source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1577

Last change on this file since 1577 was 1577, checked in by julian.reschke@…, 7 years ago

clarify that 201 doesn't require Location header fields (see #331)

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 194.2 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "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 require IETF Review
464  (see <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 require IETF Review
759  (see <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, if successful, thereafter restrict its behavior
1298   to blind 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   Any successful (2xx) response to a CONNECT request indicates that the
1313   proxy has established a connection to the requested host and port,
1314   and has switched to tunneling the current connection to that server
1315   connection.
1316   The tunneled data from the server begins immediately after the blank line
1317   that concludes the successful response's header block.
1318   A server &SHOULD-NOT; send any Transfer-Encoding or Content-Length
1319   header fields in a successful response.
1320   A client &MUST; ignore any Content-Length or Transfer-Encoding header
1321   fields received in a successful response.
1322</t>
1323<t>
1324   Any response other than a successful response indicates that the tunnel
1325   has not yet been formed and that the connection remains governed by HTTP.
1326</t>
1327<t>
1328   Proxy authentication might be used to establish the
1329   authority to create a tunnel:
1330</t>
1331<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1332CONNECT server.example.com:80 HTTP/1.1
1333Host: server.example.com:80
1334Proxy-Authorization: basic aGVsbG86d29ybGQ=
1335
1336</artwork></figure>
1337<t>
1338   A message body on a CONNECT request has no defined semantics. Sending a
1339   body on a CONNECT request might cause existing implementations to reject
1340   the request.
1341</t>
1342<t>
1343   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
1344   to server &MAY; be sent immediately after the request (before a response
1345   is received). The usual caveats also apply:
1346   data may be discarded if the eventual response is negative, and the
1347   connection may be reset with no response if more than one TCP segment
1348   is outstanding.
1349</t>
1350<t>
1351   It may be the case that the proxy itself can only reach the requested
1352   origin server through another proxy.  In this case, the first proxy
1353   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1354   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1355   unless it has either a direct or tunnel connection established to the
1356   authority.
1357</t>
1358<t>
1359   If at any point either one of the peers gets disconnected, any
1360   outstanding data that came from that peer will be passed to the other
1361   one, and after that also the other connection will be terminated by
1362   the proxy. If there is outstanding data to that peer undelivered,
1363   that data will be discarded.
1364</t>
1365<t>
1366   An origin server which receives a CONNECT request for itself &MAY;
1367   respond with a 2xx status code to indicate that a connection is
1368   established.  However, most origin servers do not implement CONNECT.
1369</t>
1370</section>
1371</section>
1372
1373
1374<section title="Status Code Definitions" anchor="status.codes">
1375<t>
1376   The first digit of the status-code defines the class of response. The
1377   last two digits do not have any categorization role. There are 5
1378   values for the first digit:
1379  <list style="symbols">
1380    <t>
1381      1xx: Informational - Request received, continuing process
1382    </t>
1383    <t>
1384      2xx: Success - The action was successfully received,
1385        understood, and accepted
1386    </t>
1387    <t>
1388      3xx: Redirection - Further action must be taken in order to
1389        complete the request
1390    </t>
1391    <t>
1392      4xx: Client Error - The request contains bad syntax or cannot
1393        be fulfilled
1394    </t>
1395    <t>
1396      5xx: Server Error - The server failed to fulfill an apparently
1397        valid request
1398    </t>
1399  </list>
1400</t>
1401<t>
1402   Each status-code is described below, including any metadata required
1403   in the response.
1404</t>
1405<t>
1406   For most status codes the response can carry a payload, in which case a
1407   Content-Type header field indicates the payload's media type
1408   (&header-content-type;).
1409</t>
1410
1411<section title="Informational 1xx" anchor="status.1xx">
1412<t>
1413   This class of status code indicates a provisional response,
1414   consisting only of the status-line and optional header fields, and is
1415   terminated by an empty line. There are no required header fields for this
1416   class of status code. Since HTTP/1.0 did not define any 1xx status
1417   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1418   except under experimental conditions.
1419</t>
1420<t>
1421   A client &MUST; be prepared to accept one or more 1xx status responses
1422   prior to a regular response, even if the client does not expect a 100
1423   (Continue) status message. Unexpected 1xx status responses &MAY; be
1424   ignored by a user agent.
1425</t>
1426<t>
1427   Proxies &MUST; forward 1xx responses, unless the connection between the
1428   proxy and its client has been closed, or unless the proxy itself
1429   requested the generation of the 1xx response. (For example, if a
1430   proxy adds a "Expect: 100-continue" field when it forwards a request,
1431   then it need not forward the corresponding 100 (Continue)
1432   response(s).)
1433</t>
1434
1435<section title="100 Continue" anchor="status.100">
1436  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1437  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1438<t>
1439   The client &SHOULD; continue with its request. This interim response is
1440   used to inform the client that the initial part of the request has
1441   been received and has not yet been rejected by the server. The client
1442   &SHOULD; continue by sending the remainder of the request or, if the
1443   request has already been completed, ignore this response. The server
1444   &MUST; send a final response after the request has been completed. See
1445   &use100; for detailed discussion of the use and handling of this
1446   status code.
1447</t>
1448</section>
1449
1450<section title="101 Switching Protocols" anchor="status.101">
1451  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1452  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1453<t>
1454   The server understands and is willing to comply with the client's
1455   request, via the Upgrade message header field (&header-upgrade;), for a
1456   change in the application protocol being used on this connection. The
1457   server will switch protocols to those defined by the response's
1458   Upgrade header field immediately after the empty line which
1459   terminates the 101 response.
1460</t>
1461<t>
1462   The protocol &SHOULD; be switched only when it is advantageous to do
1463   so. For example, switching to a newer version of HTTP is advantageous
1464   over older versions, and switching to a real-time, synchronous
1465   protocol might be advantageous when delivering resources that use
1466   such features.
1467</t>
1468</section>
1469</section>
1470
1471<section title="Successful 2xx" anchor="status.2xx">
1472<t>
1473   This class of status code indicates that the client's request was
1474   successfully received, understood, and accepted.
1475</t>
1476
1477<section title="200 OK" anchor="status.200">
1478  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1479  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1480<t>
1481   The request has succeeded. The payload returned with the response
1482   is dependent on the method used in the request, for example:
1483  <list style="hanging">
1484    <t hangText="GET">
1485      a representation of the target resource is sent in the response;
1486    </t>
1487    <t hangText="HEAD">
1488      the same representation as GET, except without the message body;
1489    </t>
1490    <t hangText="POST">
1491      a representation describing or containing the result of the action;
1492    </t>
1493    <t hangText="TRACE">
1494      a representation containing the request message as received by the
1495      end server.
1496    </t>
1497  </list>
1498</t>
1499<t>
1500   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1501   freshness for 200 responses.
1502</t>
1503</section>
1504
1505<section title="201 Created" anchor="status.201">
1506  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1507  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1508<t>
1509   The request has been fulfilled and has resulted in a new resource being
1510   created.
1511</t>
1512<t>
1513   The newly created resource is typically linked to from the response payload,
1514   with the most relevant URI also being carried in the Location header field.
1515   If the newly created resource's URI is the same as the Effective Request URI,
1516   this information can be omitted (e.g., in the case of a response to a PUT
1517   request). 
1518</t>
1519<t>
1520   The origin server &MUST; create the resource before returning the 201 status
1521   code. If the action cannot be carried out immediately, the server &SHOULD;
1522   respond with 202 (Accepted) response instead.
1523</t>
1524<t>
1525   A 201 response &MAY; contain an ETag response header field indicating
1526   the current value of the entity-tag for the representation of the resource
1527   just created (see &header-etag;).
1528</t>
1529</section>
1530
1531<section title="202 Accepted" anchor="status.202">
1532  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1533  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1534<t>
1535   The request has been accepted for processing, but the processing has
1536   not been completed.  The request might or might not eventually be
1537   acted upon, as it might be disallowed when processing actually takes
1538   place. There is no facility for re-sending a status code from an
1539   asynchronous operation such as this.
1540</t>
1541<t>
1542   The 202 response is intentionally non-committal. Its purpose is to
1543   allow a server to accept a request for some other process (perhaps a
1544   batch-oriented process that is only run once per day) without
1545   requiring that the user agent's connection to the server persist
1546   until the process is completed. The representation returned with this
1547   response &SHOULD; include an indication of the request's current status
1548   and either a pointer to a status monitor or some estimate of when the
1549   user can expect the request to be fulfilled.
1550</t>
1551</section>
1552
1553<section title="203 Non-Authoritative Information" anchor="status.203">
1554  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1555  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1556<t>
1557   The representation in the response has been transformed or otherwise
1558   modified by a transforming proxy (&intermediaries;).  Note that the
1559   behavior of transforming intermediaries is controlled by the no-transform
1560   Cache-Control directive (&header-cache-control;).
1561</t>
1562<t>
1563   This status code is only appropriate when the response status code would
1564   have been 200 (OK) otherwise. When the status code before transformation
1565   would have been different, the 214 Transformation Applied warn-code
1566   (&header-warning;) is appropriate.
1567</t>
1568<t>
1569   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1570   freshness for 203 responses.
1571</t>
1572</section>
1573
1574<section title="204 No Content" anchor="status.204">
1575  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1576  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1577<t>
1578   The 204 (No Content) status code indicates that the server has
1579   successfully fulfilled the request and that there is no additional
1580   content to return in the response payload body.  Metadata in the
1581   response header fields refer to the target resource and its current
1582   representation after the requested action.
1583</t>
1584<t>
1585   For example, if a 204 status code is received in response to a PUT
1586   request and the response contains an ETag header field, then the PUT
1587   was successful and the ETag field-value contains the entity-tag for
1588   the new representation of that target resource.
1589</t>
1590<t>
1591   The 204 response allows a server to indicate that the action has been
1592   successfully applied to the target resource while implying that the
1593   user agent &SHOULD-NOT; traverse away from its current "document view"
1594   (if any).  The server assumes that the user agent will provide some
1595   indication of the success to its user, in accord with its own interface,
1596   and apply any new or updated metadata in the response to the active
1597   representation.
1598</t>
1599<t>
1600   For example, a 204 status code is commonly used with document editing
1601   interfaces corresponding to a "save" action, such that the document
1602   being saved remains available to the user for editing. It is also
1603   frequently used with interfaces that expect automated data transfers
1604   to be prevalent, such as within distributed version control systems.
1605</t>
1606<t>
1607   The 204 response &MUST-NOT; include a message body, and thus is always
1608   terminated by the first empty line after the header fields.
1609</t>
1610</section>
1611
1612<section title="205 Reset Content" anchor="status.205">
1613  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1614  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1615<t>
1616   The server has fulfilled the request and the user agent &SHOULD; reset
1617   the document view which caused the request to be sent. This response
1618   is primarily intended to allow input for actions to take place via
1619   user input, followed by a clearing of the form in which the input is
1620   given so that the user can easily initiate another input action.
1621</t>
1622<t>   
1623   The message body included with the response &MUST; be empty. Note that
1624   receivers still need to parse the response according to the algorithm defined
1625   in &message-body;.
1626</t>
1627</section>
1628</section>
1629
1630<section title="Redirection 3xx" anchor="status.3xx">
1631<t>
1632   This class of status code indicates that further action needs to be
1633   taken by the user agent in order to fulfill the request.  If the required
1634   action involves a subsequent HTTP request, it &MAY; be carried out by the
1635   user agent without interaction with the user if and only if the method used
1636   in the second request is known to be "safe", as defined in
1637   <xref target="safe.methods"/>.
1638</t>
1639<t>
1640   There are several types of redirects:
1641   <list style="numbers">
1642      <x:lt>
1643        <t>
1644          Redirects of the request to another URI, either temporarily or
1645          permanently. The new URI is specified in the Location header field.
1646          In this specification, the status codes 301 (Moved Permanently),
1647          302 (Found), and 307 (Temporary Redirect) fall under this category.
1648        </t>
1649      </x:lt>
1650      <x:lt>
1651        <t>
1652          Redirection to a new location that represents an indirect response to
1653          the request, such as the result of a POST operation to be retrieved
1654          with a subsequent GET request. This is status code 303 (See Other).
1655        </t>
1656      </x:lt>
1657      <x:lt>
1658        <t>
1659          Redirection offering a choice of matching resources for use by
1660          agent-driven content negotiation (&agent-driven-negotiation;). This
1661          is status code 300 (Multiple Choices).
1662        </t>
1663      </x:lt>
1664      <x:lt>
1665        <t>
1666          Other kinds of redirection, such as to a cached result (status code 304
1667          (Not Modified), see &status-304;).
1668        </t>
1669      </x:lt>
1670   </list>
1671</t>
1672<x:note>
1673  <t>
1674    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1675    and 302 (Found) were defined for the first type of redirect, and the second
1676    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1677    However it turned out that web forms using POST expected redirects to change
1678    the operation for the subsequent request to retrieval (GET). To address this
1679    use case, HTTP/1.1 introduced the second type of redirect with the status
1680    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1681    As user agents did not change their behavior to maintain backwards
1682    compatibility, the first revision of HTTP/1.1 added yet another status code,
1683    307 (Temporary Redirect), for which the backwards compatibility problems did
1684    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1685    Over 10 years later, most user agents still do method rewriting for
1686    status codes 301 and 302, therefore this specification makes that behavior
1687    conformant in case the original request was POST.
1688  </t>
1689</x:note>
1690<t>
1691   A Location header field on a 3xx response indicates that a client &MAY;
1692   automatically redirect to the URI provided; see <xref target="header.location"/>.
1693</t>
1694<t>
1695   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1696   automatic redirection needs to done with care, since the redirect might
1697   change the conditions under which the request was issued.
1698</t>
1699<t>
1700   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1701   "infinite" redirection loops).
1702</t>
1703<x:note>
1704  <t>
1705    <x:h>Note:</x:h> An earlier version of this specification recommended a
1706    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1707    Content developers need to be aware that some clients might
1708    implement such a fixed limitation.
1709  </t>
1710</x:note>
1711
1712<section title="300 Multiple Choices" anchor="status.300">
1713  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1714  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1715<t>
1716   The target resource has more than one
1717   representation, each with its own specific location, and agent-driven
1718   negotiation information (&content-negotiation;) is being provided so that
1719   the user (or user agent) can select a preferred representation by
1720   redirecting its request to that location.
1721</t>
1722<t>
1723   Unless it was a HEAD request, the response &SHOULD; include a representation
1724   containing a list of representation metadata and location(s) from
1725   which the user or user agent can choose the one most appropriate. Depending
1726   upon the format and the capabilities of
1727   the user agent, selection of the most appropriate choice &MAY; be
1728   performed automatically. However, this specification does not define
1729   any standard for such automatic selection.
1730</t>
1731<t>
1732   If the server has a preferred choice of representation, it &SHOULD;
1733   include the specific URI for that representation in the Location
1734   field; user agents &MAY; use the Location field value for automatic
1735   redirection.
1736</t>
1737<t>
1738   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1739   freshness for 300 responses.
1740</t>
1741
1742</section>
1743
1744<section title="301 Moved Permanently" anchor="status.301">
1745  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1746  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1747<t>
1748   The target resource has been assigned a new permanent URI and any
1749   future references to this resource &SHOULD; use one of the returned
1750   URIs.  Clients with link editing capabilities ought to automatically
1751   re-link references to the effective request URI to one or more of the new
1752   references returned by the server, where possible.
1753</t>
1754<t>
1755   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1756   freshness for 301 responses.
1757</t>
1758<t>
1759   The new permanent URI &SHOULD; be given by the Location field in the
1760   response. A response payload can contain a short hypertext note with a
1761   hyperlink to the new URI(s).
1762</t>
1763<x:note>
1764  <t>
1765    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1766    request method from POST to GET for the subsequent request. If this
1767    behavior is undesired, status code 307 (Temporary Redirect) can be used
1768    instead.
1769  </t>
1770</x:note>
1771</section>
1772
1773<section title="302 Found" anchor="status.302">
1774  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1775  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1776<t>
1777   The target resource resides temporarily under a different URI.
1778   Since the redirection might be altered on occasion, the client &SHOULD;
1779   continue to use the effective request URI for future requests.
1780</t>
1781<t>
1782   The temporary URI &SHOULD; be given by the Location field in the
1783   response. A response payload can contain a short hypertext note with a
1784   hyperlink to the new URI(s).
1785</t>
1786<x:note>
1787  <t>
1788    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1789    request method from POST to GET for the subsequent request. If this
1790    behavior is undesired, status code 307 (Temporary Redirect) can be used
1791    instead.
1792  </t>
1793</x:note>
1794</section>
1795
1796<section title="303 See Other" anchor="status.303">
1797  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1798  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1799<t>
1800   The 303 status code indicates that the server is redirecting the
1801   user agent to a different resource, as indicated by a URI in the
1802   Location header field, that is intended to provide an indirect
1803   response to the original request.  In order to satisfy the original
1804   request, a user agent &SHOULD; perform a retrieval request using the
1805   Location URI (a GET or HEAD request if using HTTP), which
1806   may itself be redirected further, and present the eventual result as an
1807   answer to the original request.
1808   Note that the new URI in the Location header field is not considered
1809   equivalent to the effective request URI.
1810</t>
1811<t>
1812   This status code is generally applicable to any HTTP method.  It is
1813   primarily used to allow the output of a POST action to redirect
1814   the user agent to a selected resource, since doing so provides the
1815   information corresponding to the POST response in a form that
1816   can be separately identified, bookmarked, and cached independent
1817   of the original request.
1818</t>
1819<t>
1820   A 303 response to a GET request indicates that the requested
1821   resource does not have a representation of its own that can be
1822   transferred by the server over HTTP.  The Location URI indicates a
1823   resource that is descriptive of the target resource, such that the
1824   follow-on representation might be useful to recipients without
1825   implying that it adequately represents the target resource.
1826   Note that answers to the questions of what can be represented, what
1827   representations are adequate, and what might be a useful description
1828   are outside the scope of HTTP and thus entirely determined by the
1829   URI owner(s).
1830</t>
1831<t>
1832   Except for responses to a HEAD request, the representation of a 303
1833   response &SHOULD; contain a short hypertext note with a hyperlink
1834   to the Location URI.
1835</t>
1836</section>
1837
1838<section title="305 Use Proxy" anchor="status.305">
1839  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1840  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1841<t>
1842   The 305 status code was defined in a previous version of this specification
1843   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1844</t>
1845</section>
1846
1847<section title="306 (Unused)" anchor="status.306">
1848  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1849  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1850<t>
1851   The 306 status code was used in a previous version of the
1852   specification, is no longer used, and the code is reserved.
1853</t>
1854</section>
1855
1856<section title="307 Temporary Redirect" anchor="status.307">
1857  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1858  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1859<t>
1860   The target resource resides temporarily under a different URI.
1861   Since the redirection can change over time, the client &SHOULD;
1862   continue to use the effective request URI for future requests.
1863</t>
1864<t>
1865   The temporary URI &SHOULD; be given by the Location field in the
1866   response. A response payload can contain a short hypertext note with a
1867   hyperlink to the new URI(s).
1868</t>
1869<x:note>
1870  <t>
1871    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1872    it does not allow rewriting the request method from POST to GET. This
1873    specification defines no equivalent counterpart for 301 Moved Permanently.
1874  </t>
1875</x:note>
1876</section>
1877</section>
1878
1879<section title="Client Error 4xx" anchor="status.4xx">
1880<t>
1881   The 4xx class of status code is intended for cases in which the
1882   client seems to have erred. Except when responding to a HEAD request,
1883   the server &SHOULD; include a representation containing an explanation of the
1884   error situation, and whether it is a temporary or permanent
1885   condition. These status codes are applicable to any request method.
1886   User agents &SHOULD; display any included representation to the user.
1887</t>
1888
1889<section title="400 Bad Request" anchor="status.400">
1890  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1891  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1892<t>
1893   The server cannot or will not process the request, due to a client error (e.g.,
1894   malformed syntax).
1895</t>
1896</section>
1897
1898<section title="402 Payment Required" anchor="status.402">
1899  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1900  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1901<t>
1902   This code is reserved for future use.
1903</t>
1904</section>
1905
1906<section title="403 Forbidden" anchor="status.403">
1907  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1908  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1909<t>
1910   The server understood the request, but refuses to authorize it. Providing
1911   different user authentication credentials might be successful, but any
1912   credentials that were provided in the request are insufficient. The request
1913   &SHOULD-NOT; be repeated with the same credentials.
1914</t>
1915<t>
1916   If the request method was not HEAD and the server wishes to make
1917   public why the request has not been fulfilled, it &SHOULD; describe the
1918   reason for the refusal in the representation.  If the server does not wish to
1919   make this information available to the client, the status code 404
1920   (Not Found) &MAY; be used instead.
1921</t>
1922</section>
1923
1924<section title="404 Not Found" anchor="status.404">
1925  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1926  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1927<t>
1928   The server has not found anything matching the effective request URI. No
1929   indication is given of whether the condition is temporary or
1930   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1931   knows, through some internally configurable mechanism, that an old
1932   resource is permanently unavailable and has no forwarding address.
1933   This status code is commonly used when the server does not wish to
1934   reveal exactly why the request has been refused, or when no other
1935   response is applicable.
1936</t>
1937</section>
1938
1939<section title="405 Method Not Allowed" anchor="status.405">
1940  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1941  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1942<t>
1943   The method specified in the request-line is not allowed for the target
1944   resource. The response &MUST; include an Allow header field containing a
1945   list of valid methods for the requested resource.
1946</t>
1947</section>
1948
1949<section title="406 Not Acceptable" anchor="status.406">
1950  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1951  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1952<t>
1953   The resource identified by the request is only capable of generating
1954   response representations which have content characteristics not acceptable
1955   according to the Accept and Accept-* header fields sent in the request
1956   (see &p3-header-fields;).
1957</t>
1958<t>
1959   Unless it was a HEAD request, the response &SHOULD; include a representation
1960   containing a list of available representation characteristics and location(s)
1961   from which the user or user agent can choose the one most
1962   appropriate. Depending upon the format and the
1963   capabilities of the user agent, selection of the most appropriate
1964   choice &MAY; be performed automatically. However, this specification
1965   does not define any standard for such automatic selection.
1966</t>
1967<x:note>
1968  <t>
1969    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1970    not acceptable according to the accept header fields sent in the
1971    request. In some cases, this might even be preferable to sending a
1972    406 response. User agents are encouraged to inspect the header fields of
1973    an incoming response to determine if it is acceptable.
1974  </t>
1975</x:note>
1976<t>
1977   If the response could be unacceptable, a user agent &SHOULD;
1978   temporarily stop receipt of more data and query the user for a
1979   decision on further actions.
1980</t>
1981</section>
1982
1983<section title="408 Request Timeout" anchor="status.408">
1984  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1985  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1986<t>
1987   The client did not produce a request within the time that the server
1988   was prepared to wait. The client &MAY; repeat the request without
1989   modifications at any later time.
1990</t>
1991</section>
1992
1993<section title="409 Conflict" anchor="status.409">
1994  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1995  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1996<t>
1997   The request could not be completed due to a conflict with the current
1998   state of the resource. This code is only allowed in situations where
1999   it is expected that the user might be able to resolve the conflict
2000   and resubmit the request. The response body &SHOULD; include enough
2001   information for the user to recognize the source of the conflict.
2002   Ideally, the response representation would include enough information for the
2003   user or user agent to fix the problem; however, that might not be
2004   possible and is not required.
2005</t>
2006<t>
2007   Conflicts are most likely to occur in response to a PUT request. For
2008   example, if versioning were being used and the representation being PUT
2009   included changes to a resource which conflict with those made by an
2010   earlier (third-party) request, the server might use the 409 response
2011   to indicate that it can't complete the request. In this case, the
2012   response representation would likely contain a list of the differences
2013   between the two versions.
2014</t>
2015</section>
2016
2017<section title="410 Gone" anchor="status.410">
2018  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
2019  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
2020<t>
2021   The target resource is no longer available at the server and no
2022   forwarding address is known. This condition is expected to be
2023   considered permanent. Clients with link editing capabilities &SHOULD;
2024   delete references to the effective request URI after user approval. If the
2025   server does not know, or has no facility to determine, whether or not
2026   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
2027   used instead.
2028</t>
2029<t>
2030   The 410 response is primarily intended to assist the task of web
2031   maintenance by notifying the recipient that the resource is
2032   intentionally unavailable and that the server owners desire that
2033   remote links to that resource be removed. Such an event is common for
2034   limited-time, promotional services and for resources belonging to
2035   individuals no longer working at the server's site. It is not
2036   necessary to mark all permanently unavailable resources as "gone" or
2037   to keep the mark for any length of time &mdash; that is left to the
2038   discretion of the server owner.
2039</t>
2040<t>
2041   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
2042   for 410 responses.
2043</t>
2044</section>
2045
2046<section title="411 Length Required" anchor="status.411">
2047  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
2048  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
2049<t>
2050   The server refuses to accept the request without a defined Content-Length.
2051   The client &MAY; repeat the request if it adds a valid
2052   Content-Length header field containing the length of the message body
2053   in the request message.
2054</t>
2055</section>
2056
2057<section title="413 Request Representation Too Large" anchor="status.413">
2058  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
2059  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
2060<t>
2061   The server is refusing to process a request because the request
2062   representation is larger than the server is willing or able to process. The
2063   server &MAY; close the connection to prevent the client from continuing
2064   the request.
2065</t>
2066<t>
2067   If the condition is temporary, the server &SHOULD; include a Retry-After
2068   header field to indicate that it is temporary and after what
2069   time the client &MAY; try again.
2070</t>
2071</section>
2072
2073<section title="414 URI Too Long" anchor="status.414">
2074  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
2075  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
2076<t>
2077   The server is refusing to service the request because the effective request URI
2078   is longer than the server is willing to interpret. This rare
2079   condition is only likely to occur when a client has improperly
2080   converted a POST request to a GET request with long query
2081   information, when the client has descended into a URI "black hole" of
2082   redirection (e.g., a redirected URI prefix that points to a suffix of
2083   itself), or when the server is under attack by a client attempting to
2084   exploit security holes present in some servers using fixed-length
2085   buffers for reading or manipulating the effective request URI.
2086</t>
2087</section>
2088
2089<section title="415 Unsupported Media Type" anchor="status.415">
2090  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2091  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2092<t>
2093   The server is refusing to service the request because the request
2094   payload is in a format not supported by this request method on the
2095   target resource.
2096</t>
2097</section>
2098
2099<section title="417 Expectation Failed" anchor="status.417">
2100  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2101  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2102<t>
2103   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2104   could not be met by this server, or, if the server is a proxy,
2105   the server has unambiguous evidence that the request could not be met
2106   by the next-hop server.
2107</t>
2108</section>
2109
2110<section title="426 Upgrade Required" anchor="status.426">
2111  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2112  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2113<t>
2114   The request can not be completed without a prior protocol upgrade. This
2115   response &MUST; include an Upgrade header field (&header-upgrade;)
2116   specifying the required protocols.
2117</t>
2118<figure>
2119<preamble>Example:</preamble>
2120<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
2121HTTP/1.1 426 Upgrade Required
2122Upgrade: HTTP/3.0
2123Connection: Upgrade
2124Content-Length: <x:length-of target="s426body"/>
2125Content-Type: text/plain
2126
2127<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
2128</x:span></artwork></figure>
2129<t>
2130   The server &SHOULD; include a message body in the 426 response which
2131   indicates in human readable form the reason for the error and describes any
2132   alternative courses which may be available to the user.
2133</t>
2134</section>
2135</section>
2136
2137<section title="Server Error 5xx" anchor="status.5xx">
2138<t>
2139   Response status codes beginning with the digit "5" indicate cases in
2140   which the server is aware that it has erred or is incapable of
2141   performing the request. Except when responding to a HEAD request, the
2142   server &SHOULD; include a representation containing an explanation of the
2143   error situation, and whether it is a temporary or permanent
2144   condition. User agents &SHOULD; display any included representation to the
2145   user. These response codes are applicable to any request method.
2146</t>
2147
2148<section title="500 Internal Server Error" anchor="status.500">
2149  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2150  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2151<t>
2152   The server encountered an unexpected condition which prevented it
2153   from fulfilling the request.
2154</t>
2155</section>
2156
2157<section title="501 Not Implemented" anchor="status.501">
2158  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2159  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2160<t>
2161   The server does not support the functionality required to fulfill the
2162   request. This is the appropriate response when the server does not
2163   recognize the request method and is not capable of supporting it for
2164   any resource.
2165</t>
2166</section>
2167
2168<section title="502 Bad Gateway" anchor="status.502">
2169  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2170  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2171<t>
2172   The server, while acting as a gateway or proxy, received an invalid
2173   response from the upstream server it accessed in attempting to
2174   fulfill the request.
2175</t>
2176</section>
2177
2178<section title="503 Service Unavailable" anchor="status.503">
2179  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2180  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2181<t>
2182   The server is currently unable to handle the request due to a
2183   temporary overloading or maintenance of the server.
2184</t>
2185<t>
2186   The implication is that this is a temporary condition which will be
2187   alleviated after some delay. If known, the length of the delay &MAY; be
2188   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2189   If no Retry-After is given, the client &SHOULD; handle the response as it
2190   would for a 500 response.
2191</t>
2192<x:note>
2193  <t>
2194    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2195    server must use it when becoming overloaded. Some servers might wish
2196    to simply refuse the connection.
2197  </t>
2198</x:note>
2199</section>
2200
2201<section title="504 Gateway Timeout" anchor="status.504">
2202  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2203  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2204<t>
2205   The server, while acting as a gateway or proxy, did not receive a
2206   timely response from the upstream server specified by the URI (e.g.,
2207   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2208   to access in attempting to complete the request.
2209</t>
2210<x:note>
2211  <t>
2212    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2213    return 400 or 500 when DNS lookups time out.
2214  </t>
2215</x:note>
2216</section>
2217
2218<section title="505 HTTP Version Not Supported" anchor="status.505">
2219  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2220  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2221<t>
2222   The server does not support, or refuses to support, the protocol
2223   version that was used in the request message. The server is
2224   indicating that it is unable or unwilling to complete the request
2225   using the same major version as the client, as described in &http-version;,
2226   other than with this error message. The response &SHOULD; contain
2227   a representation describing why that version is not supported and what other
2228   protocols are supported by that server.
2229</t>
2230
2231</section>
2232</section>
2233</section>
2234
2235
2236<section title="Date/Time Formats" anchor="http.date">
2237  <x:anchor-alias value="HTTP-date"/>
2238<t>
2239   HTTP applications have historically allowed three different formats
2240   for date/time stamps. However, the preferred format is a fixed-length subset
2241   of that defined by <xref target="RFC1123"/>:
2242</t>
2243<figure><artwork type="example" x:indent-with="  ">
2244Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2245</artwork></figure>
2246<t>
2247   The other formats are described here only for compatibility with obsolete
2248   implementations.
2249</t>
2250<figure><artwork type="example" x:indent-with="  ">
2251Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2252Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2253</artwork></figure>
2254<t>
2255   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2256   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2257   only generate the RFC 1123 format for representing HTTP-date values
2258   in header fields.
2259</t>
2260<t>
2261   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2262   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2263   equal to UTC (Coordinated Universal Time). This is indicated in the
2264   first two formats by the inclusion of "GMT" as the three-letter
2265   abbreviation for time zone, and &MUST; be assumed when reading the
2266   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2267   additional whitespace beyond that specifically included as SP in the
2268   grammar.
2269</t>
2270<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2271  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2272</artwork></figure>
2273<t anchor="preferred.date.format">
2274  <x:anchor-alias value="rfc1123-date"/>
2275  <x:anchor-alias value="time-of-day"/>
2276  <x:anchor-alias value="hour"/>
2277  <x:anchor-alias value="minute"/>
2278  <x:anchor-alias value="second"/>
2279  <x:anchor-alias value="day-name"/>
2280  <x:anchor-alias value="day"/>
2281  <x:anchor-alias value="month"/>
2282  <x:anchor-alias value="year"/>
2283  <x:anchor-alias value="GMT"/>
2284  Preferred format:
2285</t>
2286<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"/>
2287  <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>
2288  ; fixed length subset of the format defined in
2289  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2290 
2291  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2292               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2293               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2294               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2295               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2296               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2297               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2298               
2299  <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>
2300               ; e.g., 02 Jun 1982
2301
2302  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2303  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2304               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2305               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2306               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2307               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2308               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2309               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2310               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2311               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2312               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2313               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2314               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2315  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2316
2317  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2318
2319  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2320                 ; 00:00:00 - 23:59:59
2321                 
2322  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2323  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2324  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2325</artwork></figure>
2326<t>
2327  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2328  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2329  same as those defined for the RFC 5322 constructs
2330  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2331</t>
2332<t anchor="obsolete.date.formats">
2333  <x:anchor-alias value="obs-date"/>
2334  <x:anchor-alias value="rfc850-date"/>
2335  <x:anchor-alias value="asctime-date"/>
2336  <x:anchor-alias value="date1"/>
2337  <x:anchor-alias value="date2"/>
2338  <x:anchor-alias value="date3"/>
2339  <x:anchor-alias value="rfc1123-date"/>
2340  <x:anchor-alias value="day-name-l"/>
2341  Obsolete formats:
2342</t>
2343<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2344  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2345</artwork></figure>
2346<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2347  <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>
2348  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2349                 ; day-month-year (e.g., 02-Jun-82)
2350
2351  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2352         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2353         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2354         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2355         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2356         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2357         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2358</artwork></figure>
2359<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2360  <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>
2361  <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> ))
2362                 ; month day (e.g., Jun  2)
2363</artwork></figure>
2364<x:note>
2365  <t>
2366    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2367    accepting date values that might have been sent by non-HTTP
2368    applications, as is sometimes the case when retrieving or posting
2369    messages via proxies/gateways to SMTP or NNTP.
2370  </t>
2371</x:note>
2372<x:note>
2373  <t>
2374    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2375    to their usage within the protocol stream. Clients and servers are
2376    not required to use these formats for user presentation, request
2377    logging, etc.
2378  </t>
2379</x:note>
2380</section>
2381
2382<section title="Product Tokens" anchor="product.tokens">
2383  <x:anchor-alias value="product"/>
2384  <x:anchor-alias value="product-version"/>
2385<t>
2386   Product tokens are used to allow communicating applications to
2387   identify themselves by software name and version. Most fields using
2388   product tokens also allow sub-products which form a significant part
2389   of the application to be listed, separated by whitespace. By
2390   convention, the products are listed in order of their significance
2391   for identifying the application.
2392</t>
2393<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2394  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2395  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2396</artwork></figure>
2397<t>
2398   Examples:
2399</t>
2400<figure><artwork type="example">
2401  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2402  Server: Apache/0.8.4
2403</artwork></figure>
2404<t>
2405   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2406   used for advertising or other non-essential information. Although any
2407   token octet &MAY; appear in a product-version, this token &SHOULD;
2408   only be used for a version identifier (i.e., successive versions of
2409   the same product &SHOULD; only differ in the product-version portion of
2410   the product value).
2411</t>
2412</section>
2413
2414
2415<section title="Header Field Definitions" anchor="header.field.definitions">
2416<t>
2417   This section defines the syntax and semantics of HTTP/1.1 header fields
2418   related to request and response semantics.
2419</t>
2420
2421<section title="Allow" anchor="header.allow">
2422  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2423  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2424  <x:anchor-alias value="Allow"/>
2425<t>
2426   The "Allow" header field lists the set of methods advertised as
2427   supported by the target resource. The purpose of this field is strictly to
2428   inform the recipient of valid request methods associated with the resource.
2429</t>
2430<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2431  <x:ref>Allow</x:ref> = #<x:ref>method</x:ref>
2432</artwork></figure>
2433<t>
2434   Example of use:
2435</t>
2436<figure><artwork type="example">
2437  Allow: GET, HEAD, PUT
2438</artwork></figure>
2439<t>
2440   The actual set of allowed methods is defined by the origin server at the
2441   time of each request.
2442</t>
2443<t>
2444   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2445   understand all the methods specified in order to handle them according to
2446   the generic message handling rules.
2447</t>
2448</section>
2449
2450<section title="Date" anchor="header.date">
2451  <iref primary="true" item="Date header field" x:for-anchor=""/>
2452  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2453  <x:anchor-alias value="Date"/>
2454<t>
2455   The "Date" header field represents the date and time at which
2456   the message was originated, having the same semantics as the Origination
2457   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2458   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2459   it &MUST; be sent in rfc1123-date format.
2460</t>
2461<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2462  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2463</artwork></figure>
2464<t>
2465   An example is
2466</t>
2467<figure><artwork type="example">
2468  Date: Tue, 15 Nov 1994 08:12:31 GMT
2469</artwork></figure>
2470<t>
2471   Origin servers &MUST; include a Date header field in all responses,
2472   except in these cases:
2473  <list style="numbers">
2474      <t>If the response status code is 100 (Continue) or 101 (Switching
2475         Protocols), the response &MAY; include a Date header field, at
2476         the server's option.</t>
2477
2478      <t>If the response status code conveys a server error, e.g., 500
2479         (Internal Server Error) or 503 (Service Unavailable), and it is
2480         inconvenient or impossible to generate a valid Date.</t>
2481
2482      <t>If the server does not have a clock that can provide a
2483         reasonable approximation of the current time, its responses
2484         &MUST-NOT; include a Date header field.</t>
2485  </list>
2486</t>
2487<t>
2488   A received message that does not have a Date header field &MUST; be
2489   assigned one by the recipient if the message will be cached by that
2490   recipient.
2491</t>
2492<t>
2493   Clients can use the Date header field as well; in order to keep request
2494   messages small, they are advised not to include it when it doesn't convey
2495   any useful information (as is usually the case for requests that do not
2496   contain a payload).
2497</t>
2498<t>
2499   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2500   time subsequent to the generation of the message. It &SHOULD; represent
2501   the best available approximation of the date and time of message
2502   generation, unless the implementation has no means of generating a
2503   reasonably accurate date and time. In theory, the date ought to
2504   represent the moment just before the payload is generated. In
2505   practice, the date can be generated at any time during the message
2506   origination without affecting its semantic value.
2507</t>
2508</section>
2509
2510<section title="Expect" anchor="header.expect">
2511  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2512  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2513  <x:anchor-alias value="Expect"/>
2514  <x:anchor-alias value="expectation"/>
2515  <x:anchor-alias value="expect-param"/>
2516  <x:anchor-alias value="expect-name"/>
2517  <x:anchor-alias value="expect-value"/>
2518<t>
2519   The "Expect" header field is used to indicate that particular
2520   server behaviors are required by the client.
2521</t>
2522<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"/>
2523  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2524 
2525  <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> ]
2526                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2527  <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> ]
2528 
2529  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2530  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2531</artwork></figure>
2532<t>
2533   If all received Expect header field(s) are syntactically valid but contain
2534   an expectation that the recipient does not understand or cannot comply with,
2535   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2536   recipient of a syntactically invalid Expectation header field &MUST; respond
2537   with a 4xx status code other than 417.
2538</t>
2539<t>
2540   The only expectation defined by this specification is:
2541</t>
2542<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2543  100-continue
2544   <list>
2545      <t>
2546        The "100-continue" expectation is defined &use100;. It does not support
2547        any expect-params.
2548      </t>
2549   </list>
2550</t>
2551<t>
2552   Comparison is case-insensitive for names (expect-name), and case-sensitive
2553   for values (expect-value).
2554</t>
2555<t>
2556   The Expect mechanism is hop-by-hop: the above requirements apply to any
2557   server, including proxies. However, the Expect header field itself is
2558   end-to-end; it &MUST; be forwarded if the request is forwarded.
2559</t>
2560<t>
2561   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2562   header field.
2563</t>
2564</section>
2565
2566<section title="From" anchor="header.from">
2567  <iref primary="true" item="From header field" x:for-anchor=""/>
2568  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2569  <x:anchor-alias value="From"/>
2570  <x:anchor-alias value="mailbox"/>
2571<t>
2572   The "From" header field, if given, &SHOULD; contain an Internet
2573   e-mail address for the human user who controls the requesting user
2574   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2575   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2576</t>
2577<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2578  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2579 
2580  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2581</artwork></figure>
2582<t>
2583   An example is:
2584</t>
2585<figure><artwork type="example">
2586  From: webmaster@example.org
2587</artwork></figure>
2588<t>
2589   This header field &MAY; be used for logging purposes and as a means for
2590   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2591   be used as an insecure form of access protection. The interpretation
2592   of this field is that the request is being performed on behalf of the
2593   person given, who accepts responsibility for the method performed. In
2594   particular, robot agents &SHOULD; include this header field so that the
2595   person responsible for running the robot can be contacted if problems
2596   occur on the receiving end.
2597</t>
2598<t>
2599   The Internet e-mail address in this field &MAY; be separate from the
2600   Internet host which issued the request. For example, when a request
2601   is passed through a proxy the original issuer's address &SHOULD; be
2602   used.
2603</t>
2604<t>
2605   The client &SHOULD-NOT;  send the From header field without the user's
2606   approval, as it might conflict with the user's privacy interests or
2607   their site's security policy. It is strongly recommended that the
2608   user be able to disable, enable, and modify the value of this field
2609   at any time prior to a request.
2610</t>
2611</section>
2612
2613<section title="Location" anchor="header.location">
2614  <iref primary="true" item="Location header field" x:for-anchor=""/>
2615  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2616  <x:anchor-alias value="Location"/>
2617<t>
2618   The "Location" header field &MAY; be sent in responses to refer to
2619   a specific resource in accordance with the semantics of the status
2620   code.
2621</t>
2622<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2623  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2624</artwork></figure>
2625<t>
2626   For 201 (Created) responses, the Location is the URI of the new resource
2627   which was created by the request. For 3xx responses, the location &SHOULD;
2628   indicate the server's preferred URI for automatic redirection to the
2629   resource.
2630</t>
2631<t>
2632   The field value consists of a single URI-reference. When it has the form
2633   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2634   the final value is computed by resolving it against the effective request
2635   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2636   navigated to by the user agent, did contain a fragment identifier, and the
2637   final value does not, then the original URI's fragment identifier is added
2638   to the final value.
2639</t>
2640<figure>
2641<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-->
2642<artwork type="example">
2643  Location: /pub/WWW/People.html#tim
2644</artwork>
2645<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2646</figure>
2647<figure>
2648<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-->
2649<artwork type="example">
2650  Location: http://www.example.net/index.html
2651</artwork>
2652<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2653</figure>
2654<x:note>
2655  <t>
2656    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2657    that are not valid URI references. This specification does not mandate or
2658    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2659  </t>
2660</x:note>
2661<t>
2662   There are circumstances in which a fragment identifier in a Location URI
2663   would not be appropriate. For instance, when it appears in a 201 Created
2664   response, where the Location header field specifies the URI for the entire
2665   created resource.
2666</t>
2667<x:note>
2668  <t>
2669    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2670    from Location in that the Content-Location identifies the most specific
2671    resource corresponding to the enclosed representation.
2672    It is therefore possible for a response to contain header fields for
2673    both Location and Content-Location.
2674  </t>
2675</x:note>
2676</section>
2677
2678<section title="Max-Forwards" anchor="header.max-forwards">
2679  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2680  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2681  <x:anchor-alias value="Max-Forwards"/>
2682<t>
2683   The "Max-Forwards" header field provides a mechanism with the
2684   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2685   methods to limit the number of times that the request is forwarded by
2686   proxies. This can be useful when the client is attempting to
2687   trace a request which appears to be failing or looping mid-chain.
2688</t>
2689<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2690  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2691</artwork></figure>
2692<t>
2693   The Max-Forwards value is a decimal integer indicating the remaining
2694   number of times this request message can be forwarded.
2695</t>
2696<t>
2697   Each recipient of a TRACE or OPTIONS request
2698   containing a Max-Forwards header field &MUST; check and update its
2699   value prior to forwarding the request. If the received value is zero
2700   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2701   respond as the final recipient. If the received Max-Forwards value is
2702   greater than zero, then the forwarded message &MUST; contain an updated
2703   Max-Forwards field with a value decremented by one (1).
2704</t>
2705<t>
2706   The Max-Forwards header field &MAY; be ignored for all other request
2707   methods.
2708</t>
2709</section>
2710
2711<section title="Referer" anchor="header.referer">
2712  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2713  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2714  <x:anchor-alias value="Referer"/>
2715<t>
2716   The "Referer" [sic] header field allows the client to specify the
2717   URI of the resource from which the effective request URI was obtained (the
2718   "referrer", although the header field is misspelled.).
2719</t>
2720<t>
2721   The Referer header field allows servers to generate lists of back-links to
2722   resources for interest, logging, optimized caching, etc. It also allows
2723   obsolete or mistyped links to be traced for maintenance. Some servers use
2724   Referer as a means of controlling where they allow links from (so-called
2725   "deep linking"), but legitimate requests do not always
2726   contain a Referer header field.
2727</t>
2728<t>
2729   If the effective request URI was obtained from a source that does not have its own
2730   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2731   sent with the value "about:blank", or not be sent at all. Note that this
2732   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2733</t>
2734<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2735  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2736</artwork></figure>
2737<t>
2738   Example:
2739</t>
2740<figure><artwork type="example">
2741  Referer: http://www.example.org/hypertext/Overview.html
2742</artwork></figure>
2743<t>
2744   If the field value is a relative URI, it &SHOULD; be interpreted
2745   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2746   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2747</t>
2748</section>
2749
2750<section title="Retry-After" anchor="header.retry-after">
2751  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2752  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2753  <x:anchor-alias value="Retry-After"/>
2754<t>
2755   The header "Retry-After" field can be used with a 503 (Service
2756   Unavailable) response to indicate how long the service is expected to
2757   be unavailable to the requesting client. This field &MAY; also be used
2758   with any 3xx (Redirection) response to indicate the minimum time the
2759   user-agent is asked to wait before issuing the redirected request.
2760</t>
2761<t>
2762   The value of this field can be either an HTTP-date or an integer number
2763   of seconds (in decimal) after the time of the response.
2764</t>
2765<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2766  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2767</artwork></figure>
2768<t anchor="rule.delta-seconds">
2769  <x:anchor-alias value="delta-seconds"/>
2770   Time spans are non-negative decimal integers, representing time in
2771   seconds.
2772</t>
2773<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2774  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2775</artwork></figure>
2776<t>
2777   Two examples of its use are
2778</t>
2779<figure><artwork type="example">
2780  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2781  Retry-After: 120
2782</artwork></figure>
2783<t>
2784   In the latter example, the delay is 2 minutes.
2785</t>
2786</section>
2787
2788<section title="Server" anchor="header.server">
2789  <iref primary="true" item="Server header field" x:for-anchor=""/>
2790  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2791  <x:anchor-alias value="Server"/>
2792<t>
2793   The "Server" header field contains information about the
2794   software used by the origin server to handle the request.
2795</t>
2796<t>
2797   The field can contain multiple
2798   product tokens (<xref target="product.tokens"/>) and
2799   comments (&header-fields;) identifying the server and any significant
2800   subproducts. The product tokens are listed in order of their significance
2801   for identifying the application.
2802</t>
2803<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2804  <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> ) )
2805</artwork></figure>
2806<t>
2807   Example:
2808</t>
2809<figure><artwork type="example">
2810  Server: CERN/3.0 libwww/2.17
2811</artwork></figure>
2812<t>
2813   If the response is being forwarded through a proxy, the proxy
2814   application &MUST-NOT; modify the Server header field. Instead, it
2815   &MUST; include a Via field (as described in &header-via;).
2816</t>
2817<x:note>
2818  <t>
2819    <x:h>Note:</x:h> Revealing the specific software version of the server might
2820    allow the server machine to become more vulnerable to attacks
2821    against software that is known to contain security holes. Server
2822    implementors are encouraged to make this field a configurable
2823    option.
2824  </t>
2825</x:note>
2826</section>
2827
2828<section title="User-Agent" anchor="header.user-agent">
2829  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2830  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2831  <x:anchor-alias value="User-Agent"/>
2832<t>
2833   The "User-Agent" header field contains information about the user
2834   agent originating the request. User agents &SHOULD; include this field with
2835   requests.
2836</t>
2837<t>
2838   Typically, it is used for statistical purposes, the tracing of protocol
2839   violations, and tailoring responses to avoid particular user agent
2840   limitations.
2841</t>
2842<t>
2843   The field can contain multiple
2844   product tokens (<xref target="product.tokens"/>)
2845   and comments (&header-fields;) identifying the agent and its
2846   significant subproducts. By convention, the product tokens are listed in
2847   order of their significance for identifying the application.
2848</t>
2849<t>
2850   Because this field is usually sent on every request a user agent makes,
2851   implementations are encouraged not to include needlessly fine-grained
2852   detail, and to limit (or even prohibit) the addition of subproducts by third
2853   parties. Overly long and detailed User-Agent field values make requests
2854   larger and can also be used to identify ("fingerprint") the user against
2855   their wishes.
2856</t>
2857<t>
2858   Likewise, implementations are encouraged not to use the product tokens of
2859   other implementations in order to declare compatibility with them, as this
2860   circumvents the purpose of the field. Finally, they are encouraged not to
2861   use comments to identify products; doing so makes the field value more
2862   difficult to parse.
2863</t>
2864<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2865  <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> ) )
2866</artwork></figure>
2867<t>
2868   Example:
2869</t>
2870<figure><artwork type="example">
2871  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2872</artwork></figure>
2873</section>
2874
2875</section>
2876
2877<section title="IANA Considerations" anchor="IANA.considerations">
2878
2879<section title="Method Registry" anchor="method.registration">
2880<t>
2881  The registration procedure for HTTP request methods is defined by
2882  <xref target="method.registry"/> of this document.
2883</t>
2884<t>
2885   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2886   and be populated with the registrations below:
2887</t>
2888<?BEGININC p2-semantics.iana-methods ?>
2889<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2890<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2891   <ttcol>Method</ttcol>
2892   <ttcol>Safe</ttcol>
2893   <ttcol>Reference</ttcol>
2894   <c>CONNECT</c>
2895   <c>no</c>
2896   <c>
2897      <xref target="CONNECT"/>
2898   </c>
2899   <c>DELETE</c>
2900   <c>no</c>
2901   <c>
2902      <xref target="DELETE"/>
2903   </c>
2904   <c>GET</c>
2905   <c>yes</c>
2906   <c>
2907      <xref target="GET"/>
2908   </c>
2909   <c>HEAD</c>
2910   <c>yes</c>
2911   <c>
2912      <xref target="HEAD"/>
2913   </c>
2914   <c>OPTIONS</c>
2915   <c>yes</c>
2916   <c>
2917      <xref target="OPTIONS"/>
2918   </c>
2919   <c>POST</c>
2920   <c>no</c>
2921   <c>
2922      <xref target="POST"/>
2923   </c>
2924   <c>PUT</c>
2925   <c>no</c>
2926   <c>
2927      <xref target="PUT"/>
2928   </c>
2929   <c>TRACE</c>
2930   <c>yes</c>
2931   <c>
2932      <xref target="TRACE"/>
2933   </c>
2934</texttable>
2935<!--(END)-->
2936<?ENDINC p2-semantics.iana-methods ?>
2937</section>
2938
2939<section title="Status Code Registry" anchor="status.code.registration">
2940<t>
2941   The registration procedure for HTTP Status Codes &mdash; previously defined
2942   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2943   by <xref target="status.code.registry"/> of this document.
2944</t>
2945<t>
2946   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2947   shall be updated with the registrations below:
2948</t>
2949<?BEGININC p2-semantics.iana-status-codes ?>
2950<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2951<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2952   <ttcol>Value</ttcol>
2953   <ttcol>Description</ttcol>
2954   <ttcol>Reference</ttcol>
2955   <c>100</c>
2956   <c>Continue</c>
2957   <c>
2958      <xref target="status.100"/>
2959   </c>
2960   <c>101</c>
2961   <c>Switching Protocols</c>
2962   <c>
2963      <xref target="status.101"/>
2964   </c>
2965   <c>200</c>
2966   <c>OK</c>
2967   <c>
2968      <xref target="status.200"/>
2969   </c>
2970   <c>201</c>
2971   <c>Created</c>
2972   <c>
2973      <xref target="status.201"/>
2974   </c>
2975   <c>202</c>
2976   <c>Accepted</c>
2977   <c>
2978      <xref target="status.202"/>
2979   </c>
2980   <c>203</c>
2981   <c>Non-Authoritative Information</c>
2982   <c>
2983      <xref target="status.203"/>
2984   </c>
2985   <c>204</c>
2986   <c>No Content</c>
2987   <c>
2988      <xref target="status.204"/>
2989   </c>
2990   <c>205</c>
2991   <c>Reset Content</c>
2992   <c>
2993      <xref target="status.205"/>
2994   </c>
2995   <c>300</c>
2996   <c>Multiple Choices</c>
2997   <c>
2998      <xref target="status.300"/>
2999   </c>
3000   <c>301</c>
3001   <c>Moved Permanently</c>
3002   <c>
3003      <xref target="status.301"/>
3004   </c>
3005   <c>302</c>
3006   <c>Found</c>
3007   <c>
3008      <xref target="status.302"/>
3009   </c>
3010   <c>303</c>
3011   <c>See Other</c>
3012   <c>
3013      <xref target="status.303"/>
3014   </c>
3015   <c>305</c>
3016   <c>Use Proxy</c>
3017   <c>
3018      <xref target="status.305"/>
3019   </c>
3020   <c>306</c>
3021   <c>(Unused)</c>
3022   <c>
3023      <xref target="status.306"/>
3024   </c>
3025   <c>307</c>
3026   <c>Temporary Redirect</c>
3027   <c>
3028      <xref target="status.307"/>
3029   </c>
3030   <c>400</c>
3031   <c>Bad Request</c>
3032   <c>
3033      <xref target="status.400"/>
3034   </c>
3035   <c>402</c>
3036   <c>Payment Required</c>
3037   <c>
3038      <xref target="status.402"/>
3039   </c>
3040   <c>403</c>
3041   <c>Forbidden</c>
3042   <c>
3043      <xref target="status.403"/>
3044   </c>
3045   <c>404</c>
3046   <c>Not Found</c>
3047   <c>
3048      <xref target="status.404"/>
3049   </c>
3050   <c>405</c>
3051   <c>Method Not Allowed</c>
3052   <c>
3053      <xref target="status.405"/>
3054   </c>
3055   <c>406</c>
3056   <c>Not Acceptable</c>
3057   <c>
3058      <xref target="status.406"/>
3059   </c>
3060   <c>408</c>
3061   <c>Request Timeout</c>
3062   <c>
3063      <xref target="status.408"/>
3064   </c>
3065   <c>409</c>
3066   <c>Conflict</c>
3067   <c>
3068      <xref target="status.409"/>
3069   </c>
3070   <c>410</c>
3071   <c>Gone</c>
3072   <c>
3073      <xref target="status.410"/>
3074   </c>
3075   <c>411</c>
3076   <c>Length Required</c>
3077   <c>
3078      <xref target="status.411"/>
3079   </c>
3080   <c>413</c>
3081   <c>Request Representation Too Large</c>
3082   <c>
3083      <xref target="status.413"/>
3084   </c>
3085   <c>414</c>
3086   <c>URI Too Long</c>
3087   <c>
3088      <xref target="status.414"/>
3089   </c>
3090   <c>415</c>
3091   <c>Unsupported Media Type</c>
3092   <c>
3093      <xref target="status.415"/>
3094   </c>
3095   <c>417</c>
3096   <c>Expectation Failed</c>
3097   <c>
3098      <xref target="status.417"/>
3099   </c>
3100   <c>426</c>
3101   <c>Upgrade Required</c>
3102   <c>
3103      <xref target="status.426"/>
3104   </c>
3105   <c>500</c>
3106   <c>Internal Server Error</c>
3107   <c>
3108      <xref target="status.500"/>
3109   </c>
3110   <c>501</c>
3111   <c>Not Implemented</c>
3112   <c>
3113      <xref target="status.501"/>
3114   </c>
3115   <c>502</c>
3116   <c>Bad Gateway</c>
3117   <c>
3118      <xref target="status.502"/>
3119   </c>
3120   <c>503</c>
3121   <c>Service Unavailable</c>
3122   <c>
3123      <xref target="status.503"/>
3124   </c>
3125   <c>504</c>
3126   <c>Gateway Timeout</c>
3127   <c>
3128      <xref target="status.504"/>
3129   </c>
3130   <c>505</c>
3131   <c>HTTP Version Not Supported</c>
3132   <c>
3133      <xref target="status.505"/>
3134   </c>
3135</texttable>
3136<!--(END)-->
3137<?ENDINC p2-semantics.iana-status-codes ?>
3138</section>
3139<section title="Header Field Registration" anchor="header.field.registration">
3140<t>
3141   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3142   with the permanent registrations below (see <xref target="RFC3864"/>):
3143</t>
3144<?BEGININC p2-semantics.iana-headers ?>
3145<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3146<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3147   <ttcol>Header Field Name</ttcol>
3148   <ttcol>Protocol</ttcol>
3149   <ttcol>Status</ttcol>
3150   <ttcol>Reference</ttcol>
3151
3152   <c>Allow</c>
3153   <c>http</c>
3154   <c>standard</c>
3155   <c>
3156      <xref target="header.allow"/>
3157   </c>
3158   <c>Date</c>
3159   <c>http</c>
3160   <c>standard</c>
3161   <c>
3162      <xref target="header.date"/>
3163   </c>
3164   <c>Expect</c>
3165   <c>http</c>
3166   <c>standard</c>
3167   <c>
3168      <xref target="header.expect"/>
3169   </c>
3170   <c>From</c>
3171   <c>http</c>
3172   <c>standard</c>
3173   <c>
3174      <xref target="header.from"/>
3175   </c>
3176   <c>Location</c>
3177   <c>http</c>
3178   <c>standard</c>
3179   <c>
3180      <xref target="header.location"/>
3181   </c>
3182   <c>Max-Forwards</c>
3183   <c>http</c>
3184   <c>standard</c>
3185   <c>
3186      <xref target="header.max-forwards"/>
3187   </c>
3188   <c>Referer</c>
3189   <c>http</c>
3190   <c>standard</c>
3191   <c>
3192      <xref target="header.referer"/>
3193   </c>
3194   <c>Retry-After</c>
3195   <c>http</c>
3196   <c>standard</c>
3197   <c>
3198      <xref target="header.retry-after"/>
3199   </c>
3200   <c>Server</c>
3201   <c>http</c>
3202   <c>standard</c>
3203   <c>
3204      <xref target="header.server"/>
3205   </c>
3206   <c>User-Agent</c>
3207   <c>http</c>
3208   <c>standard</c>
3209   <c>
3210      <xref target="header.user-agent"/>
3211   </c>
3212</texttable>
3213<!--(END)-->
3214<?ENDINC p2-semantics.iana-headers ?>
3215<t>
3216   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3217</t>
3218</section>
3219</section>
3220
3221<section title="Security Considerations" anchor="security.considerations">
3222<t>
3223   This section is meant to inform application developers, information
3224   providers, and users of the security limitations in HTTP/1.1 as
3225   described by this document. The discussion does not include
3226   definitive solutions to the problems revealed, though it does make
3227   some suggestions for reducing security risks.
3228</t>
3229
3230<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3231<t>
3232   Like any generic data transfer protocol, HTTP cannot regulate the
3233   content of the data that is transferred, nor is there any a priori
3234   method of determining the sensitivity of any particular piece of
3235   information within the context of any given request. Therefore,
3236   applications &SHOULD; supply as much control over this information as
3237   possible to the provider of that information. Four header fields are
3238   worth special mention in this context: Server, Via, Referer and From.
3239</t>
3240<t>
3241   Revealing the specific software version of the server might allow the
3242   server machine to become more vulnerable to attacks against software
3243   that is known to contain security holes. Implementors &SHOULD; make the
3244   Server header field a configurable option.
3245</t>
3246<t>
3247   Proxies which serve as a portal through a network firewall &SHOULD;
3248   take special precautions regarding the transfer of header information
3249   that identifies the hosts behind the firewall. In particular, they
3250   &SHOULD; remove, or replace with sanitized versions, any Via fields
3251   generated behind the firewall.
3252</t>
3253<t>
3254   The Referer header field allows reading patterns to be studied and reverse
3255   links drawn. Although it can be very useful, its power can be abused
3256   if user details are not separated from the information contained in
3257   the Referer. Even when the personal information has been removed, the
3258   Referer header field might indicate a private document's URI whose
3259   publication would be inappropriate.
3260</t>
3261<t>
3262   The information sent in the From field might conflict with the user's
3263   privacy interests or their site's security policy, and hence it
3264   &SHOULD-NOT;  be transmitted without the user being able to disable,
3265   enable, and modify the contents of the field. The user &MUST; be able
3266   to set the contents of this field within a user preference or
3267   application defaults configuration.
3268</t>
3269<t>
3270   We suggest, though do not require, that a convenient toggle interface
3271   be provided for the user to enable or disable the sending of From and
3272   Referer information.
3273</t>
3274<t>
3275   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3276   target="header.server"/>) header fields can sometimes be used to determine
3277   that a specific client or server has a particular security hole which might
3278   be exploited. Unfortunately, this same information is often used for other
3279   valuable purposes for which HTTP currently has no better mechanism.
3280</t>
3281<t>
3282   Furthermore, the User-Agent header field may contain enough entropy to be
3283   used, possibly in conjunction with other material, to uniquely identify the
3284   user.
3285</t>
3286<t>
3287   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3288   that was sent in request header fields within the body of their response.
3289   Clients &SHOULD; be careful with sensitive information, like Cookies,
3290   Authorization credentials, and other header fields that might be used to
3291   collect data from the client.
3292</t> 
3293</section>
3294
3295<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3296<t>
3297   Because the source of a link might be private information or might
3298   reveal an otherwise private information source, it is strongly
3299   recommended that the user be able to select whether or not the
3300   Referer field is sent. For example, a browser client could have a
3301   toggle switch for browsing openly/anonymously, which would
3302   respectively enable/disable the sending of Referer and From
3303   information.
3304</t>
3305<t>
3306   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3307   HTTP request if the referring page was transferred with a secure
3308   protocol.
3309</t>
3310<t>
3311   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3312   sensitive data because that data will be placed in the request-target. Many
3313   existing servers, proxies, and user agents log or display the request-target
3314   in places where it might be visible to third parties. Such services can
3315   use POST-based form submission instead.
3316</t>
3317</section>
3318
3319<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3320<t>
3321   If a single server supports multiple organizations that do not trust
3322   one another, then it &MUST; check the values of Location and Content-Location
3323   header fields in responses that are generated under control of
3324   said organizations to make sure that they do not attempt to
3325   invalidate resources over which they have no authority.
3326</t>
3327<t>
3328   Furthermore, appending the fragment identifier from one URI to another
3329   one obtained from a Location header field might leak confidential
3330   information to the target server &mdash; although the fragment identifier is
3331   not transmitted in the final request, it might be visible to the user agent
3332   through other means, such as scripting.
3333</t>
3334</section>
3335
3336<section title="Security Considerations for CONNECT">
3337<t>
3338   Since tunneled data is opaque to the proxy, there are additional
3339   risks to tunneling to other well-known or reserved ports.
3340   A HTTP client CONNECTing to port 25 could relay spam
3341   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3342   access to a small number of known ports.
3343</t>
3344</section>
3345
3346</section>
3347
3348<section title="Acknowledgments" anchor="acks">
3349<t>
3350  See &acks;.
3351</t>
3352</section>
3353</middle>
3354<back>
3355
3356<references title="Normative References">
3357
3358<reference anchor="Part1">
3359  <front>
3360    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3361    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3362      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3363      <address><email>fielding@gbiv.com</email></address>
3364    </author>
3365    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3366      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3367      <address><email>jg@freedesktop.org</email></address>
3368    </author>
3369    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3370      <organization abbrev="HP">Hewlett-Packard Company</organization>
3371      <address><email>JeffMogul@acm.org</email></address>
3372    </author>
3373    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3374      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3375      <address><email>henrikn@microsoft.com</email></address>
3376    </author>
3377    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3378      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3379      <address><email>LMM@acm.org</email></address>
3380    </author>
3381    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3382      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3383      <address><email>paulle@microsoft.com</email></address>
3384    </author>
3385    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3386      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3387      <address><email>timbl@w3.org</email></address>
3388    </author>
3389    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3390      <organization abbrev="W3C">World Wide Web Consortium</organization>
3391      <address><email>ylafon@w3.org</email></address>
3392    </author>
3393    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3394      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3395      <address><email>julian.reschke@greenbytes.de</email></address>
3396    </author>
3397    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3398  </front>
3399  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3400  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3401</reference>
3402
3403<reference anchor="Part3">
3404  <front>
3405    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3406    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3407      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3408      <address><email>fielding@gbiv.com</email></address>
3409    </author>
3410    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3411      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3412      <address><email>jg@freedesktop.org</email></address>
3413    </author>
3414    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3415      <organization abbrev="HP">Hewlett-Packard Company</organization>
3416      <address><email>JeffMogul@acm.org</email></address>
3417    </author>
3418    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3419      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3420      <address><email>henrikn@microsoft.com</email></address>
3421    </author>
3422    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3423      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3424      <address><email>LMM@acm.org</email></address>
3425    </author>
3426    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3427      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3428      <address><email>paulle@microsoft.com</email></address>
3429    </author>
3430    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3431      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3432      <address><email>timbl@w3.org</email></address>
3433    </author>
3434    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3435      <organization abbrev="W3C">World Wide Web Consortium</organization>
3436      <address><email>ylafon@w3.org</email></address>
3437    </author>
3438    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3439      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3440      <address><email>julian.reschke@greenbytes.de</email></address>
3441    </author>
3442    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3443  </front>
3444  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3445  <x:source href="p3-payload.xml" basename="p3-payload"/>
3446</reference>
3447
3448<reference anchor="Part4">
3449  <front>
3450    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3451    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3452      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3453      <address><email>fielding@gbiv.com</email></address>
3454    </author>
3455    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3456      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3457      <address><email>jg@freedesktop.org</email></address>
3458    </author>
3459    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3460      <organization abbrev="HP">Hewlett-Packard Company</organization>
3461      <address><email>JeffMogul@acm.org</email></address>
3462    </author>
3463    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3464      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3465      <address><email>henrikn@microsoft.com</email></address>
3466    </author>
3467    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3468      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3469      <address><email>LMM@acm.org</email></address>
3470    </author>
3471    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3472      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3473      <address><email>paulle@microsoft.com</email></address>
3474    </author>
3475    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3476      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3477      <address><email>timbl@w3.org</email></address>
3478    </author>
3479    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3480      <organization abbrev="W3C">World Wide Web Consortium</organization>
3481      <address><email>ylafon@w3.org</email></address>
3482    </author>
3483    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3484      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3485      <address><email>julian.reschke@greenbytes.de</email></address>
3486    </author>
3487    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3488  </front>
3489  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3490  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3491</reference>
3492
3493<reference anchor="Part5">
3494  <front>
3495    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3496    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3497      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3498      <address><email>fielding@gbiv.com</email></address>
3499    </author>
3500    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3501      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3502      <address><email>jg@freedesktop.org</email></address>
3503    </author>
3504    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3505      <organization abbrev="HP">Hewlett-Packard Company</organization>
3506      <address><email>JeffMogul@acm.org</email></address>
3507    </author>
3508    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3509      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3510      <address><email>henrikn@microsoft.com</email></address>
3511    </author>
3512    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3513      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3514      <address><email>LMM@acm.org</email></address>
3515    </author>
3516    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3517      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3518      <address><email>paulle@microsoft.com</email></address>
3519    </author>
3520    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3521      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3522      <address><email>timbl@w3.org</email></address>
3523    </author>
3524    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3525      <organization abbrev="W3C">World Wide Web Consortium</organization>
3526      <address><email>ylafon@w3.org</email></address>
3527    </author>
3528    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3529      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3530      <address><email>julian.reschke@greenbytes.de</email></address>
3531    </author>
3532    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3533  </front>
3534  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3535  <x:source href="p5-range.xml" basename="p5-range"/>
3536</reference>
3537
3538<reference anchor="Part6">
3539  <front>
3540    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3541    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3542      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3543      <address><email>fielding@gbiv.com</email></address>
3544    </author>
3545    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3546      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3547      <address><email>jg@freedesktop.org</email></address>
3548    </author>
3549    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3550      <organization abbrev="HP">Hewlett-Packard Company</organization>
3551      <address><email>JeffMogul@acm.org</email></address>
3552    </author>
3553    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3554      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3555      <address><email>henrikn@microsoft.com</email></address>
3556    </author>
3557    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3558      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3559      <address><email>LMM@acm.org</email></address>
3560    </author>
3561    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3562      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3563      <address><email>paulle@microsoft.com</email></address>
3564    </author>
3565    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3566      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3567      <address><email>timbl@w3.org</email></address>
3568    </author>
3569    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3570      <organization abbrev="W3C">World Wide Web Consortium</organization>
3571      <address><email>ylafon@w3.org</email></address>
3572    </author>
3573    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3574      <organization>Rackspace</organization>
3575      <address><email>mnot@mnot.net</email></address>
3576    </author>
3577    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3578      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3579      <address><email>julian.reschke@greenbytes.de</email></address>
3580    </author>
3581    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3582  </front>
3583  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3584  <x:source href="p6-cache.xml" basename="p6-cache"/>
3585</reference>
3586
3587<reference anchor="Part7">
3588  <front>
3589    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3590    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3591      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3592      <address><email>fielding@gbiv.com</email></address>
3593    </author>
3594    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3595      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3596      <address><email>jg@freedesktop.org</email></address>
3597    </author>
3598    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3599      <organization abbrev="HP">Hewlett-Packard Company</organization>
3600      <address><email>JeffMogul@acm.org</email></address>
3601    </author>
3602    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3603      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3604      <address><email>henrikn@microsoft.com</email></address>
3605    </author>
3606    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3607      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3608      <address><email>LMM@acm.org</email></address>
3609    </author>
3610    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3611      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3612      <address><email>paulle@microsoft.com</email></address>
3613    </author>
3614    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3615      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3616      <address><email>timbl@w3.org</email></address>
3617    </author>
3618    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3619      <organization abbrev="W3C">World Wide Web Consortium</organization>
3620      <address><email>ylafon@w3.org</email></address>
3621    </author>
3622    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3623      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3624      <address><email>julian.reschke@greenbytes.de</email></address>
3625    </author>
3626    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3627  </front>
3628  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3629  <x:source href="p7-auth.xml" basename="p7-auth"/>
3630</reference>
3631
3632<reference anchor="RFC2119">
3633  <front>
3634    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3635    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3636      <organization>Harvard University</organization>
3637      <address><email>sob@harvard.edu</email></address>
3638    </author>
3639    <date month="March" year="1997"/>
3640  </front>
3641  <seriesInfo name="BCP" value="14"/>
3642  <seriesInfo name="RFC" value="2119"/>
3643</reference>
3644
3645<reference anchor="RFC3986">
3646 <front>
3647  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3648  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3649    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3650    <address>
3651       <email>timbl@w3.org</email>
3652       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3653    </address>
3654  </author>
3655  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3656    <organization abbrev="Day Software">Day Software</organization>
3657    <address>
3658      <email>fielding@gbiv.com</email>
3659      <uri>http://roy.gbiv.com/</uri>
3660    </address>
3661  </author>
3662  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3663    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3664    <address>
3665      <email>LMM@acm.org</email>
3666      <uri>http://larry.masinter.net/</uri>
3667    </address>
3668  </author>
3669  <date month='January' year='2005'></date>
3670 </front>
3671 <seriesInfo name="STD" value="66"/>
3672 <seriesInfo name="RFC" value="3986"/>
3673</reference>
3674
3675<reference anchor="RFC5234">
3676  <front>
3677    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3678    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3679      <organization>Brandenburg InternetWorking</organization>
3680      <address>
3681        <email>dcrocker@bbiw.net</email>
3682      </address> 
3683    </author>
3684    <author initials="P." surname="Overell" fullname="Paul Overell">
3685      <organization>THUS plc.</organization>
3686      <address>
3687        <email>paul.overell@thus.net</email>
3688      </address>
3689    </author>
3690    <date month="January" year="2008"/>
3691  </front>
3692  <seriesInfo name="STD" value="68"/>
3693  <seriesInfo name="RFC" value="5234"/>
3694</reference>
3695
3696</references>
3697
3698<references title="Informative References">
3699
3700<reference anchor="RFC1123">
3701  <front>
3702    <title>Requirements for Internet Hosts - Application and Support</title>
3703    <author initials="R." surname="Braden" fullname="Robert Braden">
3704      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3705      <address><email>Braden@ISI.EDU</email></address>
3706    </author>
3707    <date month="October" year="1989"/>
3708  </front>
3709  <seriesInfo name="STD" value="3"/>
3710  <seriesInfo name="RFC" value="1123"/>
3711</reference>
3712
3713<reference anchor="RFC1945">
3714  <front>
3715    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3716    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3717      <organization>MIT, Laboratory for Computer Science</organization>
3718      <address><email>timbl@w3.org</email></address>
3719    </author>
3720    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3721      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3722      <address><email>fielding@ics.uci.edu</email></address>
3723    </author>
3724    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3725      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3726      <address><email>frystyk@w3.org</email></address>
3727    </author>
3728    <date month="May" year="1996"/>
3729  </front>
3730  <seriesInfo name="RFC" value="1945"/>
3731</reference>
3732
3733<reference anchor="RFC2068">
3734  <front>
3735    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3736    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3737      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3738      <address><email>fielding@ics.uci.edu</email></address>
3739    </author>
3740    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3741      <organization>MIT Laboratory for Computer Science</organization>
3742      <address><email>jg@w3.org</email></address>
3743    </author>
3744    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3745      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3746      <address><email>mogul@wrl.dec.com</email></address>
3747    </author>
3748    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3749      <organization>MIT Laboratory for Computer Science</organization>
3750      <address><email>frystyk@w3.org</email></address>
3751    </author>
3752    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3753      <organization>MIT Laboratory for Computer Science</organization>
3754      <address><email>timbl@w3.org</email></address>
3755    </author>
3756    <date month="January" year="1997"/>
3757  </front>
3758  <seriesInfo name="RFC" value="2068"/>
3759</reference>
3760
3761<reference anchor="RFC2616">
3762  <front>
3763    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3764    <author initials="R." surname="Fielding" fullname="R. Fielding">
3765      <organization>University of California, Irvine</organization>
3766      <address><email>fielding@ics.uci.edu</email></address>
3767    </author>
3768    <author initials="J." surname="Gettys" fullname="J. Gettys">
3769      <organization>W3C</organization>
3770      <address><email>jg@w3.org</email></address>
3771    </author>
3772    <author initials="J." surname="Mogul" fullname="J. Mogul">
3773      <organization>Compaq Computer Corporation</organization>
3774      <address><email>mogul@wrl.dec.com</email></address>
3775    </author>
3776    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3777      <organization>MIT Laboratory for Computer Science</organization>
3778      <address><email>frystyk@w3.org</email></address>
3779    </author>
3780    <author initials="L." surname="Masinter" fullname="L. Masinter">
3781      <organization>Xerox Corporation</organization>
3782      <address><email>masinter@parc.xerox.com</email></address>
3783    </author>
3784    <author initials="P." surname="Leach" fullname="P. Leach">
3785      <organization>Microsoft Corporation</organization>
3786      <address><email>paulle@microsoft.com</email></address>
3787    </author>
3788    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3789      <organization>W3C</organization>
3790      <address><email>timbl@w3.org</email></address>
3791    </author>
3792    <date month="June" year="1999"/>
3793  </front>
3794  <seriesInfo name="RFC" value="2616"/>
3795</reference>
3796
3797<reference anchor='RFC2817'>
3798  <front>
3799    <title>Upgrading to TLS Within HTTP/1.1</title>
3800    <author initials='R.' surname='Khare' fullname='R. Khare'>
3801      <organization>4K Associates / UC Irvine</organization>
3802      <address><email>rohit@4K-associates.com</email></address>
3803    </author>
3804    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3805      <organization>Agranat Systems, Inc.</organization>
3806      <address><email>lawrence@agranat.com</email></address>
3807    </author>
3808    <date year='2000' month='May' />
3809  </front>
3810  <seriesInfo name='RFC' value='2817' />
3811</reference>
3812
3813<reference anchor='RFC3864'>
3814  <front>
3815    <title>Registration Procedures for Message Header Fields</title>
3816    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3817      <organization>Nine by Nine</organization>
3818      <address><email>GK-IETF@ninebynine.org</email></address>
3819    </author>
3820    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3821      <organization>BEA Systems</organization>
3822      <address><email>mnot@pobox.com</email></address>
3823    </author>
3824    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3825      <organization>HP Labs</organization>
3826      <address><email>JeffMogul@acm.org</email></address>
3827    </author>
3828    <date year='2004' month='September' />
3829  </front>
3830  <seriesInfo name='BCP' value='90' />
3831  <seriesInfo name='RFC' value='3864' />
3832</reference>
3833
3834<reference anchor='RFC5226'>
3835  <front>
3836    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3837    <author initials='T.' surname='Narten' fullname='T. Narten'>
3838      <organization>IBM</organization>
3839      <address><email>narten@us.ibm.com</email></address>
3840    </author>
3841    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3842      <organization>Google</organization>
3843      <address><email>Harald@Alvestrand.no</email></address>
3844    </author>
3845    <date year='2008' month='May' />
3846  </front>
3847  <seriesInfo name='BCP' value='26' />
3848  <seriesInfo name='RFC' value='5226' />
3849</reference>
3850
3851<reference anchor="RFC5322">
3852  <front>
3853    <title>Internet Message Format</title>
3854    <author initials="P." surname="Resnick" fullname="P. Resnick">
3855      <organization>Qualcomm Incorporated</organization>
3856    </author>
3857    <date year="2008" month="October"/>
3858  </front> 
3859  <seriesInfo name="RFC" value="5322"/>
3860</reference>
3861
3862<reference anchor='RFC5789'>
3863  <front>
3864    <title>PATCH Method for HTTP</title>
3865    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3866      <organization>Linden Lab</organization>
3867    </author>
3868    <author initials='J.' surname='Snell' fullname='J. Snell' />
3869    <date year='2010' month='March' />
3870  </front>
3871  <seriesInfo name='RFC' value='5789' />
3872</reference>
3873
3874<reference anchor="RFC5987">
3875        <front>
3876    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3877    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3878      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3879      <address>
3880        <postal>
3881          <street>Hafenweg 16</street>
3882          <city>Muenster</city><region>NW</region><code>48155</code>
3883          <country>Germany</country>
3884        </postal>
3885        <email>julian.reschke@greenbytes.de</email>     
3886        <uri>http://greenbytes.de/tech/webdav/</uri>   
3887      </address>
3888    </author>
3889    <date month="August" year="2010"/>
3890  </front>
3891  <seriesInfo name="RFC" value="5987"/>
3892</reference>
3893
3894</references>
3895
3896<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3897<t>
3898  This document takes over the Status Code Registry, previously defined
3899  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3900  (<xref target="status.code.registry"/>)
3901</t>
3902<t>
3903  Clarify definition of POST.
3904  (<xref target="POST"/>)
3905</t>
3906<t>
3907  Remove requirement to handle all Content-* header fields; ban use of
3908  Content-Range with PUT.
3909  (<xref target="PUT"/>)
3910</t>
3911<t>
3912  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3913  (<xref target="CONNECT"/>)
3914</t>
3915<t>
3916  Broadened the definition of 203 (Non-Authoritative Information) to include
3917  cases of payload transformations as well.
3918  (<xref target="status.203"/>)
3919</t>
3920<t>
3921  Status codes 301, 302, and 307: removed the normative requirements on both
3922  response payloads and user interaction.
3923  (<xref target="status.3xx"/>)
3924</t>
3925<t>
3926  Failed to consider that there are many other request methods that are safe
3927  to automatically redirect, and further that the user agent is able to make
3928  that determination based on the request method semantics.
3929  Furthermore, allow user agents to rewrite the method from POST to GET
3930  for status codes 301 and 302.
3931  (Sections <xref format="counter" target="status.301"/>,
3932  <xref format="counter" target="status.302"/> and
3933  <xref format="counter" target="status.307"/>)
3934</t>
3935<t>
3936  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3937  It used to indicate that the target resource must be accessed through the
3938  proxy given by the Location field. The Location field gave the URI of the
3939  proxy. The recipient was expected to repeat this single request via the proxy.
3940  (<xref target="status.305"/>)
3941</t>
3942<t>
3943  Define status 426 (Upgrade Required) (this was incorporated from
3944  <xref target="RFC2817"/>).
3945  (<xref target="status.426"/>)
3946</t>
3947<t>
3948  Change ABNF productions for header fields to only define the field value.
3949  (<xref target="header.field.definitions"/>)
3950</t>
3951<t>
3952  Reclassify "Allow" as response header field, removing the option to
3953  specify it in a PUT request.
3954  Relax the server requirement on the contents of the Allow header field and
3955  remove requirement on clients to always trust the header field value.
3956  (<xref target="header.allow"/>)
3957</t>
3958<t>
3959  The ABNF for the Expect header field has been both fixed (allowing parameters
3960  for value-less expectations as well) and simplified (allowing trailing
3961  semicolons after "100-continue" when they were invalid before).
3962  (<xref target="header.expect"/>)
3963</t>
3964<t>
3965  Correct syntax of Location header field to allow URI references (including
3966  relative references and fragments), as referred symbol "absoluteURI" wasn't
3967  what was expected, and add some clarifications as to when use of fragments
3968  would not be appropriate.
3969  (<xref target="header.location"/>)
3970</t>
3971<t>
3972  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3973  extension methods could have used it as well).
3974  (<xref target="header.max-forwards"/>)
3975</t>
3976<t>
3977  Allow Referer field value of "about:blank" as alternative to not specifying it.
3978  (<xref target="header.referer"/>)
3979</t>
3980<t>
3981  In the description of the Server header field, the Via field
3982  was described as a SHOULD. The requirement was and is stated
3983  correctly in the description of the Via header field in &header-via;.
3984  (<xref target="header.server"/>)
3985</t>
3986</section>
3987
3988<?BEGININC p2-semantics.abnf-appendix ?>
3989<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3990<figure>
3991<artwork type="abnf" name="p2-semantics.parsed-abnf">
3992<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
3993
3994<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
3995
3996<x:ref>Date</x:ref> = HTTP-date
3997
3998<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3999
4000<x:ref>From</x:ref> = mailbox
4001
4002<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4003
4004<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4005
4006<x:ref>Location</x:ref> = URI-reference
4007
4008<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4009
4010<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
4011
4012<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
4013<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4014<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4015
4016<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4017
4018<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4019<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4020
4021<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4022<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4023
4024<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
4025
4026<x:ref>date1</x:ref> = day SP month SP year
4027<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4028<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4029<x:ref>day</x:ref> = 2DIGIT
4030<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4031 / %x54.75.65 ; Tue
4032 / %x57.65.64 ; Wed
4033 / %x54.68.75 ; Thu
4034 / %x46.72.69 ; Fri
4035 / %x53.61.74 ; Sat
4036 / %x53.75.6E ; Sun
4037<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4038 / %x54.75.65.73.64.61.79 ; Tuesday
4039 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4040 / %x54.68.75.72.73.64.61.79 ; Thursday
4041 / %x46.72.69.64.61.79 ; Friday
4042 / %x53.61.74.75.72.64.61.79 ; Saturday
4043 / %x53.75.6E.64.61.79 ; Sunday
4044<x:ref>delta-seconds</x:ref> = 1*DIGIT
4045
4046<x:ref>expect-name</x:ref> = token
4047<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
4048<x:ref>expect-value</x:ref> = token / quoted-string
4049<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
4050 OWS expect-param ] )
4051
4052<x:ref>hour</x:ref> = 2DIGIT
4053
4054<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4055<x:ref>method</x:ref> = token
4056<x:ref>minute</x:ref> = 2DIGIT
4057<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4058 / %x46.65.62 ; Feb
4059 / %x4D.61.72 ; Mar
4060 / %x41.70.72 ; Apr
4061 / %x4D.61.79 ; May
4062 / %x4A.75.6E ; Jun
4063 / %x4A.75.6C ; Jul
4064 / %x41.75.67 ; Aug
4065 / %x53.65.70 ; Sep
4066 / %x4F.63.74 ; Oct
4067 / %x4E.6F.76 ; Nov
4068 / %x44.65.63 ; Dec
4069
4070<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4071<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
4072
4073<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4074<x:ref>product</x:ref> = token [ "/" product-version ]
4075<x:ref>product-version</x:ref> = token
4076
4077<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
4078
4079<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4080<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4081<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4082
4083<x:ref>second</x:ref> = 2DIGIT
4084<x:ref>status-code</x:ref> = 3DIGIT
4085
4086<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4087<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
4088
4089<x:ref>year</x:ref> = 4DIGIT
4090</artwork>
4091</figure>
4092<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4093; Allow defined but not used
4094; Date defined but not used
4095; Expect defined but not used
4096; From defined but not used
4097; Location defined but not used
4098; Max-Forwards defined but not used
4099; Referer defined but not used
4100; Retry-After defined but not used
4101; Server defined but not used
4102; User-Agent defined but not used
4103; reason-phrase defined but not used
4104; status-code defined but not used
4105</artwork></figure></section>
4106<?ENDINC p2-semantics.abnf-appendix ?>
4107
4108<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4109
4110<section title="Since RFC 2616">
4111<t>
4112  Extracted relevant partitions from <xref target="RFC2616"/>.
4113</t>
4114</section>
4115
4116<section title="Since draft-ietf-httpbis-p2-semantics-00">
4117<t>
4118  Closed issues:
4119  <list style="symbols"> 
4120    <t>
4121      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4122      "Via is a MUST"
4123      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4124    </t>
4125    <t>
4126      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4127      "Fragments allowed in Location"
4128      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4129    </t>
4130    <t>
4131      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4132      "Safe Methods vs Redirection"
4133      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4134    </t>
4135    <t>
4136      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4137      "Revise description of the POST method"
4138      (<eref target="http://purl.org/NET/http-errata#post"/>)
4139    </t>
4140    <t>
4141      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4142      "Normative and Informative references"
4143    </t>
4144    <t>
4145      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4146      "RFC2606 Compliance"
4147    </t>
4148    <t>
4149      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4150      "Informative references"
4151    </t>
4152    <t>
4153      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4154      "Redundant cross-references"
4155    </t>
4156  </list>
4157</t>
4158<t>
4159  Other changes:
4160  <list style="symbols"> 
4161    <t>
4162      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4163    </t>
4164  </list>
4165</t>
4166</section>
4167
4168<section title="Since draft-ietf-httpbis-p2-semantics-01">
4169<t>
4170  Closed issues:
4171  <list style="symbols"> 
4172    <t>
4173      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4174      "PUT side effects"
4175    </t>
4176    <t>
4177      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4178      "Duplicate Host header requirements"
4179    </t>
4180  </list>
4181</t>
4182<t>
4183  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4184  <list style="symbols"> 
4185    <t>
4186      Move "Product Tokens" section (back) into Part 1, as "token" is used
4187      in the definition of the Upgrade header field.
4188    </t>
4189    <t>
4190      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4191    </t>
4192    <t>
4193      Copy definition of delta-seconds from Part6 instead of referencing it.
4194    </t>
4195  </list>
4196</t>
4197</section>
4198
4199<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4200<t>
4201  Closed issues:
4202  <list style="symbols"> 
4203    <t>
4204      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4205      "Requiring Allow in 405 responses"
4206    </t>
4207    <t>
4208      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4209      "Status Code Registry"
4210    </t>
4211    <t>
4212      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4213      "Redirection vs. Location"
4214    </t>
4215    <t>
4216      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4217      "Cacheability of 303 response"
4218    </t>
4219    <t>
4220      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4221      "305 Use Proxy"
4222    </t>
4223    <t>
4224      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4225      "Classification for Allow header"
4226    </t>
4227    <t>
4228      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4229      "PUT - 'store under' vs 'store at'"
4230    </t>
4231  </list>
4232</t>
4233<t>
4234  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4235  <list style="symbols"> 
4236    <t>
4237      Reference RFC 3984, and update header field registrations for headers defined
4238      in this document.
4239    </t>
4240  </list>
4241</t>
4242<t>
4243  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4244  <list style="symbols"> 
4245    <t>
4246      Replace string literals when the string really is case-sensitive (method).
4247    </t>
4248  </list>
4249</t>
4250</section>
4251
4252<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4253<t>
4254  Closed issues:
4255  <list style="symbols"> 
4256    <t>
4257      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4258      "OPTIONS request bodies"
4259    </t>
4260    <t>
4261      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4262      "Description of CONNECT should refer to RFC2817"
4263    </t>
4264    <t>
4265      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4266      "Location Content-Location reference request/response mixup"
4267    </t>
4268  </list>
4269</t>
4270<t>
4271  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4272  <list style="symbols"> 
4273    <t>
4274      Added initial proposal for registration process, plus initial
4275      content (non-HTTP/1.1 methods to be added by a separate specification).
4276    </t>
4277  </list>
4278</t>
4279</section>
4280
4281<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4282<t>
4283  Closed issues:
4284  <list style="symbols"> 
4285    <t>
4286      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4287      "Content-*"
4288    </t>
4289    <t>
4290      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4291      "RFC 2822 is updated by RFC 5322"
4292    </t>
4293  </list>
4294</t>
4295<t>
4296  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4297  <list style="symbols"> 
4298    <t>
4299      Use "/" instead of "|" for alternatives.
4300    </t>
4301    <t>
4302      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4303      whitespace ("OWS") and required whitespace ("RWS").
4304    </t>
4305    <t>
4306      Rewrite ABNFs to spell out whitespace rules, factor out
4307      header field value format definitions.
4308    </t>
4309  </list>
4310</t>
4311</section>
4312
4313<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4314<t>
4315  Closed issues:
4316  <list style="symbols"> 
4317    <t>
4318      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4319      "reason-phrase BNF"
4320    </t>
4321  </list>
4322</t>
4323<t>
4324  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4325  <list style="symbols"> 
4326    <t>
4327      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4328    </t>
4329  </list>
4330</t>
4331</section>
4332
4333<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4334<t>
4335  Closed issues:
4336  <list style="symbols"> 
4337    <t>
4338      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4339      "Clarify when Referer is sent"
4340    </t>
4341    <t>
4342      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4343      "status codes vs methods"
4344    </t>
4345    <t>
4346      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4347      "Do not require "updates" relation for specs that register status codes or method names"
4348    </t>
4349  </list>
4350</t>
4351</section>
4352
4353<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4354<t>
4355  Closed issues:
4356  <list style="symbols"> 
4357    <t>
4358      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4359      "Idempotency"
4360    </t>
4361    <t>
4362      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4363      "TRACE security considerations"
4364    </t>
4365    <t>
4366      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4367      "Clarify rules for determining what entities a response carries"
4368    </t>
4369    <t>
4370      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4371      "update note citing RFC 1945 and 2068"
4372    </t>
4373    <t>
4374      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4375      "update note about redirect limit"
4376    </t>
4377    <t>
4378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4379      "Location header ABNF should use 'URI'"
4380    </t>
4381    <t>
4382      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4383      "fragments in Location vs status 303"
4384    </t>
4385    <t>
4386      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4387      "move IANA registrations for optional status codes"
4388    </t>
4389  </list>
4390</t>
4391<t>
4392  Partly resolved issues:
4393  <list style="symbols"> 
4394    <t>
4395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4396      "Are OPTIONS and TRACE safe?"
4397    </t>
4398  </list>
4399</t>
4400</section>
4401
4402<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4403<t>
4404  Closed issues:
4405  <list style="symbols"> 
4406    <t>
4407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4408      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4409      status codes when fixing this previously)
4410    </t>
4411  </list>
4412</t>
4413</section>
4414
4415<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4416<t>
4417  Closed issues:
4418  <list style="symbols"> 
4419    <t>
4420      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4421      "Fragment combination / precedence during redirects"
4422    </t>
4423  </list>
4424</t>
4425<t>
4426  Partly resolved issues:
4427  <list style="symbols"> 
4428    <t>
4429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4430      "Location header payload handling"
4431    </t>
4432    <t>
4433      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4434      "Term for the requested resource's URI"
4435    </t>
4436  </list>
4437</t>
4438</section>
4439
4440<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4441<t>
4442  Closed issues:
4443  <list style="symbols"> 
4444    <t>
4445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4446      "Clarify 'Requested Variant'"
4447    </t>
4448    <t>
4449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4450      "Clarify entity / representation / variant terminology"
4451    </t>
4452    <t>
4453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4454      "Methods and Caching"
4455    </t>
4456    <t>
4457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4458      "OPTIONS vs Max-Forwards"
4459    </t>
4460    <t>
4461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4462      "Status codes and caching"
4463    </t>
4464    <t>
4465      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4466      "consider removing the 'changes from 2068' sections"
4467    </t>
4468  </list>
4469</t>
4470</section>
4471
4472<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4473<t>
4474  Closed issues:
4475  <list style="symbols"> 
4476    <t>
4477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4478      "Considerations for new status codes"
4479    </t>
4480    <t>
4481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4482      "Considerations for new methods"
4483    </t>
4484    <t>
4485      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4486      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4487    </t>
4488  </list>
4489</t>
4490</section>
4491
4492<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4493<t>
4494  Closed issues:
4495  <list style="symbols"> 
4496    <t>
4497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4498      "Fragment combination / precedence during redirects" (added warning
4499      about having a fragid on the redirect may cause inconvenience in
4500      some cases)
4501    </t>
4502    <t>
4503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4504      "Content-* vs. PUT"
4505    </t>
4506    <t>
4507      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4508      "205 Bodies"
4509    </t>
4510    <t>
4511      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4512      "Understanding Content-* on non-PUT requests"
4513    </t>
4514    <t>
4515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4516      "Content-*"
4517    </t>
4518    <t>
4519      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4520      "Header type defaulting"
4521    </t>
4522    <t>
4523      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4524      "PUT - 'store under' vs 'store at'"
4525    </t>
4526    <t>
4527      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4528      "duplicate ABNF for reason-phrase"
4529    </t>
4530    <t>
4531      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4532      "Note special status of Content-* prefix in header registration procedures"
4533    </t>
4534    <t>
4535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4536      "Max-Forwards vs extension methods"
4537    </t>
4538    <t>
4539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4540      "What is the value space of HTTP status codes?" (actually fixed in
4541      draft-ietf-httpbis-p2-semantics-11)
4542    </t>
4543    <t>
4544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4545      "Header Classification"
4546    </t>
4547    <t>
4548      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4549      "PUT side effect: invalidation or just stale?"
4550    </t>
4551    <t>
4552      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4553      "proxies not supporting certain methods"
4554    </t>
4555    <t>
4556      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4557      "Migrate CONNECT from RFC2817 to p2"
4558    </t>
4559    <t>
4560      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4561      "Migrate Upgrade details from RFC2817"
4562    </t>
4563    <t>
4564      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4565      "clarify PUT semantics'"
4566    </t>
4567    <t>
4568      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4569      "duplicate ABNF for 'Method'"
4570    </t>
4571    <t>
4572      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4573      "untangle ABNFs for header fields"
4574    </t>
4575  </list>
4576</t>
4577</section>
4578
4579<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4580<t>
4581  Closed issues:
4582  <list style="symbols"> 
4583    <t>
4584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4585      "untangle ABNFs for header fields"
4586    </t>
4587    <t>
4588      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4589      "message body in CONNECT request"
4590    </t>
4591  </list>
4592</t>
4593</section>
4594
4595<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4596<t>
4597  Closed issues:
4598  <list style="symbols"> 
4599    <t>
4600      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4601      "Clarify status code for rate limiting"
4602    </t>
4603    <t>
4604      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4605      "clarify 403 forbidden"
4606    </t>
4607    <t>
4608      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4609      "Clarify 203 Non-Authoritative Information"
4610    </t>
4611    <t>
4612      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4613      "update default reason phrase for 413"
4614    </t>
4615  </list>
4616</t>
4617</section>
4618
4619<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4620<t>
4621  Closed issues:
4622  <list style="symbols"> 
4623    <t>
4624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4625      "Strength of requirements on Accept re: 406"
4626    </t>
4627    <t>
4628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4629      "400 response isn't generic"
4630    </t>
4631  </list>
4632</t>
4633</section>
4634
4635<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4636<t>
4637  Closed issues:
4638  <list style="symbols"> 
4639    <t>
4640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4641      "Redirects and non-GET methods"
4642    </t>
4643    <t>
4644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4645      "Document HTTP's error-handling philosophy"
4646    </t>
4647    <t>
4648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4649      "Considerations for new headers"
4650    </t>
4651    <t>
4652      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4653      "clarify 303 redirect on HEAD"
4654    </t>
4655  </list>
4656</t>
4657</section>
4658
4659<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4660<t>
4661  Closed issues:
4662  <list style="symbols"> 
4663    <t>
4664      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4665      "Location header payload handling"
4666    </t>
4667    <t>
4668      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4669      "Clarify status code for rate limiting" (change backed out because
4670      a new status code is being defined for this purpose)
4671    </t>
4672    <t>
4673      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4674      "should there be a permanent variant of 307"
4675    </t>
4676    <t>
4677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4678      "When are Location's semantics triggered?"
4679    </t>
4680    <t>
4681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4682      "'expect' grammar missing OWS"
4683    </t>
4684    <t>
4685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4686      "header field considerations: quoted-string vs use of double quotes"
4687    </t>
4688  </list>
4689</t>
4690</section>
4691
4692<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4693<t>
4694  Closed issues:
4695  <list style="symbols"> 
4696    <t>
4697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4698      "Combining HEAD responses"
4699    </t>
4700    <t>
4701      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4702      "Requirements for user intervention during redirects"
4703    </t>
4704    <t>
4705      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4706      "message-body in CONNECT response"
4707    </t>
4708    <t>
4709      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4710      "Applying original fragment to 'plain' redirected URI"
4711    </t>
4712    <t>
4713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4714      "Misplaced text on connection handling in p2"
4715    </t>
4716    <t>
4717      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4718      "clarify that 201 doesn't require Location header fields"
4719    </t>
4720    <t>
4721      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4722      "relax requirements on hypertext in 3/4/5xx error responses"
4723    </t>
4724    <t>
4725      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4726      "example for 426 response should have a payload"
4727    </t>
4728    <t>
4729      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4730      "drop indirection entries for status codes"
4731    </t>
4732  </list>
4733</t>
4734</section>
4735
4736</section>
4737
4738</back>
4739</rfc>
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