source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1459

Last change on this file since 1459 was 1458, checked in by julian.reschke@…, 8 years ago

Recommend header field syntax where field-recombination using "," can be detected (see #231)

  • Property svn:eol-style set to native
File size: 193.1 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 "October">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY architecture               "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY agent-driven-negotiation   "<xref target='Part3' x:rel='#agent-driven.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY field-rules                "<xref target='Part1' x:rel='#field.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY intermediaries             "<xref target='Part1' x:rel='#intermediaries' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY chunked-encoding           "<xref target='Part1' x:rel='#chunked.encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY request-target             "<xref target='Part1' x:rel='#request-target' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-connection          "<xref target='Part1' x:rel='#header.connection' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-content-type        "<xref target='Part3' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-fields              "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
61  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
62  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
63  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
64  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
65  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
66  <!ENTITY header-upgrade             "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
67  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.te' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
68  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
69  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
70  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
71  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
72  <!ENTITY media-types                "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
73  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
74  <!ENTITY product-tokens             "<xref target='Part1' x:rel='#product.tokens' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
75  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
76  <!ENTITY status-206                 "<xref target='Part5' x:rel='#status.206' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
77  <!ENTITY status-304                 "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
78  <!ENTITY status-401                 "<xref target='Part7' x:rel='#status.401' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
79  <!ENTITY status-407                 "<xref target='Part7' x:rel='#status.407' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
80  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
81  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
82  <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
83  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
84  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
85  <!ENTITY p7-status-codes            "<xref target='Part7' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
86  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
87  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
88  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
89]>
90<?rfc toc="yes" ?>
91<?rfc symrefs="yes" ?>
92<?rfc sortrefs="yes" ?>
93<?rfc compact="yes"?>
94<?rfc subcompact="no" ?>
95<?rfc linkmailto="no" ?>
96<?rfc editing="no" ?>
97<?rfc comments="yes"?>
98<?rfc inline="yes"?>
99<?rfc rfcedstyle="yes"?>
100<?rfc-ext allow-markup-in-artwork="yes" ?>
101<?rfc-ext include-references-in-index="yes" ?>
102<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
103     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
104     xmlns:x='http://purl.org/net/xml2rfc/ext'
105     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
106<front>
107
108  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
109
110  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
111    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
112    <address>
113      <postal>
114        <street>345 Park Ave</street>
115        <city>San Jose</city>
116        <region>CA</region>
117        <code>95110</code>
118        <country>USA</country>
119      </postal>
120      <email>fielding@gbiv.com</email>
121      <uri>http://roy.gbiv.com/</uri>
122    </address>
123  </author>
124
125  <author initials="J." surname="Gettys" fullname="Jim Gettys">
126    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
127    <address>
128      <postal>
129        <street>21 Oak Knoll Road</street>
130        <city>Carlisle</city>
131        <region>MA</region>
132        <code>01741</code>
133        <country>USA</country>
134      </postal>
135      <email>jg@freedesktop.org</email>
136      <uri>http://gettys.wordpress.com/</uri>
137    </address>
138  </author>
139 
140  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
141    <organization abbrev="HP">Hewlett-Packard Company</organization>
142    <address>
143      <postal>
144        <street>HP Labs, Large Scale Systems Group</street>
145        <street>1501 Page Mill Road, MS 1177</street>
146        <city>Palo Alto</city>
147        <region>CA</region>
148        <code>94304</code>
149        <country>USA</country>
150      </postal>
151      <email>JeffMogul@acm.org</email>
152    </address>
153  </author>
154
155  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
156    <organization abbrev="Microsoft">Microsoft Corporation</organization>
157    <address>
158      <postal>
159        <street>1 Microsoft Way</street>
160        <city>Redmond</city>
161        <region>WA</region>
162        <code>98052</code>
163        <country>USA</country>
164      </postal>
165      <email>henrikn@microsoft.com</email>
166    </address>
167  </author>
168
169  <author initials="L." surname="Masinter" fullname="Larry Masinter">
170    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
171    <address>
172      <postal>
173        <street>345 Park Ave</street>
174        <city>San Jose</city>
175        <region>CA</region>
176        <code>95110</code>
177        <country>USA</country>
178      </postal>
179      <email>LMM@acm.org</email>
180      <uri>http://larry.masinter.net/</uri>
181    </address>
182  </author>
183 
184  <author initials="P." surname="Leach" fullname="Paul J. Leach">
185    <organization abbrev="Microsoft">Microsoft Corporation</organization>
186    <address>
187      <postal>
188        <street>1 Microsoft Way</street>
189        <city>Redmond</city>
190        <region>WA</region>
191        <code>98052</code>
192      </postal>
193      <email>paulle@microsoft.com</email>
194    </address>
195  </author>
196   
197  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
198    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
199    <address>
200      <postal>
201        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
202        <street>The Stata Center, Building 32</street>
203        <street>32 Vassar Street</street>
204        <city>Cambridge</city>
205        <region>MA</region>
206        <code>02139</code>
207        <country>USA</country>
208      </postal>
209      <email>timbl@w3.org</email>
210      <uri>http://www.w3.org/People/Berners-Lee/</uri>
211    </address>
212  </author>
213
214  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
215    <organization abbrev="W3C">World Wide Web Consortium</organization>
216    <address>
217      <postal>
218        <street>W3C / ERCIM</street>
219        <street>2004, rte des Lucioles</street>
220        <city>Sophia-Antipolis</city>
221        <region>AM</region>
222        <code>06902</code>
223        <country>France</country>
224      </postal>
225      <email>ylafon@w3.org</email>
226      <uri>http://www.raubacapeu.net/people/yves/</uri>
227    </address>
228  </author>
229
230  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
231    <organization abbrev="greenbytes">greenbytes GmbH</organization>
232    <address>
233      <postal>
234        <street>Hafenweg 16</street>
235        <city>Muenster</city><region>NW</region><code>48155</code>
236        <country>Germany</country>
237      </postal>
238      <phone>+49 251 2807760</phone>
239      <facsimile>+49 251 2807761</facsimile>
240      <email>julian.reschke@greenbytes.de</email>
241      <uri>http://greenbytes.de/tech/webdav/</uri>
242    </address>
243  </author>
244
245  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
246  <workgroup>HTTPbis Working Group</workgroup>
247
248<abstract>
249<t>
250   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
251   distributed, collaborative, hypertext information systems. HTTP has been in
252   use by the World Wide Web global information initiative since 1990. This
253   document is Part 2 of the seven-part specification that defines the protocol
254   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
255</t>
256<t>
257   Part 2 defines the semantics of HTTP messages as expressed by request
258   methods, request header fields, response status codes, and response header
259   fields.
260</t>
261</abstract>
262
263<note title="Editorial Note (To be removed by RFC Editor)">
264  <t>
265    Discussion of this draft should take place on the HTTPBIS working group
266    mailing list (ietf-http-wg@w3.org), which is archived at
267    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
268  </t>
269  <t>
270    The current issues list is at
271    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
272    documents (including fancy diffs) can be found at
273    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
274  </t>
275  <t>
276    The changes in this draft are summarized in <xref target="changes.since.16"/>.
277  </t>
278</note>
279</front>
280<middle>
281<section title="Introduction" anchor="introduction">
282<t>
283   This document defines HTTP/1.1 request and response semantics.  Each HTTP
284   message, as defined in &messaging;, is in the form of either a request or
285   a response.  An HTTP server listens on a connection for HTTP requests and
286   responds to each request, in the order received on that connection, with
287   one or more HTTP response messages.  This document defines the commonly
288   agreed upon semantics of the HTTP uniform interface, the intentions defined
289   by each request method, and the various response messages that might be
290   expected as a result of applying that method to the target resource.
291</t>
292<t>
293   This document is currently disorganized in order to minimize the changes
294   between drafts and enable reviewers to see the smaller errata changes.
295   A future draft will reorganize the sections to better reflect the content.
296   In particular, the sections will be ordered according to the typical
297   processing of an HTTP request message (after message parsing): resource
298   mapping, methods, request modifying header fields, response status,
299   status modifying header fields, and resource metadata.  The current mess
300   reflects how widely dispersed these topics and associated requirements
301   had become in <xref target="RFC2616"/>.
302</t>
303
304<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
305<t>
306   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
307   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
308   document are to be interpreted as described in <xref target="RFC2119"/>.
309</t>
310<t>
311   This document defines conformance criteria for several roles in HTTP
312   communication, including Senders, Recipients, Clients, Servers, User-Agents,
313   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
314   for definitions of these terms.
315</t>
316<t>
317   An implementation is considered conformant if it complies with all of the
318   requirements associated with its role(s). Note that SHOULD-level requirements
319   are relevant here, unless one of the documented exceptions is applicable.
320</t>
321<t>
322   This document also uses ABNF to define valid protocol elements
323   (<xref target="notation"/>). In addition to the prose requirements placed
324   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
325</t>
326<t>
327   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
328   protocol element from an invalid construct. However, HTTP does not define
329   specific error handling mechanisms, except in cases where it has direct
330   impact on security. This is because different uses of the protocol require
331   different error handling strategies; for example, a Web browser may wish to
332   transparently recover from a response where the Location header field
333   doesn't parse according to the ABNF, whereby in a systems control protocol
334   using HTTP, this type of error recovery could lead to dangerous consequences.
335</t>
336</section>
337
338<section title="Syntax Notation" anchor="notation">
339  <x:anchor-alias value="CR"/>
340  <x:anchor-alias value="DIGIT"/>
341  <x:anchor-alias value="LF"/>
342  <x:anchor-alias value="HTAB"/>
343  <x:anchor-alias value="VCHAR"/>
344  <x:anchor-alias value="SP"/>
345<t>
346  This specification uses the ABNF syntax defined in &notation; (which
347  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
348  <xref target="collected.abnf"/> shows the collected ABNF, with the list
349  rule expanded.
350</t>
351<t>
352  The following core rules are included by
353  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
354  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
355  DIGIT (decimal 0-9), DQUOTE (double quote),
356  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
357  OCTET (any 8-bit sequence of data), SP (space), and
358  VCHAR (any visible US-ASCII character).
359</t>
360
361<section title="Core Rules" anchor="core.rules">
362  <x:anchor-alias value="obs-text"/>
363  <x:anchor-alias value="quoted-string"/>
364  <x:anchor-alias value="token"/>
365  <x:anchor-alias value="OWS"/>
366  <x:anchor-alias value="RWS"/>
367<t>
368  The core rules below are defined in <xref target="Part1"/>:
369</t>
370<figure><artwork type="abnf2616">
371  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
372  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &basic-rules;&gt;
373  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &basic-rules;&gt;
374  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-rules;&gt;
375  <x:ref>token</x:ref>         = &lt;token, defined in &field-rules;&gt;
376</artwork></figure>
377</section>
378
379<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
380  <x:anchor-alias value="absolute-URI"/>
381  <x:anchor-alias value="comment"/>
382  <x:anchor-alias value="partial-URI"/>
383  <x:anchor-alias value="product"/>
384  <x:anchor-alias value="URI-reference"/>
385<t>
386  The ABNF rules below are defined in other parts:
387</t>
388<figure><!--Part1--><artwork type="abnf2616">
389  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
390  <x:ref>comment</x:ref>       = &lt;comment, defined in &header-fields;&gt;
391  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
392  <x:ref>product</x:ref>       = &lt;product, defined in &product-tokens;&gt;
393  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
394</artwork></figure>
395</section>
396</section>
397</section>
398
399<section title="Method" anchor="method">
400  <x:anchor-alias value="Method"/>
401  <x:anchor-alias value="extension-method"/>
402<t>
403   The Method token indicates the request method to be performed on the target
404   resource (&effective-request-uri;). The method is case-sensitive.
405</t>
406<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
407  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
408</artwork></figure>
409<t>
410   The list of methods allowed by a resource can be specified in an
411   Allow header field (<xref target="header.allow"/>). The status code of the response
412   always notifies the client whether a method is currently allowed on a
413   resource, since the set of allowed methods can change dynamically. An
414   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
415   if the method is known by the origin server but not allowed for the
416   resource, and 501 (Not Implemented) if the method is
417   unrecognized or not implemented by the origin server. The methods GET
418   and HEAD &MUST; be supported by all general-purpose servers. All other
419   methods are &OPTIONAL;; however, if the above methods are implemented,
420   they &MUST; be implemented with the same semantics as those specified
421   in <xref target="method.definitions"/>.
422</t>
423
424<section title="Overview of Methods" anchor="overview.of.methods">
425<t>
426  The methods listed below are defined in <xref target="method.definitions"/>.
427</t>
428<texttable align="left">
429  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
430 
431  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
432  <c>GET</c> <c><xref target="GET"/></c>
433  <c>HEAD</c> <c><xref target="HEAD"/></c>
434  <c>POST</c> <c><xref target="POST"/></c>
435  <c>PUT</c> <c><xref target="PUT"/></c>
436  <c>DELETE</c> <c><xref target="DELETE"/></c>
437  <c>TRACE</c> <c><xref target="TRACE"/></c>
438  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
439</texttable>
440<t>
441  Note that this list is not exhaustive &mdash; it does not include request methods defined
442  in other specifications.
443</t>
444</section>
445
446<section title="Method Registry" anchor="method.registry">
447<t>
448  The HTTP Method Registry defines the name space for the Method token in the
449  Request line of an HTTP request.
450</t>
451<t>
452  Registrations &MUST; include the following fields:
453  <list style="symbols">
454    <t>Method Name (see <xref target="method"/>)</t>
455    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
456    <t>Pointer to specification text</t>
457  </list>
458</t>
459<t>
460  Values to be added to this name space are subject to IETF review
461  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
462</t>
463<t>
464  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
465</t>
466
467<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
468<t>
469   When it is necessary to express new semantics for a HTTP request that
470   aren't specific to a single application or media type, and currently defined
471   methods are inadequate, it may be appropriate to register a new method.
472</t>
473<t>
474   HTTP methods are generic; that is, they are potentially applicable to any
475   resource, not just one particular media type, "type" of resource, or
476   application. As such, it is preferred that new HTTP methods be registered
477   in a document that isn't specific to a single application, so that this is
478   clear.
479</t>
480<t>
481   Due to the parsing rules defined in &message-body;, definitions of HTTP
482   methods cannot prohibit the presence of a message-body on either the request
483   or the response message (with responses to HEAD requests being the single
484   exception). Definitions of new methods cannot change this rule, but they can
485   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
486</t>
487<t>
488   New method definitions need to indicate whether they are safe (<xref
489   target="safe.methods"/>), what semantics (if any) the request body has,
490   and whether they are idempotent (<xref target="idempotent.methods"/>).
491   They also need to state whether they can be cached (&caching;); in
492   particular what conditions a cache may store the response, and under what
493   conditions such a stored response may be used to satisfy a subsequent
494   request.
495</t>
496</section>
497
498</section>
499</section>
500
501<section title="Header Fields" anchor="header.fields">
502<t>
503   Header fields are key value pairs that can be used to communicate data about
504   the message, its payload, the target resource, or about the connection
505   itself (i.e., control data).  See &header-fields; for a general definition
506   of their syntax.
507</t>
508
509<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
510<t>
511   New header fields are registered using the procedures described in
512   <xref target="RFC3864"/>.
513</t>
514<t>
515   The requirements for header field names are defined in
516   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
517   defining new fields are advised to keep the name as short as practical, and
518   not to prefix them with "X-" if they are to be registered (either
519   immediately or in the future).
520</t>
521<t>
522   New header field values typically have their syntax defined using ABNF
523   (<xref target="RFC5234"/>), using the extensions defined in &notation-abnf;
524   as necessary, and are usually constrained to the range of ASCII characters.
525   Header fields needing a greater range of characters can use an encoding
526   such as the one defined in <xref target="RFC5987"/>.
527</t>
528<t>
529   Because commas (",") are used as a generic delimiter between field-values,
530   they need to be treated with care if they are allowed in the field-value's
531   payload. Typically, components that might contain a comma are protected with
532   double-quotes using the quoted-string ABNF production (&field-rules;).
533</t>
534<t>
535   For example, a textual date and a URI (either of which might contain a comma)
536   could be safely carried in field-values like these:
537</t>
538<figure><artwork type="example">
539  Example-URI-Field: "http://example.com/a.html,foo",
540                     "http://without-a-comma.example.com/"
541  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
542</artwork></figure>
543<t>
544   Many header fields use a format including (case-insensitively) named
545   parameters (for instance, Content-Type, defined in &header-content-type;).
546   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
547   parameter value enables recipients to use existing parser components. Also,
548   the meaning of a value ought to be independent of the syntax variant used
549   for it (for an example, see the notes on parameter handling for media types
550   in &media-types;).
551</t>
552<t>
553   Authors of specifications defining new header fields are advised to consider
554   documenting:
555  <list style="symbols">
556    <x:lt>
557      <t>Whether the field is a single value, or whether it can be a list
558      (delimited by commas; see &header-fields;).</t>
559      <t>If it does not use the list syntax, how to treat messages where the
560      header field occurs multiple times (a sensible default would be to ignore
561      the header field, but this might not always be the right choice).</t>
562      <t>Furthermore, intermediaries and software libraries might combine
563      multiple header field instances into a single one, despite the header
564      field not allowing this. A robust format enables recipients to discover
565      these situations (good example: "Content-Type", as the comma can only
566      appear inside quoted strings; bad example: "Location", as a comma can
567      occur inside a URI).</t>
568    </x:lt>
569    <x:lt><t>Under what conditions the header field can be used; e.g., only in
570    responses or requests, in all messages, only on responses to a particular
571    request method.</t></x:lt>
572    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
573    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
574    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
575    field's value, insert or delete it.</t></x:lt>
576    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
577    <x:lt><t>Whether the header field is useful or allowable in trailers (see
578    &chunked-encoding;).</t></x:lt>
579    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
580  </list>
581</t>
582</section>
583
584<section title="Request Header Fields" anchor="request.header.fields">
585  <x:anchor-alias value="request-header"/>
586<t>
587   The request header fields allow the client to pass additional
588   information about the request, and about the client itself, to the
589   server. These fields act as request modifiers, with semantics
590   equivalent to the parameters on a programming language method
591   invocation.
592</t>
593<texttable align="left">
594  <ttcol>Header Field Name</ttcol>
595  <ttcol>Defined in...</ttcol>
596
597  <c>Accept</c> <c>&header-accept;</c>
598  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
599  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
600  <c>Accept-Language</c> <c>&header-accept-language;</c>
601  <c>Authorization</c> <c>&header-authorization;</c>
602  <c>Expect</c> <c><xref target="header.expect"/></c>
603  <c>From</c> <c><xref target="header.from"/></c>
604  <c>Host</c> <c>&header-host;</c>
605  <c>If-Match</c> <c>&header-if-match;</c>
606  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
607  <c>If-None-Match</c> <c>&header-if-none-match;</c>
608  <c>If-Range</c> <c>&header-if-range;</c>
609  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
610  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
611  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
612  <c>Range</c> <c>&header-range;</c>
613  <c>Referer</c> <c><xref target="header.referer"/></c>
614  <c>TE</c> <c>&header-te;</c>
615  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
616</texttable>
617</section>
618
619<section title="Response Header Fields" anchor="response.header.fields">
620  <x:anchor-alias value="response-header"/>
621<t>
622   The response header fields allow the server to pass additional
623   information about the response which cannot be placed in the Status-Line.
624   These header fields give information about the server and about
625   further access to the target resource (&effective-request-uri;).
626</t>
627<texttable align="left">
628  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
629
630  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
631  <c>Age</c> <c>&header-age;</c>
632  <c>Allow</c> <c><xref target="header.allow"/></c>
633  <c>Date</c> <c><xref target="header.date"/></c>
634  <c>ETag</c> <c>&header-etag;</c>
635  <c>Location</c> <c><xref target="header.location"/></c>
636  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
637  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
638  <c>Server</c> <c><xref target="header.server"/></c>
639  <c>Vary</c> <c>&header-vary;</c>
640  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
641</texttable>
642</section>
643
644</section>
645
646<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
647  <x:anchor-alias value="Reason-Phrase"/>
648  <x:anchor-alias value="Status-Code"/>
649  <x:anchor-alias value="extension-code"/>
650<t>
651   The Status-Code element is a 3-digit integer result code of the attempt to
652   understand and satisfy the request.
653</t>
654<t>
655   The Reason-Phrase is intended to give a short textual description of the
656   Status-Code and is intended for a human user. The client does not need
657   to examine or display the Reason-Phrase.
658</t>
659<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"/>
660  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
661  <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> )
662</artwork></figure>
663<t>
664   HTTP status codes are extensible. HTTP applications are not required
665   to understand the meaning of all registered status codes, though such
666   understanding is obviously desirable. However, applications &MUST;
667   understand the class of any status code, as indicated by the first
668   digit, and treat any unrecognized response as being equivalent to the
669   x00 status code of that class, with the exception that an
670   unrecognized response &MUST-NOT; be cached. For example, if an
671   unrecognized status code of 431 is received by the client, it can
672   safely assume that there was something wrong with its request and
673   treat the response as if it had received a 400 status code. In such
674   cases, user agents &SHOULD; present to the user the representation enclosed
675   with the response, since that representation is likely to include human-readable
676   information which will explain the unusual status.
677</t>
678
679<section title="Overview of Status Codes" anchor="overview.of.status.codes">
680<t> 
681   The status codes listed below are defined in <xref target="status.codes"/>
682   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
683   The reason phrases listed here are only recommendations &mdash; they can be
684   replaced by local equivalents without affecting the protocol.
685</t>
686<texttable align="left">
687  <ttcol>Status-Code</ttcol>
688  <ttcol>Reason-Phrase</ttcol>
689  <ttcol>Defined in...</ttcol>
690 
691  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
692  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
693
694  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
695  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
696  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
697  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
698  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
699  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
700  <c>206</c> <c>Partial Content</c> <c>&status-206;</c>
701
702  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
703  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
704  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
705  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
706  <c>304</c> <c>Not Modified</c> <c>&status-304;</c>
707  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
708  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
709
710  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
711  <c>401</c> <c>Unauthorized</c> <c>&status-401;</c>
712  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
713  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
714  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
715  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
716  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
717  <c>407</c> <c>Proxy Authentication Required</c> <c>&status-407;</c>
718  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
719  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
720  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
721  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
722  <c>412</c> <c>Precondition Failed</c> <c>&status-412;</c>
723  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
724  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
725  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
726  <c>416</c> <c>Requested range not satisfiable</c> <c>&status-416;</c>
727  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
728  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
729
730  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
731  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
732  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
733  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
734  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
735  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
736</texttable>
737<t>
738   Note that this list is not exhaustive &mdash; it does not include
739   extension status codes defined in other specifications.
740</t>
741</section>
742
743<section title="Status Code Registry" anchor="status.code.registry">
744<t>
745  The HTTP Status Code Registry defines the name space for the Status-Code
746  token in the Status-Line of an HTTP response.
747</t>
748<t>
749  Values to be added to this name space are subject to IETF review
750  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
751</t>
752<t>
753  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
754</t>
755
756<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
757<t>
758   When it is necessary to express new semantics for a HTTP response that
759   aren't specific to a single application or media type, and currently defined
760   status codes are inadequate, a new status code can be registered.
761</t>
762<t>
763   HTTP status codes are generic; that is, they are potentially applicable to
764   any resource, not just one particular media type, "type" of resource, or
765   application. As such, it is preferred that new HTTP status codes be
766   registered in a document that isn't specific to a single application, so
767   that this is clear.
768</t>
769<t>
770   Definitions of new HTTP status codes typically explain the request
771   conditions that produce a response containing the status code (e.g.,
772   combinations of request headers and/or method(s)), along with any
773   interactions with response headers (e.g., those that are required, those
774   that modify the semantics of the response).
775</t>
776<t>
777   New HTTP status codes are required to fall under one of the categories
778   defined in <xref target="status.codes"/>. To allow existing parsers to
779   properly handle them, new status codes cannot disallow a response body,
780   although they can mandate a zero-length response body. They can require the
781   presence of one or more particular HTTP response header(s).
782</t>
783<t>
784   Likewise, their definitions can specify that caches are allowed to use
785   heuristics to determine their freshness (see &caching;; by default, it is
786   not allowed), and can define how to determine the resource which they
787   carry a representation for (see <xref
788   target="identifying.response.associated.with.representation"/>; by default,
789   it is anonymous).
790</t>
791</section>
792
793</section>
794
795</section>
796
797<section title="Representation" anchor="representation">
798<t>
799   Request and Response messages &MAY; transfer a representation if not otherwise
800   restricted by the request method or response status code. A representation
801   consists of metadata (representation header fields) and data (representation
802   body).  When a complete or partial representation is enclosed in an HTTP message,
803   it is referred to as the payload of the message. HTTP representations
804   are defined in &payload;.
805</t>
806<t>
807   A representation body is only present in a message when a message-body is
808   present, as described in &message-body;. The representation body is obtained
809   from the message-body by decoding any Transfer-Encoding that might
810   have been applied to ensure safe and proper transfer of the message.
811</t>
812
813<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
814<t>
815   It is sometimes necessary to determine an identifier for the resource
816   associated with a representation.
817</t>
818<t>
819   An HTTP request representation, when present, is always associated with an
820   anonymous (i.e., unidentified) resource.
821</t>
822<t>
823   In the common case, an HTTP response is a representation of the target
824   resource (see &effective-request-uri;). However, this is not always the
825   case. To determine the URI of the resource a response is associated with,
826   the following rules are used (with the first applicable one being selected):
827</t>
828<t><list style="numbers">
829   <t>If the response status code is 200 or 203 and the request method was GET,
830   the response payload is a representation of the target resource.</t>
831   <t>If the response status code is 204, 206, or 304 and the request method was GET
832   or HEAD, the response payload is a partial representation of the target
833   resource.</t>
834   <t>If the response has a Content-Location header field, and that URI is the same
835   as the effective request URI, the response payload is a representation of the
836   target resource.</t>
837   <t>If the response has a Content-Location header field, and that URI is not the
838   same as the effective request URI, then the response asserts that its
839   payload is a representation of the resource identified by the
840   Content-Location URI. However, such an assertion cannot be trusted unless
841   it can be verified by other means (not defined by HTTP).</t>
842   <t>Otherwise, the response is a representation of an anonymous (i.e.,
843   unidentified) resource.</t>
844</list></t>
845<t>
846  <cref anchor="TODO-req-uri">
847   The comparison function is going to have to be defined somewhere,
848   because we already need to compare URIs for things like cache invalidation.</cref>
849</t>
850</section>
851
852</section>
853
854
855<section title="Method Definitions" anchor="method.definitions">
856<t>
857   The set of common request methods for HTTP/1.1 is defined below. Although
858   this set can be expanded, additional methods cannot be assumed to
859   share the same semantics for separately extended clients and servers.
860</t>
861
862<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
863
864<section title="Safe Methods" anchor="safe.methods">
865<iref item="Safe Methods" primary="true"/>
866<t>
867   Implementors need to be aware that the software represents the user in
868   their interactions over the Internet, and need to allow
869   the user to be aware of any actions they take which might have an
870   unexpected significance to themselves or others.
871</t>
872<t>
873   In particular, the convention has been established that the GET, HEAD,
874   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
875   of taking an action other than retrieval. These request methods ought
876   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
877   This allows user agents to represent other methods, such as POST, PUT
878   and DELETE, in a special way, so that the user is made aware of the
879   fact that a possibly unsafe action is being requested.
880</t>
881<t>
882   Naturally, it is not possible to ensure that the server does not
883   generate side-effects as a result of performing a GET request; in
884   fact, some dynamic resources consider that a feature. The important
885   distinction here is that the user did not request the side-effects,
886   so therefore cannot be held accountable for them.
887</t>
888</section>
889
890<section title="Idempotent Methods" anchor="idempotent.methods">
891<iref item="Idempotent Methods" primary="true"/>
892<t>
893   Request methods can also have the property of "idempotence" in that,
894   aside from error or expiration issues, the intended effect of multiple
895   identical requests is the same as for a single request.
896   PUT, DELETE, and all safe request methods are idempotent.
897   It is important to note that idempotence refers only to changes
898   requested by the client: a server is free to change its state due
899   to multiple requests for the purpose of tracking those requests,
900   versioning of results, etc.
901</t>
902</section>
903</section>
904
905<section title="OPTIONS" anchor="OPTIONS">
906  <rdf:Description>
907    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
908  </rdf:Description>
909  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
910  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
911<t>
912   The OPTIONS method requests information about the
913   communication options available on the request/response chain
914   identified by the effective request URI. This method allows a client to
915   determine the options and/or requirements associated with a resource,
916   or the capabilities of a server, without implying a resource action
917   or initiating a resource retrieval.
918</t>
919<t>
920   Responses to the OPTIONS method are not cacheable.
921</t>
922<t>
923   If the OPTIONS request includes a message-body (as indicated by the
924   presence of Content-Length or Transfer-Encoding), then the media type
925   &MUST; be indicated by a Content-Type field. Although this
926   specification does not define any use for such a body, future
927   extensions to HTTP might use the OPTIONS body to make more detailed
928   queries on the server.
929</t>
930<t>
931   If the request-target is an asterisk ("*"), the OPTIONS request is
932   intended to apply to the server in general rather than to a specific
933   resource. Since a server's communication options typically depend on
934   the resource, the "*" request is only useful as a "ping" or "no-op"
935   type of method; it does nothing beyond allowing the client to test
936   the capabilities of the server. For example, this can be used to test
937   a proxy for HTTP/1.1 compliance (or lack thereof).
938</t>
939<t>
940   If the request-target is not an asterisk, the OPTIONS request applies
941   only to the options that are available when communicating with that
942   resource.
943</t>
944<t>
945   A 200 response &SHOULD; include any header fields that indicate
946   optional features implemented by the server and applicable to that
947   resource (e.g., Allow), possibly including extensions not defined by
948   this specification. The response body, if any, &SHOULD; also include
949   information about the communication options. The format for such a
950   body is not defined by this specification, but might be defined by
951   future extensions to HTTP. Content negotiation &MAY; be used to select
952   the appropriate response format. If no response body is included, the
953   response &MUST; include a Content-Length field with a field-value of
954   "0".
955</t>
956<t>
957   The Max-Forwards header field &MAY; be used to target a
958   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
959   If no Max-Forwards field is present in the request, then the forwarded
960   request &MUST-NOT; include a Max-Forwards field.
961</t>
962</section>
963
964<section title="GET" anchor="GET">
965  <rdf:Description>
966    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
967  </rdf:Description>
968  <iref primary="true" item="GET method" x:for-anchor=""/>
969  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
970<t>
971   The GET method requests transfer of a current representation of
972   the target resource.
973</t>
974<t>   
975   If the target resource is a data-producing process, it is the
976   produced data which shall be returned as the representation in the response and not
977   the source text of the process, unless that text happens to be the output of
978   the process.
979</t>
980<t>
981   The semantics of the GET method change to a "conditional GET" if the
982   request message includes an If-Modified-Since, If-Unmodified-Since,
983   If-Match, If-None-Match, or If-Range header field. A conditional GET
984   requests that the representation be transferred only under the
985   circumstances described by the conditional header field(s). The
986   conditional GET request is intended to reduce unnecessary network
987   usage by allowing cached representations to be refreshed without requiring
988   multiple requests or transferring data already held by the client.
989</t>
990<t>
991   The semantics of the GET method change to a "partial GET" if the
992   request message includes a Range header field. A partial GET requests
993   that only part of the representation be transferred, as described in &header-range;.
994   The partial GET request is intended to reduce unnecessary
995   network usage by allowing partially-retrieved representations to be
996   completed without transferring data already held by the client.
997</t>
998<t>
999   Bodies on GET requests have no defined semantics. Note that sending a body
1000   on a GET request might cause some existing implementations to reject the
1001   request.
1002</t>
1003<t>
1004   The response to a GET request is cacheable and &MAY; be used to satisfy
1005   subsequent GET and HEAD requests (see &caching;).
1006</t>
1007<t>
1008   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
1009</t>
1010</section>
1011
1012<section title="HEAD" anchor="HEAD">
1013  <rdf:Description>
1014    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1015  </rdf:Description>
1016  <iref primary="true" item="HEAD method" x:for-anchor=""/>
1017  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
1018<t>
1019   The HEAD method is identical to GET except that the server &MUST-NOT;
1020   return a message-body in the response. The metadata contained
1021   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
1022   to the information sent in response to a GET request. This method can
1023   be used for obtaining metadata about the representation implied by the
1024   request without transferring the representation body. This method is
1025   often used for testing hypertext links for validity, accessibility,
1026   and recent modification.
1027</t>
1028<t>
1029   The response to a HEAD request is cacheable and &MAY; be used to satisfy
1030   a subsequent HEAD request; see &caching;. It also &MAY; be used to update a previously cached
1031   representation from that resource; if the new field values
1032   indicate that the cached representation differs from the current representation (as
1033   would be indicated by a change in Content-Length, ETag
1034   or Last-Modified), then the cache &MUST; treat the cache entry as
1035   stale.
1036</t>
1037<t>
1038   Bodies on HEAD requests have no defined semantics. Note that sending a body
1039   on a HEAD request might cause some existing implementations to reject the
1040   request.
1041</t>
1042</section>
1043
1044<section title="POST" anchor="POST">
1045  <iref primary="true" item="POST method" x:for-anchor=""/>
1046  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
1047<t>
1048   The POST method requests that the origin server accept the
1049   representation enclosed in the request as data to be processed by the
1050   target resource. POST is designed to allow a uniform method to cover the
1051   following functions:
1052  <list style="symbols">
1053    <t>
1054      Annotation of existing resources;
1055    </t>
1056    <t>
1057        Posting a message to a bulletin board, newsgroup, mailing list,
1058        or similar group of articles;
1059    </t>
1060    <t>
1061        Providing a block of data, such as the result of submitting a
1062        form, to a data-handling process;
1063    </t>
1064    <t>
1065        Extending a database through an append operation.
1066    </t>
1067  </list>
1068</t>
1069<t>
1070   The actual function performed by the POST method is determined by the
1071   server and is usually dependent on the effective request URI.
1072</t>
1073<t>
1074   The action performed by the POST method might not result in a
1075   resource that can be identified by a URI. In this case, either 200
1076   (OK) or 204 (No Content) is the appropriate response status code,
1077   depending on whether or not the response includes a representation that
1078   describes the result.
1079</t>
1080<t>
1081   If a resource has been created on the origin server, the response
1082   &SHOULD; be 201 (Created) and contain a representation which describes the
1083   status of the request and refers to the new resource, and a Location
1084   header field (see <xref target="header.location"/>).
1085</t>
1086<t>
1087   Responses to POST requests are only cacheable when they
1088   include explicit freshness information (see &p6-explicit;). A
1089   cached POST response with a Content-Location header field
1090   (see &header-content-location;) whose value is the effective
1091   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1092</t>
1093<t>
1094   Note that POST caching is not widely implemented.
1095   However, the 303 (See Other) response can be used to direct the
1096   user agent to retrieve a cacheable resource.
1097</t>
1098</section>
1099
1100<section title="PUT" anchor="PUT">
1101  <iref primary="true" item="PUT method" x:for-anchor=""/>
1102  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
1103<t>
1104   The PUT method requests that the state of the target resource
1105   be created or replaced with the state defined by the representation
1106   enclosed in the request message payload.  A successful PUT of a given
1107   representation would suggest that a subsequent GET on that same target
1108   resource will result in an equivalent representation being returned in
1109   a 200 (OK) response.  However, there is no guarantee that such a state
1110   change will be observable, since the target resource might be acted
1111   upon by other user agents in parallel, or might be subject to dynamic
1112   processing by the origin server, before any subsequent GET is received.
1113   A successful response only implies that the user agent's intent was
1114   achieved at the time of its processing by the origin server.
1115</t>
1116<t>   
1117   If the target resource does not have a current representation and
1118   the PUT successfully creates one, then the origin server &MUST; inform
1119   the user agent by sending a 201 (Created) response.  If the target
1120   resource does have a current representation and that representation is
1121   successfully modified in accordance with the state of the enclosed
1122   representation, then either a 200 (OK) or 204 (No Content) response
1123   &SHOULD; be sent to indicate successful completion of the request.
1124</t>
1125<t>
1126   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1127   as part of the resource state).
1128</t>
1129<t>
1130   An origin server &SHOULD; verify that the PUT representation is
1131   consistent with any constraints which the server has for the target
1132   resource that cannot or will not be changed by the PUT.  This is
1133   particularly important when the origin server uses internal
1134   configuration information related to the URI in order to set the
1135   values for representation metadata on GET responses.  When a PUT
1136   representation is inconsistent with the target resource, the origin
1137   server &SHOULD; either make them consistent, by transforming the
1138   representation or changing the resource configuration, or respond
1139   with an appropriate error message containing sufficient information
1140   to explain why the representation is unsuitable.  The 409 (Conflict)
1141   or 415 (Unsupported Media Type) status codes are suggested, with the
1142   latter being specific to constraints on Content-Type values.
1143</t>
1144<t>
1145   For example, if the target resource is configured to always have a
1146   Content-Type of "text/html" and the representation being PUT has a
1147   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1148   (a) reconfigure the target resource to reflect the new media type;
1149   (b) transform the PUT representation to a format consistent with that
1150   of the resource before saving it as the new resource state; or,
1151   (c) reject the request with a 415 response indicating that the target
1152   resource is limited to "text/html", perhaps including a link to a
1153   different resource that would be a suitable target for the new
1154   representation.
1155</t>
1156<t>
1157   HTTP does not define exactly how a PUT method affects the state
1158   of an origin server beyond what can be expressed by the intent of
1159   the user agent request and the semantics of the origin server response.
1160   It does not define what a resource might be, in any sense of that
1161   word, beyond the interface provided via HTTP.  It does not define
1162   how resource state is "stored", nor how such storage might change
1163   as a result of a change in resource state, nor how the origin server
1164   translates resource state into representations.  Generally speaking,
1165   all implementation details behind the resource interface are
1166   intentionally hidden by the server.
1167</t>
1168<t>
1169   The fundamental difference between the POST and PUT methods is
1170   highlighted by the different intent for the target resource.
1171   The target resource in a POST request is intended to handle the
1172   enclosed representation as a data-accepting process, such as for
1173   a gateway to some other protocol or a document that accepts annotations.
1174   In contrast, the target resource in a PUT request is intended to
1175   take the enclosed representation as a new or replacement value.
1176   Hence, the intent of PUT is idempotent and visible to intermediaries,
1177   even though the exact effect is only known by the origin server.
1178</t>
1179<t>
1180   Proper interpretation of a PUT request presumes that the user agent
1181   knows what target resource is desired.  A service that is intended
1182   to select a proper URI on behalf of the client, after receiving
1183   a state-changing request, &SHOULD; be implemented using the POST
1184   method rather than PUT.  If the origin server will not make the
1185   requested PUT state change to the target resource and instead
1186   wishes to have it applied to a different resource, such as when the
1187   resource has been moved to a different URI, then the origin server
1188   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
1189   then make its own decision regarding whether or not to redirect the
1190   request.
1191</t>
1192<t>
1193   A PUT request applied to the target resource &MAY; have side-effects
1194   on other resources.  For example, an article might have a URI for
1195   identifying "the current version" (a resource) which is separate
1196   from the URIs identifying each particular version (different
1197   resources that at one point shared the same state as the current version
1198   resource).  A successful PUT request on "the current version" URI might
1199   therefore create a new version resource in addition to changing the
1200   state of the target resource, and might also cause links to be added
1201   between the related resources.
1202</t>
1203<t>
1204   An origin server &SHOULD; reject any PUT request that contains a
1205   Content-Range header field, since it might be misinterpreted as
1206   partial content (or might be partial content that is being mistakenly
1207   PUT as a full representation).  Partial content updates are
1208   possible by targeting a separately identified resource with state
1209   that overlaps a portion of the larger resource, or by using a
1210   different method that has been specifically defined for partial
1211   updates (for example, the PATCH method defined in
1212   <xref target="RFC5789"/>).
1213</t>
1214<t>
1215   Responses to the PUT method are not cacheable. If a PUT request passes
1216   through a cache that has one or more stored responses for the effective
1217   request URI, those stored responses will be invalidated (see
1218   &p6-invalid;).
1219</t>
1220</section>
1221
1222<section title="DELETE" anchor="DELETE">
1223  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1224  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
1225<t>
1226   The DELETE method requests that the origin server delete the target
1227   resource. This method &MAY; be overridden by
1228   human intervention (or other means) on the origin server. The client cannot
1229   be guaranteed that the operation has been carried out, even if the
1230   status code returned from the origin server indicates that the action
1231   has been completed successfully. However, the server &SHOULD-NOT; 
1232   indicate success unless, at the time the response is given, it
1233   intends to delete the resource or move it to an inaccessible
1234   location.
1235</t>
1236<t>
1237   A successful response &SHOULD; be 200 (OK) if the response includes an
1238   representation describing the status, 202 (Accepted) if the action has not
1239   yet been enacted, or 204 (No Content) if the action has been enacted
1240   but the response does not include a representation.
1241</t>
1242<t>
1243   Bodies on DELETE requests have no defined semantics. Note that sending a body
1244   on a DELETE request might cause some existing implementations to reject the
1245   request.
1246</t>
1247<t>
1248   Responses to the DELETE method are not cacheable. If a DELETE request
1249   passes through a cache that has one or more stored responses for the
1250   effective request URI, those stored responses will be invalidated (see
1251   &p6-invalid;).
1252</t>
1253</section>
1254
1255<section title="TRACE" anchor="TRACE">
1256  <rdf:Description>
1257    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1258  </rdf:Description>
1259  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1260  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
1261<t>
1262   The TRACE method requests a remote, application-layer loop-back
1263   of the request message. The final recipient of the request
1264   &SHOULD; reflect the message received back to the client as the
1265   message-body of a 200 (OK) response. The final recipient is either the
1266   origin server or the first proxy to receive a Max-Forwards
1267   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1268   A TRACE request &MUST-NOT; include a message-body.
1269</t>
1270<t>
1271   TRACE allows the client to see what is being received at the other
1272   end of the request chain and use that data for testing or diagnostic
1273   information. The value of the Via header field (&header-via;) is of
1274   particular interest, since it acts as a trace of the request chain.
1275   Use of the Max-Forwards header field allows the client to limit the
1276   length of the request chain, which is useful for testing a chain of
1277   proxies forwarding messages in an infinite loop.
1278</t>
1279<t>
1280   If the request is valid, the response &SHOULD; have a Content-Type of
1281   "message/http" (see &media-type-message-http;) and contain a message-body
1282   that encloses a copy of the entire request message.
1283   Responses to the TRACE method are not cacheable.
1284</t>
1285</section>
1286
1287<section title="CONNECT" anchor="CONNECT">
1288  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1289  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1290<t>
1291   The CONNECT method requests that the proxy establish a tunnel
1292   to the request-target and then restrict its behavior to blind
1293   forwarding of packets until the connection is closed.
1294</t>
1295<t>
1296   When using CONNECT, the request-target &MUST; use the authority form
1297   (&request-target;); i.e., the request-target consists of only the
1298   host name and port number of the tunnel destination, separated by a colon.
1299   For example,
1300</t>
1301<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1302CONNECT server.example.com:80 HTTP/1.1
1303Host: server.example.com:80
1304
1305</artwork></figure>
1306<t>
1307   Other HTTP mechanisms can be used normally with the CONNECT method &mdash;
1308   except end-to-end protocol Upgrade requests, since the
1309   tunnel must be established first.
1310</t>
1311<t>
1312   For example, proxy authentication might be used to establish the
1313   authority to create a tunnel:
1314</t>
1315<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1316CONNECT server.example.com:80 HTTP/1.1
1317Host: server.example.com:80
1318Proxy-Authorization: basic aGVsbG86d29ybGQ=
1319
1320</artwork></figure>
1321<t>
1322   Bodies on CONNECT requests have no defined semantics. Note that sending a body
1323   on a CONNECT request might cause some existing implementations to reject the
1324   request.
1325</t>
1326<t>
1327   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1328   sent immediately after the blank line. The usual caveats also apply:
1329   data may be discarded if the eventual response is negative, and the
1330   connection may be reset with no response if more than one TCP segment
1331   is outstanding.
1332</t>
1333
1334<section title="Establishing a Tunnel with CONNECT">
1335<t>
1336   Any successful (2xx) response to a CONNECT request indicates that the
1337   proxy has established a connection to the requested host and port,
1338   and has switched to tunneling the current connection to that server
1339   connection.
1340</t>
1341<t>
1342   It may be the case that the proxy itself can only reach the requested
1343   origin server through another proxy.  In this case, the first proxy
1344   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1345   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1346   unless it has either a direct or tunnel connection established to the
1347   authority.
1348</t>
1349<t>
1350   An origin server which receives a CONNECT request for itself &MAY;
1351   respond with a 2xx status code to indicate that a connection is
1352   established.
1353</t>
1354<t>
1355   If at any point either one of the peers gets disconnected, any
1356   outstanding data that came from that peer will be passed to the other
1357   one, and after that also the other connection will be terminated by
1358   the proxy. If there is outstanding data to that peer undelivered,
1359   that data will be discarded.
1360</t>
1361
1362</section>
1363</section>
1364</section>
1365
1366
1367<section title="Status Code Definitions" anchor="status.codes">
1368<t>
1369   The first digit of the Status-Code defines the class of response. The
1370   last two digits do not have any categorization role. There are 5
1371   values for the first digit:
1372  <list style="symbols">
1373    <t>
1374      1xx: Informational - Request received, continuing process
1375    </t>
1376    <t>
1377      2xx: Success - The action was successfully received,
1378        understood, and accepted
1379    </t>
1380    <t>
1381      3xx: Redirection - Further action must be taken in order to
1382        complete the request
1383    </t>
1384    <t>
1385      4xx: Client Error - The request contains bad syntax or cannot
1386        be fulfilled
1387    </t>
1388    <t>
1389      5xx: Server Error - The server failed to fulfill an apparently
1390        valid request
1391    </t>
1392  </list>
1393</t>
1394<t>
1395   Each Status-Code is described below, including any metadata required
1396   in the response.
1397</t>
1398
1399<section title="Informational 1xx" anchor="status.1xx">
1400<t>
1401   This class of status code indicates a provisional response,
1402   consisting only of the Status-Line and optional header fields, and is
1403   terminated by an empty line. There are no required header fields for this
1404   class of status code. Since HTTP/1.0 did not define any 1xx status
1405   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1406   except under experimental conditions.
1407</t>
1408<t>
1409   A client &MUST; be prepared to accept one or more 1xx status responses
1410   prior to a regular response, even if the client does not expect a 100
1411   (Continue) status message. Unexpected 1xx status responses &MAY; be
1412   ignored by a user agent.
1413</t>
1414<t>
1415   Proxies &MUST; forward 1xx responses, unless the connection between the
1416   proxy and its client has been closed, or unless the proxy itself
1417   requested the generation of the 1xx response. (For example, if a
1418   proxy adds a "Expect: 100-continue" field when it forwards a request,
1419   then it need not forward the corresponding 100 (Continue)
1420   response(s).)
1421</t>
1422
1423<section title="100 Continue" anchor="status.100">
1424  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1425  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1426<t>
1427   The client &SHOULD; continue with its request. This interim response is
1428   used to inform the client that the initial part of the request has
1429   been received and has not yet been rejected by the server. The client
1430   &SHOULD; continue by sending the remainder of the request or, if the
1431   request has already been completed, ignore this response. The server
1432   &MUST; send a final response after the request has been completed. See
1433   &use100; for detailed discussion of the use and handling of this
1434   status code.
1435</t>
1436</section>
1437
1438<section title="101 Switching Protocols" anchor="status.101">
1439  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1440  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1441<t>
1442   The server understands and is willing to comply with the client's
1443   request, via the Upgrade message header field (&header-upgrade;), for a
1444   change in the application protocol being used on this connection. The
1445   server will switch protocols to those defined by the response's
1446   Upgrade header field immediately after the empty line which
1447   terminates the 101 response.
1448</t>
1449<t>
1450   The protocol &SHOULD; be switched only when it is advantageous to do
1451   so. For example, switching to a newer version of HTTP is advantageous
1452   over older versions, and switching to a real-time, synchronous
1453   protocol might be advantageous when delivering resources that use
1454   such features.
1455</t>
1456</section>
1457</section>
1458
1459<section title="Successful 2xx" anchor="status.2xx">
1460<t>
1461   This class of status code indicates that the client's request was
1462   successfully received, understood, and accepted.
1463</t>
1464
1465<section title="200 OK" anchor="status.200">
1466  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1467  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1468<t>
1469   The request has succeeded. The payload returned with the response
1470   is dependent on the method used in the request, for example:
1471  <list style="hanging">
1472    <t hangText="GET">
1473      a representation of the target resource is sent in the response;
1474    </t>
1475    <t hangText="HEAD">
1476      the same representation as GET, except without the message-body;
1477    </t>
1478    <t hangText="POST">
1479      a representation describing or containing the result of the action;
1480    </t>
1481    <t hangText="TRACE">
1482      a representation containing the request message as received by the
1483      end server.
1484    </t>
1485  </list>
1486</t>
1487<t>
1488   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1489   freshness for 200 responses.
1490</t>
1491</section>
1492
1493<section title="201 Created" anchor="status.201">
1494  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1495  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1496<t>
1497   The request has been fulfilled and has resulted in a new resource being
1498   created. The newly created resource can be referenced by the URI(s)
1499   returned in the payload of the response, with the most specific URI
1500   for the resource given by a Location header field. The response
1501   &SHOULD; include a payload containing a list of resource
1502   characteristics and location(s) from which the user or user agent can
1503   choose the one most appropriate. The payload format is specified by
1504   the media type given in the Content-Type header field. The origin
1505   server &MUST; create the resource before returning the 201 status code.
1506   If the action cannot be carried out immediately, the server &SHOULD;
1507   respond with 202 (Accepted) response instead.
1508</t>
1509<t>
1510   A 201 response &MAY; contain an ETag response header field indicating
1511   the current value of the entity-tag for the representation of the resource
1512   just created (see &header-etag;).
1513</t>
1514</section>
1515
1516<section title="202 Accepted" anchor="status.202">
1517  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1518  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1519<t>
1520   The request has been accepted for processing, but the processing has
1521   not been completed.  The request might or might not eventually be
1522   acted upon, as it might be disallowed when processing actually takes
1523   place. There is no facility for re-sending a status code from an
1524   asynchronous operation such as this.
1525</t>
1526<t>
1527   The 202 response is intentionally non-committal. Its purpose is to
1528   allow a server to accept a request for some other process (perhaps a
1529   batch-oriented process that is only run once per day) without
1530   requiring that the user agent's connection to the server persist
1531   until the process is completed. The representation returned with this
1532   response &SHOULD; include an indication of the request's current status
1533   and either a pointer to a status monitor or some estimate of when the
1534   user can expect the request to be fulfilled.
1535</t>
1536</section>
1537
1538<section title="203 Non-Authoritative Information" anchor="status.203">
1539  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1540  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1541<t>
1542   The representation in the response has been transformed or otherwise
1543   modified by a transforming proxy (&intermediaries;).  Note that the
1544   behaviour of transforming intermediaries is controlled by the no-transform
1545   Cache-Control directive (&header-cache-control;).
1546</t>
1547<t>
1548   This status code is only appropriate when the response status code would
1549   have been 200 (OK) otherwise. When the status code before transformation
1550   would have been different, the 214 Transformation Applied warn-code
1551   (&header-warning;) is appropriate.
1552</t>
1553<t>
1554   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1555   freshness for 203 responses.
1556</t>
1557</section>
1558
1559<section title="204 No Content" anchor="status.204">
1560  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1561  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1562<t>
1563   The 204 (No Content) status code indicates that the server has
1564   successfully fulfilled the request and that there is no additional
1565   content to return in the response payload body.  Metadata in the
1566   response header fields refer to the target resource and its current
1567   representation after the requested action.
1568</t>
1569<t>
1570   For example, if a 204 status code is received in response to a PUT
1571   request and the response contains an ETag header field, then the PUT
1572   was successful and the ETag field-value contains the entity-tag for
1573   the new representation of that target resource.
1574</t>
1575<t>
1576   The 204 response allows a server to indicate that the action has been
1577   successfully applied to the target resource while implying that the
1578   user agent &SHOULD-NOT; traverse away from its current "document view"
1579   (if any).  The server assumes that the user agent will provide some
1580   indication of the success to its user, in accord with its own interface,
1581   and apply any new or updated metadata in the response to the active
1582   representation.
1583</t>
1584<t>
1585   For example, a 204 status code is commonly used with document editing
1586   interfaces corresponding to a "save" action, such that the document
1587   being saved remains available to the user for editing. It is also
1588   frequently used with interfaces that expect automated data transfers
1589   to be prevalent, such as within distributed version control systems.
1590</t>
1591<t>
1592   The 204 response &MUST-NOT; include a message-body, and thus is always
1593   terminated by the first empty line after the header fields.
1594</t>
1595</section>
1596
1597<section title="205 Reset Content" anchor="status.205">
1598  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1599  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1600<t>
1601   The server has fulfilled the request and the user agent &SHOULD; reset
1602   the document view which caused the request to be sent. This response
1603   is primarily intended to allow input for actions to take place via
1604   user input, followed by a clearing of the form in which the input is
1605   given so that the user can easily initiate another input action.
1606</t>
1607<t>   
1608   The message-body included with the response &MUST; be empty. Note that
1609   receivers still need to parse the response according to the algorithm defined
1610   in &message-body;.
1611</t>
1612</section>
1613
1614<section title="206 Partial Content" anchor="status.206">
1615  <iref primary="true" item="206 Partial Content (status code)" x:for-anchor=""/>
1616  <iref primary="true" item="Status Codes" subitem="206 Partial Content" x:for-anchor=""/>
1617  <rdf:Description>
1618    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
1619  </rdf:Description>
1620<t>
1621   The server has fulfilled the partial GET request for the resource
1622   and the enclosed payload is a partial representation as defined in &status-206;.
1623</t>
1624<t>
1625   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1626   freshness for 206 responses.
1627</t>
1628</section>
1629</section>
1630
1631<section title="Redirection 3xx" anchor="status.3xx">
1632<t>
1633   This class of status code indicates that further action needs to be
1634   taken by the user agent in order to fulfill the request.  If the required
1635   action involves a subsequent HTTP request, it &MAY; be carried out by the
1636   user agent without interaction with the user if and only if the method used
1637   in the second request is known to be "safe", as defined in
1638   <xref target="safe.methods"/>.
1639</t>
1640<t>
1641   There are several types of redirects:
1642   <list style="numbers">
1643      <x:lt>
1644        <t>
1645          Redirects of the request to another URI, either temporarily or
1646          permanently. The new URI is specified in the Location header field.
1647          In this specification, the status codes 301 (Moved Permanently),
1648          302 (Found), and 307 (Temporary Redirect) fall under this category.
1649        </t>
1650      </x:lt>
1651      <x:lt>
1652        <t>
1653          Redirection to a new location that represents an indirect response to
1654          the request, such as the result of a POST operation to be retrieved
1655          with a subsequent GET request. This is status code 303 (See Other).
1656        </t>
1657      </x:lt>
1658      <x:lt>
1659        <t>
1660          Redirection offering a choice of matching resources for use by
1661          agent-driven content negotiation (&agent-driven-negotiation;). This
1662          is status code 300 (Multiple Choices).
1663        </t>
1664      </x:lt>
1665      <x:lt>
1666        <t>
1667          Other kinds of redirection, such as to a cached result (status code 304
1668          (Not Modified)).
1669        </t>
1670      </x:lt>
1671   </list>
1672</t>
1673<x:note>
1674  <t>
1675    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1676    and 302 (Found) were defined for the first type of redirect, and the second
1677    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1678    However it turned out that web forms using POST expected redirects to change
1679    the operation for the subsequent request to retrieval (GET). To address this
1680    use case, HTTP/1.1 introduced the second type of redirect with the status
1681    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1682    As user agents did not change their behavior to maintain backwards
1683    compatibility, the first revision of HTTP/1.1 added yet another status code,
1684    307 (Temporary Redirect), for which the backwards compatibility problems did
1685    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1686    Over 10 years later, most user agents still do method rewriting for
1687    status codes 301 and 302, therefore this specification makes that behavior
1688    compliant in case the original request was POST.
1689  </t>
1690</x:note>
1691<t>
1692   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1693   "infinite" redirection loops).
1694</t>
1695<x:note>
1696  <t>
1697    <x:h>Note:</x:h> An earlier version of this specification recommended a
1698    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1699    Content developers need to be aware that some clients might
1700    implement such a fixed limitation.
1701  </t>
1702</x:note>
1703
1704<section title="300 Multiple Choices" anchor="status.300">
1705  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1706  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1707<t>
1708   The target resource has more than one
1709   representation, each with its own specific location, and agent-driven
1710   negotiation information (&content-negotiation;) is being provided so that
1711   the user (or user agent) can select a preferred representation by
1712   redirecting its request to that location.
1713</t>
1714<t>
1715   Unless it was a HEAD request, the response &SHOULD; include a representation
1716   containing a list of representation metadata and location(s) from
1717   which the user or user agent can choose the one most appropriate. The
1718   data format is specified by the media type given in the Content-Type
1719   header field. Depending upon the format and the capabilities of
1720   the user agent, selection of the most appropriate choice &MAY; be
1721   performed automatically. However, this specification does not define
1722   any standard for such automatic selection.
1723</t>
1724<t>
1725   If the server has a preferred choice of representation, it &SHOULD;
1726   include the specific URI for that representation in the Location
1727   field; user agents &MAY; use the Location field value for automatic
1728   redirection.
1729</t>
1730<t>
1731   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1732   freshness for 300 responses.
1733</t>
1734
1735</section>
1736
1737<section title="301 Moved Permanently" anchor="status.301">
1738  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1739  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1740<t>
1741   The target resource has been assigned a new permanent URI and any
1742   future references to this resource &SHOULD; use one of the returned
1743   URIs.  Clients with link editing capabilities ought to automatically
1744   re-link references to the effective request URI to one or more of the new
1745   references returned by the server, where possible.
1746</t>
1747<t>
1748   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1749   freshness for 301 responses.
1750</t>
1751<t>
1752   The new permanent URI &SHOULD; be given by the Location field in the
1753   response. Unless the request method was HEAD, the representation of the
1754   response &SHOULD; contain a short hypertext note with a hyperlink to
1755   the new URI(s).
1756</t>
1757<t>
1758   If the 301 status code is received in response to a request method
1759   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1760   then the request &MAY; be automatically redirected by the user agent without
1761   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1762   request unless it can be confirmed by the user, since this might
1763   change the conditions under which the request was issued.
1764</t>
1765<x:note>
1766  <t>
1767    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1768    request method from POST to GET for the subsequent request. If this
1769    behavior is undesired, status code 307 (Temporary Redirect) can be used
1770    instead.
1771  </t>
1772</x:note>
1773</section>
1774
1775<section title="302 Found" anchor="status.302">
1776  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1777  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1778<t>
1779   The target resource resides temporarily under a different URI.
1780   Since the redirection might be altered on occasion, the client &SHOULD;
1781   continue to use the effective request URI for future requests.
1782</t>
1783<t>
1784   The temporary URI &SHOULD; be given by the Location field in the
1785   response. Unless the request method was HEAD, the representation of the
1786   response &SHOULD; contain a short hypertext note with a hyperlink to
1787   the new URI(s).
1788</t>
1789<t>
1790   If the 302 status code is received in response to a request method
1791   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1792   then the request &MAY; be automatically redirected by the user agent without
1793   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1794   request unless it can be confirmed by the user, since this might
1795   change the conditions under which the request was issued.
1796</t>
1797<x:note>
1798  <t>
1799    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1800    request method from POST to GET for the subsequent request. If this
1801    behavior is undesired, status code 307 (Temporary Redirect) can be used
1802    instead.
1803    <cref anchor="issue312">but see <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/312"/></cref>
1804  </t>
1805</x:note>
1806</section>
1807
1808<section title="303 See Other" anchor="status.303">
1809  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1810  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1811<t>
1812   The 303 status code indicates that the server is redirecting the
1813   user agent to a different resource, as indicated by a URI in the
1814   Location header field, that is intended to provide an indirect
1815   response to the original request.  In order to satisfy the original
1816   request, a user agent &SHOULD; perform a retrieval request using the
1817   Location URI (a GET or HEAD request if using HTTP), which
1818   may itself be redirected further, and present the eventual result as an
1819   answer to the original request.
1820   Note that the new URI in the Location header field is not considered
1821   equivalent to the effective request URI.
1822</t>
1823<t>
1824   This status code is generally applicable to any HTTP method.  It is
1825   primarily used to allow the output of a POST action to redirect
1826   the user agent to a selected resource, since doing so provides the
1827   information corresponding to the POST response in a form that
1828   can be separately identified, bookmarked, and cached independent
1829   of the original request.
1830</t>
1831<t>
1832   A 303 response to a GET request indicates that the requested
1833   resource does not have a representation of its own that can be
1834   transferred by the server over HTTP.  The Location URI indicates a
1835   resource that is descriptive of the target resource, such that the
1836   follow-on representation might be useful to recipients without
1837   implying that it adequately represents the target resource.
1838   Note that answers to the questions of what can be represented, what
1839   representations are adequate, and what might be a useful description
1840   are outside the scope of HTTP and thus entirely determined by the
1841   URI owner(s).
1842</t>
1843<t>
1844   Except for responses to a HEAD request, the representation of a 303
1845   response &SHOULD; contain a short hypertext note with a hyperlink
1846   to the Location URI.
1847</t>
1848</section>
1849
1850<section title="304 Not Modified" anchor="status.304">
1851  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1852  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1853  <rdf:Description>
1854    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
1855  </rdf:Description>
1856<t>
1857   The response to the request has not been modified since the conditions
1858   indicated by the client's conditional GET request, as defined in &status-304;.
1859</t>
1860</section>
1861
1862<section title="305 Use Proxy" anchor="status.305">
1863  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1864  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1865<t>
1866   The 305 status code was defined in a previous version of this specification
1867   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1868</t>
1869</section>
1870
1871<section title="306 (Unused)" anchor="status.306">
1872  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1873  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1874<t>
1875   The 306 status code was used in a previous version of the
1876   specification, is no longer used, and the code is reserved.
1877</t>
1878</section>
1879
1880<section title="307 Temporary Redirect" anchor="status.307">
1881  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1882  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1883<t>
1884   The target resource resides temporarily under a different URI.
1885   Since the redirection can change over time, the client &SHOULD;
1886   continue to use the effective request URI for future requests.
1887</t>
1888<t>
1889   The temporary URI &SHOULD; be given by the Location field in the
1890   response. Unless the request method was HEAD, the representation of the
1891   response &SHOULD; contain a short hypertext note with a hyperlink to
1892   the new URI(s), since many pre-HTTP/1.1 user agents do not
1893   understand the 307 status code. Therefore, the note &SHOULD; contain the
1894   information necessary for a user to repeat the original request on
1895   the new URI.
1896</t>
1897<t>
1898   If the 307 status code is received in response to a request method
1899   that is known to be "safe", as defined in <xref target="safe.methods"/>,
1900   then the request &MAY; be automatically redirected by the user agent without
1901   confirmation.  Otherwise, the user agent &MUST-NOT; automatically redirect the
1902   request unless it can be confirmed by the user, since this might
1903   change the conditions under which the request was issued.
1904</t>
1905</section>
1906</section>
1907
1908<section title="Client Error 4xx" anchor="status.4xx">
1909<t>
1910   The 4xx class of status code is intended for cases in which the
1911   client seems to have erred. Except when responding to a HEAD request,
1912   the server &SHOULD; include a representation containing an explanation of the
1913   error situation, and whether it is a temporary or permanent
1914   condition. These status codes are applicable to any request method.
1915   User agents &SHOULD; display any included representation to the user.
1916</t>
1917<t>
1918   If the client is sending data, a server implementation using TCP
1919   &SHOULD; be careful to ensure that the client acknowledges receipt of
1920   the packet(s) containing the response, before the server closes the
1921   input connection. If the client continues sending data to the server
1922   after the close, the server's TCP stack will send a reset packet to
1923   the client, which might erase the client's unacknowledged input buffers
1924   before they can be read and interpreted by the HTTP application.
1925</t>
1926
1927<section title="400 Bad Request" anchor="status.400">
1928  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1929  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1930<t>
1931   The server cannot or will not process the request, due to a client error (e.g.,
1932   malformed syntax).</t>
1933</section>
1934
1935<section title="401 Unauthorized" anchor="status.401">
1936  <iref primary="true" item="401 Unauthorized (status code)" x:for-anchor=""/>
1937  <iref primary="true" item="Status Codes" subitem="401 Unauthorized" x:for-anchor=""/>
1938  <rdf:Description>
1939    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part7</redirects-to>
1940  </rdf:Description>
1941<t>
1942   The request requires user authentication (see &status-401;).
1943</t>
1944</section>
1945
1946<section title="402 Payment Required" anchor="status.402">
1947  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1948  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1949<t>
1950   This code is reserved for future use.
1951</t>
1952</section>
1953
1954<section title="403 Forbidden" anchor="status.403">
1955  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1956  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1957<t>
1958   The server understood the request, but refuses to authorize it. Providing
1959   different user authentication credentials might be successful, but any
1960   credentials that were provided in the request are insufficient. The request
1961   &SHOULD-NOT; be repeated with the same credentials.
1962</t>
1963<t>
1964   If the request method was not HEAD and the server wishes to make
1965   public why the request has not been fulfilled, it &SHOULD; describe the
1966   reason for the refusal in the representation.  If the server does not wish to
1967   make this information available to the client, the status code 404
1968   (Not Found) &MAY; be used instead.
1969</t>
1970</section>
1971
1972<section title="404 Not Found" anchor="status.404">
1973  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1974  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1975<t>
1976   The server has not found anything matching the effective request URI. No
1977   indication is given of whether the condition is temporary or
1978   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1979   knows, through some internally configurable mechanism, that an old
1980   resource is permanently unavailable and has no forwarding address.
1981   This status code is commonly used when the server does not wish to
1982   reveal exactly why the request has been refused, or when no other
1983   response is applicable.
1984</t>
1985</section>
1986
1987<section title="405 Method Not Allowed" anchor="status.405">
1988  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1989  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1990<t>
1991   The method specified in the Request-Line is not allowed for the target
1992   resource. The response &MUST; include an Allow header field containing a
1993   list of valid methods for the requested resource.
1994</t>
1995</section>
1996
1997<section title="406 Not Acceptable" anchor="status.406">
1998  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1999  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
2000<t>
2001   The resource identified by the request is only capable of generating
2002   response representations which have content characteristics not acceptable
2003   according to the Accept and Accept-* header fields sent in the request
2004   (see &p3-header-fields;).
2005</t>
2006<t>
2007   Unless it was a HEAD request, the response &SHOULD; include a representation
2008   containing a list of available representation characteristics and location(s)
2009   from which the user or user agent can choose the one most
2010   appropriate. The data format is specified by the media type given
2011   in the Content-Type header field. Depending upon the format and the
2012   capabilities of the user agent, selection of the most appropriate
2013   choice &MAY; be performed automatically. However, this specification
2014   does not define any standard for such automatic selection.
2015</t>
2016<x:note>
2017  <t>
2018    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
2019    not acceptable according to the accept header fields sent in the
2020    request. In some cases, this might even be preferable to sending a
2021    406 response. User agents are encouraged to inspect the header fields of
2022    an incoming response to determine if it is acceptable.
2023  </t>
2024</x:note>
2025<t>
2026   If the response could be unacceptable, a user agent &SHOULD;
2027   temporarily stop receipt of more data and query the user for a
2028   decision on further actions.
2029</t>
2030</section>
2031
2032<section title="407 Proxy Authentication Required" anchor="status.407">
2033  <iref primary="true" item="407 Proxy Authentication Required (status code)" x:for-anchor=""/>
2034  <iref primary="true" item="Status Codes" subitem="407 Proxy Authentication Required" x:for-anchor=""/>
2035<t>
2036   This code is similar to 401 (Unauthorized), but indicates that the
2037   client must first authenticate itself with the proxy (see &status-407;).
2038</t>
2039</section>
2040
2041<section title="408 Request Timeout" anchor="status.408">
2042  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
2043  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
2044<t>
2045   The client did not produce a request within the time that the server
2046   was prepared to wait. The client &MAY; repeat the request without
2047   modifications at any later time.
2048</t>
2049</section>
2050
2051<section title="409 Conflict" anchor="status.409">
2052  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
2053  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
2054<t>
2055   The request could not be completed due to a conflict with the current
2056   state of the resource. This code is only allowed in situations where
2057   it is expected that the user might be able to resolve the conflict
2058   and resubmit the request. The response body &SHOULD; include enough
2059   information for the user to recognize the source of the conflict.
2060   Ideally, the response representation would include enough information for the
2061   user or user agent to fix the problem; however, that might not be
2062   possible and is not required.
2063</t>
2064<t>
2065   Conflicts are most likely to occur in response to a PUT request. For
2066   example, if versioning were being used and the representation being PUT
2067   included changes to a resource which conflict with those made by an
2068   earlier (third-party) request, the server might use the 409 response
2069   to indicate that it can't complete the request. In this case, the
2070   response representation would likely contain a list of the differences
2071   between the two versions in a format defined by the response
2072   Content-Type.
2073</t>
2074</section>
2075
2076<section title="410 Gone" anchor="status.410">
2077  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
2078  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
2079<t>
2080   The target resource is no longer available at the server and no
2081   forwarding address is known. This condition is expected to be
2082   considered permanent. Clients with link editing capabilities &SHOULD;
2083   delete references to the effective request URI after user approval. If the
2084   server does not know, or has no facility to determine, whether or not
2085   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
2086   used instead.
2087</t>
2088<t>
2089   The 410 response is primarily intended to assist the task of web
2090   maintenance by notifying the recipient that the resource is
2091   intentionally unavailable and that the server owners desire that
2092   remote links to that resource be removed. Such an event is common for
2093   limited-time, promotional services and for resources belonging to
2094   individuals no longer working at the server's site. It is not
2095   necessary to mark all permanently unavailable resources as "gone" or
2096   to keep the mark for any length of time &mdash; that is left to the
2097   discretion of the server owner.
2098</t>
2099<t>
2100   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
2101   for 410 responses.
2102</t>
2103
2104</section>
2105
2106<section title="411 Length Required" anchor="status.411">
2107  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
2108  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
2109<t>
2110   The server refuses to accept the request without a defined Content-Length.
2111   The client &MAY; repeat the request if it adds a valid
2112   Content-Length header field containing the length of the message-body
2113   in the request message.
2114</t>
2115</section>
2116
2117<section title="412 Precondition Failed" anchor="status.412">
2118  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
2119  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
2120  <rdf:Description>
2121    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part4</redirects-to>
2122  </rdf:Description>
2123<t>
2124   The precondition given in one or more of the header fields
2125   evaluated to false when it was tested on the server, as defined in
2126   &status-412;.
2127</t>
2128</section>
2129
2130<section title="413 Request Representation Too Large" anchor="status.413">
2131  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2132  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2133<t>
2134   The server is refusing to process a request because the request
2135   representation is larger than the server is willing or able to process. The
2136   server &MAY; close the connection to prevent the client from continuing
2137   the request.
2138</t>
2139<t>
2140   If the condition is temporary, the server &SHOULD; include a Retry-After
2141   header field to indicate that it is temporary and after what
2142   time the client &MAY; try again.
2143</t>
2144</section>
2145
2146<section title="414 URI Too Long" anchor="status.414">
2147  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2148  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
2149<t>
2150   The server is refusing to service the request because the effective request URI
2151   is longer than the server is willing to interpret. This rare
2152   condition is only likely to occur when a client has improperly
2153   converted a POST request to a GET request with long query
2154   information, when the client has descended into a URI "black hole" of
2155   redirection (e.g., a redirected URI prefix that points to a suffix of
2156   itself), or when the server is under attack by a client attempting to
2157   exploit security holes present in some servers using fixed-length
2158   buffers for reading or manipulating the effective request URI.
2159</t>
2160</section>
2161
2162<section title="415 Unsupported Media Type" anchor="status.415">
2163  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2164  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2165<t>
2166   The server is refusing to service the request because the request
2167   payload is in a format not supported by this request method on the
2168   target resource.
2169</t>
2170</section>
2171
2172<section title="416 Requested Range Not Satisfiable" anchor="status.416">
2173  <iref primary="true" item="416 Requested Range Not Satisfiable (status code)" x:for-anchor=""/>
2174  <iref primary="true" item="Status Codes" subitem="416 Requested Range Not Satisfiable" x:for-anchor=""/>
2175  <rdf:Description>
2176    <redirects-to xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">Part5</redirects-to>
2177  </rdf:Description>
2178<t>
2179   The request included a Range header field (&header-range;) and none of
2180   the range-specifier values in this field overlap the current extent
2181   of the selected resource. See &status-416;.
2182</t>
2183</section>
2184
2185<section title="417 Expectation Failed" anchor="status.417">
2186  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2187  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2188<t>
2189   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2190   could not be met by this server, or, if the server is a proxy,
2191   the server has unambiguous evidence that the request could not be met
2192   by the next-hop server.
2193</t>
2194</section>
2195
2196<section title="426 Upgrade Required" anchor="status.426">
2197  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2198  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2199<t>
2200   The request can not be completed without a prior protocol upgrade. This
2201   response &MUST; include an Upgrade header field (&header-upgrade;)
2202   specifying the required protocols.
2203</t>
2204<figure>
2205<preamble>Example:</preamble>
2206<artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2207HTTP/1.1 426 Upgrade Required
2208Upgrade: HTTP/2.0
2209Connection: Upgrade
2210
2211</artwork></figure>
2212<t>
2213   The server &SHOULD; include a message body in the 426 response which
2214   indicates in human readable form the reason for the error and describes any
2215   alternative courses which may be available to the user.
2216</t>
2217</section>
2218</section>
2219
2220<section title="Server Error 5xx" anchor="status.5xx">
2221<t>
2222   Response status codes beginning with the digit "5" indicate cases in
2223   which the server is aware that it has erred or is incapable of
2224   performing the request. Except when responding to a HEAD request, the
2225   server &SHOULD; include a representation containing an explanation of the
2226   error situation, and whether it is a temporary or permanent
2227   condition. User agents &SHOULD; display any included representation to the
2228   user. These response codes are applicable to any request method.
2229</t>
2230
2231<section title="500 Internal Server Error" anchor="status.500">
2232  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2233  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2234<t>
2235   The server encountered an unexpected condition which prevented it
2236   from fulfilling the request.
2237</t>
2238</section>
2239
2240<section title="501 Not Implemented" anchor="status.501">
2241  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2242  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2243<t>
2244   The server does not support the functionality required to fulfill the
2245   request. This is the appropriate response when the server does not
2246   recognize the request method and is not capable of supporting it for
2247   any resource.
2248</t>
2249</section>
2250
2251<section title="502 Bad Gateway" anchor="status.502">
2252  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2253  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2254<t>
2255   The server, while acting as a gateway or proxy, received an invalid
2256   response from the upstream server it accessed in attempting to
2257   fulfill the request.
2258</t>
2259</section>
2260
2261<section title="503 Service Unavailable" anchor="status.503">
2262  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2263  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2264<t>
2265   The server is currently unable or unwilling to handle the request due to
2266   reasons such as temporary overloading, maintenance of the server, or rate
2267   limiting of the client.
2268</t>
2269<t>
2270   The implication is that this is a temporary condition which will be
2271   alleviated after some delay. If known, the length of the delay &MAY; be
2272   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2273   If no Retry-After is given, the client &SHOULD; handle the response as it
2274   would for a 500 response.
2275</t>
2276<x:note>
2277  <t>
2278    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2279    server must use it when becoming overloaded. Some servers might wish
2280    to simply refuse the connection.
2281  </t>
2282</x:note>
2283</section>
2284
2285<section title="504 Gateway Timeout" anchor="status.504">
2286  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2287  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2288<t>
2289   The server, while acting as a gateway or proxy, did not receive a
2290   timely response from the upstream server specified by the URI (e.g.,
2291   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2292   to access in attempting to complete the request.
2293</t>
2294<x:note>
2295  <t>
2296    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2297    return 400 or 500 when DNS lookups time out.
2298  </t>
2299</x:note>
2300</section>
2301
2302<section title="505 HTTP Version Not Supported" anchor="status.505">
2303  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2304  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2305<t>
2306   The server does not support, or refuses to support, the protocol
2307   version that was used in the request message. The server is
2308   indicating that it is unable or unwilling to complete the request
2309   using the same major version as the client, as described in &http-version;,
2310   other than with this error message. The response &SHOULD; contain
2311   a representation describing why that version is not supported and what other
2312   protocols are supported by that server.
2313</t>
2314
2315</section>
2316</section>
2317</section>
2318
2319
2320<section title="Date/Time Formats" anchor="http.date">
2321  <x:anchor-alias value="HTTP-date"/>
2322<t>
2323   HTTP applications have historically allowed three different formats
2324   for date/time stamps. However, the preferred format is a fixed-length subset
2325   of that defined by <xref target="RFC1123"/>:
2326</t>
2327<figure><artwork type="example" x:indent-with="  ">
2328Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2329</artwork></figure>
2330<t>
2331   The other formats are described here only for compatibility with obsolete
2332   implementations.
2333</t>
2334<figure><artwork type="example" x:indent-with="  ">
2335Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2336Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2337</artwork></figure>
2338<t>
2339   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2340   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2341   only generate the RFC 1123 format for representing HTTP-date values
2342   in header fields.
2343</t>
2344<t>
2345   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2346   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2347   equal to UTC (Coordinated Universal Time). This is indicated in the
2348   first two formats by the inclusion of "GMT" as the three-letter
2349   abbreviation for time zone, and &MUST; be assumed when reading the
2350   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2351   additional whitespace beyond that specifically included as SP in the
2352   grammar.
2353</t>
2354<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2355  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2356</artwork></figure>
2357<t anchor="preferred.date.format">
2358  <x:anchor-alias value="rfc1123-date"/>
2359  <x:anchor-alias value="time-of-day"/>
2360  <x:anchor-alias value="hour"/>
2361  <x:anchor-alias value="minute"/>
2362  <x:anchor-alias value="second"/>
2363  <x:anchor-alias value="day-name"/>
2364  <x:anchor-alias value="day"/>
2365  <x:anchor-alias value="month"/>
2366  <x:anchor-alias value="year"/>
2367  <x:anchor-alias value="GMT"/>
2368  Preferred format:
2369</t>
2370<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"/>
2371  <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>
2372  ; fixed length subset of the format defined in
2373  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2374 
2375  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2376               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2377               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2378               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2379               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2380               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2381               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2382               
2383  <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>
2384               ; e.g., 02 Jun 1982
2385
2386  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2387  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2388               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2389               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2390               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2391               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2392               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2393               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2394               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2395               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2396               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2397               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2398               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2399  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2400
2401  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2402
2403  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2404                 ; 00:00:00 - 23:59:59
2405                 
2406  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2407  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2408  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2409</artwork></figure>
2410<t>
2411  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2412  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2413  same as those defined for the RFC 5322 constructs
2414  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2415</t>
2416<t anchor="obsolete.date.formats">
2417  <x:anchor-alias value="obs-date"/>
2418  <x:anchor-alias value="rfc850-date"/>
2419  <x:anchor-alias value="asctime-date"/>
2420  <x:anchor-alias value="date1"/>
2421  <x:anchor-alias value="date2"/>
2422  <x:anchor-alias value="date3"/>
2423  <x:anchor-alias value="rfc1123-date"/>
2424  <x:anchor-alias value="day-name-l"/>
2425  Obsolete formats:
2426</t>
2427<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2428  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2429</artwork></figure>
2430<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2431  <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>
2432  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2433                 ; day-month-year (e.g., 02-Jun-82)
2434
2435  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2436         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2437         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2438         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2439         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2440         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2441         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2442</artwork></figure>
2443<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2444  <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>
2445  <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> ))
2446                 ; month day (e.g., Jun  2)
2447</artwork></figure>
2448<x:note>
2449  <t>
2450    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2451    accepting date values that might have been sent by non-HTTP
2452    applications, as is sometimes the case when retrieving or posting
2453    messages via proxies/gateways to SMTP or NNTP.
2454  </t>
2455</x:note>
2456<x:note>
2457  <t>
2458    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2459    to their usage within the protocol stream. Clients and servers are
2460    not required to use these formats for user presentation, request
2461    logging, etc.
2462  </t>
2463</x:note>
2464</section>
2465
2466
2467<section title="Header Field Definitions" anchor="header.field.definitions">
2468<t>
2469   This section defines the syntax and semantics of HTTP/1.1 header fields
2470   related to request and response semantics.
2471</t>
2472
2473<section title="Allow" anchor="header.allow">
2474  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2475  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2476  <x:anchor-alias value="Allow"/>
2477<t>
2478   The "Allow" header field lists the set of methods advertised as
2479   supported by the target resource. The purpose of this field is strictly to
2480   inform the recipient of valid request methods associated with the resource.
2481</t>
2482<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2483  <x:ref>Allow</x:ref> = #<x:ref>Method</x:ref>
2484</artwork></figure>
2485<t>
2486   Example of use:
2487</t>
2488<figure><artwork type="example">
2489  Allow: GET, HEAD, PUT
2490</artwork></figure>
2491<t>
2492   The actual set of allowed methods is defined by the origin server at the
2493   time of each request.
2494</t>
2495<t>
2496   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2497   understand all the methods specified in order to handle them according to
2498   the generic message handling rules.
2499</t>
2500</section>
2501
2502<section title="Date" anchor="header.date">
2503  <iref primary="true" item="Date header field" x:for-anchor=""/>
2504  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2505  <x:anchor-alias value="Date"/>
2506<t>
2507   The "Date" header field represents the date and time at which
2508   the message was originated, having the same semantics as the Origination
2509   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2510   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2511   it &MUST; be sent in rfc1123-date format.
2512</t>
2513<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2514  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2515</artwork></figure>
2516<t>
2517   An example is
2518</t>
2519<figure><artwork type="example">
2520  Date: Tue, 15 Nov 1994 08:12:31 GMT
2521</artwork></figure>
2522<t>
2523   Origin servers &MUST; include a Date header field in all responses,
2524   except in these cases:
2525  <list style="numbers">
2526      <t>If the response status code is 100 (Continue) or 101 (Switching
2527         Protocols), the response &MAY; include a Date header field, at
2528         the server's option.</t>
2529
2530      <t>If the response status code conveys a server error, e.g., 500
2531         (Internal Server Error) or 503 (Service Unavailable), and it is
2532         inconvenient or impossible to generate a valid Date.</t>
2533
2534      <t>If the server does not have a clock that can provide a
2535         reasonable approximation of the current time, its responses
2536         &MUST-NOT; include a Date header field.</t>
2537  </list>
2538</t>
2539<t>
2540   A received message that does not have a Date header field &MUST; be
2541   assigned one by the recipient if the message will be cached by that
2542   recipient.
2543</t>
2544<t>
2545   Clients can use the Date header field as well; in order to keep request
2546   messages small, they are advised not to include it when it doesn't convey
2547   any useful information (as it is usually the case for requests that do not
2548   contain a payload).
2549</t>
2550<t>
2551   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2552   time subsequent to the generation of the message. It &SHOULD; represent
2553   the best available approximation of the date and time of message
2554   generation, unless the implementation has no means of generating a
2555   reasonably accurate date and time. In theory, the date ought to
2556   represent the moment just before the payload is generated. In
2557   practice, the date can be generated at any time during the message
2558   origination without affecting its semantic value.
2559</t>
2560</section>
2561
2562<section title="Expect" anchor="header.expect">
2563  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2564  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2565  <x:anchor-alias value="Expect"/>
2566  <x:anchor-alias value="expectation"/>
2567  <x:anchor-alias value="expectation-extension"/>
2568  <x:anchor-alias value="expect-params"/>
2569<t>
2570   The "Expect" header field is used to indicate that particular
2571   server behaviors are required by the client.
2572</t>
2573<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expectation-extension"/><iref primary="true" item="Grammar" subitem="expect-params"/>
2574  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2575 
2576  <x:ref>expectation</x:ref>  = "100-continue" / <x:ref>expectation-extension</x:ref>
2577  <x:ref>expectation-extension</x:ref> = <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> )
2578                           *<x:ref>expect-params</x:ref> ]
2579  <x:ref>expect-params</x:ref> = ";" <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2580</artwork></figure>
2581<t>
2582   A server that does not understand or is unable to comply with any of
2583   the expectation values in the Expect field of a request &MUST; respond
2584   with appropriate error status code. The server &MUST; respond with a 417
2585   (Expectation Failed) status code if any of the expectations cannot be met
2586   or, if there are other problems with the request, some other 4xx
2587   status code.
2588</t>
2589<t>
2590   This header field is defined with extensible syntax to allow for
2591   future extensions. If a server receives a request containing an
2592   Expect field that includes an expectation-extension that it does not
2593   support, it &MUST; respond with a 417 (Expectation Failed) status code.
2594</t>
2595<t>
2596   Comparison of expectation values is case-insensitive for unquoted
2597   tokens (including the 100-continue token), and is case-sensitive for
2598   quoted-string expectation-extensions.
2599</t>
2600<t>
2601   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy &MUST;
2602   return a 417 (Expectation Failed) status code if it receives a request
2603   with an expectation that it cannot meet. However, the Expect
2604   header field itself is end-to-end; it &MUST; be forwarded if the
2605   request is forwarded.
2606</t>
2607<t>
2608   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
2609   Expect header field.
2610</t>
2611<t>
2612   See &use100; for the use of the 100 (Continue) status code.
2613</t>
2614</section>
2615
2616<section title="From" anchor="header.from">
2617  <iref primary="true" item="From header field" x:for-anchor=""/>
2618  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2619  <x:anchor-alias value="From"/>
2620  <x:anchor-alias value="mailbox"/>
2621<t>
2622   The "From" header field, if given, &SHOULD; contain an Internet
2623   e-mail address for the human user who controls the requesting user
2624   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2625   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2626</t>
2627<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2628  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2629 
2630  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2631</artwork></figure>
2632<t>
2633   An example is:
2634</t>
2635<figure><artwork type="example">
2636  From: webmaster@example.org
2637</artwork></figure>
2638<t>
2639   This header field &MAY; be used for logging purposes and as a means for
2640   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2641   be used as an insecure form of access protection. The interpretation
2642   of this field is that the request is being performed on behalf of the
2643   person given, who accepts responsibility for the method performed. In
2644   particular, robot agents &SHOULD; include this header field so that the
2645   person responsible for running the robot can be contacted if problems
2646   occur on the receiving end.
2647</t>
2648<t>
2649   The Internet e-mail address in this field &MAY; be separate from the
2650   Internet host which issued the request. For example, when a request
2651   is passed through a proxy the original issuer's address &SHOULD; be
2652   used.
2653</t>
2654<t>
2655   The client &SHOULD-NOT;  send the From header field without the user's
2656   approval, as it might conflict with the user's privacy interests or
2657   their site's security policy. It is strongly recommended that the
2658   user be able to disable, enable, and modify the value of this field
2659   at any time prior to a request.
2660</t>
2661</section>
2662
2663<section title="Location" anchor="header.location">
2664  <iref primary="true" item="Location header field" x:for-anchor=""/>
2665  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2666  <x:anchor-alias value="Location"/>
2667<t>
2668   The "Location" header field is used to identify a newly created
2669   resource, or to redirect the recipient to a different location for
2670   completion of the request.
2671</t>
2672<t>
2673   For 201 (Created) responses, the Location is the URI of the new resource
2674   which was created by the request. For 3xx responses, the location &SHOULD;
2675   indicate the server's preferred URI for automatic redirection to the
2676   resource.
2677</t>
2678<t>
2679   The field value consists of a single URI-reference. When it has the form
2680   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2681   the final value is computed by resolving it against the effective request
2682   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>).
2683</t>
2684<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2685  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2686</artwork></figure>
2687<figure>
2688<preamble>Examples are:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2689<artwork type="example">
2690  Location: http://www.example.org/pub/WWW/People.html#tim
2691</artwork></figure><figure><artwork type="example">  Location: /index.html
2692</artwork></figure>
2693<t>
2694   There are circumstances in which a fragment identifier in a Location URI
2695   would not be appropriate. For instance, when it appears in a 201 Created
2696   response, where the Location header field specifies the URI for the entire
2697   created resource.
2698</t>
2699<x:note>
2700  <t>
2701    <x:h>Note:</x:h> This specification does not define precedence rules
2702    for the case where the original URI, as navigated to by the user
2703    agent, and the Location header field value both contain fragment
2704    identifiers. Thus be aware that including fragment identifiers might
2705    inconvenience anyone relying on the semantics of the original URI's
2706    fragment identifier.
2707  </t>
2708</x:note>
2709<x:note>
2710  <t>
2711    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2712    from Location in that the Content-Location identifies the most specific
2713    resource corresponding to the enclosed representation.
2714    It is therefore possible for a response to contain header fields for
2715    both Location and Content-Location.
2716  </t>
2717</x:note>
2718</section>
2719
2720<section title="Max-Forwards" anchor="header.max-forwards">
2721  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2722  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2723  <x:anchor-alias value="Max-Forwards"/>
2724<t>
2725   The "Max-Forwards" header field provides a mechanism with the
2726   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2727   methods to limit the number of times that the request is forwarded by
2728   proxies. This can be useful when the client is attempting to
2729   trace a request which appears to be failing or looping in mid-chain.
2730</t>
2731<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2732  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2733</artwork></figure>
2734<t>
2735   The Max-Forwards value is a decimal integer indicating the remaining
2736   number of times this request message can be forwarded.
2737</t>
2738<t>
2739   Each recipient of a TRACE or OPTIONS request
2740   containing a Max-Forwards header field &MUST; check and update its
2741   value prior to forwarding the request. If the received value is zero
2742   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2743   respond as the final recipient. If the received Max-Forwards value is
2744   greater than zero, then the forwarded message &MUST; contain an updated
2745   Max-Forwards field with a value decremented by one (1).
2746</t>
2747<t>
2748   The Max-Forwards header field &MAY; be ignored for all other request
2749   methods.
2750</t>
2751</section>
2752
2753<section title="Referer" anchor="header.referer">
2754  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2755  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2756  <x:anchor-alias value="Referer"/>
2757<t>
2758   The "Referer" [sic] header field allows the client to specify the
2759   URI of the resource from which the effective request URI was obtained (the
2760   "referrer", although the header field is misspelled.).
2761</t>
2762<t>
2763   The Referer header field allows servers to generate lists of back-links to
2764   resources for interest, logging, optimized caching, etc. It also allows
2765   obsolete or mistyped links to be traced for maintenance. Some servers use
2766   Referer as a means of controlling where they allow links from (so-called
2767   "deep linking"), but legitimate requests do not always
2768   contain a Referer header field.
2769</t>
2770<t>
2771   If the effective request URI was obtained from a source that does not have its own
2772   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2773   sent with the value "about:blank", or not be sent at all. Note that this
2774   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2775</t>
2776<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2777  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2778</artwork></figure>
2779<t>
2780   Example:
2781</t>
2782<figure><artwork type="example">
2783  Referer: http://www.example.org/hypertext/Overview.html
2784</artwork></figure>
2785<t>
2786   If the field value is a relative URI, it &SHOULD; be interpreted
2787   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2788   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2789</t>
2790</section>
2791
2792<section title="Retry-After" anchor="header.retry-after">
2793  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2794  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2795  <x:anchor-alias value="Retry-After"/>
2796<t>
2797   The header "Retry-After" field can be used with a 503 (Service
2798   Unavailable) response to indicate how long the service is expected to
2799   be unavailable to the requesting client. This field &MAY; also be used
2800   with any 3xx (Redirection) response to indicate the minimum time the
2801   user-agent is asked wait before issuing the redirected request.
2802</t>
2803<t>
2804   The value of this field can be either an HTTP-date or an integer number
2805   of seconds (in decimal) after the time of the response.
2806</t>
2807<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2808  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2809</artwork></figure>
2810<t anchor="rule.delta-seconds">
2811  <x:anchor-alias value="delta-seconds"/>
2812   Time spans are non-negative decimal integers, representing time in
2813   seconds.
2814</t>
2815<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2816  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2817</artwork></figure>
2818<t>
2819   Two examples of its use are
2820</t>
2821<figure><artwork type="example">
2822  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2823  Retry-After: 120
2824</artwork></figure>
2825<t>
2826   In the latter example, the delay is 2 minutes.
2827</t>
2828</section>
2829
2830<section title="Server" anchor="header.server">
2831  <iref primary="true" item="Server header field" x:for-anchor=""/>
2832  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2833  <x:anchor-alias value="Server"/>
2834<t>
2835   The "Server" header field contains information about the
2836   software used by the origin server to handle the request.
2837</t>
2838<t>
2839   The field can contain multiple product tokens (&product-tokens;) and
2840   comments (&header-fields;) identifying the server and any significant
2841   subproducts. The product tokens are listed in order of their significance
2842   for identifying the application.
2843</t>
2844<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2845  <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> ) )
2846</artwork></figure>
2847<t>
2848   Example:
2849</t>
2850<figure><artwork type="example">
2851  Server: CERN/3.0 libwww/2.17
2852</artwork></figure>
2853<t>
2854   If the response is being forwarded through a proxy, the proxy
2855   application &MUST-NOT; modify the Server header field. Instead, it
2856   &MUST; include a Via field (as described in &header-via;).
2857</t>
2858<x:note>
2859  <t>
2860    <x:h>Note:</x:h> Revealing the specific software version of the server might
2861    allow the server machine to become more vulnerable to attacks
2862    against software that is known to contain security holes. Server
2863    implementors are encouraged to make this field a configurable
2864    option.
2865  </t>
2866</x:note>
2867</section>
2868
2869<section title="User-Agent" anchor="header.user-agent">
2870  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2871  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2872  <x:anchor-alias value="User-Agent"/>
2873<t>
2874   The "User-Agent" header field contains information about the user
2875   agent originating the request. User agents &SHOULD; include this field with
2876   requests.
2877</t>
2878<t>
2879   Typically, it is used for statistical purposes, the tracing of protocol
2880   violations, and tailoring responses to avoid particular user agent
2881   limitations.
2882</t>
2883<t>
2884   The field can contain multiple product tokens (&product-tokens;)
2885   and comments (&header-fields;) identifying the agent and its
2886   significant subproducts. By convention, the product tokens are listed in
2887   order of their significance for identifying the application.
2888</t>
2889<t>
2890   Because this field is usually sent on every request a user agent makes,
2891   implementations are encouraged not to include needlessly fine-grained
2892   detail, and to limit (or even prohibit) the addition of subproducts by third
2893   parties. Overly long and detailed User-Agent field values make requests
2894   larger and can also be used to identify ("fingerprint") the user against
2895   their wishes.
2896</t>
2897<t>
2898   Likewise, implementations are encouraged not to use the product tokens of
2899   other implementations in order to declare compatibility with them, as this
2900   circumvents the purpose of the field. Finally, they are encouraged not to
2901   use comments to identify products; doing so makes the field value more
2902   difficult to parse.
2903</t>
2904<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2905  <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> ) )
2906</artwork></figure>
2907<t>
2908   Example:
2909</t>
2910<figure><artwork type="example">
2911  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2912</artwork></figure>
2913</section>
2914
2915</section>
2916
2917<section title="IANA Considerations" anchor="IANA.considerations">
2918
2919<section title="Method Registry" anchor="method.registration">
2920<t>
2921  The registration procedure for HTTP request methods is defined by
2922  <xref target="method.registry"/> of this document.
2923</t>
2924<t>
2925   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2926   and be populated with the registrations below:
2927</t>
2928<?BEGININC p2-semantics.iana-methods ?>
2929<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2930<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2931   <ttcol>Method</ttcol>
2932   <ttcol>Safe</ttcol>
2933   <ttcol>Reference</ttcol>
2934   <c>CONNECT</c>
2935   <c>no</c>
2936   <c>
2937      <xref target="CONNECT"/>
2938   </c>
2939   <c>DELETE</c>
2940   <c>no</c>
2941   <c>
2942      <xref target="DELETE"/>
2943   </c>
2944   <c>GET</c>
2945   <c>yes</c>
2946   <c>
2947      <xref target="GET"/>
2948   </c>
2949   <c>HEAD</c>
2950   <c>yes</c>
2951   <c>
2952      <xref target="HEAD"/>
2953   </c>
2954   <c>OPTIONS</c>
2955   <c>yes</c>
2956   <c>
2957      <xref target="OPTIONS"/>
2958   </c>
2959   <c>POST</c>
2960   <c>no</c>
2961   <c>
2962      <xref target="POST"/>
2963   </c>
2964   <c>PUT</c>
2965   <c>no</c>
2966   <c>
2967      <xref target="PUT"/>
2968   </c>
2969   <c>TRACE</c>
2970   <c>yes</c>
2971   <c>
2972      <xref target="TRACE"/>
2973   </c>
2974</texttable>
2975<!--(END)-->
2976<?ENDINC p2-semantics.iana-methods ?>
2977</section>
2978
2979<section title="Status Code Registry" anchor="status.code.registration">
2980<t>
2981   The registration procedure for HTTP Status Codes &mdash; previously defined
2982   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2983   by <xref target="status.code.registry"/> of this document.
2984</t>
2985<t>
2986   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2987   shall be updated with the registrations below:
2988</t>
2989<?BEGININC p2-semantics.iana-status-codes ?>
2990<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2991<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2992   <ttcol>Value</ttcol>
2993   <ttcol>Description</ttcol>
2994   <ttcol>Reference</ttcol>
2995   <c>100</c>
2996   <c>Continue</c>
2997   <c>
2998      <xref target="status.100"/>
2999   </c>
3000   <c>101</c>
3001   <c>Switching Protocols</c>
3002   <c>
3003      <xref target="status.101"/>
3004   </c>
3005   <c>200</c>
3006   <c>OK</c>
3007   <c>
3008      <xref target="status.200"/>
3009   </c>
3010   <c>201</c>
3011   <c>Created</c>
3012   <c>
3013      <xref target="status.201"/>
3014   </c>
3015   <c>202</c>
3016   <c>Accepted</c>
3017   <c>
3018      <xref target="status.202"/>
3019   </c>
3020   <c>203</c>
3021   <c>Non-Authoritative Information</c>
3022   <c>
3023      <xref target="status.203"/>
3024   </c>
3025   <c>204</c>
3026   <c>No Content</c>
3027   <c>
3028      <xref target="status.204"/>
3029   </c>
3030   <c>205</c>
3031   <c>Reset Content</c>
3032   <c>
3033      <xref target="status.205"/>
3034   </c>
3035   <c>300</c>
3036   <c>Multiple Choices</c>
3037   <c>
3038      <xref target="status.300"/>
3039   </c>
3040   <c>301</c>
3041   <c>Moved Permanently</c>
3042   <c>
3043      <xref target="status.301"/>
3044   </c>
3045   <c>302</c>
3046   <c>Found</c>
3047   <c>
3048      <xref target="status.302"/>
3049   </c>
3050   <c>303</c>
3051   <c>See Other</c>
3052   <c>
3053      <xref target="status.303"/>
3054   </c>
3055   <c>305</c>
3056   <c>Use Proxy</c>
3057   <c>
3058      <xref target="status.305"/>
3059   </c>
3060   <c>306</c>
3061   <c>(Unused)</c>
3062   <c>
3063      <xref target="status.306"/>
3064   </c>
3065   <c>307</c>
3066   <c>Temporary Redirect</c>
3067   <c>
3068      <xref target="status.307"/>
3069   </c>
3070   <c>400</c>
3071   <c>Bad Request</c>
3072   <c>
3073      <xref target="status.400"/>
3074   </c>
3075   <c>402</c>
3076   <c>Payment Required</c>
3077   <c>
3078      <xref target="status.402"/>
3079   </c>
3080   <c>403</c>
3081   <c>Forbidden</c>
3082   <c>
3083      <xref target="status.403"/>
3084   </c>
3085   <c>404</c>
3086   <c>Not Found</c>
3087   <c>
3088      <xref target="status.404"/>
3089   </c>
3090   <c>405</c>
3091   <c>Method Not Allowed</c>
3092   <c>
3093      <xref target="status.405"/>
3094   </c>
3095   <c>406</c>
3096   <c>Not Acceptable</c>
3097   <c>
3098      <xref target="status.406"/>
3099   </c>
3100   <c>407</c>
3101   <c>Proxy Authentication Required</c>
3102   <c>
3103      <xref target="status.407"/>
3104   </c>
3105   <c>408</c>
3106   <c>Request Timeout</c>
3107   <c>
3108      <xref target="status.408"/>
3109   </c>
3110   <c>409</c>
3111   <c>Conflict</c>
3112   <c>
3113      <xref target="status.409"/>
3114   </c>
3115   <c>410</c>
3116   <c>Gone</c>
3117   <c>
3118      <xref target="status.410"/>
3119   </c>
3120   <c>411</c>
3121   <c>Length Required</c>
3122   <c>
3123      <xref target="status.411"/>
3124   </c>
3125   <c>413</c>
3126   <c>Request Representation Too Large</c>
3127   <c>
3128      <xref target="status.413"/>
3129   </c>
3130   <c>414</c>
3131   <c>URI Too Long</c>
3132   <c>
3133      <xref target="status.414"/>
3134   </c>
3135   <c>415</c>
3136   <c>Unsupported Media Type</c>
3137   <c>
3138      <xref target="status.415"/>
3139   </c>
3140   <c>417</c>
3141   <c>Expectation Failed</c>
3142   <c>
3143      <xref target="status.417"/>
3144   </c>
3145   <c>426</c>
3146   <c>Upgrade Required</c>
3147   <c>
3148      <xref target="status.426"/>
3149   </c>
3150   <c>500</c>
3151   <c>Internal Server Error</c>
3152   <c>
3153      <xref target="status.500"/>
3154   </c>
3155   <c>501</c>
3156   <c>Not Implemented</c>
3157   <c>
3158      <xref target="status.501"/>
3159   </c>
3160   <c>502</c>
3161   <c>Bad Gateway</c>
3162   <c>
3163      <xref target="status.502"/>
3164   </c>
3165   <c>503</c>
3166   <c>Service Unavailable</c>
3167   <c>
3168      <xref target="status.503"/>
3169   </c>
3170   <c>504</c>
3171   <c>Gateway Timeout</c>
3172   <c>
3173      <xref target="status.504"/>
3174   </c>
3175   <c>505</c>
3176   <c>HTTP Version Not Supported</c>
3177   <c>
3178      <xref target="status.505"/>
3179   </c>
3180</texttable>
3181<!--(END)-->
3182<?ENDINC p2-semantics.iana-status-codes ?>
3183</section>
3184<section title="Header Field Registration" anchor="header.field.registration">
3185<t>
3186   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3187   with the permanent registrations below (see <xref target="RFC3864"/>):
3188</t>
3189<?BEGININC p2-semantics.iana-headers ?>
3190<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3191<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3192   <ttcol>Header Field Name</ttcol>
3193   <ttcol>Protocol</ttcol>
3194   <ttcol>Status</ttcol>
3195   <ttcol>Reference</ttcol>
3196
3197   <c>Allow</c>
3198   <c>http</c>
3199   <c>standard</c>
3200   <c>
3201      <xref target="header.allow"/>
3202   </c>
3203   <c>Date</c>
3204   <c>http</c>
3205   <c>standard</c>
3206   <c>
3207      <xref target="header.date"/>
3208   </c>
3209   <c>Expect</c>
3210   <c>http</c>
3211   <c>standard</c>
3212   <c>
3213      <xref target="header.expect"/>
3214   </c>
3215   <c>From</c>
3216   <c>http</c>
3217   <c>standard</c>
3218   <c>
3219      <xref target="header.from"/>
3220   </c>
3221   <c>Location</c>
3222   <c>http</c>
3223   <c>standard</c>
3224   <c>
3225      <xref target="header.location"/>
3226   </c>
3227   <c>Max-Forwards</c>
3228   <c>http</c>
3229   <c>standard</c>
3230   <c>
3231      <xref target="header.max-forwards"/>
3232   </c>
3233   <c>Referer</c>
3234   <c>http</c>
3235   <c>standard</c>
3236   <c>
3237      <xref target="header.referer"/>
3238   </c>
3239   <c>Retry-After</c>
3240   <c>http</c>
3241   <c>standard</c>
3242   <c>
3243      <xref target="header.retry-after"/>
3244   </c>
3245   <c>Server</c>
3246   <c>http</c>
3247   <c>standard</c>
3248   <c>
3249      <xref target="header.server"/>
3250   </c>
3251   <c>User-Agent</c>
3252   <c>http</c>
3253   <c>standard</c>
3254   <c>
3255      <xref target="header.user-agent"/>
3256   </c>
3257</texttable>
3258<!--(END)-->
3259<?ENDINC p2-semantics.iana-headers ?>
3260<t>
3261   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3262</t>
3263</section>
3264</section>
3265
3266<section title="Security Considerations" anchor="security.considerations">
3267<t>
3268   This section is meant to inform application developers, information
3269   providers, and users of the security limitations in HTTP/1.1 as
3270   described by this document. The discussion does not include
3271   definitive solutions to the problems revealed, though it does make
3272   some suggestions for reducing security risks.
3273</t>
3274
3275<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3276<t>
3277   Like any generic data transfer protocol, HTTP cannot regulate the
3278   content of the data that is transferred, nor is there any a priori
3279   method of determining the sensitivity of any particular piece of
3280   information within the context of any given request. Therefore,
3281   applications &SHOULD; supply as much control over this information as
3282   possible to the provider of that information. Four header fields are
3283   worth special mention in this context: Server, Via, Referer and From.
3284</t>
3285<t>
3286   Revealing the specific software version of the server might allow the
3287   server machine to become more vulnerable to attacks against software
3288   that is known to contain security holes. Implementors &SHOULD; make the
3289   Server header field a configurable option.
3290</t>
3291<t>
3292   Proxies which serve as a portal through a network firewall &SHOULD;
3293   take special precautions regarding the transfer of header information
3294   that identifies the hosts behind the firewall. In particular, they
3295   &SHOULD; remove, or replace with sanitized versions, any Via fields
3296   generated behind the firewall.
3297</t>
3298<t>
3299   The Referer header field allows reading patterns to be studied and reverse
3300   links drawn. Although it can be very useful, its power can be abused
3301   if user details are not separated from the information contained in
3302   the Referer. Even when the personal information has been removed, the
3303   Referer header field might indicate a private document's URI whose
3304   publication would be inappropriate.
3305</t>
3306<t>
3307   The information sent in the From field might conflict with the user's
3308   privacy interests or their site's security policy, and hence it
3309   &SHOULD-NOT;  be transmitted without the user being able to disable,
3310   enable, and modify the contents of the field. The user &MUST; be able
3311   to set the contents of this field within a user preference or
3312   application defaults configuration.
3313</t>
3314<t>
3315   We suggest, though do not require, that a convenient toggle interface
3316   be provided for the user to enable or disable the sending of From and
3317   Referer information.
3318</t>
3319<t>
3320   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3321   target="header.server"/>) header fields can sometimes be used to determine
3322   that a specific client or server have a particular security hole which might
3323   be exploited. Unfortunately, this same information is often used for other
3324   valuable purposes for which HTTP currently has no better mechanism.
3325</t>
3326<t>
3327   Furthermore, the User-Agent header field may contain enough entropy to be
3328   used, possibly in conjunction with other material, to uniquely identify the
3329   user.
3330</t>
3331<t>
3332   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3333   that was sent in request header fields within the body of their response.
3334   Clients &SHOULD; be careful with sensitive information, like Cookies,
3335   Authorization credentials, and other header fields that might be used to
3336   collect data from the client.
3337</t> 
3338</section>
3339
3340<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3341<t>
3342   Because the source of a link might be private information or might
3343   reveal an otherwise private information source, it is strongly
3344   recommended that the user be able to select whether or not the
3345   Referer field is sent. For example, a browser client could have a
3346   toggle switch for browsing openly/anonymously, which would
3347   respectively enable/disable the sending of Referer and From
3348   information.
3349</t>
3350<t>
3351   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3352   HTTP request if the referring page was transferred with a secure
3353   protocol.
3354</t>
3355<t>
3356   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3357   sensitive data because that data will be placed in the request-target. Many
3358   existing servers, proxies, and user agents log or display the request-target
3359   in places where it might be visible to third parties. Such services can
3360   use POST-based form submission instead.
3361</t>
3362</section>
3363
3364<section title="Location Headers and Spoofing" anchor="location.spoofing">
3365<t>
3366   If a single server supports multiple organizations that do not trust
3367   one another, then it &MUST; check the values of Location and Content-Location
3368   header fields in responses that are generated under control of
3369   said organizations to make sure that they do not attempt to
3370   invalidate resources over which they have no authority.
3371</t>
3372</section>
3373
3374<section title="Security Considerations for CONNECT">
3375<t>
3376   Since tunneled data is opaque to the proxy, there are additional
3377   risks to tunneling to other well-known or reserved ports.
3378   A HTTP client CONNECTing to port 25 could relay spam
3379   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3380   access to a small number of known ports.
3381</t>
3382</section>
3383
3384</section>
3385
3386<section title="Acknowledgments" anchor="acks">
3387<t>
3388  See &acks;.
3389</t>
3390</section>
3391</middle>
3392<back>
3393
3394<references title="Normative References">
3395
3396<reference anchor="Part1">
3397  <front>
3398    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3399    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3400      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3401      <address><email>fielding@gbiv.com</email></address>
3402    </author>
3403    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3404      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3405      <address><email>jg@freedesktop.org</email></address>
3406    </author>
3407    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3408      <organization abbrev="HP">Hewlett-Packard Company</organization>
3409      <address><email>JeffMogul@acm.org</email></address>
3410    </author>
3411    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3412      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3413      <address><email>henrikn@microsoft.com</email></address>
3414    </author>
3415    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3416      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3417      <address><email>LMM@acm.org</email></address>
3418    </author>
3419    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3420      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3421      <address><email>paulle@microsoft.com</email></address>
3422    </author>
3423    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3424      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3425      <address><email>timbl@w3.org</email></address>
3426    </author>
3427    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3428      <organization abbrev="W3C">World Wide Web Consortium</organization>
3429      <address><email>ylafon@w3.org</email></address>
3430    </author>
3431    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3432      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3433      <address><email>julian.reschke@greenbytes.de</email></address>
3434    </author>
3435    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3436  </front>
3437  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3438  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3439</reference>
3440
3441<reference anchor="Part3">
3442  <front>
3443    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3444    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3445      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3446      <address><email>fielding@gbiv.com</email></address>
3447    </author>
3448    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3449      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3450      <address><email>jg@freedesktop.org</email></address>
3451    </author>
3452    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3453      <organization abbrev="HP">Hewlett-Packard Company</organization>
3454      <address><email>JeffMogul@acm.org</email></address>
3455    </author>
3456    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3457      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3458      <address><email>henrikn@microsoft.com</email></address>
3459    </author>
3460    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3461      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3462      <address><email>LMM@acm.org</email></address>
3463    </author>
3464    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3465      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3466      <address><email>paulle@microsoft.com</email></address>
3467    </author>
3468    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3469      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3470      <address><email>timbl@w3.org</email></address>
3471    </author>
3472    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3473      <organization abbrev="W3C">World Wide Web Consortium</organization>
3474      <address><email>ylafon@w3.org</email></address>
3475    </author>
3476    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3477      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3478      <address><email>julian.reschke@greenbytes.de</email></address>
3479    </author>
3480    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3481  </front>
3482  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3483  <x:source href="p3-payload.xml" basename="p3-payload"/>
3484</reference>
3485
3486<reference anchor="Part4">
3487  <front>
3488    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3489    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3490      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3491      <address><email>fielding@gbiv.com</email></address>
3492    </author>
3493    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3494      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3495      <address><email>jg@freedesktop.org</email></address>
3496    </author>
3497    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3498      <organization abbrev="HP">Hewlett-Packard Company</organization>
3499      <address><email>JeffMogul@acm.org</email></address>
3500    </author>
3501    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3502      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3503      <address><email>henrikn@microsoft.com</email></address>
3504    </author>
3505    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3506      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3507      <address><email>LMM@acm.org</email></address>
3508    </author>
3509    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3510      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3511      <address><email>paulle@microsoft.com</email></address>
3512    </author>
3513    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3514      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3515      <address><email>timbl@w3.org</email></address>
3516    </author>
3517    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3518      <organization abbrev="W3C">World Wide Web Consortium</organization>
3519      <address><email>ylafon@w3.org</email></address>
3520    </author>
3521    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3522      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3523      <address><email>julian.reschke@greenbytes.de</email></address>
3524    </author>
3525    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3526  </front>
3527  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3528  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3529</reference>
3530
3531<reference anchor="Part5">
3532  <front>
3533    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3534    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3535      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3536      <address><email>fielding@gbiv.com</email></address>
3537    </author>
3538    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3539      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3540      <address><email>jg@freedesktop.org</email></address>
3541    </author>
3542    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3543      <organization abbrev="HP">Hewlett-Packard Company</organization>
3544      <address><email>JeffMogul@acm.org</email></address>
3545    </author>
3546    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3547      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3548      <address><email>henrikn@microsoft.com</email></address>
3549    </author>
3550    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3551      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3552      <address><email>LMM@acm.org</email></address>
3553    </author>
3554    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3555      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3556      <address><email>paulle@microsoft.com</email></address>
3557    </author>
3558    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3559      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3560      <address><email>timbl@w3.org</email></address>
3561    </author>
3562    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3563      <organization abbrev="W3C">World Wide Web Consortium</organization>
3564      <address><email>ylafon@w3.org</email></address>
3565    </author>
3566    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3567      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3568      <address><email>julian.reschke@greenbytes.de</email></address>
3569    </author>
3570    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3571  </front>
3572  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3573  <x:source href="p5-range.xml" basename="p5-range"/>
3574</reference>
3575
3576<reference anchor="Part6">
3577  <front>
3578    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3579    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3580      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3581      <address><email>fielding@gbiv.com</email></address>
3582    </author>
3583    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3584      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3585      <address><email>jg@freedesktop.org</email></address>
3586    </author>
3587    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3588      <organization abbrev="HP">Hewlett-Packard Company</organization>
3589      <address><email>JeffMogul@acm.org</email></address>
3590    </author>
3591    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3592      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3593      <address><email>henrikn@microsoft.com</email></address>
3594    </author>
3595    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3596      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3597      <address><email>LMM@acm.org</email></address>
3598    </author>
3599    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3600      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3601      <address><email>paulle@microsoft.com</email></address>
3602    </author>
3603    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3604      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3605      <address><email>timbl@w3.org</email></address>
3606    </author>
3607    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3608      <organization abbrev="W3C">World Wide Web Consortium</organization>
3609      <address><email>ylafon@w3.org</email></address>
3610    </author>
3611    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3612      <organization>Rackspace</organization>
3613      <address><email>mnot@mnot.net</email></address>
3614    </author>
3615    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3616      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3617      <address><email>julian.reschke@greenbytes.de</email></address>
3618    </author>
3619    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3620  </front>
3621  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3622  <x:source href="p6-cache.xml" basename="p6-cache"/>
3623</reference>
3624
3625<reference anchor="Part7">
3626  <front>
3627    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3628    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3629      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3630      <address><email>fielding@gbiv.com</email></address>
3631    </author>
3632    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3633      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3634      <address><email>jg@freedesktop.org</email></address>
3635    </author>
3636    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3637      <organization abbrev="HP">Hewlett-Packard Company</organization>
3638      <address><email>JeffMogul@acm.org</email></address>
3639    </author>
3640    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3641      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3642      <address><email>henrikn@microsoft.com</email></address>
3643    </author>
3644    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3645      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3646      <address><email>LMM@acm.org</email></address>
3647    </author>
3648    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3649      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3650      <address><email>paulle@microsoft.com</email></address>
3651    </author>
3652    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3653      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3654      <address><email>timbl@w3.org</email></address>
3655    </author>
3656    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3657      <organization abbrev="W3C">World Wide Web Consortium</organization>
3658      <address><email>ylafon@w3.org</email></address>
3659    </author>
3660    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3661      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3662      <address><email>julian.reschke@greenbytes.de</email></address>
3663    </author>
3664    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3665  </front>
3666  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3667  <x:source href="p7-auth.xml" basename="p7-auth"/>
3668</reference>
3669
3670<reference anchor="RFC2119">
3671  <front>
3672    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3673    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3674      <organization>Harvard University</organization>
3675      <address><email>sob@harvard.edu</email></address>
3676    </author>
3677    <date month="March" year="1997"/>
3678  </front>
3679  <seriesInfo name="BCP" value="14"/>
3680  <seriesInfo name="RFC" value="2119"/>
3681</reference>
3682
3683<reference anchor="RFC3986">
3684 <front>
3685  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3686  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3687    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3688    <address>
3689       <email>timbl@w3.org</email>
3690       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3691    </address>
3692  </author>
3693  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3694    <organization abbrev="Day Software">Day Software</organization>
3695    <address>
3696      <email>fielding@gbiv.com</email>
3697      <uri>http://roy.gbiv.com/</uri>
3698    </address>
3699  </author>
3700  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3701    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3702    <address>
3703      <email>LMM@acm.org</email>
3704      <uri>http://larry.masinter.net/</uri>
3705    </address>
3706  </author>
3707  <date month='January' year='2005'></date>
3708 </front>
3709 <seriesInfo name="STD" value="66"/>
3710 <seriesInfo name="RFC" value="3986"/>
3711</reference>
3712
3713<reference anchor="RFC5234">
3714  <front>
3715    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3716    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3717      <organization>Brandenburg InternetWorking</organization>
3718      <address>
3719        <email>dcrocker@bbiw.net</email>
3720      </address> 
3721    </author>
3722    <author initials="P." surname="Overell" fullname="Paul Overell">
3723      <organization>THUS plc.</organization>
3724      <address>
3725        <email>paul.overell@thus.net</email>
3726      </address>
3727    </author>
3728    <date month="January" year="2008"/>
3729  </front>
3730  <seriesInfo name="STD" value="68"/>
3731  <seriesInfo name="RFC" value="5234"/>
3732</reference>
3733
3734</references>
3735
3736<references title="Informative References">
3737
3738<reference anchor="RFC1123">
3739  <front>
3740    <title>Requirements for Internet Hosts - Application and Support</title>
3741    <author initials="R." surname="Braden" fullname="Robert Braden">
3742      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3743      <address><email>Braden@ISI.EDU</email></address>
3744    </author>
3745    <date month="October" year="1989"/>
3746  </front>
3747  <seriesInfo name="STD" value="3"/>
3748  <seriesInfo name="RFC" value="1123"/>
3749</reference>
3750
3751<reference anchor="RFC1945">
3752  <front>
3753    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3754    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3755      <organization>MIT, Laboratory for Computer Science</organization>
3756      <address><email>timbl@w3.org</email></address>
3757    </author>
3758    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3759      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3760      <address><email>fielding@ics.uci.edu</email></address>
3761    </author>
3762    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3763      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3764      <address><email>frystyk@w3.org</email></address>
3765    </author>
3766    <date month="May" year="1996"/>
3767  </front>
3768  <seriesInfo name="RFC" value="1945"/>
3769</reference>
3770
3771<reference anchor="RFC2068">
3772  <front>
3773    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3774    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3775      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3776      <address><email>fielding@ics.uci.edu</email></address>
3777    </author>
3778    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3779      <organization>MIT Laboratory for Computer Science</organization>
3780      <address><email>jg@w3.org</email></address>
3781    </author>
3782    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3783      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3784      <address><email>mogul@wrl.dec.com</email></address>
3785    </author>
3786    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3787      <organization>MIT Laboratory for Computer Science</organization>
3788      <address><email>frystyk@w3.org</email></address>
3789    </author>
3790    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3791      <organization>MIT Laboratory for Computer Science</organization>
3792      <address><email>timbl@w3.org</email></address>
3793    </author>
3794    <date month="January" year="1997"/>
3795  </front>
3796  <seriesInfo name="RFC" value="2068"/>
3797</reference>
3798
3799<reference anchor="RFC2616">
3800  <front>
3801    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3802    <author initials="R." surname="Fielding" fullname="R. Fielding">
3803      <organization>University of California, Irvine</organization>
3804      <address><email>fielding@ics.uci.edu</email></address>
3805    </author>
3806    <author initials="J." surname="Gettys" fullname="J. Gettys">
3807      <organization>W3C</organization>
3808      <address><email>jg@w3.org</email></address>
3809    </author>
3810    <author initials="J." surname="Mogul" fullname="J. Mogul">
3811      <organization>Compaq Computer Corporation</organization>
3812      <address><email>mogul@wrl.dec.com</email></address>
3813    </author>
3814    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3815      <organization>MIT Laboratory for Computer Science</organization>
3816      <address><email>frystyk@w3.org</email></address>
3817    </author>
3818    <author initials="L." surname="Masinter" fullname="L. Masinter">
3819      <organization>Xerox Corporation</organization>
3820      <address><email>masinter@parc.xerox.com</email></address>
3821    </author>
3822    <author initials="P." surname="Leach" fullname="P. Leach">
3823      <organization>Microsoft Corporation</organization>
3824      <address><email>paulle@microsoft.com</email></address>
3825    </author>
3826    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3827      <organization>W3C</organization>
3828      <address><email>timbl@w3.org</email></address>
3829    </author>
3830    <date month="June" year="1999"/>
3831  </front>
3832  <seriesInfo name="RFC" value="2616"/>
3833</reference>
3834
3835<reference anchor='RFC2817'>
3836  <front>
3837    <title>Upgrading to TLS Within HTTP/1.1</title>
3838    <author initials='R.' surname='Khare' fullname='R. Khare'>
3839      <organization>4K Associates / UC Irvine</organization>
3840      <address><email>rohit@4K-associates.com</email></address>
3841    </author>
3842    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3843      <organization>Agranat Systems, Inc.</organization>
3844      <address><email>lawrence@agranat.com</email></address>
3845    </author>
3846    <date year='2000' month='May' />
3847  </front>
3848  <seriesInfo name='RFC' value='2817' />
3849</reference>
3850
3851<reference anchor='RFC3864'>
3852  <front>
3853    <title>Registration Procedures for Message Header Fields</title>
3854    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3855      <organization>Nine by Nine</organization>
3856      <address><email>GK-IETF@ninebynine.org</email></address>
3857    </author>
3858    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3859      <organization>BEA Systems</organization>
3860      <address><email>mnot@pobox.com</email></address>
3861    </author>
3862    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3863      <organization>HP Labs</organization>
3864      <address><email>JeffMogul@acm.org</email></address>
3865    </author>
3866    <date year='2004' month='September' />
3867  </front>
3868  <seriesInfo name='BCP' value='90' />
3869  <seriesInfo name='RFC' value='3864' />
3870</reference>
3871
3872<reference anchor='RFC5226'>
3873  <front>
3874    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3875    <author initials='T.' surname='Narten' fullname='T. Narten'>
3876      <organization>IBM</organization>
3877      <address><email>narten@us.ibm.com</email></address>
3878    </author>
3879    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3880      <organization>Google</organization>
3881      <address><email>Harald@Alvestrand.no</email></address>
3882    </author>
3883    <date year='2008' month='May' />
3884  </front>
3885  <seriesInfo name='BCP' value='26' />
3886  <seriesInfo name='RFC' value='5226' />
3887</reference>
3888
3889<reference anchor="RFC5322">
3890  <front>
3891    <title>Internet Message Format</title>
3892    <author initials="P." surname="Resnick" fullname="P. Resnick">
3893      <organization>Qualcomm Incorporated</organization>
3894    </author>
3895    <date year="2008" month="October"/>
3896  </front> 
3897  <seriesInfo name="RFC" value="5322"/>
3898</reference>
3899
3900<reference anchor='RFC5789'>
3901  <front>
3902    <title>PATCH Method for HTTP</title>
3903    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3904      <organization>Linden Lab</organization>
3905    </author>
3906    <author initials='J.' surname='Snell' fullname='J. Snell' />
3907    <date year='2010' month='March' />
3908  </front>
3909  <seriesInfo name='RFC' value='5789' />
3910</reference>
3911
3912<reference anchor="RFC5987">
3913        <front>
3914    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3915    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3916      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3917      <address>
3918        <postal>
3919          <street>Hafenweg 16</street>
3920          <city>Muenster</city><region>NW</region><code>48155</code>
3921          <country>Germany</country>
3922        </postal>
3923        <email>julian.reschke@greenbytes.de</email>     
3924        <uri>http://greenbytes.de/tech/webdav/</uri>   
3925      </address>
3926    </author>
3927    <date month="August" year="2010"/>
3928  </front>
3929  <seriesInfo name="RFC" value="5987"/>
3930</reference>
3931
3932</references>
3933
3934<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3935<t>
3936  This document takes over the Status Code Registry, previously defined
3937  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3938  (<xref target="status.code.registry"/>)
3939</t>
3940<t>
3941  Clarify definition of POST.
3942  (<xref target="POST"/>)
3943</t>
3944<t>
3945  Remove requirement to handle all Content-* header fields; ban use of
3946  Content-Range with PUT.
3947  (<xref target="PUT"/>)
3948</t>
3949<t>
3950  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3951  (<xref target="CONNECT"/>)
3952</t>
3953<t>
3954  Broadened the definition of 203 (Non-Authoritative Information) to include
3955  cases of payload transformations as well.
3956  (<xref target="status.203"/>)
3957</t>
3958<t>
3959  Failed to consider that there are many other request methods that are safe
3960  to automatically redirect, and further that the user agent is able to make
3961  that determination based on the request method semantics.
3962  Furthermore, allow user agents to rewrite the method from POST to GET
3963  for status codes 301 and 302.
3964  (Sections <xref format="counter" target="status.301"/>,
3965  <xref format="counter" target="status.302"/> and
3966  <xref format="counter" target="status.307"/>)
3967</t>
3968<t>
3969  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3970  It used to indicate that the target resource must be accessed through the
3971  proxy given by the Location field. The Location field gave the URI of the
3972  proxy. The recipient was expected to repeat this single request via the proxy.
3973  (<xref target="status.305"/>)
3974</t>
3975<t>
3976  Define status 426 (Upgrade Required) (this was incorporated from
3977  <xref target="RFC2817"/>).
3978  (<xref target="status.426"/>)
3979</t>
3980<t>
3981  Change ABNF productions for header fields to only define the field value.
3982  (<xref target="header.field.definitions"/>)
3983</t>
3984<t>
3985  Reclassify "Allow" as response header field, removing the option to
3986  specify it in a PUT request.
3987  Relax the server requirement on the contents of the Allow header field and
3988  remove requirement on clients to always trust the header field value.
3989  (<xref target="header.allow"/>)
3990</t>
3991<t>
3992  Correct syntax of Location header field to allow URI references (including
3993  relative references and fragments), as referred symbol "absoluteURI" wasn't
3994  what was expected, and add some clarifications as to when use of fragments
3995  would not be appropriate.
3996  (<xref target="header.location"/>)
3997</t>
3998<t>
3999  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
4000  extension methods could have used it as well).
4001  (<xref target="header.max-forwards"/>)
4002</t>
4003<t>
4004  Allow Referer field value of "about:blank" as alternative to not specifying it.
4005  (<xref target="header.referer"/>)
4006</t>
4007<t>
4008  In the description of the Server header field, the Via field
4009  was described as a SHOULD. The requirement was and is stated
4010  correctly in the description of the Via header field in &header-via;.
4011  (<xref target="header.server"/>)
4012</t>
4013</section>
4014
4015<?BEGININC p2-semantics.abnf-appendix ?>
4016<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4017<figure>
4018<artwork type="abnf" name="p2-semantics.parsed-abnf">
4019<x:ref>Allow</x:ref> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
4020
4021<x:ref>Date</x:ref> = HTTP-date
4022
4023<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
4024
4025<x:ref>From</x:ref> = mailbox
4026
4027<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4028
4029<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4030
4031<x:ref>Location</x:ref> = URI-reference
4032
4033<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4034<x:ref>Method</x:ref> = token
4035
4036<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
4037
4038<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 1.2.2&gt;
4039<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4040<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4041<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4042
4043<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4044<x:ref>Status-Code</x:ref> = 3DIGIT
4045
4046<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4047<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4048
4049<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4050<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4051
4052<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2&gt;
4053
4054<x:ref>date1</x:ref> = day SP month SP year
4055<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4056<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4057<x:ref>day</x:ref> = 2DIGIT
4058<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4059 / %x54.75.65 ; Tue
4060 / %x57.65.64 ; Wed
4061 / %x54.68.75 ; Thu
4062 / %x46.72.69 ; Fri
4063 / %x53.61.74 ; Sat
4064 / %x53.75.6E ; Sun
4065<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4066 / %x54.75.65.73.64.61.79 ; Tuesday
4067 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4068 / %x54.68.75.72.73.64.61.79 ; Thursday
4069 / %x46.72.69.64.61.79 ; Friday
4070 / %x53.61.74.75.72.64.61.79 ; Saturday
4071 / %x53.75.6E.64.61.79 ; Sunday
4072<x:ref>delta-seconds</x:ref> = 1*DIGIT
4073
4074<x:ref>expect-params</x:ref> = ";" token [ "=" ( token / quoted-string ) ]
4075<x:ref>expectation</x:ref> = "100-continue" / expectation-extension
4076<x:ref>expectation-extension</x:ref> = token [ "=" ( token / quoted-string )
4077 *expect-params ]
4078
4079<x:ref>hour</x:ref> = 2DIGIT
4080
4081<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4082<x:ref>minute</x:ref> = 2DIGIT
4083<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4084 / %x46.65.62 ; Feb
4085 / %x4D.61.72 ; Mar
4086 / %x41.70.72 ; Apr
4087 / %x4D.61.79 ; May
4088 / %x4A.75.6E ; Jun
4089 / %x4A.75.6C ; Jul
4090 / %x41.75.67 ; Aug
4091 / %x53.65.70 ; Sep
4092 / %x4F.63.74 ; Oct
4093 / %x4E.6F.76 ; Nov
4094 / %x44.65.63 ; Dec
4095
4096<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4097<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 1.2.2&gt;
4098
4099<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4100<x:ref>product</x:ref> = &lt;product, defined in [Part1], Section 5.2&gt;
4101
4102<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.3&gt;
4103
4104<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4105<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4106
4107<x:ref>second</x:ref> = 2DIGIT
4108
4109<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4110<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.3&gt;
4111
4112<x:ref>year</x:ref> = 4DIGIT
4113</artwork>
4114</figure>
4115<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4116; Allow defined but not used
4117; Date defined but not used
4118; Expect defined but not used
4119; From defined but not used
4120; Location defined but not used
4121; Max-Forwards defined but not used
4122; Reason-Phrase defined but not used
4123; Referer defined but not used
4124; Retry-After defined but not used
4125; Server defined but not used
4126; Status-Code defined but not used
4127; User-Agent defined but not used
4128</artwork></figure></section>
4129<?ENDINC p2-semantics.abnf-appendix ?>
4130
4131<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4132
4133<section title="Since RFC 2616">
4134<t>
4135  Extracted relevant partitions from <xref target="RFC2616"/>.
4136</t>
4137</section>
4138
4139<section title="Since draft-ietf-httpbis-p2-semantics-00">
4140<t>
4141  Closed issues:
4142  <list style="symbols"> 
4143    <t>
4144      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4145      "Via is a MUST"
4146      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4147    </t>
4148    <t>
4149      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4150      "Fragments allowed in Location"
4151      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4152    </t>
4153    <t>
4154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4155      "Safe Methods vs Redirection"
4156      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4157    </t>
4158    <t>
4159      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4160      "Revise description of the POST method"
4161      (<eref target="http://purl.org/NET/http-errata#post"/>)
4162    </t>
4163    <t>
4164      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4165      "Normative and Informative references"
4166    </t>
4167    <t>
4168      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4169      "RFC2606 Compliance"
4170    </t>
4171    <t>
4172      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4173      "Informative references"
4174    </t>
4175    <t>
4176      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4177      "Redundant cross-references"
4178    </t>
4179  </list>
4180</t>
4181<t>
4182  Other changes:
4183  <list style="symbols"> 
4184    <t>
4185      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4186    </t>
4187  </list>
4188</t>
4189</section>
4190
4191<section title="Since draft-ietf-httpbis-p2-semantics-01">
4192<t>
4193  Closed issues:
4194  <list style="symbols"> 
4195    <t>
4196      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4197      "PUT side effects"
4198    </t>
4199    <t>
4200      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4201      "Duplicate Host header requirements"
4202    </t>
4203  </list>
4204</t>
4205<t>
4206  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4207  <list style="symbols"> 
4208    <t>
4209      Move "Product Tokens" section (back) into Part 1, as "token" is used
4210      in the definition of the Upgrade header field.
4211    </t>
4212    <t>
4213      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4214    </t>
4215    <t>
4216      Copy definition of delta-seconds from Part6 instead of referencing it.
4217    </t>
4218  </list>
4219</t>
4220</section>
4221
4222<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4223<t>
4224  Closed issues:
4225  <list style="symbols"> 
4226    <t>
4227      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4228      "Requiring Allow in 405 responses"
4229    </t>
4230    <t>
4231      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4232      "Status Code Registry"
4233    </t>
4234    <t>
4235      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4236      "Redirection vs. Location"
4237    </t>
4238    <t>
4239      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4240      "Cacheability of 303 response"
4241    </t>
4242    <t>
4243      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4244      "305 Use Proxy"
4245    </t>
4246    <t>
4247      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4248      "Classification for Allow header"
4249    </t>
4250    <t>
4251      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4252      "PUT - 'store under' vs 'store at'"
4253    </t>
4254  </list>
4255</t>
4256<t>
4257  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4258  <list style="symbols"> 
4259    <t>
4260      Reference RFC 3984, and update header field registrations for headers defined
4261      in this document.
4262    </t>
4263  </list>
4264</t>
4265<t>
4266  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4267  <list style="symbols"> 
4268    <t>
4269      Replace string literals when the string really is case-sensitive (method).
4270    </t>
4271  </list>
4272</t>
4273</section>
4274
4275<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4276<t>
4277  Closed issues:
4278  <list style="symbols"> 
4279    <t>
4280      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4281      "OPTIONS request bodies"
4282    </t>
4283    <t>
4284      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4285      "Description of CONNECT should refer to RFC2817"
4286    </t>
4287    <t>
4288      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4289      "Location Content-Location reference request/response mixup"
4290    </t>
4291  </list>
4292</t>
4293<t>
4294  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4295  <list style="symbols"> 
4296    <t>
4297      Added initial proposal for registration process, plus initial
4298      content (non-HTTP/1.1 methods to be added by a separate specification).
4299    </t>
4300  </list>
4301</t>
4302</section>
4303
4304<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4305<t>
4306  Closed issues:
4307  <list style="symbols"> 
4308    <t>
4309      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4310      "Content-*"
4311    </t>
4312    <t>
4313      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4314      "RFC 2822 is updated by RFC 5322"
4315    </t>
4316  </list>
4317</t>
4318<t>
4319  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4320  <list style="symbols"> 
4321    <t>
4322      Use "/" instead of "|" for alternatives.
4323    </t>
4324    <t>
4325      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4326      whitespace ("OWS") and required whitespace ("RWS").
4327    </t>
4328    <t>
4329      Rewrite ABNFs to spell out whitespace rules, factor out
4330      header field value format definitions.
4331    </t>
4332  </list>
4333</t>
4334</section>
4335
4336<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4337<t>
4338  Closed issues:
4339  <list style="symbols"> 
4340    <t>
4341      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4342      "Reason-Phrase BNF"
4343    </t>
4344  </list>
4345</t>
4346<t>
4347  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4348  <list style="symbols"> 
4349    <t>
4350      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4351    </t>
4352  </list>
4353</t>
4354</section>
4355
4356<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4357<t>
4358  Closed issues:
4359  <list style="symbols"> 
4360    <t>
4361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4362      "Clarify when Referer is sent"
4363    </t>
4364    <t>
4365      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4366      "status codes vs methods"
4367    </t>
4368    <t>
4369      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4370      "Do not require "updates" relation for specs that register status codes or method names"
4371    </t>
4372  </list>
4373</t>
4374</section>
4375
4376<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4377<t>
4378  Closed issues:
4379  <list style="symbols"> 
4380    <t>
4381      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4382      "Idempotency"
4383    </t>
4384    <t>
4385      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4386      "TRACE security considerations"
4387    </t>
4388    <t>
4389      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4390      "Clarify rules for determining what entities a response carries"
4391    </t>
4392    <t>
4393      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4394      "update note citing RFC 1945 and 2068"
4395    </t>
4396    <t>
4397      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4398      "update note about redirect limit"
4399    </t>
4400    <t>
4401      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4402      "Location header ABNF should use 'URI'"
4403    </t>
4404    <t>
4405      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4406      "fragments in Location vs status 303"
4407    </t>
4408    <t>
4409      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4410      "move IANA registrations for optional status codes"
4411    </t>
4412  </list>
4413</t>
4414<t>
4415  Partly resolved issues:
4416  <list style="symbols"> 
4417    <t>
4418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4419      "Are OPTIONS and TRACE safe?"
4420    </t>
4421  </list>
4422</t>
4423</section>
4424
4425<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4426<t>
4427  Closed issues:
4428  <list style="symbols"> 
4429    <t>
4430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4431      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4432      status codes when fixing this previously)
4433    </t>
4434  </list>
4435</t>
4436</section>
4437
4438<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4439<t>
4440  Closed issues:
4441  <list style="symbols"> 
4442    <t>
4443      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4444      "Fragment combination / precedence during redirects"
4445    </t>
4446  </list>
4447</t>
4448<t>
4449  Partly resolved issues:
4450  <list style="symbols"> 
4451    <t>
4452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4453      "Location header payload handling"
4454    </t>
4455    <t>
4456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4457      "Term for the requested resource's URI"
4458    </t>
4459  </list>
4460</t>
4461</section>
4462
4463<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4464<t>
4465  Closed issues:
4466  <list style="symbols"> 
4467    <t>
4468      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4469      "Clarify 'Requested Variant'"
4470    </t>
4471    <t>
4472      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4473      "Clarify entity / representation / variant terminology"
4474    </t>
4475    <t>
4476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4477      "Methods and Caching"
4478    </t>
4479    <t>
4480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4481      "OPTIONS vs Max-Forwards"
4482    </t>
4483    <t>
4484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4485      "Status codes and caching"
4486    </t>
4487    <t>
4488      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4489      "consider removing the 'changes from 2068' sections"
4490    </t>
4491  </list>
4492</t>
4493</section>
4494
4495<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4496<t>
4497  Closed issues:
4498  <list style="symbols"> 
4499    <t>
4500      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4501      "Considerations for new status codes"
4502    </t>
4503    <t>
4504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4505      "Considerations for new methods"
4506    </t>
4507    <t>
4508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4509      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4510    </t>
4511  </list>
4512</t>
4513</section>
4514
4515<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4516<t>
4517  Closed issues:
4518  <list style="symbols"> 
4519    <t>
4520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4521      "Fragment combination / precedence during redirects" (added warning
4522      about having a fragid on the redirect may cause inconvenience in
4523      some cases)
4524    </t>
4525    <t>
4526      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4527      "Content-* vs. PUT"
4528    </t>
4529    <t>
4530      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4531      "205 Bodies"
4532    </t>
4533    <t>
4534      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4535      "Understanding Content-* on non-PUT requests"
4536    </t>
4537    <t>
4538      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4539      "Content-*"
4540    </t>
4541    <t>
4542      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4543      "Header type defaulting"
4544    </t>
4545    <t>
4546      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4547      "PUT - 'store under' vs 'store at'"
4548    </t>
4549    <t>
4550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4551      "duplicate ABNF for Reason-Phrase"
4552    </t>
4553    <t>
4554      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4555      "Note special status of Content-* prefix in header registration procedures"
4556    </t>
4557    <t>
4558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4559      "Max-Forwards vs extension methods"
4560    </t>
4561    <t>
4562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4563      "What is the value space of HTTP status codes?" (actually fixed in
4564      draft-ietf-httpbis-p2-semantics-11)
4565    </t>
4566    <t>
4567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4568      "Header Classification"
4569    </t>
4570    <t>
4571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4572      "PUT side effect: invalidation or just stale?"
4573    </t>
4574    <t>
4575      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4576      "proxies not supporting certain methods"
4577    </t>
4578    <t>
4579      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4580      "Migrate CONNECT from RFC2817 to p2"
4581    </t>
4582    <t>
4583      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4584      "Migrate Upgrade details from RFC2817"
4585    </t>
4586    <t>
4587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4588      "clarify PUT semantics'"
4589    </t>
4590    <t>
4591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4592      "duplicate ABNF for 'Method'"
4593    </t>
4594    <t>
4595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4596      "untangle ABNFs for header fields"
4597    </t>
4598  </list>
4599</t>
4600</section>
4601
4602<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4603<t>
4604  Closed issues:
4605  <list style="symbols"> 
4606    <t>
4607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4608      "untangle ABNFs for header fields"
4609    </t>
4610    <t>
4611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4612      "message-body in CONNECT request"
4613    </t>
4614  </list>
4615</t>
4616</section>
4617
4618<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4619<t>
4620  Closed issues:
4621  <list style="symbols"> 
4622    <t>
4623      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4624      "Clarify status code for rate limiting"
4625    </t>
4626    <t>
4627      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4628      "clarify 403 forbidden"
4629    </t>
4630    <t>
4631      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4632      "Clarify 203 Non-Authoritative Information"
4633    </t>
4634    <t>
4635      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4636      "update default reason phrase for 413"
4637    </t>
4638  </list>
4639</t>
4640</section>
4641
4642<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4643<t>
4644  Closed issues:
4645  <list style="symbols"> 
4646    <t>
4647      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4648      "Strength of requirements on Accept re: 406"
4649    </t>
4650    <t>
4651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4652      "400 response isn't generic"
4653    </t>
4654  </list>
4655</t>
4656</section>
4657
4658<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4659<t>
4660  Closed issues:
4661  <list style="symbols"> 
4662    <t>
4663      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4664      "Redirects and non-GET methods"
4665    </t>
4666    <t>
4667      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4668      "Document HTTP's error-handling philosophy"
4669    </t>
4670    <t>
4671      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4672      "clarify 303 redirect on HEAD"
4673    </t>
4674  </list>
4675</t>
4676<t>
4677  Work-in-progress:
4678  <list style="symbols"> 
4679    <t>
4680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4681      "Considerations for new headers"
4682    </t>
4683  </list>
4684</t>
4685</section>
4686
4687</section>
4688
4689</back>
4690</rfc>
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