source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1587

Last change on this file since 1587 was 1586, checked in by fielding@…, 8 years ago

trim the authors list to just the current editors

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 183.7 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.18"/>.
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="Method" anchor="method">
314  <x:anchor-alias value="method"/>
315  <x:anchor-alias value="extension-method"/>
316<t>
317   The method token indicates the request method to be performed on the target
318   resource (&effective-request-uri;). The method is case-sensitive.
319</t>
320<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
321  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
322</artwork></figure>
323<t>
324   The list of methods allowed by a resource can be specified in an
325   Allow header field (<xref target="header.allow"/>). The status code of the response
326   always notifies the client whether a method is currently allowed on a
327   resource, since the set of allowed methods can change dynamically. An
328   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
329   if the method is known by the origin server but not allowed for the
330   resource, and 501 (Not Implemented) if the method is
331   unrecognized or not implemented by the origin server. The methods GET
332   and HEAD &MUST; be supported by all general-purpose servers. All other
333   methods are &OPTIONAL;; however, if the above methods are implemented,
334   they &MUST; be implemented with the same semantics as those specified
335   in <xref target="method.definitions"/>.
336</t>
337
338<section title="Overview of Methods" anchor="overview.of.methods">
339<t>
340  The methods listed below are defined in <xref target="method.definitions"/>.
341</t>
342<texttable align="left">
343  <ttcol>Method Name</ttcol><ttcol>Defined in...</ttcol>
344 
345  <c>OPTIONS</c> <c><xref target="OPTIONS"/></c>
346  <c>GET</c> <c><xref target="GET"/></c>
347  <c>HEAD</c> <c><xref target="HEAD"/></c>
348  <c>POST</c> <c><xref target="POST"/></c>
349  <c>PUT</c> <c><xref target="PUT"/></c>
350  <c>DELETE</c> <c><xref target="DELETE"/></c>
351  <c>TRACE</c> <c><xref target="TRACE"/></c>
352  <c>CONNECT</c> <c><xref target="CONNECT"/></c>
353</texttable>
354<t>
355  Note that this list is not exhaustive &mdash; it does not include request methods defined
356  in other specifications.
357</t>
358</section>
359
360<section title="Method Registry" anchor="method.registry">
361<t>
362  The HTTP Method Registry defines the name space for the method token in the
363  Request line of an HTTP request.
364</t>
365<t>
366  Registrations &MUST; include the following fields:
367  <list style="symbols">
368    <t>Method Name (see <xref target="method"/>)</t>
369    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
370    <t>Pointer to specification text</t>
371  </list>
372</t>
373<t>
374  Values to be added to this name space require IETF Review
375  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
376</t>
377<t>
378  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
379</t>
380
381<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
382<t>
383   When it is necessary to express new semantics for a HTTP request that
384   aren't specific to a single application or media type, and currently defined
385   methods are inadequate, it may be appropriate to register a new method.
386</t>
387<t>
388   HTTP methods are generic; that is, they are potentially applicable to any
389   resource, not just one particular media type, "type" of resource, or
390   application. As such, it is preferred that new HTTP methods be registered
391   in a document that isn't specific to a single application, so that this is
392   clear.
393</t>
394<t>
395   Due to the parsing rules defined in &message-body;, definitions of HTTP
396   methods cannot prohibit the presence of a message body on either the request
397   or the response message (with responses to HEAD requests being the single
398   exception). Definitions of new methods cannot change this rule, but they can
399   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
400</t>
401<t>
402   New method definitions need to indicate whether they are safe (<xref
403   target="safe.methods"/>), what semantics (if any) the request body has,
404   and whether they are idempotent (<xref target="idempotent.methods"/>).
405   They also need to state whether they can be cached (&caching;); in
406   particular what conditions a cache may store the response, and under what
407   conditions such a stored response may be used to satisfy a subsequent
408   request.
409</t>
410</section>
411
412</section>
413</section>
414
415<section title="Header Fields" anchor="header.fields">
416<t>
417   Header fields are key value pairs that can be used to communicate data about
418   the message, its payload, the target resource, or about the connection
419   itself (i.e., control data).  See &header-fields; for a general definition
420   of their syntax.
421</t>
422
423<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
424<t>
425   New header fields are registered using the procedures described in
426   <xref target="RFC3864"/>.
427</t>
428<t>
429   The requirements for header field names are defined in
430   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
431   defining new fields are advised to keep the name as short as practical, and
432   not to prefix them with "X-" if they are to be registered (either
433   immediately or in the future).
434</t>
435<t>
436   New header field values typically have their syntax defined using ABNF
437   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
438   as necessary, and are usually constrained to the range of ASCII characters.
439   Header fields needing a greater range of characters can use an encoding
440   such as the one defined in <xref target="RFC5987"/>.
441</t>
442<t>
443   Because commas (",") are used as a generic delimiter between field-values,
444   they need to be treated with care if they are allowed in the field-value's
445   payload. Typically, components that might contain a comma are protected with
446   double-quotes using the quoted-string ABNF production (&field-components;).
447</t>
448<t>
449   For example, a textual date and a URI (either of which might contain a comma)
450   could be safely carried in field-values like these:
451</t>
452<figure><artwork type="example">
453  Example-URI-Field: "http://example.com/a.html,foo",
454                     "http://without-a-comma.example.com/"
455  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
456</artwork></figure>
457<t>
458   Note that double quote delimiters almost always are used with the
459   quoted-string production; using a different syntax inside double quotes
460   will likely cause unnecessary confusion.
461</t>
462<t>
463   Many header fields use a format including (case-insensitively) named
464   parameters (for instance, Content-Type, defined in &header-content-type;).
465   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
466   parameter value enables recipients to use existing parser components. When
467   allowing both forms, the meaning of a parameter value ought to be
468   independent of the syntax used for it (for an example, see the notes on
469   parameter handling for media types in &media-types;).
470</t>
471<t>
472   Authors of specifications defining new header fields are advised to consider
473   documenting:
474  <list style="symbols">
475    <x:lt>
476      <t>Whether the field is a single value, or whether it can be a list
477      (delimited by commas; see &header-fields;).</t>
478      <t>If it does not use the list syntax, document how to treat messages
479      where the header field occurs multiple times (a sensible default would
480      be to ignore the header field, but this might not always be the right
481      choice).</t>
482      <t>Note that intermediaries and software libraries might combine
483      multiple header field instances into a single one, despite the header
484      field not allowing this. A robust format enables recipients to discover
485      these situations (good example: "Content-Type", as the comma can only
486      appear inside quoted strings; bad example: "Location", as a comma can
487      occur inside a URI).</t>
488    </x:lt>
489    <x:lt><t>Under what conditions the header field can be used; e.g., only in
490    responses or requests, in all messages, only on responses to a particular
491    request method.</t></x:lt>
492    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
493    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
494    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
495    field's value, insert or delete it.</t></x:lt>
496    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
497    <x:lt><t>Whether the header field is useful or allowable in trailers (see
498    &chunked-encoding;).</t></x:lt>
499    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
500  </list>
501</t>
502</section>
503
504<section title="Request Header Fields" anchor="request.header.fields">
505  <x:anchor-alias value="request-header"/>
506<t>
507   The request header fields allow the client to pass additional
508   information about the request, and about the client itself, to the
509   server. These fields act as request modifiers, with semantics
510   equivalent to the parameters on a programming language method
511   invocation.
512</t>
513<texttable align="left">
514  <ttcol>Header Field Name</ttcol>
515  <ttcol>Defined in...</ttcol>
516
517  <c>Accept</c> <c>&header-accept;</c>
518  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
519  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
520  <c>Accept-Language</c> <c>&header-accept-language;</c>
521  <c>Authorization</c> <c>&header-authorization;</c>
522  <c>Expect</c> <c><xref target="header.expect"/></c>
523  <c>From</c> <c><xref target="header.from"/></c>
524  <c>Host</c> <c>&header-host;</c>
525  <c>If-Match</c> <c>&header-if-match;</c>
526  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
527  <c>If-None-Match</c> <c>&header-if-none-match;</c>
528  <c>If-Range</c> <c>&header-if-range;</c>
529  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
530  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
531  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
532  <c>Range</c> <c>&header-range;</c>
533  <c>Referer</c> <c><xref target="header.referer"/></c>
534  <c>TE</c> <c>&header-te;</c>
535  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
536</texttable>
537</section>
538
539<section title="Response Header Fields" anchor="response.header.fields">
540  <x:anchor-alias value="response-header"/>
541<t>
542   The response header fields allow the server to pass additional
543   information about the response which cannot be placed in the status-line.
544   These header fields give information about the server and about
545   further access to the target resource (&effective-request-uri;).
546</t>
547<texttable align="left">
548  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
549
550  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
551  <c>Age</c> <c>&header-age;</c>
552  <c>Allow</c> <c><xref target="header.allow"/></c>
553  <c>Date</c> <c><xref target="header.date"/></c>
554  <c>ETag</c> <c>&header-etag;</c>
555  <c>Location</c> <c><xref target="header.location"/></c>
556  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
557  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
558  <c>Server</c> <c><xref target="header.server"/></c>
559  <c>Vary</c> <c>&header-vary;</c>
560  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
561</texttable>
562</section>
563
564</section>
565
566<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
567  <x:anchor-alias value="reason-phrase"/>
568  <x:anchor-alias value="status-code"/>
569  <x:anchor-alias value="extension-code"/>
570<t>
571   The status-code element is a 3-digit integer result code of the attempt to
572   understand and satisfy the request.
573</t>
574<t>
575   The reason-phrase is intended to give a short textual description of the
576   status-code and is intended for a human user. The client does not need
577   to examine or display the reason-phrase.
578</t>
579<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="reason-phrase"/>
580  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
581  <x:ref>reason-phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
582</artwork></figure>
583<t>
584   HTTP status codes are extensible. HTTP applications are not required
585   to understand the meaning of all registered status codes, though such
586   understanding is obviously desirable. However, applications &MUST;
587   understand the class of any status code, as indicated by the first
588   digit, and treat any unrecognized response as being equivalent to the
589   x00 status code of that class, with the exception that an
590   unrecognized response &MUST-NOT; be cached. For example, if an
591   unrecognized status code of 431 is received by the client, it can
592   safely assume that there was something wrong with its request and
593   treat the response as if it had received a 400 status code. In such
594   cases, user agents &SHOULD; present to the user the representation enclosed
595   with the response, since that representation is likely to include human-readable
596   information which will explain the unusual status.
597</t>
598
599<section title="Overview of Status Codes" anchor="overview.of.status.codes">
600<t> 
601   The status codes listed below are defined in <xref target="status.codes"/>
602   of this specification, &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
603   The reason phrases listed here are only recommendations &mdash; they can be
604   replaced by local equivalents without affecting the protocol.
605</t>
606<texttable align="left">
607  <ttcol>status-code</ttcol>
608  <ttcol>reason-phrase</ttcol>
609  <ttcol>Defined in...</ttcol>
610 
611  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
612  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
613
614  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
615  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
616  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
617  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
618  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
619  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
620  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
621
622  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
623  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
624  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
625  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
626  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
627  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
628  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
629
630  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
631  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
632  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
633  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
634  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
635  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
636  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
637  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
638  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
639  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
640  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
641  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
642  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
643  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
644  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
645  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
646  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
647  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
648  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
649
650  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
651  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
652  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
653  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
654  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
655  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
656</texttable>
657<t>
658   Note that this list is not exhaustive &mdash; it does not include
659   extension status codes defined in other specifications.
660</t>
661</section>
662
663<section title="Status Code Registry" anchor="status.code.registry">
664<t>
665  The HTTP Status Code Registry defines the name space for the status-code
666  token in the status-line of an HTTP response.
667</t>
668<t>
669  Values to be added to this name space require IETF Review
670  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
671</t>
672<t>
673  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
674</t>
675
676<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
677<t>
678   When it is necessary to express new semantics for a HTTP response that
679   aren't specific to a single application or media type, and currently defined
680   status codes are inadequate, a new status code can be registered.
681</t>
682<t>
683   HTTP status codes are generic; that is, they are potentially applicable to
684   any resource, not just one particular media type, "type" of resource, or
685   application. As such, it is preferred that new HTTP status codes be
686   registered in a document that isn't specific to a single application, so
687   that this is clear.
688</t>
689<t>
690   Definitions of new HTTP status codes typically explain the request
691   conditions that produce a response containing the status code (e.g.,
692   combinations of request headers and/or method(s)), along with any
693   interactions with response headers (e.g., those that are required, those
694   that modify the semantics of the response).
695</t>
696<t>
697   New HTTP status codes are required to fall under one of the categories
698   defined in <xref target="status.codes"/>. To allow existing parsers to
699   properly handle them, new status codes cannot disallow a response body,
700   although they can mandate a zero-length response body. They can require the
701   presence of one or more particular HTTP response header(s).
702</t>
703<t>
704   Likewise, their definitions can specify that caches are allowed to use
705   heuristics to determine their freshness (see &caching;; by default, it is
706   not allowed), and can define how to determine the resource which they
707   carry a representation for (see <xref
708   target="identifying.response.associated.with.representation"/>; by default,
709   it is anonymous).
710</t>
711</section>
712
713</section>
714
715</section>
716
717<section title="Representation" anchor="representation">
718<t>
719   Request and Response messages &MAY; transfer a representation if not otherwise
720   restricted by the request method or response status code. A representation
721   consists of metadata (representation header fields) and data (representation
722   body).  When a complete or partial representation is enclosed in an HTTP message,
723   it is referred to as the payload of the message. HTTP representations
724   are defined in &payload;.
725</t>
726<t>
727   A representation body is only present in a message when a message body is
728   present, as described in &message-body;. The representation body is obtained
729   from the message body by decoding any Transfer-Encoding that might
730   have been applied to ensure safe and proper transfer of the message.
731</t>
732
733<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
734<t>
735   It is sometimes necessary to determine an identifier for the resource
736   associated with a representation.
737</t>
738<t>
739   An HTTP request representation, when present, is always associated with an
740   anonymous (i.e., unidentified) resource.
741</t>
742<t>
743   In the common case, an HTTP response is a representation of the target
744   resource (see &effective-request-uri;). However, this is not always the
745   case. To determine the URI of the resource a response is associated with,
746   the following rules are used (with the first applicable one being selected):
747</t>
748<t><list style="numbers">
749   <t>If the response status code is 200 or 203 and the request method was GET,
750   the response payload is a representation of the target resource.</t>
751   <t>If the response status code is 204, 206, or 304 and the request method was GET
752   or HEAD, the response payload is a partial representation of the target
753   resource.</t>
754   <t>If the response has a Content-Location header field, and that URI is the same
755   as the effective request URI, the response payload is a representation of the
756   target resource.</t>
757   <t>If the response has a Content-Location header field, and that URI is not the
758   same as the effective request URI, then the response asserts that its
759   payload is a representation of the resource identified by the
760   Content-Location URI. However, such an assertion cannot be trusted unless
761   it can be verified by other means (not defined by HTTP).</t>
762   <t>Otherwise, the response is a representation of an anonymous (i.e.,
763   unidentified) resource.</t>
764</list></t>
765<t>
766  <cref anchor="TODO-req-uri">
767   The comparison function is going to have to be defined somewhere,
768   because we already need to compare URIs for things like cache invalidation.</cref>
769</t>
770</section>
771
772</section>
773
774
775<section title="Method Definitions" anchor="method.definitions">
776<t>
777   The set of common request methods for HTTP/1.1 is defined below. Although
778   this set can be expanded, additional methods cannot be assumed to
779   share the same semantics for separately extended clients and servers.
780</t>
781
782<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
783
784<section title="Safe Methods" anchor="safe.methods">
785<iref item="Safe Methods" primary="true"/>
786<t>
787   Implementors need to be aware that the software represents the user in
788   their interactions over the Internet, and need to allow
789   the user to be aware of any actions they take which might have an
790   unexpected significance to themselves or others.
791</t>
792<t>
793   In particular, the convention has been established that the GET, HEAD,
794   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
795   of taking an action other than retrieval. These request methods ought
796   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
797   This allows user agents to represent other methods, such as POST, PUT
798   and DELETE, in a special way, so that the user is made aware of the
799   fact that a possibly unsafe action is being requested.
800</t>
801<t>
802   Naturally, it is not possible to ensure that the server does not
803   generate side-effects as a result of performing a GET request; in
804   fact, some dynamic resources consider that a feature. The important
805   distinction here is that the user did not request the side-effects,
806   so therefore cannot be held accountable for them.
807</t>
808</section>
809
810<section title="Idempotent Methods" anchor="idempotent.methods">
811<iref item="Idempotent Methods" primary="true"/>
812<t>
813   Request methods can also have the property of "idempotence" in that,
814   aside from error or expiration issues, the intended effect of multiple
815   identical requests is the same as for a single request.
816   PUT, DELETE, and all safe request methods are idempotent.
817   It is important to note that idempotence refers only to changes
818   requested by the client: a server is free to change its state due
819   to multiple requests for the purpose of tracking those requests,
820   versioning of results, etc.
821</t>
822</section>
823</section>
824
825<section title="OPTIONS" anchor="OPTIONS">
826  <rdf:Description>
827    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
828  </rdf:Description>
829  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
830  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
831<t>
832   The OPTIONS method requests information about the
833   communication options available on the request/response chain
834   identified by the effective request URI. This method allows a client to
835   determine the options and/or requirements associated with a resource,
836   or the capabilities of a server, without implying a resource action
837   or initiating a resource retrieval.
838</t>
839<t>
840   Responses to the OPTIONS method are not cacheable.
841</t>
842<t>
843   If the OPTIONS request includes a message body (as indicated by the
844   presence of Content-Length or Transfer-Encoding), then the media type
845   &MUST; be indicated by a Content-Type field. Although this
846   specification does not define any use for such a body, future
847   extensions to HTTP might use the OPTIONS body to make more detailed
848   queries on the server.
849</t>
850<t>
851   If the request-target (&request-target;) is an asterisk ("*"),
852   the OPTIONS request is
853   intended to apply to the server in general rather than to a specific
854   resource. Since a server's communication options typically depend on
855   the resource, the "*" request is only useful as a "ping" or "no-op"
856   type of method; it does nothing beyond allowing the client to test
857   the capabilities of the server. For example, this can be used to test
858   a proxy for HTTP/1.1 conformance (or lack thereof).
859</t>
860<t>
861   If the request-target is not an asterisk, the OPTIONS request applies
862   only to the options that are available when communicating with that
863   resource.
864</t>
865<t>
866   A 200 response &SHOULD; include any header fields that indicate
867   optional features implemented by the server and applicable to that
868   resource (e.g., Allow), possibly including extensions not defined by
869   this specification. The response body, if any, &SHOULD; also include
870   information about the communication options. The format for such a
871   body is not defined by this specification, but might be defined by
872   future extensions to HTTP. Content negotiation &MAY; be used to select
873   the appropriate response format. If no response body is included, the
874   response &MUST; include a Content-Length field with a field-value of
875   "0".
876</t>
877<t>
878   The Max-Forwards header field &MAY; be used to target a
879   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
880   If no Max-Forwards field is present in the request, then the forwarded
881   request &MUST-NOT; include a Max-Forwards field.
882</t>
883</section>
884
885<section title="GET" anchor="GET">
886  <rdf:Description>
887    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
888  </rdf:Description>
889  <iref primary="true" item="GET method" x:for-anchor=""/>
890  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
891<t>
892   The GET method requests transfer of a current representation of
893   the target resource.
894</t>
895<t>   
896   If the target resource is a data-producing process, it is the
897   produced data which shall be returned as the representation in the response and not
898   the source text of the process, unless that text happens to be the output of
899   the process.
900</t>
901<t>
902   The semantics of the GET method change to a "conditional GET" if the
903   request message includes an If-Modified-Since, If-Unmodified-Since,
904   If-Match, If-None-Match, or If-Range header field. A conditional GET
905   requests that the representation be transferred only under the
906   circumstances described by the conditional header field(s). The
907   conditional GET request is intended to reduce unnecessary network
908   usage by allowing cached representations to be refreshed without requiring
909   multiple requests or transferring data already held by the client.
910</t>
911<t>
912   The semantics of the GET method change to a "partial GET" if the
913   request message includes a Range header field. A partial GET requests
914   that only part of the representation be transferred, as described in &header-range;.
915   The partial GET request is intended to reduce unnecessary
916   network usage by allowing partially-retrieved representations to be
917   completed without transferring data already held by the client.
918</t>
919<t>
920   Bodies on GET requests have no defined semantics. Note that sending a body
921   on a GET request might cause some existing implementations to reject the
922   request.
923</t>
924<t>
925   The response to a GET request is cacheable and &MAY; be used to satisfy
926   subsequent GET and HEAD requests (see &caching;).
927</t>
928<t>
929   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
930</t>
931</section>
932
933<section title="HEAD" anchor="HEAD">
934  <rdf:Description>
935    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
936  </rdf:Description>
937  <iref primary="true" item="HEAD method" x:for-anchor=""/>
938  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
939<t>
940   The HEAD method is identical to GET except that the server &MUST-NOT;
941   return a message body in the response. The metadata contained
942   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
943   to the information sent in response to a GET request. This method can
944   be used for obtaining metadata about the representation implied by the
945   request without transferring the representation body. This method is
946   often used for testing hypertext links for validity, accessibility,
947   and recent modification.
948</t>
949<t>
950   The response to a HEAD request is cacheable and &MAY; be used to satisfy
951   a subsequent HEAD request. It also has potential side effects on
952   previously stored responses to GET; see &p6-head;.
953</t>
954<t>
955   Bodies on HEAD requests have no defined semantics. Note that sending a body
956   on a HEAD request might cause some existing implementations to reject the
957   request.
958</t>
959</section>
960
961<section title="POST" anchor="POST">
962  <iref primary="true" item="POST method" x:for-anchor=""/>
963  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
964<t>
965   The POST method requests that the origin server accept the
966   representation enclosed in the request as data to be processed by the
967   target resource. POST is designed to allow a uniform method to cover the
968   following functions:
969  <list style="symbols">
970    <t>
971      Annotation of existing resources;
972    </t>
973    <t>
974        Posting a message to a bulletin board, newsgroup, mailing list,
975        or similar group of articles;
976    </t>
977    <t>
978        Providing a block of data, such as the result of submitting a
979        form, to a data-handling process;
980    </t>
981    <t>
982        Extending a database through an append operation.
983    </t>
984  </list>
985</t>
986<t>
987   The actual function performed by the POST method is determined by the
988   server and is usually dependent on the effective request URI.
989</t>
990<t>
991   The action performed by the POST method might not result in a
992   resource that can be identified by a URI. In this case, either 200
993   (OK) or 204 (No Content) is the appropriate response status code,
994   depending on whether or not the response includes a representation that
995   describes the result.
996</t>
997<t>
998   If a resource has been created on the origin server, the response
999   &SHOULD; be 201 (Created) and contain a representation which describes the
1000   status of the request and refers to the new resource, and a Location
1001   header field (see <xref target="header.location"/>).
1002</t>
1003<t>
1004   Responses to POST requests are only cacheable when they
1005   include explicit freshness information (see &p6-explicit;). A
1006   cached POST response with a Content-Location header field
1007   (see &header-content-location;) whose value is the effective
1008   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
1009</t>
1010<t>
1011   Note that POST caching is not widely implemented.
1012   However, the 303 (See Other) response can be used to direct the
1013   user agent to retrieve a cacheable resource.
1014</t>
1015</section>
1016
1017<section title="PUT" anchor="PUT">
1018  <iref primary="true" item="PUT method" x:for-anchor=""/>
1019  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
1020<t>
1021   The PUT method requests that the state of the target resource
1022   be created or replaced with the state defined by the representation
1023   enclosed in the request message payload.  A successful PUT of a given
1024   representation would suggest that a subsequent GET on that same target
1025   resource will result in an equivalent representation being returned in
1026   a 200 (OK) response.  However, there is no guarantee that such a state
1027   change will be observable, since the target resource might be acted
1028   upon by other user agents in parallel, or might be subject to dynamic
1029   processing by the origin server, before any subsequent GET is received.
1030   A successful response only implies that the user agent's intent was
1031   achieved at the time of its processing by the origin server.
1032</t>
1033<t>   
1034   If the target resource does not have a current representation and
1035   the PUT successfully creates one, then the origin server &MUST; inform
1036   the user agent by sending a 201 (Created) response.  If the target
1037   resource does have a current representation and that representation is
1038   successfully modified in accordance with the state of the enclosed
1039   representation, then either a 200 (OK) or 204 (No Content) response
1040   &SHOULD; be sent to indicate successful completion of the request.
1041</t>
1042<t>
1043   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
1044   as part of the resource state).
1045</t>
1046<t>
1047   An origin server &SHOULD; verify that the PUT representation is
1048   consistent with any constraints which the server has for the target
1049   resource that cannot or will not be changed by the PUT.  This is
1050   particularly important when the origin server uses internal
1051   configuration information related to the URI in order to set the
1052   values for representation metadata on GET responses.  When a PUT
1053   representation is inconsistent with the target resource, the origin
1054   server &SHOULD; either make them consistent, by transforming the
1055   representation or changing the resource configuration, or respond
1056   with an appropriate error message containing sufficient information
1057   to explain why the representation is unsuitable.  The 409 (Conflict)
1058   or 415 (Unsupported Media Type) status codes are suggested, with the
1059   latter being specific to constraints on Content-Type values.
1060</t>
1061<t>
1062   For example, if the target resource is configured to always have a
1063   Content-Type of "text/html" and the representation being PUT has a
1064   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
1065   (a) reconfigure the target resource to reflect the new media type;
1066   (b) transform the PUT representation to a format consistent with that
1067   of the resource before saving it as the new resource state; or,
1068   (c) reject the request with a 415 response indicating that the target
1069   resource is limited to "text/html", perhaps including a link to a
1070   different resource that would be a suitable target for the new
1071   representation.
1072</t>
1073<t>
1074   HTTP does not define exactly how a PUT method affects the state
1075   of an origin server beyond what can be expressed by the intent of
1076   the user agent request and the semantics of the origin server response.
1077   It does not define what a resource might be, in any sense of that
1078   word, beyond the interface provided via HTTP.  It does not define
1079   how resource state is "stored", nor how such storage might change
1080   as a result of a change in resource state, nor how the origin server
1081   translates resource state into representations.  Generally speaking,
1082   all implementation details behind the resource interface are
1083   intentionally hidden by the server.
1084</t>
1085<t>
1086   The fundamental difference between the POST and PUT methods is
1087   highlighted by the different intent for the target resource.
1088   The target resource in a POST request is intended to handle the
1089   enclosed representation as a data-accepting process, such as for
1090   a gateway to some other protocol or a document that accepts annotations.
1091   In contrast, the target resource in a PUT request is intended to
1092   take the enclosed representation as a new or replacement value.
1093   Hence, the intent of PUT is idempotent and visible to intermediaries,
1094   even though the exact effect is only known by the origin server.
1095</t>
1096<t>
1097   Proper interpretation of a PUT request presumes that the user agent
1098   knows what target resource is desired.  A service that is intended
1099   to select a proper URI on behalf of the client, after receiving
1100   a state-changing request, &SHOULD; be implemented using the POST
1101   method rather than PUT.  If the origin server will not make the
1102   requested PUT state change to the target resource and instead
1103   wishes to have it applied to a different resource, such as when the
1104   resource has been moved to a different URI, then the origin server
1105   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
1106   then make its own decision regarding whether or not to redirect the
1107   request.
1108</t>
1109<t>
1110   A PUT request applied to the target resource &MAY; have side-effects
1111   on other resources.  For example, an article might have a URI for
1112   identifying "the current version" (a resource) which is separate
1113   from the URIs identifying each particular version (different
1114   resources that at one point shared the same state as the current version
1115   resource).  A successful PUT request on "the current version" URI might
1116   therefore create a new version resource in addition to changing the
1117   state of the target resource, and might also cause links to be added
1118   between the related resources.
1119</t>
1120<t>
1121   An origin server &SHOULD; reject any PUT request that contains a
1122   Content-Range header field, since it might be misinterpreted as
1123   partial content (or might be partial content that is being mistakenly
1124   PUT as a full representation).  Partial content updates are
1125   possible by targeting a separately identified resource with state
1126   that overlaps a portion of the larger resource, or by using a
1127   different method that has been specifically defined for partial
1128   updates (for example, the PATCH method defined in
1129   <xref target="RFC5789"/>).
1130</t>
1131<t>
1132   Responses to the PUT method are not cacheable. If a PUT request passes
1133   through a cache that has one or more stored responses for the effective
1134   request URI, those stored responses will be invalidated (see
1135   &p6-invalid;).
1136</t>
1137</section>
1138
1139<section title="DELETE" anchor="DELETE">
1140  <iref primary="true" item="DELETE method" x:for-anchor=""/>
1141  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
1142<t>
1143   The DELETE method requests that the origin server delete the target
1144   resource. This method &MAY; be overridden by
1145   human intervention (or other means) on the origin server. The client cannot
1146   be guaranteed that the operation has been carried out, even if the
1147   status code returned from the origin server indicates that the action
1148   has been completed successfully. However, the server &SHOULD-NOT; 
1149   indicate success unless, at the time the response is given, it
1150   intends to delete the resource or move it to an inaccessible
1151   location.
1152</t>
1153<t>
1154   A successful response &SHOULD; be 200 (OK) if the response includes an
1155   representation describing the status, 202 (Accepted) if the action has not
1156   yet been enacted, or 204 (No Content) if the action has been enacted
1157   but the response does not include a representation.
1158</t>
1159<t>
1160   Bodies on DELETE requests have no defined semantics. Note that sending a body
1161   on a DELETE request might cause some existing implementations to reject the
1162   request.
1163</t>
1164<t>
1165   Responses to the DELETE method are not cacheable. If a DELETE request
1166   passes through a cache that has one or more stored responses for the
1167   effective request URI, those stored responses will be invalidated (see
1168   &p6-invalid;).
1169</t>
1170</section>
1171
1172<section title="TRACE" anchor="TRACE">
1173  <rdf:Description>
1174    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
1175  </rdf:Description>
1176  <iref primary="true" item="TRACE method" x:for-anchor=""/>
1177  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
1178<t>
1179   The TRACE method requests a remote, application-layer loop-back
1180   of the request message. The final recipient of the request
1181   &SHOULD; reflect the message received back to the client as the
1182   message body of a 200 (OK) response. The final recipient is either the
1183   origin server or the first proxy to receive a Max-Forwards
1184   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
1185   A TRACE request &MUST-NOT; include a message body.
1186</t>
1187<t>
1188   TRACE allows the client to see what is being received at the other
1189   end of the request chain and use that data for testing or diagnostic
1190   information. The value of the Via header field (&header-via;) is of
1191   particular interest, since it acts as a trace of the request chain.
1192   Use of the Max-Forwards header field allows the client to limit the
1193   length of the request chain, which is useful for testing a chain of
1194   proxies forwarding messages in an infinite loop.
1195</t>
1196<t>
1197   If the request is valid, the response &SHOULD; have a Content-Type of
1198   "message/http" (see &media-type-message-http;) and contain a message body
1199   that encloses a copy of the entire request message.
1200   Responses to the TRACE method are not cacheable.
1201</t>
1202</section>
1203
1204<section title="CONNECT" anchor="CONNECT">
1205  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
1206  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
1207<t>
1208   The CONNECT method requests that the proxy establish a tunnel
1209   to the request-target and, if successful, thereafter restrict its behavior
1210   to blind forwarding of packets until the connection is closed.
1211</t>
1212<t>
1213   When using CONNECT, the request-target &MUST; use the authority form
1214   (&request-target;); i.e., the request-target consists of only the
1215   host name and port number of the tunnel destination, separated by a colon.
1216   For example,
1217</t>
1218<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1219CONNECT server.example.com:80 HTTP/1.1
1220Host: server.example.com:80
1221
1222</artwork></figure>
1223<t>
1224   Any successful (2xx) response to a CONNECT request indicates that the
1225   proxy has established a connection to the requested host and port,
1226   and has switched to tunneling the current connection to that server
1227   connection.
1228   The tunneled data from the server begins immediately after the blank line
1229   that concludes the successful response's header block.
1230   A server &SHOULD-NOT; send any Transfer-Encoding or Content-Length
1231   header fields in a successful response.
1232   A client &MUST; ignore any Content-Length or Transfer-Encoding header
1233   fields received in a successful response.
1234</t>
1235<t>
1236   Any response other than a successful response indicates that the tunnel
1237   has not yet been formed and that the connection remains governed by HTTP.
1238</t>
1239<t>
1240   Proxy authentication might be used to establish the
1241   authority to create a tunnel:
1242</t>
1243<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1244CONNECT server.example.com:80 HTTP/1.1
1245Host: server.example.com:80
1246Proxy-Authorization: basic aGVsbG86d29ybGQ=
1247
1248</artwork></figure>
1249<t>
1250   A message body on a CONNECT request has no defined semantics. Sending a
1251   body on a CONNECT request might cause existing implementations to reject
1252   the request.
1253</t>
1254<t>
1255   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
1256   to server &MAY; be sent immediately after the request (before a response
1257   is received). The usual caveats also apply:
1258   data may be discarded if the eventual response is negative, and the
1259   connection may be reset with no response if more than one TCP segment
1260   is outstanding.
1261</t>
1262<t>
1263   It may be the case that the proxy itself can only reach the requested
1264   origin server through another proxy.  In this case, the first proxy
1265   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
1266   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
1267   unless it has either a direct or tunnel connection established to the
1268   authority.
1269</t>
1270<t>
1271   If at any point either one of the peers gets disconnected, any
1272   outstanding data that came from that peer will be passed to the other
1273   one, and after that also the other connection will be terminated by
1274   the proxy. If there is outstanding data to that peer undelivered,
1275   that data will be discarded.
1276</t>
1277<t>
1278   An origin server which receives a CONNECT request for itself &MAY;
1279   respond with a 2xx status code to indicate that a connection is
1280   established.  However, most origin servers do not implement CONNECT.
1281</t>
1282</section>
1283</section>
1284
1285
1286<section title="Status Code Definitions" anchor="status.codes">
1287<t>
1288   The first digit of the status-code defines the class of response. The
1289   last two digits do not have any categorization role. There are 5
1290   values for the first digit:
1291  <list style="symbols">
1292    <t>
1293      1xx: Informational - Request received, continuing process
1294    </t>
1295    <t>
1296      2xx: Success - The action was successfully received,
1297        understood, and accepted
1298    </t>
1299    <t>
1300      3xx: Redirection - Further action must be taken in order to
1301        complete the request
1302    </t>
1303    <t>
1304      4xx: Client Error - The request contains bad syntax or cannot
1305        be fulfilled
1306    </t>
1307    <t>
1308      5xx: Server Error - The server failed to fulfill an apparently
1309        valid request
1310    </t>
1311  </list>
1312</t>
1313<t>
1314   Each status-code is described below, including any metadata required
1315   in the response.
1316</t>
1317<t>
1318   For most status codes the response can carry a payload, in which case a
1319   Content-Type header field indicates the payload's media type
1320   (&header-content-type;).
1321</t>
1322
1323<section title="Informational 1xx" anchor="status.1xx">
1324<t>
1325   This class of status code indicates a provisional response,
1326   consisting only of the status-line and optional header fields, and is
1327   terminated by an empty line. There are no required header fields for this
1328   class of status code. Since HTTP/1.0 did not define any 1xx status
1329   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1330   except under experimental conditions.
1331</t>
1332<t>
1333   A client &MUST; be prepared to accept one or more 1xx status responses
1334   prior to a regular response, even if the client does not expect a 100
1335   (Continue) status message. Unexpected 1xx status responses &MAY; be
1336   ignored by a user agent.
1337</t>
1338<t>
1339   Proxies &MUST; forward 1xx responses, unless the connection between the
1340   proxy and its client has been closed, or unless the proxy itself
1341   requested the generation of the 1xx response. (For example, if a
1342   proxy adds a "Expect: 100-continue" field when it forwards a request,
1343   then it need not forward the corresponding 100 (Continue)
1344   response(s).)
1345</t>
1346
1347<section title="100 Continue" anchor="status.100">
1348  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1349  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1350<t>
1351   The client &SHOULD; continue with its request. This interim response is
1352   used to inform the client that the initial part of the request has
1353   been received and has not yet been rejected by the server. The client
1354   &SHOULD; continue by sending the remainder of the request or, if the
1355   request has already been completed, ignore this response. The server
1356   &MUST; send a final response after the request has been completed. See
1357   &use100; for detailed discussion of the use and handling of this
1358   status code.
1359</t>
1360</section>
1361
1362<section title="101 Switching Protocols" anchor="status.101">
1363  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1364  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1365<t>
1366   The server understands and is willing to comply with the client's
1367   request, via the Upgrade message header field (&header-upgrade;), for a
1368   change in the application protocol being used on this connection. The
1369   server will switch protocols to those defined by the response's
1370   Upgrade header field immediately after the empty line which
1371   terminates the 101 response.
1372</t>
1373<t>
1374   The protocol &SHOULD; be switched only when it is advantageous to do
1375   so. For example, switching to a newer version of HTTP is advantageous
1376   over older versions, and switching to a real-time, synchronous
1377   protocol might be advantageous when delivering resources that use
1378   such features.
1379</t>
1380</section>
1381</section>
1382
1383<section title="Successful 2xx" anchor="status.2xx">
1384<t>
1385   This class of status code indicates that the client's request was
1386   successfully received, understood, and accepted.
1387</t>
1388
1389<section title="200 OK" anchor="status.200">
1390  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1391  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1392<t>
1393   The request has succeeded. The payload returned with the response
1394   is dependent on the method used in the request, for example:
1395  <list style="hanging">
1396    <t hangText="GET">
1397      a representation of the target resource is sent in the response;
1398    </t>
1399    <t hangText="HEAD">
1400      the same representation as GET, except without the message body;
1401    </t>
1402    <t hangText="POST">
1403      a representation describing or containing the result of the action;
1404    </t>
1405    <t hangText="TRACE">
1406      a representation containing the request message as received by the
1407      end server.
1408    </t>
1409  </list>
1410</t>
1411<t>
1412   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1413   freshness for 200 responses.
1414</t>
1415</section>
1416
1417<section title="201 Created" anchor="status.201">
1418  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1419  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1420<t>
1421   The request has been fulfilled and has resulted in a new resource being
1422   created.
1423</t>
1424<t>
1425   The newly created resource is typically linked to from the response payload,
1426   with the most relevant URI also being carried in the Location header field.
1427   If the newly created resource's URI is the same as the Effective Request URI,
1428   this information can be omitted (e.g., in the case of a response to a PUT
1429   request). 
1430</t>
1431<t>
1432   The origin server &MUST; create the resource before returning the 201 status
1433   code. If the action cannot be carried out immediately, the server &SHOULD;
1434   respond with 202 (Accepted) response instead.
1435</t>
1436<t>
1437   A 201 response &MAY; contain an ETag response header field indicating
1438   the current value of the entity-tag for the representation of the resource
1439   just created (see &header-etag;).
1440</t>
1441</section>
1442
1443<section title="202 Accepted" anchor="status.202">
1444  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1445  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1446<t>
1447   The request has been accepted for processing, but the processing has
1448   not been completed.  The request might or might not eventually be
1449   acted upon, as it might be disallowed when processing actually takes
1450   place. There is no facility for re-sending a status code from an
1451   asynchronous operation such as this.
1452</t>
1453<t>
1454   The 202 response is intentionally non-committal. Its purpose is to
1455   allow a server to accept a request for some other process (perhaps a
1456   batch-oriented process that is only run once per day) without
1457   requiring that the user agent's connection to the server persist
1458   until the process is completed. The representation returned with this
1459   response &SHOULD; include an indication of the request's current status
1460   and either a pointer to a status monitor or some estimate of when the
1461   user can expect the request to be fulfilled.
1462</t>
1463</section>
1464
1465<section title="203 Non-Authoritative Information" anchor="status.203">
1466  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1467  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1468<t>
1469   The representation in the response has been transformed or otherwise
1470   modified by a transforming proxy (&intermediaries;).  Note that the
1471   behavior of transforming intermediaries is controlled by the no-transform
1472   Cache-Control directive (&header-cache-control;).
1473</t>
1474<t>
1475   This status code is only appropriate when the response status code would
1476   have been 200 (OK) otherwise. When the status code before transformation
1477   would have been different, the 214 Transformation Applied warn-code
1478   (&header-warning;) is appropriate.
1479</t>
1480<t>
1481   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1482   freshness for 203 responses.
1483</t>
1484</section>
1485
1486<section title="204 No Content" anchor="status.204">
1487  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1488  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1489<t>
1490   The 204 (No Content) status code indicates that the server has
1491   successfully fulfilled the request and that there is no additional
1492   content to return in the response payload body.  Metadata in the
1493   response header fields refer to the target resource and its current
1494   representation after the requested action.
1495</t>
1496<t>
1497   For example, if a 204 status code is received in response to a PUT
1498   request and the response contains an ETag header field, then the PUT
1499   was successful and the ETag field-value contains the entity-tag for
1500   the new representation of that target resource.
1501</t>
1502<t>
1503   The 204 response allows a server to indicate that the action has been
1504   successfully applied to the target resource while implying that the
1505   user agent &SHOULD-NOT; traverse away from its current "document view"
1506   (if any).  The server assumes that the user agent will provide some
1507   indication of the success to its user, in accord with its own interface,
1508   and apply any new or updated metadata in the response to the active
1509   representation.
1510</t>
1511<t>
1512   For example, a 204 status code is commonly used with document editing
1513   interfaces corresponding to a "save" action, such that the document
1514   being saved remains available to the user for editing. It is also
1515   frequently used with interfaces that expect automated data transfers
1516   to be prevalent, such as within distributed version control systems.
1517</t>
1518<t>
1519   The 204 response &MUST-NOT; include a message body, and thus is always
1520   terminated by the first empty line after the header fields.
1521</t>
1522</section>
1523
1524<section title="205 Reset Content" anchor="status.205">
1525  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1526  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1527<t>
1528   The server has fulfilled the request and the user agent &SHOULD; reset
1529   the document view which caused the request to be sent. This response
1530   is primarily intended to allow input for actions to take place via
1531   user input, followed by a clearing of the form in which the input is
1532   given so that the user can easily initiate another input action.
1533</t>
1534<t>   
1535   The message body included with the response &MUST; be empty. Note that
1536   receivers still need to parse the response according to the algorithm defined
1537   in &message-body;.
1538</t>
1539</section>
1540</section>
1541
1542<section title="Redirection 3xx" anchor="status.3xx">
1543<t>
1544   This class of status code indicates that further action needs to be
1545   taken by the user agent in order to fulfill the request.  If the required
1546   action involves a subsequent HTTP request, it &MAY; be carried out by the
1547   user agent without interaction with the user if and only if the method used
1548   in the second request is known to be "safe", as defined in
1549   <xref target="safe.methods"/>.
1550</t>
1551<t>
1552   There are several types of redirects:
1553   <list style="numbers">
1554      <x:lt>
1555        <t>
1556          Redirects of the request to another URI, either temporarily or
1557          permanently. The new URI is specified in the Location header field.
1558          In this specification, the status codes 301 (Moved Permanently),
1559          302 (Found), and 307 (Temporary Redirect) fall under this category.
1560        </t>
1561      </x:lt>
1562      <x:lt>
1563        <t>
1564          Redirection to a new location that represents an indirect response to
1565          the request, such as the result of a POST operation to be retrieved
1566          with a subsequent GET request. This is status code 303 (See Other).
1567        </t>
1568      </x:lt>
1569      <x:lt>
1570        <t>
1571          Redirection offering a choice of matching resources for use by
1572          agent-driven content negotiation (&agent-driven-negotiation;). This
1573          is status code 300 (Multiple Choices).
1574        </t>
1575      </x:lt>
1576      <x:lt>
1577        <t>
1578          Other kinds of redirection, such as to a cached result (status code 304
1579          (Not Modified), see &status-304;).
1580        </t>
1581      </x:lt>
1582   </list>
1583</t>
1584<x:note>
1585  <t>
1586    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1587    and 302 (Found) were defined for the first type of redirect, and the second
1588    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1589    However it turned out that web forms using POST expected redirects to change
1590    the operation for the subsequent request to retrieval (GET). To address this
1591    use case, HTTP/1.1 introduced the second type of redirect with the status
1592    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1593    As user agents did not change their behavior to maintain backwards
1594    compatibility, the first revision of HTTP/1.1 added yet another status code,
1595    307 (Temporary Redirect), for which the backwards compatibility problems did
1596    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1597    Over 10 years later, most user agents still do method rewriting for
1598    status codes 301 and 302, therefore this specification makes that behavior
1599    conformant in case the original request was POST.
1600  </t>
1601</x:note>
1602<t>
1603   A Location header field on a 3xx response indicates that a client &MAY;
1604   automatically redirect to the URI provided; see <xref target="header.location"/>.
1605</t>
1606<t>
1607   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1608   automatic redirection needs to done with care, since the redirect might
1609   change the conditions under which the request was issued.
1610</t>
1611<t>
1612   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1613   "infinite" redirection loops).
1614</t>
1615<x:note>
1616  <t>
1617    <x:h>Note:</x:h> An earlier version of this specification recommended a
1618    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1619    Content developers need to be aware that some clients might
1620    implement such a fixed limitation.
1621  </t>
1622</x:note>
1623
1624<section title="300 Multiple Choices" anchor="status.300">
1625  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1626  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1627<t>
1628   The target resource has more than one
1629   representation, each with its own specific location, and agent-driven
1630   negotiation information (&content-negotiation;) is being provided so that
1631   the user (or user agent) can select a preferred representation by
1632   redirecting its request to that location.
1633</t>
1634<t>
1635   Unless it was a HEAD request, the response &SHOULD; include a representation
1636   containing a list of representation metadata and location(s) from
1637   which the user or user agent can choose the one most appropriate. Depending
1638   upon the format and the capabilities of
1639   the user agent, selection of the most appropriate choice &MAY; be
1640   performed automatically. However, this specification does not define
1641   any standard for such automatic selection.
1642</t>
1643<t>
1644   If the server has a preferred choice of representation, it &SHOULD;
1645   include the specific URI for that representation in the Location
1646   field; user agents &MAY; use the Location field value for automatic
1647   redirection.
1648</t>
1649<t>
1650   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1651   freshness for 300 responses.
1652</t>
1653
1654</section>
1655
1656<section title="301 Moved Permanently" anchor="status.301">
1657  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1658  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1659<t>
1660   The target resource has been assigned a new permanent URI and any
1661   future references to this resource &SHOULD; use one of the returned
1662   URIs.  Clients with link editing capabilities ought to automatically
1663   re-link references to the effective request URI to one or more of the new
1664   references returned by the server, where possible.
1665</t>
1666<t>
1667   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1668   freshness for 301 responses.
1669</t>
1670<t>
1671   The new permanent URI &SHOULD; be given by the Location field in the
1672   response. A response payload can contain a short hypertext note with a
1673   hyperlink to the new URI(s).
1674</t>
1675<x:note>
1676  <t>
1677    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1678    request method from POST to GET for the subsequent request. If this
1679    behavior is undesired, status code 307 (Temporary Redirect) can be used
1680    instead.
1681  </t>
1682</x:note>
1683</section>
1684
1685<section title="302 Found" anchor="status.302">
1686  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1687  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1688<t>
1689   The target resource resides temporarily under a different URI.
1690   Since the redirection might be altered on occasion, the client &SHOULD;
1691   continue to use the effective request URI for future requests.
1692</t>
1693<t>
1694   The temporary URI &SHOULD; be given by the Location field in the
1695   response. A response payload can contain a short hypertext note with a
1696   hyperlink to the new URI(s).
1697</t>
1698<x:note>
1699  <t>
1700    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1701    request method from POST to GET for the subsequent request. If this
1702    behavior is undesired, status code 307 (Temporary Redirect) can be used
1703    instead.
1704  </t>
1705</x:note>
1706</section>
1707
1708<section title="303 See Other" anchor="status.303">
1709  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1710  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1711<t>
1712   The 303 status code indicates that the server is redirecting the
1713   user agent to a different resource, as indicated by a URI in the
1714   Location header field, that is intended to provide an indirect
1715   response to the original request.  In order to satisfy the original
1716   request, a user agent &SHOULD; perform a retrieval request using the
1717   Location URI (a GET or HEAD request if using HTTP), which
1718   may itself be redirected further, and present the eventual result as an
1719   answer to the original request.
1720   Note that the new URI in the Location header field is not considered
1721   equivalent to the effective request URI.
1722</t>
1723<t>
1724   This status code is generally applicable to any HTTP method.  It is
1725   primarily used to allow the output of a POST action to redirect
1726   the user agent to a selected resource, since doing so provides the
1727   information corresponding to the POST response in a form that
1728   can be separately identified, bookmarked, and cached independent
1729   of the original request.
1730</t>
1731<t>
1732   A 303 response to a GET request indicates that the requested
1733   resource does not have a representation of its own that can be
1734   transferred by the server over HTTP.  The Location URI indicates a
1735   resource that is descriptive of the target resource, such that the
1736   follow-on representation might be useful to recipients without
1737   implying that it adequately represents the target resource.
1738   Note that answers to the questions of what can be represented, what
1739   representations are adequate, and what might be a useful description
1740   are outside the scope of HTTP and thus entirely determined by the
1741   URI owner(s).
1742</t>
1743<t>
1744   Except for responses to a HEAD request, the representation of a 303
1745   response &SHOULD; contain a short hypertext note with a hyperlink
1746   to the Location URI.
1747</t>
1748</section>
1749
1750<section title="305 Use Proxy" anchor="status.305">
1751  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1752  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1753<t>
1754   The 305 status code was defined in a previous version of this specification
1755   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1756</t>
1757</section>
1758
1759<section title="306 (Unused)" anchor="status.306">
1760  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1761  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1762<t>
1763   The 306 status code was used in a previous version of the
1764   specification, is no longer used, and the code is reserved.
1765</t>
1766</section>
1767
1768<section title="307 Temporary Redirect" anchor="status.307">
1769  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1770  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1771<t>
1772   The target resource resides temporarily under a different URI.
1773   Since the redirection can change over time, the client &SHOULD;
1774   continue to use the effective request URI for future requests.
1775</t>
1776<t>
1777   The temporary URI &SHOULD; be given by the Location field in the
1778   response. A response payload can contain a short hypertext note with a
1779   hyperlink to the new URI(s).
1780</t>
1781<x:note>
1782  <t>
1783    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1784    it does not allow rewriting the request method from POST to GET. This
1785    specification defines no equivalent counterpart for 301 Moved Permanently.
1786  </t>
1787</x:note>
1788</section>
1789</section>
1790
1791<section title="Client Error 4xx" anchor="status.4xx">
1792<t>
1793   The 4xx class of status code is intended for cases in which the
1794   client seems to have erred. Except when responding to a HEAD request,
1795   the server &SHOULD; include a representation containing an explanation of the
1796   error situation, and whether it is a temporary or permanent
1797   condition. These status codes are applicable to any request method.
1798   User agents &SHOULD; display any included representation to the user.
1799</t>
1800
1801<section title="400 Bad Request" anchor="status.400">
1802  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1803  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1804<t>
1805   The server cannot or will not process the request, due to a client error (e.g.,
1806   malformed syntax).
1807</t>
1808</section>
1809
1810<section title="402 Payment Required" anchor="status.402">
1811  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1812  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1813<t>
1814   This code is reserved for future use.
1815</t>
1816</section>
1817
1818<section title="403 Forbidden" anchor="status.403">
1819  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1820  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1821<t>
1822   The server understood the request, but refuses to authorize it. Providing
1823   different user authentication credentials might be successful, but any
1824   credentials that were provided in the request are insufficient. The request
1825   &SHOULD-NOT; be repeated with the same credentials.
1826</t>
1827<t>
1828   If the request method was not HEAD and the server wishes to make
1829   public why the request has not been fulfilled, it &SHOULD; describe the
1830   reason for the refusal in the representation.  If the server does not wish to
1831   make this information available to the client, the status code 404
1832   (Not Found) &MAY; be used instead.
1833</t>
1834</section>
1835
1836<section title="404 Not Found" anchor="status.404">
1837  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1838  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1839<t>
1840   The server has not found anything matching the effective request URI. No
1841   indication is given of whether the condition is temporary or
1842   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1843   knows, through some internally configurable mechanism, that an old
1844   resource is permanently unavailable and has no forwarding address.
1845   This status code is commonly used when the server does not wish to
1846   reveal exactly why the request has been refused, or when no other
1847   response is applicable.
1848</t>
1849</section>
1850
1851<section title="405 Method Not Allowed" anchor="status.405">
1852  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1853  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1854<t>
1855   The method specified in the request-line is not allowed for the target
1856   resource. The response &MUST; include an Allow header field containing a
1857   list of valid methods for the requested resource.
1858</t>
1859</section>
1860
1861<section title="406 Not Acceptable" anchor="status.406">
1862  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1863  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1864<t>
1865   The resource identified by the request is only capable of generating
1866   response representations which have content characteristics not acceptable
1867   according to the Accept and Accept-* header fields sent in the request
1868   (see &p3-header-fields;).
1869</t>
1870<t>
1871   Unless it was a HEAD request, the response &SHOULD; include a representation
1872   containing a list of available representation characteristics and location(s)
1873   from which the user or user agent can choose the one most
1874   appropriate. Depending upon the format and the
1875   capabilities of the user agent, selection of the most appropriate
1876   choice &MAY; be performed automatically. However, this specification
1877   does not define any standard for such automatic selection.
1878</t>
1879<x:note>
1880  <t>
1881    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1882    not acceptable according to the accept header fields sent in the
1883    request. In some cases, this might even be preferable to sending a
1884    406 response. User agents are encouraged to inspect the header fields of
1885    an incoming response to determine if it is acceptable.
1886  </t>
1887</x:note>
1888<t>
1889   If the response could be unacceptable, a user agent &SHOULD;
1890   temporarily stop receipt of more data and query the user for a
1891   decision on further actions.
1892</t>
1893</section>
1894
1895<section title="408 Request Timeout" anchor="status.408">
1896  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1897  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1898<t>
1899   The client did not produce a request within the time that the server
1900   was prepared to wait. The client &MAY; repeat the request without
1901   modifications at any later time.
1902</t>
1903</section>
1904
1905<section title="409 Conflict" anchor="status.409">
1906  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1907  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1908<t>
1909   The request could not be completed due to a conflict with the current
1910   state of the resource. This code is only allowed in situations where
1911   it is expected that the user might be able to resolve the conflict
1912   and resubmit the request. The response body &SHOULD; include enough
1913   information for the user to recognize the source of the conflict.
1914   Ideally, the response representation would include enough information for the
1915   user or user agent to fix the problem; however, that might not be
1916   possible and is not required.
1917</t>
1918<t>
1919   Conflicts are most likely to occur in response to a PUT request. For
1920   example, if versioning were being used and the representation being PUT
1921   included changes to a resource which conflict with those made by an
1922   earlier (third-party) request, the server might use the 409 response
1923   to indicate that it can't complete the request. In this case, the
1924   response representation would likely contain a list of the differences
1925   between the two versions.
1926</t>
1927</section>
1928
1929<section title="410 Gone" anchor="status.410">
1930  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1931  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1932<t>
1933   The target resource is no longer available at the server and no
1934   forwarding address is known. This condition is expected to be
1935   considered permanent. Clients with link editing capabilities &SHOULD;
1936   delete references to the effective request URI after user approval. If the
1937   server does not know, or has no facility to determine, whether or not
1938   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1939   used instead.
1940</t>
1941<t>
1942   The 410 response is primarily intended to assist the task of web
1943   maintenance by notifying the recipient that the resource is
1944   intentionally unavailable and that the server owners desire that
1945   remote links to that resource be removed. Such an event is common for
1946   limited-time, promotional services and for resources belonging to
1947   individuals no longer working at the server's site. It is not
1948   necessary to mark all permanently unavailable resources as "gone" or
1949   to keep the mark for any length of time &mdash; that is left to the
1950   discretion of the server owner.
1951</t>
1952<t>
1953   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
1954   for 410 responses.
1955</t>
1956</section>
1957
1958<section title="411 Length Required" anchor="status.411">
1959  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1960  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1961<t>
1962   The server refuses to accept the request without a defined Content-Length.
1963   The client &MAY; repeat the request if it adds a valid
1964   Content-Length header field containing the length of the message body
1965   in the request message.
1966</t>
1967</section>
1968
1969<section title="413 Request Representation Too Large" anchor="status.413">
1970  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
1971  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
1972<t>
1973   The server is refusing to process a request because the request
1974   representation is larger than the server is willing or able to process. The
1975   server &MAY; close the connection to prevent the client from continuing
1976   the request.
1977</t>
1978<t>
1979   If the condition is temporary, the server &SHOULD; include a Retry-After
1980   header field to indicate that it is temporary and after what
1981   time the client &MAY; try again.
1982</t>
1983</section>
1984
1985<section title="414 URI Too Long" anchor="status.414">
1986  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1987  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1988<t>
1989   The server is refusing to service the request because the effective request URI
1990   is longer than the server is willing to interpret. This rare
1991   condition is only likely to occur when a client has improperly
1992   converted a POST request to a GET request with long query
1993   information, when the client has descended into a URI "black hole" of
1994   redirection (e.g., a redirected URI prefix that points to a suffix of
1995   itself), or when the server is under attack by a client attempting to
1996   exploit security holes present in some servers using fixed-length
1997   buffers for reading or manipulating the effective request URI.
1998</t>
1999</section>
2000
2001<section title="415 Unsupported Media Type" anchor="status.415">
2002  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
2003  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
2004<t>
2005   The server is refusing to service the request because the request
2006   payload is in a format not supported by this request method on the
2007   target resource.
2008</t>
2009</section>
2010
2011<section title="417 Expectation Failed" anchor="status.417">
2012  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
2013  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
2014<t>
2015   The expectation given in an Expect header field (see <xref target="header.expect"/>)
2016   could not be met by this server, or, if the server is a proxy,
2017   the server has unambiguous evidence that the request could not be met
2018   by the next-hop server.
2019</t>
2020</section>
2021
2022<section title="426 Upgrade Required" anchor="status.426">
2023  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
2024  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
2025<t>
2026   The request can not be completed without a prior protocol upgrade. This
2027   response &MUST; include an Upgrade header field (&header-upgrade;)
2028   specifying the required protocols.
2029</t>
2030<figure>
2031<preamble>Example:</preamble>
2032<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
2033HTTP/1.1 426 Upgrade Required
2034Upgrade: HTTP/3.0
2035Connection: Upgrade
2036Content-Length: <x:length-of target="s426body"/>
2037Content-Type: text/plain
2038
2039<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
2040</x:span></artwork></figure>
2041<t>
2042   The server &SHOULD; include a message body in the 426 response which
2043   indicates in human readable form the reason for the error and describes any
2044   alternative courses which may be available to the user.
2045</t>
2046</section>
2047</section>
2048
2049<section title="Server Error 5xx" anchor="status.5xx">
2050<t>
2051   Response status codes beginning with the digit "5" indicate cases in
2052   which the server is aware that it has erred or is incapable of
2053   performing the request. Except when responding to a HEAD request, the
2054   server &SHOULD; include a representation containing an explanation of the
2055   error situation, and whether it is a temporary or permanent
2056   condition. User agents &SHOULD; display any included representation to the
2057   user. These response codes are applicable to any request method.
2058</t>
2059
2060<section title="500 Internal Server Error" anchor="status.500">
2061  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2062  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2063<t>
2064   The server encountered an unexpected condition which prevented it
2065   from fulfilling the request.
2066</t>
2067</section>
2068
2069<section title="501 Not Implemented" anchor="status.501">
2070  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2071  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2072<t>
2073   The server does not support the functionality required to fulfill the
2074   request. This is the appropriate response when the server does not
2075   recognize the request method and is not capable of supporting it for
2076   any resource.
2077</t>
2078</section>
2079
2080<section title="502 Bad Gateway" anchor="status.502">
2081  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2082  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2083<t>
2084   The server, while acting as a gateway or proxy, received an invalid
2085   response from the upstream server it accessed in attempting to
2086   fulfill the request.
2087</t>
2088</section>
2089
2090<section title="503 Service Unavailable" anchor="status.503">
2091  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2092  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2093<t>
2094   The server is currently unable to handle the request due to a
2095   temporary overloading or maintenance of the server.
2096</t>
2097<t>
2098   The implication is that this is a temporary condition which will be
2099   alleviated after some delay. If known, the length of the delay &MAY; be
2100   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2101   If no Retry-After is given, the client &SHOULD; handle the response as it
2102   would for a 500 response.
2103</t>
2104<x:note>
2105  <t>
2106    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2107    server must use it when becoming overloaded. Some servers might wish
2108    to simply refuse the connection.
2109  </t>
2110</x:note>
2111</section>
2112
2113<section title="504 Gateway Timeout" anchor="status.504">
2114  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2115  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2116<t>
2117   The server, while acting as a gateway or proxy, did not receive a
2118   timely response from the upstream server specified by the URI (e.g.,
2119   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2120   to access in attempting to complete the request.
2121</t>
2122<x:note>
2123  <t>
2124    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2125    return 400 or 500 when DNS lookups time out.
2126  </t>
2127</x:note>
2128</section>
2129
2130<section title="505 HTTP Version Not Supported" anchor="status.505">
2131  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2132  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2133<t>
2134   The server does not support, or refuses to support, the protocol
2135   version that was used in the request message. The server is
2136   indicating that it is unable or unwilling to complete the request
2137   using the same major version as the client, as described in &http-version;,
2138   other than with this error message. The response &SHOULD; contain
2139   a representation describing why that version is not supported and what other
2140   protocols are supported by that server.
2141</t>
2142
2143</section>
2144</section>
2145</section>
2146
2147
2148<section title="Date/Time Formats" anchor="http.date">
2149  <x:anchor-alias value="HTTP-date"/>
2150<t>
2151   HTTP applications have historically allowed three different formats
2152   for date/time stamps. However, the preferred format is a fixed-length subset
2153   of that defined by <xref target="RFC1123"/>:
2154</t>
2155<figure><artwork type="example" x:indent-with="  ">
2156Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2157</artwork></figure>
2158<t>
2159   The other formats are described here only for compatibility with obsolete
2160   implementations.
2161</t>
2162<figure><artwork type="example" x:indent-with="  ">
2163Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2164Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2165</artwork></figure>
2166<t>
2167   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2168   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2169   only generate the RFC 1123 format for representing HTTP-date values
2170   in header fields.
2171</t>
2172<t>
2173   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2174   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2175   equal to UTC (Coordinated Universal Time). This is indicated in the
2176   first two formats by the inclusion of "GMT" as the three-letter
2177   abbreviation for time zone, and &MUST; be assumed when reading the
2178   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2179   additional whitespace beyond that specifically included as SP in the
2180   grammar.
2181</t>
2182<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2183  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2184</artwork></figure>
2185<t anchor="preferred.date.format">
2186  <x:anchor-alias value="rfc1123-date"/>
2187  <x:anchor-alias value="time-of-day"/>
2188  <x:anchor-alias value="hour"/>
2189  <x:anchor-alias value="minute"/>
2190  <x:anchor-alias value="second"/>
2191  <x:anchor-alias value="day-name"/>
2192  <x:anchor-alias value="day"/>
2193  <x:anchor-alias value="month"/>
2194  <x:anchor-alias value="year"/>
2195  <x:anchor-alias value="GMT"/>
2196  Preferred format:
2197</t>
2198<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"/>
2199  <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>
2200  ; fixed length subset of the format defined in
2201  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2202 
2203  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2204               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2205               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2206               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2207               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2208               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2209               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2210               
2211  <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>
2212               ; e.g., 02 Jun 1982
2213
2214  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2215  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2216               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2217               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2218               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2219               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2220               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2221               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2222               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2223               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2224               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2225               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2226               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2227  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2228
2229  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2230
2231  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2232                 ; 00:00:00 - 23:59:59
2233                 
2234  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2235  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2236  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2237</artwork></figure>
2238<t>
2239  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2240  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2241  same as those defined for the RFC 5322 constructs
2242  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2243</t>
2244<t anchor="obsolete.date.formats">
2245  <x:anchor-alias value="obs-date"/>
2246  <x:anchor-alias value="rfc850-date"/>
2247  <x:anchor-alias value="asctime-date"/>
2248  <x:anchor-alias value="date1"/>
2249  <x:anchor-alias value="date2"/>
2250  <x:anchor-alias value="date3"/>
2251  <x:anchor-alias value="rfc1123-date"/>
2252  <x:anchor-alias value="day-name-l"/>
2253  Obsolete formats:
2254</t>
2255<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2256  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2257</artwork></figure>
2258<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2259  <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>
2260  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2261                 ; day-month-year (e.g., 02-Jun-82)
2262
2263  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2264         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2265         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2266         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2267         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2268         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2269         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2270</artwork></figure>
2271<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2272  <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>
2273  <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> ))
2274                 ; month day (e.g., Jun  2)
2275</artwork></figure>
2276<x:note>
2277  <t>
2278    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2279    accepting date values that might have been sent by non-HTTP
2280    applications, as is sometimes the case when retrieving or posting
2281    messages via proxies/gateways to SMTP or NNTP.
2282  </t>
2283</x:note>
2284<x:note>
2285  <t>
2286    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2287    to their usage within the protocol stream. Clients and servers are
2288    not required to use these formats for user presentation, request
2289    logging, etc.
2290  </t>
2291</x:note>
2292</section>
2293
2294<section title="Product Tokens" anchor="product.tokens">
2295  <x:anchor-alias value="product"/>
2296  <x:anchor-alias value="product-version"/>
2297<t>
2298   Product tokens are used to allow communicating applications to
2299   identify themselves by software name and version. Most fields using
2300   product tokens also allow sub-products which form a significant part
2301   of the application to be listed, separated by whitespace. By
2302   convention, the products are listed in order of their significance
2303   for identifying the application.
2304</t>
2305<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2306  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2307  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2308</artwork></figure>
2309<t>
2310   Examples:
2311</t>
2312<figure><artwork type="example">
2313  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2314  Server: Apache/0.8.4
2315</artwork></figure>
2316<t>
2317   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2318   used for advertising or other non-essential information. Although any
2319   token octet &MAY; appear in a product-version, this token &SHOULD;
2320   only be used for a version identifier (i.e., successive versions of
2321   the same product &SHOULD; only differ in the product-version portion of
2322   the product value).
2323</t>
2324</section>
2325
2326
2327<section title="Header Field Definitions" anchor="header.field.definitions">
2328<t>
2329   This section defines the syntax and semantics of HTTP/1.1 header fields
2330   related to request and response semantics.
2331</t>
2332
2333<section title="Allow" anchor="header.allow">
2334  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2335  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2336  <x:anchor-alias value="Allow"/>
2337<t>
2338   The "Allow" header field lists the set of methods advertised as
2339   supported by the target resource. The purpose of this field is strictly to
2340   inform the recipient of valid request methods associated with the resource.
2341</t>
2342<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2343  <x:ref>Allow</x:ref> = #<x:ref>method</x:ref>
2344</artwork></figure>
2345<t>
2346   Example of use:
2347</t>
2348<figure><artwork type="example">
2349  Allow: GET, HEAD, PUT
2350</artwork></figure>
2351<t>
2352   The actual set of allowed methods is defined by the origin server at the
2353   time of each request.
2354</t>
2355<t>
2356   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2357   understand all the methods specified in order to handle them according to
2358   the generic message handling rules.
2359</t>
2360</section>
2361
2362<section title="Date" anchor="header.date">
2363  <iref primary="true" item="Date header field" x:for-anchor=""/>
2364  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2365  <x:anchor-alias value="Date"/>
2366<t>
2367   The "Date" header field represents the date and time at which
2368   the message was originated, having the same semantics as the Origination
2369   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2370   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2371   it &MUST; be sent in rfc1123-date format.
2372</t>
2373<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2374  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2375</artwork></figure>
2376<t>
2377   An example is
2378</t>
2379<figure><artwork type="example">
2380  Date: Tue, 15 Nov 1994 08:12:31 GMT
2381</artwork></figure>
2382<t>
2383   Origin servers &MUST; include a Date header field in all responses,
2384   except in these cases:
2385  <list style="numbers">
2386      <t>If the response status code is 100 (Continue) or 101 (Switching
2387         Protocols), the response &MAY; include a Date header field, at
2388         the server's option.</t>
2389
2390      <t>If the response status code conveys a server error, e.g., 500
2391         (Internal Server Error) or 503 (Service Unavailable), and it is
2392         inconvenient or impossible to generate a valid Date.</t>
2393
2394      <t>If the server does not have a clock that can provide a
2395         reasonable approximation of the current time, its responses
2396         &MUST-NOT; include a Date header field.</t>
2397  </list>
2398</t>
2399<t>
2400   A received message that does not have a Date header field &MUST; be
2401   assigned one by the recipient if the message will be cached by that
2402   recipient.
2403</t>
2404<t>
2405   Clients can use the Date header field as well; in order to keep request
2406   messages small, they are advised not to include it when it doesn't convey
2407   any useful information (as is usually the case for requests that do not
2408   contain a payload).
2409</t>
2410<t>
2411   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2412   time subsequent to the generation of the message. It &SHOULD; represent
2413   the best available approximation of the date and time of message
2414   generation, unless the implementation has no means of generating a
2415   reasonably accurate date and time. In theory, the date ought to
2416   represent the moment just before the payload is generated. In
2417   practice, the date can be generated at any time during the message
2418   origination without affecting its semantic value.
2419</t>
2420</section>
2421
2422<section title="Expect" anchor="header.expect">
2423  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2424  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2425  <x:anchor-alias value="Expect"/>
2426  <x:anchor-alias value="expectation"/>
2427  <x:anchor-alias value="expect-param"/>
2428  <x:anchor-alias value="expect-name"/>
2429  <x:anchor-alias value="expect-value"/>
2430<t>
2431   The "Expect" header field is used to indicate that particular
2432   server behaviors are required by the client.
2433</t>
2434<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"/>
2435  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2436 
2437  <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> ]
2438                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2439  <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> ]
2440 
2441  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2442  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2443</artwork></figure>
2444<t>
2445   If all received Expect header field(s) are syntactically valid but contain
2446   an expectation that the recipient does not understand or cannot comply with,
2447   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2448   recipient of a syntactically invalid Expectation header field &MUST; respond
2449   with a 4xx status code other than 417.
2450</t>
2451<t>
2452   The only expectation defined by this specification is:
2453</t>
2454<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2455  100-continue
2456   <list>
2457      <t>
2458        The "100-continue" expectation is defined &use100;. It does not support
2459        any expect-params.
2460      </t>
2461   </list>
2462</t>
2463<t>
2464   Comparison is case-insensitive for names (expect-name), and case-sensitive
2465   for values (expect-value).
2466</t>
2467<t>
2468   The Expect mechanism is hop-by-hop: the above requirements apply to any
2469   server, including proxies. However, the Expect header field itself is
2470   end-to-end; it &MUST; be forwarded if the request is forwarded.
2471</t>
2472<t>
2473   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2474   header field.
2475</t>
2476</section>
2477
2478<section title="From" anchor="header.from">
2479  <iref primary="true" item="From header field" x:for-anchor=""/>
2480  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2481  <x:anchor-alias value="From"/>
2482  <x:anchor-alias value="mailbox"/>
2483<t>
2484   The "From" header field, if given, &SHOULD; contain an Internet
2485   e-mail address for the human user who controls the requesting user
2486   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2487   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2488</t>
2489<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2490  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2491 
2492  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2493</artwork></figure>
2494<t>
2495   An example is:
2496</t>
2497<figure><artwork type="example">
2498  From: webmaster@example.org
2499</artwork></figure>
2500<t>
2501   This header field &MAY; be used for logging purposes and as a means for
2502   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2503   be used as an insecure form of access protection. The interpretation
2504   of this field is that the request is being performed on behalf of the
2505   person given, who accepts responsibility for the method performed. In
2506   particular, robot agents &SHOULD; include this header field so that the
2507   person responsible for running the robot can be contacted if problems
2508   occur on the receiving end.
2509</t>
2510<t>
2511   The Internet e-mail address in this field &MAY; be separate from the
2512   Internet host which issued the request. For example, when a request
2513   is passed through a proxy the original issuer's address &SHOULD; be
2514   used.
2515</t>
2516<t>
2517   The client &SHOULD-NOT;  send the From header field without the user's
2518   approval, as it might conflict with the user's privacy interests or
2519   their site's security policy. It is strongly recommended that the
2520   user be able to disable, enable, and modify the value of this field
2521   at any time prior to a request.
2522</t>
2523</section>
2524
2525<section title="Location" anchor="header.location">
2526  <iref primary="true" item="Location header field" x:for-anchor=""/>
2527  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2528  <x:anchor-alias value="Location"/>
2529<t>
2530   The "Location" header field &MAY; be sent in responses to refer to
2531   a specific resource in accordance with the semantics of the status
2532   code.
2533</t>
2534<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2535  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2536</artwork></figure>
2537<t>
2538   For 201 (Created) responses, the Location is the URI of the new resource
2539   which was created by the request. For 3xx responses, the location &SHOULD;
2540   indicate the server's preferred URI for automatic redirection to the
2541   resource.
2542</t>
2543<t>
2544   The field value consists of a single URI-reference. When it has the form
2545   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2546   the final value is computed by resolving it against the effective request
2547   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2548   navigated to by the user agent, did contain a fragment identifier, and the
2549   final value does not, then the original URI's fragment identifier is added
2550   to the final value.
2551</t>
2552<figure>
2553<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-->
2554<artwork type="example">
2555  Location: /pub/WWW/People.html#tim
2556</artwork>
2557<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2558</figure>
2559<figure>
2560<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-->
2561<artwork type="example">
2562  Location: http://www.example.net/index.html
2563</artwork>
2564<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2565</figure>
2566<x:note>
2567  <t>
2568    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2569    that are not valid URI references. This specification does not mandate or
2570    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2571  </t>
2572</x:note>
2573<t>
2574   There are circumstances in which a fragment identifier in a Location URI
2575   would not be appropriate. For instance, when it appears in a 201 Created
2576   response, where the Location header field specifies the URI for the entire
2577   created resource.
2578</t>
2579<x:note>
2580  <t>
2581    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2582    from Location in that the Content-Location identifies the most specific
2583    resource corresponding to the enclosed representation.
2584    It is therefore possible for a response to contain header fields for
2585    both Location and Content-Location.
2586  </t>
2587</x:note>
2588</section>
2589
2590<section title="Max-Forwards" anchor="header.max-forwards">
2591  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2592  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2593  <x:anchor-alias value="Max-Forwards"/>
2594<t>
2595   The "Max-Forwards" header field provides a mechanism with the
2596   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2597   methods to limit the number of times that the request is forwarded by
2598   proxies. This can be useful when the client is attempting to
2599   trace a request which appears to be failing or looping mid-chain.
2600</t>
2601<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2602  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2603</artwork></figure>
2604<t>
2605   The Max-Forwards value is a decimal integer indicating the remaining
2606   number of times this request message can be forwarded.
2607</t>
2608<t>
2609   Each recipient of a TRACE or OPTIONS request
2610   containing a Max-Forwards header field &MUST; check and update its
2611   value prior to forwarding the request. If the received value is zero
2612   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2613   respond as the final recipient. If the received Max-Forwards value is
2614   greater than zero, then the forwarded message &MUST; contain an updated
2615   Max-Forwards field with a value decremented by one (1).
2616</t>
2617<t>
2618   The Max-Forwards header field &MAY; be ignored for all other request
2619   methods.
2620</t>
2621</section>
2622
2623<section title="Referer" anchor="header.referer">
2624  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2625  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2626  <x:anchor-alias value="Referer"/>
2627<t>
2628   The "Referer" [sic] header field allows the client to specify the
2629   URI of the resource from which the effective request URI was obtained (the
2630   "referrer", although the header field is misspelled.).
2631</t>
2632<t>
2633   The Referer header field allows servers to generate lists of back-links to
2634   resources for interest, logging, optimized caching, etc. It also allows
2635   obsolete or mistyped links to be traced for maintenance. Some servers use
2636   Referer as a means of controlling where they allow links from (so-called
2637   "deep linking"), but legitimate requests do not always
2638   contain a Referer header field.
2639</t>
2640<t>
2641   If the effective request URI was obtained from a source that does not have its own
2642   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2643   sent with the value "about:blank", or not be sent at all. Note that this
2644   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2645</t>
2646<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2647  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2648</artwork></figure>
2649<t>
2650   Example:
2651</t>
2652<figure><artwork type="example">
2653  Referer: http://www.example.org/hypertext/Overview.html
2654</artwork></figure>
2655<t>
2656   If the field value is a relative URI, it &SHOULD; be interpreted
2657   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2658   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2659</t>
2660</section>
2661
2662<section title="Retry-After" anchor="header.retry-after">
2663  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2664  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2665  <x:anchor-alias value="Retry-After"/>
2666<t>
2667   The header "Retry-After" field can be used with a 503 (Service
2668   Unavailable) response to indicate how long the service is expected to
2669   be unavailable to the requesting client. This field &MAY; also be used
2670   with any 3xx (Redirection) response to indicate the minimum time the
2671   user-agent is asked to wait before issuing the redirected request.
2672</t>
2673<t>
2674   The value of this field can be either an HTTP-date or an integer number
2675   of seconds (in decimal) after the time of the response.
2676</t>
2677<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2678  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2679</artwork></figure>
2680<t anchor="rule.delta-seconds">
2681  <x:anchor-alias value="delta-seconds"/>
2682   Time spans are non-negative decimal integers, representing time in
2683   seconds.
2684</t>
2685<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2686  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2687</artwork></figure>
2688<t>
2689   Two examples of its use are
2690</t>
2691<figure><artwork type="example">
2692  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2693  Retry-After: 120
2694</artwork></figure>
2695<t>
2696   In the latter example, the delay is 2 minutes.
2697</t>
2698</section>
2699
2700<section title="Server" anchor="header.server">
2701  <iref primary="true" item="Server header field" x:for-anchor=""/>
2702  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2703  <x:anchor-alias value="Server"/>
2704<t>
2705   The "Server" header field contains information about the
2706   software used by the origin server to handle the request.
2707</t>
2708<t>
2709   The field can contain multiple
2710   product tokens (<xref target="product.tokens"/>) and
2711   comments (&header-fields;) identifying the server and any significant
2712   subproducts. The product tokens are listed in order of their significance
2713   for identifying the application.
2714</t>
2715<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2716  <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> ) )
2717</artwork></figure>
2718<t>
2719   Example:
2720</t>
2721<figure><artwork type="example">
2722  Server: CERN/3.0 libwww/2.17
2723</artwork></figure>
2724<t>
2725   If the response is being forwarded through a proxy, the proxy
2726   application &MUST-NOT; modify the Server header field. Instead, it
2727   &MUST; include a Via field (as described in &header-via;).
2728</t>
2729<x:note>
2730  <t>
2731    <x:h>Note:</x:h> Revealing the specific software version of the server might
2732    allow the server machine to become more vulnerable to attacks
2733    against software that is known to contain security holes. Server
2734    implementors are encouraged to make this field a configurable
2735    option.
2736  </t>
2737</x:note>
2738</section>
2739
2740<section title="User-Agent" anchor="header.user-agent">
2741  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2742  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2743  <x:anchor-alias value="User-Agent"/>
2744<t>
2745   The "User-Agent" header field contains information about the user
2746   agent originating the request. User agents &SHOULD; include this field with
2747   requests.
2748</t>
2749<t>
2750   Typically, it is used for statistical purposes, the tracing of protocol
2751   violations, and tailoring responses to avoid particular user agent
2752   limitations.
2753</t>
2754<t>
2755   The field can contain multiple
2756   product tokens (<xref target="product.tokens"/>)
2757   and comments (&header-fields;) identifying the agent and its
2758   significant subproducts. By convention, the product tokens are listed in
2759   order of their significance for identifying the application.
2760</t>
2761<t>
2762   Because this field is usually sent on every request a user agent makes,
2763   implementations are encouraged not to include needlessly fine-grained
2764   detail, and to limit (or even prohibit) the addition of subproducts by third
2765   parties. Overly long and detailed User-Agent field values make requests
2766   larger and can also be used to identify ("fingerprint") the user against
2767   their wishes.
2768</t>
2769<t>
2770   Likewise, implementations are encouraged not to use the product tokens of
2771   other implementations in order to declare compatibility with them, as this
2772   circumvents the purpose of the field. Finally, they are encouraged not to
2773   use comments to identify products; doing so makes the field value more
2774   difficult to parse.
2775</t>
2776<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2777  <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> ) )
2778</artwork></figure>
2779<t>
2780   Example:
2781</t>
2782<figure><artwork type="example">
2783  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2784</artwork></figure>
2785</section>
2786
2787</section>
2788
2789<section title="IANA Considerations" anchor="IANA.considerations">
2790
2791<section title="Method Registry" anchor="method.registration">
2792<t>
2793  The registration procedure for HTTP request methods is defined by
2794  <xref target="method.registry"/> of this document.
2795</t>
2796<t>
2797   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2798   and be populated with the registrations below:
2799</t>
2800<?BEGININC p2-semantics.iana-methods ?>
2801<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2802<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2803   <ttcol>Method</ttcol>
2804   <ttcol>Safe</ttcol>
2805   <ttcol>Reference</ttcol>
2806   <c>CONNECT</c>
2807   <c>no</c>
2808   <c>
2809      <xref target="CONNECT"/>
2810   </c>
2811   <c>DELETE</c>
2812   <c>no</c>
2813   <c>
2814      <xref target="DELETE"/>
2815   </c>
2816   <c>GET</c>
2817   <c>yes</c>
2818   <c>
2819      <xref target="GET"/>
2820   </c>
2821   <c>HEAD</c>
2822   <c>yes</c>
2823   <c>
2824      <xref target="HEAD"/>
2825   </c>
2826   <c>OPTIONS</c>
2827   <c>yes</c>
2828   <c>
2829      <xref target="OPTIONS"/>
2830   </c>
2831   <c>POST</c>
2832   <c>no</c>
2833   <c>
2834      <xref target="POST"/>
2835   </c>
2836   <c>PUT</c>
2837   <c>no</c>
2838   <c>
2839      <xref target="PUT"/>
2840   </c>
2841   <c>TRACE</c>
2842   <c>yes</c>
2843   <c>
2844      <xref target="TRACE"/>
2845   </c>
2846</texttable>
2847<!--(END)-->
2848<?ENDINC p2-semantics.iana-methods ?>
2849</section>
2850
2851<section title="Status Code Registry" anchor="status.code.registration">
2852<t>
2853   The registration procedure for HTTP Status Codes &mdash; previously defined
2854   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2855   by <xref target="status.code.registry"/> of this document.
2856</t>
2857<t>
2858   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2859   shall be updated with the registrations below:
2860</t>
2861<?BEGININC p2-semantics.iana-status-codes ?>
2862<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2863<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2864   <ttcol>Value</ttcol>
2865   <ttcol>Description</ttcol>
2866   <ttcol>Reference</ttcol>
2867   <c>100</c>
2868   <c>Continue</c>
2869   <c>
2870      <xref target="status.100"/>
2871   </c>
2872   <c>101</c>
2873   <c>Switching Protocols</c>
2874   <c>
2875      <xref target="status.101"/>
2876   </c>
2877   <c>200</c>
2878   <c>OK</c>
2879   <c>
2880      <xref target="status.200"/>
2881   </c>
2882   <c>201</c>
2883   <c>Created</c>
2884   <c>
2885      <xref target="status.201"/>
2886   </c>
2887   <c>202</c>
2888   <c>Accepted</c>
2889   <c>
2890      <xref target="status.202"/>
2891   </c>
2892   <c>203</c>
2893   <c>Non-Authoritative Information</c>
2894   <c>
2895      <xref target="status.203"/>
2896   </c>
2897   <c>204</c>
2898   <c>No Content</c>
2899   <c>
2900      <xref target="status.204"/>
2901   </c>
2902   <c>205</c>
2903   <c>Reset Content</c>
2904   <c>
2905      <xref target="status.205"/>
2906   </c>
2907   <c>300</c>
2908   <c>Multiple Choices</c>
2909   <c>
2910      <xref target="status.300"/>
2911   </c>
2912   <c>301</c>
2913   <c>Moved Permanently</c>
2914   <c>
2915      <xref target="status.301"/>
2916   </c>
2917   <c>302</c>
2918   <c>Found</c>
2919   <c>
2920      <xref target="status.302"/>
2921   </c>
2922   <c>303</c>
2923   <c>See Other</c>
2924   <c>
2925      <xref target="status.303"/>
2926   </c>
2927   <c>305</c>
2928   <c>Use Proxy</c>
2929   <c>
2930      <xref target="status.305"/>
2931   </c>
2932   <c>306</c>
2933   <c>(Unused)</c>
2934   <c>
2935      <xref target="status.306"/>
2936   </c>
2937   <c>307</c>
2938   <c>Temporary Redirect</c>
2939   <c>
2940      <xref target="status.307"/>
2941   </c>
2942   <c>400</c>
2943   <c>Bad Request</c>
2944   <c>
2945      <xref target="status.400"/>
2946   </c>
2947   <c>402</c>
2948   <c>Payment Required</c>
2949   <c>
2950      <xref target="status.402"/>
2951   </c>
2952   <c>403</c>
2953   <c>Forbidden</c>
2954   <c>
2955      <xref target="status.403"/>
2956   </c>
2957   <c>404</c>
2958   <c>Not Found</c>
2959   <c>
2960      <xref target="status.404"/>
2961   </c>
2962   <c>405</c>
2963   <c>Method Not Allowed</c>
2964   <c>
2965      <xref target="status.405"/>
2966   </c>
2967   <c>406</c>
2968   <c>Not Acceptable</c>
2969   <c>
2970      <xref target="status.406"/>
2971   </c>
2972   <c>408</c>
2973   <c>Request Timeout</c>
2974   <c>
2975      <xref target="status.408"/>
2976   </c>
2977   <c>409</c>
2978   <c>Conflict</c>
2979   <c>
2980      <xref target="status.409"/>
2981   </c>
2982   <c>410</c>
2983   <c>Gone</c>
2984   <c>
2985      <xref target="status.410"/>
2986   </c>
2987   <c>411</c>
2988   <c>Length Required</c>
2989   <c>
2990      <xref target="status.411"/>
2991   </c>
2992   <c>413</c>
2993   <c>Request Representation Too Large</c>
2994   <c>
2995      <xref target="status.413"/>
2996   </c>
2997   <c>414</c>
2998   <c>URI Too Long</c>
2999   <c>
3000      <xref target="status.414"/>
3001   </c>
3002   <c>415</c>
3003   <c>Unsupported Media Type</c>
3004   <c>
3005      <xref target="status.415"/>
3006   </c>
3007   <c>417</c>
3008   <c>Expectation Failed</c>
3009   <c>
3010      <xref target="status.417"/>
3011   </c>
3012   <c>426</c>
3013   <c>Upgrade Required</c>
3014   <c>
3015      <xref target="status.426"/>
3016   </c>
3017   <c>500</c>
3018   <c>Internal Server Error</c>
3019   <c>
3020      <xref target="status.500"/>
3021   </c>
3022   <c>501</c>
3023   <c>Not Implemented</c>
3024   <c>
3025      <xref target="status.501"/>
3026   </c>
3027   <c>502</c>
3028   <c>Bad Gateway</c>
3029   <c>
3030      <xref target="status.502"/>
3031   </c>
3032   <c>503</c>
3033   <c>Service Unavailable</c>
3034   <c>
3035      <xref target="status.503"/>
3036   </c>
3037   <c>504</c>
3038   <c>Gateway Timeout</c>
3039   <c>
3040      <xref target="status.504"/>
3041   </c>
3042   <c>505</c>
3043   <c>HTTP Version Not Supported</c>
3044   <c>
3045      <xref target="status.505"/>
3046   </c>
3047</texttable>
3048<!--(END)-->
3049<?ENDINC p2-semantics.iana-status-codes ?>
3050</section>
3051<section title="Header Field Registration" anchor="header.field.registration">
3052<t>
3053   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3054   with the permanent registrations below (see <xref target="RFC3864"/>):
3055</t>
3056<?BEGININC p2-semantics.iana-headers ?>
3057<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3058<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3059   <ttcol>Header Field Name</ttcol>
3060   <ttcol>Protocol</ttcol>
3061   <ttcol>Status</ttcol>
3062   <ttcol>Reference</ttcol>
3063
3064   <c>Allow</c>
3065   <c>http</c>
3066   <c>standard</c>
3067   <c>
3068      <xref target="header.allow"/>
3069   </c>
3070   <c>Date</c>
3071   <c>http</c>
3072   <c>standard</c>
3073   <c>
3074      <xref target="header.date"/>
3075   </c>
3076   <c>Expect</c>
3077   <c>http</c>
3078   <c>standard</c>
3079   <c>
3080      <xref target="header.expect"/>
3081   </c>
3082   <c>From</c>
3083   <c>http</c>
3084   <c>standard</c>
3085   <c>
3086      <xref target="header.from"/>
3087   </c>
3088   <c>Location</c>
3089   <c>http</c>
3090   <c>standard</c>
3091   <c>
3092      <xref target="header.location"/>
3093   </c>
3094   <c>Max-Forwards</c>
3095   <c>http</c>
3096   <c>standard</c>
3097   <c>
3098      <xref target="header.max-forwards"/>
3099   </c>
3100   <c>Referer</c>
3101   <c>http</c>
3102   <c>standard</c>
3103   <c>
3104      <xref target="header.referer"/>
3105   </c>
3106   <c>Retry-After</c>
3107   <c>http</c>
3108   <c>standard</c>
3109   <c>
3110      <xref target="header.retry-after"/>
3111   </c>
3112   <c>Server</c>
3113   <c>http</c>
3114   <c>standard</c>
3115   <c>
3116      <xref target="header.server"/>
3117   </c>
3118   <c>User-Agent</c>
3119   <c>http</c>
3120   <c>standard</c>
3121   <c>
3122      <xref target="header.user-agent"/>
3123   </c>
3124</texttable>
3125<!--(END)-->
3126<?ENDINC p2-semantics.iana-headers ?>
3127<t>
3128   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3129</t>
3130</section>
3131</section>
3132
3133<section title="Security Considerations" anchor="security.considerations">
3134<t>
3135   This section is meant to inform application developers, information
3136   providers, and users of the security limitations in HTTP/1.1 as
3137   described by this document. The discussion does not include
3138   definitive solutions to the problems revealed, though it does make
3139   some suggestions for reducing security risks.
3140</t>
3141
3142<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3143<t>
3144   Like any generic data transfer protocol, HTTP cannot regulate the
3145   content of the data that is transferred, nor is there any a priori
3146   method of determining the sensitivity of any particular piece of
3147   information within the context of any given request. Therefore,
3148   applications &SHOULD; supply as much control over this information as
3149   possible to the provider of that information. Four header fields are
3150   worth special mention in this context: Server, Via, Referer and From.
3151</t>
3152<t>
3153   Revealing the specific software version of the server might allow the
3154   server machine to become more vulnerable to attacks against software
3155   that is known to contain security holes. Implementors &SHOULD; make the
3156   Server header field a configurable option.
3157</t>
3158<t>
3159   Proxies which serve as a portal through a network firewall &SHOULD;
3160   take special precautions regarding the transfer of header information
3161   that identifies the hosts behind the firewall. In particular, they
3162   &SHOULD; remove, or replace with sanitized versions, any Via fields
3163   generated behind the firewall.
3164</t>
3165<t>
3166   The Referer header field allows reading patterns to be studied and reverse
3167   links drawn. Although it can be very useful, its power can be abused
3168   if user details are not separated from the information contained in
3169   the Referer. Even when the personal information has been removed, the
3170   Referer header field might indicate a private document's URI whose
3171   publication would be inappropriate.
3172</t>
3173<t>
3174   The information sent in the From field might conflict with the user's
3175   privacy interests or their site's security policy, and hence it
3176   &SHOULD-NOT;  be transmitted without the user being able to disable,
3177   enable, and modify the contents of the field. The user &MUST; be able
3178   to set the contents of this field within a user preference or
3179   application defaults configuration.
3180</t>
3181<t>
3182   We suggest, though do not require, that a convenient toggle interface
3183   be provided for the user to enable or disable the sending of From and
3184   Referer information.
3185</t>
3186<t>
3187   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3188   target="header.server"/>) header fields can sometimes be used to determine
3189   that a specific client or server has a particular security hole which might
3190   be exploited. Unfortunately, this same information is often used for other
3191   valuable purposes for which HTTP currently has no better mechanism.
3192</t>
3193<t>
3194   Furthermore, the User-Agent header field may contain enough entropy to be
3195   used, possibly in conjunction with other material, to uniquely identify the
3196   user.
3197</t>
3198<t>
3199   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3200   that was sent in request header fields within the body of their response.
3201   Clients &SHOULD; be careful with sensitive information, like Cookies,
3202   Authorization credentials, and other header fields that might be used to
3203   collect data from the client.
3204</t> 
3205</section>
3206
3207<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3208<t>
3209   Because the source of a link might be private information or might
3210   reveal an otherwise private information source, it is strongly
3211   recommended that the user be able to select whether or not the
3212   Referer field is sent. For example, a browser client could have a
3213   toggle switch for browsing openly/anonymously, which would
3214   respectively enable/disable the sending of Referer and From
3215   information.
3216</t>
3217<t>
3218   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3219   HTTP request if the referring page was transferred with a secure
3220   protocol.
3221</t>
3222<t>
3223   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3224   sensitive data because that data will be placed in the request-target. Many
3225   existing servers, proxies, and user agents log or display the request-target
3226   in places where it might be visible to third parties. Such services can
3227   use POST-based form submission instead.
3228</t>
3229</section>
3230
3231<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3232<t>
3233   If a single server supports multiple organizations that do not trust
3234   one another, then it &MUST; check the values of Location and Content-Location
3235   header fields in responses that are generated under control of
3236   said organizations to make sure that they do not attempt to
3237   invalidate resources over which they have no authority.
3238</t>
3239<t>
3240   Furthermore, appending the fragment identifier from one URI to another
3241   one obtained from a Location header field might leak confidential
3242   information to the target server &mdash; although the fragment identifier is
3243   not transmitted in the final request, it might be visible to the user agent
3244   through other means, such as scripting.
3245</t>
3246</section>
3247
3248<section title="Security Considerations for CONNECT">
3249<t>
3250   Since tunneled data is opaque to the proxy, there are additional
3251   risks to tunneling to other well-known or reserved ports.
3252   A HTTP client CONNECTing to port 25 could relay spam
3253   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3254   access to a small number of known ports.
3255</t>
3256</section>
3257
3258</section>
3259
3260<section title="Acknowledgments" anchor="acks">
3261<t>
3262  See &acks;.
3263</t>
3264</section>
3265</middle>
3266<back>
3267
3268<references title="Normative References">
3269
3270<reference anchor="Part1">
3271  <front>
3272    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3273    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3274      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3275      <address><email>fielding@gbiv.com</email></address>
3276    </author>
3277    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3278      <organization abbrev="W3C">World Wide Web Consortium</organization>
3279      <address><email>ylafon@w3.org</email></address>
3280    </author>
3281    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3282      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3283      <address><email>julian.reschke@greenbytes.de</email></address>
3284    </author>
3285    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3286  </front>
3287  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3288  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3289</reference>
3290
3291<reference anchor="Part3">
3292  <front>
3293    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3294    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3295      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3296      <address><email>fielding@gbiv.com</email></address>
3297    </author>
3298    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3299      <organization abbrev="W3C">World Wide Web Consortium</organization>
3300      <address><email>ylafon@w3.org</email></address>
3301    </author>
3302    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3303      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3304      <address><email>julian.reschke@greenbytes.de</email></address>
3305    </author>
3306    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3307  </front>
3308  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3309  <x:source href="p3-payload.xml" basename="p3-payload"/>
3310</reference>
3311
3312<reference anchor="Part4">
3313  <front>
3314    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3315    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3316      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3317      <address><email>fielding@gbiv.com</email></address>
3318    </author>
3319    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3320      <organization abbrev="W3C">World Wide Web Consortium</organization>
3321      <address><email>ylafon@w3.org</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-p4-conditional-&ID-VERSION;"/>
3330  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3331</reference>
3332
3333<reference anchor="Part5">
3334  <front>
3335    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</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-p5-range-&ID-VERSION;"/>
3351  <x:source href="p5-range.xml" basename="p5-range"/>
3352</reference>
3353
3354<reference anchor="Part6">
3355  <front>
3356    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3357    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3358      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3359      <address><email>fielding@gbiv.com</email></address>
3360    </author>
3361    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3362      <organization abbrev="W3C">World Wide Web Consortium</organization>
3363      <address><email>ylafon@w3.org</email></address>
3364    </author>
3365    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3366      <organization>Rackspace</organization>
3367      <address><email>mnot@mnot.net</email></address>
3368    </author>
3369    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3370      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3371      <address><email>julian.reschke@greenbytes.de</email></address>
3372    </author>
3373    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3374  </front>
3375  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3376  <x:source href="p6-cache.xml" basename="p6-cache"/>
3377</reference>
3378
3379<reference anchor="Part7">
3380  <front>
3381    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3382    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3383      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3384      <address><email>fielding@gbiv.com</email></address>
3385    </author>
3386    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3387      <organization abbrev="W3C">World Wide Web Consortium</organization>
3388      <address><email>ylafon@w3.org</email></address>
3389    </author>
3390    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3391      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3392      <address><email>julian.reschke@greenbytes.de</email></address>
3393    </author>
3394    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3395  </front>
3396  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3397  <x:source href="p7-auth.xml" basename="p7-auth"/>
3398</reference>
3399
3400<reference anchor="RFC2119">
3401  <front>
3402    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3403    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3404      <organization>Harvard University</organization>
3405      <address><email>sob@harvard.edu</email></address>
3406    </author>
3407    <date month="March" year="1997"/>
3408  </front>
3409  <seriesInfo name="BCP" value="14"/>
3410  <seriesInfo name="RFC" value="2119"/>
3411</reference>
3412
3413<reference anchor="RFC3986">
3414 <front>
3415  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3416  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3417    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3418    <address>
3419       <email>timbl@w3.org</email>
3420       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3421    </address>
3422  </author>
3423  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3424    <organization abbrev="Day Software">Day Software</organization>
3425    <address>
3426      <email>fielding@gbiv.com</email>
3427      <uri>http://roy.gbiv.com/</uri>
3428    </address>
3429  </author>
3430  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3431    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3432    <address>
3433      <email>LMM@acm.org</email>
3434      <uri>http://larry.masinter.net/</uri>
3435    </address>
3436  </author>
3437  <date month='January' year='2005'></date>
3438 </front>
3439 <seriesInfo name="STD" value="66"/>
3440 <seriesInfo name="RFC" value="3986"/>
3441</reference>
3442
3443<reference anchor="RFC5234">
3444  <front>
3445    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3446    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3447      <organization>Brandenburg InternetWorking</organization>
3448      <address>
3449        <email>dcrocker@bbiw.net</email>
3450      </address> 
3451    </author>
3452    <author initials="P." surname="Overell" fullname="Paul Overell">
3453      <organization>THUS plc.</organization>
3454      <address>
3455        <email>paul.overell@thus.net</email>
3456      </address>
3457    </author>
3458    <date month="January" year="2008"/>
3459  </front>
3460  <seriesInfo name="STD" value="68"/>
3461  <seriesInfo name="RFC" value="5234"/>
3462</reference>
3463
3464</references>
3465
3466<references title="Informative References">
3467
3468<reference anchor="RFC1123">
3469  <front>
3470    <title>Requirements for Internet Hosts - Application and Support</title>
3471    <author initials="R." surname="Braden" fullname="Robert Braden">
3472      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3473      <address><email>Braden@ISI.EDU</email></address>
3474    </author>
3475    <date month="October" year="1989"/>
3476  </front>
3477  <seriesInfo name="STD" value="3"/>
3478  <seriesInfo name="RFC" value="1123"/>
3479</reference>
3480
3481<reference anchor="RFC1945">
3482  <front>
3483    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3484    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3485      <organization>MIT, Laboratory for Computer Science</organization>
3486      <address><email>timbl@w3.org</email></address>
3487    </author>
3488    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3489      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3490      <address><email>fielding@ics.uci.edu</email></address>
3491    </author>
3492    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3493      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3494      <address><email>frystyk@w3.org</email></address>
3495    </author>
3496    <date month="May" year="1996"/>
3497  </front>
3498  <seriesInfo name="RFC" value="1945"/>
3499</reference>
3500
3501<reference anchor="RFC2068">
3502  <front>
3503    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3504    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3505      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3506      <address><email>fielding@ics.uci.edu</email></address>
3507    </author>
3508    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3509      <organization>MIT Laboratory for Computer Science</organization>
3510      <address><email>jg@w3.org</email></address>
3511    </author>
3512    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3513      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3514      <address><email>mogul@wrl.dec.com</email></address>
3515    </author>
3516    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3517      <organization>MIT Laboratory for Computer Science</organization>
3518      <address><email>frystyk@w3.org</email></address>
3519    </author>
3520    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3521      <organization>MIT Laboratory for Computer Science</organization>
3522      <address><email>timbl@w3.org</email></address>
3523    </author>
3524    <date month="January" year="1997"/>
3525  </front>
3526  <seriesInfo name="RFC" value="2068"/>
3527</reference>
3528
3529<reference anchor="RFC2616">
3530  <front>
3531    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3532    <author initials="R." surname="Fielding" fullname="R. Fielding">
3533      <organization>University of California, Irvine</organization>
3534      <address><email>fielding@ics.uci.edu</email></address>
3535    </author>
3536    <author initials="J." surname="Gettys" fullname="J. Gettys">
3537      <organization>W3C</organization>
3538      <address><email>jg@w3.org</email></address>
3539    </author>
3540    <author initials="J." surname="Mogul" fullname="J. Mogul">
3541      <organization>Compaq Computer Corporation</organization>
3542      <address><email>mogul@wrl.dec.com</email></address>
3543    </author>
3544    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3545      <organization>MIT Laboratory for Computer Science</organization>
3546      <address><email>frystyk@w3.org</email></address>
3547    </author>
3548    <author initials="L." surname="Masinter" fullname="L. Masinter">
3549      <organization>Xerox Corporation</organization>
3550      <address><email>masinter@parc.xerox.com</email></address>
3551    </author>
3552    <author initials="P." surname="Leach" fullname="P. Leach">
3553      <organization>Microsoft Corporation</organization>
3554      <address><email>paulle@microsoft.com</email></address>
3555    </author>
3556    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3557      <organization>W3C</organization>
3558      <address><email>timbl@w3.org</email></address>
3559    </author>
3560    <date month="June" year="1999"/>
3561  </front>
3562  <seriesInfo name="RFC" value="2616"/>
3563</reference>
3564
3565<reference anchor='RFC2817'>
3566  <front>
3567    <title>Upgrading to TLS Within HTTP/1.1</title>
3568    <author initials='R.' surname='Khare' fullname='R. Khare'>
3569      <organization>4K Associates / UC Irvine</organization>
3570      <address><email>rohit@4K-associates.com</email></address>
3571    </author>
3572    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3573      <organization>Agranat Systems, Inc.</organization>
3574      <address><email>lawrence@agranat.com</email></address>
3575    </author>
3576    <date year='2000' month='May' />
3577  </front>
3578  <seriesInfo name='RFC' value='2817' />
3579</reference>
3580
3581<reference anchor='RFC3864'>
3582  <front>
3583    <title>Registration Procedures for Message Header Fields</title>
3584    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3585      <organization>Nine by Nine</organization>
3586      <address><email>GK-IETF@ninebynine.org</email></address>
3587    </author>
3588    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3589      <organization>BEA Systems</organization>
3590      <address><email>mnot@pobox.com</email></address>
3591    </author>
3592    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3593      <organization>HP Labs</organization>
3594      <address><email>JeffMogul@acm.org</email></address>
3595    </author>
3596    <date year='2004' month='September' />
3597  </front>
3598  <seriesInfo name='BCP' value='90' />
3599  <seriesInfo name='RFC' value='3864' />
3600</reference>
3601
3602<reference anchor='RFC5226'>
3603  <front>
3604    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3605    <author initials='T.' surname='Narten' fullname='T. Narten'>
3606      <organization>IBM</organization>
3607      <address><email>narten@us.ibm.com</email></address>
3608    </author>
3609    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3610      <organization>Google</organization>
3611      <address><email>Harald@Alvestrand.no</email></address>
3612    </author>
3613    <date year='2008' month='May' />
3614  </front>
3615  <seriesInfo name='BCP' value='26' />
3616  <seriesInfo name='RFC' value='5226' />
3617</reference>
3618
3619<reference anchor="RFC5322">
3620  <front>
3621    <title>Internet Message Format</title>
3622    <author initials="P." surname="Resnick" fullname="P. Resnick">
3623      <organization>Qualcomm Incorporated</organization>
3624    </author>
3625    <date year="2008" month="October"/>
3626  </front> 
3627  <seriesInfo name="RFC" value="5322"/>
3628</reference>
3629
3630<reference anchor='RFC5789'>
3631  <front>
3632    <title>PATCH Method for HTTP</title>
3633    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3634      <organization>Linden Lab</organization>
3635    </author>
3636    <author initials='J.' surname='Snell' fullname='J. Snell' />
3637    <date year='2010' month='March' />
3638  </front>
3639  <seriesInfo name='RFC' value='5789' />
3640</reference>
3641
3642<reference anchor="RFC5987">
3643        <front>
3644    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3645    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3646      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3647      <address>
3648        <postal>
3649          <street>Hafenweg 16</street>
3650          <city>Muenster</city><region>NW</region><code>48155</code>
3651          <country>Germany</country>
3652        </postal>
3653        <email>julian.reschke@greenbytes.de</email>     
3654        <uri>http://greenbytes.de/tech/webdav/</uri>   
3655      </address>
3656    </author>
3657    <date month="August" year="2010"/>
3658  </front>
3659  <seriesInfo name="RFC" value="5987"/>
3660</reference>
3661
3662</references>
3663
3664<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3665<t>
3666  This document takes over the Status Code Registry, previously defined
3667  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3668  (<xref target="status.code.registry"/>)
3669</t>
3670<t>
3671  Clarify definition of POST.
3672  (<xref target="POST"/>)
3673</t>
3674<t>
3675  Remove requirement to handle all Content-* header fields; ban use of
3676  Content-Range with PUT.
3677  (<xref target="PUT"/>)
3678</t>
3679<t>
3680  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3681  (<xref target="CONNECT"/>)
3682</t>
3683<t>
3684  Broadened the definition of 203 (Non-Authoritative Information) to include
3685  cases of payload transformations as well.
3686  (<xref target="status.203"/>)
3687</t>
3688<t>
3689  Status codes 301, 302, and 307: removed the normative requirements on both
3690  response payloads and user interaction.
3691  (<xref target="status.3xx"/>)
3692</t>
3693<t>
3694  Failed to consider that there are many other request methods that are safe
3695  to automatically redirect, and further that the user agent is able to make
3696  that determination based on the request method semantics.
3697  Furthermore, allow user agents to rewrite the method from POST to GET
3698  for status codes 301 and 302.
3699  (Sections <xref format="counter" target="status.301"/>,
3700  <xref format="counter" target="status.302"/> and
3701  <xref format="counter" target="status.307"/>)
3702</t>
3703<t>
3704  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3705  It used to indicate that the target resource must be accessed through the
3706  proxy given by the Location field. The Location field gave the URI of the
3707  proxy. The recipient was expected to repeat this single request via the proxy.
3708  (<xref target="status.305"/>)
3709</t>
3710<t>
3711  Define status 426 (Upgrade Required) (this was incorporated from
3712  <xref target="RFC2817"/>).
3713  (<xref target="status.426"/>)
3714</t>
3715<t>
3716  Change ABNF productions for header fields to only define the field value.
3717  (<xref target="header.field.definitions"/>)
3718</t>
3719<t>
3720  Reclassify "Allow" as response header field, removing the option to
3721  specify it in a PUT request.
3722  Relax the server requirement on the contents of the Allow header field and
3723  remove requirement on clients to always trust the header field value.
3724  (<xref target="header.allow"/>)
3725</t>
3726<t>
3727  The ABNF for the Expect header field has been both fixed (allowing parameters
3728  for value-less expectations as well) and simplified (allowing trailing
3729  semicolons after "100-continue" when they were invalid before).
3730  (<xref target="header.expect"/>)
3731</t>
3732<t>
3733  Correct syntax of Location header field to allow URI references (including
3734  relative references and fragments), as referred symbol "absoluteURI" wasn't
3735  what was expected, and add some clarifications as to when use of fragments
3736  would not be appropriate.
3737  (<xref target="header.location"/>)
3738</t>
3739<t>
3740  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3741  extension methods could have used it as well).
3742  (<xref target="header.max-forwards"/>)
3743</t>
3744<t>
3745  Allow Referer field value of "about:blank" as alternative to not specifying it.
3746  (<xref target="header.referer"/>)
3747</t>
3748<t>
3749  In the description of the Server header field, the Via field
3750  was described as a SHOULD. The requirement was and is stated
3751  correctly in the description of the Via header field in &header-via;.
3752  (<xref target="header.server"/>)
3753</t>
3754</section>
3755
3756<?BEGININC p2-semantics.abnf-appendix ?>
3757<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3758<figure>
3759<artwork type="abnf" name="p2-semantics.parsed-abnf">
3760<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
3761
3762<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
3763
3764<x:ref>Date</x:ref> = HTTP-date
3765
3766<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3767
3768<x:ref>From</x:ref> = mailbox
3769
3770<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
3771
3772<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
3773
3774<x:ref>Location</x:ref> = URI-reference
3775
3776<x:ref>Max-Forwards</x:ref> = 1*DIGIT
3777
3778<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
3779
3780<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
3781<x:ref>Referer</x:ref> = absolute-URI / partial-URI
3782<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
3783
3784<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
3785
3786<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
3787<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
3788
3789<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
3790<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
3791
3792<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
3793
3794<x:ref>date1</x:ref> = day SP month SP year
3795<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
3796<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
3797<x:ref>day</x:ref> = 2DIGIT
3798<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
3799 / %x54.75.65 ; Tue
3800 / %x57.65.64 ; Wed
3801 / %x54.68.75 ; Thu
3802 / %x46.72.69 ; Fri
3803 / %x53.61.74 ; Sat
3804 / %x53.75.6E ; Sun
3805<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
3806 / %x54.75.65.73.64.61.79 ; Tuesday
3807 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
3808 / %x54.68.75.72.73.64.61.79 ; Thursday
3809 / %x46.72.69.64.61.79 ; Friday
3810 / %x53.61.74.75.72.64.61.79 ; Saturday
3811 / %x53.75.6E.64.61.79 ; Sunday
3812<x:ref>delta-seconds</x:ref> = 1*DIGIT
3813
3814<x:ref>expect-name</x:ref> = token
3815<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
3816<x:ref>expect-value</x:ref> = token / quoted-string
3817<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
3818 OWS expect-param ] )
3819
3820<x:ref>hour</x:ref> = 2DIGIT
3821
3822<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
3823<x:ref>method</x:ref> = token
3824<x:ref>minute</x:ref> = 2DIGIT
3825<x:ref>month</x:ref> = %x4A.61.6E ; Jan
3826 / %x46.65.62 ; Feb
3827 / %x4D.61.72 ; Mar
3828 / %x41.70.72 ; Apr
3829 / %x4D.61.79 ; May
3830 / %x4A.75.6E ; Jun
3831 / %x4A.75.6C ; Jul
3832 / %x41.75.67 ; Aug
3833 / %x53.65.70 ; Sep
3834 / %x4F.63.74 ; Oct
3835 / %x4E.6F.76 ; Nov
3836 / %x44.65.63 ; Dec
3837
3838<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
3839<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
3840
3841<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
3842<x:ref>product</x:ref> = token [ "/" product-version ]
3843<x:ref>product-version</x:ref> = token
3844
3845<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
3846
3847<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
3848<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
3849<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
3850
3851<x:ref>second</x:ref> = 2DIGIT
3852<x:ref>status-code</x:ref> = 3DIGIT
3853
3854<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
3855<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
3856
3857<x:ref>year</x:ref> = 4DIGIT
3858</artwork>
3859</figure>
3860<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
3861; Allow defined but not used
3862; Date defined but not used
3863; Expect defined but not used
3864; From defined but not used
3865; Location defined but not used
3866; Max-Forwards defined but not used
3867; Referer defined but not used
3868; Retry-After defined but not used
3869; Server defined but not used
3870; User-Agent defined but not used
3871; reason-phrase defined but not used
3872; status-code defined but not used
3873</artwork></figure></section>
3874<?ENDINC p2-semantics.abnf-appendix ?>
3875
3876<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3877
3878<section title="Since RFC 2616">
3879<t>
3880  Extracted relevant partitions from <xref target="RFC2616"/>.
3881</t>
3882</section>
3883
3884<section title="Since draft-ietf-httpbis-p2-semantics-00">
3885<t>
3886  Closed issues:
3887  <list style="symbols"> 
3888    <t>
3889      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3890      "Via is a MUST"
3891      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3892    </t>
3893    <t>
3894      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3895      "Fragments allowed in Location"
3896      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3897    </t>
3898    <t>
3899      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3900      "Safe Methods vs Redirection"
3901      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3902    </t>
3903    <t>
3904      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3905      "Revise description of the POST method"
3906      (<eref target="http://purl.org/NET/http-errata#post"/>)
3907    </t>
3908    <t>
3909      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3910      "Normative and Informative references"
3911    </t>
3912    <t>
3913      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3914      "RFC2606 Compliance"
3915    </t>
3916    <t>
3917      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3918      "Informative references"
3919    </t>
3920    <t>
3921      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3922      "Redundant cross-references"
3923    </t>
3924  </list>
3925</t>
3926<t>
3927  Other changes:
3928  <list style="symbols"> 
3929    <t>
3930      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3931    </t>
3932  </list>
3933</t>
3934</section>
3935
3936<section title="Since draft-ietf-httpbis-p2-semantics-01">
3937<t>
3938  Closed issues:
3939  <list style="symbols"> 
3940    <t>
3941      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3942      "PUT side effects"
3943    </t>
3944    <t>
3945      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3946      "Duplicate Host header requirements"
3947    </t>
3948  </list>
3949</t>
3950<t>
3951  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3952  <list style="symbols"> 
3953    <t>
3954      Move "Product Tokens" section (back) into Part 1, as "token" is used
3955      in the definition of the Upgrade header field.
3956    </t>
3957    <t>
3958      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3959    </t>
3960    <t>
3961      Copy definition of delta-seconds from Part6 instead of referencing it.
3962    </t>
3963  </list>
3964</t>
3965</section>
3966
3967<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3968<t>
3969  Closed issues:
3970  <list style="symbols"> 
3971    <t>
3972      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3973      "Requiring Allow in 405 responses"
3974    </t>
3975    <t>
3976      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3977      "Status Code Registry"
3978    </t>
3979    <t>
3980      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3981      "Redirection vs. Location"
3982    </t>
3983    <t>
3984      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3985      "Cacheability of 303 response"
3986    </t>
3987    <t>
3988      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3989      "305 Use Proxy"
3990    </t>
3991    <t>
3992      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3993      "Classification for Allow header"
3994    </t>
3995    <t>
3996      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3997      "PUT - 'store under' vs 'store at'"
3998    </t>
3999  </list>
4000</t>
4001<t>
4002  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4003  <list style="symbols"> 
4004    <t>
4005      Reference RFC 3984, and update header field registrations for headers defined
4006      in this document.
4007    </t>
4008  </list>
4009</t>
4010<t>
4011  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4012  <list style="symbols"> 
4013    <t>
4014      Replace string literals when the string really is case-sensitive (method).
4015    </t>
4016  </list>
4017</t>
4018</section>
4019
4020<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4021<t>
4022  Closed issues:
4023  <list style="symbols"> 
4024    <t>
4025      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4026      "OPTIONS request bodies"
4027    </t>
4028    <t>
4029      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4030      "Description of CONNECT should refer to RFC2817"
4031    </t>
4032    <t>
4033      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4034      "Location Content-Location reference request/response mixup"
4035    </t>
4036  </list>
4037</t>
4038<t>
4039  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4040  <list style="symbols"> 
4041    <t>
4042      Added initial proposal for registration process, plus initial
4043      content (non-HTTP/1.1 methods to be added by a separate specification).
4044    </t>
4045  </list>
4046</t>
4047</section>
4048
4049<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4050<t>
4051  Closed issues:
4052  <list style="symbols"> 
4053    <t>
4054      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4055      "Content-*"
4056    </t>
4057    <t>
4058      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4059      "RFC 2822 is updated by RFC 5322"
4060    </t>
4061  </list>
4062</t>
4063<t>
4064  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4065  <list style="symbols"> 
4066    <t>
4067      Use "/" instead of "|" for alternatives.
4068    </t>
4069    <t>
4070      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4071      whitespace ("OWS") and required whitespace ("RWS").
4072    </t>
4073    <t>
4074      Rewrite ABNFs to spell out whitespace rules, factor out
4075      header field value format definitions.
4076    </t>
4077  </list>
4078</t>
4079</section>
4080
4081<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4082<t>
4083  Closed issues:
4084  <list style="symbols"> 
4085    <t>
4086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4087      "reason-phrase BNF"
4088    </t>
4089  </list>
4090</t>
4091<t>
4092  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4093  <list style="symbols"> 
4094    <t>
4095      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4096    </t>
4097  </list>
4098</t>
4099</section>
4100
4101<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4102<t>
4103  Closed issues:
4104  <list style="symbols"> 
4105    <t>
4106      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4107      "Clarify when Referer is sent"
4108    </t>
4109    <t>
4110      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4111      "status codes vs methods"
4112    </t>
4113    <t>
4114      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4115      "Do not require "updates" relation for specs that register status codes or method names"
4116    </t>
4117  </list>
4118</t>
4119</section>
4120
4121<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4122<t>
4123  Closed issues:
4124  <list style="symbols"> 
4125    <t>
4126      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4127      "Idempotency"
4128    </t>
4129    <t>
4130      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4131      "TRACE security considerations"
4132    </t>
4133    <t>
4134      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4135      "Clarify rules for determining what entities a response carries"
4136    </t>
4137    <t>
4138      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4139      "update note citing RFC 1945 and 2068"
4140    </t>
4141    <t>
4142      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4143      "update note about redirect limit"
4144    </t>
4145    <t>
4146      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4147      "Location header ABNF should use 'URI'"
4148    </t>
4149    <t>
4150      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4151      "fragments in Location vs status 303"
4152    </t>
4153    <t>
4154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4155      "move IANA registrations for optional status codes"
4156    </t>
4157  </list>
4158</t>
4159<t>
4160  Partly resolved issues:
4161  <list style="symbols"> 
4162    <t>
4163      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4164      "Are OPTIONS and TRACE safe?"
4165    </t>
4166  </list>
4167</t>
4168</section>
4169
4170<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4171<t>
4172  Closed issues:
4173  <list style="symbols"> 
4174    <t>
4175      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4176      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4177      status codes when fixing this previously)
4178    </t>
4179  </list>
4180</t>
4181</section>
4182
4183<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4184<t>
4185  Closed issues:
4186  <list style="symbols"> 
4187    <t>
4188      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4189      "Fragment combination / precedence during redirects"
4190    </t>
4191  </list>
4192</t>
4193<t>
4194  Partly resolved issues:
4195  <list style="symbols"> 
4196    <t>
4197      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4198      "Location header payload handling"
4199    </t>
4200    <t>
4201      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4202      "Term for the requested resource's URI"
4203    </t>
4204  </list>
4205</t>
4206</section>
4207
4208<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4209<t>
4210  Closed issues:
4211  <list style="symbols"> 
4212    <t>
4213      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4214      "Clarify 'Requested Variant'"
4215    </t>
4216    <t>
4217      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4218      "Clarify entity / representation / variant terminology"
4219    </t>
4220    <t>
4221      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4222      "Methods and Caching"
4223    </t>
4224    <t>
4225      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4226      "OPTIONS vs Max-Forwards"
4227    </t>
4228    <t>
4229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4230      "Status codes and caching"
4231    </t>
4232    <t>
4233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4234      "consider removing the 'changes from 2068' sections"
4235    </t>
4236  </list>
4237</t>
4238</section>
4239
4240<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4241<t>
4242  Closed issues:
4243  <list style="symbols"> 
4244    <t>
4245      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4246      "Considerations for new status codes"
4247    </t>
4248    <t>
4249      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4250      "Considerations for new methods"
4251    </t>
4252    <t>
4253      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4254      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4255    </t>
4256  </list>
4257</t>
4258</section>
4259
4260<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4261<t>
4262  Closed issues:
4263  <list style="symbols"> 
4264    <t>
4265      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4266      "Fragment combination / precedence during redirects" (added warning
4267      about having a fragid on the redirect may cause inconvenience in
4268      some cases)
4269    </t>
4270    <t>
4271      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4272      "Content-* vs. PUT"
4273    </t>
4274    <t>
4275      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4276      "205 Bodies"
4277    </t>
4278    <t>
4279      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4280      "Understanding Content-* on non-PUT requests"
4281    </t>
4282    <t>
4283      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4284      "Content-*"
4285    </t>
4286    <t>
4287      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4288      "Header type defaulting"
4289    </t>
4290    <t>
4291      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4292      "PUT - 'store under' vs 'store at'"
4293    </t>
4294    <t>
4295      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4296      "duplicate ABNF for reason-phrase"
4297    </t>
4298    <t>
4299      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4300      "Note special status of Content-* prefix in header registration procedures"
4301    </t>
4302    <t>
4303      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4304      "Max-Forwards vs extension methods"
4305    </t>
4306    <t>
4307      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4308      "What is the value space of HTTP status codes?" (actually fixed in
4309      draft-ietf-httpbis-p2-semantics-11)
4310    </t>
4311    <t>
4312      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4313      "Header Classification"
4314    </t>
4315    <t>
4316      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4317      "PUT side effect: invalidation or just stale?"
4318    </t>
4319    <t>
4320      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4321      "proxies not supporting certain methods"
4322    </t>
4323    <t>
4324      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4325      "Migrate CONNECT from RFC2817 to p2"
4326    </t>
4327    <t>
4328      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4329      "Migrate Upgrade details from RFC2817"
4330    </t>
4331    <t>
4332      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4333      "clarify PUT semantics'"
4334    </t>
4335    <t>
4336      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4337      "duplicate ABNF for 'Method'"
4338    </t>
4339    <t>
4340      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4341      "untangle ABNFs for header fields"
4342    </t>
4343  </list>
4344</t>
4345</section>
4346
4347<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4348<t>
4349  Closed issues:
4350  <list style="symbols"> 
4351    <t>
4352      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4353      "untangle ABNFs for header fields"
4354    </t>
4355    <t>
4356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4357      "message body in CONNECT request"
4358    </t>
4359  </list>
4360</t>
4361</section>
4362
4363<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4364<t>
4365  Closed issues:
4366  <list style="symbols"> 
4367    <t>
4368      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4369      "Clarify status code for rate limiting"
4370    </t>
4371    <t>
4372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4373      "clarify 403 forbidden"
4374    </t>
4375    <t>
4376      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4377      "Clarify 203 Non-Authoritative Information"
4378    </t>
4379    <t>
4380      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4381      "update default reason phrase for 413"
4382    </t>
4383  </list>
4384</t>
4385</section>
4386
4387<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4388<t>
4389  Closed issues:
4390  <list style="symbols"> 
4391    <t>
4392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4393      "Strength of requirements on Accept re: 406"
4394    </t>
4395    <t>
4396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4397      "400 response isn't generic"
4398    </t>
4399  </list>
4400</t>
4401</section>
4402
4403<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4404<t>
4405  Closed issues:
4406  <list style="symbols"> 
4407    <t>
4408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4409      "Redirects and non-GET methods"
4410    </t>
4411    <t>
4412      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4413      "Document HTTP's error-handling philosophy"
4414    </t>
4415    <t>
4416      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4417      "Considerations for new headers"
4418    </t>
4419    <t>
4420      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4421      "clarify 303 redirect on HEAD"
4422    </t>
4423  </list>
4424</t>
4425</section>
4426
4427<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4428<t>
4429  Closed issues:
4430  <list style="symbols"> 
4431    <t>
4432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4433      "Location header payload handling"
4434    </t>
4435    <t>
4436      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4437      "Clarify status code for rate limiting" (change backed out because
4438      a new status code is being defined for this purpose)
4439    </t>
4440    <t>
4441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4442      "should there be a permanent variant of 307"
4443    </t>
4444    <t>
4445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4446      "When are Location's semantics triggered?"
4447    </t>
4448    <t>
4449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4450      "'expect' grammar missing OWS"
4451    </t>
4452    <t>
4453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4454      "header field considerations: quoted-string vs use of double quotes"
4455    </t>
4456  </list>
4457</t>
4458</section>
4459
4460<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4461<t>
4462  Closed issues:
4463  <list style="symbols"> 
4464    <t>
4465      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4466      "Combining HEAD responses"
4467    </t>
4468    <t>
4469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4470      "Requirements for user intervention during redirects"
4471    </t>
4472    <t>
4473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4474      "message-body in CONNECT response"
4475    </t>
4476    <t>
4477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4478      "Applying original fragment to 'plain' redirected URI"
4479    </t>
4480    <t>
4481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4482      "Misplaced text on connection handling in p2"
4483    </t>
4484    <t>
4485      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4486      "clarify that 201 doesn't require Location header fields"
4487    </t>
4488    <t>
4489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4490      "relax requirements on hypertext in 3/4/5xx error responses"
4491    </t>
4492    <t>
4493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4494      "example for 426 response should have a payload"
4495    </t>
4496    <t>
4497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4498      "drop indirection entries for status codes"
4499    </t>
4500  </list>
4501</t>
4502</section>
4503
4504</section>
4505
4506</back>
4507</rfc>
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