source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1554

Last change on this file since 1554 was 1554, checked in by mnot@…, 7 years ago

Move cache-specific HEAD language to p6; fully specify effects on cache. Addresses #227.

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 193.4 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 "March">
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  <!ENTITY p6-head                 "<xref target='Part6' x:rel='#head.effects' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
89]>
90<?rfc toc="yes" ?>
91<?rfc symrefs="yes" ?>
92<?rfc sortrefs="yes" ?>
93<?rfc compact="yes"?>
94<?rfc subcompact="no" ?>
95<?rfc linkmailto="no" ?>
96<?rfc editing="no" ?>
97<?rfc comments="yes"?>
98<?rfc inline="yes"?>
99<?rfc rfcedstyle="yes"?>
100<?rfc-ext allow-markup-in-artwork="yes" ?>
101<?rfc-ext include-references-in-index="yes" ?>
102<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="proposed"
103     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
104     xmlns:x='http://purl.org/net/xml2rfc/ext'
105     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
106<x:link rel="prev" basename="p1-messaging"/>
107<x:link rel="next" basename="p3-payload"/>
108<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
109<front>
110
111  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
112
113  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
114    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
115    <address>
116      <postal>
117        <street>345 Park Ave</street>
118        <city>San Jose</city>
119        <region>CA</region>
120        <code>95110</code>
121        <country>USA</country>
122      </postal>
123      <email>fielding@gbiv.com</email>
124      <uri>http://roy.gbiv.com/</uri>
125    </address>
126  </author>
127
128  <author initials="J." surname="Gettys" fullname="Jim Gettys">
129    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
130    <address>
131      <postal>
132        <street>21 Oak Knoll Road</street>
133        <city>Carlisle</city>
134        <region>MA</region>
135        <code>01741</code>
136        <country>USA</country>
137      </postal>
138      <email>jg@freedesktop.org</email>
139      <uri>http://gettys.wordpress.com/</uri>
140    </address>
141  </author>
142 
143  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
144    <organization abbrev="HP">Hewlett-Packard Company</organization>
145    <address>
146      <postal>
147        <street>HP Labs, Large Scale Systems Group</street>
148        <street>1501 Page Mill Road, MS 1177</street>
149        <city>Palo Alto</city>
150        <region>CA</region>
151        <code>94304</code>
152        <country>USA</country>
153      </postal>
154      <email>JeffMogul@acm.org</email>
155    </address>
156  </author>
157
158  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
159    <organization abbrev="Microsoft">Microsoft Corporation</organization>
160    <address>
161      <postal>
162        <street>1 Microsoft Way</street>
163        <city>Redmond</city>
164        <region>WA</region>
165        <code>98052</code>
166        <country>USA</country>
167      </postal>
168      <email>henrikn@microsoft.com</email>
169    </address>
170  </author>
171
172  <author initials="L." surname="Masinter" fullname="Larry Masinter">
173    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
174    <address>
175      <postal>
176        <street>345 Park Ave</street>
177        <city>San Jose</city>
178        <region>CA</region>
179        <code>95110</code>
180        <country>USA</country>
181      </postal>
182      <email>LMM@acm.org</email>
183      <uri>http://larry.masinter.net/</uri>
184    </address>
185  </author>
186 
187  <author initials="P." surname="Leach" fullname="Paul J. Leach">
188    <organization abbrev="Microsoft">Microsoft Corporation</organization>
189    <address>
190      <postal>
191        <street>1 Microsoft Way</street>
192        <city>Redmond</city>
193        <region>WA</region>
194        <code>98052</code>
195      </postal>
196      <email>paulle@microsoft.com</email>
197    </address>
198  </author>
199   
200  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
201    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
202    <address>
203      <postal>
204        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
205        <street>The Stata Center, Building 32</street>
206        <street>32 Vassar Street</street>
207        <city>Cambridge</city>
208        <region>MA</region>
209        <code>02139</code>
210        <country>USA</country>
211      </postal>
212      <email>timbl@w3.org</email>
213      <uri>http://www.w3.org/People/Berners-Lee/</uri>
214    </address>
215  </author>
216
217  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
218    <organization abbrev="W3C">World Wide Web Consortium</organization>
219    <address>
220      <postal>
221        <street>W3C / ERCIM</street>
222        <street>2004, rte des Lucioles</street>
223        <city>Sophia-Antipolis</city>
224        <region>AM</region>
225        <code>06902</code>
226        <country>France</country>
227      </postal>
228      <email>ylafon@w3.org</email>
229      <uri>http://www.raubacapeu.net/people/yves/</uri>
230    </address>
231  </author>
232
233  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
234    <organization abbrev="greenbytes">greenbytes GmbH</organization>
235    <address>
236      <postal>
237        <street>Hafenweg 16</street>
238        <city>Muenster</city><region>NW</region><code>48155</code>
239        <country>Germany</country>
240      </postal>
241      <phone>+49 251 2807760</phone>
242      <facsimile>+49 251 2807761</facsimile>
243      <email>julian.reschke@greenbytes.de</email>
244      <uri>http://greenbytes.de/tech/webdav/</uri>
245    </address>
246  </author>
247
248  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
249  <workgroup>HTTPbis Working Group</workgroup>
250
251<abstract>
252<t>
253   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
254   distributed, collaborative, hypertext information systems. HTTP has been in
255   use by the World Wide Web global information initiative since 1990. This
256   document is Part 2 of the seven-part specification that defines the protocol
257   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
258</t>
259<t>
260   Part 2 defines the semantics of HTTP messages as expressed by request
261   methods, request header fields, response status codes, and response header
262   fields.
263</t>
264</abstract>
265
266<note title="Editorial Note (To be removed by RFC Editor)">
267  <t>
268    Discussion of this draft should take place on the HTTPBIS working group
269    mailing list (ietf-http-wg@w3.org), which is archived at
270    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
271  </t>
272  <t>
273    The current issues list is at
274    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
275    documents (including fancy diffs) can be found at
276    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
277  </t>
278  <t>
279    The changes in this draft are summarized in <xref target="changes.since.18"/>.
280  </t>
281</note>
282</front>
283<middle>
284<section title="Introduction" anchor="introduction">
285<t>
286   This document defines HTTP/1.1 request and response semantics.  Each HTTP
287   message, as defined in &messaging;, is in the form of either a request or
288   a response.  An HTTP server listens on a connection for HTTP requests and
289   responds to each request, in the order received on that connection, with
290   one or more HTTP response messages.  This document defines the commonly
291   agreed upon semantics of the HTTP uniform interface, the intentions defined
292   by each request method, and the various response messages that might be
293   expected as a result of applying that method to the target resource.
294</t>
295<t>
296   This document is currently disorganized in order to minimize the changes
297   between drafts and enable reviewers to see the smaller errata changes.
298   A future draft will reorganize the sections to better reflect the content.
299   In particular, the sections will be ordered according to the typical
300   processing of an HTTP request message (after message parsing): resource
301   mapping, methods, request modifying header fields, response status,
302   status modifying header fields, and resource metadata.  The current mess
303   reflects how widely dispersed these topics and associated requirements
304   had become in <xref target="RFC2616"/>.
305</t>
306
307<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
308<t>
309   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
310   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
311   document are to be interpreted as described in <xref target="RFC2119"/>.
312</t>
313<t>
314   This document defines conformance criteria for several roles in HTTP
315   communication, including Senders, Recipients, Clients, Servers, User-Agents,
316   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
317   for definitions of these terms.
318</t>
319<t>
320   An implementation is considered conformant if it complies with all of the
321   requirements associated with its role(s). Note that SHOULD-level requirements
322   are relevant here, unless one of the documented exceptions is applicable.
323</t>
324<t>
325   This document also uses ABNF to define valid protocol elements
326   (<xref target="notation"/>). In addition to the prose requirements placed
327   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
328</t>
329<t>
330   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
331   protocol element from an invalid construct. However, HTTP does not define
332   specific error handling mechanisms, except in cases where it has direct
333   impact on security. This is because different uses of the protocol require
334   different error handling strategies; for example, a Web browser may wish to
335   transparently recover from a response where the Location header field
336   doesn't parse according to the ABNF, whereby in a systems control protocol
337   using HTTP, this type of error recovery could lead to dangerous consequences.
338</t>
339</section>
340
341<section title="Syntax Notation" anchor="notation">
342  <x:anchor-alias value="CR"/>
343  <x:anchor-alias value="DIGIT"/>
344  <x:anchor-alias value="LF"/>
345  <x:anchor-alias value="HTAB"/>
346  <x:anchor-alias value="VCHAR"/>
347  <x:anchor-alias value="SP"/>
348<t>
349   This specification uses the Augmented Backus-Naur Form (ABNF) notation
350   of <xref target="RFC5234"/> with the list rule extension defined in
351   &notation;<xref target="collected.abnf"/> shows the collected ABNF
352   with the list rule expanded.
353</t>
354<t>
355  The following core rules are included by
356  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
357  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
358  DIGIT (decimal 0-9), DQUOTE (double quote),
359  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
360  OCTET (any 8-bit sequence of data), SP (space), and
361  VCHAR (any visible US-ASCII character).
362</t>
363
364<section title="Core Rules" anchor="core.rules">
365  <x:anchor-alias value="obs-text"/>
366  <x:anchor-alias value="quoted-string"/>
367  <x:anchor-alias value="token"/>
368  <x:anchor-alias value="BWS"/>
369  <x:anchor-alias value="OWS"/>
370  <x:anchor-alias value="RWS"/>
371<t>
372  The core rules below are defined in <xref target="Part1"/>:
373</t>
374<figure><artwork type="abnf2616">
375  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &whitespace;&gt;
376  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &whitespace;&gt;
377  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &whitespace;&gt;
378  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &field-components;&gt;
379  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-components;&gt;
380  <x:ref>token</x:ref>         = &lt;token, defined in &field-components;&gt;
381</artwork></figure>
382</section>
383
384<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
385  <x:anchor-alias value="absolute-URI"/>
386  <x:anchor-alias value="comment"/>
387  <x:anchor-alias value="partial-URI"/>
388  <x:anchor-alias value="URI-reference"/>
389<t>
390  The ABNF rules below are defined in other parts:
391</t>
392<figure><!--Part1--><artwork type="abnf2616">
393  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
394  <x:ref>comment</x:ref>       = &lt;comment, defined in &field-components;&gt;
395  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
396  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
397</artwork></figure>
398</section>
399</section>
400</section>
401
402<section title="Method" anchor="method">
403  <x:anchor-alias value="Method"/>
404  <x:anchor-alias value="extension-method"/>
405<t>
406   The Method token indicates the request method to be performed on the target
407   resource (&effective-request-uri;). The method is case-sensitive.
408</t>
409<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
410  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
411</artwork></figure>
412<t>
413   The list of methods allowed by a resource can be specified in an
414   Allow header field (<xref target="header.allow"/>). The status code of the response
415   always notifies the client whether a method is currently allowed on a
416   resource, since the set of allowed methods can change dynamically. An
417   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
418   if the method is known by the origin server but not allowed for the
419   resource, and 501 (Not Implemented) if the method is
420   unrecognized or not implemented by the origin server. The methods GET
421   and HEAD &MUST; be supported by all general-purpose servers. All other
422   methods are &OPTIONAL;; however, if the above methods are implemented,
423   they &MUST; be implemented with the same semantics as those specified
424   in <xref target="method.definitions"/>.
425</t>
426
427<section title="Overview of Methods" anchor="overview.of.methods">
428<t>
429  The methods listed below are defined in <xref target="method.definitions"/>.
430</t>
431<texttable align="left">
432  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
433 
434  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
435  <c>GET</c> <c><xref target="GET"/></c>
436  <c>HEAD</c> <c><xref target="HEAD"/></c>
437  <c>POST</c> <c><xref target="POST"/></c>
438  <c>PUT</c> <c><xref target="PUT"/></c>
439  <c>DELETE</c> <c><xref target="DELETE"/></c>
440  <c>TRACE</c> <c><xref target="TRACE"/></c>
441  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
442</texttable>
443<t>
444  Note that this list is not exhaustive &mdash; it does not include request methods defined
445  in other specifications.
446</t>
447</section>
448
449<section title="Method Registry" anchor="method.registry">
450<t>
451  The HTTP Method Registry defines the name space for the Method token in the
452  Request line of an HTTP request.
453</t>
454<t>
455  Registrations &MUST; include the following fields:
456  <list style="symbols">
457    <t>Method Name (see <xref target="method"/>)</t>
458    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
459    <t>Pointer to specification text</t>
460  </list>
461</t>
462<t>
463  Values to be added to this name space are subject to IETF review
464  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
465</t>
466<t>
467  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
468</t>
469
470<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
471<t>
472   When it is necessary to express new semantics for a HTTP request that
473   aren't specific to a single application or media type, and currently defined
474   methods are inadequate, it may be appropriate to register a new method.
475</t>
476<t>
477   HTTP methods are generic; that is, they are potentially applicable to any
478   resource, not just one particular media type, "type" of resource, or
479   application. As such, it is preferred that new HTTP methods be registered
480   in a document that isn't specific to a single application, so that this is
481   clear.
482</t>
483<t>
484   Due to the parsing rules defined in &message-body;, definitions of HTTP
485   methods cannot prohibit the presence of a message body on either the request
486   or the response message (with responses to HEAD requests being the single
487   exception). Definitions of new methods cannot change this rule, but they can
488   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
489</t>
490<t>
491   New method definitions need to indicate whether they are safe (<xref
492   target="safe.methods"/>), what semantics (if any) the request body has,
493   and whether they are idempotent (<xref target="idempotent.methods"/>).
494   They also need to state whether they can be cached (&caching;); in
495   particular what conditions a cache may store the response, and under what
496   conditions such a stored response may be used to satisfy a subsequent
497   request.
498</t>
499</section>
500
501</section>
502</section>
503
504<section title="Header Fields" anchor="header.fields">
505<t>
506   Header fields are key value pairs that can be used to communicate data about
507   the message, its payload, the target resource, or about the connection
508   itself (i.e., control data).  See &header-fields; for a general definition
509   of their syntax.
510</t>
511
512<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
513<t>
514   New header fields are registered using the procedures described in
515   <xref target="RFC3864"/>.
516</t>
517<t>
518   The requirements for header field names are defined in
519   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
520   defining new fields are advised to keep the name as short as practical, and
521   not to prefix them with "X-" if they are to be registered (either
522   immediately or in the future).
523</t>
524<t>
525   New header field values typically have their syntax defined using ABNF
526   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
527   as necessary, and are usually constrained to the range of ASCII characters.
528   Header fields needing a greater range of characters can use an encoding
529   such as the one defined in <xref target="RFC5987"/>.
530</t>
531<t>
532   Because commas (",") are used as a generic delimiter between field-values,
533   they need to be treated with care if they are allowed in the field-value's
534   payload. Typically, components that might contain a comma are protected with
535   double-quotes using the quoted-string ABNF production (&field-components;).
536</t>
537<t>
538   For example, a textual date and a URI (either of which might contain a comma)
539   could be safely carried in field-values like these:
540</t>
541<figure><artwork type="example">
542  Example-URI-Field: "http://example.com/a.html,foo",
543                     "http://without-a-comma.example.com/"
544  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
545</artwork></figure>
546<t>
547   Note that double quote delimiters almost always are used with the
548   quoted-string production; using a different syntax inside double quotes
549   will likely cause unnecessary confusion.
550</t>
551<t>
552   Many header fields use a format including (case-insensitively) named
553   parameters (for instance, Content-Type, defined in &header-content-type;).
554   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
555   parameter value enables recipients to use existing parser components. When
556   allowing both forms, the meaning of a parameter value ought to be
557   independent of the syntax used for it (for an example, see the notes on
558   parameter handling for media types in &media-types;).
559</t>
560<t>
561   Authors of specifications defining new header fields are advised to consider
562   documenting:
563  <list style="symbols">
564    <x:lt>
565      <t>Whether the field is a single value, or whether it can be a list
566      (delimited by commas; see &header-fields;).</t>
567      <t>If it does not use the list syntax, document how to treat messages
568      where the header field occurs multiple times (a sensible default would
569      be to ignore the header field, but this might not always be the right
570      choice).</t>
571      <t>Note that intermediaries and software libraries might combine
572      multiple header field instances into a single one, despite the header
573      field not allowing this. A robust format enables recipients to discover
574      these situations (good example: "Content-Type", as the comma can only
575      appear inside quoted strings; bad example: "Location", as a comma can
576      occur inside a URI).</t>
577    </x:lt>
578    <x:lt><t>Under what conditions the header field can be used; e.g., only in
579    responses or requests, in all messages, only on responses to a particular
580    request method.</t></x:lt>
581    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
582    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
583    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
584    field's value, insert or delete it.</t></x:lt>
585    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
586    <x:lt><t>Whether the header field is useful or allowable in trailers (see
587    &chunked-encoding;).</t></x:lt>
588    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
589  </list>
590</t>
591</section>
592
593<section title="Request Header Fields" anchor="request.header.fields">
594  <x:anchor-alias value="request-header"/>
595<t>
596   The request header fields allow the client to pass additional
597   information about the request, and about the client itself, to the
598   server. These fields act as request modifiers, with semantics
599   equivalent to the parameters on a programming language method
600   invocation.
601</t>
602<texttable align="left">
603  <ttcol>Header Field Name</ttcol>
604  <ttcol>Defined in...</ttcol>
605
606  <c>Accept</c> <c>&header-accept;</c>
607  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
608  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
609  <c>Accept-Language</c> <c>&header-accept-language;</c>
610  <c>Authorization</c> <c>&header-authorization;</c>
611  <c>Expect</c> <c><xref target="header.expect"/></c>
612  <c>From</c> <c><xref target="header.from"/></c>
613  <c>Host</c> <c>&header-host;</c>
614  <c>If-Match</c> <c>&header-if-match;</c>
615  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
616  <c>If-None-Match</c> <c>&header-if-none-match;</c>
617  <c>If-Range</c> <c>&header-if-range;</c>
618  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
619  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
620  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
621  <c>Range</c> <c>&header-range;</c>
622  <c>Referer</c> <c><xref target="header.referer"/></c>
623  <c>TE</c> <c>&header-te;</c>
624  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
625</texttable>
626</section>
627
628<section title="Response Header Fields" anchor="response.header.fields">
629  <x:anchor-alias value="response-header"/>
630<t>
631   The response header fields allow the server to pass additional
632   information about the response which cannot be placed in the Status-Line.
633   These header fields give information about the server and about
634   further access to the target resource (&effective-request-uri;).
635</t>
636<texttable align="left">
637  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
638
639  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
640  <c>Age</c> <c>&header-age;</c>
641  <c>Allow</c> <c><xref target="header.allow"/></c>
642  <c>Date</c> <c><xref target="header.date"/></c>
643  <c>ETag</c> <c>&header-etag;</c>
644  <c>Location</c> <c><xref target="header.location"/></c>
645  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
646  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
647  <c>Server</c> <c><xref target="header.server"/></c>
648  <c>Vary</c> <c>&header-vary;</c>
649  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
650</texttable>
651</section>
652
653</section>
654
655<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
656  <x:anchor-alias value="Reason-Phrase"/>
657  <x:anchor-alias value="Status-Code"/>
658  <x:anchor-alias value="extension-code"/>
659<t>
660   The Status-Code element is a 3-digit integer result code of the attempt to
661   understand and satisfy the request.
662</t>
663<t>
664   The Reason-Phrase is intended to give a short textual description of the
665   Status-Code and is intended for a human user. The client does not need
666   to examine or display the Reason-Phrase.
667</t>
668<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"/>
669  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
670  <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> )
671</artwork></figure>
672<t>
673   HTTP status codes are extensible. HTTP applications are not required
674   to understand the meaning of all registered status codes, though such
675   understanding is obviously desirable. However, applications &MUST;
676   understand the class of any status code, as indicated by the first
677   digit, and treat any unrecognized response as being equivalent to the
678   x00 status code of that class, with the exception that an
679   unrecognized response &MUST-NOT; be cached. For example, if an
680   unrecognized status code of 431 is received by the client, it can
681   safely assume that there was something wrong with its request and
682   treat the response as if it had received a 400 status code. In such
683   cases, user agents &SHOULD; present to the user the representation enclosed
684   with the response, since that representation is likely to include human-readable
685   information which will explain the unusual status.
686</t>
687
688<section title="Overview of Status Codes" anchor="overview.of.status.codes">
689<t> 
690   The status codes listed below are defined in <xref target="status.codes"/>
691   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
692   The reason phrases listed here are only recommendations &mdash; they can be
693   replaced by local equivalents without affecting the protocol.
694</t>
695<texttable align="left">
696  <ttcol>Status-Code</ttcol>
697  <ttcol>Reason-Phrase</ttcol>
698  <ttcol>Defined in...</ttcol>
699 
700  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
701  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
702
703  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
704  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
705  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
706  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
707  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
708  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
709  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
710
711  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
712  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
713  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
714  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
715  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
716  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
717  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
718
719  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
720  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
721  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
722  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
723  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
724  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
725  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
726  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
727  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
728  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
729  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
730  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
731  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
732  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
733  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
734  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
735  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
736  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
737  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
738
739  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
740  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
741  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
742  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
743  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
744  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
745</texttable>
746<t>
747   Note that this list is not exhaustive &mdash; it does not include
748   extension status codes defined in other specifications.
749</t>
750</section>
751
752<section title="Status Code Registry" anchor="status.code.registry">
753<t>
754  The HTTP Status Code Registry defines the name space for the Status-Code
755  token in the Status-Line of an HTTP response.
756</t>
757<t>
758  Values to be added to this name space are subject to IETF review
759  (<xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
760</t>
761<t>
762  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
763</t>
764
765<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
766<t>
767   When it is necessary to express new semantics for a HTTP response that
768   aren't specific to a single application or media type, and currently defined
769   status codes are inadequate, a new status code can be registered.
770</t>
771<t>
772   HTTP status codes are generic; that is, they are potentially applicable to
773   any resource, not just one particular media type, "type" of resource, or
774   application. As such, it is preferred that new HTTP status codes be
775   registered in a document that isn't specific to a single application, so
776   that this is clear.
777</t>
778<t>
779   Definitions of new HTTP status codes typically explain the request
780   conditions that produce a response containing the status code (e.g.,
781   combinations of request headers and/or method(s)), along with any
782   interactions with response headers (e.g., those that are required, those
783   that modify the semantics of the response).
784</t>
785<t>
786   New HTTP status codes are required to fall under one of the categories
787   defined in <xref target="status.codes"/>. To allow existing parsers to
788   properly handle them, new status codes cannot disallow a response body,
789   although they can mandate a zero-length response body. They can require the
790   presence of one or more particular HTTP response header(s).
791</t>
792<t>
793   Likewise, their definitions can specify that caches are allowed to use
794   heuristics to determine their freshness (see &caching;; by default, it is
795   not allowed), and can define how to determine the resource which they
796   carry a representation for (see <xref
797   target="identifying.response.associated.with.representation"/>; by default,
798   it is anonymous).
799</t>
800</section>
801
802</section>
803
804</section>
805
806<section title="Representation" anchor="representation">
807<t>
808   Request and Response messages &MAY; transfer a representation if not otherwise
809   restricted by the request method or response status code. A representation
810   consists of metadata (representation header fields) and data (representation
811   body).  When a complete or partial representation is enclosed in an HTTP message,
812   it is referred to as the payload of the message. HTTP representations
813   are defined in &payload;.
814</t>
815<t>
816   A representation body is only present in a message when a message body is
817   present, as described in &message-body;. The representation body is obtained
818   from the message body by decoding any Transfer-Encoding that might
819   have been applied to ensure safe and proper transfer of the message.
820</t>
821
822<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
823<t>
824   It is sometimes necessary to determine an identifier for the resource
825   associated with a representation.
826</t>
827<t>
828   An HTTP request representation, when present, is always associated with an
829   anonymous (i.e., unidentified) resource.
830</t>
831<t>
832   In the common case, an HTTP response is a representation of the target
833   resource (see &effective-request-uri;). However, this is not always the
834   case. To determine the URI of the resource a response is associated with,
835   the following rules are used (with the first applicable one being selected):
836</t>
837<t><list style="numbers">
838   <t>If the response status code is 200 or 203 and the request method was GET,
839   the response payload is a representation of the target resource.</t>
840   <t>If the response status code is 204, 206, or 304 and the request method was GET
841   or HEAD, the response payload is a partial representation of the target
842   resource.</t>
843   <t>If the response has a Content-Location header field, and that URI is the same
844   as the effective request URI, the response payload is a representation of the
845   target resource.</t>
846   <t>If the response has a Content-Location header field, and that URI is not the
847   same as the effective request URI, then the response asserts that its
848   payload is a representation of the resource identified by the
849   Content-Location URI. However, such an assertion cannot be trusted unless
850   it can be verified by other means (not defined by HTTP).</t>
851   <t>Otherwise, the response is a representation of an anonymous (i.e.,
852   unidentified) resource.</t>
853</list></t>
854<t>
855  <cref anchor="TODO-req-uri">
856   The comparison function is going to have to be defined somewhere,
857   because we already need to compare URIs for things like cache invalidation.</cref>
858</t>
859</section>
860
861</section>
862
863
864<section title="Method Definitions" anchor="method.definitions">
865<t>
866   The set of common request methods for HTTP/1.1 is defined below. Although
867   this set can be expanded, additional methods cannot be assumed to
868   share the same semantics for separately extended clients and servers.
869</t>
870
871<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
872
873<section title="Safe Methods" anchor="safe.methods">
874<iref item="Safe Methods" primary="true"/>
875<t>
876   Implementors need to be aware that the software represents the user in
877   their interactions over the Internet, and need to allow
878   the user to be aware of any actions they take which might have an
879   unexpected significance to themselves or others.
880</t>
881<t>
882   In particular, the convention has been established that the GET, HEAD,
883   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
884   of taking an action other than retrieval. These request methods ought
885   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
886   This allows user agents to represent other methods, such as POST, PUT
887   and DELETE, in a special way, so that the user is made aware of the
888   fact that a possibly unsafe action is being requested.
889</t>
890<t>
891   Naturally, it is not possible to ensure that the server does not
892   generate side-effects as a result of performing a GET request; in
893   fact, some dynamic resources consider that a feature. The important
894   distinction here is that the user did not request the side-effects,
895   so therefore cannot be held accountable for them.
896</t>
897</section>
898
899<section title="Idempotent Methods" anchor="idempotent.methods">
900<iref item="Idempotent Methods" primary="true"/>
901<t>
902   Request methods can also have the property of "idempotence" in that,
903   aside from error or expiration issues, the intended effect of multiple
904   identical requests is the same as for a single request.
905   PUT, DELETE, and all safe request methods are idempotent.
906   It is important to note that idempotence refers only to changes
907   requested by the client: a server is free to change its state due
908   to multiple requests for the purpose of tracking those requests,
909   versioning of results, etc.
910</t>
911</section>
912</section>
913
914<section title="OPTIONS" anchor="OPTIONS">
915  <rdf:Description>
916    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
917  </rdf:Description>
918  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
919  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
920<t>
921   The OPTIONS method requests information about the
922   communication options available on the request/response chain
923   identified by the effective request URI. This method allows a client to
924   determine the options and/or requirements associated with a resource,
925   or the capabilities of a server, without implying a resource action
926   or initiating a resource retrieval.
927</t>
928<t>
929   Responses to the OPTIONS method are not cacheable.
930</t>
931<t>
932   If the OPTIONS request includes a message body (as indicated by the
933   presence of Content-Length or Transfer-Encoding), then the media type
934   &MUST; be indicated by a Content-Type field. Although this
935   specification does not define any use for such a body, future
936   extensions to HTTP might use the OPTIONS body to make more detailed
937   queries on the server.
938</t>
939<t>
940   If the request-target is an asterisk ("*"), the OPTIONS request is
941   intended to apply to the server in general rather than to a specific
942   resource. Since a server's communication options typically depend on
943   the resource, the "*" request is only useful as a "ping" or "no-op"
944   type of method; it does nothing beyond allowing the client to test
945   the capabilities of the server. For example, this can be used to test
946   a proxy for HTTP/1.1 conformance (or lack thereof).
947</t>
948<t>
949   If the request-target is not an asterisk, the OPTIONS request applies
950   only to the options that are available when communicating with that
951   resource.
952</t>
953<t>
954   A 200 response &SHOULD; include any header fields that indicate
955   optional features implemented by the server and applicable to that
956   resource (e.g., Allow), possibly including extensions not defined by
957   this specification. The response body, if any, &SHOULD; also include
958   information about the communication options. The format for such a
959   body is not defined by this specification, but might be defined by
960   future extensions to HTTP. Content negotiation &MAY; be used to select
961   the appropriate response format. If no response body is included, the
962   response &MUST; include a Content-Length field with a field-value of
963   "0".
964</t>
965<t>
966   The Max-Forwards header field &MAY; be used to target a
967   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
968   If no Max-Forwards field is present in the request, then the forwarded
969   request &MUST-NOT; include a Max-Forwards field.
970</t>
971</section>
972
973<section title="GET" anchor="GET">
974  <rdf:Description>
975    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
976  </rdf:Description>
977  <iref primary="true" item="GET method" x:for-anchor=""/>
978  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
979<t>
980   The GET method requests transfer of a current representation of
981   the target resource.
982</t>
983<t>   
984   If the target resource is a data-producing process, it is the
985   produced data which shall be returned as the representation in the response and not
986   the source text of the process, unless that text happens to be the output of
987   the process.
988</t>
989<t>
990   The semantics of the GET method change to a "conditional GET" if the
991   request message includes an If-Modified-Since, If-Unmodified-Since,
992   If-Match, If-None-Match, or If-Range header field. A conditional GET
993   requests that the representation be transferred only under the
994   circumstances described by the conditional header field(s). The
995   conditional GET request is intended to reduce unnecessary network
996   usage by allowing cached representations to be refreshed without requiring
997   multiple requests or transferring data already held by the client.
998</t>
999<t>
1000   The semantics of the GET method change to a "partial GET" if the
1001   request message includes a Range header field. A partial GET requests
1002   that only part of the representation be transferred, as described in &header-range;.
1003   The partial GET request is intended to reduce unnecessary
1004   network usage by allowing partially-retrieved representations to be
1005   completed without transferring data already held by the client.
1006</t>
1007<t>
1008   Bodies on GET requests have no defined semantics. Note that sending a body
1009   on a GET request might cause some existing implementations to reject the
1010   request.
1011</t>
1012<t>
1013   The response to a GET request is cacheable and &MAY; be used to satisfy
1014   subsequent GET and HEAD requests (see &caching;).
1015</t>
1016<t>
1017   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
1018</t>
1019</section>
1020
1021<section title="HEAD" anchor="HEAD">
1022  <rdf:Description>
1023    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1024  </rdf:Description>
1025  <iref primary="true" item="HEAD method" x:for-anchor=""/>
1026  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
1027<t>
1028   The HEAD method is identical to GET except that the server &MUST-NOT;
1029   return a message body in the response. The metadata contained
1030   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
1031   to the information sent in response to a GET request. This method can
1032   be used for obtaining metadata about the representation implied by the
1033   request without transferring the representation body. This method is
1034   often used for testing hypertext links for validity, accessibility,
1035   and recent modification.
1036</t>
1037<t>
1038   The response to a HEAD request is cacheable and &MAY; be used to satisfy
1039   a subsequent HEAD request. It also has potential side effects on
1040   previously stored responses to GET; see &p6-head;.
1041</t>
1042<t>
1043   Bodies on HEAD requests have no defined semantics. Note that sending a body
1044   on a HEAD request might cause some existing implementations to reject the
1045   request.
1046</t>
1047</section>
1048
1049<section title="POST" anchor="POST">
1050  <iref primary="true" item="POST method" x:for-anchor=""/>
1051  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
1052<t>
1053   The POST method requests that the origin server accept the
1054   representation enclosed in the request as data to be processed by the
1055   target resource. POST is designed to allow a uniform method to cover the
1056   following functions:
1057  <list style="symbols">
1058    <t>
1059      Annotation of existing resources;
1060    </t>
1061    <t>
1062        Posting a message to a bulletin board, newsgroup, mailing list,
1063        or similar group of articles;
1064    </t>
1065    <t>
1066        Providing a block of data, such as the result of submitting a
1067        form, to a data-handling process;
1068    </t>
1069    <t>
1070        Extending a database through an append operation.
1071    </t>
1072  </list>
1073</t>
1074<t>
1075   The actual function performed by the POST method is determined by the
1076   server and is usually dependent on the effective request URI.
1077</t>
1078<t>
1079   The action performed by the POST method might not result in a
1080   resource that can be identified by a URI. In this case, either 200
1081   (OK) or 204 (No Content) is the appropriate response status code,
1082   depending on whether or not the response includes a representation that
1083   describes the result.
1084</t>
1085<t>
1086   If a resource has been created on the origin server, the response
1087   &SHOULD; be 201 (Created) and contain a representation which describes the
1088   status of the request and refers to the new resource, and a Location
1089   header field (see <xref target="header.location"/>).
1090</t>
1091<t>
1092   Responses to POST requests are only cacheable when they
1093   include explicit freshness information (see &p6-explicit;). A
1094   cached POST response with a Content-Location header field
1095   (see &header-content-location;) whose value is the effective
1096   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1097</t>
1098<t>
1099   Note that POST caching is not widely implemented.
1100   However, the 303 (See Other) response can be used to direct the
1101   user agent to retrieve a cacheable resource.
1102</t>
1103</section>
1104
1105<section title="PUT" anchor="PUT">
1106  <iref primary="true" item="PUT method" x:for-anchor=""/>
1107  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
1108<t>
1109   The PUT method requests that the state of the target resource
1110   be created or replaced with the state defined by the representation
1111   enclosed in the request message payload.  A successful PUT of a given
1112   representation would suggest that a subsequent GET on that same target
1113   resource will result in an equivalent representation being returned in
1114   a 200 (OK) response.  However, there is no guarantee that such a state
1115   change will be observable, since the target resource might be acted
1116   upon by other user agents in parallel, or might be subject to dynamic
1117   processing by the origin server, before any subsequent GET is received.
1118   A successful response only implies that the user agent's intent was
1119   achieved at the time of its processing by the origin server.
1120</t>
1121<t>   
1122   If the target resource does not have a current representation and
1123   the PUT successfully creates one, then the origin server &MUST; inform
1124   the user agent by sending a 201 (Created) response.  If the target
1125   resource does have a current representation and that representation is
1126   successfully modified in accordance with the state of the enclosed
1127   representation, then either a 200 (OK) or 204 (No Content) response
1128   &SHOULD; be sent to indicate successful completion of the request.
1129</t>
1130<t>
1131   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1132   as part of the resource state).
1133</t>
1134<t>
1135   An origin server &SHOULD; verify that the PUT representation is
1136   consistent with any constraints which the server has for the target
1137   resource that cannot or will not be changed by the PUT.  This is
1138   particularly important when the origin server uses internal
1139   configuration information related to the URI in order to set the
1140   values for representation metadata on GET responses.  When a PUT
1141   representation is inconsistent with the target resource, the origin
1142   server &SHOULD; either make them consistent, by transforming the
1143   representation or changing the resource configuration, or respond
1144   with an appropriate error message containing sufficient information
1145   to explain why the representation is unsuitable.  The 409 (Conflict)
1146   or 415 (Unsupported Media Type) status codes are suggested, with the
1147   latter being specific to constraints on Content-Type values.
1148</t>
1149<t>
1150   For example, if the target resource is configured to always have a
1151   Content-Type of "text/html" and the representation being PUT has a
1152   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1153   (a) reconfigure the target resource to reflect the new media type;
1154   (b) transform the PUT representation to a format consistent with that
1155   of the resource before saving it as the new resource state; or,
1156   (c) reject the request with a 415 response indicating that the target
1157   resource is limited to "text/html", perhaps including a link to a
1158   different resource that would be a suitable target for the new
1159   representation.
1160</t>
1161<t>
1162   HTTP does not define exactly how a PUT method affects the state
1163   of an origin server beyond what can be expressed by the intent of
1164   the user agent request and the semantics of the origin server response.
1165   It does not define what a resource might be, in any sense of that
1166   word, beyond the interface provided via HTTP.  It does not define
1167   how resource state is "stored", nor how such storage might change
1168   as a result of a change in resource state, nor how the origin server
1169   translates resource state into representations.  Generally speaking,
1170   all implementation details behind the resource interface are
1171   intentionally hidden by the server.
1172</t>
1173<t>
1174   The fundamental difference between the POST and PUT methods is
1175   highlighted by the different intent for the target resource.
1176   The target resource in a POST request is intended to handle the
1177   enclosed representation as a data-accepting process, such as for
1178   a gateway to some other protocol or a document that accepts annotations.
1179   In contrast, the target resource in a PUT request is intended to
1180   take the enclosed representation as a new or replacement value.
1181   Hence, the intent of PUT is idempotent and visible to intermediaries,
1182   even though the exact effect is only known by the origin server.
1183</t>
1184<t>
1185   Proper interpretation of a PUT request presumes that the user agent
1186   knows what target resource is desired.  A service that is intended
1187   to select a proper URI on behalf of the client, after receiving
1188   a state-changing request, &SHOULD; be implemented using the POST
1189   method rather than PUT.  If the origin server will not make the
1190   requested PUT state change to the target resource and instead
1191   wishes to have it applied to a different resource, such as when the
1192   resource has been moved to a different URI, then the origin server
1193   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
1194   then make its own decision regarding whether or not to redirect the
1195   request.
1196</t>
1197<t>
1198   A PUT request applied to the target resource &MAY; have side-effects
1199   on other resources.  For example, an article might have a URI for
1200   identifying "the current version" (a resource) which is separate
1201   from the URIs identifying each particular version (different
1202   resources that at one point shared the same state as the current version
1203   resource).  A successful PUT request on "the current version" URI might
1204   therefore create a new version resource in addition to changing the
1205   state of the target resource, and might also cause links to be added
1206   between the related resources.
1207</t>
1208<t>
1209   An origin server &SHOULD; reject any PUT request that contains a
1210   Content-Range header field, since it might be misinterpreted as
1211   partial content (or might be partial content that is being mistakenly
1212   PUT as a full representation).  Partial content updates are
1213   possible by targeting a separately identified resource with state
1214   that overlaps a portion of the larger resource, or by using a
1215   different method that has been specifically defined for partial
1216   updates (for example, the PATCH method defined in
1217   <xref target="RFC5789"/>).
1218</t>
1219<t>
1220   Responses to the PUT method are not cacheable. If a PUT request passes
1221   through a cache that has one or more stored responses for the effective
1222   request URI, those stored responses will be invalidated (see
1223   &p6-invalid;).
1224</t>
1225</section>
1226
1227<section title="DELETE" anchor="DELETE">
1228  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1229  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
1230<t>
1231   The DELETE method requests that the origin server delete the target
1232   resource. This method &MAY; be overridden by
1233   human intervention (or other means) on the origin server. The client cannot
1234   be guaranteed that the operation has been carried out, even if the
1235   status code returned from the origin server indicates that the action
1236   has been completed successfully. However, the server &SHOULD-NOT; 
1237   indicate success unless, at the time the response is given, it
1238   intends to delete the resource or move it to an inaccessible
1239   location.
1240</t>
1241<t>
1242   A successful response &SHOULD; be 200 (OK) if the response includes an
1243   representation describing the status, 202 (Accepted) if the action has not
1244   yet been enacted, or 204 (No Content) if the action has been enacted
1245   but the response does not include a representation.
1246</t>
1247<t>
1248   Bodies on DELETE requests have no defined semantics. Note that sending a body
1249   on a DELETE request might cause some existing implementations to reject the
1250   request.
1251</t>
1252<t>
1253   Responses to the DELETE method are not cacheable. If a DELETE request
1254   passes through a cache that has one or more stored responses for the
1255   effective request URI, those stored responses will be invalidated (see
1256   &p6-invalid;).
1257</t>
1258</section>
1259
1260<section title="TRACE" anchor="TRACE">
1261  <rdf:Description>
1262    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1263  </rdf:Description>
1264  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1265  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
1266<t>
1267   The TRACE method requests a remote, application-layer loop-back
1268   of the request message. The final recipient of the request
1269   &SHOULD; reflect the message received back to the client as the
1270   message body of a 200 (OK) response. The final recipient is either the
1271   origin server or the first proxy to receive a Max-Forwards
1272   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1273   A TRACE request &MUST-NOT; include a message body.
1274</t>
1275<t>
1276   TRACE allows the client to see what is being received at the other
1277   end of the request chain and use that data for testing or diagnostic
1278   information. The value of the Via header field (&header-via;) is of
1279   particular interest, since it acts as a trace of the request chain.
1280   Use of the Max-Forwards header field allows the client to limit the
1281   length of the request chain, which is useful for testing a chain of
1282   proxies forwarding messages in an infinite loop.
1283</t>
1284<t>
1285   If the request is valid, the response &SHOULD; have a Content-Type of
1286   "message/http" (see &media-type-message-http;) and contain a message body
1287   that encloses a copy of the entire request message.
1288   Responses to the TRACE method are not cacheable.
1289</t>
1290</section>
1291
1292<section title="CONNECT" anchor="CONNECT">
1293  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1294  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1295<t>
1296   The CONNECT method requests that the proxy establish a tunnel
1297   to the request-target and then restrict its behavior to blind
1298   forwarding of packets until the connection is closed.
1299</t>
1300<t>
1301   When using CONNECT, the request-target &MUST; use the authority form
1302   (&request-target;); i.e., the request-target consists of only the
1303   host name and port number of the tunnel destination, separated by a colon.
1304   For example,
1305</t>
1306<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1307CONNECT server.example.com:80 HTTP/1.1
1308Host: server.example.com:80
1309
1310</artwork></figure>
1311<t>
1312   Other HTTP mechanisms can be used normally with the CONNECT method &mdash;
1313   except end-to-end protocol Upgrade requests, since the
1314   tunnel must be established first.
1315</t>
1316<t>
1317   For example, proxy authentication might be used to establish the
1318   authority to create a tunnel:
1319</t>
1320<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1321CONNECT server.example.com:80 HTTP/1.1
1322Host: server.example.com:80
1323Proxy-Authorization: basic aGVsbG86d29ybGQ=
1324
1325</artwork></figure>
1326<t>
1327   Bodies on CONNECT requests have no defined semantics. Note that sending a body
1328   on a CONNECT request might cause some existing implementations to reject the
1329   request.
1330</t>
1331<t>
1332   Like any other pipelined HTTP/1.1 request, data to be tunnel may be
1333   sent immediately after the blank line. The usual caveats also apply:
1334   data may be discarded if the eventual response is negative, and the
1335   connection may be reset with no response if more than one TCP segment
1336   is outstanding.
1337</t>
1338
1339<section title="Establishing a Tunnel with CONNECT">
1340<t>
1341   Any successful (2xx) response to a CONNECT request indicates that the
1342   proxy has established a connection to the requested host and port,
1343   and has switched to tunneling the current connection to that server
1344   connection.
1345</t>
1346<t>
1347   It may be the case that the proxy itself can only reach the requested
1348   origin server through another proxy.  In this case, the first proxy
1349   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1350   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1351   unless it has either a direct or tunnel connection established to the
1352   authority.
1353</t>
1354<t>
1355   An origin server which receives a CONNECT request for itself &MAY;
1356   respond with a 2xx status code to indicate that a connection is
1357   established.
1358</t>
1359<t>
1360   If at any point either one of the peers gets disconnected, any
1361   outstanding data that came from that peer will be passed to the other
1362   one, and after that also the other connection will be terminated by
1363   the proxy. If there is outstanding data to that peer undelivered,
1364   that data will be discarded.
1365</t>
1366
1367</section>
1368</section>
1369</section>
1370
1371
1372<section title="Status Code Definitions" anchor="status.codes">
1373<t>
1374   The first digit of the Status-Code defines the class of response. The
1375   last two digits do not have any categorization role. There are 5
1376   values for the first digit:
1377  <list style="symbols">
1378    <t>
1379      1xx: Informational - Request received, continuing process
1380    </t>
1381    <t>
1382      2xx: Success - The action was successfully received,
1383        understood, and accepted
1384    </t>
1385    <t>
1386      3xx: Redirection - Further action must be taken in order to
1387        complete the request
1388    </t>
1389    <t>
1390      4xx: Client Error - The request contains bad syntax or cannot
1391        be fulfilled
1392    </t>
1393    <t>
1394      5xx: Server Error - The server failed to fulfill an apparently
1395        valid request
1396    </t>
1397  </list>
1398</t>
1399<t>
1400   Each Status-Code is described below, including any metadata required
1401   in the response.
1402</t>
1403<t>
1404   For most status codes the response can carry a payload, in which case a
1405   Content-Type header field indicates the payload's media type
1406   (&header-content-type;).
1407</t>
1408
1409<section title="Informational 1xx" anchor="status.1xx">
1410<t>
1411   This class of status code indicates a provisional response,
1412   consisting only of the Status-Line and optional header fields, and is
1413   terminated by an empty line. There are no required header fields for this
1414   class of status code. Since HTTP/1.0 did not define any 1xx status
1415   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1416   except under experimental conditions.
1417</t>
1418<t>
1419   A client &MUST; be prepared to accept one or more 1xx status responses
1420   prior to a regular response, even if the client does not expect a 100
1421   (Continue) status message. Unexpected 1xx status responses &MAY; be
1422   ignored by a user agent.
1423</t>
1424<t>
1425   Proxies &MUST; forward 1xx responses, unless the connection between the
1426   proxy and its client has been closed, or unless the proxy itself
1427   requested the generation of the 1xx response. (For example, if a
1428   proxy adds a "Expect: 100-continue" field when it forwards a request,
1429   then it need not forward the corresponding 100 (Continue)
1430   response(s).)
1431</t>
1432
1433<section title="100 Continue" anchor="status.100">
1434  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1435  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1436<t>
1437   The client &SHOULD; continue with its request. This interim response is
1438   used to inform the client that the initial part of the request has
1439   been received and has not yet been rejected by the server. The client
1440   &SHOULD; continue by sending the remainder of the request or, if the
1441   request has already been completed, ignore this response. The server
1442   &MUST; send a final response after the request has been completed. See
1443   &use100; for detailed discussion of the use and handling of this
1444   status code.
1445</t>
1446</section>
1447
1448<section title="101 Switching Protocols" anchor="status.101">
1449  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1450  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1451<t>
1452   The server understands and is willing to comply with the client's
1453   request, via the Upgrade message header field (&header-upgrade;), for a
1454   change in the application protocol being used on this connection. The
1455   server will switch protocols to those defined by the response's
1456   Upgrade header field immediately after the empty line which
1457   terminates the 101 response.
1458</t>
1459<t>
1460   The protocol &SHOULD; be switched only when it is advantageous to do
1461   so. For example, switching to a newer version of HTTP is advantageous
1462   over older versions, and switching to a real-time, synchronous
1463   protocol might be advantageous when delivering resources that use
1464   such features.
1465</t>
1466</section>
1467</section>
1468
1469<section title="Successful 2xx" anchor="status.2xx">
1470<t>
1471   This class of status code indicates that the client's request was
1472   successfully received, understood, and accepted.
1473</t>
1474
1475<section title="200 OK" anchor="status.200">
1476  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1477  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1478<t>
1479   The request has succeeded. The payload returned with the response
1480   is dependent on the method used in the request, for example:
1481  <list style="hanging">
1482    <t hangText="GET">
1483      a representation of the target resource is sent in the response;
1484    </t>
1485    <t hangText="HEAD">
1486      the same representation as GET, except without the message body;
1487    </t>
1488    <t hangText="POST">
1489      a representation describing or containing the result of the action;
1490    </t>
1491    <t hangText="TRACE">
1492      a representation containing the request message as received by the
1493      end server.
1494    </t>
1495  </list>
1496</t>
1497<t>
1498   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1499   freshness for 200 responses.
1500</t>
1501</section>
1502
1503<section title="201 Created" anchor="status.201">
1504  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1505  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1506<t>
1507   The request has been fulfilled and has resulted in a new resource being
1508   created. The newly created resource can be referenced by the URI(s)
1509   returned in the payload of the response, with the most specific URI
1510   for the resource given by a Location header field. The response
1511   can include a payload containing a list of resource
1512   characteristics and location(s) from which the user or user agent can
1513   choose the one most appropriate.
1514</t>
1515<t>
1516   The origin server &MUST; create the resource before returning the 201 status
1517   code. If the action cannot be carried out immediately, the server &SHOULD;
1518   respond with 202 (Accepted) response instead.
1519</t>
1520<t>
1521   A 201 response &MAY; contain an ETag response header field indicating
1522   the current value of the entity-tag for the representation of the resource
1523   just created (see &header-etag;).
1524</t>
1525</section>
1526
1527<section title="202 Accepted" anchor="status.202">
1528  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1529  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1530<t>
1531   The request has been accepted for processing, but the processing has
1532   not been completed.  The request might or might not eventually be
1533   acted upon, as it might be disallowed when processing actually takes
1534   place. There is no facility for re-sending a status code from an
1535   asynchronous operation such as this.
1536</t>
1537<t>
1538   The 202 response is intentionally non-committal. Its purpose is to
1539   allow a server to accept a request for some other process (perhaps a
1540   batch-oriented process that is only run once per day) without
1541   requiring that the user agent's connection to the server persist
1542   until the process is completed. The representation returned with this
1543   response &SHOULD; include an indication of the request's current status
1544   and either a pointer to a status monitor or some estimate of when the
1545   user can expect the request to be fulfilled.
1546</t>
1547</section>
1548
1549<section title="203 Non-Authoritative Information" anchor="status.203">
1550  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1551  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1552<t>
1553   The representation in the response has been transformed or otherwise
1554   modified by a transforming proxy (&intermediaries;).  Note that the
1555   behavior of transforming intermediaries is controlled by the no-transform
1556   Cache-Control directive (&header-cache-control;).
1557</t>
1558<t>
1559   This status code is only appropriate when the response status code would
1560   have been 200 (OK) otherwise. When the status code before transformation
1561   would have been different, the 214 Transformation Applied warn-code
1562   (&header-warning;) is appropriate.
1563</t>
1564<t>
1565   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1566   freshness for 203 responses.
1567</t>
1568</section>
1569
1570<section title="204 No Content" anchor="status.204">
1571  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1572  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1573<t>
1574   The 204 (No Content) status code indicates that the server has
1575   successfully fulfilled the request and that there is no additional
1576   content to return in the response payload body.  Metadata in the
1577   response header fields refer to the target resource and its current
1578   representation after the requested action.
1579</t>
1580<t>
1581   For example, if a 204 status code is received in response to a PUT
1582   request and the response contains an ETag header field, then the PUT
1583   was successful and the ETag field-value contains the entity-tag for
1584   the new representation of that target resource.
1585</t>
1586<t>
1587   The 204 response allows a server to indicate that the action has been
1588   successfully applied to the target resource while implying that the
1589   user agent &SHOULD-NOT; traverse away from its current "document view"
1590   (if any).  The server assumes that the user agent will provide some
1591   indication of the success to its user, in accord with its own interface,
1592   and apply any new or updated metadata in the response to the active
1593   representation.
1594</t>
1595<t>
1596   For example, a 204 status code is commonly used with document editing
1597   interfaces corresponding to a "save" action, such that the document
1598   being saved remains available to the user for editing. It is also
1599   frequently used with interfaces that expect automated data transfers
1600   to be prevalent, such as within distributed version control systems.
1601</t>
1602<t>
1603   The 204 response &MUST-NOT; include a message body, and thus is always
1604   terminated by the first empty line after the header fields.
1605</t>
1606</section>
1607
1608<section title="205 Reset Content" anchor="status.205">
1609  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1610  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1611<t>
1612   The server has fulfilled the request and the user agent &SHOULD; reset
1613   the document view which caused the request to be sent. This response
1614   is primarily intended to allow input for actions to take place via
1615   user input, followed by a clearing of the form in which the input is
1616   given so that the user can easily initiate another input action.
1617</t>
1618<t>   
1619   The message body included with the response &MUST; be empty. Note that
1620   receivers still need to parse the response according to the algorithm defined
1621   in &message-body;.
1622</t>
1623</section>
1624</section>
1625
1626<section title="Redirection 3xx" anchor="status.3xx">
1627<t>
1628   This class of status code indicates that further action needs to be
1629   taken by the user agent in order to fulfill the request.  If the required
1630   action involves a subsequent HTTP request, it &MAY; be carried out by the
1631   user agent without interaction with the user if and only if the method used
1632   in the second request is known to be "safe", as defined in
1633   <xref target="safe.methods"/>.
1634</t>
1635<t>
1636   There are several types of redirects:
1637   <list style="numbers">
1638      <x:lt>
1639        <t>
1640          Redirects of the request to another URI, either temporarily or
1641          permanently. The new URI is specified in the Location header field.
1642          In this specification, the status codes 301 (Moved Permanently),
1643          302 (Found), and 307 (Temporary Redirect) fall under this category.
1644        </t>
1645      </x:lt>
1646      <x:lt>
1647        <t>
1648          Redirection to a new location that represents an indirect response to
1649          the request, such as the result of a POST operation to be retrieved
1650          with a subsequent GET request. This is status code 303 (See Other).
1651        </t>
1652      </x:lt>
1653      <x:lt>
1654        <t>
1655          Redirection offering a choice of matching resources for use by
1656          agent-driven content negotiation (&agent-driven-negotiation;). This
1657          is status code 300 (Multiple Choices).
1658        </t>
1659      </x:lt>
1660      <x:lt>
1661        <t>
1662          Other kinds of redirection, such as to a cached result (status code 304
1663          (Not Modified), see &status-304;).
1664        </t>
1665      </x:lt>
1666   </list>
1667</t>
1668<x:note>
1669  <t>
1670    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1671    and 302 (Found) were defined for the first type of redirect, and the second
1672    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1673    However it turned out that web forms using POST expected redirects to change
1674    the operation for the subsequent request to retrieval (GET). To address this
1675    use case, HTTP/1.1 introduced the second type of redirect with the status
1676    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1677    As user agents did not change their behavior to maintain backwards
1678    compatibility, the first revision of HTTP/1.1 added yet another status code,
1679    307 (Temporary Redirect), for which the backwards compatibility problems did
1680    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1681    Over 10 years later, most user agents still do method rewriting for
1682    status codes 301 and 302, therefore this specification makes that behavior
1683    conformant in case the original request was POST.
1684  </t>
1685</x:note>
1686<t>
1687   A Location header field on a 3xx response indicates that a client &MAY;
1688   automatically redirect to the URI provided; see <xref target="header.location"/>.
1689</t>
1690<t>
1691   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1692   automatic redirection needs to done with care, since the redirect might
1693   change the conditions under which the request was issued.
1694</t>
1695<t>
1696   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1697   "infinite" redirection loops).
1698</t>
1699<x:note>
1700  <t>
1701    <x:h>Note:</x:h> An earlier version of this specification recommended a
1702    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1703    Content developers need to be aware that some clients might
1704    implement such a fixed limitation.
1705  </t>
1706</x:note>
1707
1708<section title="300 Multiple Choices" anchor="status.300">
1709  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1710  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1711<t>
1712   The target resource has more than one
1713   representation, each with its own specific location, and agent-driven
1714   negotiation information (&content-negotiation;) is being provided so that
1715   the user (or user agent) can select a preferred representation by
1716   redirecting its request to that location.
1717</t>
1718<t>
1719   Unless it was a HEAD request, the response &SHOULD; include a representation
1720   containing a list of representation metadata and location(s) from
1721   which the user or user agent can choose the one most appropriate. Depending
1722   upon the format and the capabilities of
1723   the user agent, selection of the most appropriate choice &MAY; be
1724   performed automatically. However, this specification does not define
1725   any standard for such automatic selection.
1726</t>
1727<t>
1728   If the server has a preferred choice of representation, it &SHOULD;
1729   include the specific URI for that representation in the Location
1730   field; user agents &MAY; use the Location field value for automatic
1731   redirection.
1732</t>
1733<t>
1734   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1735   freshness for 300 responses.
1736</t>
1737
1738</section>
1739
1740<section title="301 Moved Permanently" anchor="status.301">
1741  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1742  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1743<t>
1744   The target resource has been assigned a new permanent URI and any
1745   future references to this resource &SHOULD; use one of the returned
1746   URIs.  Clients with link editing capabilities ought to automatically
1747   re-link references to the effective request URI to one or more of the new
1748   references returned by the server, where possible.
1749</t>
1750<t>
1751   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1752   freshness for 301 responses.
1753</t>
1754<t>
1755   The new permanent URI &SHOULD; be given by the Location field in the
1756   response. A response payload can contain a short hypertext note with a
1757   hyperlink to the new URI(s).
1758</t>
1759<x:note>
1760  <t>
1761    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1762    request method from POST to GET for the subsequent request. If this
1763    behavior is undesired, status code 307 (Temporary Redirect) can be used
1764    instead.
1765  </t>
1766</x:note>
1767</section>
1768
1769<section title="302 Found" anchor="status.302">
1770  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1771  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1772<t>
1773   The target resource resides temporarily under a different URI.
1774   Since the redirection might be altered on occasion, the client &SHOULD;
1775   continue to use the effective request URI for future requests.
1776</t>
1777<t>
1778   The temporary URI &SHOULD; be given by the Location field in the
1779   response. A response payload can contain a short hypertext note with a
1780   hyperlink to the new URI(s).
1781</t>
1782<x:note>
1783  <t>
1784    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1785    request method from POST to GET for the subsequent request. If this
1786    behavior is undesired, status code 307 (Temporary Redirect) can be used
1787    instead.
1788  </t>
1789</x:note>
1790</section>
1791
1792<section title="303 See Other" anchor="status.303">
1793  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1794  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1795<t>
1796   The 303 status code indicates that the server is redirecting the
1797   user agent to a different resource, as indicated by a URI in the
1798   Location header field, that is intended to provide an indirect
1799   response to the original request.  In order to satisfy the original
1800   request, a user agent &SHOULD; perform a retrieval request using the
1801   Location URI (a GET or HEAD request if using HTTP), which
1802   may itself be redirected further, and present the eventual result as an
1803   answer to the original request.
1804   Note that the new URI in the Location header field is not considered
1805   equivalent to the effective request URI.
1806</t>
1807<t>
1808   This status code is generally applicable to any HTTP method.  It is
1809   primarily used to allow the output of a POST action to redirect
1810   the user agent to a selected resource, since doing so provides the
1811   information corresponding to the POST response in a form that
1812   can be separately identified, bookmarked, and cached independent
1813   of the original request.
1814</t>
1815<t>
1816   A 303 response to a GET request indicates that the requested
1817   resource does not have a representation of its own that can be
1818   transferred by the server over HTTP.  The Location URI indicates a
1819   resource that is descriptive of the target resource, such that the
1820   follow-on representation might be useful to recipients without
1821   implying that it adequately represents the target resource.
1822   Note that answers to the questions of what can be represented, what
1823   representations are adequate, and what might be a useful description
1824   are outside the scope of HTTP and thus entirely determined by the
1825   URI owner(s).
1826</t>
1827<t>
1828   Except for responses to a HEAD request, the representation of a 303
1829   response &SHOULD; contain a short hypertext note with a hyperlink
1830   to the Location URI.
1831</t>
1832</section>
1833
1834<section title="305 Use Proxy" anchor="status.305">
1835  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1836  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1837<t>
1838   The 305 status code was defined in a previous version of this specification
1839   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1840</t>
1841</section>
1842
1843<section title="306 (Unused)" anchor="status.306">
1844  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1845  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1846<t>
1847   The 306 status code was used in a previous version of the
1848   specification, is no longer used, and the code is reserved.
1849</t>
1850</section>
1851
1852<section title="307 Temporary Redirect" anchor="status.307">
1853  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1854  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1855<t>
1856   The target resource resides temporarily under a different URI.
1857   Since the redirection can change over time, the client &SHOULD;
1858   continue to use the effective request URI for future requests.
1859</t>
1860<t>
1861   The temporary URI &SHOULD; be given by the Location field in the
1862   response. A response payload can contain a short hypertext note with a
1863   hyperlink to the new URI(s).
1864</t>
1865<x:note>
1866  <t>
1867    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1868    it does not allow rewriting the request method from POST to GET. This
1869    specification defines no equivalent counterpart for 301 Moved Permanently.
1870  </t>
1871</x:note>
1872</section>
1873</section>
1874
1875<section title="Client Error 4xx" anchor="status.4xx">
1876<t>
1877   The 4xx class of status code is intended for cases in which the
1878   client seems to have erred. Except when responding to a HEAD request,
1879   the server &SHOULD; include a representation containing an explanation of the
1880   error situation, and whether it is a temporary or permanent
1881   condition. These status codes are applicable to any request method.
1882   User agents &SHOULD; display any included representation to the user.
1883</t>
1884
1885<section title="400 Bad Request" anchor="status.400">
1886  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1887  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1888<t>
1889   The server cannot or will not process the request, due to a client error (e.g.,
1890   malformed syntax).
1891</t>
1892</section>
1893
1894<section title="402 Payment Required" anchor="status.402">
1895  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1896  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1897<t>
1898   This code is reserved for future use.
1899</t>
1900</section>
1901
1902<section title="403 Forbidden" anchor="status.403">
1903  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1904  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1905<t>
1906   The server understood the request, but refuses to authorize it. Providing
1907   different user authentication credentials might be successful, but any
1908   credentials that were provided in the request are insufficient. The request
1909   &SHOULD-NOT; be repeated with the same credentials.
1910</t>
1911<t>
1912   If the request method was not HEAD and the server wishes to make
1913   public why the request has not been fulfilled, it &SHOULD; describe the
1914   reason for the refusal in the representation.  If the server does not wish to
1915   make this information available to the client, the status code 404
1916   (Not Found) &MAY; be used instead.
1917</t>
1918</section>
1919
1920<section title="404 Not Found" anchor="status.404">
1921  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1922  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1923<t>
1924   The server has not found anything matching the effective request URI. No
1925   indication is given of whether the condition is temporary or
1926   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1927   knows, through some internally configurable mechanism, that an old
1928   resource is permanently unavailable and has no forwarding address.
1929   This status code is commonly used when the server does not wish to
1930   reveal exactly why the request has been refused, or when no other
1931   response is applicable.
1932</t>
1933</section>
1934
1935<section title="405 Method Not Allowed" anchor="status.405">
1936  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1937  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1938<t>
1939   The method specified in the Request-Line is not allowed for the target
1940   resource. The response &MUST; include an Allow header field containing a
1941   list of valid methods for the requested resource.
1942</t>
1943</section>
1944
1945<section title="406 Not Acceptable" anchor="status.406">
1946  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1947  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1948<t>
1949   The resource identified by the request is only capable of generating
1950   response representations which have content characteristics not acceptable
1951   according to the Accept and Accept-* header fields sent in the request
1952   (see &p3-header-fields;).
1953</t>
1954<t>
1955   Unless it was a HEAD request, the response &SHOULD; include a representation
1956   containing a list of available representation characteristics and location(s)
1957   from which the user or user agent can choose the one most
1958   appropriate. Depending upon the format and the
1959   capabilities of the user agent, selection of the most appropriate
1960   choice &MAY; be performed automatically. However, this specification
1961   does not define any standard for such automatic selection.
1962</t>
1963<x:note>
1964  <t>
1965    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1966    not acceptable according to the accept header fields sent in the
1967    request. In some cases, this might even be preferable to sending a
1968    406 response. User agents are encouraged to inspect the header fields of
1969    an incoming response to determine if it is acceptable.
1970  </t>
1971</x:note>
1972<t>
1973   If the response could be unacceptable, a user agent &SHOULD;
1974   temporarily stop receipt of more data and query the user for a
1975   decision on further actions.
1976</t>
1977</section>
1978
1979<section title="408 Request Timeout" anchor="status.408">
1980  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1981  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1982<t>
1983   The client did not produce a request within the time that the server
1984   was prepared to wait. The client &MAY; repeat the request without
1985   modifications at any later time.
1986</t>
1987</section>
1988
1989<section title="409 Conflict" anchor="status.409">
1990  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1991  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1992<t>
1993   The request could not be completed due to a conflict with the current
1994   state of the resource. This code is only allowed in situations where
1995   it is expected that the user might be able to resolve the conflict
1996   and resubmit the request. The response body &SHOULD; include enough
1997   information for the user to recognize the source of the conflict.
1998   Ideally, the response representation would include enough information for the
1999   user or user agent to fix the problem; however, that might not be
2000   possible and is not required.
2001</t>
2002<t>
2003   Conflicts are most likely to occur in response to a PUT request. For
2004   example, if versioning were being used and the representation being PUT
2005   included changes to a resource which conflict with those made by an
2006   earlier (third-party) request, the server might use the 409 response
2007   to indicate that it can't complete the request. In this case, the
2008   response representation would likely contain a list of the differences
2009   between the two versions.
2010</t>
2011</section>
2012
2013<section title="410 Gone" anchor="status.410">
2014  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
2015  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
2016<t>
2017   The target resource is no longer available at the server and no
2018   forwarding address is known. This condition is expected to be
2019   considered permanent. Clients with link editing capabilities &SHOULD;
2020   delete references to the effective request URI after user approval. If the
2021   server does not know, or has no facility to determine, whether or not
2022   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
2023   used instead.
2024</t>
2025<t>
2026   The 410 response is primarily intended to assist the task of web
2027   maintenance by notifying the recipient that the resource is
2028   intentionally unavailable and that the server owners desire that
2029   remote links to that resource be removed. Such an event is common for
2030   limited-time, promotional services and for resources belonging to
2031   individuals no longer working at the server's site. It is not
2032   necessary to mark all permanently unavailable resources as "gone" or
2033   to keep the mark for any length of time &mdash; that is left to the
2034   discretion of the server owner.
2035</t>
2036<t>
2037   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
2038   for 410 responses.
2039</t>
2040</section>
2041
2042<section title="411 Length Required" anchor="status.411">
2043  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
2044  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
2045<t>
2046   The server refuses to accept the request without a defined Content-Length.
2047   The client &MAY; repeat the request if it adds a valid
2048   Content-Length header field containing the length of the message body
2049   in the request message.
2050</t>
2051</section>
2052
2053<section title="413 Request Representation Too Large" anchor="status.413">
2054  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2055  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2056<t>
2057   The server is refusing to process a request because the request
2058   representation is larger than the server is willing or able to process. The
2059   server &MAY; close the connection to prevent the client from continuing
2060   the request.
2061</t>
2062<t>
2063   If the condition is temporary, the server &SHOULD; include a Retry-After
2064   header field to indicate that it is temporary and after what
2065   time the client &MAY; try again.
2066</t>
2067</section>
2068
2069<section title="414 URI Too Long" anchor="status.414">
2070  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2071  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
2072<t>
2073   The server is refusing to service the request because the effective request URI
2074   is longer than the server is willing to interpret. This rare
2075   condition is only likely to occur when a client has improperly
2076   converted a POST request to a GET request with long query
2077   information, when the client has descended into a URI "black hole" of
2078   redirection (e.g., a redirected URI prefix that points to a suffix of
2079   itself), or when the server is under attack by a client attempting to
2080   exploit security holes present in some servers using fixed-length
2081   buffers for reading or manipulating the effective request URI.
2082</t>
2083</section>
2084
2085<section title="415 Unsupported Media Type" anchor="status.415">
2086  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2087  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2088<t>
2089   The server is refusing to service the request because the request
2090   payload is in a format not supported by this request method on the
2091   target resource.
2092</t>
2093</section>
2094
2095<section title="417 Expectation Failed" anchor="status.417">
2096  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2097  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2098<t>
2099   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2100   could not be met by this server, or, if the server is a proxy,
2101   the server has unambiguous evidence that the request could not be met
2102   by the next-hop server.
2103</t>
2104</section>
2105
2106<section title="426 Upgrade Required" anchor="status.426">
2107  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2108  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2109<t>
2110   The request can not be completed without a prior protocol upgrade. This
2111   response &MUST; include an Upgrade header field (&header-upgrade;)
2112   specifying the required protocols.
2113</t>
2114<figure>
2115<preamble>Example:</preamble>
2116<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
2117HTTP/1.1 426 Upgrade Required
2118Upgrade: HTTP/3.0
2119Connection: Upgrade
2120Content-Length: <x:length-of target="s426body"/>
2121Content-Type: text/plain
2122
2123<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
2124</x:span></artwork></figure>
2125<t>
2126   The server &SHOULD; include a message body in the 426 response which
2127   indicates in human readable form the reason for the error and describes any
2128   alternative courses which may be available to the user.
2129</t>
2130</section>
2131</section>
2132
2133<section title="Server Error 5xx" anchor="status.5xx">
2134<t>
2135   Response status codes beginning with the digit "5" indicate cases in
2136   which the server is aware that it has erred or is incapable of
2137   performing the request. Except when responding to a HEAD request, the
2138   server &SHOULD; include a representation containing an explanation of the
2139   error situation, and whether it is a temporary or permanent
2140   condition. User agents &SHOULD; display any included representation to the
2141   user. These response codes are applicable to any request method.
2142</t>
2143
2144<section title="500 Internal Server Error" anchor="status.500">
2145  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2146  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2147<t>
2148   The server encountered an unexpected condition which prevented it
2149   from fulfilling the request.
2150</t>
2151</section>
2152
2153<section title="501 Not Implemented" anchor="status.501">
2154  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2155  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2156<t>
2157   The server does not support the functionality required to fulfill the
2158   request. This is the appropriate response when the server does not
2159   recognize the request method and is not capable of supporting it for
2160   any resource.
2161</t>
2162</section>
2163
2164<section title="502 Bad Gateway" anchor="status.502">
2165  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2166  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2167<t>
2168   The server, while acting as a gateway or proxy, received an invalid
2169   response from the upstream server it accessed in attempting to
2170   fulfill the request.
2171</t>
2172</section>
2173
2174<section title="503 Service Unavailable" anchor="status.503">
2175  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2176  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2177<t>
2178   The server is currently unable to handle the request due to a
2179   temporary overloading or maintenance of the server.
2180</t>
2181<t>
2182   The implication is that this is a temporary condition which will be
2183   alleviated after some delay. If known, the length of the delay &MAY; be
2184   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2185   If no Retry-After is given, the client &SHOULD; handle the response as it
2186   would for a 500 response.
2187</t>
2188<x:note>
2189  <t>
2190    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2191    server must use it when becoming overloaded. Some servers might wish
2192    to simply refuse the connection.
2193  </t>
2194</x:note>
2195</section>
2196
2197<section title="504 Gateway Timeout" anchor="status.504">
2198  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2199  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2200<t>
2201   The server, while acting as a gateway or proxy, did not receive a
2202   timely response from the upstream server specified by the URI (e.g.,
2203   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2204   to access in attempting to complete the request.
2205</t>
2206<x:note>
2207  <t>
2208    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2209    return 400 or 500 when DNS lookups time out.
2210  </t>
2211</x:note>
2212</section>
2213
2214<section title="505 HTTP Version Not Supported" anchor="status.505">
2215  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2216  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2217<t>
2218   The server does not support, or refuses to support, the protocol
2219   version that was used in the request message. The server is
2220   indicating that it is unable or unwilling to complete the request
2221   using the same major version as the client, as described in &http-version;,
2222   other than with this error message. The response &SHOULD; contain
2223   a representation describing why that version is not supported and what other
2224   protocols are supported by that server.
2225</t>
2226
2227</section>
2228</section>
2229</section>
2230
2231
2232<section title="Date/Time Formats" anchor="http.date">
2233  <x:anchor-alias value="HTTP-date"/>
2234<t>
2235   HTTP applications have historically allowed three different formats
2236   for date/time stamps. However, the preferred format is a fixed-length subset
2237   of that defined by <xref target="RFC1123"/>:
2238</t>
2239<figure><artwork type="example" x:indent-with="  ">
2240Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2241</artwork></figure>
2242<t>
2243   The other formats are described here only for compatibility with obsolete
2244   implementations.
2245</t>
2246<figure><artwork type="example" x:indent-with="  ">
2247Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2248Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2249</artwork></figure>
2250<t>
2251   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2252   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2253   only generate the RFC 1123 format for representing HTTP-date values
2254   in header fields.
2255</t>
2256<t>
2257   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2258   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2259   equal to UTC (Coordinated Universal Time). This is indicated in the
2260   first two formats by the inclusion of "GMT" as the three-letter
2261   abbreviation for time zone, and &MUST; be assumed when reading the
2262   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2263   additional whitespace beyond that specifically included as SP in the
2264   grammar.
2265</t>
2266<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2267  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2268</artwork></figure>
2269<t anchor="preferred.date.format">
2270  <x:anchor-alias value="rfc1123-date"/>
2271  <x:anchor-alias value="time-of-day"/>
2272  <x:anchor-alias value="hour"/>
2273  <x:anchor-alias value="minute"/>
2274  <x:anchor-alias value="second"/>
2275  <x:anchor-alias value="day-name"/>
2276  <x:anchor-alias value="day"/>
2277  <x:anchor-alias value="month"/>
2278  <x:anchor-alias value="year"/>
2279  <x:anchor-alias value="GMT"/>
2280  Preferred format:
2281</t>
2282<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"/>
2283  <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>
2284  ; fixed length subset of the format defined in
2285  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2286 
2287  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2288               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2289               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2290               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2291               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2292               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2293               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2294               
2295  <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>
2296               ; e.g., 02 Jun 1982
2297
2298  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2299  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2300               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2301               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2302               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2303               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2304               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2305               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2306               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2307               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2308               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2309               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2310               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2311  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2312
2313  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2314
2315  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2316                 ; 00:00:00 - 23:59:59
2317                 
2318  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2319  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2320  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2321</artwork></figure>
2322<t>
2323  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2324  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2325  same as those defined for the RFC 5322 constructs
2326  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2327</t>
2328<t anchor="obsolete.date.formats">
2329  <x:anchor-alias value="obs-date"/>
2330  <x:anchor-alias value="rfc850-date"/>
2331  <x:anchor-alias value="asctime-date"/>
2332  <x:anchor-alias value="date1"/>
2333  <x:anchor-alias value="date2"/>
2334  <x:anchor-alias value="date3"/>
2335  <x:anchor-alias value="rfc1123-date"/>
2336  <x:anchor-alias value="day-name-l"/>
2337  Obsolete formats:
2338</t>
2339<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2340  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2341</artwork></figure>
2342<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2343  <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>
2344  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2345                 ; day-month-year (e.g., 02-Jun-82)
2346
2347  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2348         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2349         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2350         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2351         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2352         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2353         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2354</artwork></figure>
2355<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2356  <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>
2357  <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> ))
2358                 ; month day (e.g., Jun  2)
2359</artwork></figure>
2360<x:note>
2361  <t>
2362    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2363    accepting date values that might have been sent by non-HTTP
2364    applications, as is sometimes the case when retrieving or posting
2365    messages via proxies/gateways to SMTP or NNTP.
2366  </t>
2367</x:note>
2368<x:note>
2369  <t>
2370    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2371    to their usage within the protocol stream. Clients and servers are
2372    not required to use these formats for user presentation, request
2373    logging, etc.
2374  </t>
2375</x:note>
2376</section>
2377
2378<section title="Product Tokens" anchor="product.tokens">
2379  <x:anchor-alias value="product"/>
2380  <x:anchor-alias value="product-version"/>
2381<t>
2382   Product tokens are used to allow communicating applications to
2383   identify themselves by software name and version. Most fields using
2384   product tokens also allow sub-products which form a significant part
2385   of the application to be listed, separated by whitespace. By
2386   convention, the products are listed in order of their significance
2387   for identifying the application.
2388</t>
2389<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2390  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2391  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2392</artwork></figure>
2393<t>
2394   Examples:
2395</t>
2396<figure><artwork type="example">
2397  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2398  Server: Apache/0.8.4
2399</artwork></figure>
2400<t>
2401   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2402   used for advertising or other non-essential information. Although any
2403   token octet &MAY; appear in a product-version, this token &SHOULD;
2404   only be used for a version identifier (i.e., successive versions of
2405   the same product &SHOULD; only differ in the product-version portion of
2406   the product value).
2407</t>
2408</section>
2409
2410
2411<section title="Header Field Definitions" anchor="header.field.definitions">
2412<t>
2413   This section defines the syntax and semantics of HTTP/1.1 header fields
2414   related to request and response semantics.
2415</t>
2416
2417<section title="Allow" anchor="header.allow">
2418  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2419  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2420  <x:anchor-alias value="Allow"/>
2421<t>
2422   The "Allow" header field lists the set of methods advertised as
2423   supported by the target resource. The purpose of this field is strictly to
2424   inform the recipient of valid request methods associated with the resource.
2425</t>
2426<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2427  <x:ref>Allow</x:ref> = #<x:ref>Method</x:ref>
2428</artwork></figure>
2429<t>
2430   Example of use:
2431</t>
2432<figure><artwork type="example">
2433  Allow: GET, HEAD, PUT
2434</artwork></figure>
2435<t>
2436   The actual set of allowed methods is defined by the origin server at the
2437   time of each request.
2438</t>
2439<t>
2440   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2441   understand all the methods specified in order to handle them according to
2442   the generic message handling rules.
2443</t>
2444</section>
2445
2446<section title="Date" anchor="header.date">
2447  <iref primary="true" item="Date header field" x:for-anchor=""/>
2448  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2449  <x:anchor-alias value="Date"/>
2450<t>
2451   The "Date" header field represents the date and time at which
2452   the message was originated, having the same semantics as the Origination
2453   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2454   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2455   it &MUST; be sent in rfc1123-date format.
2456</t>
2457<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2458  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2459</artwork></figure>
2460<t>
2461   An example is
2462</t>
2463<figure><artwork type="example">
2464  Date: Tue, 15 Nov 1994 08:12:31 GMT
2465</artwork></figure>
2466<t>
2467   Origin servers &MUST; include a Date header field in all responses,
2468   except in these cases:
2469  <list style="numbers">
2470      <t>If the response status code is 100 (Continue) or 101 (Switching
2471         Protocols), the response &MAY; include a Date header field, at
2472         the server's option.</t>
2473
2474      <t>If the response status code conveys a server error, e.g., 500
2475         (Internal Server Error) or 503 (Service Unavailable), and it is
2476         inconvenient or impossible to generate a valid Date.</t>
2477
2478      <t>If the server does not have a clock that can provide a
2479         reasonable approximation of the current time, its responses
2480         &MUST-NOT; include a Date header field.</t>
2481  </list>
2482</t>
2483<t>
2484   A received message that does not have a Date header field &MUST; be
2485   assigned one by the recipient if the message will be cached by that
2486   recipient.
2487</t>
2488<t>
2489   Clients can use the Date header field as well; in order to keep request
2490   messages small, they are advised not to include it when it doesn't convey
2491   any useful information (as is usually the case for requests that do not
2492   contain a payload).
2493</t>
2494<t>
2495   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2496   time subsequent to the generation of the message. It &SHOULD; represent
2497   the best available approximation of the date and time of message
2498   generation, unless the implementation has no means of generating a
2499   reasonably accurate date and time. In theory, the date ought to
2500   represent the moment just before the payload is generated. In
2501   practice, the date can be generated at any time during the message
2502   origination without affecting its semantic value.
2503</t>
2504</section>
2505
2506<section title="Expect" anchor="header.expect">
2507  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2508  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2509  <x:anchor-alias value="Expect"/>
2510  <x:anchor-alias value="expectation"/>
2511  <x:anchor-alias value="expect-param"/>
2512  <x:anchor-alias value="expect-name"/>
2513  <x:anchor-alias value="expect-value"/>
2514<t>
2515   The "Expect" header field is used to indicate that particular
2516   server behaviors are required by the client.
2517</t>
2518<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"/>
2519  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2520 
2521  <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> ]
2522                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2523  <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> ]
2524 
2525  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2526  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2527</artwork></figure>
2528<t>
2529   If all received Expect header field(s) are syntactically valid but contain
2530   an expectation that the recipient does not understand or cannot comply with,
2531   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2532   recipient of a syntactically invalid Expectation header field &MUST; respond
2533   with a 4xx status code other than 417.
2534</t>
2535<t>
2536   The only expectation defined by this specification is:
2537</t>
2538<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2539  100-continue
2540   <list>
2541      <t>
2542        The "100-continue" expectation is defined &use100;. It does not support
2543        any expect-params.
2544      </t>
2545   </list>
2546</t>
2547<t>
2548   Comparison is case-insensitive for names (expect-name), and case-sensitive
2549   for values (expect-value).
2550</t>
2551<t>
2552   The Expect mechanism is hop-by-hop: the above requirements apply to any
2553   server, including proxies. However, the Expect header field itself is
2554   end-to-end; it &MUST; be forwarded if the request is forwarded.
2555</t>
2556<t>
2557   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2558   header field.
2559</t>
2560</section>
2561
2562<section title="From" anchor="header.from">
2563  <iref primary="true" item="From header field" x:for-anchor=""/>
2564  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2565  <x:anchor-alias value="From"/>
2566  <x:anchor-alias value="mailbox"/>
2567<t>
2568   The "From" header field, if given, &SHOULD; contain an Internet
2569   e-mail address for the human user who controls the requesting user
2570   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2571   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2572</t>
2573<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2574  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2575 
2576  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2577</artwork></figure>
2578<t>
2579   An example is:
2580</t>
2581<figure><artwork type="example">
2582  From: webmaster@example.org
2583</artwork></figure>
2584<t>
2585   This header field &MAY; be used for logging purposes and as a means for
2586   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2587   be used as an insecure form of access protection. The interpretation
2588   of this field is that the request is being performed on behalf of the
2589   person given, who accepts responsibility for the method performed. In
2590   particular, robot agents &SHOULD; include this header field so that the
2591   person responsible for running the robot can be contacted if problems
2592   occur on the receiving end.
2593</t>
2594<t>
2595   The Internet e-mail address in this field &MAY; be separate from the
2596   Internet host which issued the request. For example, when a request
2597   is passed through a proxy the original issuer's address &SHOULD; be
2598   used.
2599</t>
2600<t>
2601   The client &SHOULD-NOT;  send the From header field without the user's
2602   approval, as it might conflict with the user's privacy interests or
2603   their site's security policy. It is strongly recommended that the
2604   user be able to disable, enable, and modify the value of this field
2605   at any time prior to a request.
2606</t>
2607</section>
2608
2609<section title="Location" anchor="header.location">
2610  <iref primary="true" item="Location header field" x:for-anchor=""/>
2611  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2612  <x:anchor-alias value="Location"/>
2613<t>
2614   The "Location" header field &MAY; be sent in responses to refer to
2615   a specific resource in accordance with the semantics of the status
2616   code.
2617</t>
2618<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2619  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2620</artwork></figure>
2621<t>
2622   For 201 (Created) responses, the Location is the URI of the new resource
2623   which was created by the request. For 3xx responses, the location &SHOULD;
2624   indicate the server's preferred URI for automatic redirection to the
2625   resource.
2626</t>
2627<t>
2628   The field value consists of a single URI-reference. When it has the form
2629   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2630   the final value is computed by resolving it against the effective request
2631   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2632   navigated to by the user agent, did contain a fragment identifier, and the
2633   final value does not, then the original URI's fragment identifier is added
2634   to the final value.
2635</t>
2636<figure>
2637<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-->
2638<artwork type="example">
2639  Location: /pub/WWW/People.html#tim
2640</artwork>
2641<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2642</figure>
2643<figure>
2644<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-->
2645<artwork type="example">
2646  Location: http://www.example.net/index.html
2647</artwork>
2648<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2649</figure>
2650<x:note>
2651  <t>
2652    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2653    that are not valid URI references. This specification does not mandate or
2654    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2655  </t>
2656</x:note>
2657<t>
2658   There are circumstances in which a fragment identifier in a Location URI
2659   would not be appropriate. For instance, when it appears in a 201 Created
2660   response, where the Location header field specifies the URI for the entire
2661   created resource.
2662</t>
2663<x:note>
2664  <t>
2665    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2666    from Location in that the Content-Location identifies the most specific
2667    resource corresponding to the enclosed representation.
2668    It is therefore possible for a response to contain header fields for
2669    both Location and Content-Location.
2670  </t>
2671</x:note>
2672</section>
2673
2674<section title="Max-Forwards" anchor="header.max-forwards">
2675  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2676  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2677  <x:anchor-alias value="Max-Forwards"/>
2678<t>
2679   The "Max-Forwards" header field provides a mechanism with the
2680   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2681   methods to limit the number of times that the request is forwarded by
2682   proxies. This can be useful when the client is attempting to
2683   trace a request which appears to be failing or looping mid-chain.
2684</t>
2685<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2686  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2687</artwork></figure>
2688<t>
2689   The Max-Forwards value is a decimal integer indicating the remaining
2690   number of times this request message can be forwarded.
2691</t>
2692<t>
2693   Each recipient of a TRACE or OPTIONS request
2694   containing a Max-Forwards header field &MUST; check and update its
2695   value prior to forwarding the request. If the received value is zero
2696   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2697   respond as the final recipient. If the received Max-Forwards value is
2698   greater than zero, then the forwarded message &MUST; contain an updated
2699   Max-Forwards field with a value decremented by one (1).
2700</t>
2701<t>
2702   The Max-Forwards header field &MAY; be ignored for all other request
2703   methods.
2704</t>
2705</section>
2706
2707<section title="Referer" anchor="header.referer">
2708  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2709  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2710  <x:anchor-alias value="Referer"/>
2711<t>
2712   The "Referer" [sic] header field allows the client to specify the
2713   URI of the resource from which the effective request URI was obtained (the
2714   "referrer", although the header field is misspelled.).
2715</t>
2716<t>
2717   The Referer header field allows servers to generate lists of back-links to
2718   resources for interest, logging, optimized caching, etc. It also allows
2719   obsolete or mistyped links to be traced for maintenance. Some servers use
2720   Referer as a means of controlling where they allow links from (so-called
2721   "deep linking"), but legitimate requests do not always
2722   contain a Referer header field.
2723</t>
2724<t>
2725   If the effective request URI was obtained from a source that does not have its own
2726   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2727   sent with the value "about:blank", or not be sent at all. Note that this
2728   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2729</t>
2730<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2731  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2732</artwork></figure>
2733<t>
2734   Example:
2735</t>
2736<figure><artwork type="example">
2737  Referer: http://www.example.org/hypertext/Overview.html
2738</artwork></figure>
2739<t>
2740   If the field value is a relative URI, it &SHOULD; be interpreted
2741   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2742   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2743</t>
2744</section>
2745
2746<section title="Retry-After" anchor="header.retry-after">
2747  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2748  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2749  <x:anchor-alias value="Retry-After"/>
2750<t>
2751   The header "Retry-After" field can be used with a 503 (Service
2752   Unavailable) response to indicate how long the service is expected to
2753   be unavailable to the requesting client. This field &MAY; also be used
2754   with any 3xx (Redirection) response to indicate the minimum time the
2755   user-agent is asked to wait before issuing the redirected request.
2756</t>
2757<t>
2758   The value of this field can be either an HTTP-date or an integer number
2759   of seconds (in decimal) after the time of the response.
2760</t>
2761<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2762  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2763</artwork></figure>
2764<t anchor="rule.delta-seconds">
2765  <x:anchor-alias value="delta-seconds"/>
2766   Time spans are non-negative decimal integers, representing time in
2767   seconds.
2768</t>
2769<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2770  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2771</artwork></figure>
2772<t>
2773   Two examples of its use are
2774</t>
2775<figure><artwork type="example">
2776  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2777  Retry-After: 120
2778</artwork></figure>
2779<t>
2780   In the latter example, the delay is 2 minutes.
2781</t>
2782</section>
2783
2784<section title="Server" anchor="header.server">
2785  <iref primary="true" item="Server header field" x:for-anchor=""/>
2786  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2787  <x:anchor-alias value="Server"/>
2788<t>
2789   The "Server" header field contains information about the
2790   software used by the origin server to handle the request.
2791</t>
2792<t>
2793   The field can contain multiple
2794   product tokens (<xref target="product.tokens"/>) and
2795   comments (&header-fields;) identifying the server and any significant
2796   subproducts. The product tokens are listed in order of their significance
2797   for identifying the application.
2798</t>
2799<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2800  <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> ) )
2801</artwork></figure>
2802<t>
2803   Example:
2804</t>
2805<figure><artwork type="example">
2806  Server: CERN/3.0 libwww/2.17
2807</artwork></figure>
2808<t>
2809   If the response is being forwarded through a proxy, the proxy
2810   application &MUST-NOT; modify the Server header field. Instead, it
2811   &MUST; include a Via field (as described in &header-via;).
2812</t>
2813<x:note>
2814  <t>
2815    <x:h>Note:</x:h> Revealing the specific software version of the server might
2816    allow the server machine to become more vulnerable to attacks
2817    against software that is known to contain security holes. Server
2818    implementors are encouraged to make this field a configurable
2819    option.
2820  </t>
2821</x:note>
2822</section>
2823
2824<section title="User-Agent" anchor="header.user-agent">
2825  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2826  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2827  <x:anchor-alias value="User-Agent"/>
2828<t>
2829   The "User-Agent" header field contains information about the user
2830   agent originating the request. User agents &SHOULD; include this field with
2831   requests.
2832</t>
2833<t>
2834   Typically, it is used for statistical purposes, the tracing of protocol
2835   violations, and tailoring responses to avoid particular user agent
2836   limitations.
2837</t>
2838<t>
2839   The field can contain multiple
2840   product tokens (<xref target="product.tokens"/>)
2841   and comments (&header-fields;) identifying the agent and its
2842   significant subproducts. By convention, the product tokens are listed in
2843   order of their significance for identifying the application.
2844</t>
2845<t>
2846   Because this field is usually sent on every request a user agent makes,
2847   implementations are encouraged not to include needlessly fine-grained
2848   detail, and to limit (or even prohibit) the addition of subproducts by third
2849   parties. Overly long and detailed User-Agent field values make requests
2850   larger and can also be used to identify ("fingerprint") the user against
2851   their wishes.
2852</t>
2853<t>
2854   Likewise, implementations are encouraged not to use the product tokens of
2855   other implementations in order to declare compatibility with them, as this
2856   circumvents the purpose of the field. Finally, they are encouraged not to
2857   use comments to identify products; doing so makes the field value more
2858   difficult to parse.
2859</t>
2860<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2861  <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> ) )
2862</artwork></figure>
2863<t>
2864   Example:
2865</t>
2866<figure><artwork type="example">
2867  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2868</artwork></figure>
2869</section>
2870
2871</section>
2872
2873<section title="IANA Considerations" anchor="IANA.considerations">
2874
2875<section title="Method Registry" anchor="method.registration">
2876<t>
2877  The registration procedure for HTTP request methods is defined by
2878  <xref target="method.registry"/> of this document.
2879</t>
2880<t>
2881   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2882   and be populated with the registrations below:
2883</t>
2884<?BEGININC p2-semantics.iana-methods ?>
2885<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2886<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2887   <ttcol>Method</ttcol>
2888   <ttcol>Safe</ttcol>
2889   <ttcol>Reference</ttcol>
2890   <c>CONNECT</c>
2891   <c>no</c>
2892   <c>
2893      <xref target="CONNECT"/>
2894   </c>
2895   <c>DELETE</c>
2896   <c>no</c>
2897   <c>
2898      <xref target="DELETE"/>
2899   </c>
2900   <c>GET</c>
2901   <c>yes</c>
2902   <c>
2903      <xref target="GET"/>
2904   </c>
2905   <c>HEAD</c>
2906   <c>yes</c>
2907   <c>
2908      <xref target="HEAD"/>
2909   </c>
2910   <c>OPTIONS</c>
2911   <c>yes</c>
2912   <c>
2913      <xref target="OPTIONS"/>
2914   </c>
2915   <c>POST</c>
2916   <c>no</c>
2917   <c>
2918      <xref target="POST"/>
2919   </c>
2920   <c>PUT</c>
2921   <c>no</c>
2922   <c>
2923      <xref target="PUT"/>
2924   </c>
2925   <c>TRACE</c>
2926   <c>yes</c>
2927   <c>
2928      <xref target="TRACE"/>
2929   </c>
2930</texttable>
2931<!--(END)-->
2932<?ENDINC p2-semantics.iana-methods ?>
2933</section>
2934
2935<section title="Status Code Registry" anchor="status.code.registration">
2936<t>
2937   The registration procedure for HTTP Status Codes &mdash; previously defined
2938   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2939   by <xref target="status.code.registry"/> of this document.
2940</t>
2941<t>
2942   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2943   shall be updated with the registrations below:
2944</t>
2945<?BEGININC p2-semantics.iana-status-codes ?>
2946<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2947<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2948   <ttcol>Value</ttcol>
2949   <ttcol>Description</ttcol>
2950   <ttcol>Reference</ttcol>
2951   <c>100</c>
2952   <c>Continue</c>
2953   <c>
2954      <xref target="status.100"/>
2955   </c>
2956   <c>101</c>
2957   <c>Switching Protocols</c>
2958   <c>
2959      <xref target="status.101"/>
2960   </c>
2961   <c>200</c>
2962   <c>OK</c>
2963   <c>
2964      <xref target="status.200"/>
2965   </c>
2966   <c>201</c>
2967   <c>Created</c>
2968   <c>
2969      <xref target="status.201"/>
2970   </c>
2971   <c>202</c>
2972   <c>Accepted</c>
2973   <c>
2974      <xref target="status.202"/>
2975   </c>
2976   <c>203</c>
2977   <c>Non-Authoritative Information</c>
2978   <c>
2979      <xref target="status.203"/>
2980   </c>
2981   <c>204</c>
2982   <c>No Content</c>
2983   <c>
2984      <xref target="status.204"/>
2985   </c>
2986   <c>205</c>
2987   <c>Reset Content</c>
2988   <c>
2989      <xref target="status.205"/>
2990   </c>
2991   <c>300</c>
2992   <c>Multiple Choices</c>
2993   <c>
2994      <xref target="status.300"/>
2995   </c>
2996   <c>301</c>
2997   <c>Moved Permanently</c>
2998   <c>
2999      <xref target="status.301"/>
3000   </c>
3001   <c>302</c>
3002   <c>Found</c>
3003   <c>
3004      <xref target="status.302"/>
3005   </c>
3006   <c>303</c>
3007   <c>See Other</c>
3008   <c>
3009      <xref target="status.303"/>
3010   </c>
3011   <c>305</c>
3012   <c>Use Proxy</c>
3013   <c>
3014      <xref target="status.305"/>
3015   </c>
3016   <c>306</c>
3017   <c>(Unused)</c>
3018   <c>
3019      <xref target="status.306"/>
3020   </c>
3021   <c>307</c>
3022   <c>Temporary Redirect</c>
3023   <c>
3024      <xref target="status.307"/>
3025   </c>
3026   <c>400</c>
3027   <c>Bad Request</c>
3028   <c>
3029      <xref target="status.400"/>
3030   </c>
3031   <c>402</c>
3032   <c>Payment Required</c>
3033   <c>
3034      <xref target="status.402"/>
3035   </c>
3036   <c>403</c>
3037   <c>Forbidden</c>
3038   <c>
3039      <xref target="status.403"/>
3040   </c>
3041   <c>404</c>
3042   <c>Not Found</c>
3043   <c>
3044      <xref target="status.404"/>
3045   </c>
3046   <c>405</c>
3047   <c>Method Not Allowed</c>
3048   <c>
3049      <xref target="status.405"/>
3050   </c>
3051   <c>406</c>
3052   <c>Not Acceptable</c>
3053   <c>
3054      <xref target="status.406"/>
3055   </c>
3056   <c>408</c>
3057   <c>Request Timeout</c>
3058   <c>
3059      <xref target="status.408"/>
3060   </c>
3061   <c>409</c>
3062   <c>Conflict</c>
3063   <c>
3064      <xref target="status.409"/>
3065   </c>
3066   <c>410</c>
3067   <c>Gone</c>
3068   <c>
3069      <xref target="status.410"/>
3070   </c>
3071   <c>411</c>
3072   <c>Length Required</c>
3073   <c>
3074      <xref target="status.411"/>
3075   </c>
3076   <c>413</c>
3077   <c>Request Representation Too Large</c>
3078   <c>
3079      <xref target="status.413"/>
3080   </c>
3081   <c>414</c>
3082   <c>URI Too Long</c>
3083   <c>
3084      <xref target="status.414"/>
3085   </c>
3086   <c>415</c>
3087   <c>Unsupported Media Type</c>
3088   <c>
3089      <xref target="status.415"/>
3090   </c>
3091   <c>417</c>
3092   <c>Expectation Failed</c>
3093   <c>
3094      <xref target="status.417"/>
3095   </c>
3096   <c>426</c>
3097   <c>Upgrade Required</c>
3098   <c>
3099      <xref target="status.426"/>
3100   </c>
3101   <c>500</c>
3102   <c>Internal Server Error</c>
3103   <c>
3104      <xref target="status.500"/>
3105   </c>
3106   <c>501</c>
3107   <c>Not Implemented</c>
3108   <c>
3109      <xref target="status.501"/>
3110   </c>
3111   <c>502</c>
3112   <c>Bad Gateway</c>
3113   <c>
3114      <xref target="status.502"/>
3115   </c>
3116   <c>503</c>
3117   <c>Service Unavailable</c>
3118   <c>
3119      <xref target="status.503"/>
3120   </c>
3121   <c>504</c>
3122   <c>Gateway Timeout</c>
3123   <c>
3124      <xref target="status.504"/>
3125   </c>
3126   <c>505</c>
3127   <c>HTTP Version Not Supported</c>
3128   <c>
3129      <xref target="status.505"/>
3130   </c>
3131</texttable>
3132<!--(END)-->
3133<?ENDINC p2-semantics.iana-status-codes ?>
3134</section>
3135<section title="Header Field Registration" anchor="header.field.registration">
3136<t>
3137   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3138   with the permanent registrations below (see <xref target="RFC3864"/>):
3139</t>
3140<?BEGININC p2-semantics.iana-headers ?>
3141<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3142<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3143   <ttcol>Header Field Name</ttcol>
3144   <ttcol>Protocol</ttcol>
3145   <ttcol>Status</ttcol>
3146   <ttcol>Reference</ttcol>
3147
3148   <c>Allow</c>
3149   <c>http</c>
3150   <c>standard</c>
3151   <c>
3152      <xref target="header.allow"/>
3153   </c>
3154   <c>Date</c>
3155   <c>http</c>
3156   <c>standard</c>
3157   <c>
3158      <xref target="header.date"/>
3159   </c>
3160   <c>Expect</c>
3161   <c>http</c>
3162   <c>standard</c>
3163   <c>
3164      <xref target="header.expect"/>
3165   </c>
3166   <c>From</c>
3167   <c>http</c>
3168   <c>standard</c>
3169   <c>
3170      <xref target="header.from"/>
3171   </c>
3172   <c>Location</c>
3173   <c>http</c>
3174   <c>standard</c>
3175   <c>
3176      <xref target="header.location"/>
3177   </c>
3178   <c>Max-Forwards</c>
3179   <c>http</c>
3180   <c>standard</c>
3181   <c>
3182      <xref target="header.max-forwards"/>
3183   </c>
3184   <c>Referer</c>
3185   <c>http</c>
3186   <c>standard</c>
3187   <c>
3188      <xref target="header.referer"/>
3189   </c>
3190   <c>Retry-After</c>
3191   <c>http</c>
3192   <c>standard</c>
3193   <c>
3194      <xref target="header.retry-after"/>
3195   </c>
3196   <c>Server</c>
3197   <c>http</c>
3198   <c>standard</c>
3199   <c>
3200      <xref target="header.server"/>
3201   </c>
3202   <c>User-Agent</c>
3203   <c>http</c>
3204   <c>standard</c>
3205   <c>
3206      <xref target="header.user-agent"/>
3207   </c>
3208</texttable>
3209<!--(END)-->
3210<?ENDINC p2-semantics.iana-headers ?>
3211<t>
3212   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3213</t>
3214</section>
3215</section>
3216
3217<section title="Security Considerations" anchor="security.considerations">
3218<t>
3219   This section is meant to inform application developers, information
3220   providers, and users of the security limitations in HTTP/1.1 as
3221   described by this document. The discussion does not include
3222   definitive solutions to the problems revealed, though it does make
3223   some suggestions for reducing security risks.
3224</t>
3225
3226<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3227<t>
3228   Like any generic data transfer protocol, HTTP cannot regulate the
3229   content of the data that is transferred, nor is there any a priori
3230   method of determining the sensitivity of any particular piece of
3231   information within the context of any given request. Therefore,
3232   applications &SHOULD; supply as much control over this information as
3233   possible to the provider of that information. Four header fields are
3234   worth special mention in this context: Server, Via, Referer and From.
3235</t>
3236<t>
3237   Revealing the specific software version of the server might allow the
3238   server machine to become more vulnerable to attacks against software
3239   that is known to contain security holes. Implementors &SHOULD; make the
3240   Server header field a configurable option.
3241</t>
3242<t>
3243   Proxies which serve as a portal through a network firewall &SHOULD;
3244   take special precautions regarding the transfer of header information
3245   that identifies the hosts behind the firewall. In particular, they
3246   &SHOULD; remove, or replace with sanitized versions, any Via fields
3247   generated behind the firewall.
3248</t>
3249<t>
3250   The Referer header field allows reading patterns to be studied and reverse
3251   links drawn. Although it can be very useful, its power can be abused
3252   if user details are not separated from the information contained in
3253   the Referer. Even when the personal information has been removed, the
3254   Referer header field might indicate a private document's URI whose
3255   publication would be inappropriate.
3256</t>
3257<t>
3258   The information sent in the From field might conflict with the user's
3259   privacy interests or their site's security policy, and hence it
3260   &SHOULD-NOT;  be transmitted without the user being able to disable,
3261   enable, and modify the contents of the field. The user &MUST; be able
3262   to set the contents of this field within a user preference or
3263   application defaults configuration.
3264</t>
3265<t>
3266   We suggest, though do not require, that a convenient toggle interface
3267   be provided for the user to enable or disable the sending of From and
3268   Referer information.
3269</t>
3270<t>
3271   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3272   target="header.server"/>) header fields can sometimes be used to determine
3273   that a specific client or server has a particular security hole which might
3274   be exploited. Unfortunately, this same information is often used for other
3275   valuable purposes for which HTTP currently has no better mechanism.
3276</t>
3277<t>
3278   Furthermore, the User-Agent header field may contain enough entropy to be
3279   used, possibly in conjunction with other material, to uniquely identify the
3280   user.
3281</t>
3282<t>
3283   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3284   that was sent in request header fields within the body of their response.
3285   Clients &SHOULD; be careful with sensitive information, like Cookies,
3286   Authorization credentials, and other header fields that might be used to
3287   collect data from the client.
3288</t> 
3289</section>
3290
3291<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3292<t>
3293   Because the source of a link might be private information or might
3294   reveal an otherwise private information source, it is strongly
3295   recommended that the user be able to select whether or not the
3296   Referer field is sent. For example, a browser client could have a
3297   toggle switch for browsing openly/anonymously, which would
3298   respectively enable/disable the sending of Referer and From
3299   information.
3300</t>
3301<t>
3302   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3303   HTTP request if the referring page was transferred with a secure
3304   protocol.
3305</t>
3306<t>
3307   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3308   sensitive data because that data will be placed in the request-target. Many
3309   existing servers, proxies, and user agents log or display the request-target
3310   in places where it might be visible to third parties. Such services can
3311   use POST-based form submission instead.
3312</t>
3313</section>
3314
3315<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3316<t>
3317   If a single server supports multiple organizations that do not trust
3318   one another, then it &MUST; check the values of Location and Content-Location
3319   header fields in responses that are generated under control of
3320   said organizations to make sure that they do not attempt to
3321   invalidate resources over which they have no authority.
3322</t>
3323<t>
3324   Furthermore, appending the fragment identifier from one URI to another
3325   one obtained from a Location header field might leak confidential
3326   information to the target server &mdash; although the fragment identifier is
3327   not transmitted in the final request, it might be visible to the user agent
3328   through other means, such as scripting.
3329</t>
3330</section>
3331
3332<section title="Security Considerations for CONNECT">
3333<t>
3334   Since tunneled data is opaque to the proxy, there are additional
3335   risks to tunneling to other well-known or reserved ports.
3336   A HTTP client CONNECTing to port 25 could relay spam
3337   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3338   access to a small number of known ports.
3339</t>
3340</section>
3341
3342</section>
3343
3344<section title="Acknowledgments" anchor="acks">
3345<t>
3346  See &acks;.
3347</t>
3348</section>
3349</middle>
3350<back>
3351
3352<references title="Normative References">
3353
3354<reference anchor="Part1">
3355  <front>
3356    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3357    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3358      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3359      <address><email>fielding@gbiv.com</email></address>
3360    </author>
3361    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3362      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3363      <address><email>jg@freedesktop.org</email></address>
3364    </author>
3365    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3366      <organization abbrev="HP">Hewlett-Packard Company</organization>
3367      <address><email>JeffMogul@acm.org</email></address>
3368    </author>
3369    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3370      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3371      <address><email>henrikn@microsoft.com</email></address>
3372    </author>
3373    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3374      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3375      <address><email>LMM@acm.org</email></address>
3376    </author>
3377    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3378      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3379      <address><email>paulle@microsoft.com</email></address>
3380    </author>
3381    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3382      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3383      <address><email>timbl@w3.org</email></address>
3384    </author>
3385    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3386      <organization abbrev="W3C">World Wide Web Consortium</organization>
3387      <address><email>ylafon@w3.org</email></address>
3388    </author>
3389    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3390      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3391      <address><email>julian.reschke@greenbytes.de</email></address>
3392    </author>
3393    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3394  </front>
3395  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3396  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3397</reference>
3398
3399<reference anchor="Part3">
3400  <front>
3401    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3402    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3403      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3404      <address><email>fielding@gbiv.com</email></address>
3405    </author>
3406    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3407      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3408      <address><email>jg@freedesktop.org</email></address>
3409    </author>
3410    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3411      <organization abbrev="HP">Hewlett-Packard Company</organization>
3412      <address><email>JeffMogul@acm.org</email></address>
3413    </author>
3414    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3415      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3416      <address><email>henrikn@microsoft.com</email></address>
3417    </author>
3418    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3419      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3420      <address><email>LMM@acm.org</email></address>
3421    </author>
3422    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3423      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3424      <address><email>paulle@microsoft.com</email></address>
3425    </author>
3426    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3427      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3428      <address><email>timbl@w3.org</email></address>
3429    </author>
3430    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3431      <organization abbrev="W3C">World Wide Web Consortium</organization>
3432      <address><email>ylafon@w3.org</email></address>
3433    </author>
3434    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3435      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3436      <address><email>julian.reschke@greenbytes.de</email></address>
3437    </author>
3438    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3439  </front>
3440  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3441  <x:source href="p3-payload.xml" basename="p3-payload"/>
3442</reference>
3443
3444<reference anchor="Part4">
3445  <front>
3446    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3447    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3448      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3449      <address><email>fielding@gbiv.com</email></address>
3450    </author>
3451    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3452      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3453      <address><email>jg@freedesktop.org</email></address>
3454    </author>
3455    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3456      <organization abbrev="HP">Hewlett-Packard Company</organization>
3457      <address><email>JeffMogul@acm.org</email></address>
3458    </author>
3459    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3460      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3461      <address><email>henrikn@microsoft.com</email></address>
3462    </author>
3463    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3464      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3465      <address><email>LMM@acm.org</email></address>
3466    </author>
3467    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3468      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3469      <address><email>paulle@microsoft.com</email></address>
3470    </author>
3471    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3472      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3473      <address><email>timbl@w3.org</email></address>
3474    </author>
3475    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3476      <organization abbrev="W3C">World Wide Web Consortium</organization>
3477      <address><email>ylafon@w3.org</email></address>
3478    </author>
3479    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3480      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3481      <address><email>julian.reschke@greenbytes.de</email></address>
3482    </author>
3483    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3484  </front>
3485  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3486  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3487</reference>
3488
3489<reference anchor="Part5">
3490  <front>
3491    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3492    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3493      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3494      <address><email>fielding@gbiv.com</email></address>
3495    </author>
3496    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3497      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3498      <address><email>jg@freedesktop.org</email></address>
3499    </author>
3500    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3501      <organization abbrev="HP">Hewlett-Packard Company</organization>
3502      <address><email>JeffMogul@acm.org</email></address>
3503    </author>
3504    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3505      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3506      <address><email>henrikn@microsoft.com</email></address>
3507    </author>
3508    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3509      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3510      <address><email>LMM@acm.org</email></address>
3511    </author>
3512    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3513      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3514      <address><email>paulle@microsoft.com</email></address>
3515    </author>
3516    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3517      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3518      <address><email>timbl@w3.org</email></address>
3519    </author>
3520    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3521      <organization abbrev="W3C">World Wide Web Consortium</organization>
3522      <address><email>ylafon@w3.org</email></address>
3523    </author>
3524    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3525      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3526      <address><email>julian.reschke@greenbytes.de</email></address>
3527    </author>
3528    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3529  </front>
3530  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3531  <x:source href="p5-range.xml" basename="p5-range"/>
3532</reference>
3533
3534<reference anchor="Part6">
3535  <front>
3536    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3537    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3538      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3539      <address><email>fielding@gbiv.com</email></address>
3540    </author>
3541    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3542      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3543      <address><email>jg@freedesktop.org</email></address>
3544    </author>
3545    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3546      <organization abbrev="HP">Hewlett-Packard Company</organization>
3547      <address><email>JeffMogul@acm.org</email></address>
3548    </author>
3549    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3550      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3551      <address><email>henrikn@microsoft.com</email></address>
3552    </author>
3553    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3554      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3555      <address><email>LMM@acm.org</email></address>
3556    </author>
3557    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3558      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3559      <address><email>paulle@microsoft.com</email></address>
3560    </author>
3561    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3562      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3563      <address><email>timbl@w3.org</email></address>
3564    </author>
3565    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3566      <organization abbrev="W3C">World Wide Web Consortium</organization>
3567      <address><email>ylafon@w3.org</email></address>
3568    </author>
3569    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3570      <organization>Rackspace</organization>
3571      <address><email>mnot@mnot.net</email></address>
3572    </author>
3573    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3574      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3575      <address><email>julian.reschke@greenbytes.de</email></address>
3576    </author>
3577    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3578  </front>
3579  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3580  <x:source href="p6-cache.xml" basename="p6-cache"/>
3581</reference>
3582
3583<reference anchor="Part7">
3584  <front>
3585    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3586    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3587      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3588      <address><email>fielding@gbiv.com</email></address>
3589    </author>
3590    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3591      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3592      <address><email>jg@freedesktop.org</email></address>
3593    </author>
3594    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3595      <organization abbrev="HP">Hewlett-Packard Company</organization>
3596      <address><email>JeffMogul@acm.org</email></address>
3597    </author>
3598    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3599      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3600      <address><email>henrikn@microsoft.com</email></address>
3601    </author>
3602    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3603      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3604      <address><email>LMM@acm.org</email></address>
3605    </author>
3606    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3607      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3608      <address><email>paulle@microsoft.com</email></address>
3609    </author>
3610    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3611      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3612      <address><email>timbl@w3.org</email></address>
3613    </author>
3614    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3615      <organization abbrev="W3C">World Wide Web Consortium</organization>
3616      <address><email>ylafon@w3.org</email></address>
3617    </author>
3618    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3619      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3620      <address><email>julian.reschke@greenbytes.de</email></address>
3621    </author>
3622    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3623  </front>
3624  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3625  <x:source href="p7-auth.xml" basename="p7-auth"/>
3626</reference>
3627
3628<reference anchor="RFC2119">
3629  <front>
3630    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3631    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3632      <organization>Harvard University</organization>
3633      <address><email>sob@harvard.edu</email></address>
3634    </author>
3635    <date month="March" year="1997"/>
3636  </front>
3637  <seriesInfo name="BCP" value="14"/>
3638  <seriesInfo name="RFC" value="2119"/>
3639</reference>
3640
3641<reference anchor="RFC3986">
3642 <front>
3643  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3644  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3645    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3646    <address>
3647       <email>timbl@w3.org</email>
3648       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3649    </address>
3650  </author>
3651  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3652    <organization abbrev="Day Software">Day Software</organization>
3653    <address>
3654      <email>fielding@gbiv.com</email>
3655      <uri>http://roy.gbiv.com/</uri>
3656    </address>
3657  </author>
3658  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3659    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3660    <address>
3661      <email>LMM@acm.org</email>
3662      <uri>http://larry.masinter.net/</uri>
3663    </address>
3664  </author>
3665  <date month='January' year='2005'></date>
3666 </front>
3667 <seriesInfo name="STD" value="66"/>
3668 <seriesInfo name="RFC" value="3986"/>
3669</reference>
3670
3671<reference anchor="RFC5234">
3672  <front>
3673    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3674    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3675      <organization>Brandenburg InternetWorking</organization>
3676      <address>
3677        <email>dcrocker@bbiw.net</email>
3678      </address> 
3679    </author>
3680    <author initials="P." surname="Overell" fullname="Paul Overell">
3681      <organization>THUS plc.</organization>
3682      <address>
3683        <email>paul.overell@thus.net</email>
3684      </address>
3685    </author>
3686    <date month="January" year="2008"/>
3687  </front>
3688  <seriesInfo name="STD" value="68"/>
3689  <seriesInfo name="RFC" value="5234"/>
3690</reference>
3691
3692</references>
3693
3694<references title="Informative References">
3695
3696<reference anchor="RFC1123">
3697  <front>
3698    <title>Requirements for Internet Hosts - Application and Support</title>
3699    <author initials="R." surname="Braden" fullname="Robert Braden">
3700      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3701      <address><email>Braden@ISI.EDU</email></address>
3702    </author>
3703    <date month="October" year="1989"/>
3704  </front>
3705  <seriesInfo name="STD" value="3"/>
3706  <seriesInfo name="RFC" value="1123"/>
3707</reference>
3708
3709<reference anchor="RFC1945">
3710  <front>
3711    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3712    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3713      <organization>MIT, Laboratory for Computer Science</organization>
3714      <address><email>timbl@w3.org</email></address>
3715    </author>
3716    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3717      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3718      <address><email>fielding@ics.uci.edu</email></address>
3719    </author>
3720    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3721      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3722      <address><email>frystyk@w3.org</email></address>
3723    </author>
3724    <date month="May" year="1996"/>
3725  </front>
3726  <seriesInfo name="RFC" value="1945"/>
3727</reference>
3728
3729<reference anchor="RFC2068">
3730  <front>
3731    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3732    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3733      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3734      <address><email>fielding@ics.uci.edu</email></address>
3735    </author>
3736    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3737      <organization>MIT Laboratory for Computer Science</organization>
3738      <address><email>jg@w3.org</email></address>
3739    </author>
3740    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3741      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3742      <address><email>mogul@wrl.dec.com</email></address>
3743    </author>
3744    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3745      <organization>MIT Laboratory for Computer Science</organization>
3746      <address><email>frystyk@w3.org</email></address>
3747    </author>
3748    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3749      <organization>MIT Laboratory for Computer Science</organization>
3750      <address><email>timbl@w3.org</email></address>
3751    </author>
3752    <date month="January" year="1997"/>
3753  </front>
3754  <seriesInfo name="RFC" value="2068"/>
3755</reference>
3756
3757<reference anchor="RFC2616">
3758  <front>
3759    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3760    <author initials="R." surname="Fielding" fullname="R. Fielding">
3761      <organization>University of California, Irvine</organization>
3762      <address><email>fielding@ics.uci.edu</email></address>
3763    </author>
3764    <author initials="J." surname="Gettys" fullname="J. Gettys">
3765      <organization>W3C</organization>
3766      <address><email>jg@w3.org</email></address>
3767    </author>
3768    <author initials="J." surname="Mogul" fullname="J. Mogul">
3769      <organization>Compaq Computer Corporation</organization>
3770      <address><email>mogul@wrl.dec.com</email></address>
3771    </author>
3772    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3773      <organization>MIT Laboratory for Computer Science</organization>
3774      <address><email>frystyk@w3.org</email></address>
3775    </author>
3776    <author initials="L." surname="Masinter" fullname="L. Masinter">
3777      <organization>Xerox Corporation</organization>
3778      <address><email>masinter@parc.xerox.com</email></address>
3779    </author>
3780    <author initials="P." surname="Leach" fullname="P. Leach">
3781      <organization>Microsoft Corporation</organization>
3782      <address><email>paulle@microsoft.com</email></address>
3783    </author>
3784    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3785      <organization>W3C</organization>
3786      <address><email>timbl@w3.org</email></address>
3787    </author>
3788    <date month="June" year="1999"/>
3789  </front>
3790  <seriesInfo name="RFC" value="2616"/>
3791</reference>
3792
3793<reference anchor='RFC2817'>
3794  <front>
3795    <title>Upgrading to TLS Within HTTP/1.1</title>
3796    <author initials='R.' surname='Khare' fullname='R. Khare'>
3797      <organization>4K Associates / UC Irvine</organization>
3798      <address><email>rohit@4K-associates.com</email></address>
3799    </author>
3800    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3801      <organization>Agranat Systems, Inc.</organization>
3802      <address><email>lawrence@agranat.com</email></address>
3803    </author>
3804    <date year='2000' month='May' />
3805  </front>
3806  <seriesInfo name='RFC' value='2817' />
3807</reference>
3808
3809<reference anchor='RFC3864'>
3810  <front>
3811    <title>Registration Procedures for Message Header Fields</title>
3812    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3813      <organization>Nine by Nine</organization>
3814      <address><email>GK-IETF@ninebynine.org</email></address>
3815    </author>
3816    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3817      <organization>BEA Systems</organization>
3818      <address><email>mnot@pobox.com</email></address>
3819    </author>
3820    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3821      <organization>HP Labs</organization>
3822      <address><email>JeffMogul@acm.org</email></address>
3823    </author>
3824    <date year='2004' month='September' />
3825  </front>
3826  <seriesInfo name='BCP' value='90' />
3827  <seriesInfo name='RFC' value='3864' />
3828</reference>
3829
3830<reference anchor='RFC5226'>
3831  <front>
3832    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3833    <author initials='T.' surname='Narten' fullname='T. Narten'>
3834      <organization>IBM</organization>
3835      <address><email>narten@us.ibm.com</email></address>
3836    </author>
3837    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3838      <organization>Google</organization>
3839      <address><email>Harald@Alvestrand.no</email></address>
3840    </author>
3841    <date year='2008' month='May' />
3842  </front>
3843  <seriesInfo name='BCP' value='26' />
3844  <seriesInfo name='RFC' value='5226' />
3845</reference>
3846
3847<reference anchor="RFC5322">
3848  <front>
3849    <title>Internet Message Format</title>
3850    <author initials="P." surname="Resnick" fullname="P. Resnick">
3851      <organization>Qualcomm Incorporated</organization>
3852    </author>
3853    <date year="2008" month="October"/>
3854  </front> 
3855  <seriesInfo name="RFC" value="5322"/>
3856</reference>
3857
3858<reference anchor='RFC5789'>
3859  <front>
3860    <title>PATCH Method for HTTP</title>
3861    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3862      <organization>Linden Lab</organization>
3863    </author>
3864    <author initials='J.' surname='Snell' fullname='J. Snell' />
3865    <date year='2010' month='March' />
3866  </front>
3867  <seriesInfo name='RFC' value='5789' />
3868</reference>
3869
3870<reference anchor="RFC5987">
3871        <front>
3872    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3873    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3874      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3875      <address>
3876        <postal>
3877          <street>Hafenweg 16</street>
3878          <city>Muenster</city><region>NW</region><code>48155</code>
3879          <country>Germany</country>
3880        </postal>
3881        <email>julian.reschke@greenbytes.de</email>     
3882        <uri>http://greenbytes.de/tech/webdav/</uri>   
3883      </address>
3884    </author>
3885    <date month="August" year="2010"/>
3886  </front>
3887  <seriesInfo name="RFC" value="5987"/>
3888</reference>
3889
3890</references>
3891
3892<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3893<t>
3894  This document takes over the Status Code Registry, previously defined
3895  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3896  (<xref target="status.code.registry"/>)
3897</t>
3898<t>
3899  Clarify definition of POST.
3900  (<xref target="POST"/>)
3901</t>
3902<t>
3903  Remove requirement to handle all Content-* header fields; ban use of
3904  Content-Range with PUT.
3905  (<xref target="PUT"/>)
3906</t>
3907<t>
3908  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3909  (<xref target="CONNECT"/>)
3910</t>
3911<t>
3912  Broadened the definition of 203 (Non-Authoritative Information) to include
3913  cases of payload transformations as well.
3914  (<xref target="status.203"/>)
3915</t>
3916<t>
3917  Status codes 301, 302, and 307: removed the normative requirements on both
3918  response payloads and user interaction.
3919  (<xref target="status.3xx"/>)
3920</t>
3921<t>
3922  Failed to consider that there are many other request methods that are safe
3923  to automatically redirect, and further that the user agent is able to make
3924  that determination based on the request method semantics.
3925  Furthermore, allow user agents to rewrite the method from POST to GET
3926  for status codes 301 and 302.
3927  (Sections <xref format="counter" target="status.301"/>,
3928  <xref format="counter" target="status.302"/> and
3929  <xref format="counter" target="status.307"/>)
3930</t>
3931<t>
3932  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3933  It used to indicate that the target resource must be accessed through the
3934  proxy given by the Location field. The Location field gave the URI of the
3935  proxy. The recipient was expected to repeat this single request via the proxy.
3936  (<xref target="status.305"/>)
3937</t>
3938<t>
3939  Define status 426 (Upgrade Required) (this was incorporated from
3940  <xref target="RFC2817"/>).
3941  (<xref target="status.426"/>)
3942</t>
3943<t>
3944  Change ABNF productions for header fields to only define the field value.
3945  (<xref target="header.field.definitions"/>)
3946</t>
3947<t>
3948  Reclassify "Allow" as response header field, removing the option to
3949  specify it in a PUT request.
3950  Relax the server requirement on the contents of the Allow header field and
3951  remove requirement on clients to always trust the header field value.
3952  (<xref target="header.allow"/>)
3953</t>
3954<t>
3955  The ABNF for the Expect header field has been both fixed (allowing parameters
3956  for value-less expectations as well) and simplified (allowing trailing
3957  semicolons after "100-continue" when they were invalid before).
3958  (<xref target="header.expect"/>)
3959</t>
3960<t>
3961  Correct syntax of Location header field to allow URI references (including
3962  relative references and fragments), as referred symbol "absoluteURI" wasn't
3963  what was expected, and add some clarifications as to when use of fragments
3964  would not be appropriate.
3965  (<xref target="header.location"/>)
3966</t>
3967<t>
3968  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3969  extension methods could have used it as well).
3970  (<xref target="header.max-forwards"/>)
3971</t>
3972<t>
3973  Allow Referer field value of "about:blank" as alternative to not specifying it.
3974  (<xref target="header.referer"/>)
3975</t>
3976<t>
3977  In the description of the Server header field, the Via field
3978  was described as a SHOULD. The requirement was and is stated
3979  correctly in the description of the Via header field in &header-via;.
3980  (<xref target="header.server"/>)
3981</t>
3982</section>
3983
3984<?BEGININC p2-semantics.abnf-appendix ?>
3985<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3986<figure>
3987<artwork type="abnf" name="p2-semantics.parsed-abnf">
3988<x:ref>Allow</x:ref> = [ ( "," / Method ) *( OWS "," [ OWS Method ] ) ]
3989
3990<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
3991
3992<x:ref>Date</x:ref> = HTTP-date
3993
3994<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3995
3996<x:ref>From</x:ref> = mailbox
3997
3998<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
3999
4000<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4001
4002<x:ref>Location</x:ref> = URI-reference
4003
4004<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4005<x:ref>Method</x:ref> = token
4006
4007<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
4008
4009<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
4010<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4011<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4012<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4013
4014<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4015<x:ref>Status-Code</x:ref> = 3DIGIT
4016
4017<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4018<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4019
4020<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4021<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4022
4023<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
4024
4025<x:ref>date1</x:ref> = day SP month SP year
4026<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4027<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4028<x:ref>day</x:ref> = 2DIGIT
4029<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4030 / %x54.75.65 ; Tue
4031 / %x57.65.64 ; Wed
4032 / %x54.68.75 ; Thu
4033 / %x46.72.69 ; Fri
4034 / %x53.61.74 ; Sat
4035 / %x53.75.6E ; Sun
4036<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4037 / %x54.75.65.73.64.61.79 ; Tuesday
4038 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4039 / %x54.68.75.72.73.64.61.79 ; Thursday
4040 / %x46.72.69.64.61.79 ; Friday
4041 / %x53.61.74.75.72.64.61.79 ; Saturday
4042 / %x53.75.6E.64.61.79 ; Sunday
4043<x:ref>delta-seconds</x:ref> = 1*DIGIT
4044
4045<x:ref>expect-name</x:ref> = token
4046<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
4047<x:ref>expect-value</x:ref> = token / quoted-string
4048<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
4049 OWS expect-param ] )
4050
4051<x:ref>hour</x:ref> = 2DIGIT
4052
4053<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4054<x:ref>minute</x:ref> = 2DIGIT
4055<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4056 / %x46.65.62 ; Feb
4057 / %x4D.61.72 ; Mar
4058 / %x41.70.72 ; Apr
4059 / %x4D.61.79 ; May
4060 / %x4A.75.6E ; Jun
4061 / %x4A.75.6C ; Jul
4062 / %x41.75.67 ; Aug
4063 / %x53.65.70 ; Sep
4064 / %x4F.63.74 ; Oct
4065 / %x4E.6F.76 ; Nov
4066 / %x44.65.63 ; Dec
4067
4068<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4069<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
4070
4071<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4072<x:ref>product</x:ref> = token [ "/" product-version ]
4073<x:ref>product-version</x:ref> = token
4074
4075<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
4076
4077<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4078<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4079
4080<x:ref>second</x:ref> = 2DIGIT
4081
4082<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4083<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
4084
4085<x:ref>year</x:ref> = 4DIGIT
4086</artwork>
4087</figure>
4088<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4089; Allow defined but not used
4090; Date defined but not used
4091; Expect defined but not used
4092; From defined but not used
4093; Location defined but not used
4094; Max-Forwards defined but not used
4095; Reason-Phrase defined but not used
4096; Referer defined but not used
4097; Retry-After defined but not used
4098; Server defined but not used
4099; Status-Code defined but not used
4100; User-Agent defined but not used
4101</artwork></figure></section>
4102<?ENDINC p2-semantics.abnf-appendix ?>
4103
4104<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4105
4106<section title="Since RFC 2616">
4107<t>
4108  Extracted relevant partitions from <xref target="RFC2616"/>.
4109</t>
4110</section>
4111
4112<section title="Since draft-ietf-httpbis-p2-semantics-00">
4113<t>
4114  Closed issues:
4115  <list style="symbols"> 
4116    <t>
4117      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4118      "Via is a MUST"
4119      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4120    </t>
4121    <t>
4122      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4123      "Fragments allowed in Location"
4124      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4125    </t>
4126    <t>
4127      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4128      "Safe Methods vs Redirection"
4129      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4130    </t>
4131    <t>
4132      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4133      "Revise description of the POST method"
4134      (<eref target="http://purl.org/NET/http-errata#post"/>)
4135    </t>
4136    <t>
4137      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4138      "Normative and Informative references"
4139    </t>
4140    <t>
4141      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4142      "RFC2606 Compliance"
4143    </t>
4144    <t>
4145      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4146      "Informative references"
4147    </t>
4148    <t>
4149      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4150      "Redundant cross-references"
4151    </t>
4152  </list>
4153</t>
4154<t>
4155  Other changes:
4156  <list style="symbols"> 
4157    <t>
4158      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4159    </t>
4160  </list>
4161</t>
4162</section>
4163
4164<section title="Since draft-ietf-httpbis-p2-semantics-01">
4165<t>
4166  Closed issues:
4167  <list style="symbols"> 
4168    <t>
4169      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4170      "PUT side effects"
4171    </t>
4172    <t>
4173      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4174      "Duplicate Host header requirements"
4175    </t>
4176  </list>
4177</t>
4178<t>
4179  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4180  <list style="symbols"> 
4181    <t>
4182      Move "Product Tokens" section (back) into Part 1, as "token" is used
4183      in the definition of the Upgrade header field.
4184    </t>
4185    <t>
4186      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4187    </t>
4188    <t>
4189      Copy definition of delta-seconds from Part6 instead of referencing it.
4190    </t>
4191  </list>
4192</t>
4193</section>
4194
4195<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4196<t>
4197  Closed issues:
4198  <list style="symbols"> 
4199    <t>
4200      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4201      "Requiring Allow in 405 responses"
4202    </t>
4203    <t>
4204      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4205      "Status Code Registry"
4206    </t>
4207    <t>
4208      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4209      "Redirection vs. Location"
4210    </t>
4211    <t>
4212      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4213      "Cacheability of 303 response"
4214    </t>
4215    <t>
4216      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4217      "305 Use Proxy"
4218    </t>
4219    <t>
4220      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4221      "Classification for Allow header"
4222    </t>
4223    <t>
4224      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4225      "PUT - 'store under' vs 'store at'"
4226    </t>
4227  </list>
4228</t>
4229<t>
4230  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4231  <list style="symbols"> 
4232    <t>
4233      Reference RFC 3984, and update header field registrations for headers defined
4234      in this document.
4235    </t>
4236  </list>
4237</t>
4238<t>
4239  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4240  <list style="symbols"> 
4241    <t>
4242      Replace string literals when the string really is case-sensitive (method).
4243    </t>
4244  </list>
4245</t>
4246</section>
4247
4248<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4249<t>
4250  Closed issues:
4251  <list style="symbols"> 
4252    <t>
4253      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4254      "OPTIONS request bodies"
4255    </t>
4256    <t>
4257      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4258      "Description of CONNECT should refer to RFC2817"
4259    </t>
4260    <t>
4261      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4262      "Location Content-Location reference request/response mixup"
4263    </t>
4264  </list>
4265</t>
4266<t>
4267  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4268  <list style="symbols"> 
4269    <t>
4270      Added initial proposal for registration process, plus initial
4271      content (non-HTTP/1.1 methods to be added by a separate specification).
4272    </t>
4273  </list>
4274</t>
4275</section>
4276
4277<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4278<t>
4279  Closed issues:
4280  <list style="symbols"> 
4281    <t>
4282      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4283      "Content-*"
4284    </t>
4285    <t>
4286      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4287      "RFC 2822 is updated by RFC 5322"
4288    </t>
4289  </list>
4290</t>
4291<t>
4292  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4293  <list style="symbols"> 
4294    <t>
4295      Use "/" instead of "|" for alternatives.
4296    </t>
4297    <t>
4298      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4299      whitespace ("OWS") and required whitespace ("RWS").
4300    </t>
4301    <t>
4302      Rewrite ABNFs to spell out whitespace rules, factor out
4303      header field value format definitions.
4304    </t>
4305  </list>
4306</t>
4307</section>
4308
4309<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4310<t>
4311  Closed issues:
4312  <list style="symbols"> 
4313    <t>
4314      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4315      "Reason-Phrase BNF"
4316    </t>
4317  </list>
4318</t>
4319<t>
4320  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4321  <list style="symbols"> 
4322    <t>
4323      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4324    </t>
4325  </list>
4326</t>
4327</section>
4328
4329<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4330<t>
4331  Closed issues:
4332  <list style="symbols"> 
4333    <t>
4334      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4335      "Clarify when Referer is sent"
4336    </t>
4337    <t>
4338      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4339      "status codes vs methods"
4340    </t>
4341    <t>
4342      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4343      "Do not require "updates" relation for specs that register status codes or method names"
4344    </t>
4345  </list>
4346</t>
4347</section>
4348
4349<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4350<t>
4351  Closed issues:
4352  <list style="symbols"> 
4353    <t>
4354      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4355      "Idempotency"
4356    </t>
4357    <t>
4358      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4359      "TRACE security considerations"
4360    </t>
4361    <t>
4362      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4363      "Clarify rules for determining what entities a response carries"
4364    </t>
4365    <t>
4366      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4367      "update note citing RFC 1945 and 2068"
4368    </t>
4369    <t>
4370      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4371      "update note about redirect limit"
4372    </t>
4373    <t>
4374      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4375      "Location header ABNF should use 'URI'"
4376    </t>
4377    <t>
4378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4379      "fragments in Location vs status 303"
4380    </t>
4381    <t>
4382      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4383      "move IANA registrations for optional status codes"
4384    </t>
4385  </list>
4386</t>
4387<t>
4388  Partly resolved issues:
4389  <list style="symbols"> 
4390    <t>
4391      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4392      "Are OPTIONS and TRACE safe?"
4393    </t>
4394  </list>
4395</t>
4396</section>
4397
4398<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4399<t>
4400  Closed issues:
4401  <list style="symbols"> 
4402    <t>
4403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4404      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4405      status codes when fixing this previously)
4406    </t>
4407  </list>
4408</t>
4409</section>
4410
4411<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4412<t>
4413  Closed issues:
4414  <list style="symbols"> 
4415    <t>
4416      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4417      "Fragment combination / precedence during redirects"
4418    </t>
4419  </list>
4420</t>
4421<t>
4422  Partly resolved issues:
4423  <list style="symbols"> 
4424    <t>
4425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4426      "Location header payload handling"
4427    </t>
4428    <t>
4429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4430      "Term for the requested resource's URI"
4431    </t>
4432  </list>
4433</t>
4434</section>
4435
4436<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4437<t>
4438  Closed issues:
4439  <list style="symbols"> 
4440    <t>
4441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4442      "Clarify 'Requested Variant'"
4443    </t>
4444    <t>
4445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4446      "Clarify entity / representation / variant terminology"
4447    </t>
4448    <t>
4449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4450      "Methods and Caching"
4451    </t>
4452    <t>
4453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4454      "OPTIONS vs Max-Forwards"
4455    </t>
4456    <t>
4457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4458      "Status codes and caching"
4459    </t>
4460    <t>
4461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4462      "consider removing the 'changes from 2068' sections"
4463    </t>
4464  </list>
4465</t>
4466</section>
4467
4468<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4469<t>
4470  Closed issues:
4471  <list style="symbols"> 
4472    <t>
4473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4474      "Considerations for new status codes"
4475    </t>
4476    <t>
4477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4478      "Considerations for new methods"
4479    </t>
4480    <t>
4481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4482      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4483    </t>
4484  </list>
4485</t>
4486</section>
4487
4488<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4489<t>
4490  Closed issues:
4491  <list style="symbols"> 
4492    <t>
4493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4494      "Fragment combination / precedence during redirects" (added warning
4495      about having a fragid on the redirect may cause inconvenience in
4496      some cases)
4497    </t>
4498    <t>
4499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4500      "Content-* vs. PUT"
4501    </t>
4502    <t>
4503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4504      "205 Bodies"
4505    </t>
4506    <t>
4507      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4508      "Understanding Content-* on non-PUT requests"
4509    </t>
4510    <t>
4511      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4512      "Content-*"
4513    </t>
4514    <t>
4515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4516      "Header type defaulting"
4517    </t>
4518    <t>
4519      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4520      "PUT - 'store under' vs 'store at'"
4521    </t>
4522    <t>
4523      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4524      "duplicate ABNF for Reason-Phrase"
4525    </t>
4526    <t>
4527      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4528      "Note special status of Content-* prefix in header registration procedures"
4529    </t>
4530    <t>
4531      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4532      "Max-Forwards vs extension methods"
4533    </t>
4534    <t>
4535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4536      "What is the value space of HTTP status codes?" (actually fixed in
4537      draft-ietf-httpbis-p2-semantics-11)
4538    </t>
4539    <t>
4540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4541      "Header Classification"
4542    </t>
4543    <t>
4544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4545      "PUT side effect: invalidation or just stale?"
4546    </t>
4547    <t>
4548      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4549      "proxies not supporting certain methods"
4550    </t>
4551    <t>
4552      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4553      "Migrate CONNECT from RFC2817 to p2"
4554    </t>
4555    <t>
4556      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4557      "Migrate Upgrade details from RFC2817"
4558    </t>
4559    <t>
4560      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4561      "clarify PUT semantics'"
4562    </t>
4563    <t>
4564      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4565      "duplicate ABNF for 'Method'"
4566    </t>
4567    <t>
4568      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4569      "untangle ABNFs for header fields"
4570    </t>
4571  </list>
4572</t>
4573</section>
4574
4575<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4576<t>
4577  Closed issues:
4578  <list style="symbols"> 
4579    <t>
4580      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4581      "untangle ABNFs for header fields"
4582    </t>
4583    <t>
4584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4585      "message body in CONNECT request"
4586    </t>
4587  </list>
4588</t>
4589</section>
4590
4591<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4592<t>
4593  Closed issues:
4594  <list style="symbols"> 
4595    <t>
4596      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4597      "Clarify status code for rate limiting"
4598    </t>
4599    <t>
4600      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4601      "clarify 403 forbidden"
4602    </t>
4603    <t>
4604      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4605      "Clarify 203 Non-Authoritative Information"
4606    </t>
4607    <t>
4608      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4609      "update default reason phrase for 413"
4610    </t>
4611  </list>
4612</t>
4613</section>
4614
4615<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4616<t>
4617  Closed issues:
4618  <list style="symbols"> 
4619    <t>
4620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4621      "Strength of requirements on Accept re: 406"
4622    </t>
4623    <t>
4624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4625      "400 response isn't generic"
4626    </t>
4627  </list>
4628</t>
4629</section>
4630
4631<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4632<t>
4633  Closed issues:
4634  <list style="symbols"> 
4635    <t>
4636      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4637      "Redirects and non-GET methods"
4638    </t>
4639    <t>
4640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4641      "Document HTTP's error-handling philosophy"
4642    </t>
4643    <t>
4644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4645      "Considerations for new headers"
4646    </t>
4647    <t>
4648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4649      "clarify 303 redirect on HEAD"
4650    </t>
4651  </list>
4652</t>
4653</section>
4654
4655<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4656<t>
4657  Closed issues:
4658  <list style="symbols"> 
4659    <t>
4660      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4661      "Location header payload handling"
4662    </t>
4663    <t>
4664      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4665      "Clarify status code for rate limiting" (change backed out because
4666      a new status code is being defined for this purpose)
4667    </t>
4668    <t>
4669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4670      "should there be a permanent variant of 307"
4671    </t>
4672    <t>
4673      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4674      "When are Location's semantics triggered?"
4675    </t>
4676    <t>
4677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4678      "'expect' grammar missing OWS"
4679    </t>
4680    <t>
4681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4682      "header field considerations: quoted-string vs use of double quotes"
4683    </t>
4684  </list>
4685</t>
4686</section>
4687
4688<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4689<t>
4690  Closed issues:
4691  <list style="symbols"> 
4692    <t>
4693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4694      "Requirements for user intervention during redirects"
4695    </t>
4696    <t>
4697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4698      "Applying original fragment to 'plain' redirected URI"
4699    </t>
4700    <t>
4701      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4702      "Misplaced text on connection handling in p2"
4703    </t>
4704    <t>
4705      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4706      "relax requirements on hypertext in 3/4/5xx error responses"
4707    </t>
4708    <t>
4709      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4710      "example for 426 response should have a payload"
4711    </t>
4712    <t>
4713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4714      "drop indirection entries for status codes"
4715    </t>
4716  </list>
4717</t>
4718</section>
4719
4720</section>
4721
4722</back>
4723</rfc>
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