source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1539

Last change on this file since 1539 was 1539, checked in by julian.reschke@…, 8 years ago

regen appendices (see [1538])

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 193.6 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "February">
16  <!ENTITY ID-YEAR "2012">
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 abnf-extension             "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY whitespace                 "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY field-components           "<xref target='Part1' x:rel='#field.components' 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 media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
75  <!ENTITY status-206                 "<xref target='Part5' x:rel='#status.206' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
76  <!ENTITY status-304                 "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
77  <!ENTITY status-401                 "<xref target='Part7' x:rel='#status.401' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
78  <!ENTITY status-407                 "<xref target='Part7' x:rel='#status.407' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
79  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
80  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
81  <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
82  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
83  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
84  <!ENTITY p7-status-codes            "<xref target='Part7' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
85  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
86  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
87  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
88]>
89<?rfc toc="yes" ?>
90<?rfc symrefs="yes" ?>
91<?rfc sortrefs="yes" ?>
92<?rfc compact="yes"?>
93<?rfc subcompact="no" ?>
94<?rfc linkmailto="no" ?>
95<?rfc editing="no" ?>
96<?rfc comments="yes"?>
97<?rfc inline="yes"?>
98<?rfc rfcedstyle="yes"?>
99<?rfc-ext allow-markup-in-artwork="yes" ?>
100<?rfc-ext include-references-in-index="yes" ?>
101<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="proposed"
102     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
103     xmlns:x='http://purl.org/net/xml2rfc/ext'
104     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
105<x:link rel="prev" basename="p1-messaging"/>
106<x:link rel="next" basename="p3-payload"/>
107<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
108<front>
109
110  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
111
112  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
113    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
114    <address>
115      <postal>
116        <street>345 Park Ave</street>
117        <city>San Jose</city>
118        <region>CA</region>
119        <code>95110</code>
120        <country>USA</country>
121      </postal>
122      <email>fielding@gbiv.com</email>
123      <uri>http://roy.gbiv.com/</uri>
124    </address>
125  </author>
126
127  <author initials="J." surname="Gettys" fullname="Jim Gettys">
128    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
129    <address>
130      <postal>
131        <street>21 Oak Knoll Road</street>
132        <city>Carlisle</city>
133        <region>MA</region>
134        <code>01741</code>
135        <country>USA</country>
136      </postal>
137      <email>jg@freedesktop.org</email>
138      <uri>http://gettys.wordpress.com/</uri>
139    </address>
140  </author>
141 
142  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
143    <organization abbrev="HP">Hewlett-Packard Company</organization>
144    <address>
145      <postal>
146        <street>HP Labs, Large Scale Systems Group</street>
147        <street>1501 Page Mill Road, MS 1177</street>
148        <city>Palo Alto</city>
149        <region>CA</region>
150        <code>94304</code>
151        <country>USA</country>
152      </postal>
153      <email>JeffMogul@acm.org</email>
154    </address>
155  </author>
156
157  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
158    <organization abbrev="Microsoft">Microsoft Corporation</organization>
159    <address>
160      <postal>
161        <street>1 Microsoft Way</street>
162        <city>Redmond</city>
163        <region>WA</region>
164        <code>98052</code>
165        <country>USA</country>
166      </postal>
167      <email>henrikn@microsoft.com</email>
168    </address>
169  </author>
170
171  <author initials="L." surname="Masinter" fullname="Larry Masinter">
172    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
173    <address>
174      <postal>
175        <street>345 Park Ave</street>
176        <city>San Jose</city>
177        <region>CA</region>
178        <code>95110</code>
179        <country>USA</country>
180      </postal>
181      <email>LMM@acm.org</email>
182      <uri>http://larry.masinter.net/</uri>
183    </address>
184  </author>
185 
186  <author initials="P." surname="Leach" fullname="Paul J. Leach">
187    <organization abbrev="Microsoft">Microsoft Corporation</organization>
188    <address>
189      <postal>
190        <street>1 Microsoft Way</street>
191        <city>Redmond</city>
192        <region>WA</region>
193        <code>98052</code>
194      </postal>
195      <email>paulle@microsoft.com</email>
196    </address>
197  </author>
198   
199  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
200    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
201    <address>
202      <postal>
203        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
204        <street>The Stata Center, Building 32</street>
205        <street>32 Vassar Street</street>
206        <city>Cambridge</city>
207        <region>MA</region>
208        <code>02139</code>
209        <country>USA</country>
210      </postal>
211      <email>timbl@w3.org</email>
212      <uri>http://www.w3.org/People/Berners-Lee/</uri>
213    </address>
214  </author>
215
216  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
217    <organization abbrev="W3C">World Wide Web Consortium</organization>
218    <address>
219      <postal>
220        <street>W3C / ERCIM</street>
221        <street>2004, rte des Lucioles</street>
222        <city>Sophia-Antipolis</city>
223        <region>AM</region>
224        <code>06902</code>
225        <country>France</country>
226      </postal>
227      <email>ylafon@w3.org</email>
228      <uri>http://www.raubacapeu.net/people/yves/</uri>
229    </address>
230  </author>
231
232  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
233    <organization abbrev="greenbytes">greenbytes GmbH</organization>
234    <address>
235      <postal>
236        <street>Hafenweg 16</street>
237        <city>Muenster</city><region>NW</region><code>48155</code>
238        <country>Germany</country>
239      </postal>
240      <phone>+49 251 2807760</phone>
241      <facsimile>+49 251 2807761</facsimile>
242      <email>julian.reschke@greenbytes.de</email>
243      <uri>http://greenbytes.de/tech/webdav/</uri>
244    </address>
245  </author>
246
247  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
248  <workgroup>HTTPbis Working Group</workgroup>
249
250<abstract>
251<t>
252   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
253   distributed, collaborative, hypertext information systems. HTTP has been in
254   use by the World Wide Web global information initiative since 1990. This
255   document is Part 2 of the seven-part specification that defines the protocol
256   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
257</t>
258<t>
259   Part 2 defines the semantics of HTTP messages as expressed by request
260   methods, request header fields, response status codes, and response header
261   fields.
262</t>
263</abstract>
264
265<note title="Editorial Note (To be removed by RFC Editor)">
266  <t>
267    Discussion of this draft should take place on the HTTPBIS working group
268    mailing list (ietf-http-wg@w3.org), which is archived at
269    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
270  </t>
271  <t>
272    The current issues list is at
273    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
274    documents (including fancy diffs) can be found at
275    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
276  </t>
277  <t>
278    The changes in this draft are summarized in <xref target="changes.since.18"/>.
279  </t>
280</note>
281</front>
282<middle>
283<section title="Introduction" anchor="introduction">
284<t>
285   This document defines HTTP/1.1 request and response semantics.  Each HTTP
286   message, as defined in &messaging;, is in the form of either a request or
287   a response.  An HTTP server listens on a connection for HTTP requests and
288   responds to each request, in the order received on that connection, with
289   one or more HTTP response messages.  This document defines the commonly
290   agreed upon semantics of the HTTP uniform interface, the intentions defined
291   by each request method, and the various response messages that might be
292   expected as a result of applying that method to the target resource.
293</t>
294<t>
295   This document is currently disorganized in order to minimize the changes
296   between drafts and enable reviewers to see the smaller errata changes.
297   A future draft will reorganize the sections to better reflect the content.
298   In particular, the sections will be ordered according to the typical
299   processing of an HTTP request message (after message parsing): resource
300   mapping, methods, request modifying header fields, response status,
301   status modifying header fields, and resource metadata.  The current mess
302   reflects how widely dispersed these topics and associated requirements
303   had become in <xref target="RFC2616"/>.
304</t>
305
306<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
307<t>
308   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
309   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
310   document are to be interpreted as described in <xref target="RFC2119"/>.
311</t>
312<t>
313   This document defines conformance criteria for several roles in HTTP
314   communication, including Senders, Recipients, Clients, Servers, User-Agents,
315   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
316   for definitions of these terms.
317</t>
318<t>
319   An implementation is considered conformant if it complies with all of the
320   requirements associated with its role(s). Note that SHOULD-level requirements
321   are relevant here, unless one of the documented exceptions is applicable.
322</t>
323<t>
324   This document also uses ABNF to define valid protocol elements
325   (<xref target="notation"/>). In addition to the prose requirements placed
326   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
327</t>
328<t>
329   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
330   protocol element from an invalid construct. However, HTTP does not define
331   specific error handling mechanisms, except in cases where it has direct
332   impact on security. This is because different uses of the protocol require
333   different error handling strategies; for example, a Web browser may wish to
334   transparently recover from a response where the Location header field
335   doesn't parse according to the ABNF, whereby in a systems control protocol
336   using HTTP, this type of error recovery could lead to dangerous consequences.
337</t>
338</section>
339
340<section title="Syntax Notation" anchor="notation">
341  <x:anchor-alias value="CR"/>
342  <x:anchor-alias value="DIGIT"/>
343  <x:anchor-alias value="LF"/>
344  <x:anchor-alias value="HTAB"/>
345  <x:anchor-alias value="VCHAR"/>
346  <x:anchor-alias value="SP"/>
347<t>
348   This specification uses the Augmented Backus-Naur Form (ABNF) notation
349   of <xref target="RFC5234"/> with the list rule extension defined in
350   &notation;<xref target="collected.abnf"/> shows the collected ABNF
351   with the list rule expanded.
352</t>
353<t>
354  The following core rules are included by
355  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
356  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
357  DIGIT (decimal 0-9), DQUOTE (double quote),
358  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
359  OCTET (any 8-bit sequence of data), SP (space), and
360  VCHAR (any visible US-ASCII character).
361</t>
362
363<section title="Core Rules" anchor="core.rules">
364  <x:anchor-alias value="obs-text"/>
365  <x:anchor-alias value="quoted-string"/>
366  <x:anchor-alias value="token"/>
367  <x:anchor-alias value="BWS"/>
368  <x:anchor-alias value="OWS"/>
369  <x:anchor-alias value="RWS"/>
370<t>
371  The core rules below are defined in <xref target="Part1"/>:
372</t>
373<figure><artwork type="abnf2616">
374  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &whitespace;&gt;
375  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &whitespace;&gt;
376  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &whitespace;&gt;
377  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &field-components;&gt;
378  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-components;&gt;
379  <x:ref>token</x:ref>         = &lt;token, defined in &field-components;&gt;
380</artwork></figure>
381</section>
382
383<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
384  <x:anchor-alias value="absolute-URI"/>
385  <x:anchor-alias value="comment"/>
386  <x:anchor-alias value="partial-URI"/>
387  <x:anchor-alias value="URI-reference"/>
388<t>
389  The ABNF rules below are defined in other parts:
390</t>
391<figure><!--Part1--><artwork type="abnf2616">
392  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
393  <x:ref>comment</x:ref>       = &lt;comment, defined in &field-components;&gt;
394  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
395  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
396</artwork></figure>
397</section>
398</section>
399</section>
400
401<section title="Method" anchor="method">
402  <x:anchor-alias value="Method"/>
403  <x:anchor-alias value="extension-method"/>
404<t>
405   The Method token indicates the request method to be performed on the target
406   resource (&effective-request-uri;). The method is case-sensitive.
407</t>
408<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
409  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
410</artwork></figure>
411<t>
412   The list of methods allowed by a resource can be specified in an
413   Allow header field (<xref target="header.allow"/>). The status code of the response
414   always notifies the client whether a method is currently allowed on a
415   resource, since the set of allowed methods can change dynamically. An
416   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
417   if the method is known by the origin server but not allowed for the
418   resource, and 501 (Not Implemented) if the method is
419   unrecognized or not implemented by the origin server. The methods GET
420   and HEAD &MUST; be supported by all general-purpose servers. All other
421   methods are &OPTIONAL;; however, if the above methods are implemented,
422   they &MUST; be implemented with the same semantics as those specified
423   in <xref target="method.definitions"/>.
424</t>
425
426<section title="Overview of Methods" anchor="overview.of.methods">
427<t>
428  The methods listed below are defined in <xref target="method.definitions"/>.
429</t>
430<texttable align="left">
431  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
432 
433  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
434  <c>GET</c> <c><xref target="GET"/></c>
435  <c>HEAD</c> <c><xref target="HEAD"/></c>
436  <c>POST</c> <c><xref target="POST"/></c>
437  <c>PUT</c> <c><xref target="PUT"/></c>
438  <c>DELETE</c> <c><xref target="DELETE"/></c>
439  <c>TRACE</c> <c><xref target="TRACE"/></c>
440  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
441</texttable>
442<t>
443  Note that this list is not exhaustive &mdash; it does not include request methods defined
444  in other specifications.
445</t>
446</section>
447
448<section title="Method Registry" anchor="method.registry">
449<t>
450  The HTTP Method Registry defines the name space for the Method token in the
451  Request line of an HTTP request.
452</t>
453<t>
454  Registrations &MUST; include the following fields:
455  <list style="symbols">
456    <t>Method Name (see <xref target="method"/>)</t>
457    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
458    <t>Pointer to specification text</t>
459  </list>
460</t>
461<t>
462  Values to be added to this name space are subject to IETF review
463  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
464</t>
465<t>
466  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
467</t>
468
469<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
470<t>
471   When it is necessary to express new semantics for a HTTP request that
472   aren't specific to a single application or media type, and currently defined
473   methods are inadequate, it may be appropriate to register a new method.
474</t>
475<t>
476   HTTP methods are generic; that is, they are potentially applicable to any
477   resource, not just one particular media type, "type" of resource, or
478   application. As such, it is preferred that new HTTP methods be registered
479   in a document that isn't specific to a single application, so that this is
480   clear.
481</t>
482<t>
483   Due to the parsing rules defined in &message-body;, definitions of HTTP
484   methods cannot prohibit the presence of a message-body on either the request
485   or the response message (with responses to HEAD requests being the single
486   exception). Definitions of new methods cannot change this rule, but they can
487   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
488</t>
489<t>
490   New method definitions need to indicate whether they are safe (<xref
491   target="safe.methods"/>), what semantics (if any) the request body has,
492   and whether they are idempotent (<xref target="idempotent.methods"/>).
493   They also need to state whether they can be cached (&caching;); in
494   particular what conditions a cache may store the response, and under what
495   conditions such a stored response may be used to satisfy a subsequent
496   request.
497</t>
498</section>
499
500</section>
501</section>
502
503<section title="Header Fields" anchor="header.fields">
504<t>
505   Header fields are key value pairs that can be used to communicate data about
506   the message, its payload, the target resource, or about the connection
507   itself (i.e., control data).  See &header-fields; for a general definition
508   of their syntax.
509</t>
510
511<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
512<t>
513   New header fields are registered using the procedures described in
514   <xref target="RFC3864"/>.
515</t>
516<t>
517   The requirements for header field names are defined in
518   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
519   defining new fields are advised to keep the name as short as practical, and
520   not to prefix them with "X-" if they are to be registered (either
521   immediately or in the future).
522</t>
523<t>
524   New header field values typically have their syntax defined using ABNF
525   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
526   as necessary, and are usually constrained to the range of ASCII characters.
527   Header fields needing a greater range of characters can use an encoding
528   such as the one defined in <xref target="RFC5987"/>.
529</t>
530<t>
531   Because commas (",") are used as a generic delimiter between field-values,
532   they need to be treated with care if they are allowed in the field-value's
533   payload. Typically, components that might contain a comma are protected with
534   double-quotes using the quoted-string ABNF production (&field-components;).
535</t>
536<t>
537   For example, a textual date and a URI (either of which might contain a comma)
538   could be safely carried in field-values like these:
539</t>
540<figure><artwork type="example">
541  Example-URI-Field: "http://example.com/a.html,foo",
542                     "http://without-a-comma.example.com/"
543  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
544</artwork></figure>
545<t>
546   Note that double quote delimiters almost always are used with the
547   quoted-string production; using a different syntax inside double quotes
548   will likely cause unnecessary confusion.
549</t>
550<t>
551   Many header fields use a format including (case-insensitively) named
552   parameters (for instance, Content-Type, defined in &header-content-type;).
553   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
554   parameter value enables recipients to use existing parser components. When
555   allowing both forms, the meaning of a parameter value ought to be
556   independent of the syntax used for it (for an example, see the notes on
557   parameter handling for media types in &media-types;).
558</t>
559<t>
560   Authors of specifications defining new header fields are advised to consider
561   documenting:
562  <list style="symbols">
563    <x:lt>
564      <t>Whether the field is a single value, or whether it can be a list
565      (delimited by commas; see &header-fields;).</t>
566      <t>If it does not use the list syntax, document how to treat messages
567      where the header field occurs multiple times (a sensible default would
568      be to ignore the header field, but this might not always be the right
569      choice).</t>
570      <t>Note that intermediaries and software libraries might combine
571      multiple header field instances into a single one, despite the header
572      field not allowing this. A robust format enables recipients to discover
573      these situations (good example: "Content-Type", as the comma can only
574      appear inside quoted strings; bad example: "Location", as a comma can
575      occur inside a URI).</t>
576    </x:lt>
577    <x:lt><t>Under what conditions the header field can be used; e.g., only in
578    responses or requests, in all messages, only on responses to a particular
579    request method.</t></x:lt>
580    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
581    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
582    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
583    field's value, insert or delete it.</t></x:lt>
584    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
585    <x:lt><t>Whether the header field is useful or allowable in trailers (see
586    &chunked-encoding;).</t></x:lt>
587    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
588  </list>
589</t>
590</section>
591
592<section title="Request Header Fields" anchor="request.header.fields">
593  <x:anchor-alias value="request-header"/>
594<t>
595   The request header fields allow the client to pass additional
596   information about the request, and about the client itself, to the
597   server. These fields act as request modifiers, with semantics
598   equivalent to the parameters on a programming language method
599   invocation.
600</t>
601<texttable align="left">
602  <ttcol>Header Field Name</ttcol>
603  <ttcol>Defined in...</ttcol>
604
605  <c>Accept</c> <c>&header-accept;</c>
606  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
607  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
608  <c>Accept-Language</c> <c>&header-accept-language;</c>
609  <c>Authorization</c> <c>&header-authorization;</c>
610  <c>Expect</c> <c><xref target="header.expect"/></c>
611  <c>From</c> <c><xref target="header.from"/></c>
612  <c>Host</c> <c>&header-host;</c>
613  <c>If-Match</c> <c>&header-if-match;</c>
614  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
615  <c>If-None-Match</c> <c>&header-if-none-match;</c>
616  <c>If-Range</c> <c>&header-if-range;</c>
617  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
618  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
619  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
620  <c>Range</c> <c>&header-range;</c>
621  <c>Referer</c> <c><xref target="header.referer"/></c>
622  <c>TE</c> <c>&header-te;</c>
623  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
624</texttable>
625</section>
626
627<section title="Response Header Fields" anchor="response.header.fields">
628  <x:anchor-alias value="response-header"/>
629<t>
630   The response header fields allow the server to pass additional
631   information about the response which cannot be placed in the Status-Line.
632   These header fields give information about the server and about
633   further access to the target resource (&effective-request-uri;).
634</t>
635<texttable align="left">
636  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
637
638  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
639  <c>Age</c> <c>&header-age;</c>
640  <c>Allow</c> <c><xref target="header.allow"/></c>
641  <c>Date</c> <c><xref target="header.date"/></c>
642  <c>ETag</c> <c>&header-etag;</c>
643  <c>Location</c> <c><xref target="header.location"/></c>
644  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
645  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
646  <c>Server</c> <c><xref target="header.server"/></c>
647  <c>Vary</c> <c>&header-vary;</c>
648  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
649</texttable>
650</section>
651
652</section>
653
654<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
655  <x:anchor-alias value="Reason-Phrase"/>
656  <x:anchor-alias value="Status-Code"/>
657  <x:anchor-alias value="extension-code"/>
658<t>
659   The Status-Code element is a 3-digit integer result code of the attempt to
660   understand and satisfy the request.
661</t>
662<t>
663   The Reason-Phrase is intended to give a short textual description of the
664   Status-Code and is intended for a human user. The client does not need
665   to examine or display the Reason-Phrase.
666</t>
667<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
668  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
669  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
670</artwork></figure>
671<t>
672   HTTP status codes are extensible. HTTP applications are not required
673   to understand the meaning of all registered status codes, though such
674   understanding is obviously desirable. However, applications &MUST;
675   understand the class of any status code, as indicated by the first
676   digit, and treat any unrecognized response as being equivalent to the
677   x00 status code of that class, with the exception that an
678   unrecognized response &MUST-NOT; be cached. For example, if an
679   unrecognized status code of 431 is received by the client, it can
680   safely assume that there was something wrong with its request and
681   treat the response as if it had received a 400 status code. In such
682   cases, user agents &SHOULD; present to the user the representation enclosed
683   with the response, since that representation is likely to include human-readable
684   information which will explain the unusual status.
685</t>
686
687<section title="Overview of Status Codes" anchor="overview.of.status.codes">
688<t> 
689   The status codes listed below are defined in <xref target="status.codes"/>
690   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
691   The reason phrases listed here are only recommendations &mdash; they can be
692   replaced by local equivalents without affecting the protocol.
693</t>
694<texttable align="left">
695  <ttcol>Status-Code</ttcol>
696  <ttcol>Reason-Phrase</ttcol>
697  <ttcol>Defined in...</ttcol>
698 
699  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
700  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
701
702  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
703  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
704  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
705  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
706  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
707  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
708  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
709
710  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
711  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
712  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
713  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
714  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
715  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
716  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
717
718  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
719  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
720  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
721  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
722  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
723  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
724  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
725  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
726  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
727  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
728  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
729  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
730  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
731  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
732  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
733  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
734  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
735  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
736  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
737
738  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
739  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
740  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
741  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
742  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
743  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
744</texttable>
745<t>
746   Note that this list is not exhaustive &mdash; it does not include
747   extension status codes defined in other specifications.
748</t>
749</section>
750
751<section title="Status Code Registry" anchor="status.code.registry">
752<t>
753  The HTTP Status Code Registry defines the name space for the Status-Code
754  token in the Status-Line of an HTTP response.
755</t>
756<t>
757  Values to be added to this name space are subject to IETF review
758  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
759</t>
760<t>
761  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
762</t>
763
764<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
765<t>
766   When it is necessary to express new semantics for a HTTP response that
767   aren't specific to a single application or media type, and currently defined
768   status codes are inadequate, a new status code can be registered.
769</t>
770<t>
771   HTTP status codes are generic; that is, they are potentially applicable to
772   any resource, not just one particular media type, "type" of resource, or
773   application. As such, it is preferred that new HTTP status codes be
774   registered in a document that isn't specific to a single application, so
775   that this is clear.
776</t>
777<t>
778   Definitions of new HTTP status codes typically explain the request
779   conditions that produce a response containing the status code (e.g.,
780   combinations of request headers and/or method(s)), along with any
781   interactions with response headers (e.g., those that are required, those
782   that modify the semantics of the response).
783</t>
784<t>
785   New HTTP status codes are required to fall under one of the categories
786   defined in <xref target="status.codes"/>. To allow existing parsers to
787   properly handle them, new status codes cannot disallow a response body,
788   although they can mandate a zero-length response body. They can require the
789   presence of one or more particular HTTP response header(s).
790</t>
791<t>
792   Likewise, their definitions can specify that caches are allowed to use
793   heuristics to determine their freshness (see &caching;; by default, it is
794   not allowed), and can define how to determine the resource which they
795   carry a representation for (see <xref
796   target="identifying.response.associated.with.representation"/>; by default,
797   it is anonymous).
798</t>
799</section>
800
801</section>
802
803</section>
804
805<section title="Representation" anchor="representation">
806<t>
807   Request and Response messages &MAY; transfer a representation if not otherwise
808   restricted by the request method or response status code. A representation
809   consists of metadata (representation header fields) and data (representation
810   body).  When a complete or partial representation is enclosed in an HTTP message,
811   it is referred to as the payload of the message. HTTP representations
812   are defined in &payload;.
813</t>
814<t>
815   A representation body is only present in a message when a message-body is
816   present, as described in &message-body;. The representation body is obtained
817   from the message-body by decoding any Transfer-Encoding that might
818   have been applied to ensure safe and proper transfer of the message.
819</t>
820
821<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
822<t>
823   It is sometimes necessary to determine an identifier for the resource
824   associated with a representation.
825</t>
826<t>
827   An HTTP request representation, when present, is always associated with an
828   anonymous (i.e., unidentified) resource.
829</t>
830<t>
831   In the common case, an HTTP response is a representation of the target
832   resource (see &effective-request-uri;). However, this is not always the
833   case. To determine the URI of the resource a response is associated with,
834   the following rules are used (with the first applicable one being selected):
835</t>
836<t><list style="numbers">
837   <t>If the response status code is 200 or 203 and the request method was GET,
838   the response payload is a representation of the target resource.</t>
839   <t>If the response status code is 204, 206, or 304 and the request method was GET
840   or HEAD, the response payload is a partial representation of the target
841   resource.</t>
842   <t>If the response has a Content-Location header field, and that URI is the same
843   as the effective request URI, the response payload is a representation of the
844   target resource.</t>
845   <t>If the response has a Content-Location header field, and that URI is not the
846   same as the effective request URI, then the response asserts that its
847   payload is a representation of the resource identified by the
848   Content-Location URI. However, such an assertion cannot be trusted unless
849   it can be verified by other means (not defined by HTTP).</t>
850   <t>Otherwise, the response is a representation of an anonymous (i.e.,
851   unidentified) resource.</t>
852</list></t>
853<t>
854  <cref anchor="TODO-req-uri">
855   The comparison function is going to have to be defined somewhere,
856   because we already need to compare URIs for things like cache invalidation.</cref>
857</t>
858</section>
859
860</section>
861
862
863<section title="Method Definitions" anchor="method.definitions">
864<t>
865   The set of common request methods for HTTP/1.1 is defined below. Although
866   this set can be expanded, additional methods cannot be assumed to
867   share the same semantics for separately extended clients and servers.
868</t>
869
870<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
871
872<section title="Safe Methods" anchor="safe.methods">
873<iref item="Safe Methods" primary="true"/>
874<t>
875   Implementors need to be aware that the software represents the user in
876   their interactions over the Internet, and need to allow
877   the user to be aware of any actions they take which might have an
878   unexpected significance to themselves or others.
879</t>
880<t>
881   In particular, the convention has been established that the GET, HEAD,
882   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
883   of taking an action other than retrieval. These request methods ought
884   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
885   This allows user agents to represent other methods, such as POST, PUT
886   and DELETE, in a special way, so that the user is made aware of the
887   fact that a possibly unsafe action is being requested.
888</t>
889<t>
890   Naturally, it is not possible to ensure that the server does not
891   generate side-effects as a result of performing a GET request; in
892   fact, some dynamic resources consider that a feature. The important
893   distinction here is that the user did not request the side-effects,
894   so therefore cannot be held accountable for them.
895</t>
896</section>
897
898<section title="Idempotent Methods" anchor="idempotent.methods">
899<iref item="Idempotent Methods" primary="true"/>
900<t>
901   Request methods can also have the property of "idempotence" in that,
902   aside from error or expiration issues, the intended effect of multiple
903   identical requests is the same as for a single request.
904   PUT, DELETE, and all safe request methods are idempotent.
905   It is important to note that idempotence refers only to changes
906   requested by the client: a server is free to change its state due
907   to multiple requests for the purpose of tracking those requests,
908   versioning of results, etc.
909</t>
910</section>
911</section>
912
913<section title="OPTIONS" anchor="OPTIONS">
914  <rdf:Description>
915    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
916  </rdf:Description>
917  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
918  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
919<t>
920   The OPTIONS method requests information about the
921   communication options available on the request/response chain
922   identified by the effective request URI. This method allows a client to
923   determine the options and/or requirements associated with a resource,
924   or the capabilities of a server, without implying a resource action
925   or initiating a resource retrieval.
926</t>
927<t>
928   Responses to the OPTIONS method are not cacheable.
929</t>
930<t>
931   If the OPTIONS request includes a message-body (as indicated by the
932   presence of Content-Length or Transfer-Encoding), then the media type
933   &MUST; be indicated by a Content-Type field. Although this
934   specification does not define any use for such a body, future
935   extensions to HTTP might use the OPTIONS body to make more detailed
936   queries on the server.
937</t>
938<t>
939   If the request-target is an asterisk ("*"), the OPTIONS request is
940   intended to apply to the server in general rather than to a specific
941   resource. Since a server's communication options typically depend on
942   the resource, the "*" request is only useful as a "ping" or "no-op"
943   type of method; it does nothing beyond allowing the client to test
944   the capabilities of the server. For example, this can be used to test
945   a proxy for HTTP/1.1 conformance (or lack thereof).
946</t>
947<t>
948   If the request-target is not an asterisk, the OPTIONS request applies
949   only to the options that are available when communicating with that
950   resource.
951</t>
952<t>
953   A 200 response &SHOULD; include any header fields that indicate
954   optional features implemented by the server and applicable to that
955   resource (e.g., Allow), possibly including extensions not defined by
956   this specification. The response body, if any, &SHOULD; also include
957   information about the communication options. The format for such a
958   body is not defined by this specification, but might be defined by
959   future extensions to HTTP. Content negotiation &MAY; be used to select
960   the appropriate response format. If no response body is included, the
961   response &MUST; include a Content-Length field with a field-value of
962   "0".
963</t>
964<t>
965   The Max-Forwards header field &MAY; be used to target a
966   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
967   If no Max-Forwards field is present in the request, then the forwarded
968   request &MUST-NOT; include a Max-Forwards field.
969</t>
970</section>
971
972<section title="GET" anchor="GET">
973  <rdf:Description>
974    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
975  </rdf:Description>
976  <iref primary="true" item="GET method" x:for-anchor=""/>
977  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
978<t>
979   The GET method requests transfer of a current representation of
980   the target resource.
981</t>
982<t>   
983   If the target resource is a data-producing process, it is the
984   produced data which shall be returned as the representation in the response and not
985   the source text of the process, unless that text happens to be the output of
986   the process.
987</t>
988<t>
989   The semantics of the GET method change to a "conditional GET" if the
990   request message includes an If-Modified-Since, If-Unmodified-Since,
991   If-Match, If-None-Match, or If-Range header field. A conditional GET
992   requests that the representation be transferred only under the
993   circumstances described by the conditional header field(s). The
994   conditional GET request is intended to reduce unnecessary network
995   usage by allowing cached representations to be refreshed without requiring
996   multiple requests or transferring data already held by the client.
997</t>
998<t>
999   The semantics of the GET method change to a "partial GET" if the
1000   request message includes a Range header field. A partial GET requests
1001   that only part of the representation be transferred, as described in &header-range;.
1002   The partial GET request is intended to reduce unnecessary
1003   network usage by allowing partially-retrieved representations to be
1004   completed without transferring data already held by the client.
1005</t>
1006<t>
1007   Bodies on GET requests have no defined semantics. Note that sending a body
1008   on a GET request might cause some existing implementations to reject the
1009   request.
1010</t>
1011<t>
1012   The response to a GET request is cacheable and &MAY; be used to satisfy
1013   subsequent GET and HEAD requests (see &caching;).
1014</t>
1015<t>
1016   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
1017</t>
1018</section>
1019
1020<section title="HEAD" anchor="HEAD">
1021  <rdf:Description>
1022    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1023  </rdf:Description>
1024  <iref primary="true" item="HEAD method" x:for-anchor=""/>
1025  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
1026<t>
1027   The HEAD method is identical to GET except that the server &MUST-NOT;
1028   return a message-body in the response. The metadata contained
1029   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
1030   to the information sent in response to a GET request. This method can
1031   be used for obtaining metadata about the representation implied by the
1032   request without transferring the representation body. This method is
1033   often used for testing hypertext links for validity, accessibility,
1034   and recent modification.
1035</t>
1036<t>
1037   The response to a HEAD request is cacheable and &MAY; be used to satisfy
1038   a subsequent HEAD request; see &caching;. It also &MAY; be used to update a previously cached
1039   representation from that resource; if the new field values
1040   indicate that the cached representation differs from the current representation (as
1041   would be indicated by a change in Content-Length, ETag
1042   or Last-Modified), then the cache &MUST; treat the cache entry as
1043   stale.
1044</t>
1045<t>
1046   Bodies on HEAD requests have no defined semantics. Note that sending a body
1047   on a HEAD request might cause some existing implementations to reject the
1048   request.
1049</t>
1050</section>
1051
1052<section title="POST" anchor="POST">
1053  <iref primary="true" item="POST method" x:for-anchor=""/>
1054  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
1055<t>
1056   The POST method requests that the origin server accept the
1057   representation enclosed in the request as data to be processed by the
1058   target resource. POST is designed to allow a uniform method to cover the
1059   following functions:
1060  <list style="symbols">
1061    <t>
1062      Annotation of existing resources;
1063    </t>
1064    <t>
1065        Posting a message to a bulletin board, newsgroup, mailing list,
1066        or similar group of articles;
1067    </t>
1068    <t>
1069        Providing a block of data, such as the result of submitting a
1070        form, to a data-handling process;
1071    </t>
1072    <t>
1073        Extending a database through an append operation.
1074    </t>
1075  </list>
1076</t>
1077<t>
1078   The actual function performed by the POST method is determined by the
1079   server and is usually dependent on the effective request URI.
1080</t>
1081<t>
1082   The action performed by the POST method might not result in a
1083   resource that can be identified by a URI. In this case, either 200
1084   (OK) or 204 (No Content) is the appropriate response status code,
1085   depending on whether or not the response includes a representation that
1086   describes the result.
1087</t>
1088<t>
1089   If a resource has been created on the origin server, the response
1090   &SHOULD; be 201 (Created) and contain a representation which describes the
1091   status of the request and refers to the new resource, and a Location
1092   header field (see <xref target="header.location"/>).
1093</t>
1094<t>
1095   Responses to POST requests are only cacheable when they
1096   include explicit freshness information (see &p6-explicit;). A
1097   cached POST response with a Content-Location header field
1098   (see &header-content-location;) whose value is the effective
1099   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1100</t>
1101<t>
1102   Note that POST caching is not widely implemented.
1103   However, the 303 (See Other) response can be used to direct the
1104   user agent to retrieve a cacheable resource.
1105</t>
1106</section>
1107
1108<section title="PUT" anchor="PUT">
1109  <iref primary="true" item="PUT method" x:for-anchor=""/>
1110  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
1111<t>
1112   The PUT method requests that the state of the target resource
1113   be created or replaced with the state defined by the representation
1114   enclosed in the request message payload.  A successful PUT of a given
1115   representation would suggest that a subsequent GET on that same target
1116   resource will result in an equivalent representation being returned in
1117   a 200 (OK) response.  However, there is no guarantee that such a state
1118   change will be observable, since the target resource might be acted
1119   upon by other user agents in parallel, or might be subject to dynamic
1120   processing by the origin server, before any subsequent GET is received.
1121   A successful response only implies that the user agent's intent was
1122   achieved at the time of its processing by the origin server.
1123</t>
1124<t>   
1125   If the target resource does not have a current representation and
1126   the PUT successfully creates one, then the origin server &MUST; inform
1127   the user agent by sending a 201 (Created) response.  If the target
1128   resource does have a current representation and that representation is
1129   successfully modified in accordance with the state of the enclosed
1130   representation, then either a 200 (OK) or 204 (No Content) response
1131   &SHOULD; be sent to indicate successful completion of the request.
1132</t>
1133<t>
1134   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1135   as part of the resource state).
1136</t>
1137<t>
1138   An origin server &SHOULD; verify that the PUT representation is
1139   consistent with any constraints which the server has for the target
1140   resource that cannot or will not be changed by the PUT.  This is
1141   particularly important when the origin server uses internal
1142   configuration information related to the URI in order to set the
1143   values for representation metadata on GET responses.  When a PUT
1144   representation is inconsistent with the target resource, the origin
1145   server &SHOULD; either make them consistent, by transforming the
1146   representation or changing the resource configuration, or respond
1147   with an appropriate error message containing sufficient information
1148   to explain why the representation is unsuitable.  The 409 (Conflict)
1149   or 415 (Unsupported Media Type) status codes are suggested, with the
1150   latter being specific to constraints on Content-Type values.
1151</t>
1152<t>
1153   For example, if the target resource is configured to always have a
1154   Content-Type of "text/html" and the representation being PUT has a
1155   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1156   (a) reconfigure the target resource to reflect the new media type;
1157   (b) transform the PUT representation to a format consistent with that
1158   of the resource before saving it as the new resource state; or,
1159   (c) reject the request with a 415 response indicating that the target
1160   resource is limited to "text/html", perhaps including a link to a
1161   different resource that would be a suitable target for the new
1162   representation.
1163</t>
1164<t>
1165   HTTP does not define exactly how a PUT method affects the state
1166   of an origin server beyond what can be expressed by the intent of
1167   the user agent request and the semantics of the origin server response.
1168   It does not define what a resource might be, in any sense of that
1169   word, beyond the interface provided via HTTP.  It does not define
1170   how resource state is "stored", nor how such storage might change
1171   as a result of a change in resource state, nor how the origin server
1172   translates resource state into representations.  Generally speaking,
1173   all implementation details behind the resource interface are
1174   intentionally hidden by the server.
1175</t>
1176<t>
1177   The fundamental difference between the POST and PUT methods is
1178   highlighted by the different intent for the target resource.
1179   The target resource in a POST request is intended to handle the
1180   enclosed representation as a data-accepting process, such as for
1181   a gateway to some other protocol or a document that accepts annotations.
1182   In contrast, the target resource in a PUT request is intended to
1183   take the enclosed representation as a new or replacement value.
1184   Hence, the intent of PUT is idempotent and visible to intermediaries,
1185   even though the exact effect is only known by the origin server.
1186</t>
1187<t>
1188   Proper interpretation of a PUT request presumes that the user agent
1189   knows what target resource is desired.  A service that is intended
1190   to select a proper URI on behalf of the client, after receiving
1191   a state-changing request, &SHOULD; be implemented using the POST
1192   method rather than PUT.  If the origin server will not make the
1193   requested PUT state change to the target resource and instead
1194   wishes to have it applied to a different resource, such as when the
1195   resource has been moved to a different URI, then the origin server
1196   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
1197   then make its own decision regarding whether or not to redirect the
1198   request.
1199</t>
1200<t>
1201   A PUT request applied to the target resource &MAY; have side-effects
1202   on other resources.  For example, an article might have a URI for
1203   identifying "the current version" (a resource) which is separate
1204   from the URIs identifying each particular version (different
1205   resources that at one point shared the same state as the current version
1206   resource).  A successful PUT request on "the current version" URI might
1207   therefore create a new version resource in addition to changing the
1208   state of the target resource, and might also cause links to be added
1209   between the related resources.
1210</t>
1211<t>
1212   An origin server &SHOULD; reject any PUT request that contains a
1213   Content-Range header field, since it might be misinterpreted as
1214   partial content (or might be partial content that is being mistakenly
1215   PUT as a full representation).  Partial content updates are
1216   possible by targeting a separately identified resource with state
1217   that overlaps a portion of the larger resource, or by using a
1218   different method that has been specifically defined for partial
1219   updates (for example, the PATCH method defined in
1220   <xref target="RFC5789"/>).
1221</t>
1222<t>
1223   Responses to the PUT method are not cacheable. If a PUT request passes
1224   through a cache that has one or more stored responses for the effective
1225   request URI, those stored responses will be invalidated (see
1226   &p6-invalid;).
1227</t>
1228</section>
1229
1230<section title="DELETE" anchor="DELETE">
1231  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1232  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
1233<t>
1234   The DELETE method requests that the origin server delete the target
1235   resource. This method &MAY; be overridden by
1236   human intervention (or other means) on the origin server. The client cannot
1237   be guaranteed that the operation has been carried out, even if the
1238   status code returned from the origin server indicates that the action
1239   has been completed successfully. However, the server &SHOULD-NOT; 
1240   indicate success unless, at the time the response is given, it
1241   intends to delete the resource or move it to an inaccessible
1242   location.
1243</t>
1244<t>
1245   A successful response &SHOULD; be 200 (OK) if the response includes an
1246   representation describing the status, 202 (Accepted) if the action has not
1247   yet been enacted, or 204 (No Content) if the action has been enacted
1248   but the response does not include a representation.
1249</t>
1250<t>
1251   Bodies on DELETE requests have no defined semantics. Note that sending a body
1252   on a DELETE request might cause some existing implementations to reject the
1253   request.
1254</t>
1255<t>
1256   Responses to the DELETE method are not cacheable. If a DELETE request
1257   passes through a cache that has one or more stored responses for the
1258   effective request URI, those stored responses will be invalidated (see
1259   &p6-invalid;).
1260</t>
1261</section>
1262
1263<section title="TRACE" anchor="TRACE">
1264  <rdf:Description>
1265    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1266  </rdf:Description>
1267  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1268  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
1269<t>
1270   The TRACE method requests a remote, application-layer loop-back
1271   of the request message. The final recipient of the request
1272   &SHOULD; reflect the message received back to the client as the
1273   message-body of a 200 (OK) response. The final recipient is either the
1274   origin server or the first proxy to receive a Max-Forwards
1275   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1276   A TRACE request &MUST-NOT; include a message-body.
1277</t>
1278<t>
1279   TRACE allows the client to see what is being received at the other
1280   end of the request chain and use that data for testing or diagnostic
1281   information. The value of the Via header field (&header-via;) is of
1282   particular interest, since it acts as a trace of the request chain.
1283   Use of the Max-Forwards header field allows the client to limit the
1284   length of the request chain, which is useful for testing a chain of
1285   proxies forwarding messages in an infinite loop.
1286</t>
1287<t>
1288   If the request is valid, the response &SHOULD; have a Content-Type of
1289   "message/http" (see &media-type-message-http;) and contain a message-body
1290   that encloses a copy of the entire request message.
1291   Responses to the TRACE method are not cacheable.
1292</t>
1293</section>
1294
1295<section title="CONNECT" anchor="CONNECT">
1296  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1297  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1298<t>
1299   The CONNECT method requests that the proxy establish a tunnel
1300   to the request-target and then restrict its behavior to blind
1301   forwarding of packets until the connection is closed.
1302</t>
1303<t>
1304   When using CONNECT, the request-target &MUST; use the authority form
1305   (&request-target;); i.e., the request-target consists of only the
1306   host name and port number of the tunnel destination, separated by a colon.
1307   For example,
1308</t>
1309<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1310CONNECT server.example.com:80 HTTP/1.1
1311Host: server.example.com:80
1312
1313</artwork></figure>
1314<t>
1315   Other HTTP mechanisms can be used normally with the CONNECT method &mdash;
1316   except end-to-end protocol Upgrade requests, since the
1317   tunnel must be established first.
1318</t>
1319<t>
1320   For example, proxy authentication might be used to establish the
1321   authority to create a tunnel:
1322</t>
1323<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1324CONNECT server.example.com:80 HTTP/1.1
1325Host: server.example.com:80
1326Proxy-Authorization: basic aGVsbG86d29ybGQ=
1327
1328</artwork></figure>
1329<t>
1330   Bodies on CONNECT requests have no defined semantics. Note that sending a body
1331   on a CONNECT request might cause some existing implementations to reject the
1332   request.
1333</t>
1334<t>
1335   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1336   sent immediately after the blank line. The usual caveats also apply:
1337   data may be discarded if the eventual response is negative, and the
1338   connection may be reset with no response if more than one TCP segment
1339   is outstanding.
1340</t>
1341
1342<section title="Establishing a Tunnel with CONNECT">
1343<t>
1344   Any successful (2xx) response to a CONNECT request indicates that the
1345   proxy has established a connection to the requested host and port,
1346   and has switched to tunneling the current connection to that server
1347   connection.
1348</t>
1349<t>
1350   It may be the case that the proxy itself can only reach the requested
1351   origin server through another proxy.  In this case, the first proxy
1352   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1353   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1354   unless it has either a direct or tunnel connection established to the
1355   authority.
1356</t>
1357<t>
1358   An origin server which receives a CONNECT request for itself &MAY;
1359   respond with a 2xx status code to indicate that a connection is
1360   established.
1361</t>
1362<t>
1363   If at any point either one of the peers gets disconnected, any
1364   outstanding data that came from that peer will be passed to the other
1365   one, and after that also the other connection will be terminated by
1366   the proxy. If there is outstanding data to that peer undelivered,
1367   that data will be discarded.
1368</t>
1369
1370</section>
1371</section>
1372</section>
1373
1374
1375<section title="Status Code Definitions" anchor="status.codes">
1376<t>
1377   The first digit of the Status-Code defines the class of response. The
1378   last two digits do not have any categorization role. There are 5
1379   values for the first digit:
1380  <list style="symbols">
1381    <t>
1382      1xx: Informational - Request received, continuing process
1383    </t>
1384    <t>
1385      2xx: Success - The action was successfully received,
1386        understood, and accepted
1387    </t>
1388    <t>
1389      3xx: Redirection - Further action must be taken in order to
1390        complete the request
1391    </t>
1392    <t>
1393      4xx: Client Error - The request contains bad syntax or cannot
1394        be fulfilled
1395    </t>
1396    <t>
1397      5xx: Server Error - The server failed to fulfill an apparently
1398        valid request
1399    </t>
1400  </list>
1401</t>
1402<t>
1403   Each Status-Code is described below, including any metadata required
1404   in the response.
1405</t>
1406<t>
1407   For most status codes the response can carry a payload, in which case a
1408   Content-Type header field indicates the payload's media type
1409   (&header-content-type;).
1410</t>
1411
1412<section title="Informational 1xx" anchor="status.1xx">
1413<t>
1414   This class of status code indicates a provisional response,
1415   consisting only of the Status-Line and optional header fields, and is
1416   terminated by an empty line. There are no required header fields for this
1417   class of status code. Since HTTP/1.0 did not define any 1xx status
1418   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1419   except under experimental conditions.
1420</t>
1421<t>
1422   A client &MUST; be prepared to accept one or more 1xx status responses
1423   prior to a regular response, even if the client does not expect a 100
1424   (Continue) status message. Unexpected 1xx status responses &MAY; be
1425   ignored by a user agent.
1426</t>
1427<t>
1428   Proxies &MUST; forward 1xx responses, unless the connection between the
1429   proxy and its client has been closed, or unless the proxy itself
1430   requested the generation of the 1xx response. (For example, if a
1431   proxy adds a "Expect: 100-continue" field when it forwards a request,
1432   then it need not forward the corresponding 100 (Continue)
1433   response(s).)
1434</t>
1435
1436<section title="100 Continue" anchor="status.100">
1437  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1438  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1439<t>
1440   The client &SHOULD; continue with its request. This interim response is
1441   used to inform the client that the initial part of the request has
1442   been received and has not yet been rejected by the server. The client
1443   &SHOULD; continue by sending the remainder of the request or, if the
1444   request has already been completed, ignore this response. The server
1445   &MUST; send a final response after the request has been completed. See
1446   &use100; for detailed discussion of the use and handling of this
1447   status code.
1448</t>
1449</section>
1450
1451<section title="101 Switching Protocols" anchor="status.101">
1452  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1453  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1454<t>
1455   The server understands and is willing to comply with the client's
1456   request, via the Upgrade message header field (&header-upgrade;), for a
1457   change in the application protocol being used on this connection. The
1458   server will switch protocols to those defined by the response's
1459   Upgrade header field immediately after the empty line which
1460   terminates the 101 response.
1461</t>
1462<t>
1463   The protocol &SHOULD; be switched only when it is advantageous to do
1464   so. For example, switching to a newer version of HTTP is advantageous
1465   over older versions, and switching to a real-time, synchronous
1466   protocol might be advantageous when delivering resources that use
1467   such features.
1468</t>
1469</section>
1470</section>
1471
1472<section title="Successful 2xx" anchor="status.2xx">
1473<t>
1474   This class of status code indicates that the client's request was
1475   successfully received, understood, and accepted.
1476</t>
1477
1478<section title="200 OK" anchor="status.200">
1479  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1480  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1481<t>
1482   The request has succeeded. The payload returned with the response
1483   is dependent on the method used in the request, for example:
1484  <list style="hanging">
1485    <t hangText="GET">
1486      a representation of the target resource is sent in the response;
1487    </t>
1488    <t hangText="HEAD">
1489      the same representation as GET, except without the message-body;
1490    </t>
1491    <t hangText="POST">
1492      a representation describing or containing the result of the action;
1493    </t>
1494    <t hangText="TRACE">
1495      a representation containing the request message as received by the
1496      end server.
1497    </t>
1498  </list>
1499</t>
1500<t>
1501   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1502   freshness for 200 responses.
1503</t>
1504</section>
1505
1506<section title="201 Created" anchor="status.201">
1507  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1508  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1509<t>
1510   The request has been fulfilled and has resulted in a new resource being
1511   created. The newly created resource can be referenced by the URI(s)
1512   returned in the payload of the response, with the most specific URI
1513   for the resource given by a Location header field. The response
1514   can include a payload containing a list of resource
1515   characteristics and location(s) from which the user or user agent can
1516   choose the one most appropriate.
1517</t>
1518<t>
1519   The origin server &MUST; create the resource before returning the 201 status
1520   code. If the action cannot be carried out immediately, the server &SHOULD;
1521   respond with 202 (Accepted) response instead.
1522</t>
1523<t>
1524   A 201 response &MAY; contain an ETag response header field indicating
1525   the current value of the entity-tag for the representation of the resource
1526   just created (see &header-etag;).
1527</t>
1528</section>
1529
1530<section title="202 Accepted" anchor="status.202">
1531  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1532  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1533<t>
1534   The request has been accepted for processing, but the processing has
1535   not been completed.  The request might or might not eventually be
1536   acted upon, as it might be disallowed when processing actually takes
1537   place. There is no facility for re-sending a status code from an
1538   asynchronous operation such as this.
1539</t>
1540<t>
1541   The 202 response is intentionally non-committal. Its purpose is to
1542   allow a server to accept a request for some other process (perhaps a
1543   batch-oriented process that is only run once per day) without
1544   requiring that the user agent's connection to the server persist
1545   until the process is completed. The representation returned with this
1546   response &SHOULD; include an indication of the request's current status
1547   and either a pointer to a status monitor or some estimate of when the
1548   user can expect the request to be fulfilled.
1549</t>
1550</section>
1551
1552<section title="203 Non-Authoritative Information" anchor="status.203">
1553  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1554  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1555<t>
1556   The representation in the response has been transformed or otherwise
1557   modified by a transforming proxy (&intermediaries;).  Note that the
1558   behavior of transforming intermediaries is controlled by the no-transform
1559   Cache-Control directive (&header-cache-control;).
1560</t>
1561<t>
1562   This status code is only appropriate when the response status code would
1563   have been 200 (OK) otherwise. When the status code before transformation
1564   would have been different, the 214 Transformation Applied warn-code
1565   (&header-warning;) is appropriate.
1566</t>
1567<t>
1568   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1569   freshness for 203 responses.
1570</t>
1571</section>
1572
1573<section title="204 No Content" anchor="status.204">
1574  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1575  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1576<t>
1577   The 204 (No Content) status code indicates that the server has
1578   successfully fulfilled the request and that there is no additional
1579   content to return in the response payload body.  Metadata in the
1580   response header fields refer to the target resource and its current
1581   representation after the requested action.
1582</t>
1583<t>
1584   For example, if a 204 status code is received in response to a PUT
1585   request and the response contains an ETag header field, then the PUT
1586   was successful and the ETag field-value contains the entity-tag for
1587   the new representation of that target resource.
1588</t>
1589<t>
1590   The 204 response allows a server to indicate that the action has been
1591   successfully applied to the target resource while implying that the
1592   user agent &SHOULD-NOT; traverse away from its current "document view"
1593   (if any).  The server assumes that the user agent will provide some
1594   indication of the success to its user, in accord with its own interface,
1595   and apply any new or updated metadata in the response to the active
1596   representation.
1597</t>
1598<t>
1599   For example, a 204 status code is commonly used with document editing
1600   interfaces corresponding to a "save" action, such that the document
1601   being saved remains available to the user for editing. It is also
1602   frequently used with interfaces that expect automated data transfers
1603   to be prevalent, such as within distributed version control systems.
1604</t>
1605<t>
1606   The 204 response &MUST-NOT; include a message-body, and thus is always
1607   terminated by the first empty line after the header fields.
1608</t>
1609</section>
1610
1611<section title="205 Reset Content" anchor="status.205">
1612  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1613  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1614<t>
1615   The server has fulfilled the request and the user agent &SHOULD; reset
1616   the document view which caused the request to be sent. This response
1617   is primarily intended to allow input for actions to take place via
1618   user input, followed by a clearing of the form in which the input is
1619   given so that the user can easily initiate another input action.
1620</t>
1621<t>   
1622   The message-body included with the response &MUST; be empty. Note that
1623   receivers still need to parse the response according to the algorithm defined
1624   in &message-body;.
1625</t>
1626</section>
1627</section>
1628
1629<section title="Redirection 3xx" anchor="status.3xx">
1630<t>
1631   This class of status code indicates that further action needs to be
1632   taken by the user agent in order to fulfill the request.  If the required
1633   action involves a subsequent HTTP request, it &MAY; be carried out by the
1634   user agent without interaction with the user if and only if the method used
1635   in the second request is known to be "safe", as defined in
1636   <xref target="safe.methods"/>.
1637</t>
1638<t>
1639   There are several types of redirects:
1640   <list style="numbers">
1641      <x:lt>
1642        <t>
1643          Redirects of the request to another URI, either temporarily or
1644          permanently. The new URI is specified in the Location header field.
1645          In this specification, the status codes 301 (Moved Permanently),
1646          302 (Found), and 307 (Temporary Redirect) fall under this category.
1647        </t>
1648      </x:lt>
1649      <x:lt>
1650        <t>
1651          Redirection to a new location that represents an indirect response to
1652          the request, such as the result of a POST operation to be retrieved
1653          with a subsequent GET request. This is status code 303 (See Other).
1654        </t>
1655      </x:lt>
1656      <x:lt>
1657        <t>
1658          Redirection offering a choice of matching resources for use by
1659          agent-driven content negotiation (&agent-driven-negotiation;). This
1660          is status code 300 (Multiple Choices).
1661        </t>
1662      </x:lt>
1663      <x:lt>
1664        <t>
1665          Other kinds of redirection, such as to a cached result (status code 304
1666          (Not Modified), see &status-304;).
1667        </t>
1668      </x:lt>
1669   </list>
1670</t>
1671<x:note>
1672  <t>
1673    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1674    and 302 (Found) were defined for the first type of redirect, and the second
1675    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1676    However it turned out that web forms using POST expected redirects to change
1677    the operation for the subsequent request to retrieval (GET). To address this
1678    use case, HTTP/1.1 introduced the second type of redirect with the status
1679    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1680    As user agents did not change their behavior to maintain backwards
1681    compatibility, the first revision of HTTP/1.1 added yet another status code,
1682    307 (Temporary Redirect), for which the backwards compatibility problems did
1683    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1684    Over 10 years later, most user agents still do method rewriting for
1685    status codes 301 and 302, therefore this specification makes that behavior
1686    conformant in case the original request was POST.
1687  </t>
1688</x:note>
1689<t>
1690   A Location header field on a 3xx response indicates that a client &MAY;
1691   automatically redirect to the URI provided; see <xref target="header.location"/>.
1692</t>
1693<t>
1694   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1695   automatic redirection needs to done with care, since the redirect might
1696   change the conditions under which the request was issued.
1697</t>
1698<t>
1699   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1700   "infinite" redirection loops).
1701</t>
1702<x:note>
1703  <t>
1704    <x:h>Note:</x:h> An earlier version of this specification recommended a
1705    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1706    Content developers need to be aware that some clients might
1707    implement such a fixed limitation.
1708  </t>
1709</x:note>
1710
1711<section title="300 Multiple Choices" anchor="status.300">
1712  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1713  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1714<t>
1715   The target resource has more than one
1716   representation, each with its own specific location, and agent-driven
1717   negotiation information (&content-negotiation;) is being provided so that
1718   the user (or user agent) can select a preferred representation by
1719   redirecting its request to that location.
1720</t>
1721<t>
1722   Unless it was a HEAD request, the response &SHOULD; include a representation
1723   containing a list of representation metadata and location(s) from
1724   which the user or user agent can choose the one most appropriate. Depending
1725   upon the format and the capabilities of
1726   the user agent, selection of the most appropriate choice &MAY; be
1727   performed automatically. However, this specification does not define
1728   any standard for such automatic selection.
1729</t>
1730<t>
1731   If the server has a preferred choice of representation, it &SHOULD;
1732   include the specific URI for that representation in the Location
1733   field; user agents &MAY; use the Location field value for automatic
1734   redirection.
1735</t>
1736<t>
1737   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1738   freshness for 300 responses.
1739</t>
1740
1741</section>
1742
1743<section title="301 Moved Permanently" anchor="status.301">
1744  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1745  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1746<t>
1747   The target resource has been assigned a new permanent URI and any
1748   future references to this resource &SHOULD; use one of the returned
1749   URIs.  Clients with link editing capabilities ought to automatically
1750   re-link references to the effective request URI to one or more of the new
1751   references returned by the server, where possible.
1752</t>
1753<t>
1754   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1755   freshness for 301 responses.
1756</t>
1757<t>
1758   The new permanent URI &SHOULD; be given by the Location field in the
1759   response. A response payload can contain a short hypertext note with a
1760   hyperlink to the new URI(s).
1761</t>
1762<x:note>
1763  <t>
1764    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1765    request method from POST to GET for the subsequent request. If this
1766    behavior is undesired, status code 307 (Temporary Redirect) can be used
1767    instead.
1768  </t>
1769</x:note>
1770</section>
1771
1772<section title="302 Found" anchor="status.302">
1773  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1774  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1775<t>
1776   The target resource resides temporarily under a different URI.
1777   Since the redirection might be altered on occasion, the client &SHOULD;
1778   continue to use the effective request URI for future requests.
1779</t>
1780<t>
1781   The temporary URI &SHOULD; be given by the Location field in the
1782   response. A response payload can contain a short hypertext note with a
1783   hyperlink to the new URI(s).
1784</t>
1785<x:note>
1786  <t>
1787    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1788    request method from POST to GET for the subsequent request. If this
1789    behavior is undesired, status code 307 (Temporary Redirect) can be used
1790    instead.
1791  </t>
1792</x:note>
1793</section>
1794
1795<section title="303 See Other" anchor="status.303">
1796  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1797  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1798<t>
1799   The 303 status code indicates that the server is redirecting the
1800   user agent to a different resource, as indicated by a URI in the
1801   Location header field, that is intended to provide an indirect
1802   response to the original request.  In order to satisfy the original
1803   request, a user agent &SHOULD; perform a retrieval request using the
1804   Location URI (a GET or HEAD request if using HTTP), which
1805   may itself be redirected further, and present the eventual result as an
1806   answer to the original request.
1807   Note that the new URI in the Location header field is not considered
1808   equivalent to the effective request URI.
1809</t>
1810<t>
1811   This status code is generally applicable to any HTTP method.  It is
1812   primarily used to allow the output of a POST action to redirect
1813   the user agent to a selected resource, since doing so provides the
1814   information corresponding to the POST response in a form that
1815   can be separately identified, bookmarked, and cached independent
1816   of the original request.
1817</t>
1818<t>
1819   A 303 response to a GET request indicates that the requested
1820   resource does not have a representation of its own that can be
1821   transferred by the server over HTTP.  The Location URI indicates a
1822   resource that is descriptive of the target resource, such that the
1823   follow-on representation might be useful to recipients without
1824   implying that it adequately represents the target resource.
1825   Note that answers to the questions of what can be represented, what
1826   representations are adequate, and what might be a useful description
1827   are outside the scope of HTTP and thus entirely determined by the
1828   URI owner(s).
1829</t>
1830<t>
1831   Except for responses to a HEAD request, the representation of a 303
1832   response &SHOULD; contain a short hypertext note with a hyperlink
1833   to the Location URI.
1834</t>
1835</section>
1836
1837<section title="305 Use Proxy" anchor="status.305">
1838  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1839  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1840<t>
1841   The 305 status code was defined in a previous version of this specification
1842   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1843</t>
1844</section>
1845
1846<section title="306 (Unused)" anchor="status.306">
1847  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1848  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1849<t>
1850   The 306 status code was used in a previous version of the
1851   specification, is no longer used, and the code is reserved.
1852</t>
1853</section>
1854
1855<section title="307 Temporary Redirect" anchor="status.307">
1856  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1857  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1858<t>
1859   The target resource resides temporarily under a different URI.
1860   Since the redirection can change over time, the client &SHOULD;
1861   continue to use the effective request URI for future requests.
1862</t>
1863<t>
1864   The temporary URI &SHOULD; be given by the Location field in the
1865   response. A response payload can contain a short hypertext note with a
1866   hyperlink to the new URI(s).
1867</t>
1868<x:note>
1869  <t>
1870    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1871    it does not allow rewriting the request method from POST to GET. This
1872    specification defines no equivalent counterpart for 301 Moved Permanently.
1873  </t>
1874</x:note>
1875</section>
1876</section>
1877
1878<section title="Client Error 4xx" anchor="status.4xx">
1879<t>
1880   The 4xx class of status code is intended for cases in which the
1881   client seems to have erred. Except when responding to a HEAD request,
1882   the server &SHOULD; include a representation containing an explanation of the
1883   error situation, and whether it is a temporary or permanent
1884   condition. These status codes are applicable to any request method.
1885   User agents &SHOULD; display any included representation to the user.
1886</t>
1887
1888<section title="400 Bad Request" anchor="status.400">
1889  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1890  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1891<t>
1892   The server cannot or will not process the request, due to a client error (e.g.,
1893   malformed syntax).
1894</t>
1895</section>
1896
1897<section title="402 Payment Required" anchor="status.402">
1898  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1899  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1900<t>
1901   This code is reserved for future use.
1902</t>
1903</section>
1904
1905<section title="403 Forbidden" anchor="status.403">
1906  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1907  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1908<t>
1909   The server understood the request, but refuses to authorize it. Providing
1910   different user authentication credentials might be successful, but any
1911   credentials that were provided in the request are insufficient. The request
1912   &SHOULD-NOT; be repeated with the same credentials.
1913</t>
1914<t>
1915   If the request method was not HEAD and the server wishes to make
1916   public why the request has not been fulfilled, it &SHOULD; describe the
1917   reason for the refusal in the representation.  If the server does not wish to
1918   make this information available to the client, the status code 404
1919   (Not Found) &MAY; be used instead.
1920</t>
1921</section>
1922
1923<section title="404 Not Found" anchor="status.404">
1924  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1925  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1926<t>
1927   The server has not found anything matching the effective request URI. No
1928   indication is given of whether the condition is temporary or
1929   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1930   knows, through some internally configurable mechanism, that an old
1931   resource is permanently unavailable and has no forwarding address.
1932   This status code is commonly used when the server does not wish to
1933   reveal exactly why the request has been refused, or when no other
1934   response is applicable.
1935</t>
1936</section>
1937
1938<section title="405 Method Not Allowed" anchor="status.405">
1939  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1940  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1941<t>
1942   The method specified in the Request-Line is not allowed for the target
1943   resource. The response &MUST; include an Allow header field containing a
1944   list of valid methods for the requested resource.
1945</t>
1946</section>
1947
1948<section title="406 Not Acceptable" anchor="status.406">
1949  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1950  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1951<t>
1952   The resource identified by the request is only capable of generating
1953   response representations which have content characteristics not acceptable
1954   according to the Accept and Accept-* header fields sent in the request
1955   (see &p3-header-fields;).
1956</t>
1957<t>
1958   Unless it was a HEAD request, the response &SHOULD; include a representation
1959   containing a list of available representation characteristics and location(s)
1960   from which the user or user agent can choose the one most
1961   appropriate. Depending upon the format and the
1962   capabilities of the user agent, selection of the most appropriate
1963   choice &MAY; be performed automatically. However, this specification
1964   does not define any standard for such automatic selection.
1965</t>
1966<x:note>
1967  <t>
1968    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1969    not acceptable according to the accept header fields sent in the
1970    request. In some cases, this might even be preferable to sending a
1971    406 response. User agents are encouraged to inspect the header fields of
1972    an incoming response to determine if it is acceptable.
1973  </t>
1974</x:note>
1975<t>
1976   If the response could be unacceptable, a user agent &SHOULD;
1977   temporarily stop receipt of more data and query the user for a
1978   decision on further actions.
1979</t>
1980</section>
1981
1982<section title="408 Request Timeout" anchor="status.408">
1983  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1984  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1985<t>
1986   The client did not produce a request within the time that the server
1987   was prepared to wait. The client &MAY; repeat the request without
1988   modifications at any later time.
1989</t>
1990</section>
1991
1992<section title="409 Conflict" anchor="status.409">
1993  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1994  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1995<t>
1996   The request could not be completed due to a conflict with the current
1997   state of the resource. This code is only allowed in situations where
1998   it is expected that the user might be able to resolve the conflict
1999   and resubmit the request. The response body &SHOULD; include enough
2000   information for the user to recognize the source of the conflict.
2001   Ideally, the response representation would include enough information for the
2002   user or user agent to fix the problem; however, that might not be
2003   possible and is not required.
2004</t>
2005<t>
2006   Conflicts are most likely to occur in response to a PUT request. For
2007   example, if versioning were being used and the representation being PUT
2008   included changes to a resource which conflict with those made by an
2009   earlier (third-party) request, the server might use the 409 response
2010   to indicate that it can't complete the request. In this case, the
2011   response representation would likely contain a list of the differences
2012   between the two versions.
2013</t>
2014</section>
2015
2016<section title="410 Gone" anchor="status.410">
2017  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
2018  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
2019<t>
2020   The target resource is no longer available at the server and no
2021   forwarding address is known. This condition is expected to be
2022   considered permanent. Clients with link editing capabilities &SHOULD;
2023   delete references to the effective request URI after user approval. If the
2024   server does not know, or has no facility to determine, whether or not
2025   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
2026   used instead.
2027</t>
2028<t>
2029   The 410 response is primarily intended to assist the task of web
2030   maintenance by notifying the recipient that the resource is
2031   intentionally unavailable and that the server owners desire that
2032   remote links to that resource be removed. Such an event is common for
2033   limited-time, promotional services and for resources belonging to
2034   individuals no longer working at the server's site. It is not
2035   necessary to mark all permanently unavailable resources as "gone" or
2036   to keep the mark for any length of time &mdash; that is left to the
2037   discretion of the server owner.
2038</t>
2039<t>
2040   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
2041   for 410 responses.
2042</t>
2043</section>
2044
2045<section title="411 Length Required" anchor="status.411">
2046  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
2047  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
2048<t>
2049   The server refuses to accept the request without a defined Content-Length.
2050   The client &MAY; repeat the request if it adds a valid
2051   Content-Length header field containing the length of the message-body
2052   in the request message.
2053</t>
2054</section>
2055
2056<section title="413 Request Representation Too Large" anchor="status.413">
2057  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2058  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2059<t>
2060   The server is refusing to process a request because the request
2061   representation is larger than the server is willing or able to process. The
2062   server &MAY; close the connection to prevent the client from continuing
2063   the request.
2064</t>
2065<t>
2066   If the condition is temporary, the server &SHOULD; include a Retry-After
2067   header field to indicate that it is temporary and after what
2068   time the client &MAY; try again.
2069</t>
2070</section>
2071
2072<section title="414 URI Too Long" anchor="status.414">
2073  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2074  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
2075<t>
2076   The server is refusing to service the request because the effective request URI
2077   is longer than the server is willing to interpret. This rare
2078   condition is only likely to occur when a client has improperly
2079   converted a POST request to a GET request with long query
2080   information, when the client has descended into a URI "black hole" of
2081   redirection (e.g., a redirected URI prefix that points to a suffix of
2082   itself), or when the server is under attack by a client attempting to
2083   exploit security holes present in some servers using fixed-length
2084   buffers for reading or manipulating the effective request URI.
2085</t>
2086</section>
2087
2088<section title="415 Unsupported Media Type" anchor="status.415">
2089  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2090  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2091<t>
2092   The server is refusing to service the request because the request
2093   payload is in a format not supported by this request method on the
2094   target resource.
2095</t>
2096</section>
2097
2098<section title="417 Expectation Failed" anchor="status.417">
2099  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2100  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2101<t>
2102   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2103   could not be met by this server, or, if the server is a proxy,
2104   the server has unambiguous evidence that the request could not be met
2105   by the next-hop server.
2106</t>
2107</section>
2108
2109<section title="426 Upgrade Required" anchor="status.426">
2110  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2111  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2112<t>
2113   The request can not be completed without a prior protocol upgrade. This
2114   response &MUST; include an Upgrade header field (&header-upgrade;)
2115   specifying the required protocols.
2116</t>
2117<figure>
2118<preamble>Example:</preamble>
2119<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
2120HTTP/1.1 426 Upgrade Required
2121Upgrade: HTTP/3.0
2122Connection: Upgrade
2123Content-Length: <x:length-of target="s426body"/>
2124Content-Type: text/plain
2125
2126<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
2127</x:span></artwork></figure>
2128<t>
2129   The server &SHOULD; include a message body in the 426 response which
2130   indicates in human readable form the reason for the error and describes any
2131   alternative courses which may be available to the user.
2132</t>
2133</section>
2134</section>
2135
2136<section title="Server Error 5xx" anchor="status.5xx">
2137<t>
2138   Response status codes beginning with the digit "5" indicate cases in
2139   which the server is aware that it has erred or is incapable of
2140   performing the request. Except when responding to a HEAD request, the
2141   server &SHOULD; include a representation containing an explanation of the
2142   error situation, and whether it is a temporary or permanent
2143   condition. User agents &SHOULD; display any included representation to the
2144   user. These response codes are applicable to any request method.
2145</t>
2146
2147<section title="500 Internal Server Error" anchor="status.500">
2148  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2149  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2150<t>
2151   The server encountered an unexpected condition which prevented it
2152   from fulfilling the request.
2153</t>
2154</section>
2155
2156<section title="501 Not Implemented" anchor="status.501">
2157  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2158  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2159<t>
2160   The server does not support the functionality required to fulfill the
2161   request. This is the appropriate response when the server does not
2162   recognize the request method and is not capable of supporting it for
2163   any resource.
2164</t>
2165</section>
2166
2167<section title="502 Bad Gateway" anchor="status.502">
2168  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2169  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2170<t>
2171   The server, while acting as a gateway or proxy, received an invalid
2172   response from the upstream server it accessed in attempting to
2173   fulfill the request.
2174</t>
2175</section>
2176
2177<section title="503 Service Unavailable" anchor="status.503">
2178  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2179  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2180<t>
2181   The server is currently unable to handle the request due to a
2182   temporary overloading or maintenance of the server.
2183</t>
2184<t>
2185   The implication is that this is a temporary condition which will be
2186   alleviated after some delay. If known, the length of the delay &MAY; be
2187   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2188   If no Retry-After is given, the client &SHOULD; handle the response as it
2189   would for a 500 response.
2190</t>
2191<x:note>
2192  <t>
2193    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2194    server must use it when becoming overloaded. Some servers might wish
2195    to simply refuse the connection.
2196  </t>
2197</x:note>
2198</section>
2199
2200<section title="504 Gateway Timeout" anchor="status.504">
2201  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2202  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2203<t>
2204   The server, while acting as a gateway or proxy, did not receive a
2205   timely response from the upstream server specified by the URI (e.g.,
2206   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2207   to access in attempting to complete the request.
2208</t>
2209<x:note>
2210  <t>
2211    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2212    return 400 or 500 when DNS lookups time out.
2213  </t>
2214</x:note>
2215</section>
2216
2217<section title="505 HTTP Version Not Supported" anchor="status.505">
2218  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2219  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2220<t>
2221   The server does not support, or refuses to support, the protocol
2222   version that was used in the request message. The server is
2223   indicating that it is unable or unwilling to complete the request
2224   using the same major version as the client, as described in &http-version;,
2225   other than with this error message. The response &SHOULD; contain
2226   a representation describing why that version is not supported and what other
2227   protocols are supported by that server.
2228</t>
2229
2230</section>
2231</section>
2232</section>
2233
2234
2235<section title="Date/Time Formats" anchor="http.date">
2236  <x:anchor-alias value="HTTP-date"/>
2237<t>
2238   HTTP applications have historically allowed three different formats
2239   for date/time stamps. However, the preferred format is a fixed-length subset
2240   of that defined by <xref target="RFC1123"/>:
2241</t>
2242<figure><artwork type="example" x:indent-with="  ">
2243Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2244</artwork></figure>
2245<t>
2246   The other formats are described here only for compatibility with obsolete
2247   implementations.
2248</t>
2249<figure><artwork type="example" x:indent-with="  ">
2250Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2251Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2252</artwork></figure>
2253<t>
2254   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2255   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2256   only generate the RFC 1123 format for representing HTTP-date values
2257   in header fields.
2258</t>
2259<t>
2260   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2261   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2262   equal to UTC (Coordinated Universal Time). This is indicated in the
2263   first two formats by the inclusion of "GMT" as the three-letter
2264   abbreviation for time zone, and &MUST; be assumed when reading the
2265   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2266   additional whitespace beyond that specifically included as SP in the
2267   grammar.
2268</t>
2269<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2270  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2271</artwork></figure>
2272<t anchor="preferred.date.format">
2273  <x:anchor-alias value="rfc1123-date"/>
2274  <x:anchor-alias value="time-of-day"/>
2275  <x:anchor-alias value="hour"/>
2276  <x:anchor-alias value="minute"/>
2277  <x:anchor-alias value="second"/>
2278  <x:anchor-alias value="day-name"/>
2279  <x:anchor-alias value="day"/>
2280  <x:anchor-alias value="month"/>
2281  <x:anchor-alias value="year"/>
2282  <x:anchor-alias value="GMT"/>
2283  Preferred format:
2284</t>
2285<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"/>
2286  <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>
2287  ; fixed length subset of the format defined in
2288  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2289 
2290  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2291               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2292               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2293               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2294               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2295               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2296               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2297               
2298  <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>
2299               ; e.g., 02 Jun 1982
2300
2301  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2302  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2303               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2304               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2305               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2306               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2307               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2308               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2309               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2310               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2311               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2312               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2313               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2314  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2315
2316  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2317
2318  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2319                 ; 00:00:00 - 23:59:59
2320                 
2321  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2322  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2323  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2324</artwork></figure>
2325<t>
2326  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2327  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2328  same as those defined for the RFC 5322 constructs
2329  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2330</t>
2331<t anchor="obsolete.date.formats">
2332  <x:anchor-alias value="obs-date"/>
2333  <x:anchor-alias value="rfc850-date"/>
2334  <x:anchor-alias value="asctime-date"/>
2335  <x:anchor-alias value="date1"/>
2336  <x:anchor-alias value="date2"/>
2337  <x:anchor-alias value="date3"/>
2338  <x:anchor-alias value="rfc1123-date"/>
2339  <x:anchor-alias value="day-name-l"/>
2340  Obsolete formats:
2341</t>
2342<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2343  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2344</artwork></figure>
2345<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2346  <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>
2347  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2348                 ; day-month-year (e.g., 02-Jun-82)
2349
2350  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2351         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2352         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2353         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2354         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2355         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2356         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2357</artwork></figure>
2358<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2359  <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>
2360  <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> ))
2361                 ; month day (e.g., Jun  2)
2362</artwork></figure>
2363<x:note>
2364  <t>
2365    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2366    accepting date values that might have been sent by non-HTTP
2367    applications, as is sometimes the case when retrieving or posting
2368    messages via proxies/gateways to SMTP or NNTP.
2369  </t>
2370</x:note>
2371<x:note>
2372  <t>
2373    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2374    to their usage within the protocol stream. Clients and servers are
2375    not required to use these formats for user presentation, request
2376    logging, etc.
2377  </t>
2378</x:note>
2379</section>
2380
2381<section title="Product Tokens" anchor="product.tokens">
2382  <x:anchor-alias value="product"/>
2383  <x:anchor-alias value="product-version"/>
2384<t>
2385   Product tokens are used to allow communicating applications to
2386   identify themselves by software name and version. Most fields using
2387   product tokens also allow sub-products which form a significant part
2388   of the application to be listed, separated by whitespace. By
2389   convention, the products are listed in order of their significance
2390   for identifying the application.
2391</t>
2392<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2393  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2394  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2395</artwork></figure>
2396<t>
2397   Examples:
2398</t>
2399<figure><artwork type="example">
2400  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2401  Server: Apache/0.8.4
2402</artwork></figure>
2403<t>
2404   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2405   used for advertising or other non-essential information. Although any
2406   token octet &MAY; appear in a product-version, this token &SHOULD;
2407   only be used for a version identifier (i.e., successive versions of
2408   the same product &SHOULD; only differ in the product-version portion of
2409   the product value).
2410</t>
2411</section>
2412
2413
2414<section title="Header Field Definitions" anchor="header.field.definitions">
2415<t>
2416   This section defines the syntax and semantics of HTTP/1.1 header fields
2417   related to request and response semantics.
2418</t>
2419
2420<section title="Allow" anchor="header.allow">
2421  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2422  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2423  <x:anchor-alias value="Allow"/>
2424<t>
2425   The "Allow" header field lists the set of methods advertised as
2426   supported by the target resource. The purpose of this field is strictly to
2427   inform the recipient of valid request methods associated with the resource.
2428</t>
2429<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2430  <x:ref>Allow</x:ref> = #<x:ref>Method</x:ref>
2431</artwork></figure>
2432<t>
2433   Example of use:
2434</t>
2435<figure><artwork type="example">
2436  Allow: GET, HEAD, PUT
2437</artwork></figure>
2438<t>
2439   The actual set of allowed methods is defined by the origin server at the
2440   time of each request.
2441</t>
2442<t>
2443   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2444   understand all the methods specified in order to handle them according to
2445   the generic message handling rules.
2446</t>
2447</section>
2448
2449<section title="Date" anchor="header.date">
2450  <iref primary="true" item="Date header field" x:for-anchor=""/>
2451  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2452  <x:anchor-alias value="Date"/>
2453<t>
2454   The "Date" header field represents the date and time at which
2455   the message was originated, having the same semantics as the Origination
2456   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2457   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2458   it &MUST; be sent in rfc1123-date format.
2459</t>
2460<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2461  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2462</artwork></figure>
2463<t>
2464   An example is
2465</t>
2466<figure><artwork type="example">
2467  Date: Tue, 15 Nov 1994 08:12:31 GMT
2468</artwork></figure>
2469<t>
2470   Origin servers &MUST; include a Date header field in all responses,
2471   except in these cases:
2472  <list style="numbers">
2473      <t>If the response status code is 100 (Continue) or 101 (Switching
2474         Protocols), the response &MAY; include a Date header field, at
2475         the server's option.</t>
2476
2477      <t>If the response status code conveys a server error, e.g., 500
2478         (Internal Server Error) or 503 (Service Unavailable), and it is
2479         inconvenient or impossible to generate a valid Date.</t>
2480
2481      <t>If the server does not have a clock that can provide a
2482         reasonable approximation of the current time, its responses
2483         &MUST-NOT; include a Date header field.</t>
2484  </list>
2485</t>
2486<t>
2487   A received message that does not have a Date header field &MUST; be
2488   assigned one by the recipient if the message will be cached by that
2489   recipient.
2490</t>
2491<t>
2492   Clients can use the Date header field as well; in order to keep request
2493   messages small, they are advised not to include it when it doesn't convey
2494   any useful information (as is usually the case for requests that do not
2495   contain a payload).
2496</t>
2497<t>
2498   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2499   time subsequent to the generation of the message. It &SHOULD; represent
2500   the best available approximation of the date and time of message
2501   generation, unless the implementation has no means of generating a
2502   reasonably accurate date and time. In theory, the date ought to
2503   represent the moment just before the payload is generated. In
2504   practice, the date can be generated at any time during the message
2505   origination without affecting its semantic value.
2506</t>
2507</section>
2508
2509<section title="Expect" anchor="header.expect">
2510  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2511  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2512  <x:anchor-alias value="Expect"/>
2513  <x:anchor-alias value="expectation"/>
2514  <x:anchor-alias value="expect-param"/>
2515  <x:anchor-alias value="expect-name"/>
2516  <x:anchor-alias value="expect-value"/>
2517<t>
2518   The "Expect" header field is used to indicate that particular
2519   server behaviors are required by the client.
2520</t>
2521<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Expect"/><iref primary="true" item="Grammar" subitem="expectation"/><iref primary="true" item="Grammar" subitem="expect-param"/><iref primary="true" item="Grammar" subitem="expect-value"/><iref primary="true" item="Grammar" subitem="expect-name"/>
2522  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2523 
2524  <x:ref>expectation</x:ref>  = <x:ref>expect-name</x:ref> [ <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>expect-value</x:ref> ]
2525                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2526  <x:ref>expect-param</x:ref> = <x:ref>expect-name</x:ref> [ <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>expect-value</x:ref> ]
2527 
2528  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2529  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2530</artwork></figure>
2531<t>
2532   If all received Expect header field(s) are syntactically valid but contain
2533   an expectation that the recipient does not understand or cannot comply with,
2534   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2535   recipient of a syntactically invalid Expectation header field &MUST; respond
2536   with a 4xx status code other than 417.
2537</t>
2538<t>
2539   The only expectation defined by this specification is:
2540</t>
2541<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2542  100-continue
2543   <list>
2544      <t>
2545        The "100-continue" expectation is defined &use100;. It does not support
2546        any expect-params.
2547      </t>
2548   </list>
2549</t>
2550<t>
2551   Comparison is case-insensitive for names (expect-name), and case-sensitive
2552   for values (expect-value).
2553</t>
2554<t>
2555   The Expect mechanism is hop-by-hop: the above requirements apply to any
2556   server, including proxies. However, the Expect header field itself is
2557   end-to-end; it &MUST; be forwarded if the request is forwarded.
2558</t>
2559<t>
2560   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2561   header field.
2562</t>
2563</section>
2564
2565<section title="From" anchor="header.from">
2566  <iref primary="true" item="From header field" x:for-anchor=""/>
2567  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2568  <x:anchor-alias value="From"/>
2569  <x:anchor-alias value="mailbox"/>
2570<t>
2571   The "From" header field, if given, &SHOULD; contain an Internet
2572   e-mail address for the human user who controls the requesting user
2573   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2574   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2575</t>
2576<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2577  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2578 
2579  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2580</artwork></figure>
2581<t>
2582   An example is:
2583</t>
2584<figure><artwork type="example">
2585  From: webmaster@example.org
2586</artwork></figure>
2587<t>
2588   This header field &MAY; be used for logging purposes and as a means for
2589   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2590   be used as an insecure form of access protection. The interpretation
2591   of this field is that the request is being performed on behalf of the
2592   person given, who accepts responsibility for the method performed. In
2593   particular, robot agents &SHOULD; include this header field so that the
2594   person responsible for running the robot can be contacted if problems
2595   occur on the receiving end.
2596</t>
2597<t>
2598   The Internet e-mail address in this field &MAY; be separate from the
2599   Internet host which issued the request. For example, when a request
2600   is passed through a proxy the original issuer's address &SHOULD; be
2601   used.
2602</t>
2603<t>
2604   The client &SHOULD-NOT;  send the From header field without the user's
2605   approval, as it might conflict with the user's privacy interests or
2606   their site's security policy. It is strongly recommended that the
2607   user be able to disable, enable, and modify the value of this field
2608   at any time prior to a request.
2609</t>
2610</section>
2611
2612<section title="Location" anchor="header.location">
2613  <iref primary="true" item="Location header field" x:for-anchor=""/>
2614  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2615  <x:anchor-alias value="Location"/>
2616<t>
2617   The "Location" header field &MAY; be sent in responses to refer to
2618   a specific resource in accordance with the semantics of the status
2619   code.
2620</t>
2621<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2622  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2623</artwork></figure>
2624<t>
2625   For 201 (Created) responses, the Location is the URI of the new resource
2626   which was created by the request. For 3xx responses, the location &SHOULD;
2627   indicate the server's preferred URI for automatic redirection to the
2628   resource.
2629</t>
2630<t>
2631   The field value consists of a single URI-reference. When it has the form
2632   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2633   the final value is computed by resolving it against the effective request
2634   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2635   navigated to by the user agent, did contain a fragment identifier, and the
2636   final value does not, then the original URI's fragment identifier is added
2637   to the final value.
2638</t>
2639<figure>
2640<preamble>For example, the original URI "http://www.example.org/~tim", combined with a field value given as:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2641<artwork type="example">
2642  Location: /pub/WWW/People.html#tim
2643</artwork>
2644<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2645</figure>
2646<figure>
2647<preamble>An original URI "http://www.example.org/index.html#larry", combined with a field value given as:</preamble><!--DO NOT DARE changing the vertical spacing below, it's necessary this way for xml2rfc-->
2648<artwork type="example">
2649  Location: http://www.example.net/index.html
2650</artwork>
2651<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2652</figure>
2653<x:note>
2654  <t>
2655    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2656    that are not valid URI references. This specification does not mandate or
2657    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2658  </t>
2659</x:note>
2660<t>
2661   There are circumstances in which a fragment identifier in a Location URI
2662   would not be appropriate. For instance, when it appears in a 201 Created
2663   response, where the Location header field specifies the URI for the entire
2664   created resource.
2665</t>
2666<x:note>
2667  <t>
2668    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2669    from Location in that the Content-Location identifies the most specific
2670    resource corresponding to the enclosed representation.
2671    It is therefore possible for a response to contain header fields for
2672    both Location and Content-Location.
2673  </t>
2674</x:note>
2675</section>
2676
2677<section title="Max-Forwards" anchor="header.max-forwards">
2678  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2679  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2680  <x:anchor-alias value="Max-Forwards"/>
2681<t>
2682   The "Max-Forwards" header field provides a mechanism with the
2683   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2684   methods to limit the number of times that the request is forwarded by
2685   proxies. This can be useful when the client is attempting to
2686   trace a request which appears to be failing or looping mid-chain.
2687</t>
2688<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2689  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2690</artwork></figure>
2691<t>
2692   The Max-Forwards value is a decimal integer indicating the remaining
2693   number of times this request message can be forwarded.
2694</t>
2695<t>
2696   Each recipient of a TRACE or OPTIONS request
2697   containing a Max-Forwards header field &MUST; check and update its
2698   value prior to forwarding the request. If the received value is zero
2699   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2700   respond as the final recipient. If the received Max-Forwards value is
2701   greater than zero, then the forwarded message &MUST; contain an updated
2702   Max-Forwards field with a value decremented by one (1).
2703</t>
2704<t>
2705   The Max-Forwards header field &MAY; be ignored for all other request
2706   methods.
2707</t>
2708</section>
2709
2710<section title="Referer" anchor="header.referer">
2711  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2712  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2713  <x:anchor-alias value="Referer"/>
2714<t>
2715   The "Referer" [sic] header field allows the client to specify the
2716   URI of the resource from which the effective request URI was obtained (the
2717   "referrer", although the header field is misspelled.).
2718</t>
2719<t>
2720   The Referer header field allows servers to generate lists of back-links to
2721   resources for interest, logging, optimized caching, etc. It also allows
2722   obsolete or mistyped links to be traced for maintenance. Some servers use
2723   Referer as a means of controlling where they allow links from (so-called
2724   "deep linking"), but legitimate requests do not always
2725   contain a Referer header field.
2726</t>
2727<t>
2728   If the effective request URI was obtained from a source that does not have its own
2729   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2730   sent with the value "about:blank", or not be sent at all. Note that this
2731   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2732</t>
2733<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2734  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2735</artwork></figure>
2736<t>
2737   Example:
2738</t>
2739<figure><artwork type="example">
2740  Referer: http://www.example.org/hypertext/Overview.html
2741</artwork></figure>
2742<t>
2743   If the field value is a relative URI, it &SHOULD; be interpreted
2744   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2745   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2746</t>
2747</section>
2748
2749<section title="Retry-After" anchor="header.retry-after">
2750  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2751  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2752  <x:anchor-alias value="Retry-After"/>
2753<t>
2754   The header "Retry-After" field can be used with a 503 (Service
2755   Unavailable) response to indicate how long the service is expected to
2756   be unavailable to the requesting client. This field &MAY; also be used
2757   with any 3xx (Redirection) response to indicate the minimum time the
2758   user-agent is asked to wait before issuing the redirected request.
2759</t>
2760<t>
2761   The value of this field can be either an HTTP-date or an integer number
2762   of seconds (in decimal) after the time of the response.
2763</t>
2764<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2765  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2766</artwork></figure>
2767<t anchor="rule.delta-seconds">
2768  <x:anchor-alias value="delta-seconds"/>
2769   Time spans are non-negative decimal integers, representing time in
2770   seconds.
2771</t>
2772<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2773  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2774</artwork></figure>
2775<t>
2776   Two examples of its use are
2777</t>
2778<figure><artwork type="example">
2779  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2780  Retry-After: 120
2781</artwork></figure>
2782<t>
2783   In the latter example, the delay is 2 minutes.
2784</t>
2785</section>
2786
2787<section title="Server" anchor="header.server">
2788  <iref primary="true" item="Server header field" x:for-anchor=""/>
2789  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2790  <x:anchor-alias value="Server"/>
2791<t>
2792   The "Server" header field contains information about the
2793   software used by the origin server to handle the request.
2794</t>
2795<t>
2796   The field can contain multiple
2797   product tokens (<xref target="product.tokens"/>) and
2798   comments (&header-fields;) identifying the server and any significant
2799   subproducts. The product tokens are listed in order of their significance
2800   for identifying the application.
2801</t>
2802<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2803  <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> ) )
2804</artwork></figure>
2805<t>
2806   Example:
2807</t>
2808<figure><artwork type="example">
2809  Server: CERN/3.0 libwww/2.17
2810</artwork></figure>
2811<t>
2812   If the response is being forwarded through a proxy, the proxy
2813   application &MUST-NOT; modify the Server header field. Instead, it
2814   &MUST; include a Via field (as described in &header-via;).
2815</t>
2816<x:note>
2817  <t>
2818    <x:h>Note:</x:h> Revealing the specific software version of the server might
2819    allow the server machine to become more vulnerable to attacks
2820    against software that is known to contain security holes. Server
2821    implementors are encouraged to make this field a configurable
2822    option.
2823  </t>
2824</x:note>
2825</section>
2826
2827<section title="User-Agent" anchor="header.user-agent">
2828  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2829  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2830  <x:anchor-alias value="User-Agent"/>
2831<t>
2832   The "User-Agent" header field contains information about the user
2833   agent originating the request. User agents &SHOULD; include this field with
2834   requests.
2835</t>
2836<t>
2837   Typically, it is used for statistical purposes, the tracing of protocol
2838   violations, and tailoring responses to avoid particular user agent
2839   limitations.
2840</t>
2841<t>
2842   The field can contain multiple
2843   product tokens (<xref target="product.tokens"/>)
2844   and comments (&header-fields;) identifying the agent and its
2845   significant subproducts. By convention, the product tokens are listed in
2846   order of their significance for identifying the application.
2847</t>
2848<t>
2849   Because this field is usually sent on every request a user agent makes,
2850   implementations are encouraged not to include needlessly fine-grained
2851   detail, and to limit (or even prohibit) the addition of subproducts by third
2852   parties. Overly long and detailed User-Agent field values make requests
2853   larger and can also be used to identify ("fingerprint") the user against
2854   their wishes.
2855</t>
2856<t>
2857   Likewise, implementations are encouraged not to use the product tokens of
2858   other implementations in order to declare compatibility with them, as this
2859   circumvents the purpose of the field. Finally, they are encouraged not to
2860   use comments to identify products; doing so makes the field value more
2861   difficult to parse.
2862</t>
2863<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2864  <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> ) )
2865</artwork></figure>
2866<t>
2867   Example:
2868</t>
2869<figure><artwork type="example">
2870  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2871</artwork></figure>
2872</section>
2873
2874</section>
2875
2876<section title="IANA Considerations" anchor="IANA.considerations">
2877
2878<section title="Method Registry" anchor="method.registration">
2879<t>
2880  The registration procedure for HTTP request methods is defined by
2881  <xref target="method.registry"/> of this document.
2882</t>
2883<t>
2884   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2885   and be populated with the registrations below:
2886</t>
2887<?BEGININC p2-semantics.iana-methods ?>
2888<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2889<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2890   <ttcol>Method</ttcol>
2891   <ttcol>Safe</ttcol>
2892   <ttcol>Reference</ttcol>
2893   <c>CONNECT</c>
2894   <c>no</c>
2895   <c>
2896      <xref target="CONNECT"/>
2897   </c>
2898   <c>DELETE</c>
2899   <c>no</c>
2900   <c>
2901      <xref target="DELETE"/>
2902   </c>
2903   <c>GET</c>
2904   <c>yes</c>
2905   <c>
2906      <xref target="GET"/>
2907   </c>
2908   <c>HEAD</c>
2909   <c>yes</c>
2910   <c>
2911      <xref target="HEAD"/>
2912   </c>
2913   <c>OPTIONS</c>
2914   <c>yes</c>
2915   <c>
2916      <xref target="OPTIONS"/>
2917   </c>
2918   <c>POST</c>
2919   <c>no</c>
2920   <c>
2921      <xref target="POST"/>
2922   </c>
2923   <c>PUT</c>
2924   <c>no</c>
2925   <c>
2926      <xref target="PUT"/>
2927   </c>
2928   <c>TRACE</c>
2929   <c>yes</c>
2930   <c>
2931      <xref target="TRACE"/>
2932   </c>
2933</texttable>
2934<!--(END)-->
2935<?ENDINC p2-semantics.iana-methods ?>
2936</section>
2937
2938<section title="Status Code Registry" anchor="status.code.registration">
2939<t>
2940   The registration procedure for HTTP Status Codes &mdash; previously defined
2941   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2942   by <xref target="status.code.registry"/> of this document.
2943</t>
2944<t>
2945   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2946   shall be updated with the registrations below:
2947</t>
2948<?BEGININC p2-semantics.iana-status-codes ?>
2949<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2950<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2951   <ttcol>Value</ttcol>
2952   <ttcol>Description</ttcol>
2953   <ttcol>Reference</ttcol>
2954   <c>100</c>
2955   <c>Continue</c>
2956   <c>
2957      <xref target="status.100"/>
2958   </c>
2959   <c>101</c>
2960   <c>Switching Protocols</c>
2961   <c>
2962      <xref target="status.101"/>
2963   </c>
2964   <c>200</c>
2965   <c>OK</c>
2966   <c>
2967      <xref target="status.200"/>
2968   </c>
2969   <c>201</c>
2970   <c>Created</c>
2971   <c>
2972      <xref target="status.201"/>
2973   </c>
2974   <c>202</c>
2975   <c>Accepted</c>
2976   <c>
2977      <xref target="status.202"/>
2978   </c>
2979   <c>203</c>
2980   <c>Non-Authoritative Information</c>
2981   <c>
2982      <xref target="status.203"/>
2983   </c>
2984   <c>204</c>
2985   <c>No Content</c>
2986   <c>
2987      <xref target="status.204"/>
2988   </c>
2989   <c>205</c>
2990   <c>Reset Content</c>
2991   <c>
2992      <xref target="status.205"/>
2993   </c>
2994   <c>300</c>
2995   <c>Multiple Choices</c>
2996   <c>
2997      <xref target="status.300"/>
2998   </c>
2999   <c>301</c>
3000   <c>Moved Permanently</c>
3001   <c>
3002      <xref target="status.301"/>
3003   </c>
3004   <c>302</c>
3005   <c>Found</c>
3006   <c>
3007      <xref target="status.302"/>
3008   </c>
3009   <c>303</c>
3010   <c>See Other</c>
3011   <c>
3012      <xref target="status.303"/>
3013   </c>
3014   <c>305</c>
3015   <c>Use Proxy</c>
3016   <c>
3017      <xref target="status.305"/>
3018   </c>
3019   <c>306</c>
3020   <c>(Unused)</c>
3021   <c>
3022      <xref target="status.306"/>
3023   </c>
3024   <c>307</c>
3025   <c>Temporary Redirect</c>
3026   <c>
3027      <xref target="status.307"/>
3028   </c>
3029   <c>400</c>
3030   <c>Bad Request</c>
3031   <c>
3032      <xref target="status.400"/>
3033   </c>
3034   <c>402</c>
3035   <c>Payment Required</c>
3036   <c>
3037      <xref target="status.402"/>
3038   </c>
3039   <c>403</c>
3040   <c>Forbidden</c>
3041   <c>
3042      <xref target="status.403"/>
3043   </c>
3044   <c>404</c>
3045   <c>Not Found</c>
3046   <c>
3047      <xref target="status.404"/>
3048   </c>
3049   <c>405</c>
3050   <c>Method Not Allowed</c>
3051   <c>
3052      <xref target="status.405"/>
3053   </c>
3054   <c>406</c>
3055   <c>Not Acceptable</c>
3056   <c>
3057      <xref target="status.406"/>
3058   </c>
3059   <c>408</c>
3060   <c>Request Timeout</c>
3061   <c>
3062      <xref target="status.408"/>
3063   </c>
3064   <c>409</c>
3065   <c>Conflict</c>
3066   <c>
3067      <xref target="status.409"/>
3068   </c>
3069   <c>410</c>
3070   <c>Gone</c>
3071   <c>
3072      <xref target="status.410"/>
3073   </c>
3074   <c>411</c>
3075   <c>Length Required</c>
3076   <c>
3077      <xref target="status.411"/>
3078   </c>
3079   <c>413</c>
3080   <c>Request Representation Too Large</c>
3081   <c>
3082      <xref target="status.413"/>
3083   </c>
3084   <c>414</c>
3085   <c>URI Too Long</c>
3086   <c>
3087      <xref target="status.414"/>
3088   </c>
3089   <c>415</c>
3090   <c>Unsupported Media Type</c>
3091   <c>
3092      <xref target="status.415"/>
3093   </c>
3094   <c>417</c>
3095   <c>Expectation Failed</c>
3096   <c>
3097      <xref target="status.417"/>
3098   </c>
3099   <c>426</c>
3100   <c>Upgrade Required</c>
3101   <c>
3102      <xref target="status.426"/>
3103   </c>
3104   <c>500</c>
3105   <c>Internal Server Error</c>
3106   <c>
3107      <xref target="status.500"/>
3108   </c>
3109   <c>501</c>
3110   <c>Not Implemented</c>
3111   <c>
3112      <xref target="status.501"/>
3113   </c>
3114   <c>502</c>
3115   <c>Bad Gateway</c>
3116   <c>
3117      <xref target="status.502"/>
3118   </c>
3119   <c>503</c>
3120   <c>Service Unavailable</c>
3121   <c>
3122      <xref target="status.503"/>
3123   </c>
3124   <c>504</c>
3125   <c>Gateway Timeout</c>
3126   <c>
3127      <xref target="status.504"/>
3128   </c>
3129   <c>505</c>
3130   <c>HTTP Version Not Supported</c>
3131   <c>
3132      <xref target="status.505"/>
3133   </c>
3134</texttable>
3135<!--(END)-->
3136<?ENDINC p2-semantics.iana-status-codes ?>
3137</section>
3138<section title="Header Field Registration" anchor="header.field.registration">
3139<t>
3140   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3141   with the permanent registrations below (see <xref target="RFC3864"/>):
3142</t>
3143<?BEGININC p2-semantics.iana-headers ?>
3144<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3145<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3146   <ttcol>Header Field Name</ttcol>
3147   <ttcol>Protocol</ttcol>
3148   <ttcol>Status</ttcol>
3149   <ttcol>Reference</ttcol>
3150
3151   <c>Allow</c>
3152   <c>http</c>
3153   <c>standard</c>
3154   <c>
3155      <xref target="header.allow"/>
3156   </c>
3157   <c>Date</c>
3158   <c>http</c>
3159   <c>standard</c>
3160   <c>
3161      <xref target="header.date"/>
3162   </c>
3163   <c>Expect</c>
3164   <c>http</c>
3165   <c>standard</c>
3166   <c>
3167      <xref target="header.expect"/>
3168   </c>
3169   <c>From</c>
3170   <c>http</c>
3171   <c>standard</c>
3172   <c>
3173      <xref target="header.from"/>
3174   </c>
3175   <c>Location</c>
3176   <c>http</c>
3177   <c>standard</c>
3178   <c>
3179      <xref target="header.location"/>
3180   </c>
3181   <c>Max-Forwards</c>
3182   <c>http</c>
3183   <c>standard</c>
3184   <c>
3185      <xref target="header.max-forwards"/>
3186   </c>
3187   <c>Referer</c>
3188   <c>http</c>
3189   <c>standard</c>
3190   <c>
3191      <xref target="header.referer"/>
3192   </c>
3193   <c>Retry-After</c>
3194   <c>http</c>
3195   <c>standard</c>
3196   <c>
3197      <xref target="header.retry-after"/>
3198   </c>
3199   <c>Server</c>
3200   <c>http</c>
3201   <c>standard</c>
3202   <c>
3203      <xref target="header.server"/>
3204   </c>
3205   <c>User-Agent</c>
3206   <c>http</c>
3207   <c>standard</c>
3208   <c>
3209      <xref target="header.user-agent"/>
3210   </c>
3211</texttable>
3212<!--(END)-->
3213<?ENDINC p2-semantics.iana-headers ?>
3214<t>
3215   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3216</t>
3217</section>
3218</section>
3219
3220<section title="Security Considerations" anchor="security.considerations">
3221<t>
3222   This section is meant to inform application developers, information
3223   providers, and users of the security limitations in HTTP/1.1 as
3224   described by this document. The discussion does not include
3225   definitive solutions to the problems revealed, though it does make
3226   some suggestions for reducing security risks.
3227</t>
3228
3229<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3230<t>
3231   Like any generic data transfer protocol, HTTP cannot regulate the
3232   content of the data that is transferred, nor is there any a priori
3233   method of determining the sensitivity of any particular piece of
3234   information within the context of any given request. Therefore,
3235   applications &SHOULD; supply as much control over this information as
3236   possible to the provider of that information. Four header fields are
3237   worth special mention in this context: Server, Via, Referer and From.
3238</t>
3239<t>
3240   Revealing the specific software version of the server might allow the
3241   server machine to become more vulnerable to attacks against software
3242   that is known to contain security holes. Implementors &SHOULD; make the
3243   Server header field a configurable option.
3244</t>
3245<t>
3246   Proxies which serve as a portal through a network firewall &SHOULD;
3247   take special precautions regarding the transfer of header information
3248   that identifies the hosts behind the firewall. In particular, they
3249   &SHOULD; remove, or replace with sanitized versions, any Via fields
3250   generated behind the firewall.
3251</t>
3252<t>
3253   The Referer header field allows reading patterns to be studied and reverse
3254   links drawn. Although it can be very useful, its power can be abused
3255   if user details are not separated from the information contained in
3256   the Referer. Even when the personal information has been removed, the
3257   Referer header field might indicate a private document's URI whose
3258   publication would be inappropriate.
3259</t>
3260<t>
3261   The information sent in the From field might conflict with the user's
3262   privacy interests or their site's security policy, and hence it
3263   &SHOULD-NOT;  be transmitted without the user being able to disable,
3264   enable, and modify the contents of the field. The user &MUST; be able
3265   to set the contents of this field within a user preference or
3266   application defaults configuration.
3267</t>
3268<t>
3269   We suggest, though do not require, that a convenient toggle interface
3270   be provided for the user to enable or disable the sending of From and
3271   Referer information.
3272</t>
3273<t>
3274   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3275   target="header.server"/>) header fields can sometimes be used to determine
3276   that a specific client or server has a particular security hole which might
3277   be exploited. Unfortunately, this same information is often used for other
3278   valuable purposes for which HTTP currently has no better mechanism.
3279</t>
3280<t>
3281   Furthermore, the User-Agent header field may contain enough entropy to be
3282   used, possibly in conjunction with other material, to uniquely identify the
3283   user.
3284</t>
3285<t>
3286   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3287   that was sent in request header fields within the body of their response.
3288   Clients &SHOULD; be careful with sensitive information, like Cookies,
3289   Authorization credentials, and other header fields that might be used to
3290   collect data from the client.
3291</t> 
3292</section>
3293
3294<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3295<t>
3296   Because the source of a link might be private information or might
3297   reveal an otherwise private information source, it is strongly
3298   recommended that the user be able to select whether or not the
3299   Referer field is sent. For example, a browser client could have a
3300   toggle switch for browsing openly/anonymously, which would
3301   respectively enable/disable the sending of Referer and From
3302   information.
3303</t>
3304<t>
3305   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3306   HTTP request if the referring page was transferred with a secure
3307   protocol.
3308</t>
3309<t>
3310   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3311   sensitive data because that data will be placed in the request-target. Many
3312   existing servers, proxies, and user agents log or display the request-target
3313   in places where it might be visible to third parties. Such services can
3314   use POST-based form submission instead.
3315</t>
3316</section>
3317
3318<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3319<t>
3320   If a single server supports multiple organizations that do not trust
3321   one another, then it &MUST; check the values of Location and Content-Location
3322   header fields in responses that are generated under control of
3323   said organizations to make sure that they do not attempt to
3324   invalidate resources over which they have no authority.
3325</t>
3326<t>
3327   Furthermore, appending the fragment identifier from one URI to another
3328   one obtained from a Location header field might leak confidential
3329   information to the target server &mdash; although the fragment identifier is
3330   not transmitted in the final request, it might be visible to the user agent
3331   through other means, such as scripting.
3332</t>
3333</section>
3334
3335<section title="Security Considerations for CONNECT">
3336<t>
3337   Since tunneled data is opaque to the proxy, there are additional
3338   risks to tunneling to other well-known or reserved ports.
3339   A HTTP client CONNECTing to port 25 could relay spam
3340   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3341   access to a small number of known ports.
3342</t>
3343</section>
3344
3345</section>
3346
3347<section title="Acknowledgments" anchor="acks">
3348<t>
3349  See &acks;.
3350</t>
3351</section>
3352</middle>
3353<back>
3354
3355<references title="Normative References">
3356
3357<reference anchor="Part1">
3358  <front>
3359    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3360    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3361      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3362      <address><email>fielding@gbiv.com</email></address>
3363    </author>
3364    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3365      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3366      <address><email>jg@freedesktop.org</email></address>
3367    </author>
3368    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3369      <organization abbrev="HP">Hewlett-Packard Company</organization>
3370      <address><email>JeffMogul@acm.org</email></address>
3371    </author>
3372    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3373      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3374      <address><email>henrikn@microsoft.com</email></address>
3375    </author>
3376    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3377      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3378      <address><email>LMM@acm.org</email></address>
3379    </author>
3380    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3381      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3382      <address><email>paulle@microsoft.com</email></address>
3383    </author>
3384    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3385      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3386      <address><email>timbl@w3.org</email></address>
3387    </author>
3388    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3389      <organization abbrev="W3C">World Wide Web Consortium</organization>
3390      <address><email>ylafon@w3.org</email></address>
3391    </author>
3392    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3393      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3394      <address><email>julian.reschke@greenbytes.de</email></address>
3395    </author>
3396    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3397  </front>
3398  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3399  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3400</reference>
3401
3402<reference anchor="Part3">
3403  <front>
3404    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3405    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3406      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3407      <address><email>fielding@gbiv.com</email></address>
3408    </author>
3409    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3410      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3411      <address><email>jg@freedesktop.org</email></address>
3412    </author>
3413    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3414      <organization abbrev="HP">Hewlett-Packard Company</organization>
3415      <address><email>JeffMogul@acm.org</email></address>
3416    </author>
3417    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3418      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3419      <address><email>henrikn@microsoft.com</email></address>
3420    </author>
3421    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3422      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3423      <address><email>LMM@acm.org</email></address>
3424    </author>
3425    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3426      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3427      <address><email>paulle@microsoft.com</email></address>
3428    </author>
3429    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3430      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3431      <address><email>timbl@w3.org</email></address>
3432    </author>
3433    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3434      <organization abbrev="W3C">World Wide Web Consortium</organization>
3435      <address><email>ylafon@w3.org</email></address>
3436    </author>
3437    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3438      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3439      <address><email>julian.reschke@greenbytes.de</email></address>
3440    </author>
3441    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3442  </front>
3443  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3444  <x:source href="p3-payload.xml" basename="p3-payload"/>
3445</reference>
3446
3447<reference anchor="Part4">
3448  <front>
3449    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3450    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3451      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3452      <address><email>fielding@gbiv.com</email></address>
3453    </author>
3454    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3455      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3456      <address><email>jg@freedesktop.org</email></address>
3457    </author>
3458    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3459      <organization abbrev="HP">Hewlett-Packard Company</organization>
3460      <address><email>JeffMogul@acm.org</email></address>
3461    </author>
3462    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3463      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3464      <address><email>henrikn@microsoft.com</email></address>
3465    </author>
3466    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3467      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3468      <address><email>LMM@acm.org</email></address>
3469    </author>
3470    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3471      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3472      <address><email>paulle@microsoft.com</email></address>
3473    </author>
3474    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3475      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3476      <address><email>timbl@w3.org</email></address>
3477    </author>
3478    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3479      <organization abbrev="W3C">World Wide Web Consortium</organization>
3480      <address><email>ylafon@w3.org</email></address>
3481    </author>
3482    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3483      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3484      <address><email>julian.reschke@greenbytes.de</email></address>
3485    </author>
3486    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3487  </front>
3488  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3489  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3490</reference>
3491
3492<reference anchor="Part5">
3493  <front>
3494    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3495    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3496      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3497      <address><email>fielding@gbiv.com</email></address>
3498    </author>
3499    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3500      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3501      <address><email>jg@freedesktop.org</email></address>
3502    </author>
3503    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3504      <organization abbrev="HP">Hewlett-Packard Company</organization>
3505      <address><email>JeffMogul@acm.org</email></address>
3506    </author>
3507    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3508      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3509      <address><email>henrikn@microsoft.com</email></address>
3510    </author>
3511    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3512      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3513      <address><email>LMM@acm.org</email></address>
3514    </author>
3515    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3516      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3517      <address><email>paulle@microsoft.com</email></address>
3518    </author>
3519    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3520      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3521      <address><email>timbl@w3.org</email></address>
3522    </author>
3523    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3524      <organization abbrev="W3C">World Wide Web Consortium</organization>
3525      <address><email>ylafon@w3.org</email></address>
3526    </author>
3527    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3528      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3529      <address><email>julian.reschke@greenbytes.de</email></address>
3530    </author>
3531    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3532  </front>
3533  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3534  <x:source href="p5-range.xml" basename="p5-range"/>
3535</reference>
3536
3537<reference anchor="Part6">
3538  <front>
3539    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3540    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3541      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3542      <address><email>fielding@gbiv.com</email></address>
3543    </author>
3544    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3545      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3546      <address><email>jg@freedesktop.org</email></address>
3547    </author>
3548    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3549      <organization abbrev="HP">Hewlett-Packard Company</organization>
3550      <address><email>JeffMogul@acm.org</email></address>
3551    </author>
3552    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3553      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3554      <address><email>henrikn@microsoft.com</email></address>
3555    </author>
3556    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3557      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3558      <address><email>LMM@acm.org</email></address>
3559    </author>
3560    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3561      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3562      <address><email>paulle@microsoft.com</email></address>
3563    </author>
3564    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3565      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3566      <address><email>timbl@w3.org</email></address>
3567    </author>
3568    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3569      <organization abbrev="W3C">World Wide Web Consortium</organization>
3570      <address><email>ylafon@w3.org</email></address>
3571    </author>
3572    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3573      <organization>Rackspace</organization>
3574      <address><email>mnot@mnot.net</email></address>
3575    </author>
3576    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3577      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3578      <address><email>julian.reschke@greenbytes.de</email></address>
3579    </author>
3580    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3581  </front>
3582  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3583  <x:source href="p6-cache.xml" basename="p6-cache"/>
3584</reference>
3585
3586<reference anchor="Part7">
3587  <front>
3588    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3589    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3590      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3591      <address><email>fielding@gbiv.com</email></address>
3592    </author>
3593    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3594      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3595      <address><email>jg@freedesktop.org</email></address>
3596    </author>
3597    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3598      <organization abbrev="HP">Hewlett-Packard Company</organization>
3599      <address><email>JeffMogul@acm.org</email></address>
3600    </author>
3601    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3602      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3603      <address><email>henrikn@microsoft.com</email></address>
3604    </author>
3605    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3606      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3607      <address><email>LMM@acm.org</email></address>
3608    </author>
3609    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3610      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3611      <address><email>paulle@microsoft.com</email></address>
3612    </author>
3613    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3614      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3615      <address><email>timbl@w3.org</email></address>
3616    </author>
3617    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3618      <organization abbrev="W3C">World Wide Web Consortium</organization>
3619      <address><email>ylafon@w3.org</email></address>
3620    </author>
3621    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3622      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3623      <address><email>julian.reschke@greenbytes.de</email></address>
3624    </author>
3625    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3626  </front>
3627  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3628  <x:source href="p7-auth.xml" basename="p7-auth"/>
3629</reference>
3630
3631<reference anchor="RFC2119">
3632  <front>
3633    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3634    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3635      <organization>Harvard University</organization>
3636      <address><email>sob@harvard.edu</email></address>
3637    </author>
3638    <date month="March" year="1997"/>
3639  </front>
3640  <seriesInfo name="BCP" value="14"/>
3641  <seriesInfo name="RFC" value="2119"/>
3642</reference>
3643
3644<reference anchor="RFC3986">
3645 <front>
3646  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3647  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3648    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3649    <address>
3650       <email>timbl@w3.org</email>
3651       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3652    </address>
3653  </author>
3654  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3655    <organization abbrev="Day Software">Day Software</organization>
3656    <address>
3657      <email>fielding@gbiv.com</email>
3658      <uri>http://roy.gbiv.com/</uri>
3659    </address>
3660  </author>
3661  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3662    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3663    <address>
3664      <email>LMM@acm.org</email>
3665      <uri>http://larry.masinter.net/</uri>
3666    </address>
3667  </author>
3668  <date month='January' year='2005'></date>
3669 </front>
3670 <seriesInfo name="STD" value="66"/>
3671 <seriesInfo name="RFC" value="3986"/>
3672</reference>
3673
3674<reference anchor="RFC5234">
3675  <front>
3676    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3677    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3678      <organization>Brandenburg InternetWorking</organization>
3679      <address>
3680        <email>dcrocker@bbiw.net</email>
3681      </address> 
3682    </author>
3683    <author initials="P." surname="Overell" fullname="Paul Overell">
3684      <organization>THUS plc.</organization>
3685      <address>
3686        <email>paul.overell@thus.net</email>
3687      </address>
3688    </author>
3689    <date month="January" year="2008"/>
3690  </front>
3691  <seriesInfo name="STD" value="68"/>
3692  <seriesInfo name="RFC" value="5234"/>
3693</reference>
3694
3695</references>
3696
3697<references title="Informative References">
3698
3699<reference anchor="RFC1123">
3700  <front>
3701    <title>Requirements for Internet Hosts - Application and Support</title>
3702    <author initials="R." surname="Braden" fullname="Robert Braden">
3703      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3704      <address><email>Braden@ISI.EDU</email></address>
3705    </author>
3706    <date month="October" year="1989"/>
3707  </front>
3708  <seriesInfo name="STD" value="3"/>
3709  <seriesInfo name="RFC" value="1123"/>
3710</reference>
3711
3712<reference anchor="RFC1945">
3713  <front>
3714    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3715    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3716      <organization>MIT, Laboratory for Computer Science</organization>
3717      <address><email>timbl@w3.org</email></address>
3718    </author>
3719    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3720      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3721      <address><email>fielding@ics.uci.edu</email></address>
3722    </author>
3723    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3724      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3725      <address><email>frystyk@w3.org</email></address>
3726    </author>
3727    <date month="May" year="1996"/>
3728  </front>
3729  <seriesInfo name="RFC" value="1945"/>
3730</reference>
3731
3732<reference anchor="RFC2068">
3733  <front>
3734    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3735    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3736      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3737      <address><email>fielding@ics.uci.edu</email></address>
3738    </author>
3739    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3740      <organization>MIT Laboratory for Computer Science</organization>
3741      <address><email>jg@w3.org</email></address>
3742    </author>
3743    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3744      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3745      <address><email>mogul@wrl.dec.com</email></address>
3746    </author>
3747    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3748      <organization>MIT Laboratory for Computer Science</organization>
3749      <address><email>frystyk@w3.org</email></address>
3750    </author>
3751    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3752      <organization>MIT Laboratory for Computer Science</organization>
3753      <address><email>timbl@w3.org</email></address>
3754    </author>
3755    <date month="January" year="1997"/>
3756  </front>
3757  <seriesInfo name="RFC" value="2068"/>
3758</reference>
3759
3760<reference anchor="RFC2616">
3761  <front>
3762    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3763    <author initials="R." surname="Fielding" fullname="R. Fielding">
3764      <organization>University of California, Irvine</organization>
3765      <address><email>fielding@ics.uci.edu</email></address>
3766    </author>
3767    <author initials="J." surname="Gettys" fullname="J. Gettys">
3768      <organization>W3C</organization>
3769      <address><email>jg@w3.org</email></address>
3770    </author>
3771    <author initials="J." surname="Mogul" fullname="J. Mogul">
3772      <organization>Compaq Computer Corporation</organization>
3773      <address><email>mogul@wrl.dec.com</email></address>
3774    </author>
3775    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3776      <organization>MIT Laboratory for Computer Science</organization>
3777      <address><email>frystyk@w3.org</email></address>
3778    </author>
3779    <author initials="L." surname="Masinter" fullname="L. Masinter">
3780      <organization>Xerox Corporation</organization>
3781      <address><email>masinter@parc.xerox.com</email></address>
3782    </author>
3783    <author initials="P." surname="Leach" fullname="P. Leach">
3784      <organization>Microsoft Corporation</organization>
3785      <address><email>paulle@microsoft.com</email></address>
3786    </author>
3787    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3788      <organization>W3C</organization>
3789      <address><email>timbl@w3.org</email></address>
3790    </author>
3791    <date month="June" year="1999"/>
3792  </front>
3793  <seriesInfo name="RFC" value="2616"/>
3794</reference>
3795
3796<reference anchor='RFC2817'>
3797  <front>
3798    <title>Upgrading to TLS Within HTTP/1.1</title>
3799    <author initials='R.' surname='Khare' fullname='R. Khare'>
3800      <organization>4K Associates / UC Irvine</organization>
3801      <address><email>rohit@4K-associates.com</email></address>
3802    </author>
3803    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3804      <organization>Agranat Systems, Inc.</organization>
3805      <address><email>lawrence@agranat.com</email></address>
3806    </author>
3807    <date year='2000' month='May' />
3808  </front>
3809  <seriesInfo name='RFC' value='2817' />
3810</reference>
3811
3812<reference anchor='RFC3864'>
3813  <front>
3814    <title>Registration Procedures for Message Header Fields</title>
3815    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3816      <organization>Nine by Nine</organization>
3817      <address><email>GK-IETF@ninebynine.org</email></address>
3818    </author>
3819    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3820      <organization>BEA Systems</organization>
3821      <address><email>mnot@pobox.com</email></address>
3822    </author>
3823    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3824      <organization>HP Labs</organization>
3825      <address><email>JeffMogul@acm.org</email></address>
3826    </author>
3827    <date year='2004' month='September' />
3828  </front>
3829  <seriesInfo name='BCP' value='90' />
3830  <seriesInfo name='RFC' value='3864' />
3831</reference>
3832
3833<reference anchor='RFC5226'>
3834  <front>
3835    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3836    <author initials='T.' surname='Narten' fullname='T. Narten'>
3837      <organization>IBM</organization>
3838      <address><email>narten@us.ibm.com</email></address>
3839    </author>
3840    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3841      <organization>Google</organization>
3842      <address><email>Harald@Alvestrand.no</email></address>
3843    </author>
3844    <date year='2008' month='May' />
3845  </front>
3846  <seriesInfo name='BCP' value='26' />
3847  <seriesInfo name='RFC' value='5226' />
3848</reference>
3849
3850<reference anchor="RFC5322">
3851  <front>
3852    <title>Internet Message Format</title>
3853    <author initials="P." surname="Resnick" fullname="P. Resnick">
3854      <organization>Qualcomm Incorporated</organization>
3855    </author>
3856    <date year="2008" month="October"/>
3857  </front> 
3858  <seriesInfo name="RFC" value="5322"/>
3859</reference>
3860
3861<reference anchor='RFC5789'>
3862  <front>
3863    <title>PATCH Method for HTTP</title>
3864    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3865      <organization>Linden Lab</organization>
3866    </author>
3867    <author initials='J.' surname='Snell' fullname='J. Snell' />
3868    <date year='2010' month='March' />
3869  </front>
3870  <seriesInfo name='RFC' value='5789' />
3871</reference>
3872
3873<reference anchor="RFC5987">
3874        <front>
3875    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3876    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3877      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3878      <address>
3879        <postal>
3880          <street>Hafenweg 16</street>
3881          <city>Muenster</city><region>NW</region><code>48155</code>
3882          <country>Germany</country>
3883        </postal>
3884        <email>julian.reschke@greenbytes.de</email>     
3885        <uri>http://greenbytes.de/tech/webdav/</uri>   
3886      </address>
3887    </author>
3888    <date month="August" year="2010"/>
3889  </front>
3890  <seriesInfo name="RFC" value="5987"/>
3891</reference>
3892
3893</references>
3894
3895<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3896<t>
3897  This document takes over the Status Code Registry, previously defined
3898  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3899  (<xref target="status.code.registry"/>)
3900</t>
3901<t>
3902  Clarify definition of POST.
3903  (<xref target="POST"/>)
3904</t>
3905<t>
3906  Remove requirement to handle all Content-* header fields; ban use of
3907  Content-Range with PUT.
3908  (<xref target="PUT"/>)
3909</t>
3910<t>
3911  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3912  (<xref target="CONNECT"/>)
3913</t>
3914<t>
3915  Broadened the definition of 203 (Non-Authoritative Information) to include
3916  cases of payload transformations as well.
3917  (<xref target="status.203"/>)
3918</t>
3919<t>
3920  Status codes 301, 302, and 307: removed the normative requirements on both
3921  response payloads and user interaction.
3922  (<xref target="status.3xx"/>)
3923</t>
3924<t>
3925  Failed to consider that there are many other request methods that are safe
3926  to automatically redirect, and further that the user agent is able to make
3927  that determination based on the request method semantics.
3928  Furthermore, allow user agents to rewrite the method from POST to GET
3929  for status codes 301 and 302.
3930  (Sections <xref format="counter" target="status.301"/>,
3931  <xref format="counter" target="status.302"/> and
3932  <xref format="counter" target="status.307"/>)
3933</t>
3934<t>
3935  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3936  It used to indicate that the target resource must be accessed through the
3937  proxy given by the Location field. The Location field gave the URI of the
3938  proxy. The recipient was expected to repeat this single request via the proxy.
3939  (<xref target="status.305"/>)
3940</t>
3941<t>
3942  Define status 426 (Upgrade Required) (this was incorporated from
3943  <xref target="RFC2817"/>).
3944  (<xref target="status.426"/>)
3945</t>
3946<t>
3947  Change ABNF productions for header fields to only define the field value.
3948  (<xref target="header.field.definitions"/>)
3949</t>
3950<t>
3951  Reclassify "Allow" as response header field, removing the option to
3952  specify it in a PUT request.
3953  Relax the server requirement on the contents of the Allow header field and
3954  remove requirement on clients to always trust the header field value.
3955  (<xref target="header.allow"/>)
3956</t>
3957<t>
3958  The ABNF for the Expect header field has been both fixed (allowing parameters
3959  for value-less expectations as well) and simplified (allowing trailing
3960  semicolons after "100-continue" when they were invalid before).
3961  (<xref target="header.expect"/>)
3962</t>
3963<t>
3964  Correct syntax of Location header field to allow URI references (including
3965  relative references and fragments), as referred symbol "absoluteURI" wasn't
3966  what was expected, and add some clarifications as to when use of fragments
3967  would not be appropriate.
3968  (<xref target="header.location"/>)
3969</t>
3970<t>
3971  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3972  extension methods could have used it as well).
3973  (<xref target="header.max-forwards"/>)
3974</t>
3975<t>
3976  Allow Referer field value of "about:blank" as alternative to not specifying it.
3977  (<xref target="header.referer"/>)
3978</t>
3979<t>
3980  In the description of the Server header field, the Via field
3981  was described as a SHOULD. The requirement was and is stated
3982  correctly in the description of the Via header field in &header-via;.
3983  (<xref target="header.server"/>)
3984</t>
3985</section>
3986
3987<?BEGININC p2-semantics.abnf-appendix ?>
3988<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3989<figure>
3990<artwork type="abnf" name="p2-semantics.parsed-abnf">
3991<x:ref>Allow</x:ref> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
3992
3993<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
3994
3995<x:ref>Date</x:ref> = HTTP-date
3996
3997<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3998
3999<x:ref>From</x:ref> = mailbox
4000
4001<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4002
4003<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4004
4005<x:ref>Location</x:ref> = URI-reference
4006
4007<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4008<x:ref>Method</x:ref> = token
4009
4010<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
4011
4012<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
4013<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4014<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4015<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4016
4017<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4018<x:ref>Status-Code</x:ref> = 3DIGIT
4019
4020<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4021<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4022
4023<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4024<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4025
4026<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
4027
4028<x:ref>date1</x:ref> = day SP month SP year
4029<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4030<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4031<x:ref>day</x:ref> = 2DIGIT
4032<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4033 / %x54.75.65 ; Tue
4034 / %x57.65.64 ; Wed
4035 / %x54.68.75 ; Thu
4036 / %x46.72.69 ; Fri
4037 / %x53.61.74 ; Sat
4038 / %x53.75.6E ; Sun
4039<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4040 / %x54.75.65.73.64.61.79 ; Tuesday
4041 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4042 / %x54.68.75.72.73.64.61.79 ; Thursday
4043 / %x46.72.69.64.61.79 ; Friday
4044 / %x53.61.74.75.72.64.61.79 ; Saturday
4045 / %x53.75.6E.64.61.79 ; Sunday
4046<x:ref>delta-seconds</x:ref> = 1*DIGIT
4047
4048<x:ref>expect-name</x:ref> = token
4049<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
4050<x:ref>expect-value</x:ref> = token / quoted-string
4051<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
4052 OWS expect-param ] )
4053
4054<x:ref>hour</x:ref> = 2DIGIT
4055
4056<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4057<x:ref>minute</x:ref> = 2DIGIT
4058<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4059 / %x46.65.62 ; Feb
4060 / %x4D.61.72 ; Mar
4061 / %x41.70.72 ; Apr
4062 / %x4D.61.79 ; May
4063 / %x4A.75.6E ; Jun
4064 / %x4A.75.6C ; Jul
4065 / %x41.75.67 ; Aug
4066 / %x53.65.70 ; Sep
4067 / %x4F.63.74 ; Oct
4068 / %x4E.6F.76 ; Nov
4069 / %x44.65.63 ; Dec
4070
4071<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4072<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
4073
4074<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4075<x:ref>product</x:ref> = token [ "/" product-version ]
4076<x:ref>product-version</x:ref> = token
4077
4078<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
4079
4080<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4081<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4082
4083<x:ref>second</x:ref> = 2DIGIT
4084
4085<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4086<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
4087
4088<x:ref>year</x:ref> = 4DIGIT
4089</artwork>
4090</figure>
4091<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4092; Allow defined but not used
4093; Date defined but not used
4094; Expect defined but not used
4095; From defined but not used
4096; Location defined but not used
4097; Max-Forwards defined but not used
4098; Reason-Phrase defined but not used
4099; Referer defined but not used
4100; Retry-After defined but not used
4101; Server defined but not used
4102; Status-Code defined but not used
4103; User-Agent defined but not used
4104</artwork></figure></section>
4105<?ENDINC p2-semantics.abnf-appendix ?>
4106
4107<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4108
4109<section title="Since RFC 2616">
4110<t>
4111  Extracted relevant partitions from <xref target="RFC2616"/>.
4112</t>
4113</section>
4114
4115<section title="Since draft-ietf-httpbis-p2-semantics-00">
4116<t>
4117  Closed issues:
4118  <list style="symbols"> 
4119    <t>
4120      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4121      "Via is a MUST"
4122      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4123    </t>
4124    <t>
4125      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4126      "Fragments allowed in Location"
4127      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4128    </t>
4129    <t>
4130      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4131      "Safe Methods vs Redirection"
4132      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4133    </t>
4134    <t>
4135      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4136      "Revise description of the POST method"
4137      (<eref target="http://purl.org/NET/http-errata#post"/>)
4138    </t>
4139    <t>
4140      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4141      "Normative and Informative references"
4142    </t>
4143    <t>
4144      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4145      "RFC2606 Compliance"
4146    </t>
4147    <t>
4148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4149      "Informative references"
4150    </t>
4151    <t>
4152      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4153      "Redundant cross-references"
4154    </t>
4155  </list>
4156</t>
4157<t>
4158  Other changes:
4159  <list style="symbols"> 
4160    <t>
4161      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4162    </t>
4163  </list>
4164</t>
4165</section>
4166
4167<section title="Since draft-ietf-httpbis-p2-semantics-01">
4168<t>
4169  Closed issues:
4170  <list style="symbols"> 
4171    <t>
4172      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4173      "PUT side effects"
4174    </t>
4175    <t>
4176      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4177      "Duplicate Host header requirements"
4178    </t>
4179  </list>
4180</t>
4181<t>
4182  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4183  <list style="symbols"> 
4184    <t>
4185      Move "Product Tokens" section (back) into Part 1, as "token" is used
4186      in the definition of the Upgrade header field.
4187    </t>
4188    <t>
4189      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4190    </t>
4191    <t>
4192      Copy definition of delta-seconds from Part6 instead of referencing it.
4193    </t>
4194  </list>
4195</t>
4196</section>
4197
4198<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4199<t>
4200  Closed issues:
4201  <list style="symbols"> 
4202    <t>
4203      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4204      "Requiring Allow in 405 responses"
4205    </t>
4206    <t>
4207      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4208      "Status Code Registry"
4209    </t>
4210    <t>
4211      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4212      "Redirection vs. Location"
4213    </t>
4214    <t>
4215      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4216      "Cacheability of 303 response"
4217    </t>
4218    <t>
4219      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4220      "305 Use Proxy"
4221    </t>
4222    <t>
4223      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4224      "Classification for Allow header"
4225    </t>
4226    <t>
4227      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4228      "PUT - 'store under' vs 'store at'"
4229    </t>
4230  </list>
4231</t>
4232<t>
4233  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4234  <list style="symbols"> 
4235    <t>
4236      Reference RFC 3984, and update header field registrations for headers defined
4237      in this document.
4238    </t>
4239  </list>
4240</t>
4241<t>
4242  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4243  <list style="symbols"> 
4244    <t>
4245      Replace string literals when the string really is case-sensitive (method).
4246    </t>
4247  </list>
4248</t>
4249</section>
4250
4251<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4252<t>
4253  Closed issues:
4254  <list style="symbols"> 
4255    <t>
4256      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4257      "OPTIONS request bodies"
4258    </t>
4259    <t>
4260      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4261      "Description of CONNECT should refer to RFC2817"
4262    </t>
4263    <t>
4264      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4265      "Location Content-Location reference request/response mixup"
4266    </t>
4267  </list>
4268</t>
4269<t>
4270  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4271  <list style="symbols"> 
4272    <t>
4273      Added initial proposal for registration process, plus initial
4274      content (non-HTTP/1.1 methods to be added by a separate specification).
4275    </t>
4276  </list>
4277</t>
4278</section>
4279
4280<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4281<t>
4282  Closed issues:
4283  <list style="symbols"> 
4284    <t>
4285      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4286      "Content-*"
4287    </t>
4288    <t>
4289      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4290      "RFC 2822 is updated by RFC 5322"
4291    </t>
4292  </list>
4293</t>
4294<t>
4295  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4296  <list style="symbols"> 
4297    <t>
4298      Use "/" instead of "|" for alternatives.
4299    </t>
4300    <t>
4301      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4302      whitespace ("OWS") and required whitespace ("RWS").
4303    </t>
4304    <t>
4305      Rewrite ABNFs to spell out whitespace rules, factor out
4306      header field value format definitions.
4307    </t>
4308  </list>
4309</t>
4310</section>
4311
4312<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4313<t>
4314  Closed issues:
4315  <list style="symbols"> 
4316    <t>
4317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4318      "Reason-Phrase BNF"
4319    </t>
4320  </list>
4321</t>
4322<t>
4323  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4324  <list style="symbols"> 
4325    <t>
4326      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4327    </t>
4328  </list>
4329</t>
4330</section>
4331
4332<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4333<t>
4334  Closed issues:
4335  <list style="symbols"> 
4336    <t>
4337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4338      "Clarify when Referer is sent"
4339    </t>
4340    <t>
4341      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4342      "status codes vs methods"
4343    </t>
4344    <t>
4345      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4346      "Do not require "updates" relation for specs that register status codes or method names"
4347    </t>
4348  </list>
4349</t>
4350</section>
4351
4352<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4353<t>
4354  Closed issues:
4355  <list style="symbols"> 
4356    <t>
4357      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4358      "Idempotency"
4359    </t>
4360    <t>
4361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4362      "TRACE security considerations"
4363    </t>
4364    <t>
4365      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4366      "Clarify rules for determining what entities a response carries"
4367    </t>
4368    <t>
4369      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4370      "update note citing RFC 1945 and 2068"
4371    </t>
4372    <t>
4373      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4374      "update note about redirect limit"
4375    </t>
4376    <t>
4377      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4378      "Location header ABNF should use 'URI'"
4379    </t>
4380    <t>
4381      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4382      "fragments in Location vs status 303"
4383    </t>
4384    <t>
4385      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4386      "move IANA registrations for optional status codes"
4387    </t>
4388  </list>
4389</t>
4390<t>
4391  Partly resolved issues:
4392  <list style="symbols"> 
4393    <t>
4394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4395      "Are OPTIONS and TRACE safe?"
4396    </t>
4397  </list>
4398</t>
4399</section>
4400
4401<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4402<t>
4403  Closed issues:
4404  <list style="symbols"> 
4405    <t>
4406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4407      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4408      status codes when fixing this previously)
4409    </t>
4410  </list>
4411</t>
4412</section>
4413
4414<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4415<t>
4416  Closed issues:
4417  <list style="symbols"> 
4418    <t>
4419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4420      "Fragment combination / precedence during redirects"
4421    </t>
4422  </list>
4423</t>
4424<t>
4425  Partly resolved issues:
4426  <list style="symbols"> 
4427    <t>
4428      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4429      "Location header payload handling"
4430    </t>
4431    <t>
4432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4433      "Term for the requested resource's URI"
4434    </t>
4435  </list>
4436</t>
4437</section>
4438
4439<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4440<t>
4441  Closed issues:
4442  <list style="symbols"> 
4443    <t>
4444      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4445      "Clarify 'Requested Variant'"
4446    </t>
4447    <t>
4448      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4449      "Clarify entity / representation / variant terminology"
4450    </t>
4451    <t>
4452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4453      "Methods and Caching"
4454    </t>
4455    <t>
4456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4457      "OPTIONS vs Max-Forwards"
4458    </t>
4459    <t>
4460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4461      "Status codes and caching"
4462    </t>
4463    <t>
4464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4465      "consider removing the 'changes from 2068' sections"
4466    </t>
4467  </list>
4468</t>
4469</section>
4470
4471<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4472<t>
4473  Closed issues:
4474  <list style="symbols"> 
4475    <t>
4476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4477      "Considerations for new status codes"
4478    </t>
4479    <t>
4480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4481      "Considerations for new methods"
4482    </t>
4483    <t>
4484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4485      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4486    </t>
4487  </list>
4488</t>
4489</section>
4490
4491<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4492<t>
4493  Closed issues:
4494  <list style="symbols"> 
4495    <t>
4496      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4497      "Fragment combination / precedence during redirects" (added warning
4498      about having a fragid on the redirect may cause inconvenience in
4499      some cases)
4500    </t>
4501    <t>
4502      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4503      "Content-* vs. PUT"
4504    </t>
4505    <t>
4506      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4507      "205 Bodies"
4508    </t>
4509    <t>
4510      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4511      "Understanding Content-* on non-PUT requests"
4512    </t>
4513    <t>
4514      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4515      "Content-*"
4516    </t>
4517    <t>
4518      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4519      "Header type defaulting"
4520    </t>
4521    <t>
4522      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4523      "PUT - 'store under' vs 'store at'"
4524    </t>
4525    <t>
4526      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4527      "duplicate ABNF for Reason-Phrase"
4528    </t>
4529    <t>
4530      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4531      "Note special status of Content-* prefix in header registration procedures"
4532    </t>
4533    <t>
4534      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4535      "Max-Forwards vs extension methods"
4536    </t>
4537    <t>
4538      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4539      "What is the value space of HTTP status codes?" (actually fixed in
4540      draft-ietf-httpbis-p2-semantics-11)
4541    </t>
4542    <t>
4543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4544      "Header Classification"
4545    </t>
4546    <t>
4547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4548      "PUT side effect: invalidation or just stale?"
4549    </t>
4550    <t>
4551      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4552      "proxies not supporting certain methods"
4553    </t>
4554    <t>
4555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4556      "Migrate CONNECT from RFC2817 to p2"
4557    </t>
4558    <t>
4559      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4560      "Migrate Upgrade details from RFC2817"
4561    </t>
4562    <t>
4563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4564      "clarify PUT semantics'"
4565    </t>
4566    <t>
4567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4568      "duplicate ABNF for 'Method'"
4569    </t>
4570    <t>
4571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4572      "untangle ABNFs for header fields"
4573    </t>
4574  </list>
4575</t>
4576</section>
4577
4578<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4579<t>
4580  Closed issues:
4581  <list style="symbols"> 
4582    <t>
4583      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4584      "untangle ABNFs for header fields"
4585    </t>
4586    <t>
4587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4588      "message-body in CONNECT request"
4589    </t>
4590  </list>
4591</t>
4592</section>
4593
4594<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4595<t>
4596  Closed issues:
4597  <list style="symbols"> 
4598    <t>
4599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4600      "Clarify status code for rate limiting"
4601    </t>
4602    <t>
4603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4604      "clarify 403 forbidden"
4605    </t>
4606    <t>
4607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4608      "Clarify 203 Non-Authoritative Information"
4609    </t>
4610    <t>
4611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4612      "update default reason phrase for 413"
4613    </t>
4614  </list>
4615</t>
4616</section>
4617
4618<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4619<t>
4620  Closed issues:
4621  <list style="symbols"> 
4622    <t>
4623      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4624      "Strength of requirements on Accept re: 406"
4625    </t>
4626    <t>
4627      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4628      "400 response isn't generic"
4629    </t>
4630  </list>
4631</t>
4632</section>
4633
4634<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4635<t>
4636  Closed issues:
4637  <list style="symbols"> 
4638    <t>
4639      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4640      "Redirects and non-GET methods"
4641    </t>
4642    <t>
4643      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4644      "Document HTTP's error-handling philosophy"
4645    </t>
4646    <t>
4647      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4648      "Considerations for new headers"
4649    </t>
4650    <t>
4651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4652      "clarify 303 redirect on HEAD"
4653    </t>
4654  </list>
4655</t>
4656</section>
4657
4658<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4659<t>
4660  Closed issues:
4661  <list style="symbols"> 
4662    <t>
4663      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4664      "Location header payload handling"
4665    </t>
4666    <t>
4667      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4668      "Clarify status code for rate limiting" (change backed out because
4669      a new status code is being defined for this purpose)
4670    </t>
4671    <t>
4672      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4673      "should there be a permanent variant of 307"
4674    </t>
4675    <t>
4676      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4677      "When are Location's semantics triggered?"
4678    </t>
4679    <t>
4680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4681      "'expect' grammar missing OWS"
4682    </t>
4683    <t>
4684      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4685      "header field considerations: quoted-string vs use of double quotes"
4686    </t>
4687  </list>
4688</t>
4689</section>
4690
4691<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4692<t>
4693  Closed issues:
4694  <list style="symbols"> 
4695    <t>
4696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4697      "Requirements for user intervention during redirects"
4698    </t>
4699    <t>
4700      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4701      "Applying original fragment to 'plain' redirected URI"
4702    </t>
4703    <t>
4704      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4705      "Misplaced text on connection handling in p2"
4706    </t>
4707    <t>
4708      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4709      "relax requirements on hypertext in 3/4/5xx error responses"
4710    </t>
4711    <t>
4712      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4713      "example for 426 response should have a payload"
4714    </t>
4715    <t>
4716      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4717      "drop indirection entries for status codes"
4718    </t>
4719  </list>
4720</t>
4721</section>
4722
4723</section>
4724
4725</back>
4726</rfc>
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