source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1635

Last change on this file since 1635 was 1635, checked in by julian.reschke@…, 8 years ago

remove redundant ABNF, fix section title

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 182.7 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="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
129    <organization abbrev="W3C">World Wide Web Consortium</organization>
130    <address>
131      <postal>
132        <street>W3C / ERCIM</street>
133        <street>2004, rte des Lucioles</street>
134        <city>Sophia-Antipolis</city>
135        <region>AM</region>
136        <code>06902</code>
137        <country>France</country>
138      </postal>
139      <email>ylafon@w3.org</email>
140      <uri>http://www.raubacapeu.net/people/yves/</uri>
141    </address>
142  </author>
143
144  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
145    <organization abbrev="greenbytes">greenbytes GmbH</organization>
146    <address>
147      <postal>
148        <street>Hafenweg 16</street>
149        <city>Muenster</city><region>NW</region><code>48155</code>
150        <country>Germany</country>
151      </postal>
152      <phone>+49 251 2807760</phone>
153      <facsimile>+49 251 2807761</facsimile>
154      <email>julian.reschke@greenbytes.de</email>
155      <uri>http://greenbytes.de/tech/webdav/</uri>
156    </address>
157  </author>
158
159  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
160  <workgroup>HTTPbis Working Group</workgroup>
161
162<abstract>
163<t>
164   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
165   distributed, collaborative, hypertext information systems. HTTP has been in
166   use by the World Wide Web global information initiative since 1990. This
167   document is Part 2 of the seven-part specification that defines the protocol
168   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
169</t>
170<t>
171   Part 2 defines the semantics of HTTP messages as expressed by request
172   methods, request header fields, response status codes, and response header
173   fields.
174</t>
175</abstract>
176
177<note title="Editorial Note (To be removed by RFC Editor)">
178  <t>
179    Discussion of this draft should take place on the HTTPBIS working group
180    mailing list (ietf-http-wg@w3.org), which is archived at
181    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
182  </t>
183  <t>
184    The current issues list is at
185    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
186    documents (including fancy diffs) can be found at
187    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
188  </t>
189  <t>
190    The changes in this draft are summarized in <xref target="changes.since.19"/>.
191  </t>
192</note>
193</front>
194<middle>
195<section title="Introduction" anchor="introduction">
196<t>
197   This document defines HTTP/1.1 request and response semantics.  Each HTTP
198   message, as defined in &messaging;, is in the form of either a request or
199   a response.  An HTTP server listens on a connection for HTTP requests and
200   responds to each request, in the order received on that connection, with
201   one or more HTTP response messages.  This document defines the commonly
202   agreed upon semantics of the HTTP uniform interface, the intentions defined
203   by each request method, and the various response messages that might be
204   expected as a result of applying that method to the target resource.
205</t>
206<t>
207   This document is currently disorganized in order to minimize the changes
208   between drafts and enable reviewers to see the smaller errata changes.
209   A future draft will reorganize the sections to better reflect the content.
210   In particular, the sections will be ordered according to the typical
211   processing of an HTTP request message (after message parsing): resource
212   mapping, methods, request modifying header fields, response status,
213   status modifying header fields, and resource metadata.  The current mess
214   reflects how widely dispersed these topics and associated requirements
215   had become in <xref target="RFC2616"/>.
216</t>
217
218<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
219<t>
220   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
221   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
222   document are to be interpreted as described in <xref target="RFC2119"/>.
223</t>
224<t>
225   This document defines conformance criteria for several roles in HTTP
226   communication, including Senders, Recipients, Clients, Servers, User-Agents,
227   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
228   for definitions of these terms.
229</t>
230<t>
231   An implementation is considered conformant if it complies with all of the
232   requirements associated with its role(s). Note that SHOULD-level requirements
233   are relevant here, unless one of the documented exceptions is applicable.
234</t>
235<t>
236   This document also uses ABNF to define valid protocol elements
237   (<xref target="notation"/>). In addition to the prose requirements placed
238   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
239</t>
240<t>
241   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
242   protocol element from an invalid construct. However, HTTP does not define
243   specific error handling mechanisms, except in cases where it has direct
244   impact on security. This is because different uses of the protocol require
245   different error handling strategies; for example, a Web browser may wish to
246   transparently recover from a response where the Location header field
247   doesn't parse according to the ABNF, whereby in a systems control protocol
248   using HTTP, this type of error recovery could lead to dangerous consequences.
249</t>
250</section>
251
252<section title="Syntax Notation" anchor="notation">
253  <x:anchor-alias value="CR"/>
254  <x:anchor-alias value="DIGIT"/>
255  <x:anchor-alias value="LF"/>
256  <x:anchor-alias value="HTAB"/>
257  <x:anchor-alias value="VCHAR"/>
258  <x:anchor-alias value="SP"/>
259<t>
260   This specification uses the Augmented Backus-Naur Form (ABNF) notation
261   of <xref target="RFC5234"/> with the list rule extension defined in
262   &notation;<xref target="collected.abnf"/> shows the collected ABNF
263   with the list rule expanded.
264</t>
265<t>
266  The following core rules are included by
267  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
268  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
269  DIGIT (decimal 0-9), DQUOTE (double quote),
270  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
271  OCTET (any 8-bit sequence of data), SP (space), and
272  VCHAR (any visible US-ASCII character).
273</t>
274
275<section title="Core Rules" anchor="core.rules">
276  <x:anchor-alias value="obs-text"/>
277  <x:anchor-alias value="quoted-string"/>
278  <x:anchor-alias value="token"/>
279  <x:anchor-alias value="BWS"/>
280  <x:anchor-alias value="OWS"/>
281  <x:anchor-alias value="RWS"/>
282<t>
283  The core rules below are defined in <xref target="Part1"/>:
284</t>
285<figure><artwork type="abnf2616">
286  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &whitespace;&gt;
287  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &whitespace;&gt;
288  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &whitespace;&gt;
289  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &field-components;&gt;
290  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-components;&gt;
291  <x:ref>token</x:ref>         = &lt;token, defined in &field-components;&gt;
292</artwork></figure>
293</section>
294
295<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
296  <x:anchor-alias value="absolute-URI"/>
297  <x:anchor-alias value="comment"/>
298  <x:anchor-alias value="partial-URI"/>
299  <x:anchor-alias value="URI-reference"/>
300<t>
301  The ABNF rules below are defined in other parts:
302</t>
303<figure><!--Part1--><artwork type="abnf2616">
304  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
305  <x:ref>comment</x:ref>       = &lt;comment, defined in &field-components;&gt;
306  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
307  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
308</artwork></figure>
309</section>
310</section>
311</section>
312
313<section title="Methods" anchor="methods">
314  <x:anchor-alias value="method"/>
315<t>
316   The method token indicates the request method to be performed on the target
317   resource (&effective-request-uri;). The method is case-sensitive.
318</t>
319<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
320  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
321</artwork></figure>
322<t>
323   The list of methods allowed by a resource can be specified in an
324   Allow header field (<xref target="header.allow"/>). The status code of the response
325   always notifies the client whether a method is currently allowed on a
326   resource, since the set of allowed methods can change dynamically. An
327   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
328   if the method is known by the origin server but not allowed for the
329   resource, and 501 (Not Implemented) if the method is
330   unrecognized or not implemented by the origin server. The methods GET
331   and HEAD &MUST; be supported by all general-purpose servers. All other
332   methods are &OPTIONAL;; however, if the above methods are implemented,
333   they &MUST; be implemented with the same semantics as those specified
334   in <xref target="method.definitions"/>.
335</t>
336
337<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
338
339<section title="Safe Methods" anchor="safe.methods">
340<iref item="Safe Methods" primary="true"/>
341<t>
342   Implementors need to be aware that the software represents the user in
343   their interactions over the Internet, and need to allow
344   the user to be aware of any actions they take which might have an
345   unexpected significance to themselves or others.
346</t>
347<t>
348   In particular, the convention has been established that the GET, HEAD,
349   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
350   of taking an action other than retrieval. These request methods ought
351   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
352   This allows user agents to represent other methods, such as POST, PUT
353   and DELETE, in a special way, so that the user is made aware of the
354   fact that a possibly unsafe action is being requested.
355</t>
356<t>
357   Naturally, it is not possible to ensure that the server does not
358   generate side-effects as a result of performing a GET request; in
359   fact, some dynamic resources consider that a feature. The important
360   distinction here is that the user did not request the side-effects,
361   so therefore cannot be held accountable for them.
362</t>
363</section>
364
365<section title="Idempotent Methods" anchor="idempotent.methods">
366<iref item="Idempotent Methods" primary="true"/>
367<t>
368   Request methods can also have the property of "idempotence" in that,
369   aside from error or expiration issues, the intended effect of multiple
370   identical requests is the same as for a single request.
371   PUT, DELETE, and all safe request methods are idempotent.
372   It is important to note that idempotence refers only to changes
373   requested by the client: a server is free to change its state due
374   to multiple requests for the purpose of tracking those requests,
375   versioning of results, etc.
376</t>
377</section>
378</section>
379
380<section title="Method Registry" anchor="method.registry">
381<t>
382  The HTTP Method Registry defines the name space for the method token in the
383  Request line of an HTTP request.
384</t>
385<t>
386  Registrations &MUST; include the following fields:
387  <list style="symbols">
388    <t>Method Name (see <xref target="methods"/>)</t>
389    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
390    <t>Pointer to specification text</t>
391  </list>
392</t>
393<t>
394  Values to be added to this name space require IETF Review
395  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
396</t>
397<t>
398  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
399</t>
400
401<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
402<t>
403   When it is necessary to express new semantics for a HTTP request that
404   aren't specific to a single application or media type, and currently defined
405   methods are inadequate, it may be appropriate to register a new method.
406</t>
407<t>
408   HTTP methods are generic; that is, they are potentially applicable to any
409   resource, not just one particular media type, "type" of resource, or
410   application. As such, it is preferred that new HTTP methods be registered
411   in a document that isn't specific to a single application, so that this is
412   clear.
413</t>
414<t>
415   Due to the parsing rules defined in &message-body;, definitions of HTTP
416   methods cannot prohibit the presence of a message body on either the request
417   or the response message (with responses to HEAD requests being the single
418   exception). Definitions of new methods cannot change this rule, but they can
419   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
420</t>
421<t>
422   New method definitions need to indicate whether they are safe (<xref
423   target="safe.methods"/>), what semantics (if any) the request body has,
424   and whether they are idempotent (<xref target="idempotent.methods"/>).
425   They also need to state whether they can be cached (&caching;); in
426   particular what conditions a cache may store the response, and under what
427   conditions such a stored response may be used to satisfy a subsequent
428   request.
429</t>
430</section>
431</section>
432
433<section title="Method Definitions" anchor="method.definitions">
434
435<section title="OPTIONS" anchor="OPTIONS">
436  <rdf:Description>
437    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
438  </rdf:Description>
439  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
440  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
441<t>
442   The OPTIONS method requests information about the
443   communication options available on the request/response chain
444   identified by the effective request URI. This method allows a client to
445   determine the options and/or requirements associated with a resource,
446   or the capabilities of a server, without implying a resource action
447   or initiating a resource retrieval.
448</t>
449<t>
450   Responses to the OPTIONS method are not cacheable.
451</t>
452<t>
453   If the OPTIONS request includes a message body (as indicated by the
454   presence of Content-Length or Transfer-Encoding), then the media type
455   &MUST; be indicated by a Content-Type field. Although this
456   specification does not define any use for such a body, future
457   extensions to HTTP might use the OPTIONS body to make more detailed
458   queries on the server.
459</t>
460<t>
461   If the request-target (&request-target;) is an asterisk ("*"),
462   the OPTIONS request is
463   intended to apply to the server in general rather than to a specific
464   resource. Since a server's communication options typically depend on
465   the resource, the "*" request is only useful as a "ping" or "no-op"
466   type of method; it does nothing beyond allowing the client to test
467   the capabilities of the server. For example, this can be used to test
468   a proxy for HTTP/1.1 conformance (or lack thereof).
469</t>
470<t>
471   If the request-target is not an asterisk, the OPTIONS request applies
472   only to the options that are available when communicating with that
473   resource.
474</t>
475<t>
476   A 200 response &SHOULD; include any header fields that indicate
477   optional features implemented by the server and applicable to that
478   resource (e.g., Allow), possibly including extensions not defined by
479   this specification. The response body, if any, &SHOULD; also include
480   information about the communication options. The format for such a
481   body is not defined by this specification, but might be defined by
482   future extensions to HTTP. Content negotiation &MAY; be used to select
483   the appropriate response format. If no response body is included, the
484   response &MUST; include a Content-Length field with a field-value of
485   "0".
486</t>
487<t>
488   The Max-Forwards header field &MAY; be used to target a
489   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
490   If no Max-Forwards field is present in the request, then the forwarded
491   request &MUST-NOT; include a Max-Forwards field.
492</t>
493</section>
494
495<section title="GET" anchor="GET">
496  <rdf:Description>
497    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
498  </rdf:Description>
499  <iref primary="true" item="GET method" x:for-anchor=""/>
500  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
501<t>
502   The GET method requests transfer of a current representation of
503   the target resource.
504</t>
505<t>   
506   If the target resource is a data-producing process, it is the
507   produced data which shall be returned as the representation in the response and not
508   the source text of the process, unless that text happens to be the output of
509   the process.
510</t>
511<t>
512   The semantics of the GET method change to a "conditional GET" if the
513   request message includes an If-Modified-Since, If-Unmodified-Since,
514   If-Match, If-None-Match, or If-Range header field. A conditional GET
515   requests that the representation be transferred only under the
516   circumstances described by the conditional header field(s). The
517   conditional GET request is intended to reduce unnecessary network
518   usage by allowing cached representations to be refreshed without requiring
519   multiple requests or transferring data already held by the client.
520</t>
521<t>
522   The semantics of the GET method change to a "partial GET" if the
523   request message includes a Range header field. A partial GET requests
524   that only part of the representation be transferred, as described in &header-range;.
525   The partial GET request is intended to reduce unnecessary
526   network usage by allowing partially-retrieved representations to be
527   completed without transferring data already held by the client.
528</t>
529<t>
530   Bodies on GET requests have no defined semantics. Note that sending a body
531   on a GET request might cause some existing implementations to reject the
532   request.
533</t>
534<t>
535   The response to a GET request is cacheable and &MAY; be used to satisfy
536   subsequent GET and HEAD requests (see &caching;).
537</t>
538<t>
539   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
540</t>
541</section>
542
543<section title="HEAD" anchor="HEAD">
544  <rdf:Description>
545    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
546  </rdf:Description>
547  <iref primary="true" item="HEAD method" x:for-anchor=""/>
548  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
549<t>
550   The HEAD method is identical to GET except that the server &MUST-NOT;
551   return a message body in the response. The metadata contained
552   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
553   to the information sent in response to a GET request. This method can
554   be used for obtaining metadata about the representation implied by the
555   request without transferring the representation body. This method is
556   often used for testing hypertext links for validity, accessibility,
557   and recent modification.
558</t>
559<t>
560   The response to a HEAD request is cacheable and &MAY; be used to satisfy
561   a subsequent HEAD request. It also has potential side effects on
562   previously stored responses to GET; see &p6-head;.
563</t>
564<t>
565   Bodies on HEAD requests have no defined semantics. Note that sending a body
566   on a HEAD request might cause some existing implementations to reject the
567   request.
568</t>
569</section>
570
571<section title="POST" anchor="POST">
572  <iref primary="true" item="POST method" x:for-anchor=""/>
573  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
574<t>
575   The POST method requests that the origin server accept the
576   representation enclosed in the request as data to be processed by the
577   target resource. POST is designed to allow a uniform method to cover the
578   following functions:
579  <list style="symbols">
580    <t>
581      Annotation of existing resources;
582    </t>
583    <t>
584        Posting a message to a bulletin board, newsgroup, mailing list,
585        or similar group of articles;
586    </t>
587    <t>
588        Providing a block of data, such as the result of submitting a
589        form, to a data-handling process;
590    </t>
591    <t>
592        Extending a database through an append operation.
593    </t>
594  </list>
595</t>
596<t>
597   The actual function performed by the POST method is determined by the
598   server and is usually dependent on the effective request URI.
599</t>
600<t>
601   The action performed by the POST method might not result in a
602   resource that can be identified by a URI. In this case, either 200
603   (OK) or 204 (No Content) is the appropriate response status code,
604   depending on whether or not the response includes a representation that
605   describes the result.
606</t>
607<t>
608   If a resource has been created on the origin server, the response
609   &SHOULD; be 201 (Created) and contain a representation which describes the
610   status of the request and refers to the new resource, and a Location
611   header field (see <xref target="header.location"/>).
612</t>
613<t>
614   Responses to POST requests are only cacheable when they
615   include explicit freshness information (see &p6-explicit;). A
616   cached POST response with a Content-Location header field
617   (see &header-content-location;) whose value is the effective
618   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
619</t>
620<t>
621   Note that POST caching is not widely implemented.
622   However, the 303 (See Other) response can be used to direct the
623   user agent to retrieve a cacheable representation of the resource.
624</t>
625</section>
626
627<section title="PUT" anchor="PUT">
628  <iref primary="true" item="PUT method" x:for-anchor=""/>
629  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
630<t>
631   The PUT method requests that the state of the target resource
632   be created or replaced with the state defined by the representation
633   enclosed in the request message payload.  A successful PUT of a given
634   representation would suggest that a subsequent GET on that same target
635   resource will result in an equivalent representation being returned in
636   a 200 (OK) response.  However, there is no guarantee that such a state
637   change will be observable, since the target resource might be acted
638   upon by other user agents in parallel, or might be subject to dynamic
639   processing by the origin server, before any subsequent GET is received.
640   A successful response only implies that the user agent's intent was
641   achieved at the time of its processing by the origin server.
642</t>
643<t>   
644   If the target resource does not have a current representation and
645   the PUT successfully creates one, then the origin server &MUST; inform
646   the user agent by sending a 201 (Created) response.  If the target
647   resource does have a current representation and that representation is
648   successfully modified in accordance with the state of the enclosed
649   representation, then either a 200 (OK) or 204 (No Content) response
650   &SHOULD; be sent to indicate successful completion of the request.
651</t>
652<t>
653   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
654   as part of the resource state).
655</t>
656<t>
657   An origin server &SHOULD; verify that the PUT representation is
658   consistent with any constraints which the server has for the target
659   resource that cannot or will not be changed by the PUT.  This is
660   particularly important when the origin server uses internal
661   configuration information related to the URI in order to set the
662   values for representation metadata on GET responses.  When a PUT
663   representation is inconsistent with the target resource, the origin
664   server &SHOULD; either make them consistent, by transforming the
665   representation or changing the resource configuration, or respond
666   with an appropriate error message containing sufficient information
667   to explain why the representation is unsuitable.  The 409 (Conflict)
668   or 415 (Unsupported Media Type) status codes are suggested, with the
669   latter being specific to constraints on Content-Type values.
670</t>
671<t>
672   For example, if the target resource is configured to always have a
673   Content-Type of "text/html" and the representation being PUT has a
674   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
675   (a) reconfigure the target resource to reflect the new media type;
676   (b) transform the PUT representation to a format consistent with that
677   of the resource before saving it as the new resource state; or,
678   (c) reject the request with a 415 response indicating that the target
679   resource is limited to "text/html", perhaps including a link to a
680   different resource that would be a suitable target for the new
681   representation.
682</t>
683<t>
684   HTTP does not define exactly how a PUT method affects the state
685   of an origin server beyond what can be expressed by the intent of
686   the user agent request and the semantics of the origin server response.
687   It does not define what a resource might be, in any sense of that
688   word, beyond the interface provided via HTTP.  It does not define
689   how resource state is "stored", nor how such storage might change
690   as a result of a change in resource state, nor how the origin server
691   translates resource state into representations.  Generally speaking,
692   all implementation details behind the resource interface are
693   intentionally hidden by the server.
694</t>
695<t>
696   The fundamental difference between the POST and PUT methods is
697   highlighted by the different intent for the target resource.
698   The target resource in a POST request is intended to handle the
699   enclosed representation as a data-accepting process, such as for
700   a gateway to some other protocol or a document that accepts annotations.
701   In contrast, the target resource in a PUT request is intended to
702   take the enclosed representation as a new or replacement value.
703   Hence, the intent of PUT is idempotent and visible to intermediaries,
704   even though the exact effect is only known by the origin server.
705</t>
706<t>
707   Proper interpretation of a PUT request presumes that the user agent
708   knows what target resource is desired.  A service that is intended
709   to select a proper URI on behalf of the client, after receiving
710   a state-changing request, &SHOULD; be implemented using the POST
711   method rather than PUT.  If the origin server will not make the
712   requested PUT state change to the target resource and instead
713   wishes to have it applied to a different resource, such as when the
714   resource has been moved to a different URI, then the origin server
715   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
716   then make its own decision regarding whether or not to redirect the
717   request.
718</t>
719<t>
720   A PUT request applied to the target resource &MAY; have side-effects
721   on other resources.  For example, an article might have a URI for
722   identifying "the current version" (a resource) which is separate
723   from the URIs identifying each particular version (different
724   resources that at one point shared the same state as the current version
725   resource).  A successful PUT request on "the current version" URI might
726   therefore create a new version resource in addition to changing the
727   state of the target resource, and might also cause links to be added
728   between the related resources.
729</t>
730<t>
731   An origin server &SHOULD; reject any PUT request that contains a
732   Content-Range header field, since it might be misinterpreted as
733   partial content (or might be partial content that is being mistakenly
734   PUT as a full representation).  Partial content updates are
735   possible by targeting a separately identified resource with state
736   that overlaps a portion of the larger resource, or by using a
737   different method that has been specifically defined for partial
738   updates (for example, the PATCH method defined in
739   <xref target="RFC5789"/>).
740</t>
741<t>
742   Responses to the PUT method are not cacheable. If a PUT request passes
743   through a cache that has one or more stored responses for the effective
744   request URI, those stored responses will be invalidated (see
745   &p6-invalid;).
746</t>
747</section>
748
749<section title="DELETE" anchor="DELETE">
750  <iref primary="true" item="DELETE method" x:for-anchor=""/>
751  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
752<t>
753   The DELETE method requests that the origin server delete the target
754   resource. This method &MAY; be overridden by
755   human intervention (or other means) on the origin server. The client cannot
756   be guaranteed that the operation has been carried out, even if the
757   status code returned from the origin server indicates that the action
758   has been completed successfully. However, the server &SHOULD-NOT; 
759   indicate success unless, at the time the response is given, it
760   intends to delete the resource or move it to an inaccessible
761   location.
762</t>
763<t>
764   A successful response &SHOULD; be 200 (OK) if the response includes an
765   representation describing the status, 202 (Accepted) if the action has not
766   yet been enacted, or 204 (No Content) if the action has been enacted
767   but the response does not include a representation.
768</t>
769<t>
770   Bodies on DELETE requests have no defined semantics. Note that sending a body
771   on a DELETE request might cause some existing implementations to reject the
772   request.
773</t>
774<t>
775   Responses to the DELETE method are not cacheable. If a DELETE request
776   passes through a cache that has one or more stored responses for the
777   effective request URI, those stored responses will be invalidated (see
778   &p6-invalid;).
779</t>
780</section>
781
782<section title="TRACE" anchor="TRACE">
783  <rdf:Description>
784    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
785  </rdf:Description>
786  <iref primary="true" item="TRACE method" x:for-anchor=""/>
787  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
788<t>
789   The TRACE method requests a remote, application-layer loop-back
790   of the request message. The final recipient of the request
791   &SHOULD; reflect the message received back to the client as the
792   message body of a 200 (OK) response. The final recipient is either the
793   origin server or the first proxy to receive a Max-Forwards
794   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
795   A TRACE request &MUST-NOT; include a message body.
796</t>
797<t>
798   TRACE allows the client to see what is being received at the other
799   end of the request chain and use that data for testing or diagnostic
800   information. The value of the Via header field (&header-via;) is of
801   particular interest, since it acts as a trace of the request chain.
802   Use of the Max-Forwards header field allows the client to limit the
803   length of the request chain, which is useful for testing a chain of
804   proxies forwarding messages in an infinite loop.
805</t>
806<t>
807   If the request is valid, the response &SHOULD; have a Content-Type of
808   "message/http" (see &media-type-message-http;) and contain a message body
809   that encloses a copy of the entire request message.
810   Responses to the TRACE method are not cacheable.
811</t>
812</section>
813
814<section title="CONNECT" anchor="CONNECT">
815  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
816  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
817<t>
818   The CONNECT method requests that the proxy establish a tunnel
819   to the request-target and, if successful, thereafter restrict its behavior
820   to blind forwarding of packets until the connection is closed.
821</t>
822<t>
823   When using CONNECT, the request-target &MUST; use the authority form
824   (&request-target;); i.e., the request-target consists of only the
825   host name and port number of the tunnel destination, separated by a colon.
826   For example,
827</t>
828<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
829CONNECT server.example.com:80 HTTP/1.1
830Host: server.example.com:80
831
832</artwork></figure>
833<t>
834   Any successful (2xx) response to a CONNECT request indicates that the
835   proxy has established a connection to the requested host and port,
836   and has switched to tunneling the current connection to that server
837   connection.
838   The tunneled data from the server begins immediately after the blank line
839   that concludes the successful response's header block.
840   A server &SHOULD-NOT; send any Transfer-Encoding or Content-Length
841   header fields in a successful response.
842   A client &MUST; ignore any Content-Length or Transfer-Encoding header
843   fields received in a successful response.
844</t>
845<t>
846   Any response other than a successful response indicates that the tunnel
847   has not yet been formed and that the connection remains governed by HTTP.
848</t>
849<t>
850   Proxy authentication might be used to establish the
851   authority to create a tunnel:
852</t>
853<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
854CONNECT server.example.com:80 HTTP/1.1
855Host: server.example.com:80
856Proxy-Authorization: basic aGVsbG86d29ybGQ=
857
858</artwork></figure>
859<t>
860   A message body on a CONNECT request has no defined semantics. Sending a
861   body on a CONNECT request might cause existing implementations to reject
862   the request.
863</t>
864<t>
865   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
866   to server &MAY; be sent immediately after the request (before a response
867   is received). The usual caveats also apply:
868   data may be discarded if the eventual response is negative, and the
869   connection may be reset with no response if more than one TCP segment
870   is outstanding.
871</t>
872<t>
873   It may be the case that the proxy itself can only reach the requested
874   origin server through another proxy.  In this case, the first proxy
875   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
876   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
877   unless it has either a direct or tunnel connection established to the
878   authority.
879</t>
880<t>
881   If at any point either one of the peers gets disconnected, any
882   outstanding data that came from that peer will be passed to the other
883   one, and after that also the other connection will be terminated by
884   the proxy. If there is outstanding data to that peer undelivered,
885   that data will be discarded.
886</t>
887<t>
888   An origin server which receives a CONNECT request for itself &MAY;
889   respond with a 2xx status code to indicate that a connection is
890   established.  However, most origin servers do not implement CONNECT.
891</t>
892</section>
893</section>
894
895</section>
896
897<section title="Header Fields" anchor="header.fields">
898<t>
899   Header fields are key value pairs that can be used to communicate data about
900   the message, its payload, the target resource, or about the connection
901   itself (i.e., control data).  See &header-fields; for a general definition
902   of their syntax.
903</t>
904
905<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
906<t>
907   New header fields are registered using the procedures described in
908   <xref target="RFC3864"/>.
909</t>
910<t>
911   The requirements for header field names are defined in
912   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
913   defining new fields are advised to keep the name as short as practical, and
914   not to prefix them with "X-" if they are to be registered (either
915   immediately or in the future).
916</t>
917<t>
918   New header field values typically have their syntax defined using ABNF
919   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
920   as necessary, and are usually constrained to the range of ASCII characters.
921   Header fields needing a greater range of characters can use an encoding
922   such as the one defined in <xref target="RFC5987"/>.
923</t>
924<t>
925   Because commas (",") are used as a generic delimiter between field-values,
926   they need to be treated with care if they are allowed in the field-value's
927   payload. Typically, components that might contain a comma are protected with
928   double-quotes using the quoted-string ABNF production (&field-components;).
929</t>
930<t>
931   For example, a textual date and a URI (either of which might contain a comma)
932   could be safely carried in field-values like these:
933</t>
934<figure><artwork type="example">
935  Example-URI-Field: "http://example.com/a.html,foo",
936                     "http://without-a-comma.example.com/"
937  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
938</artwork></figure>
939<t>
940   Note that double quote delimiters almost always are used with the
941   quoted-string production; using a different syntax inside double quotes
942   will likely cause unnecessary confusion.
943</t>
944<t>
945   Many header fields use a format including (case-insensitively) named
946   parameters (for instance, Content-Type, defined in &header-content-type;).
947   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
948   parameter value enables recipients to use existing parser components. When
949   allowing both forms, the meaning of a parameter value ought to be
950   independent of the syntax used for it (for an example, see the notes on
951   parameter handling for media types in &media-types;).
952</t>
953<t>
954   Authors of specifications defining new header fields are advised to consider
955   documenting:
956  <list style="symbols">
957    <x:lt>
958      <t>Whether the field is a single value, or whether it can be a list
959      (delimited by commas; see &header-fields;).</t>
960      <t>If it does not use the list syntax, document how to treat messages
961      where the header field occurs multiple times (a sensible default would
962      be to ignore the header field, but this might not always be the right
963      choice).</t>
964      <t>Note that intermediaries and software libraries might combine
965      multiple header field instances into a single one, despite the header
966      field not allowing this. A robust format enables recipients to discover
967      these situations (good example: "Content-Type", as the comma can only
968      appear inside quoted strings; bad example: "Location", as a comma can
969      occur inside a URI).</t>
970    </x:lt>
971    <x:lt><t>Under what conditions the header field can be used; e.g., only in
972    responses or requests, in all messages, only on responses to a particular
973    request method.</t></x:lt>
974    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
975    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
976    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
977    field's value, insert or delete it.</t></x:lt>
978    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
979    <x:lt><t>Whether the header field is useful or allowable in trailers (see
980    &chunked-encoding;).</t></x:lt>
981    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
982  </list>
983</t>
984</section>
985
986<section title="Request Header Fields" anchor="request.header.fields">
987  <x:anchor-alias value="request-header"/>
988<t>
989   The request header fields allow the client to pass additional
990   information about the request, and about the client itself, to the
991   server. These fields act as request modifiers, with semantics
992   equivalent to the parameters on a programming language method
993   invocation.
994</t>
995<texttable align="left">
996  <ttcol>Header Field Name</ttcol>
997  <ttcol>Defined in...</ttcol>
998
999  <c>Accept</c> <c>&header-accept;</c>
1000  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
1001  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
1002  <c>Accept-Language</c> <c>&header-accept-language;</c>
1003  <c>Authorization</c> <c>&header-authorization;</c>
1004  <c>Expect</c> <c><xref target="header.expect"/></c>
1005  <c>From</c> <c><xref target="header.from"/></c>
1006  <c>Host</c> <c>&header-host;</c>
1007  <c>If-Match</c> <c>&header-if-match;</c>
1008  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
1009  <c>If-None-Match</c> <c>&header-if-none-match;</c>
1010  <c>If-Range</c> <c>&header-if-range;</c>
1011  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
1012  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
1013  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
1014  <c>Range</c> <c>&header-range;</c>
1015  <c>Referer</c> <c><xref target="header.referer"/></c>
1016  <c>TE</c> <c>&header-te;</c>
1017  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
1018</texttable>
1019</section>
1020
1021<section title="Response Header Fields" anchor="response.header.fields">
1022  <x:anchor-alias value="response-header"/>
1023<t>
1024   The response header fields allow the server to pass additional
1025   information about the response which cannot be placed in the status-line.
1026   These header fields give information about the server and about
1027   further access to the target resource (&effective-request-uri;).
1028</t>
1029<texttable align="left">
1030  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
1031
1032  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
1033  <c>Age</c> <c>&header-age;</c>
1034  <c>Allow</c> <c><xref target="header.allow"/></c>
1035  <c>Date</c> <c><xref target="header.date"/></c>
1036  <c>ETag</c> <c>&header-etag;</c>
1037  <c>Location</c> <c><xref target="header.location"/></c>
1038  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
1039  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
1040  <c>Server</c> <c><xref target="header.server"/></c>
1041  <c>Vary</c> <c>&header-vary;</c>
1042  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
1043</texttable>
1044</section>
1045
1046</section>
1047
1048<section title="Status Codes" anchor="status.codes">
1049<t>
1050   The status-code element is a 3-digit integer result code of the attempt to
1051   understand and satisfy the request.
1052</t>
1053<t>
1054   HTTP status codes are extensible. HTTP applications are not required
1055   to understand the meaning of all registered status codes, though such
1056   understanding is obviously desirable. However, applications &MUST;
1057   understand the class of any status code, as indicated by the first
1058   digit, and treat any unrecognized response as being equivalent to the
1059   x00 status code of that class, with the exception that an
1060   unrecognized response &MUST-NOT; be cached. For example, if an
1061   unrecognized status code of 431 is received by the client, it can
1062   safely assume that there was something wrong with its request and
1063   treat the response as if it had received a 400 status code. In such
1064   cases, user agents &SHOULD; present to the user the representation enclosed
1065   with the response, since that representation is likely to include human-readable
1066   information which will explain the unusual status.
1067</t>
1068<t>
1069   The first digit of the status-code defines the class of response. The
1070   last two digits do not have any categorization role. There are 5
1071   values for the first digit:
1072  <list style="symbols">
1073    <t>
1074      1xx: Informational - Request received, continuing process
1075    </t>
1076    <t>
1077      2xx: Success - The action was successfully received,
1078        understood, and accepted
1079    </t>
1080    <t>
1081      3xx: Redirection - Further action needs to be taken in order to
1082        complete the request
1083    </t>
1084    <t>
1085      4xx: Client Error - The request contains bad syntax or cannot
1086        be fulfilled
1087    </t>
1088    <t>
1089      5xx: Server Error - The server failed to fulfill an apparently
1090        valid request
1091    </t>
1092  </list>
1093</t>
1094<t>
1095   For most status codes the response can carry a payload, in which case a
1096   Content-Type header field indicates the payload's media type
1097   (&header-content-type;).
1098</t>
1099
1100<section title="Overview of Status Codes" anchor="overview.of.status.codes">
1101<t> 
1102   The status codes listed below are defined in this specification,
1103   &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
1104   The reason phrases listed here are only recommendations &mdash; they can be
1105   replaced by local equivalents without affecting the protocol.
1106</t>
1107<texttable align="left">
1108  <ttcol>status-code</ttcol>
1109  <ttcol>reason-phrase</ttcol>
1110  <ttcol>Defined in...</ttcol>
1111 
1112  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
1113  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
1114
1115  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
1116  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
1117  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
1118  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
1119  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
1120  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
1121  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
1122
1123  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
1124  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
1125  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
1126  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
1127  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
1128  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
1129  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
1130
1131  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
1132  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
1133  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
1134  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
1135  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
1136  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
1137  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
1138  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
1139  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
1140  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
1141  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
1142  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
1143  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
1144  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
1145  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
1146  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
1147  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
1148  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
1149  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
1150
1151  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
1152  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
1153  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
1154  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
1155  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
1156  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
1157</texttable>
1158<t>
1159   Note that this list is not exhaustive &mdash; it does not include
1160   extension status codes defined in other specifications.
1161</t>
1162</section>
1163
1164<section title="Status Code Registry" anchor="status.code.registry">
1165<t>
1166  The HTTP Status Code Registry defines the name space for the status-code
1167  token in the status-line of an HTTP response.
1168</t>
1169<t>
1170  Values to be added to this name space require IETF Review
1171  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
1172</t>
1173<t>
1174  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
1175</t>
1176
1177<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
1178<t>
1179   When it is necessary to express new semantics for a HTTP response that
1180   aren't specific to a single application or media type, and currently defined
1181   status codes are inadequate, a new status code can be registered.
1182</t>
1183<t>
1184   HTTP status codes are generic; that is, they are potentially applicable to
1185   any resource, not just one particular media type, "type" of resource, or
1186   application. As such, it is preferred that new HTTP status codes be
1187   registered in a document that isn't specific to a single application, so
1188   that this is clear.
1189</t>
1190<t>
1191   Definitions of new HTTP status codes typically explain the request
1192   conditions that produce a response containing the status code (e.g.,
1193   combinations of request headers and/or method(s)), along with any
1194   interactions with response headers (e.g., those that are required, those
1195   that modify the semantics of the response).
1196</t>
1197<t>
1198   New HTTP status codes are required to fall under one of the categories
1199   defined in <xref target="status.codes"/>. To allow existing parsers to
1200   properly handle them, new status codes cannot disallow a response body,
1201   although they can mandate a zero-length response body. They can require the
1202   presence of one or more particular HTTP response header(s).
1203</t>
1204<t>
1205   Likewise, their definitions can specify that caches are allowed to use
1206   heuristics to determine their freshness (see &caching;; by default, it is
1207   not allowed), and can define how to determine the resource which they
1208   carry a representation for (see <xref
1209   target="identifying.response.associated.with.representation"/>; by default,
1210   it is anonymous).
1211</t>
1212</section>
1213
1214</section>
1215
1216<section title="Informational 1xx" anchor="status.1xx">
1217<t>
1218   This class of status code indicates a provisional response,
1219   consisting only of the status-line and optional header fields, and is
1220   terminated by an empty line. There are no required header fields for this
1221   class of status code. Since HTTP/1.0 did not define any 1xx status
1222   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1223   except under experimental conditions.
1224</t>
1225<t>
1226   A client &MUST; be prepared to accept one or more 1xx status responses
1227   prior to a regular response, even if the client does not expect a 100
1228   (Continue) status message. Unexpected 1xx status responses &MAY; be
1229   ignored by a user agent.
1230</t>
1231<t>
1232   Proxies &MUST; forward 1xx responses, unless the connection between the
1233   proxy and its client has been closed, or unless the proxy itself
1234   requested the generation of the 1xx response. (For example, if a
1235   proxy adds a "Expect: 100-continue" field when it forwards a request,
1236   then it need not forward the corresponding 100 (Continue)
1237   response(s).)
1238</t>
1239
1240<section title="100 Continue" anchor="status.100">
1241  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1242  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1243<t>
1244   The client &SHOULD; continue with its request. This interim response is
1245   used to inform the client that the initial part of the request has
1246   been received and has not yet been rejected by the server. The client
1247   &SHOULD; continue by sending the remainder of the request or, if the
1248   request has already been completed, ignore this response. The server
1249   &MUST; send a final response after the request has been completed. See
1250   &use100; for detailed discussion of the use and handling of this
1251   status code.
1252</t>
1253</section>
1254
1255<section title="101 Switching Protocols" anchor="status.101">
1256  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1257  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1258<t>
1259   The server understands and is willing to comply with the client's
1260   request, via the Upgrade message header field (&header-upgrade;), for a
1261   change in the application protocol being used on this connection. The
1262   server will switch protocols to those defined by the response's
1263   Upgrade header field immediately after the empty line which
1264   terminates the 101 response.
1265</t>
1266<t>
1267   The protocol &SHOULD; be switched only when it is advantageous to do
1268   so. For example, switching to a newer version of HTTP is advantageous
1269   over older versions, and switching to a real-time, synchronous
1270   protocol might be advantageous when delivering resources that use
1271   such features.
1272</t>
1273</section>
1274</section>
1275
1276<section title="Successful 2xx" anchor="status.2xx">
1277<t>
1278   This class of status code indicates that the client's request was
1279   successfully received, understood, and accepted.
1280</t>
1281
1282<section title="200 OK" anchor="status.200">
1283  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1284  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1285<t>
1286   The request has succeeded. The payload returned with the response
1287   is dependent on the method used in the request, for example:
1288  <list style="hanging">
1289    <t hangText="GET">
1290      a representation of the target resource is sent in the response;
1291    </t>
1292    <t hangText="HEAD">
1293      the same representation as GET, except without the message body;
1294    </t>
1295    <t hangText="POST">
1296      a representation describing or containing the result of the action;
1297    </t>
1298    <t hangText="TRACE">
1299      a representation containing the request message as received by the
1300      end server.
1301    </t>
1302  </list>
1303</t>
1304<t>
1305   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1306   freshness for 200 responses.
1307</t>
1308</section>
1309
1310<section title="201 Created" anchor="status.201">
1311  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1312  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1313<t>
1314   The request has been fulfilled and has resulted in a new resource being
1315   created.
1316</t>
1317<t>
1318   The newly created resource is typically linked to from the response payload,
1319   with the most relevant URI also being carried in the Location header field.
1320   If the newly created resource's URI is the same as the Effective Request URI,
1321   this information can be omitted (e.g., in the case of a response to a PUT
1322   request). 
1323</t>
1324<t>
1325   The origin server &MUST; create the resource before returning the 201 status
1326   code. If the action cannot be carried out immediately, the server &SHOULD;
1327   respond with 202 (Accepted) response instead.
1328</t>
1329<t>
1330   A 201 response &MAY; contain an ETag response header field indicating
1331   the current value of the entity-tag for the representation of the resource
1332   just created (see &header-etag;).
1333</t>
1334</section>
1335
1336<section title="202 Accepted" anchor="status.202">
1337  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1338  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1339<t>
1340   The request has been accepted for processing, but the processing has
1341   not been completed.  The request might or might not eventually be
1342   acted upon, as it might be disallowed when processing actually takes
1343   place. There is no facility for re-sending a status code from an
1344   asynchronous operation such as this.
1345</t>
1346<t>
1347   The 202 response is intentionally non-committal. Its purpose is to
1348   allow a server to accept a request for some other process (perhaps a
1349   batch-oriented process that is only run once per day) without
1350   requiring that the user agent's connection to the server persist
1351   until the process is completed. The representation returned with this
1352   response &SHOULD; include an indication of the request's current status
1353   and either a pointer to a status monitor or some estimate of when the
1354   user can expect the request to be fulfilled.
1355</t>
1356</section>
1357
1358<section title="203 Non-Authoritative Information" anchor="status.203">
1359  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1360  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1361<t>
1362   The representation in the response has been transformed or otherwise
1363   modified by a transforming proxy (&intermediaries;).  Note that the
1364   behavior of transforming intermediaries is controlled by the no-transform
1365   Cache-Control directive (&header-cache-control;).
1366</t>
1367<t>
1368   This status code is only appropriate when the response status code would
1369   have been 200 (OK) otherwise. When the status code before transformation
1370   would have been different, the 214 Transformation Applied warn-code
1371   (&header-warning;) is appropriate.
1372</t>
1373<t>
1374   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1375   freshness for 203 responses.
1376</t>
1377</section>
1378
1379<section title="204 No Content" anchor="status.204">
1380  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1381  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1382<t>
1383   The 204 (No Content) status code indicates that the server has
1384   successfully fulfilled the request and that there is no additional
1385   content to return in the response payload body.  Metadata in the
1386   response header fields refer to the target resource and its current
1387   representation after the requested action.
1388</t>
1389<t>
1390   For example, if a 204 status code is received in response to a PUT
1391   request and the response contains an ETag header field, then the PUT
1392   was successful and the ETag field-value contains the entity-tag for
1393   the new representation of that target resource.
1394</t>
1395<t>
1396   The 204 response allows a server to indicate that the action has been
1397   successfully applied to the target resource while implying that the
1398   user agent &SHOULD-NOT; traverse away from its current "document view"
1399   (if any).  The server assumes that the user agent will provide some
1400   indication of the success to its user, in accord with its own interface,
1401   and apply any new or updated metadata in the response to the active
1402   representation.
1403</t>
1404<t>
1405   For example, a 204 status code is commonly used with document editing
1406   interfaces corresponding to a "save" action, such that the document
1407   being saved remains available to the user for editing. It is also
1408   frequently used with interfaces that expect automated data transfers
1409   to be prevalent, such as within distributed version control systems.
1410</t>
1411<t>
1412   The 204 response &MUST-NOT; include a message body, and thus is always
1413   terminated by the first empty line after the header fields.
1414</t>
1415</section>
1416
1417<section title="205 Reset Content" anchor="status.205">
1418  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1419  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1420<t>
1421   The server has fulfilled the request and the user agent &SHOULD; reset
1422   the document view which caused the request to be sent. This response
1423   is primarily intended to allow input for actions to take place via
1424   user input, followed by a clearing of the form in which the input is
1425   given so that the user can easily initiate another input action.
1426</t>
1427<t>   
1428   The message body included with the response &MUST; be empty. Note that
1429   receivers still need to parse the response according to the algorithm defined
1430   in &message-body;.
1431</t>
1432</section>
1433</section>
1434
1435<section title="Redirection 3xx" anchor="status.3xx">
1436<t>
1437   This class of status code indicates that further action needs to be
1438   taken by the user agent in order to fulfill the request.  If the required
1439   action involves a subsequent HTTP request, it &MAY; be carried out by the
1440   user agent without interaction with the user if and only if the method used
1441   in the second request is known to be "safe", as defined in
1442   <xref target="safe.methods"/>.
1443</t>
1444<t>
1445   There are several types of redirects:
1446   <list style="numbers">
1447      <x:lt>
1448        <t>
1449          Redirects of the request to another URI, either temporarily or
1450          permanently. The new URI is specified in the Location header field.
1451          In this specification, the status codes 301 (Moved Permanently),
1452          302 (Found), and 307 (Temporary Redirect) fall under this category.
1453        </t>
1454      </x:lt>
1455      <x:lt>
1456        <t>
1457          Redirection to a new location that represents an indirect response to
1458          the request, such as the result of a POST operation to be retrieved
1459          with a subsequent GET request. This is status code 303 (See Other).
1460        </t>
1461      </x:lt>
1462      <x:lt>
1463        <t>
1464          Redirection offering a choice of matching resources for use by
1465          agent-driven content negotiation (&agent-driven-negotiation;). This
1466          is status code 300 (Multiple Choices).
1467        </t>
1468      </x:lt>
1469      <x:lt>
1470        <t>
1471          Other kinds of redirection, such as to a cached result (status code 304
1472          (Not Modified), see &status-304;).
1473        </t>
1474      </x:lt>
1475   </list>
1476</t>
1477<x:note>
1478  <t>
1479    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1480    and 302 (Found) were defined for the first type of redirect, and the second
1481    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1482    However it turned out that web forms using POST expected redirects to change
1483    the operation for the subsequent request to retrieval (GET). To address this
1484    use case, HTTP/1.1 introduced the second type of redirect with the status
1485    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1486    As user agents did not change their behavior to maintain backwards
1487    compatibility, the first revision of HTTP/1.1 added yet another status code,
1488    307 (Temporary Redirect), for which the backwards compatibility problems did
1489    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1490    Over 10 years later, most user agents still do method rewriting for
1491    status codes 301 and 302, therefore this specification makes that behavior
1492    conformant in case the original request was POST.
1493  </t>
1494</x:note>
1495<t>
1496   A Location header field on a 3xx response indicates that a client &MAY;
1497   automatically redirect to the URI provided; see <xref target="header.location"/>.
1498</t>
1499<t>
1500   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1501   automatic redirection needs to done with care, since the redirect might
1502   change the conditions under which the request was issued.
1503</t>
1504<t>
1505   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1506   "infinite" redirection loops).
1507</t>
1508<x:note>
1509  <t>
1510    <x:h>Note:</x:h> An earlier version of this specification recommended a
1511    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1512    Content developers need to be aware that some clients might
1513    implement such a fixed limitation.
1514  </t>
1515</x:note>
1516
1517<section title="300 Multiple Choices" anchor="status.300">
1518  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1519  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1520<t>
1521   The target resource has more than one
1522   representation, each with its own specific location, and agent-driven
1523   negotiation information (&content-negotiation;) is being provided so that
1524   the user (or user agent) can select a preferred representation by
1525   redirecting its request to that location.
1526</t>
1527<t>
1528   Unless it was a HEAD request, the response &SHOULD; include a representation
1529   containing a list of representation metadata and location(s) from
1530   which the user or user agent can choose the one most appropriate. Depending
1531   upon the format and the capabilities of
1532   the user agent, selection of the most appropriate choice &MAY; be
1533   performed automatically. However, this specification does not define
1534   any standard for such automatic selection.
1535</t>
1536<t>
1537   If the server has a preferred choice of representation, it &SHOULD;
1538   include the specific URI for that representation in the Location
1539   field; user agents &MAY; use the Location field value for automatic
1540   redirection.
1541</t>
1542<t>
1543   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1544   freshness for 300 responses.
1545</t>
1546
1547</section>
1548
1549<section title="301 Moved Permanently" anchor="status.301">
1550  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1551  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1552<t>
1553   The target resource has been assigned a new permanent URI and any
1554   future references to this resource &SHOULD; use one of the returned
1555   URIs.  Clients with link editing capabilities ought to automatically
1556   re-link references to the effective request URI to one or more of the new
1557   references returned by the server, where possible.
1558</t>
1559<t>
1560   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1561   freshness for 301 responses.
1562</t>
1563<t>
1564   The new permanent URI &SHOULD; be given by the Location field in the
1565   response. A response payload can contain a short hypertext note with a
1566   hyperlink to the new URI(s).
1567</t>
1568<x:note>
1569  <t>
1570    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1571    request method from POST to GET for the subsequent request. If this
1572    behavior is undesired, status code 307 (Temporary Redirect) can be used
1573    instead.
1574  </t>
1575</x:note>
1576</section>
1577
1578<section title="302 Found" anchor="status.302">
1579  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1580  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1581<t>
1582   The target resource resides temporarily under a different URI.
1583   Since the redirection might be altered on occasion, the client &SHOULD;
1584   continue to use the effective request URI for future requests.
1585</t>
1586<t>
1587   The temporary URI &SHOULD; be given by the Location field in the
1588   response. A response payload can contain a short hypertext note with a
1589   hyperlink to the new URI(s).
1590</t>
1591<x:note>
1592  <t>
1593    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1594    request method from POST to GET for the subsequent request. If this
1595    behavior is undesired, status code 307 (Temporary Redirect) can be used
1596    instead.
1597  </t>
1598</x:note>
1599</section>
1600
1601<section title="303 See Other" anchor="status.303">
1602  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1603  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1604<t>
1605   The 303 status code indicates that the server is redirecting the
1606   user agent to a different resource, as indicated by a URI in the
1607   Location header field, that is intended to provide an indirect
1608   response to the original request.  In order to satisfy the original
1609   request, a user agent &SHOULD; perform a retrieval request using the
1610   Location URI (a GET or HEAD request if using HTTP), which
1611   may itself be redirected further, and present the eventual result as an
1612   answer to the original request.
1613   Note that the new URI in the Location header field is not considered
1614   equivalent to the effective request URI.
1615</t>
1616<t>
1617   This status code is generally applicable to any HTTP method.  It is
1618   primarily used to allow the output of a POST action to redirect
1619   the user agent to a selected resource, since doing so provides the
1620   information corresponding to the POST response in a form that
1621   can be separately identified, bookmarked, and cached independent
1622   of the original request.
1623</t>
1624<t>
1625   A 303 response to a GET request indicates that the requested
1626   resource does not have a representation of its own that can be
1627   transferred by the server over HTTP.  The Location URI indicates a
1628   resource that is descriptive of the target resource, such that the
1629   follow-on representation might be useful to recipients without
1630   implying that it adequately represents the target resource.
1631   Note that answers to the questions of what can be represented, what
1632   representations are adequate, and what might be a useful description
1633   are outside the scope of HTTP and thus entirely determined by the
1634   URI owner(s).
1635</t>
1636<t>
1637   Except for responses to a HEAD request, the representation of a 303
1638   response &SHOULD; contain a short hypertext note with a hyperlink
1639   to the Location URI.
1640</t>
1641</section>
1642
1643<section title="305 Use Proxy" anchor="status.305">
1644  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1645  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1646<t>
1647   The 305 status code was defined in a previous version of this specification
1648   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1649</t>
1650</section>
1651
1652<section title="306 (Unused)" anchor="status.306">
1653  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1654  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1655<t>
1656   The 306 status code was used in a previous version of the
1657   specification, is no longer used, and the code is reserved.
1658</t>
1659</section>
1660
1661<section title="307 Temporary Redirect" anchor="status.307">
1662  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1663  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1664<t>
1665   The target resource resides temporarily under a different URI.
1666   Since the redirection can change over time, the client &SHOULD;
1667   continue to use the effective request URI for future requests.
1668</t>
1669<t>
1670   The temporary URI &SHOULD; be given by the Location field in the
1671   response. A response payload can contain a short hypertext note with a
1672   hyperlink to the new URI(s).
1673</t>
1674<x:note>
1675  <t>
1676    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1677    it does not allow rewriting the request method from POST to GET. This
1678    specification defines no equivalent counterpart for 301 Moved Permanently
1679    (<xref target="draft-reschke-http-status-308"/>, however, defines the
1680    status code 308 Permanent Redirect for this purpose).
1681  </t>
1682</x:note>
1683</section>
1684</section>
1685
1686<section title="Client Error 4xx" anchor="status.4xx">
1687<t>
1688   The 4xx class of status code is intended for cases in which the
1689   client seems to have erred. Except when responding to a HEAD request,
1690   the server &SHOULD; include a representation containing an explanation of the
1691   error situation, and whether it is a temporary or permanent
1692   condition. These status codes are applicable to any request method.
1693   User agents &SHOULD; display any included representation to the user.
1694</t>
1695
1696<section title="400 Bad Request" anchor="status.400">
1697  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1698  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1699<t>
1700   The server cannot or will not process the request, due to a client error (e.g.,
1701   malformed syntax).
1702</t>
1703</section>
1704
1705<section title="402 Payment Required" anchor="status.402">
1706  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1707  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1708<t>
1709   This code is reserved for future use.
1710</t>
1711</section>
1712
1713<section title="403 Forbidden" anchor="status.403">
1714  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1715  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1716<t>
1717   The server understood the request, but refuses to authorize it. Providing
1718   different user authentication credentials might be successful, but any
1719   credentials that were provided in the request are insufficient. The request
1720   &SHOULD-NOT; be repeated with the same credentials.
1721</t>
1722<t>
1723   If the request method was not HEAD and the server wishes to make
1724   public why the request has not been fulfilled, it &SHOULD; describe the
1725   reason for the refusal in the representation.  If the server does not wish to
1726   make this information available to the client, the status code 404
1727   (Not Found) &MAY; be used instead.
1728</t>
1729</section>
1730
1731<section title="404 Not Found" anchor="status.404">
1732  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1733  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1734<t>
1735   The server has not found anything matching the effective request URI. No
1736   indication is given of whether the condition is temporary or
1737   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1738   knows, through some internally configurable mechanism, that an old
1739   resource is permanently unavailable and has no forwarding address.
1740   This status code is commonly used when the server does not wish to
1741   reveal exactly why the request has been refused, or when no other
1742   response is applicable.
1743</t>
1744</section>
1745
1746<section title="405 Method Not Allowed" anchor="status.405">
1747  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1748  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1749<t>
1750   The method specified in the request-line is not allowed for the target
1751   resource. The response &MUST; include an Allow header field containing a
1752   list of valid methods for the requested resource.
1753</t>
1754</section>
1755
1756<section title="406 Not Acceptable" anchor="status.406">
1757  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1758  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1759<t>
1760   The resource identified by the request is only capable of generating
1761   response representations which have content characteristics not acceptable
1762   according to the Accept and Accept-* header fields sent in the request
1763   (see &p3-header-fields;).
1764</t>
1765<t>
1766   Unless it was a HEAD request, the response &SHOULD; include a representation
1767   containing a list of available representation characteristics and location(s)
1768   from which the user or user agent can choose the one most
1769   appropriate. Depending upon the format and the
1770   capabilities of the user agent, selection of the most appropriate
1771   choice &MAY; be performed automatically. However, this specification
1772   does not define any standard for such automatic selection.
1773</t>
1774<x:note>
1775  <t>
1776    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1777    not acceptable according to the accept header fields sent in the
1778    request. In some cases, this might even be preferable to sending a
1779    406 response. User agents are encouraged to inspect the header fields of
1780    an incoming response to determine if it is acceptable.
1781  </t>
1782</x:note>
1783<t>
1784   If the response could be unacceptable, a user agent &SHOULD;
1785   temporarily stop receipt of more data and query the user for a
1786   decision on further actions.
1787</t>
1788</section>
1789
1790<section title="408 Request Timeout" anchor="status.408">
1791  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1792  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1793<t>
1794   The client did not produce a request within the time that the server
1795   was prepared to wait. The client &MAY; repeat the request without
1796   modifications at any later time.
1797</t>
1798</section>
1799
1800<section title="409 Conflict" anchor="status.409">
1801  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1802  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1803<t>
1804   The request could not be completed due to a conflict with the current
1805   state of the resource. This code is only allowed in situations where
1806   it is expected that the user might be able to resolve the conflict
1807   and resubmit the request. The response body &SHOULD; include enough
1808   information for the user to recognize the source of the conflict.
1809   Ideally, the response representation would include enough information for the
1810   user or user agent to fix the problem; however, that might not be
1811   possible and is not required.
1812</t>
1813<t>
1814   Conflicts are most likely to occur in response to a PUT request. For
1815   example, if versioning were being used and the representation being PUT
1816   included changes to a resource which conflict with those made by an
1817   earlier (third-party) request, the server might use the 409 response
1818   to indicate that it can't complete the request. In this case, the
1819   response representation would likely contain a list of the differences
1820   between the two versions.
1821</t>
1822</section>
1823
1824<section title="410 Gone" anchor="status.410">
1825  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1826  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1827<t>
1828   The target resource is no longer available at the server and no
1829   forwarding address is known. This condition is expected to be
1830   considered permanent. Clients with link editing capabilities &SHOULD;
1831   delete references to the effective request URI after user approval. If the
1832   server does not know, or has no facility to determine, whether or not
1833   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1834   used instead.
1835</t>
1836<t>
1837   The 410 response is primarily intended to assist the task of web
1838   maintenance by notifying the recipient that the resource is
1839   intentionally unavailable and that the server owners desire that
1840   remote links to that resource be removed. Such an event is common for
1841   limited-time, promotional services and for resources belonging to
1842   individuals no longer working at the server's site. It is not
1843   necessary to mark all permanently unavailable resources as "gone" or
1844   to keep the mark for any length of time &mdash; that is left to the
1845   discretion of the server owner.
1846</t>
1847<t>
1848   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
1849   for 410 responses.
1850</t>
1851</section>
1852
1853<section title="411 Length Required" anchor="status.411">
1854  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1855  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1856<t>
1857   The server refuses to accept the request without a defined Content-Length.
1858   The client &MAY; repeat the request if it adds a valid
1859   Content-Length header field containing the length of the message body
1860   in the request message.
1861</t>
1862</section>
1863
1864<section title="413 Request Representation Too Large" anchor="status.413">
1865  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
1866  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
1867<t>
1868   The server is refusing to process a request because the request
1869   representation is larger than the server is willing or able to process. The
1870   server &MAY; close the connection to prevent the client from continuing
1871   the request.
1872</t>
1873<t>
1874   If the condition is temporary, the server &SHOULD; include a Retry-After
1875   header field to indicate that it is temporary and after what
1876   time the client &MAY; try again.
1877</t>
1878</section>
1879
1880<section title="414 URI Too Long" anchor="status.414">
1881  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1882  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1883<t>
1884   The server is refusing to service the request because the effective request URI
1885   is longer than the server is willing to interpret. This rare
1886   condition is only likely to occur when a client has improperly
1887   converted a POST request to a GET request with long query
1888   information, when the client has descended into a URI "black hole" of
1889   redirection (e.g., a redirected URI prefix that points to a suffix of
1890   itself), or when the server is under attack by a client attempting to
1891   exploit security holes present in some servers using fixed-length
1892   buffers for reading or manipulating the request-target.
1893</t>
1894</section>
1895
1896<section title="415 Unsupported Media Type" anchor="status.415">
1897  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1898  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1899<t>
1900   The server is refusing to service the request because the request
1901   payload is in a format not supported by this request method on the
1902   target resource.
1903</t>
1904</section>
1905
1906<section title="417 Expectation Failed" anchor="status.417">
1907  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1908  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1909<t>
1910   The expectation given in an Expect header field (see <xref target="header.expect"/>)
1911   could not be met by this server, or, if the server is a proxy,
1912   the server has unambiguous evidence that the request could not be met
1913   by the next-hop server.
1914</t>
1915</section>
1916
1917<section title="426 Upgrade Required" anchor="status.426">
1918  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
1919  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
1920<t>
1921   The request can not be completed without a prior protocol upgrade. This
1922   response &MUST; include an Upgrade header field (&header-upgrade;)
1923   specifying the required protocols.
1924</t>
1925<figure>
1926<preamble>Example:</preamble>
1927<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
1928HTTP/1.1 426 Upgrade Required
1929Upgrade: HTTP/3.0
1930Connection: Upgrade
1931Content-Length: <x:length-of target="s426body"/>
1932Content-Type: text/plain
1933
1934<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
1935</x:span></artwork></figure>
1936<t>
1937   The server &SHOULD; include a message body in the 426 response which
1938   indicates in human readable form the reason for the error and describes any
1939   alternative courses which may be available to the user.
1940</t>
1941</section>
1942</section>
1943
1944<section title="Server Error 5xx" anchor="status.5xx">
1945<t>
1946   Response status codes beginning with the digit "5" indicate cases in
1947   which the server is aware that it has erred or is incapable of
1948   performing the request. Except when responding to a HEAD request, the
1949   server &SHOULD; include a representation containing an explanation of the
1950   error situation, and whether it is a temporary or permanent
1951   condition. User agents &SHOULD; display any included representation to the
1952   user. These response codes are applicable to any request method.
1953</t>
1954
1955<section title="500 Internal Server Error" anchor="status.500">
1956  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1957  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1958<t>
1959   The server encountered an unexpected condition which prevented it
1960   from fulfilling the request.
1961</t>
1962</section>
1963
1964<section title="501 Not Implemented" anchor="status.501">
1965  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1966  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1967<t>
1968   The server does not support the functionality required to fulfill the
1969   request. This is the appropriate response when the server does not
1970   recognize the request method and is not capable of supporting it for
1971   any resource.
1972</t>
1973</section>
1974
1975<section title="502 Bad Gateway" anchor="status.502">
1976  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1977  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1978<t>
1979   The server, while acting as a gateway or proxy, received an invalid
1980   response from the upstream server it accessed in attempting to
1981   fulfill the request.
1982</t>
1983</section>
1984
1985<section title="503 Service Unavailable" anchor="status.503">
1986  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1987  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
1988<t>
1989   The server is currently unable to handle the request due to a
1990   temporary overloading or maintenance of the server.
1991</t>
1992<t>
1993   The implication is that this is a temporary condition which will be
1994   alleviated after some delay. If known, the length of the delay &MAY; be
1995   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
1996   If no Retry-After is given, the client &SHOULD; handle the response as it
1997   would for a 500 response.
1998</t>
1999<x:note>
2000  <t>
2001    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2002    server has to use it when becoming overloaded. Some servers might wish
2003    to simply refuse the connection.
2004  </t>
2005</x:note>
2006</section>
2007
2008<section title="504 Gateway Timeout" anchor="status.504">
2009  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2010  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2011<t>
2012   The server, while acting as a gateway or proxy, did not receive a
2013   timely response from the upstream server specified by the URI (e.g.,
2014   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2015   to access in attempting to complete the request.
2016</t>
2017<x:note>
2018  <t>
2019    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2020    return 400 or 500 when DNS lookups time out.
2021  </t>
2022</x:note>
2023</section>
2024
2025<section title="505 HTTP Version Not Supported" anchor="status.505">
2026  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2027  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2028<t>
2029   The server does not support, or refuses to support, the protocol
2030   version that was used in the request message. The server is
2031   indicating that it is unable or unwilling to complete the request
2032   using the same major version as the client, as described in &http-version;,
2033   other than with this error message. The response &SHOULD; contain
2034   a representation describing why that version is not supported and what other
2035   protocols are supported by that server.
2036</t>
2037
2038</section>
2039</section>
2040
2041</section>
2042
2043<section title="Representation" anchor="representation">
2044<t>
2045   Request and Response messages &MAY; transfer a representation if not otherwise
2046   restricted by the request method or response status code. A representation
2047   consists of metadata (representation header fields) and data (representation
2048   body).  When a complete or partial representation is enclosed in an HTTP message,
2049   it is referred to as the payload of the message. HTTP representations
2050   are defined in &payload;.
2051</t>
2052<t>
2053   A representation body is only present in a message when a message body is
2054   present, as described in &message-body;. The representation body is obtained
2055   from the message body by decoding any Transfer-Encoding that might
2056   have been applied to ensure safe and proper transfer of the message.
2057</t>
2058
2059<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
2060<t>
2061   It is sometimes necessary to determine an identifier for the resource
2062   associated with a representation.
2063</t>
2064<t>
2065   An HTTP request representation, when present, is always associated with an
2066   anonymous (i.e., unidentified) resource.
2067</t>
2068<t>
2069   In the common case, an HTTP response is a representation of the target
2070   resource (see &effective-request-uri;). However, this is not always the
2071   case. To determine the URI of the resource a response is associated with,
2072   the following rules are used (with the first applicable one being selected):
2073</t>
2074<t><list style="numbers">
2075   <t>If the response status code is 200 or 203 and the request method was GET,
2076   the response payload is a representation of the target resource.</t>
2077   <t>If the response status code is 204, 206, or 304 and the request method was GET
2078   or HEAD, the response payload is a partial representation of the target
2079   resource.</t>
2080   <t>If the response has a Content-Location header field, and that URI is the same
2081   as the effective request URI, the response payload is a representation of the
2082   target resource.</t>
2083   <t>If the response has a Content-Location header field, and that URI is not the
2084   same as the effective request URI, then the response asserts that its
2085   payload is a representation of the resource identified by the
2086   Content-Location URI. However, such an assertion cannot be trusted unless
2087   it can be verified by other means (not defined by HTTP).</t>
2088   <t>Otherwise, the response is a representation of an anonymous (i.e.,
2089   unidentified) resource.</t>
2090</list></t>
2091<t>
2092  <cref anchor="TODO-req-uri">
2093   The comparison function is going to have to be defined somewhere,
2094   because we already need to compare URIs for things like cache invalidation.</cref>
2095</t>
2096</section>
2097
2098</section>
2099
2100
2101<section title="Common Protocol Parameters" anchor="common.protocol.parameters">
2102<section title="Date/Time Formats" anchor="http.date">
2103  <x:anchor-alias value="HTTP-date"/>
2104<t>
2105   HTTP applications have historically allowed three different formats
2106   for date/time stamps. However, the preferred format is a fixed-length subset
2107   of that defined by <xref target="RFC1123"/>:
2108</t>
2109<figure><artwork type="example" x:indent-with="  ">
2110Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2111</artwork></figure>
2112<t>
2113   The other formats are described here only for compatibility with obsolete
2114   implementations.
2115</t>
2116<figure><artwork type="example" x:indent-with="  ">
2117Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2118Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2119</artwork></figure>
2120<t>
2121   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2122   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2123   only generate the RFC 1123 format for representing HTTP-date values
2124   in header fields.
2125</t>
2126<t>
2127   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2128   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2129   equal to UTC (Coordinated Universal Time). This is indicated in the
2130   first two formats by the inclusion of "GMT" as the three-letter
2131   abbreviation for time zone, and &MUST; be assumed when reading the
2132   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2133   additional whitespace beyond that specifically included as SP in the
2134   grammar.
2135</t>
2136<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2137  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2138</artwork></figure>
2139<t anchor="preferred.date.format">
2140  <x:anchor-alias value="rfc1123-date"/>
2141  <x:anchor-alias value="time-of-day"/>
2142  <x:anchor-alias value="hour"/>
2143  <x:anchor-alias value="minute"/>
2144  <x:anchor-alias value="second"/>
2145  <x:anchor-alias value="day-name"/>
2146  <x:anchor-alias value="day"/>
2147  <x:anchor-alias value="month"/>
2148  <x:anchor-alias value="year"/>
2149  <x:anchor-alias value="GMT"/>
2150  Preferred format:
2151</t>
2152<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"/>
2153  <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>
2154  ; fixed length subset of the format defined in
2155  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2156 
2157  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2158               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2159               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2160               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2161               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2162               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2163               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2164               
2165  <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>
2166               ; e.g., 02 Jun 1982
2167
2168  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2169  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2170               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2171               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2172               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2173               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2174               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2175               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2176               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2177               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2178               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2179               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2180               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2181  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2182
2183  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2184
2185  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2186                 ; 00:00:00 - 23:59:59
2187                 
2188  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2189  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2190  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2191</artwork></figure>
2192<t>
2193  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2194  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2195  same as those defined for the RFC 5322 constructs
2196  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2197</t>
2198<t anchor="obsolete.date.formats">
2199  <x:anchor-alias value="obs-date"/>
2200  <x:anchor-alias value="rfc850-date"/>
2201  <x:anchor-alias value="asctime-date"/>
2202  <x:anchor-alias value="date1"/>
2203  <x:anchor-alias value="date2"/>
2204  <x:anchor-alias value="date3"/>
2205  <x:anchor-alias value="rfc1123-date"/>
2206  <x:anchor-alias value="day-name-l"/>
2207  Obsolete formats:
2208</t>
2209<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2210  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2211</artwork></figure>
2212<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2213  <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>
2214  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2215                 ; day-month-year (e.g., 02-Jun-82)
2216
2217  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2218         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2219         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2220         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2221         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2222         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2223         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2224</artwork></figure>
2225<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2226  <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>
2227  <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> ))
2228                 ; month day (e.g., Jun  2)
2229</artwork></figure>
2230<x:note>
2231  <t>
2232    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2233    accepting date values that might have been sent by non-HTTP
2234    applications, as is sometimes the case when retrieving or posting
2235    messages via proxies/gateways to SMTP or NNTP.
2236  </t>
2237</x:note>
2238<x:note>
2239  <t>
2240    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2241    to their usage within the protocol stream. Clients and servers are
2242    not required to use these formats for user presentation, request
2243    logging, etc.
2244  </t>
2245</x:note>
2246</section>
2247
2248<section title="Product Tokens" anchor="product.tokens">
2249  <x:anchor-alias value="product"/>
2250  <x:anchor-alias value="product-version"/>
2251<t>
2252   Product tokens are used to allow communicating applications to
2253   identify themselves by software name and version. Most fields using
2254   product tokens also allow sub-products which form a significant part
2255   of the application to be listed, separated by whitespace. By
2256   convention, the products are listed in order of their significance
2257   for identifying the application.
2258</t>
2259<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2260  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2261  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2262</artwork></figure>
2263<t>
2264   Examples:
2265</t>
2266<figure><artwork type="example">
2267  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2268  Server: Apache/0.8.4
2269</artwork></figure>
2270<t>
2271   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2272   used for advertising or other non-essential information. Although any
2273   token octet &MAY; appear in a product-version, this token &SHOULD;
2274   only be used for a version identifier (i.e., successive versions of
2275   the same product &SHOULD; only differ in the product-version portion of
2276   the product value).
2277</t>
2278</section>
2279</section>
2280
2281<section title="Header Field Definitions" anchor="header.field.definitions">
2282<t>
2283   This section defines the syntax and semantics of HTTP/1.1 header fields
2284   related to request and response semantics.
2285</t>
2286
2287<section title="Allow" anchor="header.allow">
2288  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2289  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2290  <x:anchor-alias value="Allow"/>
2291<t>
2292   The "Allow" header field lists the set of methods advertised as
2293   supported by the target resource. The purpose of this field is strictly to
2294   inform the recipient of valid request methods associated with the resource.
2295</t>
2296<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2297  <x:ref>Allow</x:ref> = #<x:ref>method</x:ref>
2298</artwork></figure>
2299<t>
2300   Example of use:
2301</t>
2302<figure><artwork type="example">
2303  Allow: GET, HEAD, PUT
2304</artwork></figure>
2305<t>
2306   The actual set of allowed methods is defined by the origin server at the
2307   time of each request.
2308</t>
2309<t>
2310   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2311   understand all the methods specified in order to handle them according to
2312   the generic message handling rules.
2313</t>
2314</section>
2315
2316<section title="Date" anchor="header.date">
2317  <iref primary="true" item="Date header field" x:for-anchor=""/>
2318  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2319  <x:anchor-alias value="Date"/>
2320<t>
2321   The "Date" header field represents the date and time at which
2322   the message was originated, having the same semantics as the Origination
2323   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2324   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2325   it &MUST; be sent in rfc1123-date format.
2326</t>
2327<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2328  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2329</artwork></figure>
2330<t>
2331   An example is
2332</t>
2333<figure><artwork type="example">
2334  Date: Tue, 15 Nov 1994 08:12:31 GMT
2335</artwork></figure>
2336<t>
2337   Origin servers &MUST; include a Date header field in all responses,
2338   except in these cases:
2339  <list style="numbers">
2340      <t>If the response status code is 100 (Continue) or 101 (Switching
2341         Protocols), the response &MAY; include a Date header field, at
2342         the server's option.</t>
2343
2344      <t>If the response status code conveys a server error, e.g., 500
2345         (Internal Server Error) or 503 (Service Unavailable), and it is
2346         inconvenient or impossible to generate a valid Date.</t>
2347
2348      <t>If the server does not have a clock that can provide a
2349         reasonable approximation of the current time, its responses
2350         &MUST-NOT; include a Date header field.</t>
2351  </list>
2352</t>
2353<t>
2354   A received message that does not have a Date header field &MUST; be
2355   assigned one by the recipient if the message will be cached by that
2356   recipient.
2357</t>
2358<t>
2359   Clients can use the Date header field as well; in order to keep request
2360   messages small, they are advised not to include it when it doesn't convey
2361   any useful information (as is usually the case for requests that do not
2362   contain a payload).
2363</t>
2364<t>
2365   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2366   time subsequent to the generation of the message. It &SHOULD; represent
2367   the best available approximation of the date and time of message
2368   generation, unless the implementation has no means of generating a
2369   reasonably accurate date and time. In theory, the date ought to
2370   represent the moment just before the payload is generated. In
2371   practice, the date can be generated at any time during the message
2372   origination without affecting its semantic value.
2373</t>
2374</section>
2375
2376<section title="Expect" anchor="header.expect">
2377  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2378  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2379  <x:anchor-alias value="Expect"/>
2380  <x:anchor-alias value="expectation"/>
2381  <x:anchor-alias value="expect-param"/>
2382  <x:anchor-alias value="expect-name"/>
2383  <x:anchor-alias value="expect-value"/>
2384<t>
2385   The "Expect" header field is used to indicate that particular
2386   server behaviors are required by the client.
2387</t>
2388<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"/>
2389  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2390 
2391  <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> ]
2392                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2393  <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> ]
2394 
2395  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2396  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2397</artwork></figure>
2398<t>
2399   If all received Expect header field(s) are syntactically valid but contain
2400   an expectation that the recipient does not understand or cannot comply with,
2401   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2402   recipient of a syntactically invalid Expectation header field &MUST; respond
2403   with a 4xx status code other than 417.
2404</t>
2405<t>
2406   The only expectation defined by this specification is:
2407</t>
2408<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2409  100-continue
2410   <list>
2411      <t>
2412        The "100-continue" expectation is defined &use100;. It does not support
2413        any expect-params.
2414      </t>
2415   </list>
2416</t>
2417<t>
2418   Comparison is case-insensitive for names (expect-name), and case-sensitive
2419   for values (expect-value).
2420</t>
2421<t>
2422   The Expect mechanism is hop-by-hop: the above requirements apply to any
2423   server, including proxies. However, the Expect header field itself is
2424   end-to-end; it &MUST; be forwarded if the request is forwarded.
2425</t>
2426<t>
2427   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2428   header field.
2429</t>
2430</section>
2431
2432<section title="From" anchor="header.from">
2433  <iref primary="true" item="From header field" x:for-anchor=""/>
2434  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2435  <x:anchor-alias value="From"/>
2436  <x:anchor-alias value="mailbox"/>
2437<t>
2438   The "From" header field, if given, &SHOULD; contain an Internet
2439   e-mail address for the human user who controls the requesting user
2440   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2441   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2442</t>
2443<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2444  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2445 
2446  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2447</artwork></figure>
2448<t>
2449   An example is:
2450</t>
2451<figure><artwork type="example">
2452  From: webmaster@example.org
2453</artwork></figure>
2454<t>
2455   This header field &MAY; be used for logging purposes and as a means for
2456   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2457   be used as an insecure form of access protection. The interpretation
2458   of this field is that the request is being performed on behalf of the
2459   person given, who accepts responsibility for the method performed. In
2460   particular, robot agents &SHOULD; include this header field so that the
2461   person responsible for running the robot can be contacted if problems
2462   occur on the receiving end.
2463</t>
2464<t>
2465   The Internet e-mail address in this field &MAY; be separate from the
2466   Internet host which issued the request. For example, when a request
2467   is passed through a proxy the original issuer's address &SHOULD; be
2468   used.
2469</t>
2470<t>
2471   The client &SHOULD-NOT;  send the From header field without the user's
2472   approval, as it might conflict with the user's privacy interests or
2473   their site's security policy. It is strongly recommended that the
2474   user be able to disable, enable, and modify the value of this field
2475   at any time prior to a request.
2476</t>
2477</section>
2478
2479<section title="Location" anchor="header.location">
2480  <iref primary="true" item="Location header field" x:for-anchor=""/>
2481  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2482  <x:anchor-alias value="Location"/>
2483<t>
2484   The "Location" header field &MAY; be sent in responses to refer to
2485   a specific resource in accordance with the semantics of the status
2486   code.
2487</t>
2488<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2489  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2490</artwork></figure>
2491<t>
2492   For 201 (Created) responses, the Location is the URI of the new resource
2493   which was created by the request. For 3xx responses, the location &SHOULD;
2494   indicate the server's preferred URI for automatic redirection to the
2495   resource.
2496</t>
2497<t>
2498   The field value consists of a single URI-reference. When it has the form
2499   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2500   the final value is computed by resolving it against the effective request
2501   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2502   navigated to by the user agent, did contain a fragment identifier, and the
2503   final value does not, then the original URI's fragment identifier is added
2504   to the final value.
2505</t>
2506<figure>
2507<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-->
2508<artwork type="example">
2509  Location: /pub/WWW/People.html#tim
2510</artwork>
2511<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2512</figure>
2513<figure>
2514<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-->
2515<artwork type="example">
2516  Location: http://www.example.net/index.html
2517</artwork>
2518<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2519</figure>
2520<x:note>
2521  <t>
2522    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2523    that are not valid URI references. This specification does not mandate or
2524    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2525  </t>
2526</x:note>
2527<t>
2528   There are circumstances in which a fragment identifier in a Location URI
2529   would not be appropriate. For instance, when it appears in a 201 Created
2530   response, where the Location header field specifies the URI for the entire
2531   created resource.
2532</t>
2533<x:note>
2534  <t>
2535    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2536    from Location in that the Content-Location identifies the most specific
2537    resource corresponding to the enclosed representation.
2538    It is therefore possible for a response to contain header fields for
2539    both Location and Content-Location.
2540  </t>
2541</x:note>
2542</section>
2543
2544<section title="Max-Forwards" anchor="header.max-forwards">
2545  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2546  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2547  <x:anchor-alias value="Max-Forwards"/>
2548<t>
2549   The "Max-Forwards" header field provides a mechanism with the
2550   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2551   methods to limit the number of times that the request is forwarded by
2552   proxies. This can be useful when the client is attempting to
2553   trace a request which appears to be failing or looping mid-chain.
2554</t>
2555<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2556  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2557</artwork></figure>
2558<t>
2559   The Max-Forwards value is a decimal integer indicating the remaining
2560   number of times this request message can be forwarded.
2561</t>
2562<t>
2563   Each recipient of a TRACE or OPTIONS request
2564   containing a Max-Forwards header field &MUST; check and update its
2565   value prior to forwarding the request. If the received value is zero
2566   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2567   respond as the final recipient. If the received Max-Forwards value is
2568   greater than zero, then the forwarded message &MUST; contain an updated
2569   Max-Forwards field with a value decremented by one (1).
2570</t>
2571<t>
2572   The Max-Forwards header field &MAY; be ignored for all other request
2573   methods.
2574</t>
2575</section>
2576
2577<section title="Referer" anchor="header.referer">
2578  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2579  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2580  <x:anchor-alias value="Referer"/>
2581<t>
2582   The "Referer" [sic] header field allows the client to specify the
2583   URI of the resource from which the target URI was obtained (the
2584   "referrer", although the header field is misspelled.).
2585</t>
2586<t>
2587   The Referer header field allows servers to generate lists of back-links to
2588   resources for interest, logging, optimized caching, etc. It also allows
2589   obsolete or mistyped links to be traced for maintenance. Some servers use
2590   Referer as a means of controlling where they allow links from (so-called
2591   "deep linking"), but legitimate requests do not always
2592   contain a Referer header field.
2593</t>
2594<t>
2595   If the target URI was obtained from a source that does not have its own
2596   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2597   sent with the value "about:blank", or not be sent at all. Note that this
2598   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2599</t>
2600<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2601  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2602</artwork></figure>
2603<t>
2604   Example:
2605</t>
2606<figure><artwork type="example">
2607  Referer: http://www.example.org/hypertext/Overview.html
2608</artwork></figure>
2609<t>
2610   If the field value is a relative URI, it &SHOULD; be interpreted
2611   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2612   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2613</t>
2614</section>
2615
2616<section title="Retry-After" anchor="header.retry-after">
2617  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2618  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2619  <x:anchor-alias value="Retry-After"/>
2620<t>
2621   The header "Retry-After" field can be used with a 503 (Service
2622   Unavailable) response to indicate how long the service is expected to
2623   be unavailable to the requesting client. This field &MAY; also be used
2624   with any 3xx (Redirection) response to indicate the minimum time the
2625   user-agent is asked to wait before issuing the redirected request.
2626</t>
2627<t>
2628   The value of this field can be either an HTTP-date or an integer number
2629   of seconds (in decimal) after the time of the response.
2630</t>
2631<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2632  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2633</artwork></figure>
2634<t anchor="rule.delta-seconds">
2635  <x:anchor-alias value="delta-seconds"/>
2636   Time spans are non-negative decimal integers, representing time in
2637   seconds.
2638</t>
2639<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2640  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2641</artwork></figure>
2642<t>
2643   Two examples of its use are
2644</t>
2645<figure><artwork type="example">
2646  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2647  Retry-After: 120
2648</artwork></figure>
2649<t>
2650   In the latter example, the delay is 2 minutes.
2651</t>
2652</section>
2653
2654<section title="Server" anchor="header.server">
2655  <iref primary="true" item="Server header field" x:for-anchor=""/>
2656  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2657  <x:anchor-alias value="Server"/>
2658<t>
2659   The "Server" header field contains information about the
2660   software used by the origin server to handle the request.
2661</t>
2662<t>
2663   The field can contain multiple
2664   product tokens (<xref target="product.tokens"/>) and
2665   comments (&header-fields;) identifying the server and any significant
2666   subproducts. The product tokens are listed in order of their significance
2667   for identifying the application.
2668</t>
2669<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2670  <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> ) )
2671</artwork></figure>
2672<t>
2673   Example:
2674</t>
2675<figure><artwork type="example">
2676  Server: CERN/3.0 libwww/2.17
2677</artwork></figure>
2678<t>
2679   If the response is being forwarded through a proxy, the proxy
2680   application &MUST-NOT; modify the Server header field. Instead, it
2681   &MUST; include a Via field (as described in &header-via;).
2682</t>
2683<x:note>
2684  <t>
2685    <x:h>Note:</x:h> Revealing the specific software version of the server might
2686    allow the server machine to become more vulnerable to attacks
2687    against software that is known to contain security holes. Server
2688    implementors are encouraged to make this field a configurable
2689    option.
2690  </t>
2691</x:note>
2692</section>
2693
2694<section title="User-Agent" anchor="header.user-agent">
2695  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2696  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2697  <x:anchor-alias value="User-Agent"/>
2698<t>
2699   The "User-Agent" header field contains information about the user
2700   agent originating the request. User agents &SHOULD; include this field with
2701   requests.
2702</t>
2703<t>
2704   Typically, it is used for statistical purposes, the tracing of protocol
2705   violations, and tailoring responses to avoid particular user agent
2706   limitations.
2707</t>
2708<t>
2709   The field can contain multiple
2710   product tokens (<xref target="product.tokens"/>)
2711   and comments (&header-fields;) identifying the agent and its
2712   significant subproducts. By convention, the product tokens are listed in
2713   order of their significance for identifying the application.
2714</t>
2715<t>
2716   Because this field is usually sent on every request a user agent makes,
2717   implementations are encouraged not to include needlessly fine-grained
2718   detail, and to limit (or even prohibit) the addition of subproducts by third
2719   parties. Overly long and detailed User-Agent field values make requests
2720   larger and can also be used to identify ("fingerprint") the user against
2721   their wishes.
2722</t>
2723<t>
2724   Likewise, implementations are encouraged not to use the product tokens of
2725   other implementations in order to declare compatibility with them, as this
2726   circumvents the purpose of the field. Finally, they are encouraged not to
2727   use comments to identify products; doing so makes the field value more
2728   difficult to parse.
2729</t>
2730<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2731  <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> ) )
2732</artwork></figure>
2733<t>
2734   Example:
2735</t>
2736<figure><artwork type="example">
2737  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2738</artwork></figure>
2739</section>
2740
2741</section>
2742
2743<section title="IANA Considerations" anchor="IANA.considerations">
2744
2745<section title="Method Registry" anchor="method.registration">
2746<t>
2747  The registration procedure for HTTP request methods is defined by
2748  <xref target="method.registry"/> of this document.
2749</t>
2750<t>
2751   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2752   and be populated with the registrations below:
2753</t>
2754<?BEGININC p2-semantics.iana-methods ?>
2755<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2756<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2757   <ttcol>Method</ttcol>
2758   <ttcol>Safe</ttcol>
2759   <ttcol>Reference</ttcol>
2760   <c>CONNECT</c>
2761   <c>no</c>
2762   <c>
2763      <xref target="CONNECT"/>
2764   </c>
2765   <c>DELETE</c>
2766   <c>no</c>
2767   <c>
2768      <xref target="DELETE"/>
2769   </c>
2770   <c>GET</c>
2771   <c>yes</c>
2772   <c>
2773      <xref target="GET"/>
2774   </c>
2775   <c>HEAD</c>
2776   <c>yes</c>
2777   <c>
2778      <xref target="HEAD"/>
2779   </c>
2780   <c>OPTIONS</c>
2781   <c>yes</c>
2782   <c>
2783      <xref target="OPTIONS"/>
2784   </c>
2785   <c>POST</c>
2786   <c>no</c>
2787   <c>
2788      <xref target="POST"/>
2789   </c>
2790   <c>PUT</c>
2791   <c>no</c>
2792   <c>
2793      <xref target="PUT"/>
2794   </c>
2795   <c>TRACE</c>
2796   <c>yes</c>
2797   <c>
2798      <xref target="TRACE"/>
2799   </c>
2800</texttable>
2801<!--(END)-->
2802<?ENDINC p2-semantics.iana-methods ?>
2803</section>
2804
2805<section title="Status Code Registry" anchor="status.code.registration">
2806<t>
2807   The registration procedure for HTTP Status Codes &mdash; previously defined
2808   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2809   by <xref target="status.code.registry"/> of this document.
2810</t>
2811<t>
2812   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2813   shall be updated with the registrations below:
2814</t>
2815<?BEGININC p2-semantics.iana-status-codes ?>
2816<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2817<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2818   <ttcol>Value</ttcol>
2819   <ttcol>Description</ttcol>
2820   <ttcol>Reference</ttcol>
2821   <c>100</c>
2822   <c>Continue</c>
2823   <c>
2824      <xref target="status.100"/>
2825   </c>
2826   <c>101</c>
2827   <c>Switching Protocols</c>
2828   <c>
2829      <xref target="status.101"/>
2830   </c>
2831   <c>200</c>
2832   <c>OK</c>
2833   <c>
2834      <xref target="status.200"/>
2835   </c>
2836   <c>201</c>
2837   <c>Created</c>
2838   <c>
2839      <xref target="status.201"/>
2840   </c>
2841   <c>202</c>
2842   <c>Accepted</c>
2843   <c>
2844      <xref target="status.202"/>
2845   </c>
2846   <c>203</c>
2847   <c>Non-Authoritative Information</c>
2848   <c>
2849      <xref target="status.203"/>
2850   </c>
2851   <c>204</c>
2852   <c>No Content</c>
2853   <c>
2854      <xref target="status.204"/>
2855   </c>
2856   <c>205</c>
2857   <c>Reset Content</c>
2858   <c>
2859      <xref target="status.205"/>
2860   </c>
2861   <c>300</c>
2862   <c>Multiple Choices</c>
2863   <c>
2864      <xref target="status.300"/>
2865   </c>
2866   <c>301</c>
2867   <c>Moved Permanently</c>
2868   <c>
2869      <xref target="status.301"/>
2870   </c>
2871   <c>302</c>
2872   <c>Found</c>
2873   <c>
2874      <xref target="status.302"/>
2875   </c>
2876   <c>303</c>
2877   <c>See Other</c>
2878   <c>
2879      <xref target="status.303"/>
2880   </c>
2881   <c>305</c>
2882   <c>Use Proxy</c>
2883   <c>
2884      <xref target="status.305"/>
2885   </c>
2886   <c>306</c>
2887   <c>(Unused)</c>
2888   <c>
2889      <xref target="status.306"/>
2890   </c>
2891   <c>307</c>
2892   <c>Temporary Redirect</c>
2893   <c>
2894      <xref target="status.307"/>
2895   </c>
2896   <c>400</c>
2897   <c>Bad Request</c>
2898   <c>
2899      <xref target="status.400"/>
2900   </c>
2901   <c>402</c>
2902   <c>Payment Required</c>
2903   <c>
2904      <xref target="status.402"/>
2905   </c>
2906   <c>403</c>
2907   <c>Forbidden</c>
2908   <c>
2909      <xref target="status.403"/>
2910   </c>
2911   <c>404</c>
2912   <c>Not Found</c>
2913   <c>
2914      <xref target="status.404"/>
2915   </c>
2916   <c>405</c>
2917   <c>Method Not Allowed</c>
2918   <c>
2919      <xref target="status.405"/>
2920   </c>
2921   <c>406</c>
2922   <c>Not Acceptable</c>
2923   <c>
2924      <xref target="status.406"/>
2925   </c>
2926   <c>408</c>
2927   <c>Request Timeout</c>
2928   <c>
2929      <xref target="status.408"/>
2930   </c>
2931   <c>409</c>
2932   <c>Conflict</c>
2933   <c>
2934      <xref target="status.409"/>
2935   </c>
2936   <c>410</c>
2937   <c>Gone</c>
2938   <c>
2939      <xref target="status.410"/>
2940   </c>
2941   <c>411</c>
2942   <c>Length Required</c>
2943   <c>
2944      <xref target="status.411"/>
2945   </c>
2946   <c>413</c>
2947   <c>Request Representation Too Large</c>
2948   <c>
2949      <xref target="status.413"/>
2950   </c>
2951   <c>414</c>
2952   <c>URI Too Long</c>
2953   <c>
2954      <xref target="status.414"/>
2955   </c>
2956   <c>415</c>
2957   <c>Unsupported Media Type</c>
2958   <c>
2959      <xref target="status.415"/>
2960   </c>
2961   <c>417</c>
2962   <c>Expectation Failed</c>
2963   <c>
2964      <xref target="status.417"/>
2965   </c>
2966   <c>426</c>
2967   <c>Upgrade Required</c>
2968   <c>
2969      <xref target="status.426"/>
2970   </c>
2971   <c>500</c>
2972   <c>Internal Server Error</c>
2973   <c>
2974      <xref target="status.500"/>
2975   </c>
2976   <c>501</c>
2977   <c>Not Implemented</c>
2978   <c>
2979      <xref target="status.501"/>
2980   </c>
2981   <c>502</c>
2982   <c>Bad Gateway</c>
2983   <c>
2984      <xref target="status.502"/>
2985   </c>
2986   <c>503</c>
2987   <c>Service Unavailable</c>
2988   <c>
2989      <xref target="status.503"/>
2990   </c>
2991   <c>504</c>
2992   <c>Gateway Timeout</c>
2993   <c>
2994      <xref target="status.504"/>
2995   </c>
2996   <c>505</c>
2997   <c>HTTP Version Not Supported</c>
2998   <c>
2999      <xref target="status.505"/>
3000   </c>
3001</texttable>
3002<!--(END)-->
3003<?ENDINC p2-semantics.iana-status-codes ?>
3004</section>
3005<section title="Header Field Registration" anchor="header.field.registration">
3006<t>
3007   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3008   with the permanent registrations below (see <xref target="RFC3864"/>):
3009</t>
3010<?BEGININC p2-semantics.iana-headers ?>
3011<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3012<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3013   <ttcol>Header Field Name</ttcol>
3014   <ttcol>Protocol</ttcol>
3015   <ttcol>Status</ttcol>
3016   <ttcol>Reference</ttcol>
3017
3018   <c>Allow</c>
3019   <c>http</c>
3020   <c>standard</c>
3021   <c>
3022      <xref target="header.allow"/>
3023   </c>
3024   <c>Date</c>
3025   <c>http</c>
3026   <c>standard</c>
3027   <c>
3028      <xref target="header.date"/>
3029   </c>
3030   <c>Expect</c>
3031   <c>http</c>
3032   <c>standard</c>
3033   <c>
3034      <xref target="header.expect"/>
3035   </c>
3036   <c>From</c>
3037   <c>http</c>
3038   <c>standard</c>
3039   <c>
3040      <xref target="header.from"/>
3041   </c>
3042   <c>Location</c>
3043   <c>http</c>
3044   <c>standard</c>
3045   <c>
3046      <xref target="header.location"/>
3047   </c>
3048   <c>Max-Forwards</c>
3049   <c>http</c>
3050   <c>standard</c>
3051   <c>
3052      <xref target="header.max-forwards"/>
3053   </c>
3054   <c>Referer</c>
3055   <c>http</c>
3056   <c>standard</c>
3057   <c>
3058      <xref target="header.referer"/>
3059   </c>
3060   <c>Retry-After</c>
3061   <c>http</c>
3062   <c>standard</c>
3063   <c>
3064      <xref target="header.retry-after"/>
3065   </c>
3066   <c>Server</c>
3067   <c>http</c>
3068   <c>standard</c>
3069   <c>
3070      <xref target="header.server"/>
3071   </c>
3072   <c>User-Agent</c>
3073   <c>http</c>
3074   <c>standard</c>
3075   <c>
3076      <xref target="header.user-agent"/>
3077   </c>
3078</texttable>
3079<!--(END)-->
3080<?ENDINC p2-semantics.iana-headers ?>
3081<t>
3082   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3083</t>
3084</section>
3085</section>
3086
3087<section title="Security Considerations" anchor="security.considerations">
3088<t>
3089   This section is meant to inform application developers, information
3090   providers, and users of the security limitations in HTTP/1.1 as
3091   described by this document. The discussion does not include
3092   definitive solutions to the problems revealed, though it does make
3093   some suggestions for reducing security risks.
3094</t>
3095
3096<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3097<t>
3098   Like any generic data transfer protocol, HTTP cannot regulate the
3099   content of the data that is transferred, nor is there any a priori
3100   method of determining the sensitivity of any particular piece of
3101   information within the context of any given request. Therefore,
3102   applications &SHOULD; supply as much control over this information as
3103   possible to the provider of that information. Four header fields are
3104   worth special mention in this context: Server, Via, Referer and From.
3105</t>
3106<t>
3107   Revealing the specific software version of the server might allow the
3108   server machine to become more vulnerable to attacks against software
3109   that is known to contain security holes. Implementors &SHOULD; make the
3110   Server header field a configurable option.
3111</t>
3112<t>
3113   Proxies which serve as a portal through a network firewall &SHOULD;
3114   take special precautions regarding the transfer of header information
3115   that identifies the hosts behind the firewall. In particular, they
3116   &SHOULD; remove, or replace with sanitized versions, any Via fields
3117   generated behind the firewall.
3118</t>
3119<t>
3120   The Referer header field allows reading patterns to be studied and reverse
3121   links drawn. Although it can be very useful, its power can be abused
3122   if user details are not separated from the information contained in
3123   the Referer. Even when the personal information has been removed, the
3124   Referer header field might indicate a private document's URI whose
3125   publication would be inappropriate.
3126</t>
3127<t>
3128   The information sent in the From field might conflict with the user's
3129   privacy interests or their site's security policy, and hence it
3130   &SHOULD-NOT;  be transmitted without the user being able to disable,
3131   enable, and modify the contents of the field. The user &MUST; be able
3132   to set the contents of this field within a user preference or
3133   application defaults configuration.
3134</t>
3135<t>
3136   We suggest, though do not require, that a convenient toggle interface
3137   be provided for the user to enable or disable the sending of From and
3138   Referer information.
3139</t>
3140<t>
3141   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3142   target="header.server"/>) header fields can sometimes be used to determine
3143   that a specific client or server has a particular security hole which might
3144   be exploited. Unfortunately, this same information is often used for other
3145   valuable purposes for which HTTP currently has no better mechanism.
3146</t>
3147<t>
3148   Furthermore, the User-Agent header field may contain enough entropy to be
3149   used, possibly in conjunction with other material, to uniquely identify the
3150   user.
3151</t>
3152<t>
3153   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3154   that was sent in request header fields within the body of their response.
3155   Clients &SHOULD; be careful with sensitive information, like Cookies,
3156   Authorization credentials, and other header fields that might be used to
3157   collect data from the client.
3158</t> 
3159</section>
3160
3161<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3162<t>
3163   Because the source of a link might be private information or might
3164   reveal an otherwise private information source, it is strongly
3165   recommended that the user be able to select whether or not the
3166   Referer field is sent. For example, a browser client could have a
3167   toggle switch for browsing openly/anonymously, which would
3168   respectively enable/disable the sending of Referer and From
3169   information.
3170</t>
3171<t>
3172   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3173   HTTP request if the referring page was transferred with a secure
3174   protocol.
3175</t>
3176<t>
3177   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3178   sensitive data because that data will be placed in the request-target. Many
3179   existing servers, proxies, and user agents log or display the request-target
3180   in places where it might be visible to third parties. Such services can
3181   use POST-based form submission instead.
3182</t>
3183</section>
3184
3185<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3186<t>
3187   If a single server supports multiple organizations that do not trust
3188   one another, then it &MUST; check the values of Location and Content-Location
3189   header fields in responses that are generated under control of
3190   said organizations to make sure that they do not attempt to
3191   invalidate resources over which they have no authority.
3192</t>
3193<t>
3194   Furthermore, appending the fragment identifier from one URI to another
3195   one obtained from a Location header field might leak confidential
3196   information to the target server &mdash; although the fragment identifier is
3197   not transmitted in the final request, it might be visible to the user agent
3198   through other means, such as scripting.
3199</t>
3200</section>
3201
3202<section title="Security Considerations for CONNECT">
3203<t>
3204   Since tunneled data is opaque to the proxy, there are additional
3205   risks to tunneling to other well-known or reserved ports.
3206   A HTTP client CONNECTing to port 25 could relay spam
3207   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3208   access to a small number of known ports.
3209</t>
3210</section>
3211
3212</section>
3213
3214<section title="Acknowledgments" anchor="acks">
3215<t>
3216  See &acks;.
3217</t>
3218</section>
3219</middle>
3220<back>
3221
3222<references title="Normative References">
3223
3224<reference anchor="Part1">
3225  <front>
3226    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3227    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3228      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3229      <address><email>fielding@gbiv.com</email></address>
3230    </author>
3231    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3232      <organization abbrev="W3C">World Wide Web Consortium</organization>
3233      <address><email>ylafon@w3.org</email></address>
3234    </author>
3235    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3236      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3237      <address><email>julian.reschke@greenbytes.de</email></address>
3238    </author>
3239    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3240  </front>
3241  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3242  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3243</reference>
3244
3245<reference anchor="Part3">
3246  <front>
3247    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3248    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3249      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3250      <address><email>fielding@gbiv.com</email></address>
3251    </author>
3252    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3253      <organization abbrev="W3C">World Wide Web Consortium</organization>
3254      <address><email>ylafon@w3.org</email></address>
3255    </author>
3256    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3257      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3258      <address><email>julian.reschke@greenbytes.de</email></address>
3259    </author>
3260    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3261  </front>
3262  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3263  <x:source href="p3-payload.xml" basename="p3-payload"/>
3264</reference>
3265
3266<reference anchor="Part4">
3267  <front>
3268    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3269    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3270      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3271      <address><email>fielding@gbiv.com</email></address>
3272    </author>
3273    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3274      <organization abbrev="W3C">World Wide Web Consortium</organization>
3275      <address><email>ylafon@w3.org</email></address>
3276    </author>
3277    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3278      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3279      <address><email>julian.reschke@greenbytes.de</email></address>
3280    </author>
3281    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3282  </front>
3283  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3284  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3285</reference>
3286
3287<reference anchor="Part5">
3288  <front>
3289    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3290    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3291      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3292      <address><email>fielding@gbiv.com</email></address>
3293    </author>
3294    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3295      <organization abbrev="W3C">World Wide Web Consortium</organization>
3296      <address><email>ylafon@w3.org</email></address>
3297    </author>
3298    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3299      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3300      <address><email>julian.reschke@greenbytes.de</email></address>
3301    </author>
3302    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3303  </front>
3304  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3305  <x:source href="p5-range.xml" basename="p5-range"/>
3306</reference>
3307
3308<reference anchor="Part6">
3309  <front>
3310    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3311    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3312      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3313      <address><email>fielding@gbiv.com</email></address>
3314    </author>
3315    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3316      <organization abbrev="W3C">World Wide Web Consortium</organization>
3317      <address><email>ylafon@w3.org</email></address>
3318    </author>
3319    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3320      <organization>Rackspace</organization>
3321      <address><email>mnot@mnot.net</email></address>
3322    </author>
3323    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3324      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3325      <address><email>julian.reschke@greenbytes.de</email></address>
3326    </author>
3327    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3328  </front>
3329  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3330  <x:source href="p6-cache.xml" basename="p6-cache"/>
3331</reference>
3332
3333<reference anchor="Part7">
3334  <front>
3335    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3336    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3337      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3338      <address><email>fielding@gbiv.com</email></address>
3339    </author>
3340    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3341      <organization abbrev="W3C">World Wide Web Consortium</organization>
3342      <address><email>ylafon@w3.org</email></address>
3343    </author>
3344    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3345      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3346      <address><email>julian.reschke@greenbytes.de</email></address>
3347    </author>
3348    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3349  </front>
3350  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3351  <x:source href="p7-auth.xml" basename="p7-auth"/>
3352</reference>
3353
3354<reference anchor="RFC2119">
3355  <front>
3356    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3357    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3358      <organization>Harvard University</organization>
3359      <address><email>sob@harvard.edu</email></address>
3360    </author>
3361    <date month="March" year="1997"/>
3362  </front>
3363  <seriesInfo name="BCP" value="14"/>
3364  <seriesInfo name="RFC" value="2119"/>
3365</reference>
3366
3367<reference anchor="RFC3986">
3368 <front>
3369  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3370  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3371    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3372    <address>
3373       <email>timbl@w3.org</email>
3374       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3375    </address>
3376  </author>
3377  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3378    <organization abbrev="Day Software">Day Software</organization>
3379    <address>
3380      <email>fielding@gbiv.com</email>
3381      <uri>http://roy.gbiv.com/</uri>
3382    </address>
3383  </author>
3384  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3385    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3386    <address>
3387      <email>LMM@acm.org</email>
3388      <uri>http://larry.masinter.net/</uri>
3389    </address>
3390  </author>
3391  <date month='January' year='2005'></date>
3392 </front>
3393 <seriesInfo name="STD" value="66"/>
3394 <seriesInfo name="RFC" value="3986"/>
3395</reference>
3396
3397<reference anchor="RFC5234">
3398  <front>
3399    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3400    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3401      <organization>Brandenburg InternetWorking</organization>
3402      <address>
3403        <email>dcrocker@bbiw.net</email>
3404      </address> 
3405    </author>
3406    <author initials="P." surname="Overell" fullname="Paul Overell">
3407      <organization>THUS plc.</organization>
3408      <address>
3409        <email>paul.overell@thus.net</email>
3410      </address>
3411    </author>
3412    <date month="January" year="2008"/>
3413  </front>
3414  <seriesInfo name="STD" value="68"/>
3415  <seriesInfo name="RFC" value="5234"/>
3416</reference>
3417
3418</references>
3419
3420<references title="Informative References">
3421
3422<reference anchor="RFC1123">
3423  <front>
3424    <title>Requirements for Internet Hosts - Application and Support</title>
3425    <author initials="R." surname="Braden" fullname="Robert Braden">
3426      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3427      <address><email>Braden@ISI.EDU</email></address>
3428    </author>
3429    <date month="October" year="1989"/>
3430  </front>
3431  <seriesInfo name="STD" value="3"/>
3432  <seriesInfo name="RFC" value="1123"/>
3433</reference>
3434
3435<reference anchor="RFC1945">
3436  <front>
3437    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3438    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3439      <organization>MIT, Laboratory for Computer Science</organization>
3440      <address><email>timbl@w3.org</email></address>
3441    </author>
3442    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3443      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3444      <address><email>fielding@ics.uci.edu</email></address>
3445    </author>
3446    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3447      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3448      <address><email>frystyk@w3.org</email></address>
3449    </author>
3450    <date month="May" year="1996"/>
3451  </front>
3452  <seriesInfo name="RFC" value="1945"/>
3453</reference>
3454
3455<reference anchor="RFC2068">
3456  <front>
3457    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3458    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3459      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3460      <address><email>fielding@ics.uci.edu</email></address>
3461    </author>
3462    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3463      <organization>MIT Laboratory for Computer Science</organization>
3464      <address><email>jg@w3.org</email></address>
3465    </author>
3466    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3467      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3468      <address><email>mogul@wrl.dec.com</email></address>
3469    </author>
3470    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3471      <organization>MIT Laboratory for Computer Science</organization>
3472      <address><email>frystyk@w3.org</email></address>
3473    </author>
3474    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3475      <organization>MIT Laboratory for Computer Science</organization>
3476      <address><email>timbl@w3.org</email></address>
3477    </author>
3478    <date month="January" year="1997"/>
3479  </front>
3480  <seriesInfo name="RFC" value="2068"/>
3481</reference>
3482
3483<reference anchor="RFC2616">
3484  <front>
3485    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3486    <author initials="R." surname="Fielding" fullname="R. Fielding">
3487      <organization>University of California, Irvine</organization>
3488      <address><email>fielding@ics.uci.edu</email></address>
3489    </author>
3490    <author initials="J." surname="Gettys" fullname="J. Gettys">
3491      <organization>W3C</organization>
3492      <address><email>jg@w3.org</email></address>
3493    </author>
3494    <author initials="J." surname="Mogul" fullname="J. Mogul">
3495      <organization>Compaq Computer Corporation</organization>
3496      <address><email>mogul@wrl.dec.com</email></address>
3497    </author>
3498    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3499      <organization>MIT Laboratory for Computer Science</organization>
3500      <address><email>frystyk@w3.org</email></address>
3501    </author>
3502    <author initials="L." surname="Masinter" fullname="L. Masinter">
3503      <organization>Xerox Corporation</organization>
3504      <address><email>masinter@parc.xerox.com</email></address>
3505    </author>
3506    <author initials="P." surname="Leach" fullname="P. Leach">
3507      <organization>Microsoft Corporation</organization>
3508      <address><email>paulle@microsoft.com</email></address>
3509    </author>
3510    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3511      <organization>W3C</organization>
3512      <address><email>timbl@w3.org</email></address>
3513    </author>
3514    <date month="June" year="1999"/>
3515  </front>
3516  <seriesInfo name="RFC" value="2616"/>
3517</reference>
3518
3519<reference anchor='RFC2817'>
3520  <front>
3521    <title>Upgrading to TLS Within HTTP/1.1</title>
3522    <author initials='R.' surname='Khare' fullname='R. Khare'>
3523      <organization>4K Associates / UC Irvine</organization>
3524      <address><email>rohit@4K-associates.com</email></address>
3525    </author>
3526    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3527      <organization>Agranat Systems, Inc.</organization>
3528      <address><email>lawrence@agranat.com</email></address>
3529    </author>
3530    <date year='2000' month='May' />
3531  </front>
3532  <seriesInfo name='RFC' value='2817' />
3533</reference>
3534
3535<reference anchor='RFC3864'>
3536  <front>
3537    <title>Registration Procedures for Message Header Fields</title>
3538    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3539      <organization>Nine by Nine</organization>
3540      <address><email>GK-IETF@ninebynine.org</email></address>
3541    </author>
3542    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3543      <organization>BEA Systems</organization>
3544      <address><email>mnot@pobox.com</email></address>
3545    </author>
3546    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3547      <organization>HP Labs</organization>
3548      <address><email>JeffMogul@acm.org</email></address>
3549    </author>
3550    <date year='2004' month='September' />
3551  </front>
3552  <seriesInfo name='BCP' value='90' />
3553  <seriesInfo name='RFC' value='3864' />
3554</reference>
3555
3556<reference anchor='RFC5226'>
3557  <front>
3558    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3559    <author initials='T.' surname='Narten' fullname='T. Narten'>
3560      <organization>IBM</organization>
3561      <address><email>narten@us.ibm.com</email></address>
3562    </author>
3563    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3564      <organization>Google</organization>
3565      <address><email>Harald@Alvestrand.no</email></address>
3566    </author>
3567    <date year='2008' month='May' />
3568  </front>
3569  <seriesInfo name='BCP' value='26' />
3570  <seriesInfo name='RFC' value='5226' />
3571</reference>
3572
3573<reference anchor="RFC5322">
3574  <front>
3575    <title>Internet Message Format</title>
3576    <author initials="P." surname="Resnick" fullname="P. Resnick">
3577      <organization>Qualcomm Incorporated</organization>
3578    </author>
3579    <date year="2008" month="October"/>
3580  </front> 
3581  <seriesInfo name="RFC" value="5322"/>
3582</reference>
3583
3584<reference anchor='RFC5789'>
3585  <front>
3586    <title>PATCH Method for HTTP</title>
3587    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3588      <organization>Linden Lab</organization>
3589    </author>
3590    <author initials='J.' surname='Snell' fullname='J. Snell' />
3591    <date year='2010' month='March' />
3592  </front>
3593  <seriesInfo name='RFC' value='5789' />
3594</reference>
3595
3596<reference anchor="RFC5987">
3597        <front>
3598    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3599    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3600      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3601      <address>
3602        <postal>
3603          <street>Hafenweg 16</street>
3604          <city>Muenster</city><region>NW</region><code>48155</code>
3605          <country>Germany</country>
3606        </postal>
3607        <email>julian.reschke@greenbytes.de</email>     
3608        <uri>http://greenbytes.de/tech/webdav/</uri>   
3609      </address>
3610    </author>
3611    <date month="August" year="2010"/>
3612  </front>
3613  <seriesInfo name="RFC" value="5987"/>
3614</reference>
3615
3616<reference anchor="draft-reschke-http-status-308">
3617        <front>
3618    <title abbrev="HTTP Status Code 308">The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)</title>
3619    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3620      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3621      <address>
3622        <email>julian.reschke@greenbytes.de</email>     
3623      </address>
3624    </author>
3625    <date month="March" year="2012"/>
3626  </front>
3627  <seriesInfo name="Internet-Draft" value="draft-reschke-http-status-308-07"/>
3628</reference>
3629
3630</references>
3631
3632<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3633<t>
3634  Clarify definition of POST.
3635  (<xref target="POST"/>)
3636</t>
3637<t>
3638  Remove requirement to handle all Content-* header fields; ban use of
3639  Content-Range with PUT.
3640  (<xref target="PUT"/>)
3641</t>
3642<t>
3643  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3644  (<xref target="CONNECT"/>)
3645</t>
3646<t>
3647  This document takes over the Status Code Registry, previously defined
3648  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3649  (<xref target="status.code.registry"/>)
3650</t>
3651<t>
3652  Broadened the definition of 203 (Non-Authoritative Information) to include
3653  cases of payload transformations as well.
3654  (<xref target="status.203"/>)
3655</t>
3656<t>
3657  Status codes 301, 302, and 307: removed the normative requirements on both
3658  response payloads and user interaction.
3659  (<xref target="status.3xx"/>)
3660</t>
3661<t>
3662  Failed to consider that there are many other request methods that are safe
3663  to automatically redirect, and further that the user agent is able to make
3664  that determination based on the request method semantics.
3665  Furthermore, allow user agents to rewrite the method from POST to GET
3666  for status codes 301 and 302.
3667  (Sections <xref format="counter" target="status.301"/>,
3668  <xref format="counter" target="status.302"/> and
3669  <xref format="counter" target="status.307"/>)
3670</t>
3671<t>
3672  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3673  It used to indicate that the target resource needs to be accessed through the
3674  proxy given by the Location field. The Location field gave the URI of the
3675  proxy. The recipient was expected to repeat this single request via the proxy.
3676  (<xref target="status.305"/>)
3677</t>
3678<t>
3679  Define status 426 (Upgrade Required) (this was incorporated from
3680  <xref target="RFC2817"/>).
3681  (<xref target="status.426"/>)
3682</t>
3683<t>
3684  Change ABNF productions for header fields to only define the field value.
3685  (<xref target="header.field.definitions"/>)
3686</t>
3687<t>
3688  Reclassify "Allow" as response header field, removing the option to
3689  specify it in a PUT request.
3690  Relax the server requirement on the contents of the Allow header field and
3691  remove requirement on clients to always trust the header field value.
3692  (<xref target="header.allow"/>)
3693</t>
3694<t>
3695  The ABNF for the Expect header field has been both fixed (allowing parameters
3696  for value-less expectations as well) and simplified (allowing trailing
3697  semicolons after "100-continue" when they were invalid before).
3698  (<xref target="header.expect"/>)
3699</t>
3700<t>
3701  Correct syntax of Location header field to allow URI references (including
3702  relative references and fragments), as referred symbol "absoluteURI" wasn't
3703  what was expected, and add some clarifications as to when use of fragments
3704  would not be appropriate.
3705  (<xref target="header.location"/>)
3706</t>
3707<t>
3708  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3709  extension methods could have used it as well).
3710  (<xref target="header.max-forwards"/>)
3711</t>
3712<t>
3713  Allow Referer field value of "about:blank" as alternative to not specifying it.
3714  (<xref target="header.referer"/>)
3715</t>
3716<t>
3717  In the description of the Server header field, the Via field
3718  was described as a SHOULD. The requirement was and is stated
3719  correctly in the description of the Via header field in &header-via;.
3720  (<xref target="header.server"/>)
3721</t>
3722</section>
3723
3724<?BEGININC p2-semantics.abnf-appendix ?>
3725<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3726<figure>
3727<artwork type="abnf" name="p2-semantics.parsed-abnf">
3728<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
3729
3730<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
3731
3732<x:ref>Date</x:ref> = HTTP-date
3733
3734<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3735
3736<x:ref>From</x:ref> = mailbox
3737
3738<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
3739
3740<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
3741
3742<x:ref>Location</x:ref> = URI-reference
3743
3744<x:ref>Max-Forwards</x:ref> = 1*DIGIT
3745
3746<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
3747
3748<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
3749<x:ref>Referer</x:ref> = absolute-URI / partial-URI
3750<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
3751
3752<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
3753
3754<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
3755<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
3756
3757<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
3758<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
3759
3760<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
3761
3762<x:ref>date1</x:ref> = day SP month SP year
3763<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
3764<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
3765<x:ref>day</x:ref> = 2DIGIT
3766<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
3767 / %x54.75.65 ; Tue
3768 / %x57.65.64 ; Wed
3769 / %x54.68.75 ; Thu
3770 / %x46.72.69 ; Fri
3771 / %x53.61.74 ; Sat
3772 / %x53.75.6E ; Sun
3773<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
3774 / %x54.75.65.73.64.61.79 ; Tuesday
3775 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
3776 / %x54.68.75.72.73.64.61.79 ; Thursday
3777 / %x46.72.69.64.61.79 ; Friday
3778 / %x53.61.74.75.72.64.61.79 ; Saturday
3779 / %x53.75.6E.64.61.79 ; Sunday
3780<x:ref>delta-seconds</x:ref> = 1*DIGIT
3781
3782<x:ref>expect-name</x:ref> = token
3783<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
3784<x:ref>expect-value</x:ref> = token / quoted-string
3785<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
3786 OWS expect-param ] )
3787
3788<x:ref>hour</x:ref> = 2DIGIT
3789
3790<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
3791<x:ref>method</x:ref> = token
3792<x:ref>minute</x:ref> = 2DIGIT
3793<x:ref>month</x:ref> = %x4A.61.6E ; Jan
3794 / %x46.65.62 ; Feb
3795 / %x4D.61.72 ; Mar
3796 / %x41.70.72 ; Apr
3797 / %x4D.61.79 ; May
3798 / %x4A.75.6E ; Jun
3799 / %x4A.75.6C ; Jul
3800 / %x41.75.67 ; Aug
3801 / %x53.65.70 ; Sep
3802 / %x4F.63.74 ; Oct
3803 / %x4E.6F.76 ; Nov
3804 / %x44.65.63 ; Dec
3805
3806<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
3807<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
3808
3809<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
3810<x:ref>product</x:ref> = token [ "/" product-version ]
3811<x:ref>product-version</x:ref> = token
3812
3813<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
3814
3815<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
3816<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
3817
3818<x:ref>second</x:ref> = 2DIGIT
3819
3820<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
3821<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
3822
3823<x:ref>year</x:ref> = 4DIGIT
3824</artwork>
3825</figure>
3826<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
3827; Allow defined but not used
3828; Date defined but not used
3829; Expect defined but not used
3830; From defined but not used
3831; Location defined but not used
3832; Max-Forwards defined but not used
3833; Referer defined but not used
3834; Retry-After defined but not used
3835; Server defined but not used
3836; User-Agent defined but not used
3837; obs-text defined but not used
3838</artwork></figure></section>
3839<?ENDINC p2-semantics.abnf-appendix ?>
3840
3841<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3842
3843<section title="Since RFC 2616">
3844<t>
3845  Extracted relevant partitions from <xref target="RFC2616"/>.
3846</t>
3847</section>
3848
3849<section title="Since draft-ietf-httpbis-p2-semantics-00">
3850<t>
3851  Closed issues:
3852  <list style="symbols"> 
3853    <t>
3854      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3855      "Via is a MUST"
3856      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3857    </t>
3858    <t>
3859      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3860      "Fragments allowed in Location"
3861      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3862    </t>
3863    <t>
3864      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3865      "Safe Methods vs Redirection"
3866      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3867    </t>
3868    <t>
3869      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3870      "Revise description of the POST method"
3871      (<eref target="http://purl.org/NET/http-errata#post"/>)
3872    </t>
3873    <t>
3874      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3875      "Normative and Informative references"
3876    </t>
3877    <t>
3878      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3879      "RFC2606 Compliance"
3880    </t>
3881    <t>
3882      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3883      "Informative references"
3884    </t>
3885    <t>
3886      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3887      "Redundant cross-references"
3888    </t>
3889  </list>
3890</t>
3891<t>
3892  Other changes:
3893  <list style="symbols"> 
3894    <t>
3895      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3896    </t>
3897  </list>
3898</t>
3899</section>
3900
3901<section title="Since draft-ietf-httpbis-p2-semantics-01">
3902<t>
3903  Closed issues:
3904  <list style="symbols"> 
3905    <t>
3906      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3907      "PUT side effects"
3908    </t>
3909    <t>
3910      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3911      "Duplicate Host header requirements"
3912    </t>
3913  </list>
3914</t>
3915<t>
3916  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3917  <list style="symbols"> 
3918    <t>
3919      Move "Product Tokens" section (back) into Part 1, as "token" is used
3920      in the definition of the Upgrade header field.
3921    </t>
3922    <t>
3923      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3924    </t>
3925    <t>
3926      Copy definition of delta-seconds from Part6 instead of referencing it.
3927    </t>
3928  </list>
3929</t>
3930</section>
3931
3932<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3933<t>
3934  Closed issues:
3935  <list style="symbols"> 
3936    <t>
3937      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3938      "Requiring Allow in 405 responses"
3939    </t>
3940    <t>
3941      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3942      "Status Code Registry"
3943    </t>
3944    <t>
3945      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3946      "Redirection vs. Location"
3947    </t>
3948    <t>
3949      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3950      "Cacheability of 303 response"
3951    </t>
3952    <t>
3953      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3954      "305 Use Proxy"
3955    </t>
3956    <t>
3957      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3958      "Classification for Allow header"
3959    </t>
3960    <t>
3961      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3962      "PUT - 'store under' vs 'store at'"
3963    </t>
3964  </list>
3965</t>
3966<t>
3967  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3968  <list style="symbols"> 
3969    <t>
3970      Reference RFC 3984, and update header field registrations for headers defined
3971      in this document.
3972    </t>
3973  </list>
3974</t>
3975<t>
3976  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3977  <list style="symbols"> 
3978    <t>
3979      Replace string literals when the string really is case-sensitive (method).
3980    </t>
3981  </list>
3982</t>
3983</section>
3984
3985<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
3986<t>
3987  Closed issues:
3988  <list style="symbols"> 
3989    <t>
3990      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
3991      "OPTIONS request bodies"
3992    </t>
3993    <t>
3994      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
3995      "Description of CONNECT should refer to RFC2817"
3996    </t>
3997    <t>
3998      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
3999      "Location Content-Location reference request/response mixup"
4000    </t>
4001  </list>
4002</t>
4003<t>
4004  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4005  <list style="symbols"> 
4006    <t>
4007      Added initial proposal for registration process, plus initial
4008      content (non-HTTP/1.1 methods to be added by a separate specification).
4009    </t>
4010  </list>
4011</t>
4012</section>
4013
4014<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4015<t>
4016  Closed issues:
4017  <list style="symbols"> 
4018    <t>
4019      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4020      "Content-*"
4021    </t>
4022    <t>
4023      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4024      "RFC 2822 is updated by RFC 5322"
4025    </t>
4026  </list>
4027</t>
4028<t>
4029  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4030  <list style="symbols"> 
4031    <t>
4032      Use "/" instead of "|" for alternatives.
4033    </t>
4034    <t>
4035      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4036      whitespace ("OWS") and required whitespace ("RWS").
4037    </t>
4038    <t>
4039      Rewrite ABNFs to spell out whitespace rules, factor out
4040      header field value format definitions.
4041    </t>
4042  </list>
4043</t>
4044</section>
4045
4046<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4047<t>
4048  Closed issues:
4049  <list style="symbols"> 
4050    <t>
4051      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4052      "reason-phrase BNF"
4053    </t>
4054  </list>
4055</t>
4056<t>
4057  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4058  <list style="symbols"> 
4059    <t>
4060      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4061    </t>
4062  </list>
4063</t>
4064</section>
4065
4066<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4067<t>
4068  Closed issues:
4069  <list style="symbols"> 
4070    <t>
4071      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4072      "Clarify when Referer is sent"
4073    </t>
4074    <t>
4075      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4076      "status codes vs methods"
4077    </t>
4078    <t>
4079      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4080      "Do not require "updates" relation for specs that register status codes or method names"
4081    </t>
4082  </list>
4083</t>
4084</section>
4085
4086<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4087<t>
4088  Closed issues:
4089  <list style="symbols"> 
4090    <t>
4091      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4092      "Idempotency"
4093    </t>
4094    <t>
4095      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4096      "TRACE security considerations"
4097    </t>
4098    <t>
4099      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4100      "Clarify rules for determining what entities a response carries"
4101    </t>
4102    <t>
4103      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4104      "update note citing RFC 1945 and 2068"
4105    </t>
4106    <t>
4107      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4108      "update note about redirect limit"
4109    </t>
4110    <t>
4111      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4112      "Location header ABNF should use 'URI'"
4113    </t>
4114    <t>
4115      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4116      "fragments in Location vs status 303"
4117    </t>
4118    <t>
4119      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4120      "move IANA registrations for optional status codes"
4121    </t>
4122  </list>
4123</t>
4124<t>
4125  Partly resolved issues:
4126  <list style="symbols"> 
4127    <t>
4128      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4129      "Are OPTIONS and TRACE safe?"
4130    </t>
4131  </list>
4132</t>
4133</section>
4134
4135<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4136<t>
4137  Closed issues:
4138  <list style="symbols"> 
4139    <t>
4140      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4141      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4142      status codes when fixing this previously)
4143    </t>
4144  </list>
4145</t>
4146</section>
4147
4148<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4149<t>
4150  Closed issues:
4151  <list style="symbols"> 
4152    <t>
4153      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4154      "Fragment combination / precedence during redirects"
4155    </t>
4156  </list>
4157</t>
4158<t>
4159  Partly resolved issues:
4160  <list style="symbols"> 
4161    <t>
4162      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4163      "Location header payload handling"
4164    </t>
4165    <t>
4166      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4167      "Term for the requested resource's URI"
4168    </t>
4169  </list>
4170</t>
4171</section>
4172
4173<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4174<t>
4175  Closed issues:
4176  <list style="symbols"> 
4177    <t>
4178      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4179      "Clarify 'Requested Variant'"
4180    </t>
4181    <t>
4182      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4183      "Clarify entity / representation / variant terminology"
4184    </t>
4185    <t>
4186      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4187      "Methods and Caching"
4188    </t>
4189    <t>
4190      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4191      "OPTIONS vs Max-Forwards"
4192    </t>
4193    <t>
4194      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4195      "Status codes and caching"
4196    </t>
4197    <t>
4198      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4199      "consider removing the 'changes from 2068' sections"
4200    </t>
4201  </list>
4202</t>
4203</section>
4204
4205<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4206<t>
4207  Closed issues:
4208  <list style="symbols"> 
4209    <t>
4210      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4211      "Considerations for new status codes"
4212    </t>
4213    <t>
4214      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4215      "Considerations for new methods"
4216    </t>
4217    <t>
4218      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4219      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4220    </t>
4221  </list>
4222</t>
4223</section>
4224
4225<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4226<t>
4227  Closed issues:
4228  <list style="symbols"> 
4229    <t>
4230      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4231      "Fragment combination / precedence during redirects" (added warning
4232      about having a fragid on the redirect may cause inconvenience in
4233      some cases)
4234    </t>
4235    <t>
4236      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4237      "Content-* vs. PUT"
4238    </t>
4239    <t>
4240      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4241      "205 Bodies"
4242    </t>
4243    <t>
4244      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4245      "Understanding Content-* on non-PUT requests"
4246    </t>
4247    <t>
4248      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4249      "Content-*"
4250    </t>
4251    <t>
4252      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4253      "Header type defaulting"
4254    </t>
4255    <t>
4256      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4257      "PUT - 'store under' vs 'store at'"
4258    </t>
4259    <t>
4260      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4261      "duplicate ABNF for reason-phrase"
4262    </t>
4263    <t>
4264      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4265      "Note special status of Content-* prefix in header registration procedures"
4266    </t>
4267    <t>
4268      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4269      "Max-Forwards vs extension methods"
4270    </t>
4271    <t>
4272      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4273      "What is the value space of HTTP status codes?" (actually fixed in
4274      draft-ietf-httpbis-p2-semantics-11)
4275    </t>
4276    <t>
4277      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4278      "Header Classification"
4279    </t>
4280    <t>
4281      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4282      "PUT side effect: invalidation or just stale?"
4283    </t>
4284    <t>
4285      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4286      "proxies not supporting certain methods"
4287    </t>
4288    <t>
4289      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4290      "Migrate CONNECT from RFC2817 to p2"
4291    </t>
4292    <t>
4293      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4294      "Migrate Upgrade details from RFC2817"
4295    </t>
4296    <t>
4297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4298      "clarify PUT semantics'"
4299    </t>
4300    <t>
4301      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4302      "duplicate ABNF for 'Method'"
4303    </t>
4304    <t>
4305      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4306      "untangle ABNFs for header fields"
4307    </t>
4308  </list>
4309</t>
4310</section>
4311
4312<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4313<t>
4314  Closed issues:
4315  <list style="symbols"> 
4316    <t>
4317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4318      "untangle ABNFs for header fields"
4319    </t>
4320    <t>
4321      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4322      "message body in CONNECT request"
4323    </t>
4324  </list>
4325</t>
4326</section>
4327
4328<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4329<t>
4330  Closed issues:
4331  <list style="symbols"> 
4332    <t>
4333      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4334      "Clarify status code for rate limiting"
4335    </t>
4336    <t>
4337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4338      "clarify 403 forbidden"
4339    </t>
4340    <t>
4341      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4342      "Clarify 203 Non-Authoritative Information"
4343    </t>
4344    <t>
4345      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4346      "update default reason phrase for 413"
4347    </t>
4348  </list>
4349</t>
4350</section>
4351
4352<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4353<t>
4354  Closed issues:
4355  <list style="symbols"> 
4356    <t>
4357      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4358      "Strength of requirements on Accept re: 406"
4359    </t>
4360    <t>
4361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4362      "400 response isn't generic"
4363    </t>
4364  </list>
4365</t>
4366</section>
4367
4368<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4369<t>
4370  Closed issues:
4371  <list style="symbols"> 
4372    <t>
4373      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4374      "Redirects and non-GET methods"
4375    </t>
4376    <t>
4377      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4378      "Document HTTP's error-handling philosophy"
4379    </t>
4380    <t>
4381      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4382      "Considerations for new headers"
4383    </t>
4384    <t>
4385      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4386      "clarify 303 redirect on HEAD"
4387    </t>
4388  </list>
4389</t>
4390</section>
4391
4392<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4393<t>
4394  Closed issues:
4395  <list style="symbols"> 
4396    <t>
4397      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4398      "Location header payload handling"
4399    </t>
4400    <t>
4401      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4402      "Clarify status code for rate limiting" (change backed out because
4403      a new status code is being defined for this purpose)
4404    </t>
4405    <t>
4406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4407      "should there be a permanent variant of 307"
4408    </t>
4409    <t>
4410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4411      "When are Location's semantics triggered?"
4412    </t>
4413    <t>
4414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4415      "'expect' grammar missing OWS"
4416    </t>
4417    <t>
4418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4419      "header field considerations: quoted-string vs use of double quotes"
4420    </t>
4421  </list>
4422</t>
4423</section>
4424
4425<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4426<t>
4427  Closed issues:
4428  <list style="symbols"> 
4429    <t>
4430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4431      "Combining HEAD responses"
4432    </t>
4433    <t>
4434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4435      "Requirements for user intervention during redirects"
4436    </t>
4437    <t>
4438      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4439      "message-body in CONNECT response"
4440    </t>
4441    <t>
4442      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4443      "Applying original fragment to 'plain' redirected URI"
4444    </t>
4445    <t>
4446      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4447      "Misplaced text on connection handling in p2"
4448    </t>
4449    <t>
4450      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4451      "clarify that 201 doesn't require Location header fields"
4452    </t>
4453    <t>
4454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4455      "relax requirements on hypertext in 3/4/5xx error responses"
4456    </t>
4457    <t>
4458      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4459      "example for 426 response should have a payload"
4460    </t>
4461    <t>
4462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4463      "drop indirection entries for status codes"
4464    </t>
4465  </list>
4466</t>
4467</section>
4468
4469<section title="Since draft-ietf-httpbis-p2-semantics-19" anchor="changes.since.19">
4470<t>
4471  Closed issues:
4472  <list style="symbols"> 
4473    <t>
4474      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4475      "should there be a permanent variant of 307"
4476    </t>
4477  </list>
4478</t>
4479</section>
4480
4481</section>
4482
4483</back>
4484</rfc>
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