the robot can be contacted if problems
2655   occur on the receiving end.
2656</t>
2657<t>
2658   The Internet e-mail address in this field &MAY; be separate from the
2659   Internet host which issued the request. For example, when a request
2660   is passed through a proxy the original issuer's address &SHOULD; be
2661   used.
2662</t>
2663<t>
2664   The client &SHOULD-NOT;  send the From header field without the user's
2665   approval, as it might conflict with the user's privacy interests or
2666   their site's security policy. It is strongly recommended that the
2667   user be able to disable, enable, and modify the value of this field
2668   at any time prior to a request.
2669</t>
2670</section>
2671
2672<section title="Location" anchor="header.location">
2673  <iref primary="true" item="Location header field" x:for-anchor=""/>
2674  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2675  <x:anchor-alias value="Location"/>
2676<t>
2677   The "Location" header field is used to identify a newly created
2678   resource, or to redirect the recipient to a different location for
2679   completion of the request.
2680</t>
2681<t>
2682   For 201 (Created) responses, the Location is the URI of the new resource
2683   which was created by the request. For 3xx responses, the location &SHOULD;
2684   indicate the server's preferred URI for automatic redirection to the
2685   resource.
2686</t>
2687<t>
2688   The field value consists of a single URI-reference. When it has the form
2689   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2690   the final value is computed by resolving it against the effective request
2691   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>).
2692</t>
2693<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2694  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2695</artwork></figure>
2696<figure>
2697<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2698<artwork type="example">
2699  Location: http://www.example.org/pub/WWW/People.html#tim
2700</artwork></figure><figure><artwork type="example">  Location: /index.html
2701</artwork></figure>
2702<t>
2703   There are circumstances in which a fragment identifier in a Location URI
2704   would not be appropriate. For instance, when it appears in a 201 Created
2705   response, where the Location header field specifies the URI for the entire
2706   created resource.
2707</t>
2708<x:note>
2709  <t>
2710    <x:h>Note:</x:h> This specification does not define precedence rules
2711    for the case where the original URI, as navigated to by the user
2712    agent, and the Location header field value both contain fragment
2713    identifiers. Thus be aware that including fragment identifiers might
2714    inconvenience anyone relying on the semantics of the original URI's
2715    fragment identifier.
2716  </t>
2717</x:note>
2718<x:note>
2719  <t>
2720    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2721    from Location in that the Content-Location identifies the most specific
2722    resource corresponding to the enclosed representation.
2723    It is therefore possible for a response to contain header fields for
2724    both Location and Content-Location.
2725  </t>
2726</x:note>
2727</section>
2728
2729<section title="Max-Forwards" anchor="header.max-forwards">
2730  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2731  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2732  <x:anchor-alias value="Max-Forwards"/>
2733<t>
2734   The "Max-Forwards" header field provides a mechanism with the
2735   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2736   methods to limit the number of times that the request is forwarded by
2737   proxies. This can be useful when the client is attempting to
2738   trace a request which appears to be failing or looping in mid-chain.
2739</t>
2740<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2741  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2742</artwork></figure>
2743<t>
2744   The Max-Forwards value is a decimal integer indicating the remaining
2745   number of times this request message can be forwarded.
2746</t>
2747<t>
2748   Each recipient of a TRACE or OPTIONS request
2749   containing a Max-Forwards header field &MUST; check and update its
2750   value prior to forwarding the request. If the received value is zero
2751   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2752   respond as the final recipient. If the received Max-Forwards value is
2753   greater than zero, then the forwarded message &MUST; contain an updated
2754   Max-Forwards field with a value decremented by one (1).
2755</t>
2756<t>
2757   The Max-Forwards header field &MAY; be ignored for all other request
2758   methods.
2759</t>
2760</section>
2761
2762<section title="Referer" anchor="header.referer">
2763  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2764  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2765  <x:anchor-alias value="Referer"/>
2766<t>
2767   The "Referer" [sic] header field allows the client to specify the
2768   URI of the resource from which the effective request URI was obtained (the
2769   "referrer", although the header field is misspelled.).
2770</t>
2771<t>
2772   The Referer header field allows servers to generate lists of back-links to
2773   resources for interest, logging, optimized caching, etc. It also allows
2774   obsolete or mistyped links to be traced for maintenance. Some servers use
2775   Referer as a means of controlling where they allow links from (so-called
2776   "deep linking"), but legitimate requests do not always
2777   contain a Referer header field.
2778</t>
2779<t>
2780   If the effective request URI was obtained from a source that does not have its own
2781   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2782   sent with the value "about:blank", or not be sent at all. Note that this
2783   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2784</t>
2785<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2786  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2787</artwork></figure>
2788<t>
2789   Example:
2790</t>
2791<figure><artwork type="example">
2792  Referer: http://www.example.org/hypertext/Overview.html
2793</artwork></figure>
2794<t>
2795   If the field value is a relative URI, it &SHOULD; be interpreted
2796   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2797   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2798</t>
2799</section>
2800
2801<section title="Retry-After" anchor="header.retry-after">
2802  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2803  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2804  <x:anchor-alias value="Retry-After"/>
2805<t>
2806   The header "Retry-After" field can be used with a 503 (Service
2807   Unavailable) response to indicate how long the service is expected to
2808   be unavailable to the requesting client. This field &MAY; also be used
2809   with any 3xx (Redirection) response to indicate the minimum time the
2810   user-agent is asked wait before issuing the redirected request.
2811</t>
2812<t>
2813   The value of this field can be either an HTTP-date or an integer number
2814   of seconds (in decimal) after the time of the response.
2815</t>
2816<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2817  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2818</artwork></figure>
2819<t anchor="rule.delta-seconds">
2820  <x:anchor-alias value="delta-seconds"/>
2821   Time spans are non-negative decimal integers, representing time in
2822   seconds.
2823</t>
2824<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2825  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2826</artwork></figure>
2827<t>
2828   Two examples of its use are
2829</t>
2830<figure><artwork type="example">
2831  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2832  Retry-After: 120
2833</artwork></figure>
2834<t>
2835   In the latter example, the delay is 2 minutes.
2836</t>
2837</section>
2838
2839<section title="Server" anchor="header.server">
2840  <iref primary="true" item="Server header field" x:for-anchor=""/>
2841  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2842  <x:anchor-alias value="Server"/>
2843<t>
2844   The "Server" header field contains information about the
2845   software used by the origin server to handle the request.
2846</t>
2847<t>
2848   The field can contain multiple product tokens (&product-tokens;) and
2849   comments (&header-fields;) identifying the server and any significant
2850   subproducts. The product tokens are listed in order of their significance
2851   for identifying the application.
2852</t>
2853<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2854  <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> ) )
2855</artwork></figure>
2856<t>
2857   Example:
2858</t>
2859<figure><artwork type="example">
2860  Server: CERN/3.0 libwww/2.17
2861</artwork></figure>
2862<t>
2863   If the response is being forwarded through a proxy, the proxy
2864   application &MUST-NOT; modify the Server header field. Instead, it
2865   &MUST; include a Via field (as described in &header-via;).
2866</t>
2867<x:note>
2868  <t>
2869    <x:h>Note:</x:h> Revealing the specific software version of the server might
2870    allow the server machine to become more vulnerable to attacks
2871    against software that is known to contain security holes. Server
2872    implementors are encouraged to make this field a configurable
2873    option.
2874  </t>
2875</x:note>
2876</section>
2877
2878<section title="User-Agent" anchor="header.user-agent">
2879  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2880  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2881  <x:anchor-alias value="User-Agent"/>
2882<t>
2883   The "User-Agent" header field contains information about the user
2884   agent originating the request. User agents &SHOULD; include this field with
2885   requests.
2886</t>
2887<t>
2888   Typically, it is used for statistical purposes, the tracing of protocol
2889   violations, and tailoring responses to avoid particular user agent
2890   limitations.
2891</t>
2892<t>
2893   The field can contain multiple product tokens (&product-tokens;)
2894   and comments (&header-fields;) identifying the agent and its
2895   significant subproducts. By convention, the product tokens are listed in
2896   order of their significance for identifying the application.
2897</t>
2898<t>
2899   Because this field is usually sent on every request a user agent makes,
2900   implementations are encouraged not to include needlessly fine-grained
2901   detail, and to limit (or even prohibit) the addition of subproducts by third
2902   parties. Overly long and detailed User-Agent field values make requests
2903   larger and can also be used to identify ("fingerprint") the user against
2904   their wishes.
2905</t>
2906<t>
2907   Likewise, implementations are encouraged not to use the product tokens of
2908   other implementations in order to declare compatibility with them, as this
2909   circumvents the purpose of the field. Finally, they are encouraged not to
2910   use comments to identify products; doing so makes the field value more
2911   difficult to parse.
2912</t>
2913<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2914  <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> ) )
2915</artwork></figure>
2916<t>
2917   Example:
2918</t>
2919<figure><artwork type="example">
2920  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2921</artwork></figure>
2922</section>
2923
2924</section>
2925
2926<section title="IANA Considerations" anchor="IANA.considerations">
2927
2928<section title="Method Registry" anchor="method.registration">
2929<t>
2930  The registration procedure for HTTP request methods is defined by
2931  <xref target="method.registry"/> of this document.
2932</t>
2933<t>
2934   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2935   and be populated with the registrations below:
2936</t>
2937<?BEGININC p2-semantics.iana-methods ?>
2938<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2939<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2940   <ttcol>Method</ttcol>
2941   <ttcol>Safe</ttcol>
2942   <ttcol>Reference</ttcol>
2943   <c>CONNECT</c>
2944   <c>no</c>
2945   <c>
2946      <xref target="CONNECT"/>
2947   </c>
2948   <c>DELETE</c>
2949   <c>no</c>
2950   <c>
2951      <xref target="DELETE"/>
2952   </c>
2953   <c>GET</c>
2954   <c>yes</c>
2955   <c>
2956      <xref target="GET"/>
2957   </c>
2958   <c>HEAD</c>
2959   <c>yes</c>
2960   <c>
2961      <xref target="HEAD"/>
2962   </c>
2963   <c>OPTIONS</c>
2964   <c>yes</c>
2965   <c>
2966      <xref target="OPTIONS"/>
2967   </c>
2968   <c>POST</c>
2969   <c>no</c>
2970   <c>
2971      <xref target="POST"/>
2972   </c>
2973   <c>PUT</c>
2974   <c>no</c>
2975   <c>
2976      <xref target="PUT"/>
2977   </c>
2978   <c>TRACE</c>
2979   <c>yes</c>
2980   <c>
2981      <xref target="TRACE"/>
2982   </c>
2983</texttable>
2984<!--(END)-->
2985<?ENDINC p2-semantics.iana-methods ?>
2986</section>
2987
2988<section title="Status Code Registry" anchor="status.code.registration">
2989<t>
2990   The registration procedure for HTTP Status Codes &mdash; previously defined
2991   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2992   by <xref target="status.code.registry"/> of this document.
2993</t>
2994<t>
2995   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2996   shall be updated with the registrations below:
2997</t>
2998<?BEGININC p2-semantics.iana-status-codes ?>
2999<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
3000<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
3001   <ttcol>Value</ttcol>
3002   <ttcol>Description</ttcol>
3003   <ttcol>Reference</ttcol>
3004   <c>100</c>
3005   <c>Continue</c>
3006   <c>
3007      <xref target="status.100"/>
3008   </c>
3009   <c>101</c>
3010   <c>Switching Protocols</c>
3011   <c>
3012      <xref target="status.101"/>
3013   </c>
3014   <c>200</c>
3015   <c>OK</c>
3016   <c>
3017      <xref target="status.200"/>
3018   </c>
3019   <c>201</c>
3020   <c>Created</c>
3021   <c>
3022      <xref target="status.201"/>
3023   </c>
3024   <c>202</c>
3025   <c>Accepted</c>
3026   <c>
3027      <xref target="status.202"/>
3028   </c>
3029   <c>203</c>
3030   <c>Non-Authoritative Information</c>
3031   <c>
3032      <xref target="status.203"/>
3033   </c>
3034   <c>204</c>
3035   <c>No Content</c>
3036   <c>
3037      <xref target="status.204"/>
3038   </c>
3039   <c>205</c>
3040   <c>Reset Content</c>
3041   <c>
3042      <xref target="status.205"/>
3043   </c>
3044   <c>300</c>
3045   <c>Multiple Choices</c>
3046   <c>
3047      <xref target="status.300"/>
3048   </c>
3049   <c>301</c>
3050   <c>Moved Permanently</c>
3051   <c>
3052      <xref target="status.301"/>
3053   </c>
3054   <c>302</c>
3055   <c>Found</c>
3056   <c>
3057      <xref target="status.302"/>
3058   </c>
3059   <c>303</c>
3060   <c>See Other</c>
3061   <c>
3062      <xref target="status.303"/>
3063   </c>
3064   <c>305</c>
3065   <c>Use Proxy</c>
3066   <c>
3067      <xref target="status.305"/>
3068   </c>
3069   <c>306</c>
3070   <c>(Unused)</c>
3071   <c>
3072      <xref target="status.306"/>
3073   </c>
3074   <c>307</c>
3075   <c>Temporary Redirect</c>
3076   <c>
3077      <xref target="status.307"/>
3078   </c>
3079   <c>400</c>
3080   <c>Bad Request</c>
3081   <c>
3082      <xref target="status.400"/>
3083   </c>
3084   <c>402</c>
3085   <c>Payment Required</c>
3086   <c>
3087      <xref target="status.402"/>
3088   </c>
3089   <c>403</c>
3090   <c>Forbidden</c>
3091   <c>
3092      <xref target="status.403"/>
3093   </c>
3094   <c>404</c>
3095   <c>Not Found</c>
3096   <c>
3097      <xref target="status.404"/>
3098   </c>
3099   <c>405</c>
3100   <c>Method Not Allowed</c>
3101   <c>
3102      <xref target="status.405"/>
3103   </c>
3104   <c>406</c>
3105   <c>Not Acceptable</c>
3106   <c>
3107      <xref target="status.406"/>
3108   </c>
3109   <c>407</c>
3110   <c>Proxy Authentication Required</c>
3111   <c>
3112      <xref target="status.407"/>
3113   </c>
3114   <c>408</c>
3115   <c>Request Timeout</c>
3116   <c>
3117      <xref target="status.408"/>
3118   </c>
3119   <c>409</c>
3120   <c>Conflict</c>
3121   <c>
3122      <xref target="status.409"/>
3123   </c>
3124   <c>410</c>
3125   <c>Gone</c>
3126   <c>
3127      <xref target="status.410"/>
3128   </c>
3129   <c>411</c>
3130   <c>Length Required</c>
3131   <c>
3132      <xref target="status.411"/>
3133   </c>
3134   <c>413</c>
3135   <c>Request Representation Too Large</c>
3136   <c>
3137      <xref target="status.413"/>
3138   </c>
3139   <c>414</c>
3140   <c>URI Too Long</c>
3141   <c>
3142      <xref target="status.414"/>
3143   </c>
3144   <c>415</c>
3145   <c>Unsupported Media Type</c>
3146   <c>
3147      <xref target="status.415"/>
3148   </c>
3149   <c>417</c>
3150   <c>Expectation Failed</c>
3151   <c>
3152      <xref target="status.417"/>
3153   </c>
3154   <c>426</c>
3155   <c>Upgrade Required</c>
3156   <c>
3157      <xref target="status.426"/>
3158   </c>
3159   <c>500</c>
3160   <c>Internal Server Error</c>
3161   <c>
3162      <xref target="status.500"/>
3163   </c>
3164   <c>501</c>
3165   <c>Not Implemented</c>
3166   <c>
3167      <xref target="status.501"/>
3168   </c>
3169   <c>502</c>
3170   <c>Bad Gateway</c>
3171   <c>
3172      <xref target="status.502"/>
3173   </c>
3174   <c>503</c>
3175   <c>Service Unavailable</c>
3176   <c>
3177      <xref target="status.503"/>
3178   </c>
3179   <c>504</c>
3180   <c>Gateway Timeout</c>
3181   <c>
3182      <xref target="status.504"/>
3183   </c>
3184   <c>505</c>
3185   <c>HTTP Version Not Supported</c>
3186   <c>
3187      <xref target="status.505"/>
3188   </c>
3189</texttable>
3190<!--(END)-->
3191<?ENDINC p2-semantics.iana-status-codes ?>
3192</section>
3193<section title="Header Field Registration" anchor="header.field.registration">
3194<t>
3195   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3196   with the permanent registrations below (see <xref target="RFC3864"/>):
3197</t>
3198<?BEGININC p2-semantics.iana-headers ?>
3199<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3200<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3201   <ttcol>Header Field Name</ttcol>
3202   <ttcol>Protocol</ttcol>
3203   <ttcol>Status</ttcol>
3204   <ttcol>Reference</ttcol>
3205
3206   <c>Allow</c>
3207   <c>http</c>
3208   <c>standard</c>
3209   <c>
3210      <xref target="header.allow"/>
3211   </c>
3212   <c>Date</c>
3213   <c>http</c>
3214   <c>standard</c>
3215   <c>
3216      <xref target="header.date"/>
3217   </c>
3218   <c>Expect</c>
3219   <c>http</c>
3220   <c>standard</c>
3221   <c>
3222      <xref target="header.expect"/>
3223   </c>
3224   <c>From</c>
3225   <c>http</c>
3226   <c>standard</c>
3227   <c>
3228      <xref target="header.from"/>
3229   </c>
3230   <c>Location</c>
3231   <c>http</c>
3232   <c>standard</c>
3233   <c>
3234      <xref target="header.location"/>
3235   </c>
3236   <c>Max-Forwards</c>
3237   <c>http</c>
3238   <c>standard</c>
3239   <c>
3240      <xref target="header.max-forwards"/>
3241   </c>
3242   <c>Referer</c>
3243   <c>http</c>
3244   <c>standard</c>
3245   <c>
3246      <xref target="header.referer"/>
3247   </c>
3248   <c>Retry-After</c>
3249   <c>http</c>
3250   <c>standard</c>
3251   <c>
3252      <xref target="header.retry-after"/>
3253   </c>
3254   <c>Server</c>
3255   <c>http</c>
3256   <c>standard</c>
3257   <c>
3258      <xref target="header.server"/>
3259   </c>
3260   <c>User-Agent</c>
3261   <c>http</c>
3262   <c>standard</c>
3263   <c>
3264      <xref target="header.user-agent"/>
3265   </c>
3266</texttable>
3267<!--(END)-->
3268<?ENDINC p2-semantics.iana-headers ?>
3269<t>
3270   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3271</t>
3272</section>
3273</section>
3274
3275<section title="Security Considerations" anchor="security.considerations">
3276<t>
3277   This section is meant to inform application developers, information
3278   providers, and users of the security limitations in HTTP/1.1 as
3279   described by this document. The discussion does not include
3280   definitive solutions to the problems revealed, though it does make
3281   some suggestions for reducing security risks.
3282</t>
3283
3284<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3285<t>
3286   Like any generic data transfer protocol, HTTP cannot regulate the
3287   content of the data that is transferred, nor is there any a priori
3288   method of determining the sensitivity of any particular piece of
3289   information within the context of any given request. Therefore,
3290   applications &SHOULD; supply as much control over this information as
3291   possible to the provider of that information. Four header fields are
3292   worth special mention in this context: Server, Via, Referer and From.
3293</t>
3294<t>
3295   Revealing the specific software version of the server might allow the
3296   server machine to become more vulnerable to attacks against software
3297   that is known to contain security holes. Implementors &SHOULD; make the
3298   Server header field a configurable option.
3299</t>
3300<t>
3301   Proxies which serve as a portal through a network firewall &SHOULD;
3302   take special precautions regarding the transfer of header information
3303   that identifies the hosts behind the firewall. In particular, they
3304   &SHOULD; remove, or replace with sanitized versions, any Via fields
3305   generated behind the firewall.
3306</t>
3307<t>
3308   The Referer header field allows reading patterns to be studied and reverse
3309   links drawn. Although it can be very useful, its power can be abused
3310   if user details are not separated from the information contained in
3311   the Referer. Even when the personal information has been removed, the
3312   Referer header field might indicate a private document's URI whose
3313   publication would be inappropriate.
3314</t>
3315<t>
3316   The information sent in the From field might conflict with the user's
3317   privacy interests or their site's security policy, and hence it
3318   &SHOULD-NOT;  be transmitted without the user being able to disable,
3319   enable, and modify the contents of the field. The user &MUST; be able
3320   to set the contents of this field within a user preference or
3321   application defaults configuration.
3322</t>
3323<t>
3324   We suggest, though do not require, that a convenient toggle interface
3325   be provided for the user to enable or disable the sending of From and
3326   Referer information.
3327</t>
3328<t>
3329   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3330   target="header.server"/>) header fields can sometimes be used to determine
3331   that a specific client or server have a particular security hole which might
3332   be exploited. Unfortunately, this same information is often used for other
3333   valuable purposes for which HTTP currently has no better mechanism.
3334</t>
3335<t>
3336   Furthermore, the User-Agent header field may contain enough entropy to be
3337   used, possibly in conjunction with other material, to uniquely identify the
3338   user.
3339</t>
3340<t>
3341   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3342   that was sent in request header fields within the body of their response.
3343   Clients &SHOULD; be careful with sensitive information, like Cookies,
3344   Authorization credentials, and other header fields that might be used to
3345   collect data from the client.
3346</t> 
3347</section>
3348
3349<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3350<t>
3351   Because the source of a link might be private information or might
3352   reveal an otherwise private information source, it is strongly
3353   recommended that the user be able to select whether or not the
3354   Referer field is sent. For example, a browser client could have a
3355   toggle switch for browsing openly/anonymously, which would
3356   respectively enable/disable the sending of Referer and From
3357   information.
3358</t>
3359<t>
3360   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3361   HTTP request if the referring page was transferred with a secure
3362   protocol.
3363</t>
3364<t>
3365   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3366   sensitive data because that data will be placed in the request-target. Many
3367   existing servers, proxies, and user agents log or display the request-target
3368   in places where it might be visible to third parties. Such services can
3369   use POST-based form submission instead.
3370</t>
3371</section>
3372
3373<section title="Location Headers and Spoofing" anchor="location.spoofing">
3374<t>
3375   If a single server supports multiple organizations that do not trust
3376   one another, then it &MUST; check the values of Location and Content-Location
3377   header fields in responses that are generated under control of
3378   said organizations to make sure that they do not attempt to
3379   invalidate resources over which they have no authority.
3380</t>
3381</section>
3382
3383<section title="Security Considerations for CONNECT">
3384<t>
3385   Since tunneled data is opaque to the proxy, there are additional
3386   risks to tunneling to other well-known or reserved ports.
3387   A HTTP client CONNECTing to port 25 could relay spam
3388   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3389   access to a small number of known ports.
3390</t>
3391</section>
3392
3393</section>
3394
3395<section title="Acknowledgments" anchor="acks">
3396<t>
3397  See &acks;.
3398</t>
3399</section>
3400</middle>
3401<back>
3402
3403<references title="Normative References">
3404
3405<reference anchor="Part1">
3406  <front>
3407    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3408    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3409      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3410      <address><email>fielding@gbiv.com</email></address>
3411    </author>
3412    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3413      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3414      <address><email>jg@freedesktop.org</email></address>
3415    </author>
3416    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3417      <organization abbrev="HP">Hewlett-Packard Company</organization>
3418      <address><email>JeffMogul@acm.org</email></address>
3419    </author>
3420    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3421      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3422      <address><email>henrikn@microsoft.com</email></address>
3423    </author>
3424    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3425      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3426      <address><email>LMM@acm.org</email></address>
3427    </author>
3428    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3429      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3430      <address><email>paulle@microsoft.com</email></address>
3431    </author>
3432    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3433      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3434      <address><email>timbl@w3.org</email></address>
3435    </author>
3436    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3437      <organization abbrev="W3C">World Wide Web Consortium</organization>
3438      <address><email>ylafon@w3.org</email></address>
3439    </author>
3440    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3441      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3442      <address><email>julian.reschke@greenbytes.de</email></address>
3443    </author>
3444    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3445  </front>
3446  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3447  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3448</reference>
3449
3450<reference anchor="Part3">
3451  <front>
3452    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3453    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3454      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3455      <address><email>fielding@gbiv.com</email></address>
3456    </author>
3457    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3458      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3459      <address><email>jg@freedesktop.org</email></address>
3460    </author>
3461    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3462      <organization abbrev="HP">Hewlett-Packard Company</organization>
3463      <address><email>JeffMogul@acm.org</email></address>
3464    </author>
3465    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3466      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3467      <address><email>henrikn@microsoft.com</email></address>
3468    </author>
3469    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3470      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3471      <address><email>LMM@acm.org</email></address>
3472    </author>
3473    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3474      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3475      <address><email>paulle@microsoft.com</email></address>
3476    </author>
3477    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3478      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3479      <address><email>timbl@w3.org</email></address>
3480    </author>
3481    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3482      <organization abbrev="W3C">World Wide Web Consortium</organization>
3483      <address><email>ylafon@w3.org</email></address>
3484    </author>
3485    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3486      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3487      <address><email>julian.reschke@greenbytes.de</email></address>
3488    </author>
3489    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3490  </front>
3491  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3492  <x:source href="p3-payload.xml" basename="p3-payload"/>
3493</reference>
3494
3495<reference anchor="Part4">
3496  <front>
3497    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3498    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3499      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3500      <address><email>fielding@gbiv.com</email></address>
3501    </author>
3502    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3503      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3504      <address><email>jg@freedesktop.org</email></address>
3505    </author>
3506    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3507      <organization abbrev="HP">Hewlett-Packard Company</organization>
3508      <address><email>JeffMogul@acm.org</email></address>
3509    </author>
3510    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3511      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3512      <address><email>henrikn@microsoft.com</email></address>
3513    </author>
3514    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3515      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3516      <address><email>LMM@acm.org</email></address>
3517    </author>
3518    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3519      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3520      <address><email>paulle@microsoft.com</email></address>
3521    </author>
3522    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3523      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3524      <address><email>timbl@w3.org</email></address>
3525    </author>
3526    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3527      <organization abbrev="W3C">World Wide Web Consortium</organization>
3528      <address><email>ylafon@w3.org</email></address>
3529    </author>
3530    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3531      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3532      <address><email>julian.reschke@greenbytes.de</email></address>
3533    </author>
3534    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3535  </front>
3536  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3537  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3538</reference>
3539
3540<reference anchor="Part5">
3541  <front>
3542    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3543    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3544      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3545      <address><email>fielding@gbiv.com</email></address>
3546    </author>
3547    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3548      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3549      <address><email>jg@freedesktop.org</email></address>
3550    </author>
3551    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3552      <organization abbrev="HP">Hewlett-Packard Company</organization>
3553      <address><email>JeffMogul@acm.org</email></address>
3554    </author>
3555    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3556      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3557      <address><email>henrikn@microsoft.com</email></address>
3558    </author>
3559    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3560      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3561      <address><email>LMM@acm.org</email></address>
3562    </author>
3563    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3564      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3565      <address><email>paulle@microsoft.com</email></address>
3566    </author>
3567    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3568      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3569      <address><email>timbl@w3.org</email></address>
3570    </author>
3571    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3572      <organization abbrev="W3C">World Wide Web Consortium</organization>
3573      <address><email>ylafon@w3.org</email></address>
3574    </author>
3575    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3576      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3577      <address><email>julian.reschke@greenbytes.de</email></address>
3578    </author>
3579    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3580  </front>
3581  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3582  <x:source href="p5-range.xml" basename="p5-range"/>
3583</reference>
3584
3585<reference anchor="Part6">
3586  <front>
3587    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3588    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3589      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3590      <address><email>fielding@gbiv.com</email></address>
3591    </author>
3592    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3593      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3594      <address><email>jg@freedesktop.org</email></address>
3595    </author>
3596    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3597      <organization abbrev="HP">Hewlett-Packard Company</organization>
3598      <address><email>JeffMogul@acm.org</email></address>
3599    </author>
3600    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3601      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3602      <address><email>henrikn@microsoft.com</email></address>
3603    </author>
3604    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3605      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3606      <address><email>LMM@acm.org</email></address>
3607    </author>
3608    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3609      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3610      <address><email>paulle@microsoft.com</email></address>
3611    </author>
3612    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3613      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3614      <address><email>timbl@w3.org</email></address>
3615    </author>
3616    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3617      <organization abbrev="W3C">World Wide Web Consortium</organization>
3618      <address><email>ylafon@w3.org</email></address>
3619    </author>
3620    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3621      <organization>Rackspace</organization>
3622      <address><email>mnot@mnot.net</email></address>
3623    </author>
3624    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3625      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3626      <address><email>julian.reschke@greenbytes.de</email></address>
3627    </author>
3628    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3629  </front>
3630  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3631  <x:source href="p6-cache.xml" basename="p6-cache"/>
3632</reference>
3633
3634<reference anchor="Part7">
3635  <front>
3636    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3637    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3638      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3639      <address><email>fielding@gbiv.com</email></address>
3640    </author>
3641    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3642      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3643      <address><email>jg@freedesktop.org</email></address>
3644    </author>
3645    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3646      <organization abbrev="HP">Hewlett-Packard Company</organization>
3647      <address><email>JeffMogul@acm.org</email></address>
3648    </author>
3649    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3650      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3651      <address><email>henrikn@microsoft.com</email></address>
3652    </author>
3653    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3654      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3655      <address><email>LMM@acm.org</email></address>
3656    </author>
3657    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3658      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3659      <address><email>paulle@microsoft.com</email></address>
3660    </author>
3661    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3662      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3663      <address><email>timbl@w3.org</email></address>
3664    </author>
3665    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3666      <organization abbrev="W3C">World Wide Web Consortium</organization>
3667      <address><email>ylafon@w3.org</email></address>
3668    </author>
3669    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3670      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3671      <address><email>julian.reschke@greenbytes.de</email></address>
3672    </author>
3673    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3674  </front>
3675  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3676  <x:source href="p7-auth.xml" basename="p7-auth"/>
3677</reference>
3678
3679<reference anchor="RFC2119">
3680  <front>
3681    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3682    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3683      <organization>Harvard University</organization>
3684      <address><email>sob@harvard.edu</email></address>
3685    </author>
3686    <date month="March" year="1997"/>
3687  </front>
3688  <seriesInfo name="BCP" value="14"/>
3689  <seriesInfo name="RFC" value="2119"/>
3690</reference>
3691
3692<reference anchor="RFC3986">
3693 <front>
3694  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3695  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3696    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3697    <address>
3698       <email>timbl@w3.org</email>
3699       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3700    </address>
3701  </author>
3702  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3703    <organization abbrev="Day Software">Day Software</organization>
3704    <address>
3705      <email>fielding@gbiv.com</email>
3706      <uri>http://roy.gbiv.com/</uri>
3707    </address>
3708  </author>
3709  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3710    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3711    <address>
3712      <email>LMM@acm.org</email>
3713      <uri>http://larry.masinter.net/</uri>
3714    </address>
3715  </author>
3716  <date month='January' year='2005'></date>
3717 </front>
3718 <seriesInfo name="STD" value="66"/>
3719 <seriesInfo name="RFC" value="3986"/>
3720</reference>
3721
3722<reference anchor="RFC5234">
3723  <front>
3724    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3725    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3726      <organization>Brandenburg InternetWorking</organization>
3727      <address>
3728        <email>dcrocker@bbiw.net</email>
3729      </address> 
3730    </author>
3731    <author initials="P." surname="Overell" fullname="Paul Overell">
3732      <organization>THUS plc.</organization>
3733      <address>
3734        <email>paul.overell@thus.net</email>
3735      </address>
3736    </author>
3737    <date month="January" year="2008"/>
3738  </front>
3739  <seriesInfo name="STD" value="68"/>
3740  <seriesInfo name="RFC" value="5234"/>
3741</reference>
3742
3743</references>
3744
3745<references title="Informative References">
3746
3747<reference anchor="RFC1123">
3748  <front>
3749    <title>Requirements for Internet Hosts - Application and Support</title>
3750    <author initials="R." surname="Braden" fullname="Robert Braden">
3751      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3752      <address><email>Braden@ISI.EDU</email></address>
3753    </author>
3754    <date month="October" year="1989"/>
3755  </front>
3756  <seriesInfo name="STD" value="3"/>
3757  <seriesInfo name="RFC" value="1123"/>
3758</reference>
3759
3760<reference anchor="RFC1945">
3761  <front>
3762    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3763    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3764      <organization>MIT, Laboratory for Computer Science</organization>
3765      <address><email>timbl@w3.org</email></address>
3766    </author>
3767    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3768      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3769      <address><email>fielding@ics.uci.edu</email></address>
3770    </author>
3771    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3772      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3773      <address><email>frystyk@w3.org</email></address>
3774    </author>
3775    <date month="May" year="1996"/>
3776  </front>
3777  <seriesInfo name="RFC" value="1945"/>
3778</reference>
3779
3780<reference anchor="RFC2068">
3781  <front>
3782    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3783    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3784      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3785      <address><email>fielding@ics.uci.edu</email></address>
3786    </author>
3787    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3788      <organization>MIT Laboratory for Computer Science</organization>
3789      <address><email>jg@w3.org</email></address>
3790    </author>
3791    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3792      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3793      <address><email>mogul@wrl.dec.com</email></address>
3794    </author>
3795    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3796      <organization>MIT Laboratory for Computer Science</organization>
3797      <address><email>frystyk@w3.org</email></address>
3798    </author>
3799    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3800      <organization>MIT Laboratory for Computer Science</organization>
3801      <address><email>timbl@w3.org</email></address>
3802    </author>
3803    <date month="January" year="1997"/>
3804  </front>
3805  <seriesInfo name="RFC" value="2068"/>
3806</reference>
3807
3808<reference anchor="RFC2616">
3809  <front>
3810    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3811    <author initials="R." surname="Fielding" fullname="R. Fielding">
3812      <organization>University of California, Irvine</organization>
3813      <address><email>fielding@ics.uci.edu</email></address>
3814    </author>
3815    <author initials="J." surname="Gettys" fullname="J. Gettys">
3816      <organization>W3C</organization>
3817      <address><email>jg@w3.org</email></address>
3818    </author>
3819    <author initials="J." surname="Mogul" fullname="J. Mogul">
3820      <organization>Compaq Computer Corporation</organization>
3821      <address><email>mogul@wrl.dec.com</email></address>
3822    </author>
3823    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3824      <organization>MIT Laboratory for Computer Science</organization>
3825      <address><email>frystyk@w3.org</email></address>
3826    </author>
3827    <author initials="L." surname="Masinter" fullname="L. Masinter">
3828      <organization>Xerox Corporation</organization>
3829      <address><email>masinter@parc.xerox.com</email></address>
3830    </author>
3831    <author initials="P." surname="Leach" fullname="P. Leach">
3832      <organization>Microsoft Corporation</organization>
3833      <address><email>paulle@microsoft.com</email></address>
3834    </author>
3835    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3836      <organization>W3C</organization>
3837      <address><email>timbl@w3.org</email></address>
3838    </author>
3839    <date month="June" year="1999"/>
3840  </front>
3841  <seriesInfo name="RFC" value="2616"/>
3842</reference>
3843
3844<reference anchor='RFC2817'>
3845  <front>
3846    <title>Upgrading to TLS Within HTTP/1.1</title>
3847    <author initials='R.' surname='Khare' fullname='R. Khare'>
3848      <organization>4K Associates / UC Irvine</organization>
3849      <address><email>rohit@4K-associates.com</email></address>
3850    </author>
3851    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3852      <organization>Agranat Systems, Inc.</organization>
3853      <address><email>lawrence@agranat.com</email></address>
3854    </author>
3855    <date year='2000' month='May' />
3856  </front>
3857  <seriesInfo name='RFC' value='2817' />
3858</reference>
3859
3860<reference anchor='RFC3864'>
3861  <front>
3862    <title>Registration Procedures for Message Header Fields</title>
3863    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3864      <organization>Nine by Nine</organization>
3865      <address><email>GK-IETF@ninebynine.org</email></address>
3866    </author>
3867    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3868      <organization>BEA Systems</organization>
3869      <address><email>mnot@pobox.com</email></address>
3870    </author>
3871    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3872      <organization>HP Labs</organization>
3873      <address><email>JeffMogul@acm.org</email></address>
3874    </author>
3875    <date year='2004' month='September' />
3876  </front>
3877  <seriesInfo name='BCP' value='90' />
3878  <seriesInfo name='RFC' value='3864' />
3879</reference>
3880
3881<reference anchor='RFC5226'>
3882  <front>
3883    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3884    <author initials='T.' surname='Narten' fullname='T. Narten'>
3885      <organization>IBM</organization>
3886      <address><email>narten@us.ibm.com</email></address>
3887    </author>
3888    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3889      <organization>Google</organization>
3890      <address><email>Harald@Alvestrand.no</email></address>
3891    </author>
3892    <date year='2008' month='May' />
3893  </front>
3894  <seriesInfo name='BCP' value='26' />
3895  <seriesInfo name='RFC' value='5226' />
3896</reference>
3897
3898<reference anchor="RFC5322">
3899  <front>
3900    <title>Internet Message Format</title>
3901    <author initials="P." surname="Resnick" fullname="P. Resnick">
3902      <organization>Qualcomm Incorporated</organization>
3903    </author>
3904    <date year="2008" month="October"/>
3905  </front> 
3906  <seriesInfo name="RFC" value="5322"/>
3907</reference>
3908
3909<reference anchor='RFC5789'>
3910  <front>
3911    <title>PATCH Method for HTTP</title>
3912    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3913      <organization>Linden Lab</organization>
3914    </author>
3915    <author initials='J.' surname='Snell' fullname='J. Snell' />
3916    <date year='2010' month='March' />
3917  </front>
3918  <seriesInfo name='RFC' value='5789' />
3919</reference>
3920
3921<reference anchor="RFC5987">
3922        <front>
3923    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3924    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3925      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3926      <address>
3927        <postal>
3928          <street>Hafenweg 16</street>
3929          <city>Muenster</city><region>NW</region><code>48155</code>
3930          <country>Germany</country>
3931        </postal>
3932        <email>julian.reschke@greenbytes.de</email>     
3933        <uri>http://greenbytes.de/tech/webdav/</uri>   
3934      </address>
3935    </author>
3936    <date month="August" year="2010"/>
3937  </front>
3938  <seriesInfo name="RFC" value="5987"/>
3939</reference>
3940
3941</references>
3942
3943<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3944<t>
3945  This document takes over the Status Code Registry, previously defined
3946  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3947  (<xref target="status.code.registry"/>)
3948</t>
3949<t>
3950  Clarify definition of POST.
3951  (<xref target="POST"/>)
3952</t>
3953<t>
3954  Remove requirement to handle all Content-* header fields; ban use of
3955  Content-Range with PUT.
3956  (<xref target="PUT"/>)
3957</t>
3958<t>
3959  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3960  (<xref target="CONNECT"/>)
3961</t>
3962<t>
3963  Broadened the definition of 203 (Non-Authoritative Information) to include
3964  cases of payload transformations as well.
3965  (<xref target="status.203"/>)
3966</t>
3967<t>
3968  Failed to consider that there are many other request methods that are safe
3969  to automatically redirect, and further that the user agent is able to make
3970  that determination based on the request method semantics.
3971  Furthermore, allow user agents to rewrite the method from POST to GET
3972  for status codes 301 and 302.
3973  (Sections <xref format="counter" target="status.301"/>,
3974  <xref format="counter" target="status.302"/> and
3975  <xref format="counter" target="status.307"/>)
3976</t>
3977<t>
3978  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3979  It used to indicate that the target resource must be accessed through the
3980  proxy given by the Location field. The Location field gave the URI of the
3981  proxy. The recipient was expected to repeat this single request via the proxy.
3982  (<xref target="status.305"/>)
3983</t>
3984<t>
3985  Define status 426 (Upgrade Required) (this was incorporated from
3986  <xref target="RFC2817"/>).
3987  (<xref target="status.426"/>)
3988</t>
3989<t>
3990  Change ABNF productions for header fields to only define the field value.
3991  (<xref target="header.field.definitions"/>)
3992</t>
3993<t>
3994  Reclassify "Allow" as response header field, removing the option to
3995  specify it in a PUT request.
3996  Relax the server requirement on the contents of the Allow header field and
3997  remove requirement on clients to always trust the header field value.
3998  (<xref target="header.allow"/>)
3999</t>
4000<t>
4001  Correct syntax of Location header field to allow URI references (including
4002  relative references and fragments), as referred symbol "absoluteURI" wasn't
4003  what was expected, and add some clarifications as to when use of fragments
4004  would not be appropriate.
4005  (<xref target="header.location"/>)
4006</t>
4007<t>
4008  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
4009  extension methods could have used it as well).
4010  (<xref target="header.max-forwards"/>)
4011</t>
4012<t>
4013  Allow Referer field value of "about:blank" as alternative to not specifying it.
4014  (<xref target="header.referer"/>)
4015</t>
4016<t>
4017  In the description of the Server header field, the Via field
4018  was described as a SHOULD. The requirement was and is stated
4019  correctly in the description of the Via header field in &header-via;.
4020  (<xref target="header.server"/>)
4021</t>
4022</section>
4023
4024<?BEGININC p2-semantics.abnf-appendix ?>
4025<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4026<figure>
4027<artwork type="abnf" name="p2-semantics.parsed-abnf">
4028<x:ref>Allow</x:ref> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
4029
4030<x:ref>Date</x:ref> = HTTP-date
4031
4032<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
4033
4034<x:ref>From</x:ref> = mailbox
4035
4036<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4037
4038<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4039
4040<x:ref>Location</x:ref> = URI-reference
4041
4042<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4043<x:ref>Method</x:ref> = token
4044
4045<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
4046
4047<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 1.2.2&gt;
4048<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4049<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4050<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4051
4052<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4053<x:ref>Status-Code</x:ref> = 3DIGIT
4054
4055<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4056<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4057
4058<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4059<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4060
4061<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2&gt;
4062
4063<x:ref>date1</x:ref> = day SP month SP year
4064<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4065<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4066<x:ref>day</x:ref> = 2DIGIT
4067<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4068 / %x54.75.65 ; Tue
4069 / %x57.65.64 ; Wed
4070 / %x54.68.75 ; Thu
4071 / %x46.72.69 ; Fri
4072 / %x53.61.74 ; Sat
4073 / %x53.75.6E ; Sun
4074<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4075 / %x54.75.65.73.64.61.79 ; Tuesday
4076 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4077 / %x54.68.75.72.73.64.61.79 ; Thursday
4078 / %x46.72.69.64.61.79 ; Friday
4079 / %x53.61.74.75.72.64.61.79 ; Saturday
4080 / %x53.75.6E.64.61.79 ; Sunday
4081<x:ref>delta-seconds</x:ref> = 1*DIGIT
4082
4083<x:ref>expect-param</x:ref> = token [ "=" ( token / quoted-string ) ]
4084<x:ref>expectation</x:ref> = "100-continue" / expectation-extension
4085<x:ref>expectation-extension</x:ref> = token [ "=" ( token / quoted-string ) *( ";"
4086 expect-param ) ]
4087
4088<x:ref>hour</x:ref> = 2DIGIT
4089
4090<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4091<x:ref>minute</x:ref> = 2DIGIT
4092<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4093 / %x46.65.62 ; Feb
4094 / %x4D.61.72 ; Mar
4095 / %x41.70.72 ; Apr
4096 / %x4D.61.79 ; May
4097 / %x4A.75.6E ; Jun
4098 / %x4A.75.6C ; Jul
4099 / %x41.75.67 ; Aug
4100 / %x53.65.70 ; Sep
4101 / %x4F.63.74 ; Oct
4102 / %x4E.6F.76 ; Nov
4103 / %x44.65.63 ; Dec
4104
4105<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4106<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 1.2.2&gt;
4107
4108<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4109<x:ref>product</x:ref> = &lt;product, defined in [Part1], Section 5.2&gt;
4110
4111<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.3&gt;
4112
4113<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4114<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4115
4116<x:ref>second</x:ref> = 2DIGIT
4117
4118<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4119<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.3&gt;
4120
4121<x:ref>year</x:ref> = 4DIGIT
4122</artwork>
4123</figure>
4124<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4125; Allow defined but not used
4126; Date defined but not used
4127; Expect defined but not used
4128; From defined but not used
4129; Location defined but not used
4130; Max-Forwards defined but not used
4131; Reason-Phrase defined but not used
4132; Referer defined but not used
4133; Retry-After defined but not used
4134; Server defined but not used
4135; Status-Code defined but not used
4136; User-Agent defined but not used
4137</artwork></figure></section>
4138<?ENDINC p2-semantics.abnf-appendix ?>
4139
4140<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4141
4142<section title="Since RFC 2616">
4143<t>
4144  Extracted relevant partitions from <xref target="RFC2616"/>.
4145</t>
4146</section>
4147
4148<section title="Since draft-ietf-httpbis-p2-semantics-00">
4149<t>
4150  Closed issues:
4151  <list style="symbols"> 
4152    <t>
4153      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4154      "Via is a MUST"
4155      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4156    </t>
4157    <t>
4158      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4159      "Fragments allowed in Location"
4160      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4161    </t>
4162    <t>
4163      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4164      "Safe Methods vs Redirection"
4165      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4166    </t>
4167    <t>
4168      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4169      "Revise description of the POST method"
4170      (<eref target="http://purl.org/NET/http-errata#post"/>)
4171    </t>
4172    <t>
4173      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4174      "Normative and Informative references"
4175    </t>
4176    <t>
4177      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4178      "RFC2606 Compliance"
4179    </t>
4180    <t>
4181      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4182      "Informative references"
4183    </t>
4184    <t>
4185      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4186      "Redundant cross-references"
4187    </t>
4188  </list>
4189</t>
4190<t>
4191  Other changes:
4192  <list style="symbols"> 
4193    <t>
4194      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4195    </t>
4196  </list>
4197</t>
4198</section>
4199
4200<section title="Since draft-ietf-httpbis-p2-semantics-01">
4201<t>
4202  Closed issues:
4203  <list style="symbols"> 
4204    <t>
4205      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4206      "PUT side effects"
4207    </t>
4208    <t>
4209      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4210      "Duplicate Host header requirements"
4211    </t>
4212  </list>
4213</t>
4214<t>
4215  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4216  <list style="symbols"> 
4217    <t>
4218      Move "Product Tokens" section (back) into Part 1, as "token" is used
4219      in the definition of the Upgrade header field.
4220    </t>
4221    <t>
4222      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4223    </t>
4224    <t>
4225      Copy definition of delta-seconds from Part6 instead of referencing it.
4226    </t>
4227  </list>
4228</t>
4229</section>
4230
4231<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4232<t>
4233  Closed issues:
4234  <list style="symbols"> 
4235    <t>
4236      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4237      "Requiring Allow in 405 responses"
4238    </t>
4239    <t>
4240      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4241      "Status Code Registry"
4242    </t>
4243    <t>
4244      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4245      "Redirection vs. Location"
4246    </t>
4247    <t>
4248      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4249      "Cacheability of 303 response"
4250    </t>
4251    <t>
4252      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4253      "305 Use Proxy"
4254    </t>
4255    <t>
4256      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4257      "Classification for Allow header"
4258    </t>
4259    <t>
4260      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4261      "PUT - 'store under' vs 'store at'"
4262    </t>
4263  </list>
4264</t>
4265<t>
4266  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4267  <list style="symbols"> 
4268    <t>
4269      Reference RFC 3984, and update header field registrations for headers defined
4270      in this document.
4271    </t>
4272  </list>
4273</t>
4274<t>
4275  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4276  <list style="symbols"> 
4277    <t>
4278      Replace string literals when the string really is case-sensitive (method).
4279    </t>
4280  </list>
4281</t>
4282</section>
4283
4284<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4285<t>
4286  Closed issues:
4287  <list style="symbols"> 
4288    <t>
4289      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4290      "OPTIONS request bodies"
4291    </t>
4292    <t>
4293      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4294      "Description of CONNECT should refer to RFC2817"
4295    </t>
4296    <t>
4297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4298      "Location Content-Location reference request/response mixup"
4299    </t>
4300  </list>
4301</t>
4302<t>
4303  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4304  <list style="symbols"> 
4305    <t>
4306      Added initial proposal for registration process, plus initial
4307      content (non-HTTP/1.1 methods to be added by a separate specification).
4308    </t>
4309  </list>
4310</t>
4311</section>
4312
4313<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4314<t>
4315  Closed issues:
4316  <list style="symbols"> 
4317    <t>
4318      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4319      "Content-*"
4320    </t>
4321    <t>
4322      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4323      "RFC 2822 is updated by RFC 5322"
4324    </t>
4325  </list>
4326</t>
4327<t>
4328  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4329  <list style="symbols"> 
4330    <t>
4331      Use "/" instead of "|" for alternatives.
4332    </t>
4333    <t>
4334      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4335      whitespace ("OWS") and required whitespace ("RWS").
4336    </t>
4337    <t>
4338      Rewrite ABNFs to spell out whitespace rules, factor out
4339      header field value format definitions.
4340    </t>
4341  </list>
4342</t>
4343</section>
4344
4345<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4346<t>
4347  Closed issues:
4348  <list style="symbols"> 
4349    <t>
4350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4351      "Reason-Phrase BNF"
4352    </t>
4353  </list>
4354</t>
4355<t>
4356  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4357  <list style="symbols"> 
4358    <t>
4359      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4360    </t>
4361  </list>
4362</t>
4363</section>
4364
4365<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4366<t>
4367  Closed issues:
4368  <list style="symbols"> 
4369    <t>
4370      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4371      "Clarify when Referer is sent"
4372    </t>
4373    <t>
4374      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4375      "status codes vs methods"
4376    </t>
4377    <t>
4378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4379      "Do not require "updates" relation for specs that register status codes or method names"
4380    </t>
4381  </list>
4382</t>
4383</section>
4384
4385<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4386<t>
4387  Closed issues:
4388  <list style="symbols"> 
4389    <t>
4390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4391      "Idempotency"
4392    </t>
4393    <t>
4394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4395      "TRACE security considerations"
4396    </t>
4397    <t>
4398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4399      "Clarify rules for determining what entities a response carries"
4400    </t>
4401    <t>
4402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4403      "update note citing RFC 1945 and 2068"
4404    </t>
4405    <t>
4406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4407      "update note about redirect limit"
4408    </t>
4409    <t>
4410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4411      "Location header ABNF should use 'URI'"
4412    </t>
4413    <t>
4414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4415      "fragments in Location vs status 303"
4416    </t>
4417    <t>
4418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4419      "move IANA registrations for optional status codes"
4420    </t>
4421  </list>
4422</t>
4423<t>
4424  Partly resolved issues:
4425  <list style="symbols"> 
4426    <t>
4427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4428      "Are OPTIONS and TRACE safe?"
4429    </t>
4430  </list>
4431</t>
4432</section>
4433
4434<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4435<t>
4436  Closed issues:
4437  <list style="symbols"> 
4438    <t>
4439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4440      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4441      status codes when fixing this previously)
4442    </t>
4443  </list>
4444</t>
4445</section>
4446
4447<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4448<t>
4449  Closed issues:
4450  <list style="symbols"> 
4451    <t>
4452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4453      "Fragment combination / precedence during redirects"
4454    </t>
4455  </list>
4456</t>
4457<t>
4458  Partly resolved issues:
4459  <list style="symbols"> 
4460    <t>
4461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4462      "Location header payload handling"
4463    </t>
4464    <t>
4465      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4466      "Term for the requested resource's URI"
4467    </t>
4468  </list>
4469</t>
4470</section>
4471
4472<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4473<t>
4474  Closed issues:
4475  <list style="symbols"> 
4476    <t>
4477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4478      "Clarify 'Requested Variant'"
4479    </t>
4480    <t>
4481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4482      "Clarify entity / representation / variant terminology"
4483    </t>
4484    <t>
4485      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4486      "Methods and Caching"
4487    </t>
4488    <t>
4489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4490      "OPTIONS vs Max-Forwards"
4491    </t>
4492    <t>
4493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4494      "Status codes and caching"
4495    </t>
4496    <t>
4497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4498      "consider removing the 'changes from 2068' sections"
4499    </t>
4500  </list>
4501</t>
4502</section>
4503
4504<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4505<t>
4506  Closed issues:
4507  <list style="symbols"> 
4508    <t>
4509      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4510      "Considerations for new status codes"
4511    </t>
4512    <t>
4513      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4514      "Considerations for new methods"
4515    </t>
4516    <t>
4517      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4518      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4519    </t>
4520  </list>
4521</t>
4522</section>
4523
4524<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4525<t>
4526  Closed issues:
4527  <list style="symbols"> 
4528    <t>
4529      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4530      "Fragment combination / precedence during redirects" (added warning
4531      about having a fragid on the redirect may cause inconvenience in
4532      some cases)
4533    </t>
4534    <t>
4535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4536      "Content-* vs. PUT"
4537    </t>
4538    <t>
4539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4540      "205 Bodies"
4541    </t>
4542    <t>
4543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4544      "Understanding Content-* on non-PUT requests"
4545    </t>
4546    <t>
4547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4548      "Content-*"
4549    </t>
4550    <t>
4551      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4552      "Header type defaulting"
4553    </t>
4554    <t>
4555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4556      "PUT - 'store under' vs 'store at'"
4557    </t>
4558    <t>
4559      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4560      "duplicate ABNF for Reason-Phrase"
4561    </t>
4562    <t>
4563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4564      "Note special status of Content-* prefix in header registration procedures"
4565    </t>
4566    <t>
4567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4568      "Max-Forwards vs extension methods"
4569    </t>
4570    <t>
4571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4572      "What is the value space of HTTP status codes?" (actually fixed in
4573      draft-ietf-httpbis-p2-semantics-11)
4574    </t>
4575    <t>
4576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4577      "Header Classification"
4578    </t>
4579    <t>
4580      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4581      "PUT side effect: invalidation or just stale?"
4582    </t>
4583    <t>
4584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4585      "proxies not supporting certain methods"
4586    </t>
4587    <t>
4588      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4589      "Migrate CONNECT from RFC2817 to p2"
4590    </t>
4591    <t>
4592      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4593      "Migrate Upgrade details from RFC2817"
4594    </t>
4595    <t>
4596      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4597      "clarify PUT semantics'"
4598    </t>
4599    <t>
4600      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4601      "duplicate ABNF for 'Method'"
4602    </t>
4603    <t>
4604      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4605      "untangle ABNFs for header fields"
4606    </t>
4607  </list>
4608</t>
4609</section>
4610
4611<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4612<t>
4613  Closed issues:
4614  <list style="symbols"> 
4615    <t>
4616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4617      "untangle ABNFs for header fields"
4618    </t>
4619    <t>
4620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4621      "message-body in CONNECT request"
4622    </t>
4623  </list>
4624</t>
4625</section>
4626
4627<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4628<t>
4629  Closed issues:
4630  <list style="symbols"> 
4631    <t>
4632      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4633      "Clarify status code for rate limiting"
4634    </t>
4635    <t>
4636      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4637      "clarify 403 forbidden"
4638    </t>
4639    <t>
4640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4641      "Clarify 203 Non-Authoritative Information"
4642    </t>
4643    <t>
4644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4645      "update default reason phrase for 413"
4646    </t>
4647  </list>
4648</t>
4649</section>
4650
4651<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4652<t>
4653  Closed issues:
4654  <list style="symbols"> 
4655    <t>
4656      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4657      "Strength of requirements on Accept re: 406"
4658    </t>
4659    <t>
4660      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4661      "400 response isn't generic"
4662    </t>
4663  </list>
4664</t>
4665</section>
4666
4667<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4668<t>
4669  Closed issues:
4670  <list style="symbols"> 
4671    <t>
4672      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4673      "Redirects and non-GET methods"
4674    </t>
4675    <t>
4676      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4677      "Document HTTP's error-handling philosophy"
4678    </t>
4679    <t>
4680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4681      "Considerations for new headers"
4682    </t>
4683    <t>
4684      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4685      "clarify 303 redirect on HEAD"
4686    </t>
4687  </list>
4688</t>
4689</section>
4690
4691<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4692<t>
4693  Closed issues:
4694  <list style="symbols"> 
4695    <t>
4696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4697      "Clarify status code for rate limiting" (change backed out because
4698      a new status code is being defined for this purpose)
4699    </t>
4700    <t>
4701      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4702      "should there be a permanent variant of 307"
4703    </t>
4704  </list>
4705</t>
4706</section>
4707
4708</section>
4709
4710</back>
4711</rfc>
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